Wireless Communication Tutorial

Wireless communication involves the transmission of information over a distance without the help of wires, cables or any other forms of electrical conductors.

Wireless communication is a broad term that incorporates all procedures and forms of connecting and communicating between two or more devices using a wireless signal through wireless communication technologies and devices.

Features of Wireless Communication

The evolution of wireless technology has brought many advancements with its effective features.

· The transmitted distance can be anywhere between a few meters (for example, a television's remote control) and thousands of kilometers (for example, radio communication).

· Wireless communication can be used for cellular telephony, wireless access to the internet, wireless home networking, and so on.

· Other examples of applications of radio wireless technology include GPS units, garage door openers, wireless computer mice, keyboards and headsets, headphones, radio receivers, satellite television, broadcast television and cordless telephones.

Wireless - Advantages

Wireless communication involves transfer of information without any physical connection between two or more points. Because of this absence of any 'physical infrastructure', wireless communication has certain advantages. This would often include collapsing distance or space.

Wireless communication has several advantages; the most important ones are discussed below −

Cost effectiveness

Wired communication entails the use of connection wires. In wireless networks, communication does not require elaborate physical infrastructure or maintenance practices. Hence the cost is reduced.

Example − Any company providing wireless communication services does not incur a lot of costs, and as a result, it is able to charge cheaply with regard to its customer fees.

Flexibility

Wireless communication enables people to communicate regardless of their location. It is not necessary to be in an office or some telephone booth in order to pass and receive messages.

Miners in the outback can rely on satellite phones to call their loved ones, and thus, help improve their general welfare by keeping them in touch with the people who mean the most to them.

Convenience

Wireless communication devices like mobile phones are quite simple and therefore allow anyone to use them, wherever they may be. There is no need to physically connect anything in order to receive or pass messages.

Example − Wireless communications services can also be seen in Internet technologies such as Wi-Fi. With no network cables hampering movement, we can now connect with almost anyone, anywhere, anytime.

Speed

Improvements can also be seen in speed. The network connectivity or the accessibility were much improved in accuracy and speed.

Example − A wireless remote can operate a system faster than a wired one. The wireless control of a machine can easily stop its working if something goes wrong, whereas direct operation can’t act so fast.

Accessibility

The wireless technology helps easy accessibility as the remote areas where ground lines can’t be properly laid, are being easily connected to the network.

Example − In rural regions, online education is now possible. Educators no longer need to travel to far-flung areas to teach their lessons. Thanks to live streaming of their educational modules.

Constant connectivity

Constant connectivity also ensures that people can respond to emergencies relatively quickly.

Example − A wireless mobile can ensure you a constant connectivity though you move from place to place or while you travel, whereas a wired land line can’t.

DCN - Wireless Transmission

Wireless transmission is a form of unguided media. Wireless communication involves no physical link established between two or more devices, communicating wirelessly. Wireless signals are spread over in the air and are received and interpreted by appropriate antennas.

When an antenna is attached to electrical circuit of a computer or wireless device, it converts the digital data into wireless signals and spread all over within its frequency range. The receptor on the other end receives these signals and converts them back to digital data.

A little part of electromagnetic spectrum can be used for wireless transmission.

Radio Transmission

Radio frequency is easier to generate and because of its large wavelength it can penetrate through walls and structures alike.Radio waves can have wavelength from 1 mm – 100,000 km and have frequency ranging from 3 Hz (Extremely Low Frequency) to 300 GHz (Extremely High Frequency). Radio frequencies are sub-divided into six bands.

Radio waves at lower frequencies can travel through walls whereas higher RF can travel in straight line and bounce back.The power of low frequency waves decreases sharply as they cover long distance. High frequency radio waves have more power.

Lower frequencies such as VLF, LF, MF bands can travel on the ground up to 1000 kilometers, over the earth’s surface.

Radio waves of high frequencies are prone to be absorbed by rain and other obstacles. They use Ionosphere of earth atmosphere. High frequency radio waves such as HF and VHF bands are spread upwards. When they reach Ionosphere, they are refracted back to the earth.

Microwave Transmission

Electromagnetic waves above 100 MHz tend to travel in a straight line and signals over them can be sent by beaming those waves towards one particular station. Because Microwaves travels in straight lines, both sender and receiver must be aligned to be strictly in line-of-sight.

Microwaves can have wavelength ranging from 1 mm – 1 meter and frequency ranging from 300 MHz to 300 GHz.

Microwave antennas concentrate the waves making a beam of it. As shown in picture above, multiple antennas can be aligned to reach farther. Microwaves have higher frequencies and do not penetrate wall like obstacles.

Microwave transmission depends highly upon the weather conditions and the frequency it is using.

Infrared Transmission

Infrared wave lies in between visible light spectrum and microwaves. It has wavelength of 700-nm to 1-mm and frequency ranges from 300-GHz to 430-THz.

Infrared wave is used for very short range communication purposes such as television and it’s remote. Infrared travels in a straight line hence it is directional by nature. Because of high frequency range, Infrared cannot cross wall-like obstacles.

Light Transmission

Highest most electromagnetic spectrum which can be used for data transmission is light or optical signaling. This is achieved by means of LASER.

Because of frequency light uses, it tends to travel strictly in straight line.Hence the sender and receiver must be in the line-of-sight. Because laser transmission is unidirectional, at both ends of communication the laser and the photo-detector needs to be installed. Laser beam is generally 1mm wide hence it is a work of precision to align two far receptors each pointing to lasers source.

Laser works as Tx (transmitter) and photo-detectors works as Rx (receiver).

Lasers cannot penetrate obstacles such as walls, rain, and thick fog. Additionally, laser beam is distorted by wind, atmosphere temperature, or variation in temperature in the path.

Laser is safe for data transmission as it is very difficult to tap 1mm wide laser without interrupting the communication channel.

DCN - Multiplexing

Multiplexing is a technique by which different analog and digital streams of transmission can be simultaneously processed over a shared link. Multiplexing divides the high capacity medium into low capacity logical medium which is then shared by different streams.

Communication is possible over the air (radio frequency), using a physical media (cable), and light (optical fiber). All mediums are capable of multiplexing.

When multiple senders try to send over a single medium, a device called Multiplexer divides the physical channel and allocates one to each. On the other end of communication, a De-multiplexer receives data from a single medium, identifies each, and sends to different receivers.

Frequency Division Multiplexing

When the carrier is frequency, FDM is used. FDM is an analog technology. FDM divides the spectrum or carrier bandwidth in logical channels and allocates one user to each channel. Each user can use the channel frequency independently and has exclusive access of it. All channels are divided in such a way that they do not overlap with each other. Channels are separated by guard bands. Guard band is a frequency which is not used by either channel.

Time Division Multiplexing

TDM is applied primarily on digital signals but can be applied on analog signals as well. In TDM the shared channel is divided among its user by means of time slot. Each user can transmit data within the provided time slot only. Digital signals are divided in frames, equivalent to time slot i.e. frame of an optimal size which can be transmitted in given time slot.

TDM works in synchronized mode. Both ends, i.e. Multiplexer and De-multiplexer are timely synchronized and both switch to next channel simultaneously.

When channel A transmits its frame at one end,the De-multiplexer provides media to channel A on the other end.As soon as the channel A’s time slot expires, this side switches to channel B. On the other end, the De-multiplexer works in a synchronized manner and provides media to channel B. Signals from different channels travel the path in interleaved manner.

Wavelength Division Multiplexing

Light has different wavelength (colors). In fiber optic mode, multiple optical carrier signals are multiplexed into an optical fiber by using different wavelengths. This is an analog multiplexing technique and is done conceptually in the same manner as FDM but uses light as signals.

Further, on each wavelength time division multiplexing can be incorporated to accommodate more data signals.

Code Division Multiplexing

Multiple data signals can be transmitted over a single frequency by using Code Division Multiplexing. FDM divides the frequency in smaller channels but CDM allows its users to full bandwidth and transmit signals all the time using a unique code. CDM uses orthogonal codes to spread signals.

Each station is assigned with a unique code, called chip. Signals travel with these codes independently, inside the whole bandwidth.The receiver knows in advance the chip code signal it has to receive.

Spread Spectrum Modulation

A collective class of signaling techniques are employed before transmitting a signal to provide a secure communication, known as the Spread Spectrum Modulation. The main advantage of spread spectrum communication technique is to prevent “interference” whether it is intentional or unintentional.

The signals modulated with these techniques are hard to interfere and cannot be jammed. An intruder with no official access is never allowed to crack them. Hence, these techniques are used for military purposes. These spread spectrum signals transmit at low power density and has a wide spread of signals.

Pseudo-Noise Sequence

A coded sequence of 1s and 0s with certain auto-correlation properties, called as Pseudo-Noise coding sequence is used in spread spectrum techniques. It is a maximum-length sequence, which is a type of cyclic code.

Narrow-band and Spread-spectrum Signals

Both the Narrow band and Spread spectrum signals can be understood easily by observing their frequency spectrum as shown in the following figures.

Narrow-band Signals

The Narrow-band signals have the signal strength concentrated as shown in the following frequency spectrum figure.

Following are some of its features −

Band of signals occupy a narrow range of frequencies.
Power density is high.
Spread of energy is low and concentrated.

Though the features are good, these signals are prone to interference.

Spread Spectrum Signals

The spread spectrum signals have the signal strength distributed as shown in the following frequency spectrum figure.

Following are some of its features −

Band of signals occupy a wide range of frequencies.
Power density is very low.
Energy is wide spread.

With these features, the spread spectrum signals are highly resistant to interference or jamming. Since multiple users can share the same spread spectrum bandwidth without interfering with one another, these can be called as multiple access techniques.

FHSS and DSSS / CDMA

Spread spectrum multiple access techniques uses signals which have a transmission bandwidth of a magnitude greater than the minimum required RF bandwidth.

These are of two types.

Frequency Hopped Spread Spectrum (FHSS)
Direct Sequence Spread Spectrum (DSSS)

Frequency Hopped Spread Spectrum (FHSS)

This is frequency hopping technique, where the users are made to change the frequencies of usage, from one to another in a specified time interval, hence called as frequency hopping. For example, a frequency was allotted to sender 1 for a particular period of time. Now, after a while, sender 1 hops to the other frequency and sender 2 uses the first frequency, which was previously used by sender 1. This is called as frequency reuse.

The frequencies of the data are hopped from one to another in order to provide a secure transmission. The amount of time spent on each frequency hop is called as Dwell time.

Direct Sequence Spread Spectrum (DSSS)

Whenever a user wants to send data using this DSSS technique, each and every bit of the user data is multiplied by a secret code, called as chipping code. This chipping code is nothing but the spreading code which is multiplied with the original message and transmitted. The receiver uses the same code to retrieve the original message.

Comparison between FHSS and DSSS/CDMA

Both the spread spectrum techniques are popular for their characteristics. To have a clear understanding, let us take a look at their comparisons.

FHSS	DSSS / CDMA
Multiple frequencies are used	Single frequency is used
Hard to find the user’s frequency at any instant of time	User frequency, once allotted is always the same
Frequency reuse is allowed	Frequency reuse is not allowed
Sender need not wait	Sender has to wait if the spectrum is busy
Power strength of the signal is high	Power strength of the signal is low
Stronger and penetrates through the obstacles	It is weaker compared to FHSS
It is never affected by interference	It can be affected by interference
It is cheaper	It is expensive
This is the commonly used technique	This technique is not frequently used

Advantages of Spread Spectrum

Following are the advantages of spread spectrum −

Cross-talk elimination
Better output with data integrity
Reduced effect of multipath fading
Better security
Reduction in noise
Co-existence with other systems
Longer operative distances
Hard to detect
Not easy to demodulate/decode
Difficult to jam the signals

Although spread spectrum techniques were originally designed for military uses, they are now being used widely for commercial purpose.

Antenna Theory - Fundamentals

A person, who needs to convey a thought, an idea or a doubt, can do so by voice communication.

The following illustration shows two individuals communicating with each other. Here, communication takes place through sound waves. However, if two people want to communicate who are at longer distances, then we have to convert these sound waves into electromagnetic waves. The device, which converts the required information signal into electromagnetic waves, is known as an Antenna.

What is an Antenna ?

An Antenna is a transducer, which converts electrical power into electromagnetic waves and vice versa.

An Antenna can be used either as a transmitting antenna or a receiving antenna.

· A transmitting antenna is one, which converts electrical signals into electromagnetic waves and radiates them.

· A receiving antenna is one, which converts electromagnetic waves from the received beam into electrical signals.

· In two-way communication, the same antenna can be used for both transmission and reception.

Antenna can also be termed as an Aerial. Plural of it is, antennae or antennas. Now-adays, antennas have undergone many changes, in accordance with their size and shape. There are many types of antennas depending upon their wide variety of applications.

Following pictures are examples of different types of Antennas.

In this chapter, you are going to learn the basic concepts of antenna, specifications and different types of antennas.

Need of Antenna

In the field of communication systems, whenever the need for wireless communication arises, there occurs the necessity of an antenna. Antenna has the capability of sending or receiving the electromagnetic waves for the sake of communication, where you cannot expect to lay down a wiring system. The following scenario explains this.

Scenario

In order to contact a remote area, the wiring has to be laid down throughout the whole route along the valleys, the mountains, the tedious paths, the tunnels etc., to reach the remote location. The evolution of wireless technology has made this whole process very simple. Antenna is the key element of this wireless technology.

In the above image, the antennas help the communication to be established in the whole area, including the valleys and mountains. This process would obviously be easier than laying a wiring system throughout the area.

Radiation Mechanism

The sole functionality of an antenna is power radiation or reception. Antenna (whether it transmits or receives or does both) can be connected to the circuitry at the station through a transmission line. The functioning of an antenna depends upon the radiation mechanism of a transmission line.

A conductor, which is designed to carry current over large distances with minimum losses, is termed as a transmission line. For example, a wire, which is connected to an antenna. A transmission line conducting current with uniform velocity, and the line being a straight one with infinite extent, radiates no power.

For a transmission line, to become a waveguide or to radiate power, has to be processed as such.

· If the power has to be radiated, though the current conduction is with uniform velocity, the wire or transmission line should be bent, truncated or terminated.

· If this transmission line has current, which accelerates or decelerates with a timevarying constant, then it radiates the power even though the wire is straight.

· The device or tube, if bent or terminated to radiate energy, then it is called as waveguide. These are especially used for the microwave transmission or reception.

This can be well understood by observing the following diagram −

The above diagram represents a waveguide, which acts as an antenna. The power from the transmission line travels through the waveguide which has an aperture, to radiate the energy.

Basic Types of Antennas

Antennas may be divided into various types depending upon −

· The physical structure of the antenna.

· The frequency ranges of operation.

· The mode of applications etc.

Physical structure

Following are the types of antennas according to the physical structure. You will learn about these antennas in later chapters.

Wire antennas
Aperture antennas
Reflector antennas
Lens antennas
Micro strip antennas
Array antennas

Frequency of operation

Following are the types of antennas according to the frequency of operation.

Very Low Frequency (VLF)
Low Frequency (LF)
Medium Frequency (MF)
High Frequency (HF)
Very High Frequency (VHF)
Ultra High Frequency (UHF)
Super High Frequency (SHF)
Micro wave
Radio wave

Mode of Applications

Following are the types of antennas according to the modes of applications −

Point-to-point communications
Broadcasting applications
Radar communications
Satellite communications

Medium Access Control Sublayer (MAC sublayer)

The medium access control (MAC) is a sublayer of the data link layer of the open system interconnections (OSI) reference model for data transmission. It is responsible for flow control and multiplexing for transmission medium. It controls the transmission of data packets via remotely shared channels. It sends data over the network interface card.

MAC Layer in the OSI Model

The Open System Interconnections (OSI) model is a layered networking framework that conceptualizes how communications should be done between heterogeneous systems. The data link layer is the second lowest layer. It is divided into two sublayers −

· The logical link control (LLC) sublayer

· The medium access control (MAC) sublayer

The following diagram depicts the position of the MAC layer −

https://www.tutorialspoint.com/assets/questions/media/20058/application.jpg

Functions of MAC Layer

· It provides an abstraction of the physical layer to the LLC and upper layers of the OSI network.

· It is responsible for encapsulating frames so that they are suitable for transmission via the physical medium.

· It resolves the addressing of source station as well as the destination station, or groups of destination stations.

· It performs multiple access resolutions when more than one data frame is to be transmitted. It determines the channel access methods for transmission.

· It also performs collision resolution and initiating retransmission in case of collisions.

· It generates the frame check sequences and thus contributes to protection against transmission errors.

MAC Addresses

MAC address or media access control address is a unique identifier allotted to a network interface controller (NIC) of a device. It is used as a network address for data transmission within a network segment like Ethernet, Wi-Fi, and Bluetooth.

MAC address is assigned to a network adapter at the time of manufacturing. It is hardwired or hard-coded in the network interface card (NIC). A MAC address comprises of six groups of two hexadecimal digits, separated by hyphens, colons, or no separators. An example of a MAC address is 00:0A:89:5B:F0:11.

Wireless Communication - Multiple Access

Multiple access schemes are used to allow many mobile users to share simultaneously a finite amount of radio spectrum.

Multiple Access Techniques

In wireless communication systems, it is often desirable to allow the subscriber to send information simultaneously from the mobile station to the base station while receiving information from the base station to the mobile station.

A cellular system divides any given area into cells where a mobile unit in each cell communicates with a base station. The main aim in the cellular system design is to be able to increase the capacity of the channel, i.e., to handle as many calls as possible in a given bandwidth with a sufficient level of quality of service.

There are several different ways to allow access to the channel. These includes mainly the following −

Frequency division multiple-access (FDMA)
Time division multiple-access (TDMA)
Code division multiple-access (CDMA)
Space division multiple access (SDMA)

Depending on how the available bandwidth is allocated to the users, these techniques can be classified as narrowband and wideband systems.

Narrowband Systems

Systems operating with channels substantially narrower than the coherence bandwidth are called as Narrow band systems. Narrow band TDMA allows users to use the same channel but allocates a unique time slot to each user on the channel, thus separating a small number of users in time on a single channel.

Wideband Systems

In wideband systems, the transmission bandwidth of a single channel is much larger than the coherence bandwidth of the channel. Thus, multipath fading doesn’t greatly affect the received signal within a wideband channel, and frequency selective fades occur only in a small fraction of the signal bandwidth.

Frequency Division Multiple Access (FDMA)

FDMA is the basic technology for advanced mobile phone services. The features of FDMA are as follows.

FDMA allots a different sub-band of frequency to each different user to access the network.
If FDMA is not in use, the channel is left idle instead of allotting to the other users.
FDMA is implemented in Narrowband systems and it is less complex than TDMA.
Tight filtering is done here to reduce adjacent channel interference.
The base station BS and mobile station MS, transmit and receive simultaneously and continuously in FDMA.

Time Division Multiple Access (TDMA)

In the cases where continuous transmission is not required, there TDMA is used instead of FDMA. The features of TDMA include the following.

TDMA shares a single carrier frequency with several users where each users makes use of non-overlapping time slots.
Data transmission in TDMA is not continuous, but occurs in bursts. Hence handsoff process is simpler.
TDMA uses different time slots for transmission and reception thus duplexers are not required.
TDMA has an advantage that is possible to allocate different numbers of time slots per frame to different users.
Bandwidth can be supplied on demand to different users by concatenating or reassigning time slot based on priority.

Code Division Multiple Access (CDMA)

Code division multiple access technique is an example of multiple access where several transmitters use a single channel to send information simultaneously. Its features are as follows.

In CDMA every user uses the full available spectrum instead of getting allotted by separate frequency.
CDMA is much recommended for voice and data communications.
While multiple codes occupy the same channel in CDMA, the users having same code can communicate with each other.
CDMA offers more air-space capacity than TDMA.
The hands-off between base stations is very well handled by CDMA.

Space Division Multiple Access (SDMA)

Space division multiple access or spatial division multiple access is a technique which is MIMO (multiple-input multiple-output) architecture and used mostly in wireless and satellite communication. It has the following features.

All users can communicate at the same time using the same channel.
SDMA is completely free from interference.
A single satellite can communicate with more satellites receivers of the same frequency.
The directional spot-beam antennas are used and hence the base station in SDMA, can track a moving user.
Controls the radiated energy for each user in space.

Spread Spectrum Multiple Access

Spread spectrum multiple access (SSMA) uses signals which have a transmission bandwidth whose magnitude is greater than the minimum required RF bandwidth.

There are two main types of spread spectrum multiple access techniques −

Frequency hopped spread spectrum (FHSS)
Direct sequence spread spectrum (DSSS)

Frequency Hopped Spread Spectrum (FHSS)

This is a digital multiple access system in which the carrier frequencies of the individual users are varied in a pseudo random fashion within a wideband channel. The digital data is broken into uniform sized bursts which is then transmitted on different carrier frequencies.

Direct Sequence Spread Spectrum (DSSS)

This is the most commonly used technology for CDMA. In DS-SS, the message signal is multiplied by a Pseudo Random Noise Code. Each user is given his own code word which is orthogonal to the codes of other users and in order to detect the user, the receiver must know the code word used by the transmitter.

The combinational sequences called as hybrid are also used as another type of spread spectrum. Time hopping is also another type which is rarely mentioned.

Since many users can share the same spread spectrum bandwidth without interfering with one another, spread spectrum systems become bandwidth efficient in a multiple user environment.

Wireless Telecommunications Systems

What is GSM?

If you are in Europe or Asia and using a mobile phone, then most probably you are using GSM technology in your mobile phone.

· GSM stands for Global System for Mobile Communication. It is a digital cellular technology used for transmitting mobile voice and data services.

· The concept of GSM emerged from a cell-based mobile radio system at Bell Laboratories in the early 1970s.

· GSM is the name of a standardization group established in 1982 to create a common European mobile telephone standard.

· GSM is the most widely accepted standard in telecommunications and it is implemented globally.

· GSM is a circuit-switched system that divides each 200 kHz channel into eight 25 kHz time-slots. GSM operates on the mobile communication bands 900 MHz and 1800 MHz in most parts of the world. In the US, GSM operates in the bands 850 MHz and 1900 MHz.

· GSM owns a market share of more than 70 percent of the world's digital cellular subscribers.

· GSM makes use of narrowband Time Division Multiple Access (TDMA) technique for transmitting signals.

· GSM was developed using digital technology. It has an ability to carry 64 kbps to 120 Mbps of data rates.

· Presently GSM supports more than one billion mobile subscribers in more than 210 countries throughout the world.

· GSM provides basic to advanced voice and data services including roaming service. Roaming is the ability to use your GSM phone number in another GSM network.

GSM digitizes and compresses data, then sends it down through a channel with two other streams of user data, each in its own timeslot.

Why GSM?

Listed below are the features of GSM that account for its popularity and wide acceptance.

· Improved spectrum efficiency

· International roaming

· Low-cost mobile sets and base stations (BSs)

· High-quality speech

· Compatibility with Integrated Services Digital Network (ISDN) and other telephone company services

GSM - Architecture

A GSM network comprises of many functional units. These functions and interfaces are explained in this chapter. The GSM network can be broadly divided into:

· The Mobile Station (MS)

· The Base Station Subsystem (BSS)

· The Network Switching Subsystem (NSS)

· The Operation Support Subsystem (OSS)

Given below is a simple pictorial view of the GSM architecture.

The additional components of the GSM architecture comprise of databases and messaging systems functions:

Home Location Register (HLR)
Visitor Location Register (VLR)
Equipment Identity Register (EIR)
Authentication Center (AuC)
SMS Serving Center (SMS SC)
Gateway MSC (GMSC)
Chargeback Center (CBC)
Transcoder and Adaptation Unit (TRAU)

The following diagram shows the GSM network along with the added elements:

The MS and the BSS communicate across the Um interface. It is also known as the air interface or the radio link. The BSS communicates with the Network Service Switching (NSS) center across the A interface.

GSM network areas

In a GSM network, the following areas are defined:

· Cell : Cell is the basic service area; one BTS covers one cell. Each cell is given a Cell Global Identity (CGI), a number that uniquely identifies the cell.

· Location Area : A group of cells form a Location Area (LA). This is the area that is paged when a subscriber gets an incoming call. Each LA is assigned a Location Area Identity (LAI). Each LA is served by one or more BSCs.

· MSC/VLR Service Area : The area covered by one MSC is called the MSC/VLR service area.

· PLMN : The area covered by one network operator is called the Public Land Mobile Network (PLMN). A PLMN can contain one or more MSCs.

DECT (Digital Enhanced Cordless Telecommunications)

Unlike the analog cordless phones you may have in your home, DECT (Digital Enhanced Cordless Telecommunications) is a digital wireless telephone technology that is expected to make cordless phones much more common in both businesses and homes in the future. Formerly called the Digital European Cordless Telecommunications standard because it was developed by European companies, DECT's present name reflects its global acceptance. Like another important wireless standard, Global System for Mobile communication (GSM), DECT uses time division multiple access (TDMA) to transmit radio signals to phones. Whereas GSM is optimized for mobile travel over large areas, DECT is designed especially for a smaller area with a large number of users, such as in cities and corporate complexes. A user can have a telephone equipped for both GSM and DECT (this is known as a dual-modephone) and they can operate seamlessly.

DECT has five major applications:

1) The "cordless private branch exchange." A company can connect to a wired telephone company and redistribute signals by radio antenna to a large number of telephone users within the company, each with their own number. A cordless PBX would be especially useful and save costs in a company with a number of mobile employees such as those in a large warehouse.

2) Wireless Local Loop (WLL). Users in a neighborhood typically served by a telephone company wired local loop can be connected instead by a cordless phone that exchanges signals with a neighborhood antenna. A standard telephone (or any device containing a telephone such as a computer modem or fax machine) is simply plugged into a fixed access unit (FAU), which contains a transceiver. The Wireless Local Loop can be installed in an urban area where many users share the same antenna.

3) Cordless Terminal Mobility. The arrangement used by businesses for a cordless PBX can also be used by a service that provided cordless phone numbers for individual subscribers. In general, the mobility would be less than that available for GSM users.

4) Home cordless phones. A homeowner could install a single-cell antenna within the home and use it for a number of cordless phones throughout the home and garden.

5) GSM/DECT internetworking. Part of the DECT standard describes how it can interact with the GSM standard so that users can be free to move with a telephone from the outdoors (and GSM signals) into an indoor environment (and a DECT system). It's expected that many GSM service providers may want to extend their service to support DECT signals inside buildings. A dual-mode phone would automatically search first for a DECT connection, then for a GSM connection if DECT is not available.

TETRA (Terrestrial Trunked Radio)

Posted by: Margaret Rouse

WhatIs.com

Contributor(s): Mike Geldart

TETRA (Terrestrial Trunked Radio) is a set of standards developed by the European Telecommunications Standardisation Institute (ETSI) that describes a common mobile radio communications infrastructure throughout Europe. This infrastructure is targeted primarily at the mobile radio needs of public safety groups (such as police and fire departments), utility companies, and other enterprises that provide voice and data communications services.

All of these groups have been high-end users of private/professional mobile radio (PMR) or public access mobile radio (PAMR) technology. This is especially true in the areas of law enforcement and public safety, where fast and accurate field communications to and from a central office or dispatcher are often critical. TETRA is a standard solution for groups that use both PMR and PAMR.

In recent years, when European disasters have struck, emergency response teams from several European nations had a difficult time communicating with each other, due in part to the lack of standardization in their mobile radio equipment. The TETRA standards evolved to answer this communication challenge as well as others faced or anticipated by the European Commission (EC) in its efforts to unify European countries.

Based on digital, trunked radio technology, TETRA is believed to be the next-generation architecture and standard for current, analog PMR and PAMR markets. TETRA actually takes its features from several different technological areas:? mobile radio, digital cellular telephone, paging, and wireless data.

TETRA relies on digital trunking. TETRA-based products come with built-in encryptionfeatures to ensure the privacy and confidentiality of sensitive data/voice communications. These products are also designed with the ability to transfer data at faster rates than seen before in mobile communications.

UMTS Tutorial

The Universal Mobile Telecommunications System (UMTS), based on the GSM standards, is a mobile cellular system of third generation that is maintained by 3GPP (3rd Generation Partnership Project). It specifies a complete network system and the technology described in it is popularly referred as Freedom of Mobile Multimedia Access (FOMA). This tutorial starts off with a brief introduction to the history of mobile communication and cellular concepts and gradually moves on to explain the basics of GSM, GPRS, and EDGE, before getting into the concepts of UMTS.

IMT-2000

International Mobile Telecommunications for the year 2000 (IMT-2000) is a worldwide set of requirements for a family of standards for the 3^rdgeneration of mobile communications. The IMT-2000 "umbrella specifications" are developed by the International Telecommunicatons Union (ITU). Originally it was the intention to have only one truly global standard but that turned out to be impossible. IMT-2000 should provide worldwide mobile broadband multimedia services via a single global frequency band. The frequency range should be around 2000 MHz.

In the umbrella specification a number of characteristics are defined which the underying technologies should meet. The main characteristics are:

Worldwide usage,
integration of satellite and terrestrial systems to provide global coverage;
Used for all radio environments,
(LAN, cordless, cellular, satellite);
Wide range of telecommunications services,
(voice, data, multimedia, internet);
Support both packet-switched (PS) and circuit-switched (CS) data transmission;
Offer high data rates up to 2 Mbps,

144 kbps for high mobility,
384 kbps with restricted mobility and,
2 Mbps in an indoor office environment;

Offer high spectrum efficiency;

Family members
For the terrestrial mobile network, there are six family members identified as being IMT-2000 compatible:

IMT Direct Spread (IMT-DS; also known as UMTS/UTRA-FDD);
IMT Multicarrier (IMT-MC; also known as CDMA2000);
IMT Time Code (IMT-TC; also known as UMTS/UTRA-TDD, TD-CDMA and TD-SCDMA “narrowband TDD”);
IMT Single Carrier (IMT-SC; also known as UWC-136 or EDGE);
IMT Frequency Time (IMT-FT; also known as DECT).
IMT OFDMA TDD WMAN (also known as mobile WiMAX)

Originally, the IMT family consisted of five familiy members. The sixth family member (mobile WiMAX) was added later, in october 2007.

Frequency bands
The frequency bands 1885-2025 MHz and 2110-2200 MHz were identified for IMT-2000 by the ITU in 1992. Terrestrial IMT-2000 networks will operate in the following bands:

1920 - 1980 MHz paired with 2110 - 2170 MHz,
FDD with mobile stations transmitting in the lower sub-band.
1885 - 1920 MHz and 2010 - 2025 MHz,
unpaired for TDD operation.

In Europe is the TDD band from 1885-1900 MHz not available for licenses use of IMT-2000, this is used by cordless telephony (DECT).

In addition to this core-band the frequency band 2500 to 2690 MHz was identified in 2000, of which the edges, ranging from 2500-2520 and 2670-2690 MHz, are at first identified for satellite communications. Existing second generation bands (including GSM bands) 806 to 960 MHz, 1429 to 1501 MHz and 1710 to 1885 MHz are also identified for IMT-2000 in the long term.

LTE Overview

LTE stands for Long Term Evolution and it was started as a project in 2004 by telecommunication body known as the Third Generation Partnership Project (3GPP). SAE (System Architecture Evolution) is the corresponding evolution of the GPRS/3G packet core network evolution. The term LTE is typically used to represent both LTE and SAE.

LTE evolved from an earlier 3GPP system known as the Universal Mobile Telecommunication System (UMTS), which in turn evolved from the Global System for Mobile Communications (GSM). Even related specifications were formally known as the evolved UMTS terrestrial radio access (E-UTRA) and evolved UMTS terrestrial radio access network (E-UTRAN). First version of LTE was documented in Release 8 of the 3GPP specifications.

A rapid increase of mobile data usage and emergence of new applications such as MMOG (Multimedia Online Gaming), mobile TV, Web 2.0, streaming contents have motivated the 3rd Generation Partnership Project (3GPP) to work on the Long-Term Evolution (LTE) on the way towards fourth-generation mobile.

The main goal of LTE is to provide a high data rate, low latency and packet optimized radioaccess technology supporting flexible bandwidth deployments. Same time its network architecture has been designed with the goal to support packet-switched traffic with seamless mobility and great quality of service.

Facts about LTE

· LTE is the successor technology not only of UMTS but also of CDMA 2000.

· LTE is important because it will bring up to 50 times performance improvement and much better spectral efficiency to cellular networks.

· LTE introduced to get higher data rates, 300Mbps peak downlink and 75 Mbps peak uplink. In a 20MHz carrier, data rates beyond 300Mbps can be achieved under very good signal conditions.

· LTE is an ideal technology to support high date rates for the services such as voice over IP (VOIP), streaming multimedia, videoconferencing or even a high-speed cellular modem.

· LTE uses both Time Division Duplex (TDD) and Frequency Division Duplex (FDD) mode. In FDD uplink and downlink transmission used different frequency, while in TDD both uplink and downlink use the same carrier and are separated in Time.

· LTE supports flexible carrier bandwidths, from 1.4 MHz up to 20 MHz as well as both FDD and TDD. LTE designed with a scalable carrier bandwidth from 1.4 MHz up to 20 MHz which bandwidth is used depends on the frequency band and the amount of spectrum available with a network operator.

· All LTE devices have to support (MIMO) Multiple Input Multiple Output transmissions, which allow the base station to transmit several data streams over the same carrier simultaneously.

· All interfaces between network nodes in LTE are now IP based, including the backhaul connection to the radio base stations. This is great simplification compared to earlier technologies that were initially based on E1/T1, ATM and frame relay links, with most of them being narrowband and expensive.

· Quality of Service (QoS) mechanism have been standardized on all interfaces to ensure that the requirement of voice calls for a constant delay and bandwidth, can still be met when capacity limits are reached.

· Works with GSM/EDGE/UMTS systems utilizing existing 2G and 3G spectrum and new spectrum. Supports hand-over and roaming to existing mobile networks.

Advantages of LTE

· High throughput: High data rates can be achieved in both downlink as well as uplink. This causes high throughput.

· Low latency: Time required to connect to the network is in range of a few hundred milliseconds and power saving states can now be entered and exited very quickly.

· FDD and TDD in the same platform: Frequency Division Duplex (FDD) and Time Division Duplex (TDD), both schemes can be used on same platform.

· Superior end-user experience: Optimized signaling for connection establishment and other air interface and mobility management procedures have further improved the user experience. Reduced latency (to 10 ms) for better user experience.

· Seamless Connection: LTE will also support seamless connection to existing networks such as GSM, CDMA and WCDMA.

· Plug and play: The user does not have to manually install drivers for the device. Instead system automatically recognizes the device, loads new drivers for the hardware if needed, and begins to work with the newly connected device.

· Simple architecture: Because of Simple architecture low operating expenditure (OPEX).

There are four types of EPS bearers:

· GBR Bearer resources permanently allocated by admission control

· Non-GBR Bearer no admission control

· Dedicated Bearer associated with specific TFT (GBR or non-GBR)

· Default Bearer Non GBR, catch-all for unassigned traffic

Satellite Communication Tutorial

In general terms, a satellite is a smaller object that revolves around a larger object in space. For example, moon is a natural satellite of earth.

We know that Communication refers to the exchange (sharing) of information between two or more entities, through any medium or channel. In other words, it is nothing but sending, receiving and processing of information.

If the communication takes place between any two earth stations through a satellite, then it is called as satellite communication. In this communication, electromagnetic waves are used as carrier signals. These signals carry the information such as voice, audio, video or any other data between ground and space and vice-versa.

Soviet Union had launched the world's first artificial satellite named, Sputnik 1 in 1957. Nearly after 18 years, India also launched the artificial satellite named, Aryabhata in 1975.

Need of Satellite Communication

The following two kinds of propagation are used earlier for communication up to some distance.

· Ground wave propagation − Ground wave propagation is suitable for frequencies up to 30MHz. This method of communication makes use of the troposphere conditions of the earth.

· Sky wave propagation − The suitable bandwidth for this type of communication is broadly between 30–40 MHz and it makes use of the ionosphere properties of the earth.

The maximum hop or the station distance is limited to 1500KM only in both ground wave propagation and sky wave propagation. Satellite communication overcomes this limitation. In this method, satellites provide communication for long distances, which is well beyond the line of sight.

Since the satellites locate at certain height above earth, the communication takes place between any two earth stations easily via satellite. So, it overcomes the limitation of communication between two earth stations due to earth’s curvature.

How a Satellite Works

A satellite is a body that moves around another body in a particular path. A communication satellite is nothing but a microwave repeater station in space. It is helpful in telecommunications, radio and television along with internet applications.

A repeater is a circuit, which increases the strength of the received signal and then transmits it. But, this repeater works as a transponder. That means, it changes the frequency band of the transmitted signal from the received one.

The frequency with which, the signal is sent into the space is called as Uplink frequency. Similarly, the frequency with which, the signal is sent by the transponder is called as Downlink frequency. The following figure illustrates this concept clearly.

The transmission of signal from first earth station to satellite through a channel is called as uplink. Similarly, the transmission of signal from satellite to second earth station through a channel is called as downlink.

Uplink frequency is the frequency at which, the first earth station is communicating with satellite. The satellite transponder converts this signal into another frequency and sends it down to the second earth station. This frequency is called as Downlink frequency. In similar way, second earth station can also communicate with the first one.

The process of satellite communication begins at an earth station. Here, an installation is designed to transmit and receive signals from a satellite in an orbit around the earth. Earth stations send the information to satellites in the form of high powered, high frequency (GHz range) signals.

The satellites receive and retransmit the signals back to earth where they are received by other earth stations in the coverage area of the satellite. Satellite's footprint is the area which receives a signal of useful strength from the satellite.

Pros and Cons of Satellite Communication

In this section, let us have a look at the advantages and disadvantages of satellite communication.

Following are the advantages of using satellite communication:

· Area of coverage is more than that of terrestrial systems

· Each and every corner of the earth can be covered

· Transmission cost is independent of coverage area

· More bandwidth and broadcasting possibilites

Following are the disadvantages of using satellite communication −

· Launching of satellites into orbits is a costly process.

· Propagation delay of satellite systems is more than that of conventional terrestrial systems.

· Difficult to provide repairing activities if any problem occurs in a satellite system.

· Free space loss is more

· There can be congestion of frequencies.

Applications of Satellite Communication

Satellite communication plays a vital role in our daily life. Following are the applications of satellite communication −

· Radio broadcasting and voice communications

· TV broadcasting such as Direct To Home (DTH)

· Internet applications such as providing Internet connection for data transfer, GPS applications, Internet surfing, etc.

· Military applications and navigations

· Remote sensing applications

· Weather condition monitoring & Forecasting

Satellite Communication - Introduction

Soviet Union had launched the world's first artificial satellite named, Sputnik 1 in 1957. Nearly after 18 years, India also launched the artificial satellite named, Aryabhata in 1975.

Need of Satellite Communication

The following two kinds of propagation are used earlier for communication up to some distance.

· Ground wave propagation − Ground wave propagation is suitable for frequencies up to 30MHz. This method of communication makes use of the troposphere conditions of the earth.

· Sky wave propagation − The suitable bandwidth for this type of communication is broadly between 30–40 MHz and it makes use of the ionosphere properties of the earth.

How a Satellite Works

Pros and Cons of Satellite Communication

In this section, let us have a look at the advantages and disadvantages of satellite communication.

Following are the advantages of using satellite communication:

· Area of coverage is more than that of terrestrial systems

· Each and every corner of the earth can be covered

· Transmission cost is independent of coverage area

· More bandwidth and broadcasting possibilites

Following are the disadvantages of using satellite communication −

· Launching of satellites into orbits is a costly process.

· Propagation delay of satellite systems is more than that of conventional terrestrial systems.

· Difficult to provide repairing activities if any problem occurs in a satellite system.

· Free space loss is more

· There can be congestion of frequencies.

Applications of Satellite Communication

Satellite communication plays a vital role in our daily life. Following are the applications of satellite communication −

· Radio broadcasting and voice communications

· TV broadcasting such as Direct To Home (DTH)

· Internet applications such as providing Internet connection for data transfer, GPS applications, Internet surfing, etc.

· Military applications and navigations

· Remote sensing applications

· Weather condition monitoring & Forecasting

Low-Earth Orbit Satellites

Low earth orbit (LEO) satellites systems orbit below 2000 km from the earth’s surface, i.e. below the lower Van Allen belt. They move at very high speeds and may not have any fixed space with respect to the earth.

The following diagram depicts LEO satellites in their orbits.

Features of LEO Satellites

· A network of LEO satellites are needed for global coverage as their orbits are not geostationary.

· These satellites are not as powerful as the MEO and GEO satellites.

· Due to their high speeds, satellites move in and out of the earth station’s range from time to time. So, data is handed off from one satellite to the other to achieve uninterrupted data communication.

· They are very much energy efficient. It takes much less energy to place the LEO satellites in their orbits, in comparison to MEOs and GEOs. Also, their amplifiers consume less power.

· They are quite cheap in comparison with other data communication modes. So, they can be used as a more economic way of communication for underdeveloped areas.

· They can be used for establishing networks in remote terrains where it is not feasible to lay land lines.

Types of LEO Satellites and their Uses

· Communication Satellites − They are used for low cost data communication.

· Earth Monitoring Satellites − They are used for monitoring ground features. They are better than satellites placed far away since they have a clearer view of the earth’s surface.

· International Space Station − They provide research laboratory to conduct experiments within space environment. It is suited for testing spacecraft systems

Geostationary Satellite and Geostationary Orbit (GEO)

A circular geosynchronous satellite which is placed at 0^o angle to the equatorial plane is called a geostationary satellite. It appears to be stationary at a fixed position of the sky throughout the day by a ground observer.

The orbit in which a geostationary satellite is placed is called a geostationary orbit (GEO). It is placed 35, 800 km above the earth’s equator and has an orbital period equal to the sidereal day.

Uses and Examples of Geosynchronous Satellites

Uses

· Voice and data communication

· Internet

· Broadcasting cable TV and radio signals

Examples

· Raduga 29 of Russia

· Astra 1C of India

· MEASAT 2 of Malaysia

Uses and Examples of Geostationary Satellites

Uses

· Weather reports about a particular region

· Weather forecasting

· Terrestrial reports of a geographical area

· Spy networks

Examples

· Geostationary Operational Environmental Satellite (GEOS) of USA

· INSAT of India

· Himawari of Japan

· Fengyun of China

· Meteostat of Europe

Medium Earth Orbit Satellites

Medium Earth Orbit (MEO) satellites will orbit at distances of about 8000 miles from earth's surface. Signals transmitted from a MEO satellite travel a shorter distance. Due to this, the signal strength at the receiving end gets improved. This shows that smaller and light weight receiving terminals can be used at the receiving end.

Transmission delay can be defined as the time it takes for a signal to travel up to a satellite and back down to a receiving station. In this case, there is less transmission delay. Because, the signal travels for a shorter distance to and from the MEO satellite.

For real-time communications, the shorter the transmission delay, the better will be the communication system. As an example, if a GEO satellite requires 0.25 seconds for a round trip, then MEO satellite requires less than 0.1 seconds to complete the same trip. MEOs operate in the frequency range of 2 GHz and above.

These satellites are used for High speed telephone signals. Ten or more MEO satellites are required in order to cover entire earth.

Low Earth Orbit Satellites

Low Earth Orbit LEO) satellites are mainly classified into three categories. Those are little LEOs, big LEOs, and Mega-LEOs. LEOs will orbit at a distance of 500 to 1000 miles above the earth's surface. These satellites are used for satellite phones and GPS.

This relatively short distance reduces transmission delay to only 0.05 seconds. This further reduces the need for sensitive and bulky receiving equipment. Twenty or more LEO satellites are required to cover entire earth.

Little LEOs will operate in the 800 MHz (0.8 GHz) range. Big LEOs will operate in the 2 GHz or above range, and Mega-LEOs operates in the 20-30 GHz range.

The higher frequencies associated with Mega-LEOs translates into more information carrying capacity and yields to the capability of real-time, low delay video transmission scheme.

The following figure depicts the paths of LEO, MEO and GEO

Satellite Communication - Introduction

In general terms, a satellite is a smaller object that revolves around a larger object in space. For example, moon is a natural satellite of earth.

Soviet Union had launched the world's first artificial satellite named, Sputnik 1 in 1957. Nearly after 18 years, India also launched the artificial satellite named, Aryabhata in 1975.

Need of Satellite Communication

The following two kinds of propagation are used earlier for communication up to some distance.

· Ground wave propagation − Ground wave propagation is suitable for frequencies up to 30MHz. This method of communication makes use of the troposphere conditions of the earth.

· Sky wave propagation − The suitable bandwidth for this type of communication is broadly between 30–40 MHz and it makes use of the ionosphere properties of the earth.

How a Satellite Works

Pros and Cons of Satellite Communication

In this section, let us have a look at the advantages and disadvantages of satellite communication.

Following are the advantages of using satellite communication:

· Area of coverage is more than that of terrestrial systems

· Each and every corner of the earth can be covered

· Transmission cost is independent of coverage area

· More bandwidth and broadcasting possibilites

Following are the disadvantages of using satellite communication −

· Launching of satellites into orbits is a costly process.

· Propagation delay of satellite systems is more than that of conventional terrestrial systems.

· Difficult to provide repairing activities if any problem occurs in a satellite system.

· Free space loss is more

· There can be congestion of frequencies.

Applications of Satellite Communication

Satellite communication plays a vital role in our daily life. Following are the applications of satellite communication −

· Radio broadcasting and voice communications

· TV broadcasting such as Direct To Home (DTH)

· Internet applications such as providing Internet connection for data transfer, GPS applications, Internet surfing, etc.

· Military applications and navigations

· Remote sensing applications

· Weather condition monitoring & Forecasting

Satellite Channel Access

Multiple Access Techniques

Sometimes a satellite’s service is present at a particular location on the earth station and sometimes it is not present. That means, a satellite may have different service stations of its own located at different places on the earth. They send carrier signal for the satellite.

In this situation, we do multiple access to enable satellite to take or give signals from different stations at time without any interference between them. Following are the three types of multiple access techniques.

FDMA (Frequency Division Multiple Access)
TDMA (Time Division Multiple Access)
CDMA (Code Division Multiple Access)

Handoff in Mobile Connections

In cellular communications, the handoff is the process of transferring an active call or data session from one cell in a cellular network or from one channel to another. In satellite communications, it is the process of transferring control from one earth station to another. Handoff is necessary for preventing loss of interruption of service to a caller or a data session user. Handoff is also called handover.

Situations for triggering Handoff

Handoffs are triggered in any of the following situations −

· If a subscriber who is in a call or a data session moves out of coverage of one cell and enters coverage area of another cell, a handoff is triggered for a continuum of service. The tasks that were being performed by the first cell are delineating to the latter cell.

· Each cell has a pre-defined capacity, i.e. it can handle only a specific number of subscribers. If the number of users using a particular cell reaches its maximum capacity, then a handoff occurs. Some of the calls are transferred to adjoining cells, provided that the subscriber is in the overlapping coverage area of both the cells.

· Cells are often sub-divided into microcells. A handoff may occur when there is a transfer of duties from the large cell to the smaller cell and vice versa. For example, there is a traveling user moving within the jurisdiction of a large cell. If the traveler stops, then the jurisdiction is transferred to a microcell to relieve the load on the large cell.

· Handoffs may also occur when there is an interference of calls using the same frequency for communication.

Types of Handoffs

There are two types of handoffs −

· Hard Handoff − In a hard handoff, an actual break in the connection occurs while switching from one cell to another. The radio links from the mobile station to the existing cell is broken before establishing a link with the next cell. It is generally an inter-frequency handoff. It is a “break before make” policy.

· Soft Handoff − In soft handoff, at least one of the links is kept when radio links are added and removed to the mobile station. This ensures that during the handoff, no break occurs. This is generally adopted in co-located sites. It is a “make before break” policy.

Mobile Assisted Handoff

Mobile Assisted Handoff (MAHO) is a technique in which the mobile devices assist the Base Station Controller (BSC) to transfer a call to another BSC. It is used in GSM cellular networks. In other systems, like AMPS, a handoff is solely the job of the BSC and the Mobile Switching Centre (MSC), without any participation of the mobile device. However, in GSM, when a mobile station is not using its time slots for communicating, it measures signal quality to nearby BSC and sends this information to the BSC. The BSC performs handoff according to this information.

Satellite Communication - Services

The services of satellite communication can be classified into the following two categories.

One-way satellite communication link service
Two-way satellite communication link service

Now, let us discuss about each service one by one

One-way Satellite Communication Link Service

In one-way satellite communication link service, the information can be transferred from one earth station to one or more earth stations through a satellite. That means, it provides both point to point connectivity and point to multi point connectivity.

Below figure shows an example of one-way satellite communication link service.

Here, the communication takes place between first earth station (transmitter) and second earth station (receiver) on earth’s surface through a satellite in one direction.

Following are some of the one-way satellite communication link services.

· Broadcasting satellite services like Radio, TV and Internet services.

· Space operations services like Telemetry, Tracking and Commanding services.

· Radio determination satellite service like Position location service.

Two-way Satellite Communication Link Service

In two-way satellite communication link, the information can be exchanged between any two earth stations through a satellite. That means, it provides only point to point connectivity.

The following figure shows an example of two-way satellite communication link service.

Here, the communication takes place between first earth station (transmitter) and second earth station (receiver) on earth’s surface through a satellite in two (both) directions.

Following are some of the two-way satellite communication link services.

· Fixed satellite services like Telephone, Fax and Data of high bit rate services.

· Mobile satellite services like Land mobile, Maritime and Aero mobile communication services.

GPS Receiver

There exists only one-way transmission from satellite to users in GPS system. Hence, the individual user does not need the transmitter, but only a GPS receiver. It is mainly used to find the accurate location of an object. It performs this task by using the signals received from satellites.

The block diagram of GPS receiver is shown in below figure.

Wireless LAN and IEEE 802.11

Wireless LANs are those Local Area Networks that use high frequency radio waves instead of cables for connecting the devices in LAN. Users connected by WLANs can move around within the area of network coverage. Most WLANs are based upon the standard IEEE 802.11 or WiFi.

IEEE 802.11 Architecture

The components of an IEEE 802.11 architecture are as follows

1) Stations (STA): Stations comprise all devices and equipments that are connected to the wireless LAN. A station can be of two types:

1. Wireless Access Pointz (WAP): WAPs or simply access points (AP) are generally wireless routers that form the base stations or access.

2. Client. : Clients are workstations, computers, laptops, printers, smartphones, etc.

Each station has a wireless network interface controller.

2) Basic Service Set (BSS): A basic service set is a group of stations communicating at physical layer level. BSS can be of two categories depending upon mode of operation:

1. Infrastructure BSS: Here, the devices communicate with other devices through access points.

2. Independent BSS: Here, the devices communicate in peer-to-peer basis in an ad hoc manner.

3) Extended Service Set (ESS): It is a set of all connected BSS.

4) Distribution System (DS): It connects access points in ESS.

Advantages of WLANs

1. They provide clutter free homes, offices and other networked places.

2. The LANs are scalable in nature, i.e. devices may be added or removed from the network at a greater ease than wired LANs.

3. The system is portable within the network coverage and access to the network is not bounded by the length of the cables.

4. Installation and setup is much easier than wired counterparts.

5. The equipment and setup costs are reduced.

Disadvantages of WLANs

1. Since radio waves are used for communications, the signals are noisier with more interference from nearby systems.

2. Greater care is needed for encrypting information. Also, they are more prone to errors. So, they require greater bandwidth than the wired LANs.

3. WLANs are slower than wired LANs.

Wireless Communication - Bluetooth

Bluetooth wireless technology is a short range communications technology intended to replace the cables connecting portable unit and maintaining high levels of security. Bluetooth technology is based on Ad-hoc technology also known as Ad-hoc Pico nets, which is a local area network with a very limited coverage.

History of Bluetooth

WLAN technology enables device connectivity to infrastructure based services through a wireless carrier provider. The need for personal devices to communicate wirelessly with one another without an established infrastructure has led to the emergence of Personal Area Networks (PANs).

· Ericsson's Bluetooth project in 1994 defines the standard for PANs to enable communication between mobile phones using low power and low cost radio interfaces.

· In May 1988, Companies such as IBM, Intel, Nokia and Toshiba joined Ericsson to form the Bluetooth Special Interest Group (SIG) whose aim was to develop a defacto standard for PANs.

· IEEE has approved a Bluetooth based standard named IEEE 802.15.1 for Wireless Personal Area Networks (WPANs). IEEE standard covers MAC and Physical layer applications.

Bluetooth specification details the entire protocol stack. Bluetooth employs Radio Frequency (RF) for communication. It makes use of frequency modulation to generate radio waves in the ISM band.

The usage of Bluetooth has widely increased for its special features.

· Bluetooth offers a uniform structure for a wide range of devices to connect and communicate with each other.

· Bluetooth technology has achieved global acceptance such that any Bluetooth enabled device, almost everywhere in the world, can be connected with Bluetooth enabled devices.

· Low power consumption of Bluetooth technology and an offered range of up to ten meters has paved the way for several usage models.

· Bluetooth offers interactive conference by establishing an adhoc network of laptops.

· Bluetooth usage model includes cordless computer, intercom, cordless phone and mobile phones.

Piconets and Scatternets

Bluetooth enabled electronic devices connect and communicate wirelessly through shortrange devices known as Piconets. Bluetooth devices exist in small ad-hoc configurations with the ability to act either as master or slave the specification allows a mechanism for master and slave to switch their roles. Point to point configuration with one master and one slave is the simplest configuration.

When more than two Bluetooth devices communicate with one another, this is called a PICONET. A Piconet can contain up to seven slaves clustered around a single master. The device that initializes establishment of the Piconet becomes the master.

The master is responsible for transmission control by dividing the network into a series of time slots amongst the network members, as a part of time division multiplexing scheme which is shown below.

The features of Piconets are as follows −

· Within a Piconet, the timing of various devices and the frequency hopping sequence of individual devices is determined by the clock and unique 48-bit address of master.

· Each device can communicate simultaneously with up to seven other devices within a single Piconet.

· Each device can communicate with several piconets simultaneously.

· Piconets are established dynamically and automatically as Bluetooth enabled devices enter and leave piconets.

· There is no direct connection between the slaves and all the connections are essentially master-to-slave or slave-to-master.

· Slaves are allowed to transmit once these have been polled by the master.

· Transmission starts in the slave-to-master time slot immediately following a polling packet from the master.

· A device can be a member of two or more piconets, jumping from one piconet to another by adjusting the transmission regime-timing and frequency hopping sequence dictated by the master device of the second piconet.

· It can be a slave in one piconet and master in another. It however cannot be a master in more than once piconet.

· Devices resident in adjacent piconets provide a bridge to support inner-piconet connections, allowing assemblies of linked piconets to form a physically extensible communication infrastructure known as Scatternet.

Spectrum

Bluetooth technology operates in the unlicensed industrial, scientific and medical (ISM) band at 2.4 to 2.485 GHZ, using a spread spectrum hopping, full-duplex signal at a nominal rate of 1600 hops/sec. the 2.4 GHZ ISM band is available and unlicensed in most countries.

Range

Bluetooth operating range depends on the device Class 3 radios have a range of up to 1 meter or 3 feet Class 2 radios are most commonly found in mobile devices have a range of 10 meters or 30 feet Class 1 radios are used primarily in industrial use cases have a range of 100 meters or 300 feet.

Data rate

Bluetooth supports 1Mbps data rate for version 1.2 and 3Mbps data rate for Version 2.0 combined with Error Data Rate.

RFID Introduction

Radio frequency identification (RFID) is a general term that is used to describe a system that transmits the identity (in the form of a unique serial number) of an object wirelessly, using radio waves.

RFID technologies are grouped under the more generic Automatic Identification(Auto ID) technologies.

The barcode labels that triggered a revolution in identification systems long time ago, are inadequate in an increasing number of cases. They are cheap but the stumbling block is their low storage capacity and the fact that they cannot be reprogrammed.

an RFID System can be visualized as the sum of the following three components:

1. RFID tag or transponder
2. RFID reader or transceiver
3. Data processing subsystem

Some other areas where passive RFID has been applied in recent past are:

· Person Identification

· Food Production Control

· Vehicle Parking Monitoring

· Toxic Waste Monitoring

· Valuable Objects Insurance Identification

· Asset Management

· Access Control

Wireless Security Tutorial

In this tutorial, you will be taken on a journey through different methods of wireless communication. You will learn about Wireless Local Area Network(WLAN) as most of us know it, and then go deeper into the practical aspects behind wireless security. You will be amazed at how easy it is to collect a lot of sensitive information about wireless network and the data flowing through it, using basic tools that are easily available for anyone who knows how to use it.

Before we go deeper into the "hacking" side of the wireless communication, you will need to go through a plethora of theoretical concepts and diagrams of normal wireless system operation. Nevertheless, theoretical content will be kept to absolutely minimum throughout this Tutorial - it is the practical side of the things that is most encouraging and the most enjoyable part for everyone!

When we think about wireless communication, we imagine some systems connected to antennas that speak together over the air using radio waves that are invisible to human eye. Honestly speaking, this is perfectly a true definition, but in order to break things (or rather you prefer the word "hack") you need to learn how all those concepts and architectures work together.

Wireless Terminologies

First, let's go through the bunch of basic terms, related to wireless communication. Progressively, we will get into more advanced stuff going all along this path together.

Wireless Communication

Wireless communication refers to any type of data exchange between the parties that is performed wirelessly (over the air). This definition is extremely wide, since it may correspond to many types of wireless technologies, like −

Wi-Fi Network Communication
Bluetooth Communication
Satellite Communication
Mobile Communication

All the technologies mentioned above use different communication architecture, however they all share the same "Wireless Medium" capability.

Wi-Fi

Wireless Fidelity (Wi-Fi) refers to wireless local area network, as we all know them. It is based on IEEE 802.11 standard. Wi-Fi is a type of wireless network you meet almost everywhere, at your home, workplace, in hotels, restaurants and even in taxis, trains or planes. These 802.11 communication standards operate on either 2.4 GHz or 5 GHz ISM radio bands.

These devices are easily available in the shops that are compatible with Wi-Fi standard, they have following image visible on the device itself. I bet you have seen it hundreds of times in various shops or other public places!

Due to the fact, that 802.11 based wireless network are so heavily used in all types of environments - they are also the biggest subject for various security researches across other 802.11 standards.

Wireless Clients

Wireless clients are considered to be any end-devices with a wireless card or wireless adapter installed. Now, in this 21^st century, those devices can be almost anything −

· Modern Smartphones − These are one of the most universally used wireless devices you see in the market. They support multiple wireless standards on one box, for example, Bluetooth, Wi-Fi, GSM.

· Laptops − These are a type of device which we all use every single day!

· Smartwatch − An example of Sony based smartwatch is shown here. It can synchronize with your smartphone via a Bluetooth.

· Smart-home Equipment − With the current progress of the technology, smart-home equipment might be for example a freezer that you can control over Wi-Fi or a temperature controller.

The list of possible client devices is growing every single day. It sounds a little scary that all of those devices/utilities we use on a daily basis can be controlled via a wireless network so easily. But at the same time, remember that all the communication flowing through a wireless medium can be intercepted by anyone who is just standing at the right place at the right time.

Mobile IP: A Complete Solution for Emerging Communications

Mobile IP (or MIP) is an Internet Engineering Task Force (IETF) standard communications protocol that is designed to allow mobile device users to move from one network to another while maintaining a permanent IP address.

It enables the transfer of information to and from mobile computers, such as laptops and wireless communications. The mobile computer can change its location to a foreign network and still access and communicate with and through the mobile computer’s home network.

Mobile IP for better Mobility

Mobile IP – A technology which supports mobile data and applications that are dealing with wireless connectivity. A user may now disconnect his computer in the office and reconnect from another site within the same office or elsewhere.

http://www.tutorialspoint.com/articles/wp-content/uploads/2016/02/14475176_xl-1.jpg

Mobile IP or IP-Mobility Management (IP-MM) is an open standard communication protocol defined by Internet Engineering Task Force (IETF) that allows mobile device users to move from one network to another without changing their IP address as a change in the IP address will interrupt ongoing TCP/IP communications. Mobile IP is an enhancement of the Internet Protocol (IP) which allows a node to change its point of attachment to the Internet without needing to change its IP address.

Mobile IP is independent of the physical layer technology as the mobility functions are performed at the network layer – any media that can support IP can support Mobile IP.

Components of a Mobile IP Network

Mobile IP has three major components as mentioned below –

· Mobile Node: A device such as a cell phone, personal digital assistant, or laptop whose software enables network roaming capabilities.

· The Home Agent: A router on the home network serving as the anchor point for communication with the mobile node; its tunnel packets from a device on the Internet, called a correspondent node, to the roaming mobile node.

· The Foreign Agent: A router that may function as the point of attachment for the mobile node when it roams to a foreign network delivers packets from the home agent to the mobile node.

The Mobile IP process has three main phases –

Phase I: Agent Discovery

This is the phase where mobile node discovers its foreign and home agents. A mobile node first determines its connected location by using ICMP router discovery messages. If it’s connected location is with the local network, then the normal IP routing is used for the communication. When a mobile node determines that it has moved to a foreign network it obtains a care-of address from the foreign agent reflecting its current location.

Two types of “care-of” addresses exist –

· The care-of addresses acquired from a Foreign Agent: An IP address of a Foreign Agent that has an interface on the foreign network being visited by a Mobile node.

· The collocated care-of address: This represents the current position of the Mobile Node on the foreign network and can be used by only one Mobile Node at a time.

Phase II: Registration

This the phase, where a mobile node registers its current location with the foreign agent and the home agent. If the connected location is identified as foreign location, then the mobile node looks for a foreign agent and registers itself with the foreign location and the foreign agent, in turn, notifies the home agent and creates a tunnel between itself and the home agent. During this phase, the Mobile node sends a registration request message to the foreign agent which forwards the message to the home agent. The home agent sends back a reply after updating its registration table with the home address and “care-of” address mapping. The flow of these messages is described in the figure below. Mobile IP

Thus, a successful Mobile IP registration sets up the routing mechanism for transporting packets to and from the mobile node as it roams.

Phase III: Tunneling

This is the phase where a reciprocal tunnel is set up by the home agent to the care-of address to route packets to the mobile node as it roams. The method by which mobile IP receives information from a network is called tunneling.

It has two primary functions:

1. Encapsulation of the data packet to reach the tunnel endpoint.

2. Decapsulation, when the packet is delivered at that endpoint.

After the registration phase, the home agent now encapsulates all the packets intended for the mobile node and forwards those packets through the tunnel to the foreign agent. The foreign agent de-encapsulates the packet and forwards them to the mobile node. The return path from the mobile node is as per the standard IP routing principle where the foreign agent acts as a gateway for the mobile node.

Mobile IP tutorial

As the internet demand is growing across the world, it has become very important to maintain internet connectivity of the device while moving from place to place. This is achieved using mobile IP concept. Mobile IP can be used for both wired connectivity as well as wireless. In wired connectivity, mobile IP device can be unplugged from one attachment and connected to the other attachment. Mobile IP is more suited to the wireless connection.

In non mobile IP systems, user travelling from one place to the other need to terminate and establish the IP connection each time. Each time connection is established, new temporary IP address is assigned to the user for all the applications. In Mobile IP systems, user is connected with all the applications inspite of movement from one place to the other. The connections is being maintained automatically despite of move.

Figure-1 depicts typical mobile IP scenario for mobile node-A moving from one place to the other. As shown, a mobile node-A is assigned particular network referred as home network. IP address assigned here is referred as home address, which is static. When the host moves to the other network which is referred here as foreign network. One nodeis re-attached it will register with foreign network. It will does this through router referred as foreign agent here. Mobile node communicates care-of address to the home agent, so that it will know the foreign agent's location. This will help in exchange of IP datagrams across the Mobile IP network.

Mobile IP Protocol

To support the communications of IP datagrams mobile IP supports following capabilities.
•  Discovery:Mobile node uses discovery procedure to identify prospective home and foreign agents.
•  Registration: Mobile node uses registration procedure to communicate home agent about its care-of address while on move.
•  Tunneling: It is used to forward IP datagrams from home address to care-of address location.

DHCP (Dynamic Host Configuration Protocol)

Posted by: Margaret Rouse

WhatIs.com

Contributor(s): John Burke and Kate Gerwig

DHCP (Dynamic Host Configuration Protocol) is a network management protocol used to dynamically assign an Internet Protocol (IP) address to any device, or node, on a network so they can communicate using IP. DHCP automates and centrally manages these configurations rather than requiring network administrators to manually assign IP addresses to all network devices. DHCP can be implemented on small local networks as well as large enterprise networks.

DHCP will assign new IP addresses in each location when devices are moved from place to place, which means network administrators do not have to manually initially configure each device with a valid IP address or reconfigure the device with a new IP address if it moves to a new location on the network. Versions of DHCP are available for use in Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6).

How DHCP works

DHCP runs at the application layer of the Transmission Control Protocol/IP (TCP/IP) protocol stack to dynamically assign IP addresses to DHCP clients and to allocate TCP/IP configuration information to DHCP clients. This includes subnet mask information, default gateway IP addresses and domain name system (DNS) addresses.

DHCP is a client-server protocol in which servers manage a pool of unique IP addresses, as well as information about client configuration parameters, and assign addresses out of those address pools. DHCP-enabled clients send a request to the DHCP server whenever they connect to a network.

Clients configured with DHCP broadcast a request to the DHCP server and request network configuration information for the local network to which they're attached. A client typically broadcasts a query for this information immediately after booting up. The DHCP server responds to the client request by providing IP configuration information previously specified by a network administrator. This includes a specific IP address as well as for the time period, also called a lease, for which the allocation is valid. When refreshing an assignment, a DHCP client requests the same parameters, but the DHCP server may assign a new IP address based on policies set by administrators.

Ad Hoc Networks

The ad hoc wireless network is basically a decentralized form of a wireless network. The network is not dependent upon the common wireless infrastruct

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The ad hoc wireless network is basically a decentralized form of a wireless network. The network is not dependent upon the common wireless infrastructure which includes routers and access points that is why it is an ad hoc network. More detail...

Ad-Hoc Networks Routing Protocols

BY DINESH THAKUR Category: Network Technologies

Routing is the primary element of an ad-hoc network. It takes routing software in each network node to manage the transfer of IP packets. The simplest solution is obviously to have a direct routing, as illustrated in Figure, in which each network station can directly reach another station, without going through an intermediary. The simplest case corresponds to a small cell, with a diameter less than 100 m, as in an 802.11 network in ad-hoc mode.

The classic case of routing in an ad-hoc network is to pass through intermediate nodes. They must have a routing table adapted to direct the packet to the recipient. The whole strategy of an ad hoc network is to optimize the routing tables for updates more or less regular. If the updates are too regular, it can overload the network. However, this solution has the advantage of maintaining updated tables and therefore allow rapid packet routing. An update only when the arrival of a new wave restricted load circulating in the network, but unloads the many streams supervision network.

It should happen in this case to set up routing tables may make the delivery within an acceptable time.

Direct communication between machines on a ad-hoc network

Figure illustrates the case of an ad-hoc network in which, to get from one node to another, it may be necessary to traverse the intermediate nodes. Many pitfalls can be on the road to building the routing table. For example, signal for transmission, it is possible that the connection is not symmetrical, a sense of communication are acceptable and not the other. The routing table should reflect this. The radio signals are susceptible to interference; asymmetric links can also be complicated by possible fainting links.

For all these reasons, the network routes to be constantly modified, hence the eternal question discussed at the IETF: should maintain the routing tables in the nodes of a mobile ad-hoc network? In other words, is it worthwhile to keep updated routing tables ever changing, or is it not more sensible to determine the routing table denier now?

As explained above, the reactive protocols work by flooding to determine the best route when a packet stream is ready to be issued. So there is no exchange of outside supervision control packets to determine the path of the flood. The supervisory packet which is broadcast to all neighboring nodes is played again by the neighboring nodes to reach the receiver. Depending on the chosen technique, one can avail of the road determined by the first supervision package that arrives at the receiver or provide several routes in case of problems on the main road.

Proactive protocols behave totally differently. Supervision packets are transmitted continuously in order to keep updated the routing table by adding new lines and removing some. The routing tables are dynamic and change according supervision packets arriving at the various nodes. A difficulty in this case is to calculate a routing table that is compatible with the routing tables of the different nodes so that there is no loop.

Another possibility is to find a compromise between the two systems. That is to regularly calculate routing tables as the network is lightly loaded. Thus, the performances of user streams in transit are not too changed. When traffic increases, the updates are slowed. This method simplifies the implementation of a reactive routing table when a request reaches the network.

The proposed protocols for the normalization of the group are summarized in MANET Table. Different metrics can be used to calculate the best Road:

• The distance vectors give a weight to each link and add the weights to determine the best route, which corresponds to the least significant.

• The source routing to determine the best route as one that allows the supervision package to arrive first to the recipient.

• The states of links indicate the links that are interesting to take and those who are less so.

Metric	Reactive	Proactive
Vector distance	AODV (Ad-hoc On demand Distance Vector)	DSDV (Destination Sequence Distance Vector)
Source routing	DSR (Dynamic Source Routing)
Link Status		OLSR (Optimized LinkState Routing Protocol)

In conclusion, if MANET group studies are almost finished regarding routing, almost everything remains to be done to the quality of service, safety and power consumption.

The following briefly describes the two main routing protocols in ad hoc networks MANET standardized by the group.

OLSR (Optimized LinkState Routing)

OLSR (Optimized Link State Routing) is certainly the most used ad-hoc routing protocols. It is proactive type.

To avoid carrying too much supervision packets, OLSR relies on the concept of multipoint relays, or MPR (MultipointRelay). The CPMs are important nodes that have the distinction of being the best crossing points to reach all the nodes in a flooding process without spreading in all directions. The link state being sent by the MPR, it reduces all supervisory posts.

Knowledge of its neighbors is obtained by Hello messages that are sent in broadcast. This helps to identify the neighbors and to send the information status necessary link to the routing algorithm. The Hello messages also indicate the MPR to its neighbors. These Hello messages are intended only neighboring nodes and can not be routed to a destination with two jumps. The structure of the Hello packet is illustrated in Figure.

The Reserved field contains only 0, the HTime field indicates the time interval between Hello, Willingness the application field to a node to become a MPR, the Link Code field to pass the link state information between transmitter and receivers indicated in the list of "Neighbor Interface Address".

TC packets (Topology Control) are issued only by the MPR, always with a broadcast address. The transmitted information indicates a list of all the neighbors that have chosen this node as MPR and allows, through the knowledge of all MPR and link state, to deduce the routing table. These messages are broadcast across the network with a value of 255 in the TTL field. The structure of the TC packet is shown in Figure.

Wireless Sensor Network Architecture and Its Applications

Currently, WSN (Wireless Sensor Network) is the most standard services employed in commercial and industrial applications, because of its technical development in a processor, communication, and low-power usage of embedded computing devices. The WSN is built with nodes that are used to observe the surroundings like temperature, humidity, pressure, position, vibration, sound etc. These nodes can be used in various real-time applications to perform various tasks like smart detecting, a discovery of neighbor node, data processing and storage, data collection, target tracking, monitor and controlling, synchronization, node localization, and effective routing between the base station and nodes.

Presently, WSNs are beginning to be organized in an enhanced step. It is not awkward to expect that in 10 to 15 years that the world will be protected with WSNs with entree to them via the Internet. This can be measured as the Internet becoming a physical n/w. This technology is thrilling with infinite potential for many application areas like medical, environmental, transportation, military, entertainment, homeland defense, crisis management and also smart spaces.

What is a Wireless Sensor Network?

A Wireless Sensor Network is one kind of wireless network includes a large number of circulating, self-directed, minute, low powered devices named sensor nodes called motes. These networks certainly cover a huge number of spatially distributed, little, battery-operated, embedded devices that are networked to caringly collect, process, and transfer data to the operators, and it has controlled the capabilities of computing & processing. Nodes are the tiny computers, which work jointly to form the networks.

Wireless Sensor Network

The sensor node is a multi-functional, energy efficient wireless device. The applications of motes in industrial are widespread. A collection of sensor nodes collects the data from the surroundings to achieve specific application objectives. The communication between motes can be done with each other using transceivers. In a wireless sensor network, the number of motes can be in the order of hundreds/ even thousands. In contrast with sensor n/ws, Ad Hoc networks will have fewer nodes without any structure.

Wireless Sensor Network Architecture

The most common WSN architecture follows the OSI architecture Model. The architecture of the WSN includes five layers and three cross layers. Mostly in sensor n/w we require five layers, namely application, transport, n/w, data link & physical layer. The three cross planes are namely power management, mobility management, and task management. These layers of the WSN are used to accomplish the n/w and make the sensors work together in order to raise the complete efficiency of the network.Please follow the below link for: Types of wireless sensor networks and WSN topologies

Wireless Sensor Network Architecture

Application Layer

The application layer is liable for traffic management and offers software for numerous applications that convert the data in a clear form to find positive information. Sensor networks arranged in numerous applications in different fields such as agricultural, military, environment, medical, etc.

Transport Layer

The function of the transport layer is to deliver congestion avoidance and reliability where a lot of protocols intended to offer this function are either practical on the upstream. These protocols use dissimilar mechanisms for loss recognition and loss recovery. The transport layer is exactly needed when a system is planned to contact other networks.

Providing a reliable loss recovery is more energy efficient and that is one of the main reasons why TCP is not fit for WSN. In general, Transport layers can be separated into Packet driven, Event driven. There are some popular protocols in the transport layer namely STCP (Sensor Transmission Control Protocol), PORT (Price-Oriented Reliable Transport Protocol and PSFQ (pump slow fetch quick).

Network Layer

The main function of the network layer is routing, it has a lot of tasks based on the application, but actually, the main tasks are in the power conserving, partial memory, buffers, and sensor don’t have a universal ID and have to be self-organized.

The simple idea of the routing protocol is to explain a reliable lane and redundant lanes, according to a convinced scale called metric, which varies from protocol to protocol. There are a lot of existing protocols for this network layer, they can be separate into; flat routing and hierarchal routing or can be separated into time driven, query-driven & event driven.

Data Link Layer

The data link layer is liable for multiplexing data frame detection, data streams, MAC, & error control, confirm the reliability of point–point (or) point– multipoint.

Physical Layer

The physical layer provides an edge for transferring a stream of bits above physical medium. This layer is responsible for the selection of frequency, generation of a carrier frequency, signal detection, Modulation & data encryption. IEEE 802.15.4 is suggested as typical for low rate particular areas & wireless sensor network with low cost, power consumption, density, the range of communication to improve the battery life. CSMA/CA is used to support star & peer to peer topology. There are several versions of IEEE 802.15.4.V.

Characteristics of Wireless Sensor Network

The characteristics of WSN include the following.

· The consumption of Power limits for nodes with batteries

· Capacity to handle with node failures

· Some mobility of nodes and Heterogeneity of nodes

· Scalability to large scale of distribution

· Capability to ensure strict environmental conditions

· Simple to use

· Cross-layer design

Advantages of Wireless Sensor Networks

The advantages of WSN include the following

· Network arrangements can be carried out without immovable infrastructure.

· Apt for the non-reachable places like mountains, over the sea, rural areas and deep forests.

· Flexible if there is a casual situation when an additional workstation is required.

· Execution pricing is inexpensive.

· It avoids plenty of wiring.

· It might provide accommodations for the new devices at any time.

· It can be opened by using a centralized monitoring.

Wireless Sensor Network Applications

Wireless sensor networks may comprise of numerous different types of sensors like low sampling rate, seismic, magnetic, thermal, visual, infrared, radar, and acoustic, which are clever to monitor a wide range of ambient situations. Sensor nodes are used for constant sensing, event ID, event detection & local control of actuators. The applications of wireless sensor network mainly include health, military, environmental, home, & other commercial areas.

· Military Applications

· Health Applications

· Environmental Applications

· Home Applications

· Commercial Applications

· Area monitoring

· Health care monitoring

· Environmental/Earth sensings

· Air pollution monitoring

· Forest fire detection

· Landslide detection

· Water quality monitoring

· Industrial monitoring

Wireless Communication - TCP/IP

Layers in the TCP/IP Suite

The four layers of the TCP/IP model are the host-to-network layer, internet/network layer, transport layer and the application layer. The purpose of each layer in the TCP/IP protocol suite is detailed below.

The above image represents the layers of TCP/IP protocol suite.

Physical Layer

TCP/IP does not define any specific protocol for the physical layer. It supports all of the standard and proprietary protocols.

· At this level, the communication is between two hops or nodes, either a computer or router. The unit of communication is a single bit.

· When the connection is established between the two nodes, a stream of bits is flowing between them. The physical layer, however, treats each bit individually.

The responsibility of the physical layer, in addition to delivery of bits, matches with what mentioned for the physical layer of the OSI model, but it mostly depends on the underlying technologies that provide links.

Data Link Layer

TCP/IP does not define any specific protocol for the data link layer either. It supports all of the standard and proprietary protocols.

· At this level also, the communication is between two hops or nodes. The unit of communication however, is a packet called a frame.

· A frame is a packet that encapsulates the data received from the network layer with an added header and sometimes a trailer.

· The head, among other communication information, includes the source and destination of frame.

· The destination address is needed to define the right recipient of the frame because many nodes may have been connected to the link.

· The source address is needed for possible response or acknowledgment as may be required by some protocols.

LAN, Packet Radio and Point-to-Point protocols are supported in this layer

Network Layer

At the network layer, TCP/IP supports the Internet Protocol (IP). The Internet Protocol (IP) is the transmission mechanism used by the TCP/IP protocols.

IP transports data in packets called datagrams, each of which is transported separately.
Datagrams can travel along different routes and can arrive out of sequence or be duplicated.

IP does not keep track of the routes and has no facility for reordering datagrams once they arrive at their destination.

Transport Layer

There is a main difference between the transport layer and the network layer. Although all nodes in a network need to have the network layer, only the two end computers need to have the transport layer.

· The network layer is responsible for sending individual datagrams from computer A to computer B; the transport layer is responsible for delivering the whole message, which is called a segment, from A to B.

· A segment may consist of a few or tens of datagrams. The segments need to be broken into datagrams and each datagram has to be delivered to the network layer for transmission.

· Since the Internet defines a different route for each datagram, the datagrams may arrive out of order and may be lost.

· The transport layer at computer B needs to wait until all of these datagrams to arrive, assemble them and make a segment out of them.

Traditionally, the transport layer was represented in the TCP/IP suite by two protocols: User Datagram Protocol (UDP) and Transmission Control Protocol (TCP).

A new protocol called Stream Control Transmission Protocol (SCTP) has been introduced in the last few years.

Application Layer

The application layer in TCP/IP is equivalent to the combined session, presentation, and application layers in the OSI model.

· The application layer allows a user to access the services of our private internet or the global Internet.

· Many protocols are defined at this layer to provide services such as electronic mail file transfer, accessing the World Wide Web, and so on.

· The protocols supported in this layer are TELNET, FTP and HTTP.

Network Applications

Computer systems and peripherals are connected to form a network.They provide numerous advantages:

Resource sharing such as printers and storage devices
Exchange of information by means of e-Mails and FTP
Information sharing by using Web or Internet
Interaction with other users using dynamic web pages
IP phones
Video conferences
Parallel computing
Instant messaging

Effect of User Mobility on Communication Systems

User movements affect the communication system at many layers:

At the physical layer, channel characteristics vary with the location of the user and because of mobility, vary in time. Because antennas mounted on vehicles have rather unfavourable positions and little 'clearance', the propagation characteristics in the mobile radio channel are notoriously poor. A mobile radio link is hindered by a number of propagation mechanisms, viz., multipath scattering from objects near the mobile antenna, shadowing by dominant obstacles and attenuation mechanisms on the propagation path between transmitter and receiver.

Multipath reception causes rapid fluctuations of the received signal power, whereas shadowing is experienced as a slow amplitude effect. Adaptive transmit power control can mitigate the adverse effects of individual shadowing to some extent. Since most mobile networks are interference-limited rather than noise-limited, interfering signals are likely to produce substantially greater adverse collective impact if adaptive power control is used to overcome shadowing on their own transmission path. Mobile systems must live with signal fluctuations during transmission. Because of high demands on spectrum efficiency, extensive frequency re-use and mutual interference must be accepted. This means that the classical system analysis inspired by the stationary AWGN channel of conventional information theory may not be applicable.

At the data link layer, channel coding is to be chosen in accordance with the specific character of the fading radio channel. In contrast to AWGN channels with errors randomly distributed in time, bursts (i.e., clusters of) errors are experienced in the mobile channel. A typical mobile channel allows relatively reliable communication during certain periods, interrupted by other periods of particularly poor communication. The latter are called 'fades'.
At the network layer, the routing of signals may change from time to time as the user moves through the service area of the network. This may require localisation of the terminal (or localisation of a specific user in more sophisticated 'personal' communication systems) to find optimum routing.
Transport layer protocols and applications should anticipate to fading and channel throughput fluctuations. This many be at odds with strictly OSI layered protocol stacks.
At the presentation layer, improved (speech and video) source coding techniques have helped in achieving acceptable spectrum efficiency with digital systems.
At the application layer (and above), personal mobility and transportation of goods require specific services and facilities.

file system

A file system typically manages operations, such as storage management, file naming, directories/folders, metadata, access rules and privileges. Commonly used file systems include File Allocation Table 32 (FAT 32), New Technology File System (NTFS) and Hierarchical File System (HFS).

Database is a collection of related data and data is a collection of facts and figures that can be processed to produce information.

Mostly data represents recordable facts. Data aids in producing information, which is based on facts. For example, if we have data about marks obtained by all students, we can then conclude about toppers and average marks.

A database management system stores data in such a way that it becomes easier to retrieve, manipulate, and produce information.

https://www.tutorialspoint.com/dbms/images/dbms_users.png

WWW stands for World Wide Web. A technical definition of the World Wide Web is : all the resources and users on the Internet that are using the Hypertext Transfer Protocol (HTTP).

A broader definition comes from the organization that Web inventor Tim Berners-Lee helped found, the World Wide Web Consortium (W3C).

The World Wide Web is the universe of network-accessible information, an embodiment of human knowledge.

In simple terms, The World Wide Web is a way of exchanging information between computers on the Internet, tying them together into a vast collection of interactive multimedia resources.

Internet and Web is not the same thing: Web uses internet to pass over the information.

WAP - Introduction

WAP - Introduction

[WAP is] the de facto worldwide standard for providing Internet communications and advanced telephony services on digital mobile phones, pagers, personal digital assistants, and other wireless terminals − WAP Forum.

WAP stands for Wireless Application Protocol. The dictionary definition of these terms are as follows −

· Wireless − Lacking or not requiring a wire or wires pertaining to radio transmission.

· Application − A computer program or piece of computer software that is designed to do a specific task.

· Protocol − A set of technical rules about how information should be transmitted and received using computers.

WAP is the set of rules governing the transmission and reception of data by computer applications on or via wireless devices like mobile phones. WAP allows wireless devices to view specifically designed pages from the Internet using only plain text and very simple black-and-white pictures.

WAP is a standardized technology for cross-platform, distributed computing very similar to the Internet's combination of Hypertext Markup Language (HTML) and Hypertext Transfer Protocol (HTTP), except that it is optimized for:

· low-display capability

· low-memory

· low-bandwidth devices, such as personal digital assistants (PDAs), wireless phones, and pagers.

DCN - Application Layer Introduction

Application layer is the top most layer in OSI and TCP/IP layered model. This layer exists in both layered Models because of its significance, of interacting with user and user applications. This layer is for applications which are involved in communication system.

A user may or may not directly interacts with the applications. Application layer is where the actual communication is initiated and reflects. Because this layer is on the top of the layer stack, it does not serve any other layers. Application layer takes the help of Transport and all layers below it to communicate or transfer its data to the remote host.

When an application layer protocol wants to communicate with its peer application layer protocol on remote host, it hands over the data or information to the Transport layer. The transport layer does the rest with the help of all the layers below it.

There’is an ambiguity in understanding Application Layer and its protocol. Not every user application can be put into Application Layer. except those applications which interact with the communication system. For example, designing software or text-editor cannot be considered as application layer programs.

On the other hand, when we use a Web Browser, which is actually using Hyper Text Transfer Protocol (HTTP) to interact with the network. HTTP is Application Layer protocol.

Another example is File Transfer Protocol, which helps a user to transfer text based or binary files across the network. A user can use this protocol in either GUI based software like FileZilla or CuteFTP and the same user can use FTP in Command Line mode.

Hence, irrespective of which software you use, it is the protocol which is considered at Application Layer used by that software. DNS is a protocol which helps user application protocols such as HTTP to accomplish its work.

Thursday, 23 May 2019

M.tech 2nd sem MTCS202 Wireless Mobile Networks

Features of Wireless Communication

Wireless - Advantages

Cost effectiveness

Flexibility

Convenience

Speed

Accessibility

Constant connectivity

DCN - Wireless Transmission

Radio Transmission

Microwave Transmission

Infrared Transmission

Light Transmission

DCN - Multiplexing

Frequency Division Multiplexing

Time Division Multiplexing

Wavelength Division Multiplexing

Code Division Multiplexing

Spread Spectrum Modulation

Pseudo-Noise Sequence

Narrow-band and Spread-spectrum Signals

Narrow-band Signals

Spread Spectrum Signals

FHSS and DSSS / CDMA

Frequency Hopped Spread Spectrum (FHSS)

Direct Sequence Spread Spectrum (DSSS)

Comparison between FHSS and DSSS/CDMA

Advantages of Spread Spectrum

Antenna Theory - Fundamentals

What is an Antenna ?

Need of Antenna

Scenario

Radiation Mechanism

Basic Types of Antennas

Physical structure

Frequency of operation

Mode of Applications

Medium Access Control Sublayer (MAC sublayer)

MAC Layer in the OSI Model

Functions of MAC Layer

MAC Addresses

Wireless Communication - Multiple Access

Multiple Access Techniques

Narrowband Systems

Wideband Systems

Frequency Division Multiple Access (FDMA)

Time Division Multiple Access (TDMA)

Code Division Multiple Access (CDMA)

Space Division Multiple Access (SDMA)

Spread Spectrum Multiple Access

Frequency Hopped Spread Spectrum (FHSS)

Direct Sequence Spread Spectrum (DSSS)

Wireless Telecommunications Systems

What is GSM?

Why GSM?

GSM - Architecture

GSM network areas

DECT (Digital Enhanced Cordless Telecommunications)

UMTS Tutorial

LTE Overview

Facts about LTE

Advantages of LTE

Satellite Communication Tutorial

Need of Satellite Communication

How a Satellite Works

Pros and Cons of Satellite Communication

Applications of Satellite Communication

Satellite Communication - Introduction

Need of Satellite Communication

How a Satellite Works

Pros and Cons of Satellite Communication

Applications of Satellite Communication

Low-Earth Orbit Satellites

Features of LEO Satellites

Types of LEO Satellites and their Uses

Geostationary Satellite and Geostationary Orbit (GEO)

Uses and Examples of Geosynchronous Satellites

Uses