ASSIGNMENT OF WIRELESS AND MOBILE COMMUNICATION

Question No.1 Describe Wireless Communication. Explain its advantages.

Wireless Communication:-

A telecommunication system or communication system is a collection of interconnected equipment’s or communication devices. The prime objective of the communication system is to exchange data or information among these devices. The data or information may be a voice data like human conversation of any electronic data like a web data. The devices associated in a communication system may generate data; consume data or forward data from one device to another. Some examples of devices that generate and consume data are a mobile phone or a computer terminal. A relay station on the other hand is an example of device that forwards data. In a communication system transmission media plays a vital role to transferring data from one device to another device. These transmission media may be a wire connecting two devices or a radio wave used for transferring data without any physical cable. In information technology, a computer network, or simply a network, is a collection of computers and devices interconnected by communications media to facilitate information exchange. It also can be used to share resources like printer, storage devices, data etc. In the earlier days the computer networks were used only by large companies due to high cost of network installation but now it is affordable even for individuals. computer networking it requires at least two computers, a protocol and the transmission media (say cable) hardware to connect them. Businesses aren't the only ones that can benefit from creating a network. Home users can enjoy sharing music, movies and printers from any computer. Home users can enjoy sharing music, movies and printers from any computer. Few major use of network is listed below.

1.   File sharing

2.  Printers

3.  Sharing storage media

4.  Media Centre server

5.  Video games

Advantages of wireless communication systems:-

Although the benefits of a communication system are very large, however the setting up of a communication system or a computer network using wired links is comparatively difficult. These difficulties are arises from the requirement of Ethernet cables to connect computers to a Digital Subscriber Link (DSL) cable modem. Because, the lay down of cables for connecting devices is often quite hazy. Most people do not prefer cables to be laid down throughout their home. Compared to wired system, wireless networks have many advantages. Few of them are listed below. The wireless network can be configured without the use of physical cable to connect computers and other networked devices. So it is the preferred way to setup a network without using cables. If the users of the network ever have to move then it is as easy to install in your next place by simply relocating the wireless devices in the new place. It is quite common however for people to use a mix of wired and wireless solutions on their home networks. It is possible as almost all wireless routers also have normal network ports to add wired computers to the network. For an already existing wired network a wireless router is the cheapest way to add wireless connections to extend the network segment. Wireless Networks can help make connecting to the internet much more convenient. Wireless network can be set-up on demand.

Question No.2 Describe any five GSM PLMN basic services.

Basic services:-

All activities that may be done in the GSM network, such as establishing a voice call, establishing a data call, sending a short message, etc., are classified as basic services. In order for a subscriber to use a GSM basic service, the subscriber must have a subscription to that service. These tele services in details are discussed briefly below.

1. Dual-Tone multi frequency (DTMF):

The automatic answering machines used in wireless telephone network needs a controlling mechanism. For this purpose the GSM PLMN uses a tone signaling service called Dual-Tone Multi frequency. It facilitates subscribers with

automatic answering capability whenever necessary.

2. Facsimile group III:

Standard fax machines need to be connected to a telephone using analog signals, so a special fax converter needs to be installed in the GSM system. This will help the fax to be connected to the GSM and thus communicate with any other analog fax in the

network.

3. Short message services (SMS):

The SMS allows subscribers to send a message consisting of a fixed maximum length of alphanumeric characters among mobile stations. It also facilitates the subscriber by taking care of the message delivery in case of user’s temporary absence from the network. If the user’s mobile is switched off or out of coverage area, the message is stored and offered back to the user when the mobile is powered on or re-entered the coverage area of the network.

4. Cell broadcast:

A message whose maximum length is 93 characters can be broadcasted to all the users who are in particular geographical region. This facility is primarily used for network management especially when traffic congestion is reported. The broadcasted messages may be used to warn different controlling devices about the congestion and any failure in the network.

5. Voice mail:

This service is provides a method of answering unattended calls automatically. These answering machines are located within the network and calls are forwarded to the subscriber’s voice-mail box if it is not attended during a stipulated time. When the subscriber checks for

messages via a personal security code he can here the voice recorded in the voice-mail box.

6. Fax mail:

The user can receive fax messages at any fax machine. The messages are stored in a service Centre from which they can be retrieved by the subscriber via a personal security code to the desired fax number.

Question No. 3 Explain the use of control channels in GSM network.

Common control channels:-

Control channels are communication channels which are used only for sending and receiving command messages between communication devices in a system. In GSM network the control channels are used to send messages for alerting a device about a incoming call, for accessing control and transmitting broadcast information to all devices. There are several control channels available for the GSM architecture. The Paging Channel (PCH), the Access Grant Channel (AGCH) and the Random Access Channel (RACH). The PCH transmits a paging message at certain time intervals to indicate an MS listens to the PCH. The paging message contains the subscriber identity number and the mobile station that matches the identity responds. The message in PCH indicates that the mobile station whose identity appears in the PCH is informed that the network wishes to contact. The base station than receives a response from the mobile station through RACH. The mobile station receives an reply through the RACH channel from the base station.

Dedicated control channels:-

The dedicated control channels are communication channels that transfer signaling messages to specific devices in a GSM network. There are three dedicated control channels found in GSM network. They are the Standalone Dedicated Control Channel (SDCCH), the slow associated control channel (SACCH) and the fast associated control channel (FACCH). The GSM SDCCH is used for signaling between base station and mobile station during call setup. The GSM slow associated control channel (SACCH) is used to measure the signal strength periodically. If the mobile station detects a change in current signal strength then it initiates a handover to any nearby cell. The GSM fast associated control channel (FACCH) is also used for the same purpose as the SDCCH, but it makes use of the unused capacity of a traffic channel.

Question No. 4 What is CDMA? Explain the history of CDMA.

CDMA (CDMA stands for Code Division):-

CDMA stands for Code Division Multiple Access and in the cellular world, CDMA technology was originally known as IS-95. Basically CDMA is a "spread spectrum" technology that has been used in digital cellular radio communications and advanced wireless technologies, and allows many users to occupy the same time and frequency allocations in a given band. In

CDMA unique codes are assigned to each communication in order to differentiate each others in the same spectrum. Also note that CDMA does not assign a specific frequency, but the full available spectrum to each user and a unique code is used for each signal, so that they can be differentiated. In other words, all users can use the same frequency and transmit at the same time but the users are separated by unique code. This allows a large number of users to share the same frequency band at the same time, without any interference. The receiving device is such that it uses the code to extract the data out of the received signal. The services available to CDMA users are: m-commerce such as paying bills, purchasing, MMS (multimedia messaging services), web browsing, entertainment (streaming video, games), email, video conferencing and file download.

                       

History of CDMA:-

CDMA was first used in the military during World War 2. Digital cellular applications based on CDMA were developed with the collaboration of several carrier and equipment manufacturers, such as Motorola, P.C.S., and NOKIA. The first generation of cellular systems, was introduced in the early 1980s.This include the Advanced Mobile Phone Systems (AMPS).These systems used analog frequency modulation (FM) and have a frequency division multiple access (FDMA) based media access control (MAC) architecture. Within a few years, market demands and capacity requirements began to grow hitting the practical limitations. These limitations motivated the development of the second generation cellular systems, which improved compatibility and accommodated higher capacity than the first generation systems. These systems use digital modulation and processing techniques. TDMA (Time Division Multiple Access), GSM (Global System for Mobile Communication) and (narrowband). CDMA belong to the second generation

systems. CDMA was introduced in 1994, by Qualcomm, Inc. and later enhanced by Ericsson. CDMA is characterized by high capacity and small cell radius, employing spread-spectrum technology and a special coding scheme. The world is demanding more from wireless communication technologies than ever before as more people around the world are subscribing to wireless. Add in exciting Third-Generation (3G) wireless data services and applications – such as wireless email, web, digital picture taking/sending, assisted-GPS position location applications, video and audio streaming and TV broadcasting – and wireless networks are doing much more than just a few years ago. This is where CDMA technology fits in. 2G CDMA standards are branded cdma one and include IS-95A and IS-95B. CDMA consistently provides better capacity for voice and data communications than other commercial mobile technologies. This allows more and more subscribers to connect at any given time and today, CDMA is the basis to the third generation market in the United States and other places in the world. The two dominant IMT-2000 standards, CDMA2000 and WCDMA, are based on CDMA. The CDMA air interface is used in both 2G and 3G networks.

Question No. 5 Identify detailed implementation about A5 algorithm?

A5 Algorithm – An A5 encryption algorithm scrambles the user's voice and data traffic between the handset and the base station to provide privacy. An A5 algorithm is implemented in both the handset and the base station subsystem (BSS). This algorithm is used to encipher and decipher the data that is being transmitted on the Um interface. The Kc (ciphering key) and the plaintext data are inputted into the A5 algorithm and the output is enciphered data. The A5 algorithm is a function of the Mobile Equipment (ME) and not a function of the SIM card. The BTS also makes use of the A5 algorithm. There are three versions of the A5 algorithm:

A5/1 – it is a current standard for U.S. and European networks. A5/1 is a stream cipher.

A5/2 – This is a deliberately weakened version of A5/1 that is intended for export to non-western countries. A5/2 is a stream cipher.

A5/3 – it is a newly developed algorithm not yet in full use. A5/3 is a block cipher. The details of the implementation, as well as some documented facts about A5, are summarized below:

1.   A5 is a stream cipher involves three clock-controlled LFSRs of degree 19, 22, and 23.

2.  The clock control is a threshold function of the middle bits of each of the three shift registers.

3.  The sum of the degrees of the three shift registers is 64 (19+22+23). The 64-bit session key is used to initialize the contents of the shift registers.

4.  This shift registers contains a 22bit TDMA frame number.

5.  For each TDMA frame two 114-bit key streams can be produced, which are XOR-edwith the uplink and downlink traffic channels.

6.  A5 algorithm has an "effective" key length of 40 bits. The use of authentication, encryption, and temporary identification numbers ensures the privacy and secrecy of the system's users, as well as the protection of the system against fraudulent use. Even GSM systems with the

7.  A5/2 encryption algorithm are inherently more secure than analog systems due to their use of speech coding, digital modulation, and TDMA channel access.

Question No.6 List and explain the different path loss models?

Path Loss Models:-

Path loss models describe the signal attenuation between a transmit and a receive antenna as a function of the propagation distance and other parameters. Some models include many details of the topography profile to estimate the signal reduction, whereas others just consider carrier frequency and distance. Path loss is the reduction in power density of an electromagnetic wave as it propagates through space. It is a major component in the analysis and design of the link budget of a telecommunication system. It represents signal level attenuation caused by free space propagation, reflection, diffraction and scattering. There are basically 4 types of path loss models

1. Mega cell Path loss models

2. Macro cell Path loss models

3. Micro cell Path loss models

4. Pico cell Path loss models

1. Mega cell Path loss models: Mega cell path loss models are those where the communication is over extremely large cells spanning hundreds of kilometres. Mega cells are served mostly by mobile satellites. The path loss is usually the same as that of free space.

2. Macro cell Path loss models: Macro cell path loss models span a few kilometres to tens of kilometres, depending on the location. These are the traditional “cells” corresponding to the coverage area of a base station associated with traditional cellular telephony base stations. The frequency of operation is mostly around 900 MHz, though the emergence of PCS has resulted in frequencies around 1,800 to 1,900 MHz for such cells.

3. Micro cell Path loss models: Micro cells are cells that span hundreds of meters to a kilometre and are usually supported by below rooftop level base station antennas mounted on lampposts or utility poles. The shapes of the microcells are also no longer circular because they are deployed in streets in urban areas where tall buildings create urban canyons. There is little or no propagation of signals through buildings, and the shape of a microcell is more liked a cross or a rectangle, depending on the placement of base station antennas at the intersection of streets or in between intersection.

4. Pico cell Path loss models: In pico cell path loss model base station antenna located inside the building. Pico cells correspond to radio cells covering a building or parts of buildings. The span of pico cells is anywhere between 30m and 100m. Usually, Pico cells are employed for WLANs, wireless PBX (Private branch exchange) systems, and PCSs operating in indoor areas. In a pico-cell, the shorter transmission distance coupled with lower transmit power, enhances both capacity as well as the Signal to Interference Noise Ratio (SINR) achievable within the cell.

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