Mobile telephone systems

generation of mobile telephone system in computer networks, classification of mobile phone in computer networks.

1. THE MOBILE TELEPHONE SYSTEMS

2. Wireless telephones come in two basic varieties: Cordless phones – A set for use within the home. Mobile phones – 3 distinet generations, with different technologies. a) analog voice. b) digital voice. c) digital voice and data ( internet, e-mail etc)

3. Advanced Mobile Phone System Advanced mobile phone system (AMPS) was a standard for analog cellular phone system developed by Bell Labs and officially introduced by AT&T in 1983 . Features It is an analog system based on the initial electromagnetic spectrum allocation for cellular service by the Federal Communications Commission. It uses frequency division multiple access (FDMA) for multiple simultaneous conversations.

4. Frequency ranges within the 800 and 900 MHz are allocated for cellular telephones in AMPS. Half of the signal is used for sending signals and half is used for receiving signals. It has a high bandwidth requirement particularly when the number of conversations is very high. It was the first system to use hexagonal cells. So, the pioneers of AMPS had coined the term coined cellular. The cells in AMPS are 10km to 20 km across. Since, it was an analog technology, it suffered from noise and eavesdropping.

5. Channels: The AMPS system uses 832 full-duplex channels, each consisting of a pair of simplex channels. There are 832 simplex transmission channels from 824 to 849Mhz and 832 simplex receive channels from 869 to 894 Mhz. Each of these simplex channels is 30KHz AMPS uses FDM to separate the channels

6. The 832 channels are divided into four categories: Control to manage the system. (base to mobile) Paging to alert mobile users to calls for them. ( base to mobile) Access for call setup and channel assignment. (bidirectional) Data for voice, fax or data. (bidirectional)

7. Call management Each mobile telephone in AMPS has a 32-bit serial number and a 10-digit telephone number in its PROM. The telephone number is represented as a 3-digits are code in 10-bits, and 7-digit subscriber number inn 24 bits.

8. Call management Each mobile telephone in AMPS has a 32-bit serial number and a 10-digit telephone number in its PROM. The telephone number is represented as a 3-digits are code in 10-bits, and 7-digit subscriber number inn 24 bits.

9. Digital Advanced Mobile Phone System Digital Advanced Mobile Phone System (D-AMPS)is a digital version of Advanced Mobile Phone Systems (AMPS), the original analog standard for cellular phones. D-AMPS uses a combination of time division multiple access (TDMA) and frequency division multiple access (FDMA). It adds TDMA to get three channels per AMPS channel, thus tripling the number of calls on a channel.

10. Features They are standardised by IS-54 and IS-136. As in AMPS, D-AMPS also uses frequencies from 800 to 900MHz for transmission. Half of the spectrum is used for sending signals and the other half is used for receiving signals. The frequency band is divided into 30KHz sub-bands, called channels, by FDMA. The channels for uplink are called forward channels and the channels for downlink are called reverse channels.

11. TDMA is applied to each channel thus tripling the number of available channels. Presently, all D-AMPS channels are replaced by GSM or CDMA technology.

12. GSM—The Global System for Mobile Communications (1) GSM mobile network architecture. Computer Networks , Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education-Prentice Hall, 2011

13. Global System for Mobile Communications Global System for Mobile communication (GSM) is the most widely used digital mobile telephony system. GSM technology was first launched in Finland in 1991. It was developed by European Telecommunications Standards Institute (ETSI) to describe the protocols for 2G mobile communications . Presently , GSM comprises of approximately 90% of mobile connections worldwide.

14. Features Original 2G standard was a digital, circuit-switched, full duplex network. GSM is part of the evolution of wireless mobile telecommunications including High-Speed Circuit-Switched Data (HSCSD), General Packet Radio Services (GPRS), Enhanced Data GSM Environment (EDGE), and Universal Mobile Telecommunications Service (UMTS). GSM operates at either 900 MHz or 1800 MHz frequency bands of the electromagnetic spectrum . It provides improved spectrum efficiency.

15. It uses a variation of time division multiple access (TDMA) for placing multiple calls simultaneously over the same channel. It gives support for a number of new services like International roaming Compatibility with integrated services digital network (ISDN) Short message service (SMS) SIM phonebook management Fixed dialing number (FDN) Digital technology assures high-quality voice communications and advanced encryption of voice and data signals that prevents eavesdropping.

16. GSM—The Global System for Mobile Communications (2) GSM uses 124 frequency channels, each of which uses an eight-slot TDM system. Computer Networks , Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education-Prentice Hall, 2011

17. GSM—The Global System for Mobile Communications

18. The use both FDM and TDM to divide the spectrum into channels and the channels into time slots. CDMA is completely different from AMPS, D-AMPS, and GSM. Instead of dividing the allowed frequency range into a few hundred narrow channels. It allows each station to transmit over the entire frequency spectrum all the time. Multiple simultaneous transmissions are separated using coding theory.

19. Each bit time is subdivided into m short intervals called chips. (64 or 128 chips) Each station is assigned a unique m-bit code called a chip sequence. To transmit a 1 bit, a station sends its chip sequence. To transmit a 0 bit, it sends the one’s complement of its chip sequence. No other patterns are permitted.

20. Example M=8, A is assigned the chip sequence 00011011, it sends cca 1 bit by sending 00011011 and 0 bit by sending 11100100. Information to be sent from b bits/sec to mb chips/sec. Bandwidth available is m. It more convenient to use bipolar notation, binary 0 being -1 and binary 1 being +1. So a 1 bit for station A now becomes (-1-1-1+1+1-1+1+1)

21. A: 00011011 B: 00101110 C: 01011100 D: 01000010 A: (-1-1-1+1+1-1+1+1) B: (-1-1+1-1+1+1+1-1) C: (-1+1-1+1+1+1-1-1) D: (-1+1-1-1-1-1+1-1) Binary chip sequences for four stations Bipolar chip sequences

22. - 1 - C 1 1 1 B + C 1 0 - - A + B(B bar) 1 0 1 - - A + B (B bar)+ C 1 1 1 1 A + B + C + D 1 1 0 1 A + B + C (C bar) + D six example of transmission

23. S1= (-1+1-1+1+1+1-1-1) S2= B + C B= -1-1+1-1+1+1+1-1 C= -1+1-1+1+1+1-1-1 B + C = -2 0 0 0 +2 +2 0 -2

24. Recovery of station C’s signal. S1 .C = (1+1+1+1+1+1+1+1)/8=1 S1 = -1+1-1+1+1+1-1-1 C = -1+1-1+1+1+1-1-1

25. Digital Voice and Data (1) Basic services intend by IMT-2000 network High-quality voice transmission. Messaging (replacing email, fax, SMS, chat). Multimedia (music, videos, films, television). Internet access (Web surfing, incl. audio, video). Computer Networks , Fifth Edition by Andrew Tanenbaum and David Wetherall, © Pearson Education-Prentice Hall, 2011

26. W-CDMA (Wideband CDMA) was proposed by Ericsson. Direct sequence spread spectrum It runs in a 5MHz bandwidth has been design to interwork with GSM networks. UMTS (Universal mobile telecommunications system) CDMA2000, proposed by Qualcomm Direct sequence spread spectrum design, basically an extension of IS-95