The document summarizes the evolution of mobile telephone systems from analog to digital technologies. It describes early analog systems like Advanced Mobile Phone System (AMPS) and its features. It then discusses the transition to digital with Digital AMPS (D-AMPS) and the widespread adoption of Global System for Mobile Communications (GSM) as the dominant 2G standard. It also provides a brief overview of Code Division Multiple Access (CDMA) technology and 3G standards like W-CDMA and CDMA2000.

1. THE MOBILETELEPHONE SYSTEMS

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

7. 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.

8.  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.

14. 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

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

16. 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.

17. 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.

19. 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.

20. 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.

21.  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.

23. 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

24. 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.

25. 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.

26.  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.

27. 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

28. GSM—The Global System for Mobile
Communications

30.  The use both FDM andTDM 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.

31.  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.

32. 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)

33. 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

34. - - 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

35. 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

36.  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

38. 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

39.  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