History of Mobile Communications

The history of mobile communications

can be divided into the following

categories:

• First Generation (1G) Systems

• Second Generation (2G) Systems

• Third Generation (3G) Systems

1G

First Generation Systems use analog communication techniques to transmit voice data over the radio spectrum. There are a number of different protocols for 1G systems. These are:

• Nordic Mobile Telephone (NMT) systems

• Advanced Mobile Phone Services (AMPS)

• Total Access Communication System (TACS)

• The first cellular commercial systems were not installed until the late 1970s with the implementation of the Nordic Mobile Telephone (NMT) system in Europe in 1979. There are two versions of the NMT system, NMT-450 and NMT-900.

• These use different carrier frequencies and were implemented in some countries because of lack of capacity on the 450MHz bandwidth. The Advanced Mobile Phone Service (AMPS) was implemented in the US in 1982. The Total Access Communication System (TACS) followed in the UK in 1983.

The following table describes 1G systems that

have been implemented:

AMPS TACS NMT450 NMT900

Base Tx (MHz)

869-894 935-960 463-468 935-960

Base Rx (MHz)

824-849 890-915 453-458 890-915

Multiple Access

Method

FDMA FDMA FDMA FDMA

Modulation Technique

FM FM FM FM

Radio Channel Spacing

30 kHz 25 kHz 25 kHz 12.5 kHz

Number of Channels

832 1000 200 1999

Spectrum Allocation

50 MHz 50 MHz 10 MHz 50 MHz

2G

For second generation systems digital radio techniques are used. 2G systems have a much higher capacity, greater security and more advanced services than 1G systems. For 2G systems a frequency channel is simultaneously divided amongst several users using techniques such as code division and time division. Current 2G mobile phones send and receive data at 9.6 kbps. 2G systems were introduced in the mid 1990s.

The main standards for 2G systems

are:

• Global System for Mobile Communications (GSM)

• Code-Division Multiple Access (CDMA)

• Interim Standard 136 (IS-136) TDMA

• For 2G systems different countries have adopted different standards. However, by far the most successful and widely used 2G system is the GSM system. Only in North America has GSM not reached a dominant position. GSM is the main 2G system implemented throughout Europe and Asia, as well as Australia.

• GSM uses the 900MHz band, but there are also several derivatives (GSM-1800, GSM-1900). These differ in the frequency band used for the carrier frequency.

• The main reason for introducing the derivatives was because of lack of capacity in the 900MHz band. GSM is a Time Division Multiple Access (TDMA) system.

• CDMA is a 2G system where different transmissions are separated by codes instead of by other techniques. CDMA becomes very important for 3G systems because 3G communications is based on this technology. CDMA will be discussed in depth later. CDMA has been implemented throughout North America as a 2G system

• IS-136 is a 2G system also implemented in North America. It is a digital upgrade of the AMPS 1G system and it uses TDMA as its radio transmission technology.

The following table shows the

differences between 2G technologies: GSM CDMA (IS-95) IS-136

Base Tx (MHz) 925-960 869-894 851-866

Base Rx (MHz) 880-915 869-894 806-821

Multiple Access

Method TDMA/FDMA CDMA TDMA

Modulation 0.3 GMSK QPSK Pi/4DPSK

Radio Channel

Spacing 200 kHz 1.25 MHz 30 kHz

Users/Channel 8 64 3

Number of

Channels 124 19 600

CODEC RELP-LTP/ACELP CELP ACELP

Spectrum

Allocation 50 MHz 50 MHz 30 MHz

2.5G Systems

• 2G systems have limited capabilities due to their data rate. A typical data rate for a 2G system is 9.6 kbps.

• Generation 2.5 (2.5G) systems is a term which broadly

includes all advanced upgrades of the 2G systems. It is the generation of mobile phones following 2G and can be seen as a transitional stage between 2G and 3G systems. The aim of upgrading the system is to increase the data rate of the communication system. Generally, a 2.5G GSM system includes at least one of the following technologies:

• High Speed Circuit-Switched Data (HSCSD)

• General Packet Radio Services (GPRS)

• Enhanced Data Rates for Global Evolution (EDGE)

• Code Division Multiple Access (CDMA2000) (phase 1)

• Note that the line as to what is a 2.5G technology and what is a 3G technology is somewhat blurry. A 3G device is defined as a mobile device which is capable of transmitting at 144 kbps. Note that some of the technologies included in this report are capable of transmitting at this data rate, but their average user data rate is lower than 144 kbps.

The following table shows the

differences between 2G and 2.5G

systems:

Technology Features Average Data

Rate

Time to download a 3 min MP3 song

2G

Phone Calls Voice Mail Receive Simple

text messages

10 kbps 31-41 min

2.5G

Phone Calls Fax Messages Voice Mail Send/receive large

email messages Web Browsing Video and Picture

Messaging

64-144 kbps 6-9 min

3G

• 3G Mobile communications is defined as the third generation of wireless (mobile) communication technology. A 3G device will provide a huge range of functionality to your mobile phone. 3G devices will allow for simultaneous transmission of speech, data, text, video, pictures and audio. 3G networks have the capability to provide the following services to users:

• Voice/phone services

• High Speed mobile internet access

• Entertainment on demand, including music and movies

• Mobile Video conferencing

• Video and picture messaging capabilities

• Mobile shopping services

• Multimedia Broadcast/Multicast services. This involves sending information to a particular group of users (subscribers). An example of this is sending news/sports updates to those users that subscribe to this service.

• 3G devices will contain an all-in-one mobile phone, palmtop computer and entertainment system. The 3G device will contain a mobile phone, high resolution screen, MP3 player, camera, and user interfaces for the palmtop computer (keyboard/mouse etc.)

• A 3G network must be capable of providing users with very fast data rates. The International Telecommunications Union (ITU) defined a 3G device as a device capable of transmitting at 144 kbps or more. Current 2G data rates are approximately 9.6 kbps. The following table gives a description of the advantages and differences of 3G technology to earlier technology (2G and 2.5G systems).

Technology Features Transmission Speed

Average Time to

download a 3 min MP3

song

2G: The technology of most

current digital mobile

phones

Phone Calls

Voice Mail

Receive simple data

files (text email

messages)

10 kbit/sec 31-41mins

2.5G Wireless: The best

technology now widely

available

Phone calls

Fax messages

Voice mail

Send/receive large

email messages

Web browsing

64-144 kbit/sec 6-9 mins

3G Wireless: Combines a

mobile phone, laptop PC

and TV

Phone calls

Fax messages

Global roaming

Send/receive large

email messages

High speed web

navigation and

browsing

Videoconferencing

TV streaming

144 kbit/sec for high

mobility traffic eg. in moving

car 384 kbits/sec for low mobility traffic

eg. user is travelling at walking pace

2 Mbits/sec in good conditions eg.

user is stationary

11sec-1.5 mins

• There are many different competing standards (protocols) for 3G technology. A protocol defines the rules for which communication can take place eg. what frequency spectrum and carrier is used, what modulation/demodulation techniques are used etc. The International Telecommunications Union (ITU) considered the proposals put forward by a number of groups to provide 3G technology. The proposals which were accepted by the ITU in IMT-2000 are as follows:

• Wideband CDMA (WCDMA), which is also known as UMTS

• Time-Division Synchronous CDMA (TD-SCDMA)

• CDMA2000