1.4.5.2 Common Channels

These channels do not carry traffic and are organized based on a cycle of 51 slots (51 × 8 BP). This cycle is deliberately chosen differently from 26 slots of traffic channels so as not to have a common divider between the two. This allows mobiles in a dedicated channel to listen to synchronization channels (SCHs) and frequency correction channels (FCCHs) of the surrounding cells, which helps mobiles to stay in synchronization. Each SCH and FCCH uses 5 slots in a 51-slot cycle with SCH following FCCH 8 BP later. This helps mobiles to find SCH once it has located FCCH. The other downlink common channels defined include BCCH for broadcasting and PAGCH for paging. For uplink, a channel RACH is defined.

1.4.5.3 Burst Format

The quantum of transmission in GSM is 1 BP, which is 7500/13 s in duration and is occupied by about (156 + 1/4) b. In GSM several burst formats have been defined and these are used for different purposes.

Access burst is used in uplink direction from the mobile to the base during the initial phase. This is the first access of the mobile to the base. The burst has constant amplitude for the period of 87 b. The structure of the burst consists of 7 b of tail followed by 41 b of training sequence, 36 b of information, and 3 b of tail on the other side. A single training sequence is specified for this burst. The access burst is the first burst from the mobile to the base and contains required demodulation information for the base.

The S burst is similar to the access burst but it is transmitted from the base to the mobile. It is the first burst from the base and has 64 training sequence bits surrounded by 39 information bits and 3 tail bits. The training sequence is unique and chosen so that the mobile knows which sequence the base has chosen.

The F burst enables the mobile to find and demodulate the S burst. All of its 148 b are set to zero, resulting in a pure sine wave of 1625/24 kHz.

The normal burst is used for all other purposes. Its amplitude stays constant covering 147 b. It has 26 training sequence bits surrounded by 58 information bits and 3 tail bits. Eight different training sequences have been specified to distinguish co-channel signals. For more details on the GSM system, see, for example, Reference [51].

1.4.5 Cordless Mobiles

The first generation analog cordless phones were designed to communicate with a single base station, effectively replacing telephone cord with a wireless link to provide terminal mobility in a small coverage area such as a house or an office. The aim of the second-generation digital cordless system is to use the same terminal in residential as well as public access areas such as offices, shopping malls, train stations, and so on to receive and to originate calls. The cordless systems differ from cellular systems in a number of ways. Their cell size is small, typically less than half a kilometer, and their antenna elevation is low. These are designed for low-speed mobiles, typically on foot, and provide coverage in specific zones instead of continuous wide-area coverage provided by cellular systems. Cordless handsets transmit very low power. A typical average transmitted power is about 5 to 10 mW compared with a few hundred milliwatt for cellular handsets [1].

Most of the cordless systems use TDD as duplexing techniques compared with FDD employed by cellular systems.

Some of the popular digital cordless standard include CT2, a British standard; digital European cordless telecommunication (DECT) standard; personal handyphone system (PHS) of Japan, and personal access communication service (PACS) of the United States. Some of the parameters of these systems are compared in Table 1.3. More details on these may be found in Reference [1] and references therein.

1.5 Third-Generation Systems

The third-generation systems aim to provide a seamless network that can provide users voice, data, multimedia, and video services regardless of their location on the network: fixed, cordless, cellular,

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TABLE 1.3 Digital Cordless System Parameters

Parameter	CT2	DECT	PACS	PHS
Frequency (MHz)	864–868	1880–1900	1850–1910 and	1895–1918
			1930–1990
Channel spacing (kHz)	100	1728	300	300
Duplexing	TDD	TDD	FDD	TDD
Channel rate (kbps)	72	1152	384	384
Transmitted power (mW)
Average	5	10	25	10
Peak	10	250	200	80
Frame duration (ms)	2	10	2.5	5
Channels per carrier	1	12	8	4

satellite, and so on. The networks support global roaming while providing high-speed data and multimedia applications of up to 144 kbps on the move and up to 2 Mbps in a local area.

Third-generation systems are currently being defined by both the International Telecommunications Union (ITU) and regional standardization bodies. Globally, the ITU has been defining third-generation systems since the late 1980s through work on the IMT-2000 system, formerly called the Future Public Land Mobile Telecommunications Service (FPLMTS) [52]. The ITU is now in the process of seeking candidate technologies to be evaluated in accordance with agreed guidelines [53]. The European proposal for IMT-2000 is known as the Universal Mobile Telecommunications System (UMTS) — see discussions in References [54–57] — and is being defined by the European Telecommunications Standards Institute (ETSI), which has been responsible for UMTS standardization since the 1980s.

Although UMTS will provide significant changes for customers and technologies, systems will be deployed within a short time frame. Japan plans to launch its UMTS network in the year 2001; and the United Kingdom wants its UMTS radio interface working alongside enhanced GSM networks by the year 2002, with a fully working UMTS network operating by 2005. Third-generation networks are planned for the United States sometime between 2003 and 2005 [58]. Additional updates on IMT-2000 developments in the Asia Pacific Region can be found in References [59–62].

IMT-2000 defines systems capable of providing continuous mobile telecommunications coverage for any point on the earth’s surface. Access to IMT-2000 is via either a fixed terminal or a small, light, portable mobile terminal (MT) [63].

Several different radio environments are utilized to provide the required layers of coverage. These range from very small indoor picocells with high capacity, through to terrestrial microand macrocells, to satellite megacells. IMT-2000 recommendations aim to maximize commonality between the various radio interfaces involved, to simplify the task of developing multimode terminals for the various operating environments [64]. In this section some salient features of IMT-2000 are discussed [4, 5].

1.5.1Key Features and Objectives of International Mobile Telecommunications-2000

The key features and objectives of IMT-2000 include [64]

1.Integration of current firstand second-generation terrestrial and satellite-based communications systems into a third-generation system

2.Ensuring a high degree of commonality of design at a global layer

3.Compatibility of services within IMT-2000 and with fixed networks

4.Ensuring high quality and integrity of communications, comparable to the fixed network

5.Accommodation of a variety of types of terminals including pocket-size terminals

6.Use of terminals worldwide

7.Provision for connection of mobile users to other mobile users or fixed users

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8.Provision of services by more than one network in any coverage area

9.Availability to mobile users of a range of voice and nonvoice services

10.Provision of services over a wide range of user densities and coverage areas

11.Efficient use of the radio spectrum consistent with providing service at acceptable cost

12.Provision of a framework for the continuing expansion of mobile network services and for the access to services and facilities of the fixed network

13.Number portability independent of service provider

14.Open architecture that accommodates advances in technology and different applications

15.Modular structure that allows the system to grow as needed

1.5.2International Mobile Telecommunications-2000 Services

IMT-2000 supports a wide range of services, including those based on the fixed telecommunication network and those that are specific to mobile users. Services are available in a variety of environments ranging from dense urban situations, including high intensity office use, through to suburban and rural areas [64]. The actual services obtained by a user depend on the capabilities of their terminal, their subscribed set of services, and the services offered by the relevant network operator and service provider [65].

Global roaming users have access to at least a minimum set of services comprising voice telephony, selection of data services, and indication of other services available. IMT-2000 also provides services to fixed users and if required, can provide rapid and economical implementation of wide-area communications, which is particularly relevant to developing countries [64].

The general service objectives of IMT-2000 are to [66]

1.Provide a wide range of telecommunication services to mobile or stationary users by means of one or more radio links

2.Make these services available for mobile terminals located anywhere (subject to economic constraints)

3.Provide for flexibility of service provision

4.Promote flexible introduction of services

5.Ensure that a user is provided with an indication of service availability

6.Provide access to voice telephony

7.Provide access to a selection of data services

8.Provide services that depend on terminal type, location, and availability from the network operator

9.Provide a temporary or permanent substitute to fixed networks in rural or urban areas under conditions approved by the appropriate national or regional regulation authority

The general service requirements of IMT-2000 are to provide

1.Validation and authentication procedures to facilitate billing and accounting based on ITU-T X509

2.Additional layer of security for mobile telecommunications services

3.Privacy of location of a roaming user when desired by the called or calling party

4.Quality of service comparable with that of fixed networks

The general access requirements are as follows:

1.For access to fixed networks, IMT-2000 may be either an adjunct to, or an integral part of, the PSTN/ISDN.

2.For global use, IMT-2000 should allow international operation and automatic roaming of terminals.

3.For maritime and aeronautical use, operation should be facilitated to the extent permitted by the relevant regulatory body.

4.For satellite operation, IMT-2000 should facilitate direct and indirect satellite operation.

The first phase of IMT-2000 provides several telecommunications services, most of which are based on ITU-T E and F series recommendations.

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