| Summary: | This thesis is concerned with provision of multimedia services in cellular mobile/personal communication systems. It is a recognised fact that the success of mobile radio systems, in keeping a competitive edge with fixed telecommunication systems, depends on their capability to support as many services as possible and with comparative quality to that offered by the fixed networks. The first generation cellular systems (analogue) and second generation mobile communication systems (digital) were all designed primarily to support telephony services. Now there are worldwide standards activities in ETSI and ITU working towards a third generation system (digital) which aims to support services of up to 2Mbps. ETSI and ITU systems are called Universal Mobile Telecommunication System (UMTS) and Future Public Land Mobile Telecommunication System (FPLMTS), which has recently been named International Mobile Telecommunications for year 2000 at 2000 MHz or (IMT-2000) respectively. These systems are to operate, in allocated WARC'92 frequency bands between 1.885 GHz to 2.5 GHz. This thesis is aimed at an evaluation of possible potentials offered by the second generation systems, particularly GSM, and to propose new protocols for supporting data services whilst at the same time increasing spectral efficiency of the system and keeping intact the offered quality of telephony services. It must be emphasised that, the support of low bit rate data services, if not carefully incorporated, could result in inefficient use of the scarce radio spectrum. Therefore, major concern in this work is with accommodation of the low bit rate data services. Higher bit rate services (higher than voice codec rates) can be accommodated differently. Possible solutions are also proposed. This thesis is structured in a way that, hopefully, provides a logical approach to the problem and eventually to the proposed solutions. The introduction chapter starts with a brief account of the services envisaged for the third generation systems. To be able to evaluate the capability and suitability of already existing multiple access protocols and multiple access schemes, in chapter 2, a list of performance criteria is derived. As a result of these comparisons, TDMA as an access scheme and the GSM system were selected for further evaluation. In chapter 3, all the relevant aspect of the GSM system, for this research, are presented. Chapter 4, deals mainly with all of the characteristics of speech; discusses and tabulates all the possible parameters which can affect the speech quality, and that are essential to be taken account of when designing a telephony communication system. As a result of this, a model for speech is derived and adopted for further analysis. In chapter 5 all the currently proposed reservation-based multiple access protocols, suitable for statistical multiplexing of voice and data services are critically discussed. A new and generic mathematical technique, based on queuing theory, is derived and promising protocols such as PRMA and PRMA++ (candidate access protocols for the third generation mobile system) are evaluated. Detailed analysis of the PRMA protocol leads to new modifications which greatly enhances all of the statistics of PRMA and its derivatives. In chapter 5, it is also shown that PRMA increases system capacity at the cost of service quality. The present TDMA access protocol used in GSM was realised to be too rigid to efficiently support data services, especially low rate data services, so this research work was mainly directed to including some flexibility into GSM access protocols, without sacrificing voice service quality. Finally four novel protocols are identified and in chapter 6, their performance is thoroughly evaluated for mixed services in the GSM TDMA frame structure. Alternative frame structures are also investigated which can support even higher bit rate data services than those supportable within the current GSM frame structure. Finally, chapters 7 and 8, respectively, deal with conclusions of this research work and the list of references used in this investigation.
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