VIEWS: 1 PAGES: 6 POSTED ON: 4/22/2010 Public Domain
PACKET SPEECH INTERPOLATION IN MOBILE TELEPHONE SYSTEMS A thesis ...
Pi Z<A 5M PACKET SPEECH INTERPOLATION IN MOBILE TELEPHONE SYSTEMS A thesis submitted in fulfilment of the requirement for the degree of DOCTOR OF PHILOSOPHY in the Department of Electrical Engineering, The University of Adelaide by B.Sc., B.E.(Hons) JOHN CHARLES ELLERSHAW, June 1979 TABLE OF CONTENTS (v) Abstract (vii) (viii) Statement Acknowledgements (ix) List of Symbols Introduction 1. 1.1 Background 1 1.2 Packet Radio Techniques 2 1.3 Interpolation 4 Comparison of Mobile Telephone Schemes 1.4 6 Further Applications 1.5 7 2. A Digital Mobile Telephone Schemeâ¨ALOHA Schemes 2.1 8 Digital Encoding of Speech Digital Transmission in the Urban Environment A Basic Mobile Telephone System 2.2 15 2.3 21 2.4 30 32 Design of a TDM Systemâ¨Conclusions 2.5 38 2.6 Interpolation of Speech in Packets 3. Interpolation 40 3.1 41 Speech Characteristics 3.2 53 The Request Channel 3.3 Delays in the Digital Schemes 60 3.4 Subpackets Subjective Effects of Telephone Delays 3.5 65 69 3.6 73 3.7 Conclusions (iii) Glitches in Packet Speech Interpolationâ¨Slot Assignment Delayâ¨Theoretical Glitch Probabilityâ¨Glitch Rate and the Use of Subpacketsâ¨Computer Simulation Programmeâ¨Optimization of Subpacketsâ¨Conclusions 4. 4.1 76 4.2 78 4.3 84 4.4 89 4.5 97 4.6 105 The Complete Mobile Telephone System System Simulation Effect of the Request Channel 5. 5.1 107 5.2 112 Dependence of Glitch Rate on System Parametersâ¨Optimization of System Parameters 5.3 121 5.4 128 Distribution of Glitches 5.5 136 Subjective Speech Trials 5.6 147 Conclusions 5.7 153 A Comparison of Mobile Telephone Schemesâ¨The Complete Packet Interpolation System 6. 6.1 156 Alternative Mobile Telephone Systems 6.2 162 Comparison of Digital and Small Cell Systems 6.3 165 Small Cell Packet Systems 171 6.4 Conclusions 175 6.5 A Pure TASI Mobile Telephone Systemâ¨System Descriptionâ¨Theoretical Freezeout Fraction 7. 178 7.1 179 7.2 186 7.3 Effects of the Request Channel Simulation of the TASI System 189 7.4 191 Comparison with the Packet System 7.5 (iv) TASI System with Delay 7.6 197 Conclusions 7.7 202 PCM and Other Alternative Applicationsâ¨TASI-PCM Systemsâ¨Packet PCM Systems Alternative Digital Speech Interpolation Methodsâ¨Interpolation in Satellite Channelsâ¨Integrated Speech and Data Networks 8. 8.1 205 8.2 210 8.3 215 217 8.4 219 8.5 221 Conclusions 8.6 Conclusions and Further Work 224 9. Determination of the correct queue arrangementâ¨Queues with dependent inputs Appendix Aâ¨Appendix Bâ¨Appendix C 228 231 Simulation programmes and flowcharts 235 250 References Iâ¨1 \ (V) ABSTRACT Mobile telephone services are presently provided by frequency A voice circuit in the form of a division multiplexing techniques. radio frequency channel is allocated to a subscriber for his sole use during a telephone call,â¨division multiplexing and provide voice circuits on a digital basis. An alternative to this is to employ time In such a scheme speech is digitized and formed into packetsâ¨for transmission. It is possible to interpolate packets from differentâ¨conversations onto a single high capacity radio channel. This is aâ¨form of time division multiple access and is best implemented by aâ¨technique termed reservation ALOHA. When a packet is prepared at aâ¨mobile telephone a request is sent, over a small capacity channel, forâ¨transmission space in the main or speech channel. To determine the efficiency of this process the characteristics of speech in packets are investigated through computer simulation. Anâ¨optimum packet length is shown to exist and is obtained for a wideâ¨variety of different systems. Various delays are inherent in packet speech interpolation and The most important is the delay involved these are considered in turn. in assigning space in the speech channel in times of greater than averÂ¬â¨age speech activity. Limiting this delay to maintain reasonable speechâ¨quality results in certain packets not being transmitted. Such packetsâ¨are said to have been glitched. The nature and extent of glitches is studied both theoretically and by further simulation. Their subjective effects are also considered (vi) and acceptable rates of speech loss are determined,â¨straint and another imposed upon the total delay, an optimized packet This is capable of servicing over 4000 subscribers Within this con- system is designed,â¨in a total capacity of 2.16 Mbit/s. A comparison is performed between the above packet system andâ¨alternative small cell frequency modulated (FM) systems which employ It is shown that with similar channel repetitionâ¨the packet scheme can provide more telephone connections within a givenâ¨There are however penalties of greater cost and complexity.â¨A compromise system incorporating interpolation with the small cell FMâ¨structure is shown to be superior to both, at least for applications inâ¨the near future. radio channel reuse. bandwidth. Alternative areas for packet speech interpolation such as pulse code modulation telephone links, satellite systems and integrated dataâ¨and speech networks are also considered. much parallel the mobile telephone situation and that the resultsâ¨obtained for the latter are of direct relevance. It is found that these very In some ways these areas are better suited to the use of packet speech interpolation than is a mobile telephone system and they offer the best opportunity for its implementation at the present time.
Pages to are hidden for
"PACKET SPEECH INTERPOLATION IN MOBILE TELEPHONE SYSTEMS A thesis "Please download to view full document