| Author | Fernando, Warnakulasuriya Anil Chandana |
| Call Number | AIT Thesis no.TC-97-7 |
| Subject(s) | Mobile communication systems
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| Note | A thesis submitted in partial fulfillment of the requirement for the degree of Master of Engineering. |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. TC-97-7 |
| Abstract | The earth's surface is being covered by telephone in increasingly impressive increments. The new systems such as Iridium, Teledesic systems will soon contribute to this global coverage by making it possible to use a handheld telephone to call practically anywhere in the world. New features such as cellular roaming service will further enhance global wireless communications by translating different cellular technologies and linking with ·low earth orbit (LEO) satellite services. In this thesis, different coding techniques with orthogonal frequency division multiplexing (OFDM) for a LEO satellite channel, have been analyzed. Special attention is also given to peak to average power ratio with coding. Among the channel coding techniques, convolutional coding (CC), trellis coded modulation (TCM) and turbo coding (TC) have been considered. All these coding techniques are considered with OFDM for Rician fading channel in L band and Ka band. The specifications are based on the Iridium system which will start the service by next year. Bit error rate (BER) for different coding systems are analyzed with reference to their uncoded systems. To reduce the peak to average power ratio, partial transmit sequence method is considered with coding. 4-PSK, 8-PSK, 16-QAM, 32-QAM, 64-QAM and 256-QAM modulation schemes are considered with coding. Coding gain is considered at two different values of BER. These two levels of BER are selected because BER of 10"2 is considered for most of the voice communication applications and 10·4 can be considered for data communication applications. It has been found that turbo codes give the best performance compared to the convolutional coding and trellis coded modulation, for all modulation schemes considered. Turbo codes can achieve higher coding gain with respect to convolutional coding and coding gain with respect to TCM is not high as convolutional codes. Comparison is made with respect to the spectral efficiency of the schemes. Partial transmit sequence method can reduce peak to average power ratio by approximately 2.0dB. Results also show that there is not much significant difference between the L and Ka band in terms of performance. All these results with different coding schemes indicate that COFDM can be used as a suitable modulation scheme for LEO satellite channels. In summary, the application of COFDM for LEO satellite mobile communication systems has been considered. This modulation system is a promising technique for satellite mobile communication systems where multipath propagation can cause significant signal distortions. Although we couldn't find any domestic portable handset receivers with this technique up to now , due to the rapid pace of development in communications the complexities of COFDM are likely to be implemented in the near future. |
| Year | 1997 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. TC-97-7 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Department of Information and Communications Technologies (DICT) |
| Academic Program/FoS | Telecommunications (TC) |
| Chairperson(s) | Premanandana Rajatheva |
| Examination Committee(s) | Ahmed, Kazi;Makelainen, Kimme |
| Scholarship Donor(s) | Government of Finland. |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1997 |