Doctor of Philosophy
School of Electrical, Computer and Telecommunications Engineering - Faculty of Informatics
Vial, Peter J, On an approach to provide space diversity to an ultra wideband time hopping pulse position modulated wireless communication system, PhD thesis, School of Electrical, Computer and Telecommunications Engineering, University of Wollongong, 2009. http://ro.uow.edu.au/theses/811
The hypothesis question, which is addressed in this PhD dissertation, is how to use two transmission antennas in an Ultra Wide Band Time Hopping Pulse Position Modulation system to take advantage of space diversity in such a way as to not significantly degrade the communication link compared to using only one transmit antenna. In answering the hypothesis question, this dissertation proposes a novel technique, based on Space Time Spreading, to allow an Ultra Wideband Time Hopping Pulse Position Modulation system to obtain full advantage from space diversity using two transmit antennas and one receive antenna, showing how such a Multiple Input Multiple Output system is designed. This is achieved with the added advantage of transmitting the same two symbols simultaneously on each antenna link. This means that for the proposed system, should a fade occur on one of the two antenna links, the two symbols transmitted will still be received with a slight increased cost in average Bit Error Rate (BER) performance as Signal to Noise Ratio (SNR) or measured Eb/No is increased. Results are first provided for wideband Space Time Spreading in the presence of Multiple Access Interference when using two, four and eight transmit antennas. A system is developed in simulation using modules provided by MATLABs Simulink program. It is then shown that using low correlation Wysocki spreading code set results in an improved BER performance compared to the more often used Walsh Hadamard spreading code set. A Simulink Ultra Wide Band Pulse Position Modulation Single Input Single Output system is developed and validated against published peer reviewed material. This is then modified to consider the use of Space Time Spreading in a Single Input Single Output system and it is shown that improved performance over an Ultra Wide Band Pulse Position Modulated Single Input Single Output is possible. It is also shown that this improvement allows the transmission of two symbols in the same time that the original system only transmits one symbol. The thesis also investigates a system which uses two transmit antennas but a hard decision is made on a chip by chip basis. Its performance, compared to an equivalent Single Input Single Output comparable system, is suboptimal. It does, however, have the advantage that it sends two symbols in the same time that the equivalent Single Input Single output Ultra Wide Band Pulse Position Modulation system sends one, and its implementation is simpler to codify. Also, it has the feature that both symbols are sent simultaneously on each antenna link. The simulator is then modified to make a hard decision after all chips of a spreading sequence for two antennas are received and it is shown that this system, in simulation and analysis, has a similar performance to that for a comparable Single Input Single Output system with the added advantage that both antenna links send the same two symbols simultaneously. It is further demonstrated in simulation and analysis that such systems can be affected by Multiple Access Interference. In addition, it is shown, using simulation, that the choice of spreading sequence set does have an impact on the average BER performance of the proposed Space Time Spreading Time Hopping Ultra Wideband Pulse Position Modulation system. The thesis finally proposes some extensions using the developed simulator which are outlined in future work.
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