Recently there has been considerable interest in spread spectrum techniques for use in commercial communication systems. One particular area where there may be considerable benefit is in mobile radio systems. Many of the difficulties presented by mobile radio communications result from the multipath fading which is present on the channel. This can lead to large reductions in the available channel capacity if measures are not taken to combat its effects. The use of diversity is highly effective in ameliorating the effects of fading. This research is concerned with an anti-multipath receiver architecture, the RAKE receiver, which uses the inherent multipath diversity of the received spread spectrum signal. As a precursor to this work we describe a spread spectrum correlator architecture, the serial-parallel receiver, which is capable of resolving the multipath diversity signals which are subsequently used in the RAKE receiver. A digital serial-parallel correlator is developed which has negligible implementation loss, fast PN code synchronisation, and can provide very large processing gains. The performance obtained from this spread spectrum receiver architecture is demonstrated using a DSP based implementation, and is shown to improve upon previous analogue implementations in most respects. It is particularly attractive for mobile communications since it can resolve the multipath signal components without the need for a large time-bandwidth product matched filter, or multiple active correlators. The performance of an adaptive RAKE receiver, using simple alpha tracker profile estimation filters, is analysed for a simulated UFG mobile channel (vehicular and hand-held) for a typical urban environment. Bit error rate graphs indicate that the performance approaches the theoretical upper bound when the signal fading is slow relative to the bit rate of the system (e.g. hand-held operation).
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660713 |
| Date | January 1992 |
| Creators | Povey, Gordon J. R. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12133 |
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