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“Precoding Techniques for Efficient Ultra-Wideband (UWB) Communication Systems”
by Yu-Hao Chang
December 2007
It is always desirable to have a cheap and low power mobile receiver in a wireless communication environment. As for the ultra-wideband (UWB) system, the complexity of channel equalization could be high due to the long UWB channel impulse response. As a result, the UWB receiver design is not simple. However, the overhead of UWB channel equalization could be shifted from the receiver to the transmitter by the use of precoding so that a low cost receiver is possible. Precoding techniques, such as time-reversal prefilter (TRP) and the transmit minimum mean square error (Tx-MMSE) prefilter, pre-equalize the transmit signal based on the current channel information, which can be estimated and fed back to the transmitter by the corresponding receiver. Since the UWB channel contains a great number of multipath components, sending the complete channel information to the transmitter demands a lot of feedback channel capacity and is not practical.In the first half of this thesis, different UWB precoding techniques that requires only partial knowledge about the current channel, for example, reduced-rank UWB precoding and channel phase precoded UWB (CPP-UWB) systems, are proposed to save the feedback overhead. As simulation results suggest, these precoding schemes provide different trade-offs between decoding performance and fed back information quantity. Later, the performance degradation of both TRP and CPP systems due to clock jitter is analyzed. It is shown that CPP is not only simpler in design but also more robust than TRP against timing jitter. Finally, CPP-Rake and CPP-MTA systems, which utilize the Rake receiver and multiple transmit antennas, respectively, are proposed to lower the decoding error of CPP-UWB systems as well.
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