Multiple access with ultrawide-band impulse radio modulation using spread-spectrum time hopping and block-waveform pulse-position-modulated signals.

摘要

Impulse radio (IR) is an ultra-wideband (UWB) modulation that uses waveforms that consist of trains of time-shifted subnanosecond pulses. Data is transmitted using pulse position modulation at a rate of many pulses per symbol. Multiple access capability is achieved using spread spectrum time hopping. Impulse radio promises to be a viable technique to build relatively simple and low-cost, low-power transceivers that can be used for short range, high speed multiple-access communications over the multipath indoor wireless channel.; In [8] the single-user multiple-access performance of IR assuming free space propagation conditions and additive white Gaussian noise (AWGN) was studied. The analysis assumed that binary pulse-position-modulated (PPM) signals based on binary time-shift-keyed (TSK) modulation are detected using a correlation receiver. The analysis in [8] is quite similar to that for code-division multiple-access made in [44] and is based on the fact that both designs use single-channel correlation receivers for phase-coherent detection of the bit waveform.; In this dissertation we generalize the ideas in [8] to investigate the use of block-waveform signals to increase the data transmission rate supported by the system without degrading the multiple-access performance for a given number of users, or to increase the number of users supported by the system for a given multiple-access performance and bit transmission rate. More specifically, we present three M-ary block-coded PPM signal designs and analyze the multiple-access performance of IR using these PPM signals. We also discuss some of the tradeoffs between performance and receiver complexity. Using this idealized analysis, numerical examples given in chapter 5 show that IR modulation is potentially able to support hundreds of users, each transmitting at a rate over a Megabit per second at bit error rates as low as 10–8. Similarly, it is shown that IR is potentially able to support thousands of users, each transmitting at a rate about ten Kilobits per second at bit error rates in the order of 10–4. In either case, the combined transmission rates give a transmission capacity of over 500 Megabits per second using receivers of moderate complexity.; We also include an assessment of the performance of IR modulation in the presence of dense multipath (no multiple-access interference is considered in this assessment). Numerical results in chapter 6 show that for a particular set of M = 4 signals and symbol error probability of 10 –3, the performance in the presence of multipath using a mismatched Rake receiver with K = 10 fingers is, on average, just 3 dB worse than performance in the absence of multipath using a correlation receiver.