Multi-user performance issues in wireless impulse radio networks [electronic resource] /

by Lovelace, William M.

LOVELACE, WILLIAM MATHIESON. Multi-User Performance Issues in Wireless Impulse Radio Networks (Under the direction of Professor Keith J. Townsend). There has been a growing interest in Ultra Wide Band (UWB) communication technologies over the last ten years. Motivated by advances in narrow pulse generation techniques and the potential for VLSI digital receivers, much fundamental research has been devoted to UWB. Most of the research to date has been dedicated to the potential for dense multi-user environments, narrow band interference issues, and multi-path considerations. While Impulse Radio (IR) has shown tremendous potential for high throughput local area networks based on time domain separation techniques, the stringent parametric assumptions required for practical implementation have not been clearly evaluated. Specifically, two of the more common constraints required to meet the projected UWB performance measures are timing tolerances and multi-user interference control. The work here has addressed both of these critical issues. Our work is the first to quantify the effects of timing jitter and tracking on time-hopping UWB multi-user performance. The investigations of these issues show that the performance of binary and 4-ary impulse radio is very sensitive to timing jitter and tracking errors. Supported multi-user performance is quantified through simulation and finds orthogonal pulse position modulation (PPM) out performed binary offset PPM at all jitter levels in thermal and pulse noise. We also compare accepted narrowband tracking techniques to an efficient error tracking method adapted to UWB. With adequate understanding of the effects of timing jitter an IR receiver can be designed to meet a given performance. However, the control of local user power for a given receiver is not always guaranteed in practical environments or under complete control of the receiver. A typical spread-spectrum IR that employs a matched filter sum for bit decisions is susceptible to small numbers of large power pulses that can dominate the bit decision statistics. We propose a simple chip discrimination technique for use with UWB that improves performance for large near/far interference ratios. The technique exploits the unique time domain characteristics that only UWB systems can provide by applying individual chip discrimination prior to the spreading summation. A statistical model is devel- oped that predicts bit error performance for binary offset pulse position modulation (PPM) as a function of near/far density and power for varying discrimination thresholds. We find that even a small number of very near interferers can greatly reduce the performance of a system without blanking or discrimination. Results show substantial improvement using our method for near interferers with near/far power ratios greater than 20 dB. By further adapting the chip discrimination method to the dynamics of a bursty packet network, we derive a technique for adjusting the number of chips per bit to maximize throughput of a transmission queue. Leveraging the information derived from the chip discrimination approach, as a component to a peer-to-peer MAC layer protocol, we can affect more efficient transmission rate control. The combination of these two techniques greatly improves performance in poor near-far power ratios and out performs fixed parameter links. The efficiency of this method is demonstrated using simulation in bursty, pulse limited environments and compared to equivalent M|D|1 queue statistics as a benchmark. Theoretical solutions for perfect blanking cases are derived to support simulation results and provide parametric optimization tools. Adaptation of these methods are applied to a simple ALOHA packet network to illustrate the effectiveness of chip discrimination and rate control to overall network throughput. Multi-User Performance Issues in Wireless Impulse Radio Networks by William M. Lovelace A dissertation submitted to the Graduate Faculty of North Carolina State University in partial satisfaction of the requirements for the Degree of Doctor of Philosophy Department of Electrical and Computer Engineering Raleigh 2004