Chip discrimination for UWB impulse radio networks in multipath channels

by (Jon Robert), 1981- Ward

WARD, JON ROBERT. Chip Discrimination for UWB Impulse Radio Networks in Multipath Channels (Under the direction of Professor J. Keith Townsend). The recent need for increasingly higher data rates and the ability to utilize unused spectrum has fueled growing interest in UWB from both academia and industry. A variety of UWB physical layer applications have been proposed and implemented including: highspeed, short-range indoor wireless personal area networks (WPAN’s), product sensor tags, and low-power, covert military networks. Much of the UWB literature focuses on the Impulse Radio (IR) variety which is characterized by the transmission of multiple timedithered, short duration pulses per data bit. Researchers have consistently studied IR by making key assumptions to simplify system analysis, namely perfect multi-user power control and single path of signal arrival. In the military networks of interest, a variety of line-of-sight (LOS) and non line-ofsight (NLOS) paths exist between transceivers operating at different power levels. Careful power control becomes complex when no central node provides service to the entire network and a small number of high-powered co-located users can quickly degenerate system performance. We use computer simulation to investigate the system degradation incurred, in terms of Bit Error Rate (BER), in a multi-user IR network with large near-far power disparity operating in a multi-user indoor environment. We then extend the work presented in [1] for the multi-user Gaussian channel as a solution to mitigate the effects of high-powered interferer signals in the IEEE 802.15.3a indoor multipath environment. Three varieties of RAKE receivers commonly found in literature are investigated: A- RAKE, S-RAKE, and P-RAKE. We introduce a novel chip discriminator located at each RAKE finger output that selectively removes finger demodulation metrics based on the product of a constant threshold level Tin and the estimated channel tap coefficient ?k. A multi-user environment is considered where the desired user’s signals pass through the NLOS channel CM2 and the co-located user’s transmit through the LOS channel CM1. We quantify the performance of a system employing chip discrimination as well as its sensitivities to system parameters under the assumption of perfect channel estimation and maximal ratio combining (MRC). Chip Discrimination for UWB Impulse Radio Networks in Multipath Channels by Jon R. Ward A thesis submitted to the Graduate Faculty of North Carolina State University in partial satisfaction of the requirements for the Degree of Master of Science Department of Electrical and Computer Engineering Raleigh August 2005 Approved By: Dr. Huaiyu Dai Dr. J. Keith Townsend Chair of Advisory Committee Dr. Brian L. Hughes To Leigh and my family. ii iii Biography Jon Robert Ward was born on January 10, 1981 in Greensboro, NC, the oldest child of Bruce and Sandra Ward. He graduated from Ragsdale High School in June, 1999. He received a B.S. degree in Computer and Electrical Engineering from North Carolina State University in May, 2003. He received his M.S. degree in Electrical Engineering in August 2005. After graduation he will join the Communication Systems Network Engineering Group (VIC) in the Power Projection Systems Department at the Johns Hopkins Applied Physics Laboratory. iv