Performance and Capacity of PAM and PPM UWB Time-Hopping Multiple Access Communications with Receive Diversity
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Performance and Capacity of PAM and PPM UWB Time-Hopping Multiple Access Communications with Receive Diversity Hao Zhang Department of Electrical & Computer Engineering, University of Victoria, BC, Canada V8W 3P6 Email: [email protected]
T. Aaron Gulliver Department of Electrical & Computer Engineering, University of Victoria, BC, Canada V8W 3P6 Email: [email protected] Received 29 September 2003; Revised 9 April 2004 The error probability and capacity of a time-hopping ultra-wideband (UWB) communication system with receive diversity are investigated. We consider pulse amplitude modulation (PAM) and pulse-position modulation (PPM) over additive white Gaussian channels for a single-user system. A multiuser environment with PPM is also investigated. It is shown that the communication distance and error performance are improved by employing receive diversity. The channel capacity of PPM and PAM is determined subject to the power constraints of FCC part 15 rules to illustrate the relationship between reliable communication distance and signal-to-noise ratio. The error probability with PAM and receive diversity is derived for the single-user case. The error probability and performance bounds with PPM are derived for both the single-user and multiuser cases. Keywords and phrases: ultra-wideband communications, PAM, PPM, multiple access, channel capacity.
1. INTRODUCTION An ultra-wideband (UWB) [1] communication system transmits information using ultrashort impulses that spread the energy of the signal typically from near DC to several GHz. Unlike conventional communication systems, UWB systems operate at baseband, and thus involve no intermediate frequency and no carrier synchronization. UWB theoretically promises a very high data rate by employing a large signal bandwidth. However, due to possible interference to existing communication systems, power spectrum density limitations such as FCC part 15 rules are imposed, which greatly limits the system capabilities. In particular, UWB systems under FCC part 15 rules provide reliable communications only over small to medium distances. Typically pulse amplitude modulation (PAM), pulse-position modulation (PPM), or on/off keying (OOK) modulation is employed. PPM modulation uses the precise collocation of the impulses in time to convey information, while PAM and OOK use amplitude for this purpose. Note that the multipath signal is resolvable down to path delays on the order of a nanosecond or less due to the use of ultrashort impulses. This can be exploited to significantly reduce the effects of fading in a wireless environment.
UWB systems with PAM and PPM modulation have been extensively investigated. In [1, 2, 3, 4], a time-hopping multiple access scheme for UWB systems with PPM was considered. A PPM UWB system over an AWGN channel was considered from the capacity perspective (subject to FCC part 15 rules) in [5, 6]. The performance of a PAM UWB system with a RAKE receiver was investigated in [7, 8] for an indoor wireless channel with multipath interference. An all-digita
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