Performance Analysis and Comparison of Time-Hopping and Direct-Sequence UWB-MIMO Systems
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Performance Analysis and Comparison of Time-Hopping and Direct-Sequence UWB-MIMO Systems W. Pam Siriwongpairat Department of Electrical and Computer Engineering, University of Maryland, College Park, MD 20742, USA Email: [email protected]
Masoud Olfat Department of Electrical and Computer Engineering, University of Maryland, College Park, MD 20742, USA Email: [email protected]
K. J. Ray Liu Department of Electrical and Computer Engineering, University of Maryland, College Park, MD 20742, USA Email: [email protected] Received 15 October 2003; Revised 5 April 2004 We analyze the performance of ultra-wideband (UWB) multiple-input multiple-output (MIMO) systems employing various modulation and multiple access (MA) schemes including time-hopping (TH) binary pulse-position modulation (BPPM), TH binary phase-shift keying (BPSK), and direct-sequence (DS-) BPSK. We quantify the performance merits of UWB space-time (ST) systems regardless of specific coding scheme. For each modulation technique, we introduce a framework that enables us to compare UWB-MIMO systems with conventional UWB single-input single-output (SISO) systems in terms of diversity and coding gains. We show that the combination of ST coding and RAKE receiver is capable of exploiting spatial diversity as well as multipath diversity, richly inherent in UWB environments. In addition, we adopt the real orthogonal design (ROD) as the engine code for UWB-ST codes. We find the upper bound of the average pairwise error probability (PEP) under the hypothesis of quasistatic Nakagami-m frequency-selective fading channels. The performance comparison of ROD-ST codes with different rates is also addressed. Finally, simulation results are presented to support the theoretical analysis. Keywords and phrases: ultra-wideband, time hopping, direct sequence, UWB-MIMO, multiple antennas, space-time coding.
1.
INTRODUCTION
Ultra-wideband (UWB) technology has recently gained considerable interest due to the Federal Communications Commission (FCC) approval, which allows the use of UWB on an unlicensed basis following the Part 15 rules [1]. UWB transmission, also referred to as impulse communications, is characterized by a sequence of extremely short duration, broad spectrum chirps of radio waves. According to the FCC definition, UWB technology is a transmission scheme that occupies a bandwidth of more than 20% of its center frequency, or nominally more than 500 MHz. The UWB nature offers several advantages over narrowband technology including high data rate, extensive multipath diversity, low power consumption, and support for multiple access (MA) [2]. These unique characteristics of UWB make it a viable candidate for future short-range wireless communications,
especially indoor wireless and home entertainment systems. However, since UWB utilizes overlapping frequencies with the existing narrowband devices, its transmit power spectral density is limited according to the FCC regulations [1]. For example, the FCC Part 15.209 rules limit the emissions for intentional radiators to
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