Performance Analysis of Multiple-Symbol Differential Detection for OFDM over Both Time- and Frequency-Selective Rayleigh
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Performance Analysis of Multiple-Symbol Differential Detection for OFDM over Both Time- and Frequency-Selective Rayleigh Fading Channels Akira Ishii Department of Communications and Systems, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu-shi, Tokyo 182-8585, Japan Email: [email protected]
Hideki Ochiai Division of Physics, Electrical and Computer Engineering, Yokohama National University, 79-1 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan Email: [email protected]
Tadashi Fujino Department of Communications and Systems, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu-shi, Tokyo 182-8585, Japan Email: [email protected] Received 28 February 2003; Revised 8 October 2003 The performance of orthogonal frequency-division multiplexing (OFDM) system with multiple-symbol differential detection (MSDD) is analyzed over both time- and frequency-selective Rayleigh fading channels. The optimal decision metrics of timedomain MSDD (TD-MSDD) and frequency-domain MSDD (FD-MSDD) are derived by calculating the exact covariance matrix under the assumption that the guard time is longer than the delay spread, thus causing no effective intersymbol interference (ISI). Since the complexity of calculating the exact covariance matrix turns out to be substantial for FD-MSDD, we also develop a suboptimal metric based on the simplified covariance matrix. The comparative analysis between TD-MSDD and FD-MSDD suggests that the most significant improvement is achieved by the FD-MSDD with the optimal metric and a large symbol observation interval, since the time selectiveness of the channel has a dominant effect on the bit error rate of the OFDM system. Keywords and phrases: orthogonal frequency-division multiplexing, multiple-symbol differential detection, time- and frequencyselective channels, Rayleigh fading.
1.
INTRODUCTION
In mobile communications systems, there has been a growing demand for high data rate services such as video phone, high-quality digital distribution of music, and digital television terrestrial broadcasting (DTTB) [1]. In such systems, the delay spread of the channel becomes a major impairment to cope with, since it may cause a severe intersymbol interference (ISI). It is well known that the orthogonal frequency-division multiplexing (OFDM), which transmits the information symbols in parallel over a number of spectrally overlapping but temporally orthogonal subchannels [2], is an effective technique to combat the ISI. With a guard interval longer than the maximum delay spread of
the channel, OFDM can effectively avoid the ISI with high spectral efficiency and reasonable complexity. However, the time-selective nature of the channel due to the Doppler shift also results in the loss of orthogonality among subcarriers, causing a considerable interchannel interference (ICI) [3]. When the time selectiveness of the channel becomes severe, that is, both amplitude and phase of the received signal vary fast, the reliable estimation of the channel state information (CSI) becomes challenging. In such cases, the
