Channel Estimation Improvement for OFDM with Side Information

J.-C. Guey (USA)

Keywords

Channel Estimation, OFDM, CDMA, Enhanced BroadcastMulticast, HRPD

Abstract

Pilot Symbol Assisted Modulation (PSAM) is commonly used in an Orthogonal Frequency Division Multiplexing (OFDM) system for channel estimation. Estimators with various criteria such as Minimum Mean Square Error (MMSE) and Least Square (LS) can be employed to in terpolate the channel’s frequency response from the obser vations of the periodically inserted known symbols. Al though extensively studied, the problem of channel esti mation for OFDM has mostly been focused on applying these techniques exclusively to the pilot symbols. In prac tice, however, there might be known signals in the system other than the frequency domain pilot symbols. For ex ample, a Direct Spread (DS) pseudo random sequence is often time-multiplexed with the OFDM symbols as a syn chronization signal. This paper proposes several methods for improving the channel estimation performance of an OFDM system by incorporating the side information pro vided by these additional known signals into the channel estimator. Simulation results show a gain of 2 to 3 dB for a reduced-complexity suboptimal approach in a typical fre quency selective channel. An additional 1 to 2 dB improve ment can be achieved with the optimal solution.

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