Impact of timing error on BER performance of TDD pre-equalized MPSK OFDM systems

Time division duplex (TDD) pre-equalized orthogonal frequency division multiplexing (OFDM) systems can save system resources by omitting pilot symbols. Meanwhile, a new problem arises that the timing error would degrade system performance, because this error cannot be revised in the absence of pilot symbols. The paper investigates the impact of timing error on the receiver´s bit error rate (BER) performance for TDD pre-equalized OFDM systems using phase-shift keying (PSK) modulation. The analytic binary PSK (BPSK) and quadrature PSK (QPSK) BER expressions of ideally and nonideally pre-equalized OFDM systems are obtained, in multipath Rayleigh fading environment. The corresponding simulations verify the analytic expressions. Compared with the theoretical system performance bound, the performance of ideal and nonideal pre-equalized BPSK systems entail loss of 1 dB and 3 dB respectively when the normalized timing error is 1/8. When it is 1/4, the performances of both systems degrade severely. At the same time, the gap between them diminishes. In that case, timing error becomes dominant among those elements which would affect systems performance. The higher the modulation order adopted, the more sensitive to timing error the system performance becomes.