Impact of Timing Error on DS-CDMA with Frequency-domain Equalization

Abstract Recently, the frequency-domain equalization (FDE) has been attracting much attention since it is an effective equalization technique for direct-sequence code division multiple access (DS-CDMA) signal transmission in a frequency-selective fading channel. In practical systems, the square-root Nyquist transmit and receive filters are used for the bandwidth limitation of the transmitted signals. The presence of timing error produces the inter-symbol interference (ISI) and thus degrades the transmission performance. In this paper, we present a theoretical analysis on the bit error rate (BER) performance of DS-CDMA using FDE in the presence of timing error and the analysis is confirmed by computer simulation. In the presence of timing error, the received signal spreads in the time domain and the FFT window should be shifted to contain most of desired signal components. The optimum rolloff factor that minimizes the average BER is around 0.2. Keyword DS-CDMA, frequency-domain equalization, timing error, Nyquist filter