Code acquisition in a CDMA system based on Barker sequence and differential detection
D. Yan, Paul K. M. Ho · 2002
Code division multiple access (CDMA) based on direct sequence (DS) spread spectrum (SS) modulation has been advocated for next generation personal/cellular communications. The topic of code acquisition is an important design issue in a CDMA system that supports multimedia services. Although in isolation acquisition is a physical layer design issue, the performance of this subsystem has a strong impact on the overall system design. As an example, the system designer has to decide for bursty traffic applications whether it is more desirable to acquire on a per packet basis or is it better to transmit a low rate signal to keep the communication link in synchronism (both in terms of chip timing and power control) in between data bursts. We present an acquisition procedure, based on a differentially encoded Barker sequence as the preamble, for CDMA packet radio systems that is able to provide frame and chip synchronization simultaneously. We also introduce a two-step algorithm and a windowing technique which we found effective in overcoming the partial correlation problem. With simulation studies, we found that the new scheme outperforms other conventional schemes both under a frequency selective fading channel and a AWGN channel.