Performance of an asynchronous DS-CDMA system with long and short spreading codes-a simulation study

The bit error rate (BER) performance of an asynchronous direct-sequence (DS) code-division multiple-access (CDMA) system is studied by means of Monte Carlo simulation using SPW^TM software. The effect of the spreading code length on system performance is of special interest. The probability of a partial cross-correlation value between segments of long sequences is also discussed. The values of the spreading factor for a BPSK type spectrum spreading are 127 and 255. Ideal code, carrier and symbol synchronization, and additive white Gaussian noise (AWGN) channel are employed in the system model. Results indicate that the system performance with long spreading codes (period of 2³⁰-1) is about 1.0 dB worse than that of short CDMA sequences when E_h/N₀ is about 10 dB. The loss in BER or in signal-to-noise ratio is tolerable, since long codes allow individual user addresses to be implemented for each user of a large asynchronous cellular CDMA network without need for re-allocation of codes. The network planning and implementation becomes easier as there is no need for code change in a handover situation. Long spreading codes also provide flexibility with respect to multiple bit rates and variable spreading factors