Performance analysis of optical CDMA communication systems with M‐ary PWM signalling

Abstract

ABSTRACTIn this paper, a novel M‐ary pulse‐width modulation (PWM) coded optical code division multiple access (O‐CDMA) system is proposed. At the transmitter end, in order to increase the number of transmitted bits per pulse, each chip of signature sequence is further divided into M time slots to realise the M‐ary PWM signal format. Two types of detection schemes are developed, and the performance in terms of symbol error rate is analysed. In the first scheme, the correlation receiver is employed followed by an M‐level threshold detection. To enhance the multiuser interference suppression capability, we apply the chip‐level‐based diversity detection in the second scheme. Adding optical hard‐limiters at the front end of the receiver, both schemes are free from the near–far problem that is suffered severely in O‐CDMA system employing pulse‐amplitude modulation (PAM). Numerical results demonstrate that the proposed M‐ary PWM O‐CDMA system with the chip‐level receiver achieves better symbol error rate and multiuser interference mitigation capability than the correlation receiver. Moreover, the performance of the proposed M‐ary PWM O‐CDMA system is much better than the M‐ary pulse‐amplitude modulation scheme. And the complexity is substantially reduced as we compare to the existing M‐ary pulse‐position modulation O‐CDMA system. Copyright © 2014 John Wiley & Sons, Ltd.