Combined effectiveness of optical hard-limiting and guard-time in optical CDMA systems

Simple computer simulations show that guard-times (and decreasing the RZ duty cycle) improve the Q-factor of optical CDMA matrix codes, at the expense of spectral efficiency. The use of optical hard-limiting further improves the Q-factor. Optical hard-limiting has the effect of clamping the peak power of the signal and reducing its variance; it has less effect on the multi-access interference (MAI), so other MAI mitigation techniques need to be developed. Up to K∼12, the receiver can use a simple threshold based on the number of users (e.g. making the threshold proportional to the average power). At K>12, code acquisition and synchronization in the receiver are required because signal and MAI have comparable peak powers.