Direct-detection optical synchronous CDMA systems with interference canceller using group information codes

We propose an interference cancellation technique using a reference signal for optical synchronous code-division multiple-access (CDMA) systems. In the proposed system, we use the signature code sequences composed of the group information codes and the modified prime code sequences. The group information codes are added in the forefront of the signature code sequences to estimate the amount of the multiple access interference (MAI). The proposed cancellation technique can be realized with a simpler structure than the conventional canceller using the time division reference signal, because it can reduce the number of optical correlators from P to two, where P is the prime number. Considering the effects of the MAI, avalanche photodiode (APD) noise, and thermal noise, we analyze the performance of the proposed system. We show that the proposed canceller achieves better bit error probability than the conventional canceller.