Cochannel interference reduction in optical PPM-CDMA systems

A multiple-user interference reduction technique is proposed for optical code-division multiple-access (CDMA) systems. Data symbols from each user are encoded using a pulse-position modulation (PPM) scheme before multiplexing. Modified prime sequences are adopted as the signature codes in the multiplexing process. An interesting property of this code is the uniformity of the cross correlation among its sequences. This property is the main key in constructing the multiple-access interference canceler. In addition to its simplicity, this canceler offers a great improvement in the error probability as compared to the system without cancellation. A simple modification to this canceler that enhances its performance is proposed as well.