Optical CDMA Networks: Principles, Analysis and Applications

Chapter 5

Incoherent Temporal OCDMA Networks

5.1 Introduction

On-off keying (OOK) and pulse position modulation (PPM) OCDMA are two popular modulation schemes for incoherent OCDMA networks. PPM, as an energy efficient modulation, excels over OOK if the average power rather than chip time is the constraining factor [1]; however, in practical OCDMA systems the chip time is important, whereas power issues become critical in mobile and personal devices. In this chapter, we have also analysed Manchester codes which give further improvement to OCDMA system performance when they are assigned to users. In the analysis we have assumed that the multiple access interference (MAI) is the dominant noise in the OCDMA system.

Here incoherent synchronous OCDMA employing PPM signalling alongside its transmitters and receivers architectures are analysed. The analysis leads to the system bit error rate (BER) with respect to the group-padded modified prime code (GPMPC). This spreading code was introduced in Section 2.4.5.

The PPM-OCDMA system without an interference canceller becomes unreliable as the number of simultaneous subscribers increases. The reason is that MAI increases rapidly as the number of active users increases. Increasing the multiplicity M and the prime number P is helpful for improving the overall system performance, but it is not realistic to increase M and P continuously. Moreover, increasing M and P will increase the system complexity. If the amount of MAI can be reduced or removed, ...