Optical Code Division Multiple Access (OCDMA) provides increased security communications with large dedicated bandwidth to end users and simplified network control. We analyse the call-level performance of an OCDMA Passive Optical Network (PON) configuration, which accommodates multiple service-classes with finite traffic source population. The considered user activity is in accordance with the bursty nature of traffic, so that calls may alternate between active (steady transmission of a burst) and passive states (no transmission at all). Parameters related to multiple access interference, additive noise, user activity and number of traffic sources are incorporated to our analysis, which is based on a two-dimensional Markov chain. An approximate recursive formula is derived for efficient calculation of call blocking probability. Furthermore, we determine the burst blocking probability; burst blocking occurs when a burst delays its returning from passive to active state. The accuracy of the model is completely satisfactory and is verified through simulation. Moreover, we reveal the consistency and necessity of the proposed model.

The traditional waveform coding techniques for digital communication systems convert the original analog input signal into a digital bit stream using uniform sampling in the time domain, i.e. PCM, DM, ADPCM. We propose the time code modulation (TCM) technique as an alternative coding scheme, where information is extracted from the signal, only at the time instants when necessary. This results in a variable sampling rate, where its mean value is significantly less than the Nyquist rate. In addition we suggest a general theoretical model for TCM and we present simulation results for various implementations of TCM coders and decoders. A theoretical estimation of SNR vs. sampling rate performance is also presented.