Rate adaptation of convolutional coded optical CDMA systems for improved goodput

Rate adaptation is a technique that enables the selection of the most suitable error-correction coding rate according to the real-time channel quality, therefore increasing the overall throughput. We propose the use of rate adaptive convolutional codes for amplitude encoded, binary on-off keyed optical code-division multiple access (OCDMA) systems. Conventional OCDMA systems have a bit error probability floor due to optical multiple-user interference (OMUI). A convolutional coded OCDMA system (CC-OCDMA) lowers the error floors with increased coding rates but at the expense of reduced goodput (throughput minus the redundancy bits or symbols). However, by exploiting the variation of OMUI with user number, it is shown here that rate adaptation offers larger and consistent goodput improvements compared to fixed coding rate CC-OCDMA systems for various traffic profiles. This advantage is also observed in comparisons with OCDMA systems using improved receiver designs and 2D wavelength/time signatures codes. Based on the analytical results obtained here and the commercial availability of convolutional coding chipsets, rate-adaptive convolutional coding for OCDMA systems is worth to be considered for practical implementation.