Performance evaluation of asynchronous random access CDMA with block FEC coding

The authors present an analysis of asynchronous random access packet CDMA (code-division multiple-access) channels with block FEC (forward error correction) coding. A procedure for calculating the error probability of an L bit packet in the variable message length, multiuser CDMA environment is presented. This procedure is used in conjunction with appropriate flow equilibrium traffic models to compute performance measures such as throughput and delay. Using as an example a direct sequence spread-spectrum multiple-access system with BCH block coding for FEC, the analytical model is used to obtain throughput vs. channel traffic curves over a range of code rates, leading to an assessment of maximum achievable throughput and the associated optimum FEC code rate. The results show that the use of block FEC coding provides a significant improvement in the normalized net channel throughput, approach values which are competitive with those for nonspread-spectrum ALOHA-type random access channels