Coding for FFH-CDMA Systems - Part I: Capacity and Cutoff Rate

This paper considers a fast frequency-hopping code division multiple access (FFH-CDMA) system used in a mobile radio environment. In the receiver, maximum likelihood (ML) detection with un-quantized detector outputs implies the use of a nonlinearity of difficult implementation. To approximate this nonlinearity, we propose to use an unique perceptron. The system performance with this approximation is almost identical to ML detection. A system with un-quantized detector outputs can support, a considerable greater number of simultaneous active users then a system with hard quantization of outputs. By calculating the capacity (per dimension) and the cutoff rate of the FFH-CDMA systems, we show that hard limiting of detector outputs can also significantly degrade system performance or reduce the number of active users