Provision of variable data rates in third generation wideband DS CDMA systems

Provision of a large variety of services is expected in the upcoming third generation wireless systems. Users with very different and even time varying rate and quality of service (QoS) requirements will need to be accommodated. In order to provide such diversity, the network has to be able to statistically multiplex different rate and QoS users together while maximizing the spectral efficiency. In a given fixed channel bandwidth, there are two basic methods with which variable rate services may be implemented in the forward link physical layer of a DS CDMA system: allocating each user one code channel that has a variable spreading factor or allocating multiple codes to each user so that the individual user data streams are split into parallel lower rate streams which in turn are each spread by different, higher order orthogonal codes. Clearly, hybrids of the two methods are feasible as well. This paper is concerned with investigating the effects of these configurations on the overall system performance. Impact on both uniform and hybrid traffic is considered for a multitude of channel models.