Variable Spreading Gain Research Articles

Admission control for variable spreading gain CDMA wireless packet networks

A technique for variable spreading gain code-division multiple access (VSG-CDMA) with transmit power control has been proposed in I and Sabnani (1995) to provide integrated services in a wireless packet network. System capacities of VSG-CDMA networks with and without considering user activity factors were derived. The analysis gives a lower bound of system capacity because a user's transmitted power is considered part of the interference to its own signal. In this paper, we present an optimistic upper bound assuming that there is no multipath fading or the energy of a signal in all multipath components can be fully resolved. An optimum power vector assignment and a simple criterion for all users to simultaneously achieve their quality of service (QoS) requirements (in terms of bit energy-to-interference density ratios) are derived. We found from numerical examples that, compared with the lower bound given in I and Sabnani, significant improvement can be obtained if multipath fading can be satisfactorily handled. Several access control schemes are also studied to guarantee delay bound requirements. Simulation results reveal that more connections can be further accommodated with access control.