Throughput evaluation of a satellite switched CDMA (SS/CDMA) demand assignment system

This paper presents throughput evaluation of a satellite switched code division multiple access (SS/CDMA) system which operates under demand assignment control. The SS/CDMA provides both multiple access and switching to a geostationary multibeam satellite. Multiple access is resolved by space, frequency and code division. Space division is introduced by the multibeam antennae that provide frequency reuse in each beam. The spectrum is then channelized into frequency bands where each band is accessed by code division for both the uplink and the downlink. The satellite on-board performs the switching function which is also based on compatible code multiplexed switching. The switch may route both circuit calls and data packets which are assigned upon request. The on-board code division switch operates under the control of a channel assignment algorithm. We provide channel assignment algorithms for optimum, sub-optimum and random switch operation. Computer simulation has been used to evaluate the performance of the three algorithms. It is shown that their circuit call blocking probabilities are almost the same. The optimum algorithm achieves the minimum data packet delay, while the performance of the sub-optimum algorithm is slightly better than the random one. Furthermore, data packets may be routed via the switch with small delay, even with heavy load of circuit calls