Throughput evaluation of a satellite-switched CDMA (SS/CDMA) demandassignment system

摘要

This paper presents throughput evaluation of a satellite-switchedncode-division multiple-access (SS/CDMA) system which operates underndemand assignment control. SS/CDMA provides both multiple access andnswitching to a geostationary multibeam satellite. Multiple access isnresolved by space, frequency, and code division. Space division isnintroduced by the multibeam antennas that provide frequency reuse inneach beam. The spectrum is then channelized into frequency bands whereneach band is accessed by code division for both the uplink and downlink.nThe satellite on-board performs the switching function, which is alsonbased on compatible code-multiplexed switching. The switch may routenboth circuit calls and data packets which are assigned upon request. Thenon-board code-division switch operates under the control of a channelnassignment algorithm. We provide channel assignment algorithms fornoptimum, suboptimum, and random switch operation. The system throughputnhas been evaluated for each case and compared. Performance analysis hasnbeen carried out for the case of the optimum switch scheduling. Thenanalysis is based on a discrete-time Markovian model, and provides thencall-blocking probabilities and data packet delays. Computer simulationsnhave been used to evaluate the performance of the optimum, suboptimum,nand random cases. It is shown that the circuit call-blockingnprobabilities achieved for these cases are almost the same. The optimumnalgorithm achieves the minimum data packet delay, while the performancenof the suboptimum algorithm is slightly better than the random one.nFurthermore, data packets may be routed via the switch with limitedndelays, even with a heavy load of circuit calls