Performance of Combined Free/Demand Assignment Multiple-Access Schemes in Satellite Communications

By combining free assignment with demand assignment, the combined free/demand assignment multiple-access (CFDAMA) protocol offers a much shorter delay at low and medium traffic loads while maintaining the high channel utility of the demand-assignment multiple-access (DAMA) technique. In these schemes, reservation can be made using pre-assigned (PA) or random-access (RA) request slots, or piggy-backing (PB) the request on a data packet. This paper presents a performance analysis of CFDAMA schemes in packet satellite communications. Illustrative examples are given. They show a good agreement between analytical and simulation results. For low and medium sizes of terminal population, the CFDAMA-PA scheme has an excellent delay-throughput performance. As the terminal population increases, its performance is gradually degraded due to the long waiting time for a request. For a very large number of terminals, the CFDAMA-RA becomes more effective than CFDAMA-PA. This indicates that a CFDAMA scheme using a hybrid PB/RA requesting protocol can provide the best performance for a wide range of terminal population sizes.