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 sho rter delay at low and medium traffic loads while maintaining the high channel utility of the demand-assignment multiple-access (DAMA) techni que. In these schemes, reservation can be made using pre-assigned (PA) or random-access (RA) request slots, or piggy-backing (PB) the reques t on a data packet. This paper presents a performance analysis of CFDA MA schemes in packet satellite communications. Illustrative examples a re 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 termin al population increases, its performance is gradually degraded due to the long waiting time for a request. For a very large number of termin als, the CFDAMA-RA becomes more effective than CFDAMA-PA. This indicat es that a CFDAMA scheme using a hybrid PB/RA requesting protocol can p rovide the best performance for a wide range of terminal population si zes.