Multiple Access Protocols for Satellite Mobile Radio Talk-group: Performance and Analysis

Satellite Mobile Radio Talk-group (SMRT) multi-group service is envisaged to operate in geo-stationary orbit and serve to facilitate communication among terminal users, under emergency situations. The terminal users are assigned in groups at the time of registration and the channel allocation is done on the basis of the groups. SMRT multi-group service makes use of two types of channels: signaling channel which is shared by all groups and voice channels which are assigned to individual groups by making use of multiple assignment scheme called Demand Assigned Multiple Access (DAMA). A critical issue in design of SMRT multi-group service is to facilitate a collision free communication between terminal users. This paper analyses different types of multi-access protocols and narrows down to a protocol technique which will give better results when implemented on the signaling channel in SMRT multi-group service. The aid of protocol in the signaling channel of SMRT multi-group service improves throughput and channel capacity, as numbers of retransmission which are caused because of collisions gets reduced. The protocols are evaluated on the basis of probability of error, throughput and delay by varying parameters like channel load, number of users, spreading factor, signal to noise ratio, receiver power level and signal to interference ratio. Spread spectrum protocols are found to be outperforming other protocols which are enlisted in the paper.