On access control disciplines for a TDMA system with multiple-rate real-time sources

We consider a communication medium, such as a satellite communication channel, which is shared by a number of sources on a time-division multiple-access (TDMA) basis. Sources require real-time transmission over the channel. A central controller stores the requests for transmission by the sources and assigns the freed slots within the time-frame to the appropriate sources, following a dynamic demand-assignment access control discipline. Sources are further assumed to require real-time transmission at different information rates, and thus require different number of slots per frame. Two access-control disciplines are studied, structurally optimized, and compared. A fixed-assignment discipline divides the frame slots among the various source classes on a predetermined basis. A priority-assignment discipline dynamically modifies the latter division by allowing one class of requests to utilize the freed slots of the other. The analysis demonstrates the extent to which the second scheme is preferrable, incorporating a message maximal waiting-time objective function and adaptability considerations.