An analysis of queuing strategies for SCA data broadcast systems

Subcarrier audio channels (SCAs) are used to support a wide-area data communication system. Text or data messages can be transmitted nationally using satellite delivery, and locally using FM broadcasting stations´ subcarriers. The time delay that messages experience in the national buffer at the satellite head-end or the local buffer is examined. The delay for various throughput data rates is evaluated to identify an optimum range for this capacity. A realistic set of messages statistics is developed to model SCA traffic. Three different queueing strategies are used to examine the delay that messages obeying these statistics would experience: first-come-first-served, fixed-priority, and delay-dependent priority. It is shown that, as the throughput is increased, the effect of priority on the system is less discernible. As the output capacity is decreased, the effect of a priority structure can be seen to enhance traffic flow. Total message time delay is examined using a delay-dependent priority scheme. Results indicate that the choice of an appropriate queuing strategy will enhance the flow of priority message traffic