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.<
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