Random Signal Levels for Channel Access in Packet Broadcast Networks

In this paper, it is proposed to employ random multiple signal levels for channel access in packet broadcast networks. We present priority-free random access protocols that possess the advantage of capture effect. The presented schemes are applied to the slotted ALOHA, and the performance is analyzed based on a conservative capture model. Closed-form expressions for the system throughput are derived for a general two-signal level system and a generalm-signallevel system. It is shown that the maximum throughput for the twolevel system increases from 0.47 to 0.52 as the separation between the two levels increases. For them-level system, the maximum throughput increases from 0.52 to 0.66 asmincreases from three to infinity. Then a rotary-priority sure-capture random access scheme is presented, which can achieve perfect channel utilization. The time-delay characteristic and the throughput-delay tradeoff are analyzed for the simplest two-level system for which the higher level is double the lower level. The results compare favorably to those of the conventional slotted ALOHA system which employs a single signal level for packet transmission. A number of open problems are addressed.