A new access scheme for pure aloha using capture effect by time‐varying power control

Abstract

The advent of VSAT (very small aperture terminal) has made it possible to consider a new utilization of satellite communication. This paper proposes a new access protocol v‐ALOHA, which is matched to the characteristics of the packet switching network based on VSAT. p‐ALOHA is used as a means to cope with the requirement for simplification. To complement its disadvantage of low through‐put, a new control scheme is combined based on the new utilization. The performance is improved by the capture effect. The basic idea of the control scheme is to vary the power with time while transmitting packets. The difference in the transmission‐start time is converted into the power difference and produces the capture effect, thereby improving the performance. Thus, an access protocol is realized which improves the low throughput of p‐ALOHA while preserving its simplicity. This paper describes the basic idea of this v‐ALOHA and the protocol structure, indicating qualitatively its features. Then the throughput performance is formulated through a quantitative analysis. It is shown from the numerical results for the fixed‐length packet that the performance of the proposed scheme is better than other capture schemes, approaching sufficiently the performance of s‐ALOHA. For the case of the variable‐length packet, there is no slot loss as in s‐ALOHA, and the proposed scheme is shown, using an example, to be better sometimes than s‐ALOHA.

A distributed routing scheme in a mobile communication system

“…The capture effect is produced by the power difference between the received packets. By the present receiver technology, the effect is produced when the ratio of the signal and the interference waves (capture effect) is 1.5 to 3 dB [16,17]. From this viewpoint, the capture effect is considered when the capture ratio is 3 dB or larger because of the effect of distance.…”