A packet radio network using inhibit sense multiple access with capture

The throughput and delay of the mobile-to-base channel of a packet radio network employing a nonpersistent inhibit sense multiple access (ISMA) technique are investigated using analysis and discrete event simulation. Land-mobile packet radio networks typically employ frequency modulation, which exhibits a distinct capture effect. The capture phenomenon and the distribution of received packet amplitudes caused by propagation losses and multipath effects allow a packet sent on the mobile-to-base channel to be successfully received in the presence of interfering packets. It is found that, under these conditions, the capacity of ISMA can be substantially higher than that of the same protocol without capture. Furthermore, at high channel loading, the packet delivery delay of ISMA with capture is noticeably smaller than the delay of a channel without capture. The particular distribution of received packet signal strengths is a key factor in determining the throughput characteristic with capture. Reducing the capture ratio by choice of modulation technique and error control is therefore a step that system designers can take to improve the capacity of packet radio systems