Performance of RSS-, SIR-based Handoff and Soft Handoff in Microcellular Environments

Abstract

In microcellular systems the “corner effect” require that handoffs can be performed fast and at high reliability. This requirement is in contrast to the desire to keep the handoff rate low, i.e., the risk for “flip-flopping” of the call between base stations should be minimized. Handoff decisions are usually based on estimates of what signal quality that can be provided by different base stations. These estimates can be constituted by, e.g., received power (RSS) and/or signal-to-interference ratio (SIR) of used and target channels. In this work we compare the performance of an RSS-based handoff with the performance of a SIR-based scheme. We also analyze the behavior of a soft handoff (SOHO) scheme where several base stations simultaneously “listen” to a mobile while only one base station is transmitting.

We show that incorporating SIR estimates of the channels in the handoff decisions can reduce the handoff rate by 50% with the same signal quality as compared to the RSS-based scheme. For the RSS-based, and the SIR-based handoff schemes, the corner effect limits the maximum allowed speed around the corner for a given signal quality due to signal outages in the uplink. The receiver diversity in the uplink for the SOHO scheme makes the uplink practically insensitive to the corner effect. For this scheme the maximum speed is limited by the quality in the downlink, which allows much higher speeds.