On the Use of Uplink Received Signal Strength Measurements for Handover

In most cellular systems, handover decisions are based on measurements of the downlink signal strength. When the average path gain in downlink and uplink is similar, such principles yield good performance in both directions of transmission. In cases with systematic imbalances between downlink and uplink however, it is not evident that the uplink performance is optimized. In this paper, a handover scheme based on a combination of downlink and uplink path gain measurements is outlined, and its performance is evaluated in a system with systematic downlink and uplink imbalances. As a reference, a downlink-based only mechanism is used. Results indicate that the combined scheme yields an insignificant gain in uplink signal to interference ratio (SINR). This gain is considerably lower than the corresponding loss in the SINR of users in the downlink. The reason for the low uplink gain is that uplink interference is higher in the cells with higher uplink/downlink imbalance ratio than in adjacent cells in equally loaded cells. As a result, users which are connected to cells with better uplink/downlink imbalance ratio than their adjacent cells also experience higher interference levels, which results in a limited gain in signal-to-interference ratio.