LTE Advanced: 3GPP Solution for IMT-Advanced

13.7 Uplink CoMP Gains

Uplink CoMP reception techniques can improve uplink performance basically in two ways. Firstly, the desired signal quality can be improved by simply collecting more signal energy and by increasing available receive antenna diversity. Secondly, coordinated reception over multiple cells can significantly enhance inter-cell interference cancellation or suppression. From the CoMP reception methods listed in Figure 13.6, soft combining improves desired signal quality, but does not enhance interference mitigation, whereas a distributed IC receiver focuses solely on improving inter-cell interference mitigation. Joint multi-cell equalizers enhance both desired signal quality as well as interference mitigation.

The focus of achievable gains is on cell edge data rates, as desired signals can be received by multiple cells with comparable signal power levels only for cell edge UEs. Gains depend also on the accuracy of cell selection. Gains remain moderate with accurate cell selection, as received signal powers in neighbouring cells are below the received signal power level at the selected cell. Gains, of course, increase in case of less optimal cell selection. One particular case is seen with heterogeneous networks, where cell selection is a complex trade-off between downlink signal quality and cell splitting gains, as well as with uplink signal quality. As base station transmission power is considerably lower in small cells than in macrocells, small cell downlink coverage ...