Interference-Weighted Channel Sounding for Cellular SDMA-TDD Systems

In future time division duplex (TDD) wireless systems, where channel reciprocity is maintained, uplink (UL) channel sounding method is considered as one of the most promising feedback methods due to its bandwidth and delay efficiency. Conventional channel sounding only conveys the channel state information (CSI) of each active user to the base station (BS). Due to the limitation in system performance because of co- channel interference (CCI) from adjacent cells in interference- limited scenarios, CSI is only a suboptimal metric for multiuser spatial multiplexing optimization. Interference-weighted channel sounding (IWCS) is a spectrally efficient feedback technique that provides the base station (BS) with implicit knowledge about the interference experienced by each active user. The main contribution of this paper is to propose a novel way to make the IWCS pilots usable for improved UL performance. In this context, it is proposed to weight the metric obtained from the IWCS pilots by the interference experienced at the BS. The resultant new metric, which is implicitly dependent on downlink (DL) and UL interference, provides link-protection awareness and is used to jointly improve spectral efficiency in UL as well in DL. Using maximum capacity scheduling criterion, the link-protection aware metric results in a gain in the median system sum capacity of 26.7% and 12.5% in DL and UL respectively compared to the case when conventional channel sounding techniques are used.