Investigation on advanced receiver employing interference rejection combining for space-frequency block code transmit diversity in LTE-Advanced downlink

The interference rejection combining (IRC) receiver, which can suppress inter-cell interference, is effective in improving the cell edge user throughput, and is required to function effectively in various development scenarios, e.g., in both closed-loop and open-loop multiple input multiple output (MIMO) multiplexing. The IRC receiver is typically based on the minimum mean square error (MMSE) criteria, which requires highly accurate channel estimation and covariance matrix estimation that includes inter-cell interference. We investigated a covariance matrix estimation scheme that employs received signals and the known sequence of downlink reference signals (RSs), and evaluated the performance gain of the scheme assuming closed-loop MIMO multiplexing. However, for open-loop MIMO multiplexing assuming one-stream transmission, i.e., open-loop transmit diversity employing the space-frequency block code (SFBC), the IRC receiver must detect the SFBC signals and suppress the interference signals at the same time. Although it is required for the extended covariance matrix estimation, some elements cannot be estimated using the RS-based estimation scheme. Therefore, this paper proposes inserting zero values in the unknown elements, and investigates the performance gains. The results of simulations assuming the LTE/LTE-Advanced downlink show that the IRC receiver using the proposed scheme, which has two receiver antenna branches, suppresses the inter-cell interference and improves the throughput by approximately 12% to 15% compared to that for the conventional maximal ratio combining (MRC) receiver when a cell edge environment is assumed.