Receiver Performance Improvement via Intercell Spatial Demultiplexing for Low C/I Terminals in MIMO Systems

Although spatial multiplexing (SM) is an efficient means to enhance the data throughput in multiple-input multiple-output (MIMO) systems, its performance becomes seriously degraded when the receiver carrier-to-interference ratio (CIR) becomes low. In such a situation, which is typical for mobile terminals located near the boundaries of cells with low frequency reuse, transmission schemes with reduced spatial rate including space-time coding (STC) and the cyclic delay diversity (CDD) exhibit improved performance. In this paper, we consider rate-1 downlink transmission for MIMO systems with multi-antenna terminals in use, and focus on the analysis of the receiver performance at the low CIR region (cell boundary). Instead of using the conventional signal detection scheme under the 2-Tx and 2-Rx channel model, we show the effective CIR increases when the spatial demultiplexing (SD) detection is performed under the 4-Tx and 2-Rx model considering the strongest interfering signal as well as the desired signal. Through the evaluation of the effective CIR, the performance improvement at the cell boundary by using this "intercell SD (ISD)" which can cancel out or mitigate the strongest interference is demonstrated. It is shown the proposed scheme has the effective CIR gain of 3.04 dB at the cell boundary location.