System Performance of Transmit Diversity Schemes for Interference-Limited Cellular Systems

This paper compares the system performance of transmit diversity schemes for use in interference-limited cellular systems. We focus on evaluating the performance of Alamouti space time block codes (STBC) and cyclic delay diversity (CDD) codes, which are being actively considered for adoption within the 3 GPP-long-term-evolution (LTE) and 802.16e WiMAX standards. While the performance of transmit diversity schemes has been extensively evaluated in noise-limited scenarios, their performance in co-channel interference (CCI) limited cellular systems has received limited attention so far. As cellular systems adopt frequency reuse of one, co-channel interference from other cells becomes a major limitation to system performance. We present system simulation results comparing the performance of transmit diversity schemes using matched filter reception for a multi-carrier OFDM-based cellular system. In particular, the performance of STBC and CDD schemes is compared with respect to the evolving third generation 3 GPP-LTE standard. Our comparison highlights the spatial as well as the multi-user diversity aspects of these schemes and considers a variety of scenarios that will require their use. Our results show that CDD can significantly improve the system spectral efficiency and cell-edge performance over STBC, when used in combination with frequency-dependent scheduling. For open loop transmission without scheduling, the relative diversity gains of STBC and CDD at link layer depend on the interference scenario considered, while the system performance of these schemes is very similar.