Polarisation dependent MIMO gains on multiuser downlink OFDMA with a 3GPP LTE air interface in typical urban outdoor scenarios

Recent studies on spatial multiplexing gain based on antenna polarisation diversity are mostly based on channel measurements or theoretical propagation models. The advantage of using XPD cross-polarised antennas in cellular MIMO-OFDM systems is that XPD antennas save costs and space achieved by a more compact antenna design. The throughput performance is generally considered to be similar to co-polarised antennas with pre-coding. In this paper we show the achievable gains of using cross-polarised antennas as compared to co-polarised antennas at the base station. These cross-polarised antennas are used for adaptive MIMO transmission for typical outdoor scenarios. Our results are based on real-time multiuser (MU) multi-antenna capacity measurements taken with a MIMO-OFDMA system with parameters close to the current 3G-Long-Term-Evolution (LTE) standard. Downlink transmission is considered in a single-cell outdoor scenario. We demonstrate the significant effect of polarisation on the overall system performance, especially on user sum rates when fairness scheduling in OFDMA is applied.