Multiple input multiple output transmission techniques and link adaptation in wireless systems with dual-polarized antennas

Abstract

The use of dual-polarized antennas theoretically double the number of virtual antennas used in the system. On the other hand, the correlation effects and the crosspolar discrimination (XPD) deteriorates the system performance. When considering 2×2 dual-polarized multiple input multiple output (MIMO) communication system, a virtual 4×4 system is obtained where the hybrid MIMO options can also be carried out to maximize detection performance and multiplexing gain of the system. In this thesis, we propose a new hybrid approach and present performance analysis of a dual-polarized 2 × 2 system for space-time-block coding (STBC), spatial multiplexing (SM) and hybrid schemes. We also present simulation results for these multi-antenna signalling techniques under various XPD and correlation scenarios. Both the theoretical analysis and the simulation results show a significant performance gain by joint utilization of space, time and polarization diversity over the uni-polarized MIMO systems. However, the complexity of the system increases rapidly with respect to modulation order in the case of optimal detection at the receiver. In this regard, we propose a low complexity iterative receiver based on joint use of linear minimum mean squared error (MMSE) equalization and soft interference cancellation (SIC) process. In order to have efficient link adaptation, we design an unique receiver that has capability to detect symbols belonging to these four MIMO options. When combining four MIMO options with modulation and coding schemes (MCS) introduced in 802.11n and WiMAX, a transmission channel can be fully utilized with an proper adaptive switching mechanism. Therefore, as an example we employ the standard link adaptation technique for IEEE 802.11n standard. Simulation results indicate that a double throughput and significant range improvement can be achieved via the use of dual-polarized antenna elements.