Exploiting Polarization Diversity in Massive MIMO Systems using Hyper- Complex Variables

Abstract

Space time block coding (STBCs) improves the reliability of transmission by sending multiple copies of data through multiple antennas. Recently, the study of orthogonal designs in higher dimensions has supported higher diversity gains, i.e. combining STBCs with different forms of diversity. Also, designing codes with higher code rates is a desired aim for future communication networks but the complexity of the receiver has always limited this freedom. Quaternion orthogonal designs (QODs) have been derived mostly from complex orthogonal codes (CODs). This supports the idea and benefits of using QODs to achieve higher code rates but it remained limited in fully exploiting the use of dual-polarized antennas. The real essence of adding the polarization diversity to the coding designs still remains unexplored. This research targets this research gap and presents a thorough analysis of using higher dimensional variables not only to achieve efficient code designs with higher code rates but also to investigate mechanisms to optimize the receiver design. Based on these aims, this research takes two major paths. First, it studies the impact of using quaternion designs with dual-polarized antennas. The underlying channel between the dual-polarized transmit and receive antennas is discussed when the pure QODs are transmitted. These QODs provide promising diversity gains and shows comparative code rates similar to the state-of-the-art Alamouti codes. Secondly, this research work presents viii ix linear and decoupled decoders for pure QODs, that was not possible before. As an application of the proposals in this work, quaternionic channel-based modulation has been discussed that fully exploits the polarization diversity without considerable limitations on the transmit and receiver dimensions. The design of wireless communication systems using pure QODs transmitted using dual-polarized antennas will open new horizons of research. It will support higher data rates and improved receiver efficiency, that are the two main targets of the future generations of wireless systems.