Degrees of freedom and impairments in massive MIMO systems -

Abstract

Massive multiple-input multiple-output (MIMO) systems is an emerging technology that is paving its way into wireless communication systems. Massive MIMO consists of tens or hundreds of antennas, which will result in huge increase in capacity, reliability and performance. However, massive MIMO is facing complexity issues in terms of channel estimation, RF impairments and RF design due to the large number of antennas. On the other hand, sparse code multiple access (SCMA) is a multi-dimensional system with codebook based on non-orthogonal coding technique offering high bitrate. It is presented as one of the potential candidates for LTE-A systems and beyond. In SCMA, the procedure of bit to QAM symbol mapping and spreading are combined and incoming bits are directly mapped to multi-dimensional codewords of SCMA codebook sets. In this thesis, we explore degrees of freedom and constraints offered in the combination of SCMA-MIMO systems in terms of capacity and RF impairments. The interest of MIMO-SCMA resides in the need of lower number of antennas while preserving the system capacity thanks to the overload in SCMA. Using some properties from Random Matrix and free probability theories, we derive analytical approximations of the Signal to Interference and Noise Ratio (SINR) and capacity expressions in the presence of RF impairments (mainly carrier frequency offset and phase noise) of the combined systems. The latter are independent of the code design but depend on the code length and the overload factor. We show that there is exists a tradeoff between SCMA and MIMO in terms of performance and complexity. All derivations are validated by extensive simulation results.