The interplay between mapping/demapping and non-binary LDPC coding in MIMO wireless communication systems

Recently, the need for innovative services available for the end users has led to an increasing demand of higher throughputs of wireless systems. On the other hand higher throughput means wider bandwidth, so that channel selectivity and fading might be a severe challenge to combat in order to ensure high level of Quality of Service (QoS). In this scenario one of the possible approach to increase the system throughput is the use of multiple antennas, both at the transmitter and the receiver side. Instead the typical manner to combat channel effects is to employ powerful channel coding schemes, which target the mitigation of these propagation effects. This work follows this approach combining the MIMO techniques jointly with the powerful channel coding scheme of non-binary LDPC. The expression "non-binary" refers to the fact that these codes are defined over high order Galois Field. These codes have been researched in the literature to achieve higher error protection than conventional binary codes for transmission over different noisy channels. The main novelty of this work is related to the mapping and demapping of the non-binary information. Typically the main contributions in the literature focus on the low complexity decoders, whilst the demapping complexity is neglected. However, the demapping complexity might become a real bottleneck in the global receiver complexity, so that we decide to investigate this topic. A strategy is devised to guarantee an efficient mapping at the transmitter, together with an algorithm for low complexity soft demapping at the receiver. The proposed solutions target the best trade-off between performance and complexity, for any combination of the Galois field order, QAM constellation order, and MIMO scheme.