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A novel receiver architecture for single carrier noma transmission in wideband sparse mimo channel.

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2019
Halil, Bura
In contemporary wireless communication systems, it became necessary to provide better solutions than current communication standards because of the increasing demand for massive connectivity and throughput. Non-Orthogonal Multiple Access (NOMA) has become one of the promising candidates for fifth generation (5G) communication networks. In this thesis, Sparse Code Multiple Access (SCMA) is utilized as a single carrier NOMA technique. SCMA is a transmission protocol, in which multiple users shares same time slot simultaneously. Although for 5G networks, NOMA brings many advantages such as spectral efficiency, on the other hand it demands more complex receiver designs since users share same time-slot simultaneously unlike the current systems. In order to overcome this problem, a factor-graph based novel receiver architecture is proposed. In this thesis, firstly single tap channel is analyzed in multiuser scenario and performance of the factor-graph based receiver architecture is analyzed. Secondly, MIMO is utilized for multi-tap channel scenario. In massive MIMO case, different parts of receiver antennas can be allocated for different groups. Every group consists of users with spatially correlated multi-tap channels. Thus, receiver massive antenna array block can serve more than one group simultaneously. In this thesis, performance of a single group is analyzed. Several antenna inputs are combined together and used as a single input of a factor-graph based message passing algorithm (MPA). Also for each user's data prediction, received signal is passed through matched filter of that user. In the proposed receiver design, output of the factor graph is processed in order to predict possible "inter symbol interference (ISI)" from other symbols and "inter chip interference (ICI)" from other time slots of the same symbol. Therefore, the lost sparsity is recovered with the help of proposed processing. The system performance is analyzed for various channels with different number of taps, antennas, constellation points, angular spread (AS) and different levels of noise figure.