NOMA-RA: protocolo de acesso aleatório baseado em múltiplo acesso não ortogonal para MIMO massivo

Abstract

In this thesis, we investigate the random access (RA) problem in a massive MIMO scenario. In 5G networks, devices/users willing to connect to the base station (BS) need to choose a pilot sequence from a set of available orthogonal sequences. However, considering the internet of things (IoT) scenario, the number of users/devices trying to access the BS is much higher than the number of available pilot sequences, só that collisions may occur frequently. Considering this scenario, the strongest-user collision resolution (SUCRe) protocol is modified to include a non-orthogonal multiple access (NOMA) approach. The proposed NOMA-RA protocol allows to resolve collisions between users who try to access the medium using the same pilot signal. Numerical results show that the proposed NOMA-RA strategy achieves a better performance in terms of sum-rate with lower average delay in comparison with the traditional SUCRe scheme, even considering imperfect channel estimation and successive interference cancellation (SIC). For instance, in a scenario when 10 pilot sequences are available and 20 devices compete to access the channel, comparing with the SUCRe protocol, the average delay is reduced by 30% while the sum-rate is improved by 33% and 22% considering, respectively, perfect and imperfect SIC decoders, when the imperfection of SIC was fixed in 10%. In addition, the percentage of users that fail to access the BS in this situation drops from 66.5% with SUCRe to 38.5% with the proposed NOMA-RA scheme.