Low-complexity fairness-driven pilot decontamination schemes for multi-cell massive MIMO systems

In this paper the time division duplexing (TDD) is considered for a massive multiple input multiple output (MIMO) system, where in the training phase, the channel state information (CSI) is deviated from its exact value due to pilot contamination. To mitigate this effect, at first, a centralized pilot assignment scheme is presented whose complexity order is of much lower value compared to that of the conventional algorithms. Secondly, an attempt is made to further lessen the complexity by proposing a relaxed version of this scheme, which results in a partially centralized strategy. Finally, a relaxed low-complexity form of the exhaustive search algorithm is presented, and it is compared to the other schemes in terms of overhead and complexity. Numerical results demonstrate that although the centralized pilot assignment scheme undergoes much smaller complexity in comparison with the exhaustive search algorithm, its performance faces merely a minor degradation. Moreover, the performances of the partially centralized and the relaxed low-complexity strategies are compared to the centralized pilot assignment scheme, and it is evident that their major drop in complexity causes a negligible performance loss. However, as the complexity mitigation is of significant value, the decline in performances seems to be entirely worth the cost.