Effective pilot assignment approach with ant colony optimization for pilot contamination mitigation in next generation mobile communication systems

Next generation mobile communication systems, improvements are expected to reduce latency, increase data rate, save energy, reduce costs, and spectrum efficiency. Although there are advantages of using Massive Multiple Input Multiple Output systems with many antennas, we meet some difficulties. One of these difficulties is pilot contamination. During uplink transmission, each user transmits pilot sequences of length τ to the base station. These large length orthogonal pilot sequences, which are proportional to the number of system terminals, affect the data rate due to the channel coherence interval. It is necessary to reuse the pilot sequences to serve more terminals and increase the efficiency of the system. Since there are limitations such as a limited bandwidth and coherence time, an unlimited number of pilot sequence assignments cannot be performed. Pilot contamination occurs in the system since the signal transmitted by the users using the same pilot sequences do not show orthogonality with each other. In this thesis, pilot assignment studies aimed at eliminating the effects of pilot contamination are examined. Pilot assignment methods are used as some coordinated methods based on assigning different pilot sequences to carefully selected user groups. In some studies, the cells were divided into two sides as center and edge, while in others, assignments were made separately considering the high and low interference users in the system. In this study, unlike other studies, the meta heuristic optimization method has been used for pilot assignment. In order to mitigate pilot contamination problem by using ant colony optimization, performance evaluation has been performance with the simulation program deemed appropriate and better system performance has been obtained compared to other comparable methods.