Abstract
Pilot contamination is a major factor that restricts the system performance of time division duplex (TDD) massive multiple-input multiple-output (MIMO) systems. Reasonable pilot allocation is an effective method to reduce pilot contamination. However, most of the existing pilot allocation methods focus on cells of the same size, a regular shape, an equal number of users per cell, and/or independent fading channels. When they are generalized or modified to actual scenes (in which cells have irregular shapes, users are randomly distributed, and channels are correlated fading channels), they are inflexible and cannot guarantee the target performance requirement. Considering both flexibility of pilot allocation and system performance, this paper introduces the idea of a coalition game into pilot allocation and proposes a pilot allocation scheme based on the coalition game. Different utility functions are analyzed under correlated fading channels; the adjustment principle of coalition structure and the coalition formation algorithm are given. Simulation results show that the proposed scheme can be used in any actual scene as well as guarantee the target performance requirement.
Highlights
1.1 The research background of this paper With the appearance of smartphones and tablets, wireless communication requires increasingly higher communication rates
The “coalition game, mean square error (MSE)-SD, minimum mean square error (MMSE),” “coalition game, mean square error of signal detection (MSE-SD), zero-forcing combining (ZFC),” and “coalition game, MSE-SD, maximum ratio combining (MRC)” means the pilot allocation scheme based on the coalition game when utility function is MSE-SD with the MMSE scheme, when utility function is MSE-SD with the ZFC scheme, and when utility function is MSE-SD with the MRC scheme, respectively
For each combining scheme (MMSE, ZFC, or MRC), the coalition game is better than random coalition
Summary
1.1 The research background of this paper With the appearance of smartphones and tablets, wireless communication requires increasingly higher communication rates. Paper [7] proposes a spatial domain method with the main idea that users with high channel orthogonality can use the same pilot This method assumes that cells have a regular shape and that the number of users in each cell is fixed and equal. When the number of base station antennas is very large, it is difficult to ensure the distance between the antennas, and it is difficult to ensure that all channels are independent Most of these pilot allocation methods (in references [4,5,6,7,8,9,10,11,12,13]) assume that the number of users per cell is equal or fixed for two main reasons. 1) To be applied in arbitrary actual scene (with irregular shape cells, unequal number of users per cell, and correlated fading channels) and provide target performance guarantee, a novel pilot allocation scheme based on the coalition game is proposed. The proof of theorem is given in the Appendices 1, 2, and 3
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