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We propose four hybrid combiner/precoder for downlink mmWave massive MU-MIMO systems.The design of a hybrid combiner/precoder is divided in two parts, analog and digital. The system baseband model shows that the signal processed by the mobile station can be interpreted as a received signal in the presence of colored Gaussian noise, therefore, since the digital part of the combiner and precoder do not have constraints for their generation, their designs can be based on any traditional signal processing that takes into account this kind of noise. To the best of our knowledge, this was not considered by previous works. A more realistic and appropriate design is described in this paper.Also, the approaches adopted in the literature for the designing of the combiner'/precoder' analog parts do not try to avoid or even reduce the inter user/symbol interference, they concentrate on increasing the signal-to-noise ratio (SNR). We propose a simple solution that decreases the interference while maintaining large SNR. In addition, one of the proposed hybrid combiners reaches the maximum value of our objective function according with the Hadamard's inequality. Numerical results illustrate the BER performance improvements resulting from our proposals. In addition, a simple detection approach can be used for data estimation without significant performance loss. Index TermsMassive MIMO, hybrid precoding, hybrid combining, millimeter wave (mmWave), RF chain number limitations, multiuser.

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This work focuses on a new methodology for use in a Multi-branch Serial Interference Cancellation (MB-SIC) type of MIMO detector. The proposed structure incorporates a low complexity ordering scheme and a variable amount of branches, whose number is controlled by a metric that reflects the quality of the current signal vector estimate. Single and multiple-user environments with both correlated and uncorrelated channels scenarios are considered. Bit error rate results, obtained through simulation, and complexity results, expressed in terms of the required number of flops per detected signal vector, are compared with the corresponding results of previously proposed MB-SIC schemes.

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