Hybrid Combining Design for User Clustering in mmWave MIMO Systems

Hybrid architectures for millimeter-wave (mmWave) multiple-input multiple-output (MIMO) transceivers allow high data rates at an affordable radio frequency (RF) cost and power consumption. In the uplink of a multiuser mmWave MIMO system, the hardware reduction obtained with hybrid transceivers is limited by the number of individual user data streams to be synchronously collected by the base station (BS). Contrarily to most works in the literature, we focus on a scenario with more users than RF chains at the BS. We also consider the sources produce correlated information, a scenario applicable to wireless sensor networks (WSNs). In order to handle more users than RF chains, we propose a user clustering approach to superimpose the user symbols by means of distributed quantizer linear coding (DQLC) mappings and focus on the hybrid analog-digital design of the BS combining. Numerical results show the advantage of employing the proposed scheme to significantly reduce the hardware complexity in mmWave MIMO systems.