Abstract
Hybrid analog/digital schemes for precoding/combining have proved to be a low-complexity and/or low-power strategy to obtain reasonable beamforming gains in multiuser millimeter-wave (mmWave) multiple-input multiple-output (MIMO) systems. Hybrid precoding/combining performs jointly baseband processing and analog processing in the radio frequency (RF) domain. In these systems, the number of RF chains limits the maximum number of streams simultaneously handled by the transceivers. In the uplink of a multiuser mmWave MIMO system, the hardware reduction based on hybrid transceivers is limited by the number of data streams that must be simultaneously served by the centralized node. Most works approach hybrid transceiver design by considering more RF chains than data streams, an unrealistic assumption when the number of nodes is large. On the other hand, statistically independent information is conventionally assumed in multiuser mmWave systems. This assumption does not hold in scenarios like wireless sensor networks (WSNs), where the sources produce correlated information. In this paper, by enabling inter-user correlation exploitation, we propose a grouping approach to handle a high number of individual sources with a limited number of RF chains through distributed quantizer linear coding (DQLC) mappings. The allocation of the users per group and the hybrid design of the combiner at the common central node to serve the grouped users is also analyzed. We also propose a hybrid minimum mean square error (MMSE) combining design in order to exploit the spatial correlation between the sources in a conventional uncoded mmWave uplink. Simulation results show the performance advantages of the proposed approaches in various hardware-constrained system settings.
Highlights
Millimeter-wave multiple-input multiple-output (MIMO) systems are being considered for future wireless communications systems [1], [2]
This problem is commonly handled by decoupling the fully digital precoder/combiner into a baseband part and an analog processing radio frequency (RF) part utilized to change the antenna signals phase via variable phase shifters [5]. This strategy is extensively considered in the state-of-the-art under the name of hybrid analog-digital architecture for mmWave and allows to significantly reduce the number of RF chains [4], [6]–[10]. According to their connectivity level, hybrid mmWave MIMO architectures can be distinguished in two classes [11]: fully-connected structure (FCS) [12]–[14] where each antenna is connected to each deployed RF chain, VOLUME 8, 2020
In this work, we explore a new strategy for the design of practical mmWave massive MIMO systems which are able to deal with these requirements in terms of hardware complexity and delay
Summary
Millimeter-wave (mmWave) MIMO systems are being considered for future wireless communications systems [1], [2]. A. CONTRIBUTIONS In this paper, we propose a low-complexity system which enables the correlation exploitation and allows the reduction of the number of RF chains for multiuser mmWave massive MIMO communications by considering a FCS-based hybrid combiner at the common BS. We address the design of practical solutions to exploit the source correlation in a less restrictive scenario where the number of RF chains is allowed to be equal to the number of available streams to be transmitted In such a scenario, a MMSE-based hybrid design of the combiner inspired by [13] and [21] is proposed to exploit the inter-user correlation for the uplink of conventional ungrouped mmWave MIMO systems. · stands for the rounding operation and expectation is denoted by E[·]
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