Channel estimation and hybrid combining for mmWave: Phase shifters or switches?

Abstract

Precodinglcombining and large antenna arra y s are essential in millimeter wave (mmWave) s y stems. In traditional MIMO s y stems, precodinglcombining is usuall y done digitall y at baseband with one radio frequenc y (RF) chain and one analog-to-digital converter (ADC) per antenna. The high cost and power consumption of RF chains and ADCs at mmWave frequencies make an all-digital processing approach prohibitive.When onl y a limited number of RF chains is available, h y brid architectures that split the precodinglcombining processing into the analog and digital domains are attractive. A previousl y proposed h y brid solution emplo y s phase shifters and mixers in the RF precodinglcombining stage. It obtains near optimal spectral efficiencies with a reduced number of RF channels. In this paper we propose a different h y brid architecture, which simplifies the hardware at the receiver b y replacing the phase shifters with switches. We present a new approach for compressed sensing based channel estimation for the h y brid architectures.Given the channel estimate, we propose a novel algorihtm that jointl y designs the antenna subsets selected and the baseband combining. Using power consumption calculations and achievable rates, we compare the performance of h y brid combining with antenna switching and phase shifting, showing that antenna selection is preferred in a range of operating conditions. I. INT RODUCTIONCommunication over millimeter wave (lmnWave) frequen cies [1] is the frontier for commercial wireless communication systems. Initial applications of mmWave to personal area networks (PAN) and local area networks (LAN) through the 60GHz unlicensed band are already standardized [2] and commercially available. The large bandwidths available at mmWave carrier frequencies also makes it interesting for 5G cellular systems [3], [4], [5], [6].MmWave communication requires very large multiple-input multiple-output (MIMO) systems to provide sufficient antenna aperture. Unfortunately, at mmWave there are additional hard ware constraints that have to imposed due to the practical limitations on the cost, complexity and power consumption with the current technology [7]. Due to mixed signal and baseband processing requirements, it may not be feasible to use one complete RF chain and one DAC or ADC per antenna, so precoding and combining can not be done entirely in the baseband. For this reason, systems like IEEE 802.11ad use analog beamforming / combining and only support single stream MIMO communication.of streams requires the use of precoding and combining, mak ing functions like low complexity and low overhead channel estimation more essential.In previous work, a hybrid architecture that accounts for hardware constraints has been proposed [8], [9], resulting in precoder/combiner design algorithms that divide the op timization process into the RF and the baseband stages, and channel estimation methods that exploit the sparse nature of the mmWave channel. This architecture is based on quantized phase shifters, as illustrate...

Energy Efficiency and Asymptotic Performance Evaluation of Beamforming Structures in Doubly Massive MIMO mmWave Systems

“…In [8], it is shown that a HY beamformer with a number of RF chains that is twice the number of transmitted data streams may exactly mimic a FD beamformer; the analysis, which neglects energy efficiency issues, is however limited to either a single-user MIMO system or a MU-MIMO system with single-antenna receivers. The paper [9] proposes a new low-complexity post-coding structure, based on switches rather than on analog phase shifters; the performance of this new structure is evaluated in a rather simple scenario, i.e.…”

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A Sparse SAR Imaging Method Based on Multiple Measurement Vectors Model

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Channel estimation and training design for hybrid multi-carrier MmWave massive MIMO systems: The beamspace ESPRIT approach

“…However, one RF chain per antenna is impractical because the involved power consumption and the hardware cost are too high. To exploit the MIMO gain under a reasonable cost, one promising solution is to deploy hybrid analog-digital precoding schemes, realized using phase shifters or switches in the RF domain [3], and digital precoding schemes, implemented in the digital baseband domain as in conventional MIMO. If analog precoding is achieved using phase shifters only, the analog precoding matrix should have only constant modulus entries [4], [5], [6].…”

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