Dynamic Subarrays for Hybrid Precoding in Wideband mmWave MIMO Systems

Abstract

Hybrid analog/digital precoding architectures can address the trade-off between achievable spectral efficiency and power consumption in large-scale MIMO systems. This makes it a promising candidate for millimeter wave systems, which require deploying large antenna arrays at both the transmitter and receiver to guarantee sufficient received signal power. Most prior work on hybrid precoding focused on narrowband channels and assumed fully-connected hybrid architectures. MmWave systems, though, are expected to be wideband with frequency selectivity. In this paper, a closed-form solution for fullyconnected OFDM-based hybrid analog/digital precoding is developed for frequency selective mmWave systems. This solution is then extended to partially-connected but fixed architectures in which each RF chain is connected to a specific subset of the antennas. The derived solutions give insights into how the hybrid subarray structures should be designed. Based on them, a novel technique that dynamically constructs the hybrid subarrays based on the long-term channel characteristics is developed. Simulation results show that the proposed hybrid precoding solutions achieve spectral efficiencies close to that obtained with fully-digital architectures in wideband mmWave channels. Further, the results indicate that the developed dynamic subarray solution outperforms the fixed hybrid subarray structures in various system and channel conditions.

GMD-Based Hybrid Beamforming for Large Reconfigurable Intelligent Surface Assisted Millimeter-Wave Massive MIMO

“…[21] proposes a limited feedback for channel state information (CSI) and presents a hybrid analog-digital beamforming codebook design for wideband case. Some other solutions to further reduce the cost of hardware or feedback, such as dynamic partially-connected structure or low-resolution hybrid beamforming have also been considered in [19], [22], [23]. Now with the emergence of RIS, beamforming becomes more flexible and controllable.…”

Hybrid Beamforming for MIMO-OFDM Terahertz Wireless Systems over Frequency Selective Channels

“…A useful criterion for hybrid codebook construction was also developed in [20], where both the baseband and radio frequency (RF) precoders are taken from quantized codebooks. Following [20], [21] considered the dynamic subarrays architecture for wideband hybrid beamforming, where a criterion for constructing the optimal subarrays that maximize the spectral efficiency was proposed. Furthermore, [22] showed that hybrid beamforming with a small number of RF chains can asymptotically approach the performance of fully digital beamforming for a sufficiently large number of transceiver antennas.…”

Design of Low-Complexity Hybrid Precoder and Inkjet-Printed Antenna Array for Massive MIMO Downlink Systems

“…Since the array size of the massive MIMO system is typically large, digital precoding becomes more complex in terms of area, cost, and power limitations. But the hybrid precoder architecture shown in Figure 1 groups the transmitting antenna elements into a number of subarray modules [10]. Hence, separate RF chains are assigned for each subarray module rather than individual antenna element which reduces the cost of the system considerably.…”

“…The digital precoder controls the signal supplied to the RF precoder by the complex weight matrix W D , and the complex analog weight matrix W A of the RF precoder controls the phase shift network of the antenna array. More extensive research works have been carried out on developing hybrid precoding algorithms in [9][10][11][12]. All these works devise various hybrid algorithms for massive antenna systems based on computationally intensive block diagonalization and eigenvalue decomposition methods.…”

“…Finally, the RF and digital precoders can be designed using the relations (10) and (12), respectively, for the hybrid precoder architecture.…”