Generalized Framework for Hybrid Analog/Digital Signal Processing in Massive and Ultra-Massive-MIMO Systems

Abstract

The conventional fully-digital implementation of massive-MIMO systems is not efficient due to the large required number of radio-frequency (RF) chains. To address this issue, hybrid analog/digital (A/D) beamforming was proposed and to date remains a topic of ongoing research. In this paper, we explore the hybrid A/D structure as a general framework for signal processing in massive and ultra-massive-MIMO systems. To exploit the full potential of the analog domain, we first focus on the analog signal processing (ASP) network. We investigate a mathematical representation suitable for any arbitrarily connected feed-forward ASP network comprised of the common RF hardware elements in the context of hybrid A/D systems, i.e., phase-shifter and power-divider/combiner. A novel ASP structure is then proposed which is not bound to the unit modulus constraint, thereby facilitating the hybrid A/D systems design. We then study MIMO transmitter and receiver designs to exploit the full potential of digital processing as well. It is shown that replacing the linear transformation in the digital domain with a generic mapping can improve the system performance. In some cases, the performance of optimal fully-digital MIMO systems can be achieved without extra calculations compared to sub-optimal hybrid A/D techniques. An optimization model based on the proposed structure is presented that can be used for hybrid A/D system design. Specifically, precoding and combining designs under different conditions are discussed as examples. Finally, simulation results are presented which illustrate the superiority of the proposed architecture to the conventional hybrid designs for massive-MIMO systems. INDEX TERMS Hybrid beamforming, hybrid analog and digital signal processing, ultra massive MIMO, massive MIMO, precoding, combining, beamforming.

Integration of Hybrid Networks, AI, Ultra Massive-MIMO, THz Frequency, and FBMC Modulation Toward 6G Requirements: A Review

“…Analog beamforming can create high directional gain beams using phase shifters as used in massive MIMO [165]. Although fully digital beamforming is more accurate in um-MIMO, it is costly and consumes high power [166]. Hybrid beamforming is a promising solution to the issues stated above.…”

Deep Learning-Based Hybrid Analog-Digital Signal Processing in mmWave Massive-MIMO Systems

“…Hybrid analog-digital signal processing (HSP) is an ingenious and effective approach to facilitate the implementation of mmWave massive-MIMO transceivers [12]- [26]. In an HSP transmitter, which includes hybrid beamforming (HBF) as a special case, a low-dimensional baseband signal (e.g., precoder output) is converted to RF and then mapped into a higher-dimensional signal for transmission by the antennas, where the mapping is achieved by an analog processing network comprised of basic RF components such as phaseshifters, combiners and dividers; in an HSP receiver, the dual operations are performed in reverse order.…”

MARS: Message Passing for Antenna and RF Chain Selection for Hybrid Beamforming in MIMO Communication Systems

“…Nonetheless, the performance of sub-arrays is potentially limited due to its inflexibility and inaccessibility of information from other RF chains or antenna sets. In [18], the authors discuss about different RF connections for sub-array based HBF; while the work of [19] minimizes the bit error rate under various RF/antenna connections. Therefore, it becomes compellingly important to design a novel architecture of HBF in order to achieve the benefits of high operational flexibility and asymptotic performance of digital beamforming.…”

“…However, with increasingly large-scale HBF with enormous antennas and RF chains serving multiple devices, it will lead to substantially-high overhead in terms of power and complexity, which is not considered in the above-mentioned works of [10]- [19]. In [20]- [23], the authors address the importance of optimizing EE from either architecture or hardware perspective.…”