Abstract
Ever since the deployment of the first-generation of mobile telecommunications, wireless communication technology has evolved at a dramatically fast pace over the past four decades. The upcoming fifth-generation (5G) holds a great promise in providing an ultra-fast data rate, a very low latency, and a significantly improved spectral efficiency by exploiting the millimeter-wave spectrum for the first time in mobile communication infrastructures. In the years beyond 2030, newly emerged data-hungry applications and the greatly expanded wireless network will call for the sixth-generation (6G) communication that represents a significant upgrade from the 5G network - covering almost the entire surface of the earth and the near outer space. In both the 5G and future 6G networks, millimeter-wave technologies will play an important role in accomplishing the envisioned network performance and communication tasks. In this paper, the relevant millimeter-wave enabling technologies are reviewed: they include the recent developments on the system architectures of active beamforming arrays, beamforming integrated circuits, antennas for base stations and user terminals, system measurement and calibration, and channel characterization. The requirements of each part for future 6G communications are also briefly discussed.
Highlights
More than a century ago, in the 1890s, the capability of using electromagnetic waves to transmit signals wirelessly was demonstrated, for the first time, in the famous wireless telegraphy experiment conducted by Nobel Laureate G
The recent development of mmWave channel measurement techniques using virtual antenna arrays reveal that the spaced elements will observe different sets of clusters, which can be modeled as a birth-death process [191]
The recent developments are described with examples, and the requirements and challenges for 6G communications are discussed
Summary
More than a century ago, in the 1890s, the capability of using electromagnetic waves to transmit signals wirelessly was demonstrated, for the first time, in the famous wireless telegraphy experiment conducted by Nobel Laureate G. The mmWave technologies that are important to 5G communications are reviewed, including the massive MIMO system architectures, beamforming chips, antennas for base stations (BSs) and user terminals (UTs), system measurement and calibration techniques, and wireless channel characterization. In [44], the authors presented a hybrid beamformer consisting of two RF channels connecting to the baseband and a 128-element antenna array [see Fig. 7] In such a structure, the phase distribution is realized in both the digital and analog domains, leading to a significant reduction in the number of RF chains. To obtain a broad spatial coverage, many AIPs or AIMs are required to be integrated together Such hybrid beamforming structures can have a satisfactory performance with relatively lower complexity, enabling large scale deployment. It allows for open interfaces for 5G equipment, aiming at establishing a healthier eco-system for 5G communications
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