Millimeter-wave (mmWave) technology has been well studied for both outdoor long-distance transmission and indoor short-range communication. In the recently emerging fiber-to-the-room (FTTR) architecture in the home network of the fifth generation fixed networks (F5G), mmWave technology can be cascaded well to a new optical network terminal in the room to enable extremely high data rate communication (i.e.,>10 Gb/s). In the FTTR+mmWave scenario, the rapid degradation of the mmWave signal in long-distance transmission and the significant loss against wall penetration are no longer the bottlenecks for real application. Moreover, the surrounding walls of every room provide excellent isolation to avoid interference and guarantee security. This paper provides insights and analysis for the new FTTR+mmWave architecture to improve the customer experience in future broadband services such as immersive audiovisual videos.

As the fifth-generation (5G) mobile communication system is being commercialized, extensive studies on the evolution of 5G and sixth-generation (6G) mobile communication systems have been conducted. Future mobile communication systems are evidently evolving toward a more intelligent and software-reconfigurable functionality paradigm that can provide ubiquitous communication, as well as sense, control, and optimize wireless environments. Thus, integrating communication and localization using the highly directional transmission characteristics of millimeter waves (mmWaves) is a promising route. This approach not only expands the localization capabilities of a communication system but also provides new concepts and opportunities to enhance communication. In this paper, we explain the integrated communication and localization in mmWave systems, in which these processes share the same set of hardware architecture and algorithms. We also provide an overview of the key enabling technologies and the basic knowledge on localization. Then, we provide two promising directions for studies on localization with an extremely large antenna array and model-based (or model-driven) neural networks. We also discuss a comprehensive guidance for location-assisted mmWave communications in terms of channel estimation, channel state information feedback, beam tracking, synchronization, interference control, resource allocation, and user selection. Finally, we outline the future trends on the mutual assistance and enhancement of communication and localization in integrated systems.

The deployment of millimeter-wave (mmWave) cellular systems in dense urban environments with an acceptable coverage and cost-efficient transmission scheme is essential for the rollout of fifth-generation and beyond technology. In this paper, cluster-based analysis of mmWave channel characteristics in two typical dense urban environments is performed. First, radio propagation measurement campaigns are conducted in two identified mmWave bands of 28 and 39 GHz in a central business district and a dense residential area. The customdesigned channel sounder supports high-efficiency directional scanning sounding, which helps collect sufficient data for statistical channel modeling. Next, using an improved auto-clustering algorithm, multipath clusters and their scattering sources are identified. An appropriate measure for inter- and intra-cluster characteristics is provided, which includes the cluster number, the Ricean K-factor, root-mean-squared (RMS) delay spread, RMS angular spread, and their correlations. Comparisons of these parameters across two mmWave bands for both line-of-sight (LoS) and non-light-of-sight (NLoS) links are given. To shed light on the blockage effects, detailed analysis of the propagation mechanisms corresponding to each NLoS cluster is provided, including reflection from exterior walls and diffraction over building corners and rooftops. Finally, the results show that the cluster-based analysis takes full advantage of mmWave beamspace channel characteristics and has further implications for the design and deployment of mmWave wireless networks.

This paper presents an empirical study of the uplink and downlink azimuth angle of arrival (AoA) in an urban micro (UMi) scenario at 28 GHz. At present, most UMi measurements are conducted in the downlink and then the uplink situation is inferred assuming channel reciprocity. Although the channel correlation coefficient of the uplink and downlink can be as high as 0.8, this does not mean that they are the same. Only a real uplink measurement can accurately describe its channel conditions, and this is what this study does. A receiver equipped with a rotatable horn antenna is mounted at the base station and the user terminal, respectively, in simulating the uplink and downlink. To improve the angular resolution, we extract the multipath components (MPCs) using the space-alternating generalized expectation-maximization algorithm. Also, a spatial lobe approach is used to cluster the MPCs in the power angular spectrum. By matching MPCs with objects in the environment, we find that direct propagation and first-order reflections are dominant in line-of-sight and non-line-of-sight cases. By comparing our measurement with those in standard channel models, we verify that the AoA of clusters follows a Gaussian distribution in the uplink and downlink. In addition, a two-dimensional Gaussian distribution for ray AoA and power is established to reflect their correlation.

With the increased demand for unmanned driving technology and big-data transmission between vehicles, millimeter-wave (mmWave) technology, due to its characteristics of large bandwidth and low latency, is considered to be the key technology in future vehicular communication systems. Different from traditional cellular communication, the vehicular communication environment has the characteristics of long distance and high moving speed. However, the existing communication channel tests mostly select low-speed and small-range communication scenarios for testing. The test results are insufficient to provide good data support for the existing vehicular communication research; therefore, in this paper, we carry out a large number of channel measurements in mmWave vehicle-toinfrastructure (V2I) long-distance communication scenarios in the 41 GHz band. We study the received signal strength (RSS) in detail and find that the vibration features of RSS can be best modeled by the modified two-path model considering road roughness. Based on the obtained RSS, a novel close-in (CI) model considering the effect of the transmitter (TX) and receiver (RX) antenna heights (CI-TRH model) is developed. As for the channel characteristics, the distribution of the root-mean-square (RMS) delay spread is analyzed. We also extend the twosection exponential power delay profile (PDP) model to a more general form so that the distance-dependent features of the mmWave channel can be better modeled. Furthermore, the variation in both RMS delay spread and PDP shape parameters with TX-RX distance is analyzed. Analysis results show that TX and RX antenna heights have an effect on large-scale fading. Our modified two-path model, CI-TRH model, and two-section exponential PDP model are proved to be effective.

Orthogonal time frequency space (OTFS) modulation has been widely considered for high-mobility scenarios. Satellite-to-ground communications have recently received much attention as a typical high-mobility scenario and face great challenges due to the high Doppler shift. To enable reliable communications and high spectral efficiency in satellite mobile communications, we evaluate OTFS modulation performance for geostationary Earth orbit and low Earth orbit satellite-to-ground channels at sub-6-GHz and millimeter-wave bands in both lineof-sight and non-line-of-sight cases. The minimum mean squared error with successive detection (MMSE-SD) is used to improve the bit error rate performance. The adaptability of OTFS and the signal detection technologies in satellite-to-ground channels are analyzed. Simulation results confirm the feasibility of applying OTFS modulation to satellite-to-ground communications with high mobility. Because full diversity in the delay-Doppler domain can be explored, different terminal movement velocities do not have a significant impact on the performance of OTFS modulation, and OTFS modulation can achieve better performance compared with classical orthogonal frequency division multiplexing in satellite-to-ground channels. It is found that MMSE-SD can improve the performance of OTFS modulation compared with an MMSE equalizer.

In recent years, the conventional degrees of freedom in frequency and time have been fully used. It is difficult to further improve the performance of communication systems with such degrees of freedom. Orbital angular momentum (OAM), which provides a new degree of freedom for millimeter-wave (mmWave) wireless communication systems, has been recognized as a key enabling technique for future mobile communication networks. By combining OAM beams that have theoretically infinite and mutually orthogonal states with the generalized spatial modulation (GSM) strategy, a new OAM-GSM mmWave wireless communication system is designed in this paper. A bit error rate (BER) model of the OAM-GSM system is established based on channel flip precoding. The channel capacity, energy efficiency, and BER of the proposed OAM-GSM mmWave wireless communication system are simulated. Numerical results show that, compared with traditional GSM systems, the OAM-GSM system has more complex transmission and reception mechanisms but the channel capacity and maximum achievable energy efficiency are increased by 80% and 54%, respectively, and the BER drops by 91.5%.

Millimeter-wave (mmWave) communication is regarded as the key enabling component for fifth-generation (5G) cellular systems due to the large available spectrum bandwidth. To make mmWave new radio (NR) a reality, tremendous efforts have been exerted from the industry and academia. Performance evaluation of mmWave NR is a mandatory step and the key to ensuring the success of mmWave 5G deployment. Over-the-air (OTA) radiated method of testing mmWave NR in laboratory conditions is highly attractive, since it facilitates virtual field testing of mmWave devices in realistic propagation conditions. In this paper, we first discuss the need for and challenges in OTA measurement of mmWave 5G NR under fading channel conditions. After that, two promising candidate solutions, i.e., wireless cable and multi-probe anechoic chamber (MPAC), are detailed. Their principles, applicability for mmWave NR, and main challenges are discussed. Furthermore, preliminary experimental validation results in a frequency range 2 anechoic chamber are demonstrated for the wireless cable and MPAC methods at 28 GHz.

An ultra-massive phased array can be deployed in high-throughput millimeter-wave (mmWave) communication systems to increase the transmission distance. However, when the signal bandwidth is large, the antenna array response changes with the frequency, causing beam squint. In this paper, we investigate the beam squint effect on a high-throughput mmWave communication system with the single-carrier frequency-domain equalization transmission scheme. Specifically, we first view analog beamforming and the physical channel as a spatial equivalent channel. The characteristics of the spatial equivalent channel are analyzed which behaves like frequency-selective fading. To eliminate the deep fading points in the spatial equivalent channel, an advanced analog beamforming method is proposed based on the Zadoff-Chu (ZC) sequence. Then, the low-complexity linear zero-forcing and minimum mean squared error equalizers are considered at the receiver. Simulation results indicate that the proposed ZC-based analog beamforming method can effectively mitigate the performance loss by the beam squint.

In this study, we consider a multi-cell millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) system with a mixed analog-to-digital converter (mixed-ADC) and hybrid beamforming architecture, in which antenna selection is applied to achieve intelligent assignment of high- and low-resolution ADCs. Both exact and approximate closed-form expressions for the uplink achievable rate are derived in the case of maximum-ratio combining reception. The impacts on the achievable rate of user transmit power, number of radio frequency chains at a base station, ratio of high-resolution ADCs, number of propagation paths, and number of quantization bits are analyzed. It is shown that the user transmit power can be scaled down inversely proportional to the number of antennas at the base station. We propose an efficient power allocation scheme by solving a complementary geometric programming problem. In addition, the energy efficiency is investigated, and an optimal tradeoff between the achievable rate and power consumption is discussed. Our results will provide a useful reference for the study of mixed-ADC multi-cell mmWave massive MIMO systems with antenna selection.

A 9.8–30.1 GHz CMOS low-noise amplifier (LNA) with a 3.2-dB minimum noise figure (NF) is presented. At the architecture level, a topology based on common-gate (CG) cascading with a common-source (CS) amplifier is proposed for simultaneous wideband input matching and relatively high gain. At the circuit level, multiple techniques are proposed to improve LNA performance. First, in the CG stage, loading effect is properly used instead of the conventional feedback technique, to enable simultaneous impedance and noise matching. Second, based on in-depth theoretical analysis, the inductor- and transformer-based g_m-boosting techniques are employed for the CG and CS stages, respectively, to enhance the gain and reduce power consumption. Third, the floating-body method, which was originally proposed to lower NF in CS amplifiers, is adopted in the CG stage to further reduce NF. Fabricated in a 65-nm CMOS technology, the LNA chip occupies an area of only 0.2 mm² and measures a maximum power gain of 10.9 dB with −3 dB bandwidth from 9.8 to 30.1 GHz. The NF exhibits a minimum value of 3.2 dB at 15 GHz and is below 5.7 dB across the entire bandwidth. The LNA consumes 15.6 mW from a 1.2-V supply.

We introduce a dual-polarized (DP) Fabry–Pérot cavity (FPC) antenna operating at the millimeter-wave (mmWave) frequency band with high-gain and wideband characteristics. A DP feeding source and a partially reflective surface (PRS) integrated with a Fresnel zone lens are suggested to realize dual-polarization wave radiation over a wide impedance bandwidth. The feeding source provides vertical and horizontal polarizations while keeping high isolation between the two polarizations. PRS is used to realize Fabry cavity to produce a directive beam radiation. The integrated Fresnel zone rings are introduced for phase correction, leading to a significant gain enhancement for the antenna. For verification, a 60-GHz FPC antenna prototype with DP radiation is designed and fabricated with measurement results. It consists of a feeding source, a PRS integrated with a Fresnel zone lens, a quasi-curved reflector, and four three-dimensional printed supporters. The results illustrate that the peak gains of vertical and horizontal polarizations are 18.4 and 17.6 dBi, respectively. The impedance matching bandwidth for the two polarizations is 14%. The performance ensures that the proposed DP FPC antenna is a promising candidate for the fifth-generation wireless communication systems in the mmWave band.