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This study investigates the application of adaptive beamforming techniques within D-band sub-terahertz (sub-THz) communication systems tailored for 6G applications. We present a hardware-in-the-loop transmission system utilizing newly developed prototypes of transmit and receive front ends operating in the frequency range from 150 to 170 GHz. The front ends’ analog beamforming architecture enables the generation of eight distinct beams with 6° separation in azimuth, thus creating a field of view with 48° one dimensional angular scanning range on either side of the link. The system implements dynamic beamforming based on the 5G New Radio (NR) waveform’s design principles for the initial access/beam acquisition procedure. Experimental performance assessments conducted in an indoor environment prove the system’s potential to support mobility and mitigate the effects of signal blockage. Specifically, when encountering a lineof-sight link blockage event, the system successfully transitioned to a reflected propagation path, incurring approximately 4dB of loss. Additionally, a mobile receiver could be tracked while maintaining a 1dB variation in the wireless link budget. These results demonstrate the feasibility of D-band adaptive beamforming.

The authors present a W-band Rotman lens (RL) beamformer with WR-10 waveguide interfaces. Radio frequency characteristics, such as phase relationships and insertion losses, including the beamforming capabilities of the RL were simulated and measured to validate the performance of generating four RF beams with ±60° field of view. Subsequently, the RL as beamformer was integrated into a transmitter setup in conjunction with the array antenna, in addition to a receiver setup that was constructed from off-the-shelf components. Both W-band transmitter and receiver were used to demonstrate a wireless link transmission in an outdoor urban - mobile user access or mobile backhauling - deployment scenario; over 85 GHz carrier frequency. The demonstration used a 5G-NR Release-15 conform waveform with 400 MHz of bandwidth and up to 256 quadrature amplitude modulation (QAM). The demonstration trial was conducted including line-of-sight (LOS), obstructed line-of-sight (OLoS), and none-line-of-sight (NLoS) scenarios; and reported a successful 16QAM over 184 meters OLoS link and 16QAM over 116 meters NLoS link. The work provides experimental evidence of the potential for high-frequency bands like the W-band to be utilized in future (6G and beyond) wireless communication networks.

This paper reports the development outcomes of the world's first integrated analog beamforming - transmit and receive - wireless front-ends operating in the D-band (a sub-THz band), particularly designed to operate within 150 GHz to 170 GHz frequency range. Front-end hardware development includes monolithic microwave integrated circuit (MMIC) chips of the multichannel power amplifier, multichannel low-noise amplifier, and RF switches. Moreover, the development includes an analog beamforming RF network and a low-profile microstrip 1-by-8 uniform linear antenna array, which were both developed on a resistive silicon substrate. The paper also features a successful long-range (320-meter) line-of-sight unidirectional point-to-point wireless transmission experiment, utilizing a 5G-NR orthogonal frequency division multiplexing (OFDM) waveform over a 160-GHz carrier frequency. The experiment demonstrated a successful transmission of OFDM waveforms using up to a 16-QAM (quadrature amplitude modulation) scheme in the D-band.

This paper presents the results of several over-the-air (OTA) transmission experiments utilizing fifth-generation new-radio (5G-NR) waveforms in the W-Band (75 GHz – 110 GHz) – a candidate frequency band for the sixth-generation (6G) mobile network in the near-sub-terahertz region. These experiments were conducted in an outdoor environment, including line-of-sight, non-line-of-sight, and obstructed-line-of-sight scenarios. To perform these experiments, we constructed transmit front-end and receive front-end prototypes operating in the W-band. In addition, the components of these front-ends prototypes were developed, including a Rotman lens, power divider/combiner, sector horn antenna array, and an antenna feeder in our transmitter setup. The carrier frequency was 85 GHz, and the transmitted signal bandwidth was up to 400 MHz. The experiment reported in the line-of-sight scenario a successfully transmitted 5G-NR downlink waveforms over a 600 meters distance with 64 quadrature amplitude modulation (64 QAM) for the data channel. The experiment outcome demonstrates the W-band’s potential as a frequency band for mobile access in future 6G mobile networks.

The article discusses a radio-frequency-based self-interference cancellation (SIC) technique to handle the self-interference signal segment associated with the self-interference caused by antennas’ mutual coupling, particularly for dedicated-transmit-and-receive antenna configurations. The technique is a novel SIC technique based on antenna decoupling utilizing a lossless network in the radio frequency domain. At first, the authors present a fundamental physical and mathematical description of the self-interference radio channel, employing antenna scattering matrix representation and spherical vector wave expansion. Then, the article presents the experimental results of two antenna mutual coupling measurements – including a single-input-single-output setup and a$2\times 2$dual-polarized multiple-input-multiple-output (MIMO) setup. Afterward, the authors discuss the lossless network decoupling technique for MIMO full-duplex wireless transceivers. Finally, the authors present a generalized-$\Pi $synthesizing topology of the lossless decoupling network and empirically evaluate its SIC performance by leveraging the conducted antenna mutual coupling measurement results. The empirical evaluation validates the effectiveness of the lossless decoupling network in canceling the self-interference entirely for a specific design frequency – narrowband systems. Moreover, the evaluation reveals the degradation of the network SIC performance with respect to system bandwidth and the deviation of antennas’ separation distance from its nominal design value.

In full-duplex wireless communication systems, transmission signals travel through self-interference radio channels before they will be received by the local receivers. This paper studies time dispersion characteristics of these channels for an indoor cross-polarized 2x2 multiple-input-multiple-output antenna (MIMO) system. Four cross- polarized radio channels - excited by two transmit antennas and captured by two receive antennas perpendicularly polarized to the transmit antennas - were measured in an indoor spacious foyer (entrance hall) environment. By means of a vector network analyzer, one gigahertz of bandwidth, which occupies 2-to-3-GHz frequency band, was swept to sound these self-interference channels. The four vector network analyzer test ports were connected to two dually- polarized magnetoelectric dipole antennas that were utilized to observe the self-interference channels. Each of the dipole antennas possesses: Two radio-frequency ports, a hemispherical radiation pattern, and an excellent cross-polarization discrimination properties. The antennas were placed at two meter height and moved in track along the room circumference to measure the self-interference channels at 27 positions. The excellent cross-polarization isolation properties of the utilized antennas has allowed to capture a time- domain instantaneous channel dynamic that exceeds 120 dB - normalized with respect to the transmit power at the antennas' physical ports. This vast dynamic has used to analyze the channel with sliding sensitivity threshold. The channel measurement reports maximum excess delays up to 689 ns. Furthermore, time dispersion parameters and their associated values are discussed and reported in this paper based on the conducted self-interference channel measurements.

In this paper, novel self-interference cancellation technique is proposed. The technique addresses in particularly the transceivers where dedicated-transmit-and-receive antenna configurations are embraced. The technique, moreover, relies on a lossless decoupling network, which interconnects the transceiver's chains to the antenna elements. The values of the network's reactive components, which are the building blocks of the lossless network, can be computed to suppress the self-interference at the local receivers for the targeted frequency. Thus, the technique provides a self-interference suppression method at the radio-frequency domain, which does not waste energy for cancellation purpose. Moreover, the technique can implicitly assure optimized power delivery among the antenna array elements and the transceiver front-ends. Network analysis of a multiple-input-multiple-output antenna array in a full-duplex transceiver is presented in order to characterize the self-interference in terms of mutual coupling phenomenon among the antenna array elements. Mutual coupling measurements of two identical antennas setup are presented and analyzed. Finally, empirical assessment of the proposed self-interference cancellation technique is provided, to show that the self-interference cancellation levels can exceed 70 dB by employing the proposed technique.