An extra-large antenna array prototype operating between 3.35 GHz and 3.6 GHz was developed to experimentally study near-field beamfocusing and its distance-dependent radiation patterns. Using a 1×24 uniform linear sub-array, a 3 dB beam depth of 0.6 m was achieved at a beamfocusing distance of 0.8 m from the array. When transmitting a 64QAM 20 MHz modulated signal, the near-field beamfocusing approach yielded 9.6 dB higher received in-band power and improved error vector magnitude by 6.4 dB compared to the conventional far-field beamforming vector, resulting in high-quality constellation diagrams. Extensive measurements were conducted in the anechoic chamber to evaluate the distance-dependent radiation patterns and beam depth of uniform linear arrays with varying aperture sizes. Simulation results incorporating spherical wavefront characteristics demonstrated good agreement with the experimental observations.

A wideband, dual-layer metamaterial-based patch antenna operating at 10 GHz is proposed for centimeter-wave full-duplex (FD) massive multiple-input multiple-output systems. Full-wave simulations reveal an effective and wide impedance bandwidth of over$19 \%(1.9 \text{GHz})$, spanning from 9.5 GHz to 11.4 GHz. The antenna achieves a gain of 5.5 dB with a radiation efficiency exceeding 98 %. The introduction of a specially designed L-shaped cutting slot enables high circular polarization (CP) purity, achieving an axial ratio of 0.6 dB at 10.25 GHz and better than 3 dB across a 1.3 GHz (13 %) bandwidth. The resulting pure CP antennas support the creation of cross-polarized Tx-Rx antenna element pairs for FD operation. An improvement in Tx-Rx isolation of better than$\text{1 0 ~ d B}$is observed, reducing mutual coupling to better than -40 dB with an element separation of 4.6 cm (1.5 wavelengths).

This study employs a uniform rectangular array (URA) sub-connected hybrid beamforming (SC-HBF) architecture to provide a novel self-interference (SI) suppression scheme in a full-duplex (FD) massive multiple-input multiple-output (mMIMO) system. Our primary objective is to mitigate the strong SI through the design of RF beamforming stages for uplink and downlink transmissions that utilize the spatial degrees of freedom provided due to the use of large array structures. We propose a non-constant modulus RF beamforming (NCM-BF-SIS) scheme that incorporates the gain controllers for both transmit (Tx) and receive (Rx) RF beamforming stages and optimizes the uplink and downlink beam directions jointly with gain controller coefficients. To solve this challenging non-convex optimization problem, we propose a swarm intelligence-based algorithmic solution that finds the optimal beam perturbations while also adjusting the Tx/Rx gain controllers to alleviate SI subject to the directivity degradation constraints for the beams. The data-driven analysis based on the measured SI channel in an anechoic chamber shows that the proposed NCM-BF-SIS scheme can suppress SI by around 80 dB in FD mMIMO systems.

This study considers a novel full-duplex (FD) massive multiple-input multiple-output (mMIMO) system using hybrid beamforming (HBF) architecture, which allows for simultaneous uplink (UL) and downlink (DL) transmission over the same frequency band. Particularly, our objective is to mitigate the strong self-interference (SI) solely on the design of UL and DL RF beamforming stages jointly with sub-array selection (SAS) for transmit (Tx) and receive (Rx) sub-arrays at base station (BS). Based on the measured SI channel in an anechoic chamber, we propose a min-SI beamforming scheme with SAS, which applies perturbations to the beam directivity to enhance SI suppression in UL and DL beam directions. To solve this challenging nonconvex optimization problem, we propose a swarm intelligence-based algorithmic solution to find the optimal perturbations as well as the Tx and Rx sub-arrays to minimize SI subject to the directivity degradation constraints for the UL and DL beams. The results show that the proposed min-SI BF scheme can achieve SI suppression as high as 78 dB in FD mMIMO systems.

A perturbation-based adaptive beamforming scheme employing particle swarm optimization is proposed to mitigate multi-user interference by creating deep nulls in the potential interference directions. The paper uses an 8x8 circularly-polarized antenna array prototype as an example and examines the variation in antenna element radiation patterns at different positions on the large array, as well as their impact on the adaptive beamforming performance. The proposed scheme considers the measured element patterns and uses weights generated by the Linearly Constrained Minimum Variance method as a starting point to search for new optimal steering weights, which create deep nulls with a slight tradeoff in the directivity. The illustrative results show the proposed algorithm can achieve normalized nulls lower than -48.1dB with an accurate nulling location control. Compared to the linear constraint adaptive beamforming scheme, the proposed approach demonstrates improved results, achieving on average 22.9dB deeper arbitrary nulls with a tradeoff of 0.7 dB drop in the beam directivity.

This paper proposes a novel dual-layer electromagnetic bandgap slotted circularly polarized patch antenna to design an 8x8 antenna array for massive MIMO operating at 3.5GHz. The antenna element structure achieves a bandwidth of 250 MHz (7.1% at 3.5GHz). It has a gain of 5.1dB, a directivity of 6.1dB, and a 3dB-beamwidth of 94 degrees. With EBG elements underneath, the radiating patch size can be reduced by 65% while the top EBG layer provides a high surface impedance and an isolation of 14.3dB between radiating patches with a separation distance of 0.32 wavelength. Simulation and measured results of the designed 8x8 antenna array on return loss, radiation patterns, mutual coupling, and beamforming performance in different scenarios are discussed and shown to be in good agreement.

We consider the problem of joint channel assignment and power allocation in underlaid cellular vehicular-to-everything (C-V2X) systems where multiple vehicle-to-network (V2N) uplinks share the time-frequency resources with multiple vehicle-to-vehicle (V2V) platoons that enable groups of connected and autonomous vehicles to travel closely together. Due to the nature of high user mobility in vehicular environment, traditional centralized optimization approach relying on global channel information might not be viable in C-V2X systems with large number of users. Utilizing a multi-agent reinforcement learning (RL) approach, we propose a distributed resource allocation (RA) algorithm to overcome this challenge. Specifically, we model the RA problem as a multi-agent system. Based solely on the local channel information, each platoon leader, acting as an agent, collectively interacts with each other and accordingly selects the optimal combination of sub-band and power level to transmit its signals. Toward this end, we utilize the double deep Q-learning algorithm to jointly train the agents under the objectives of simultaneously maximizing the sum-rate of V2N links and satisfying the packet delivery probability of each V2V link in a desired latency limitation. Simulation results show that our proposed RL-based algorithm provides a close performance compared to that of the well-known exhaustive search algorithm.

This paper presents a semi-deterministic groupwise channel estimation method to generate UT-group CSI of user terminal (UT) zones in the service area for the angular-based hybrid precoding (AB-HP) in multi-user massive multiple-input multiple-output (MU-mMIMO) systems based on geospatial data and the fuzzy c-Means (FCM) clustering algorithm. The slow time-varying UT-level channel state information (CSI) between the base station (BS) and all possible UTs are generated by a ray tracing algorithm and grouped into clusters by a proposed FCM clustering. The service area is then divided into a number of non-overlapping UT zones, where each is characterized by a corresponding set of clusters used as UT-group CSI for RF beamformer to eliminate the required large online CSI acquisition overhead. Simulations are performed in both outdoor and indoor scenarios to evaluate the performance of the proposed channel estimation approach. Illustrative results show that the proposed method identifies clusters robust to imprecise UT-level CSI and provides RF beamformer with the UT-group CSI for different UT zones in the service area. Meanwhile, with the UT- group CSI, the AB-HP can successfully achieve a comparable sum-rate performance as the fully-digital precoding (FDP) system for UTs in specific zones without large dimensional CSI overhead.

This paper presents a compact, highly-linear RF/Analog self-interference canceller (SIC) for a 2×2 MIMO full-duplex (FD) transceiver to suppress the existing strong selfinterference (SI) at the receiver input in order to prevent the receiver from saturation. Linearity requirements of RF/Analog SIC, as well as corresponding variable attenuator and delay/phase module, are derived and a RF/Analog SIC with good linearity for high power transmission is proposed. A prototype with compact size is fabricated on a multilayer PCB for a 2×2 MIMO inband FD transceiver, and is implemented with highly-linear, custom-made tunable attenuator and delay/phase-shift module to suppress nonlinear distortion. The measurement results in anechoic-chamber reveal that this RF/Analog SIC prototype integrated with a dual-polarized antenna can provide over 80dB cancellation for +30dBm and 20MHz OFDM signal centered at 2.27GHz. Typical 34dBm OIP3 of the prototype is measured. The simulation with following digital canceller reveals a negligible SNR degradation of 0.3dB due to the nonlinear distortion of this prototype.

This paper investigates the wideband self-interference (SI) channel characteristics for a 2×2 MIMO full-duplex (FD) transceiver with dual-polarized antennas. The measurements, carried out at 2.45GHz with 500MHz span in various environments: anechoic chamber, laboratory- room, and corridor, show that the SI-channel can be represented by a multipath model consisting of two segments: a quasistatic internal SI-sub-channel due to the specific Tx/Rx antenna structure and a time-varying or dynamic external SI-sub-channel due to possible reflections from the surrounding environment. The quasi-static internal SI-sub-channel parameters can be derived from the Tx/Rx antenna structure specifications. The dynamic external SI-channel exhibits cluster reflection arrival features and can be modeled by a modified Saleh-Valenzuela (S-V) model, and the cluster power decays exponentially with cluster arrival delay. However, the path power-versus-arrival delay decay is exponential in a laboratory-room environment while it follows the power law in a corridor environment.