The THz band (0.1-10 THz) has attracted considerable attention for next-generation wireless communications due to the large amount of available bandwidth that may be key to meet the rapidly increasing data rate requirements. Before deploying a system in this band, a detailed wireless channel analysis is required as the basis for proper design and testing of system implementations. One of the most important deployment scenarios of this band is the outdoor microcellular environment, where the Transmitter (Tx) and the Receiver (Rx) have a significant height difference (typically ≥ 10 m). In this paper, we present double-directional (i.e., directionally resolved at both link ends) channel measurements in such a microcellular scenario encompassing street canyons and an open square. Measurements are done for a 1 GHz bandwidth between 145-146 GHz and an antenna beamwidth of 13 degree; distances between Tx and Rx are up to 85 m and the Tx is at a height of 11.5 m from the ground. The measurements are analyzed to estimate path loss, shadowing, delay spread, angular spread, and multipath component (MPC) power distribution. These results allow the development of more realistic and detailed THz system performance assessment.

Condensed channel parameters, such as Root Mean Square (RMS) delay spread and angular spread, are essential ways of representing results from the measurement of wireless propagation channels. However, real-world measurements are invariably affected by noise, which is not inherently reduced by the Fourier processing - in contrast to high-resolution parameter estimation. Even when the signal-to-noise ratio is relatively high, e.g., 20 dB, the impact of the noise on the condensed parameters can be significant and lead to erroneous estimates. This can be explained, e.g., for the computation of the RMS delay spread, where long delays (which often carry noise only) are "up-weighted" by the square of the delay. While techniques like noise thresholding are often applied, the reasons for choosing thresholds are usually not described in detail. This paper systematically analyzes noise thresholding for joint delay-angle measurements and derives equations for the impact of thresholds on the computation of delay and angle RMS spreads and window parameters under various measurement circumstances. The paper provides results based on closed-form equations, as well as MonteCarlo (MC) simulations, and application to real-world measurements in the sub-THz band.

The availability of large bandwidths in the terahertz (THz) band will be a crucial enabler of high data rate applications in next-generation wireless communication systems. The urban microcellular scenario is an essential deployment scenario where the base station (BS) is significantly higher than the user equipment (UE). Under practical operating conditions, moving objects (i.e., blockers) can intermittently obstruct various parts of the BS- UE link. Therefore, in the current paper, we analyze the effect of such blockers. We assume a blockage of the strongest beam pair and investigate the availability and extent of angular diversity, i.e., alternative beampairs that can sustain communication when the strongest is blocked. The analysis uses double-directional channel measurements in urban microcellular scenarios for 145– 146 GHz with BS-UE distances between 18 to 83 m. We relate the communication-system quantities of beam diversity and capacity to the wireless propagation conditions. We show that the SNR loss due to blockage depends on the blocked angular range and the specific location, and we find mean blockage loss to be on the order of 10–20 dB in line-of-sight (LOS) and 5–12 dB in NLOS (non-LOS). This analysis can contribute to the design of intelligent algorithms or devices (e.g., beamforming, intelligent reflective surfaces) to overcome the impact of the blockage.

This paper discusses a new 5G-Advanced duplex scheme called sub-band full-duplex (SBFD) and the details of implementing it for 5G TDD spectrum. The SBFD requires an advanced self interference cancellation (SIC) which is designed to handle extremely high level of cross link interference. Novel SIC techniques were designed for base stations (BSs) operating on 3.4 GHz with massive MIMO and on 26 GHz with multi-beam capability. By utilizing electromagnetic walls in conjunction with electromagnetic bandgap, an extremely high level of isolation between transmit and receive antennas is achieved. Residual interference is further removed using fractional nonlinear interference estimation in baseband. Two Proofs-of-Concepts (PoCs) have been implemented for feasibility verification. The first PoC was for a massive MIMO BS operating with 32 cross polarized antenna ports on 3.4 GHz and a bandwidth of 100 MHz. The second PoC was for a multi-beam BS with 256 antenna elements operating on 26 GHz and a bandwidth of 400 MHz. It was observed that the self-interference in SBFD can be suppressed in real time to a level of less than 0.7 dB over the RX noise floor for both 3.4 GHz and 26 GHz in an outdoor environment.

THz band is envisioned to be used in 6G systems to meet the ever-increasing demand for data rate. However, before an eventual system design and deployment can proceed, detailed channel sounding measurements are required to understand key channel characteristics. In this paper, we present a first extensive set of channel measurements for urban outdoor environments that are ultra-wideband, and double-directional where both transmitter and receiver are at the same height. In all, we present measurements at 38 locations, consisting of nearly 50,000 impulse responses, representing both line-of-sight (LoS) and non-line-of-sight (NLoS) cases in the 1-100 m range between 145-146 GHz. We provide modeling for path loss, shadowing, delay spread, angular spread, multipath component (MPC) power distribution and Qtapnumber. We find, among other things, that outdoor communication over tens of meters is feasible in this frequency range even in NLoS scenarios, that omni-directional delay spreads of up to 100 ns, and directional delay spreads of up to 10 ns are observed, while angular spreads are also quite significant, and a surprisingly large number of MPCs are observed for 1 GHz bandwidth and 13° beamwidth. These results constitute an important first step towards better understanding the wireless channel in the THz band.

THz communication has attracted a great deal of attention due to the large bandwidth available in this band. However, system development and deployment requires detailed knowledge of the wireless channel, which must be provided by measurements (channel sounding) and subsequent modeling in key scenarios of interest. One important scenario in this regard is the urban outdoor microcellular scenario where the Transmitter (Tx) and the Receiver (Rx) have a significant height difference. In this paper, we present ultra-wideband double-directional channel measurements in a microcellular scenario for the band between 145-146 GHz in a street canyon with Tx-Rx of distances up to 67 m. The results are analyzed in the delay and angular domain, and the impact of the street canyon on the power delay profiles and angular power spectra is detailed. These measurements thus contribute towards the creation of a more realistic and detailed THz channel model in these scenarios.

Wireless communications in the THz frequency range can allow data rates of hundreds of Gbit/s, and will thus be an important part of 6G. A first important step for system design is an understanding of the underlying propagation channel. In this paper, we present results from one of the first measurement campaigns for medium-distance (up to 35 m) outdoor channels in urban environments where both the directions and delays of multipath are measured with good resolution. The results show a surprisingly rich multipath environment, leading to significant dispersion in both delay and angular domains. We also find that metallic-covered surfaces lead to a considerable enhancement of multipath, which indicates an important impact of building materials. Overall, the results indicate that relying on pronounced sparsity for THz system design might not always be valid in this type of environment.

In this paper, an advanced duplex scheme, referred to as cross division duplex (XDD), is proposed to use flexible downlink (DL) and uplink (UL) allocation in time division duplex (TDD) carrier. By implementing self-interference cancellation (SIC) functions at the base station, the proposed XDD enables to simultaneously operate UL and DL on different frequency subband in the same channel. To do so, both TDD's ability to efficiently handle asymmetric UL and DL traffic and frequency division duplexing's coverage and latency advantage can be achieved together. To verify the feasibility of XDD, a Proof-of-Concept is developed and self-interference can be removed almost perfectly with proper implementation of SIC without guardband between DL and UL subband. From evaluation results, UL coverage, as well as latency, was improved using a longer UL duty period in XDD. Based on XDD, in 5G-Advanced, a significantly higher resource utilization than the existing 5G will be possible.

This paper investigates the capability of millimeter-wave (mmWave) channel sounders with phased arrays to perform super-resolution parameter estimation, i.e., determine the parameters of multipath components (MPC), such as direction of arrival and delay, with resolution better than the Fourier resolution of the setup. We analyze the question both generally, and with respect to a particular novel multi-beam mmWave channel sounder that is capable of performing multiple-input-multiple-output (MIMO) measurements in dynamic environments. We firstly propose a novel two-step calibration procedure that provides higher-accuracy calibration data that are required for Rimax or SAGE. Secondly, we investigate the impact of center misalignment and residual phase noise on the performance of the parameter estimator. Finally we experimentally verify the calibration results and demonstrate the capability of our sounder to perform super-resolution parameter estimation.

Massive multi-input multi-output (MIMO) is shown to significantly increase spectral efficiency by exploiting a large number of antennas to support high-order multiuser MIMO. In 3GPP Release-13, a full-dimension MIMO (FD-MIMO) technology was introduced to address practical aspects for massive MIMO in cellular systems; extensive simulations show 2–4 times capacity gain compared with current LTE systems. FD-MIMO has been identified as one of the key 5G technologies and is being continuously improved in 3GPP new radio standards. However, several practical challenges such as interference mitigation among MIMO streams for a large number of users with limited channel feedback, hardware limitations, such as calibration errors that limit the precoding capabilities need to be addressed carefully. A proof of concept (PoC) base-station and user equipment (UE) prototype has been designed to validate the potential of FD-MIMO technology and demonstrate commercial implementation feasibility. In this paper, we present theory and architecture behind an FD-MIMO prototype and share the field test results with LTE-based UEs in a multi-user MIMO setup. We also analyze the impact of transmitter and receiver calibration errors on the performance of the FD-MIMO system.

In this paper, we present a novel FPGA-based high-throughput beamforming MIMO receiver for millimeter wave mobile communication. With vast spectrum and small antenna element size, millimeter wave communication becomes very attractive and promising to support next generation mobile communication (5G). However, the high data rate requirement challenges both algorithm and architecture. In order to support the high data rate and to reduce the overhead of selecting the best beam pair, we propose a novel beamforming synchronization scheme more suitable for mobile communication. By further optimizing the algorithm and the architecture, we present a complete mobile receiver based on FPGA, which includes RF frontend, ADC, beamforming control, synchronization, channel estimator, soft MAP detector, and channel decoder. The design operates at 28 GHz carrier frequency with 500 MHz bandwidth. The throughput can reach 1.52 Gbps. We also performed the indoor and outdoor over-the-air transmission field tests. This work provides a platform for future millimeter wave mobile communication research.