Modeling of SHF/EHF Radio-Wave Scattering for Curved Surfaces with Voxel Cone Tracing

Efficient and accurate radio propagation modeling is essential for optimization of both radio sensing and communication systems. However, highly accurate full-wave methods remain inefficient at high frequencies, as unit of computation (typically, a voxel) has to be made much smaller than the wavelength. On the other hand, ray-based approaches offer the desired speed, but the surface element (typically, a triangle) must be made much larger than the wavelength, making it difficult to represent complex curved surfaces of common objects such as cars or unmanned aerial vehicles. As a result, for SHF/EHF bands, it is challenging to select a method that is both fast and capable of capturing curved surfaces correctly. To address this matter, we present a method that offers a reasonable trade-off between speed and accuracy for radio propagation modeling in the bands of interest. Specifically, we combine efficient voxel scene representation targeting a cone tracing algorithm with a statistical scattering model. To confirm the validity of our approach, we report the dependence of reflected power on the distance for basic primitives such as cone and sphere, for which closed-form radar cross-section solutions are known.acceptedVersionPeer reviewe

Integrated Access and Backhaul in Millimeter-Wave Cellular : Benefits and Challenges

The recently proposed NR-ready integrated access and backhaul (IAB) architecture promises to bring a cost-efficient deployment solution for both coverage extension and capacity boosting in the emerging 5G/5G+ systems. While its impact on the coverage extension was thoroughly addressed in the literature, the effect of advanced functionalities such as multihop, multi-connectivity, and multi-beam operations on the throughput remained unclear. We review and characterize the system-level impact of these capabilities on the performance of self-backhauled IAB systems operating in half-duplex mode and utilizing millimeter-wave (mmWave) technology across both access and backhaul. Our results indicate that the throughput gain of multihopping and multi-beaming is significant even without multi-connectivity operation. Another important lesson is that in all-mmWave systems with link blockage, multi-connectivity with link switching allows achieving self-load balancing. Finally, we outline future research directions.acceptedVersionPeer reviewe

Resource Allocation and Multi-Connectivity Operation in Cellular IAB Networks

The emerging 5G technology promises a capacity boost for future cellular networks due to the utilization of the millimeter-wave (mmWave) spectrum. However, radio propagation over mmWave bands implies higher propagation losses, resulting in reduced coverage for the 5G base station (gNB); thus, deployments become ultra-dense. Under the described conditions, using conventional wired backhaul may not be cost-efficient for network operators. Therefore, the concept of wireless backhaul is being considered by 3GPP, which is called integrated access and backhaul (IAB). On the one hand, this technology allows the deployment cost to be reduced. On the other hand, wireless backhaul raises multiple challenges. This includes the half-duplex constraint, which complicates the resource allocation procedure. In addition, the inherent properties of mmWave frequencies make a wireless connection more susceptible to blockage. Therefore, this study characterizes resource allocation, interference, and blockage avoidance techniques in the context of IAB networks. The results of the research demonstrate that interference caused by mutual reception at the IAB node can be avoided using spatial diversity. The critical angular distance of more than 25 deg. is identified as the point at which mutual receptions start to influence each other. The dynamic resource allocation scheme is proposed, which enables load balancing in IAB networks limited by the half-duplex constraint. Finally, multi-connectivity and single connectivity with fast switching are examined as the means to combat the blockage. It is demonstrated that when switching to another gNB, the load should be considered together with the link quality

Ray-Based Modeling of Directional Millimeter-Wave V2V Transmissions in Highway Scenarios

Due to the need for larger bandwidth, future mobile networks may primarily operate over millimeter-wave (mmWave) bands. In this regard, one of the central research topics today is mmWave channel modeling. However, highly mobile vehicle-to-vehicle (V2V) mmWave channels pose an open question because conducting measurements may be challenging in this environment. The existing publications on mmWave V2V channel modeling consider line-of-sight (LoS) or single-blocker scenarios. Accordingly, the impact of interference from adjacent vehicles is not taken into account. Conventional analytical models suggest that path loss (PL) strikes equally in all directions whereas measurements are inherently directional, especially in the case of mmWave propagation. Recently, it was proposed to synthesize the omnidirectional PL from directional measurements. However, with this method, the resulting PL is underestimated. Moreover, theoretical models assume that vehicular transceivers follow a certain predetermined distribution, which may not be accurate in real-world scenarios. Several works take into account the directionality of an antenna pattern when the antenna orientation is known. However, the effects of reflection, diffraction, and transmission through obstacles are not considered. One way to avoid these limitations is to use ray-based simulations. However, the ray-launching (RL) approach does not specify any criteria for the directionality of the antenna patterns. Assuming omnidirectional PL appears impractical for mmWave transmission where directional communication is crucial to combat high PL. In this paper, we propose an approach for synthesizing directional PL based on extensive RL modeling. For the obtained directional and omnidirectional PL, we parametrize the close-in (CI) and float-intercept (FI) channel models. As a result of our modeling, from 0.1 to 2.7 for the LoS and from 0.1 to 2.6 for the non-LoS (NLoS) higher PL exponent is observed as compared to the omnidirectional case.publishedVersionPeer reviewe

Geometry-Based V2V Channel Modeling over Millimeter-Wave in Highway Scenarious

As of today, mmimeter-wave (mmWave) bands are employed as part of the emerging 5G technology to provide high data rates for vehicle-to-vehicle (V2V) communications. However, V2V channels over mmWave have not been well studied as of yet due to the complexity of measurements, especially if there is a need to estimate the contribution of adjacent interfering vehicular transceivers. Moreover, the channel models that are currently in use consider vehicles on the road according to a certain distribution, which may not be accurate in practice. Also, past models do not take into account the effects of reflection, diffraction, and transmission through obstacles, as well as the physical properties of vehicles themselves. In this paper, using geometric ray-based simulations, in which the aforementioned effects are incorporated, we present mmWave V2V channel modeling for a highway scenario at 28 and 72 GHz carrier frequencies with both low and high density of vehicles. Our results include such characteristics as path loss, fading, root-mean-square (RMS) delay spread, and angular spread.acceptedVersionPeer reviewe

Self-Interference Assessment and Mitigation in 3GPP IAB Deployments

The high propagation losses and sensitivity to link blockage naturally require dense deployments of millimeter-wave (mmWave) 5G New Radio (NR) systems. One of the inherent challenges in these deployments is cost-efficient backhauling. Addressing this issue, 3GPP has recently proposed the concept of integrated access and backhaul (IAB) to reduce the deployment costs by enabling wireless backhaul. The efficient utilization of spectrum in these systems is conditional on the ability of IAB nodes to simultaneously receive signals on their sectoral antennas. In this paper, we investigate the interference caused by this functionality and identify countermeasures including angular and spatial diversities. Our numerical results demonstrate that the angular distance of 25° between the user equipment (UE) served by adjacent sectoral antennas is sufficient to efficiently mitigate interference. A comparable reduction in the interference level can also be achieved by utilizing spatial diversity with antenna separation of at least 20 m. By combining these methods, one can identify the target levels of angular and spatial diversities suitable for the particular deployment restrictions.acceptedVersionPeer reviewe

Integrated Access and Backhaul in Millimeter-Wave Cellular: Benefits and Challenges

The recently proposed NR-ready integrated access and backhaul (IAB) architecture promises to bring a cost-efficient deployment solution for both coverage extension and capacity boosting in future 5G/5G+ systems. While its impact on the coverage extension was thoughtfully addressed in the literature, the effect of advanced functionalities such as multi-hop, multi-connectivity, and multi-beam operations on the throughput remains unclear. We review and characterize the system-level impact of these capabilities on the performance of self-backhauled IAB systems operating in half-duplex mode and utilizing millimeter-wave (mmWave) technology across both access and backhaul. Our results indicate that the throughput gain of multi-hopping and multi-beaming is significant even without multi-connectivity operation. Another important learning is that in all-mmWave systems with link blockage, multi-connectivity with link switching allows achieving self-load balancing. Finally, we outline future research directions.Comment: Accepted for publishing in the IEEE Communications Magazin