Shadowing from vehicles can significantly degrade the performance of vehicle-to-vehicle (V2V) communication in multilink systems, e.g., vehicular ad-hoc networks (VANETs). It is thus important to characterize and model the influence of common shadowing objects like cars properly when designing these VANETs. Despite the fact that for multilink systems it is essential to model the joint effects on the different links, the multilink shadowing effects of V2V channels on VANET simulations are not yet well understood. In this paper we present a measurement based analysis of multilink shadowing effects in a V2V communication system with cars as blocking objects. In particular we analyze, characterize and model the large scale fading, both regarding the autocorrelation and the joint multilink cross-correlation process, for communication at 5.9 GHz between four cars in a highway convoy scenario. The results show that it is essential to separate the instantaneous propagation condition into line-of-sight (LOS) and obstructed LOS (OLOS), by other cars, and then apply an appropriate pathloss model for each of the two cases. The choice of the pathloss model not only influences the autocorrelation but also changes the cross-correlation of the large scale fading process between different links. By this, we conclude that it is important that VANET simulators should use geometry based models, that distinguish between LOS and OLOS communication. Otherwise, the VANET simulators need to consider the cross-correlation between different communication links to achieve results close to reality.

A Measurement Based Multilink Shadowing Model for V2V Network Simulations of 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.

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

An important and typical scenario of radio propagation in a railway or subway tunnel environment is the cascaded straight and curved tunnel. In this paper, we propose a joint path loss model for cascaded tunnels at 3.5 GHz and 5.6 GHz frequency bands. By combining the waveguide mode theory and the method of shooting and bouncing ray (SBR), it is found that the curvature of tunnels introduces an extra loss in the far-field region, which can be modeled as a linear function of the propagation distance of the signal in the curved tunnel. The channel of the cascaded straight and curved tunnel is thus characterized using the extra loss coefficient (ELC). Based on the ray-tracing (RT) method, an empirical formula between ELC and the radius of the curvature is provided for 3.5 GHz and 5.6 GHz, respectively. Finally, the accuracy of the proposed model is verified by measurement and simulation results. It is shown that the proposed model can predict path loss in cascaded tunnels with desirable accuracy and low complexity.

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Path Loss Model for 3.5 GHz and 5.6 GHz Bands in Cascaded Tunnel Environments

Vehicle-to-vehicle (V2V) communication has proven to enhance road safety and transportation systems. Currently, there are two approaches to enable transmission between moving vehicles. The first one is the 3rd Generation Partnership Project (3GPP) cellular vehicle-to-everything (V2X) specifications. Another approach is based on the IEEE 802.11 family of standards. The latter group is commonly known as dedicated short-range communications (DSRC). While the 3GPP V2X may provide higher throughput by the adoption of the millimeter-wave (mmWave) spectrum, its reliability depends on the availability of the infrastructure. On the other hand, DSRC is more intensively deployed. However, the supported throughput is significantly lower compared to the new radio (NR)-based technology. This drawback can be overcome by exploiting the mmWave bands by DSRC. In this letter, we evaluate the performance of the 802.11p technology at 28 GHz. Besides, several equalizing techniques are applied in order to improve the multipath immunity of the considered setup.

Dedicated Short-Range Communications: Performance Evaluation Over mmWave and Potential Adjustments

This work continues the development of the ray-tracing method of de Jong (2021) for computing the scattered fields from metasurfaces characterized by locally periodic reflection and transmission coefficients. In this work, instead of describing the metasurface in terms of scattering coefficients that depend on the incidence direction, its scattering behavior is characterized by the surface susceptibility tensors that appear in the generalized sheet transition conditions (GSTCs). As the latter quantities are constitutive parameters, they do not depend on the incident field and, thus, enable a more compact and physically motivated description of the surface. The locally periodic susceptibility profile is expanded into a Fourier series subject to a spatially varying phase parameter, and the GSTCs are rewritten in a form that enables them to be numerically solved for the reflected and transmitted surface fields. The phase parameter can either be determined from a prescribed surface transformation or extracted from known surface susceptibilities. A method for the extraction of this phase parameter from a susceptibility profile using a spatial variant of the short-time Fourier transform (STFT) is proposed. The scattered field at arbitrary detector locations is constructed by evaluating critical-point contributions of the first and second kinds using a forward ray-tracing (FRT) scheme. The accuracy of the resulting framework has been verified with an integral equation-based boundary element method (BEM)-GSTC full-wave solver for a variety of examples, such as a periodically modulated metasurface, a metasurface diffuser, and a beam collimator. 

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Ray-Optical Evaluation of Scattering From Electrically Large Metasurfaces Characterized by Locally Periodic Surface Susceptibilities

5G new radio (NR) requires a very dense deployment of cellular infrastructure, which poses a great economical challenge if traditional fiber backhaul links are used. To cope with this problem, 3GPP introduced integrated access and backhaul (IAB), aiming to use wireless backhaul to provide high capacity and great deployment flexibility. The multi-hop and multi-route topology for this new type of access networks challenges the existing retransmission-/repetition-based reliability-enhancing technique, such as ARQ/HARQ and packet duplication. However, it also opens up new opportunities for novel reliability enhancement techniques. In this paper, taking advantage of the more complex network topology of IAB, we propose to use linear network coding as a potentially better solution to improve end-to-end latency and reliability. We discuss its placement in the IAB protocol stack, and propose two novel schemes to improve the performance of network coding in the IAB network: the rate-proportional traffic splitting scheme in the multi-route scenario, and the adaptive coded-forwarding scheme in the multi-hop scenario. Simulation results show that in some typical IAB scenarios our network coding solution has considerable performance gains over the existing repetition-based technology.

Network Coding for Integrated Access and Backhaul Wireless Networks

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.

Self-Interference Assessment and Mitigation in 3GPP IAB Deployments

With the increasing densification of cellular networks, it has become exceedingly difficult to provide traditional fiber backhaul access to each cell site, which is especially true for small cell base stations (SBSs). The increasing maturity of millimeter wave (mmWave) communication coupled with multiple-input-multiple-output (MIMO) and beamforming technologies has opened up the possibility of providing high-speed wireless backhaul to such cell sites. The third generation partnership project (3GPP) is defining an integrated access and backhaul (IAB) architecture for the fifth generation (5G) cellular networks, in which the same infrastructure and spectral resources are used for both, the access and the backhaul. In IAB networks, SBSs, so called IAB nodes, act either as relay nodes carrying the traffic through multiple hops from a macro cell to an end user and vice versa or as access points to serve user equipment (UEs) in their proximity. To this end, the topology of such IAB networks is essential to enable efficient traffic flow and minimize congestion or increase robustness to backhaul link failure. In this paper, we propose a topology formation algorithm together with methodologies to implement it in real networks and compare it with a standard random sequence approach as well as with an optimal topology obtained using dynamic programming. Our simulation results demonstrate that the proposed algorithm outperforms the random sequence approach by 26\% on average in terms of lower bound of the network capacity and is up to 99.7\% close to the optimal solution, while being significantly less complex.

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Optimal Topology Formation and Adaptation of Integrated Access and Backhaul Networks

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.

Wei Mao

Papers

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

Network Coding for Integrated Access and Backhaul Wireless Networks

Self-Interference Assessment and Mitigation in 3GPP IAB Deployments

Optimal Topology Formation and Adaptation of Integrated Access and Backhaul Networks

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