Sub-6GHz Assisted MAC for Millimeter Wave Vehicular Communications

Sub-6GHz vehicular communications (using DSRC, ITS-G5 or C-V2X) have been developed to support active safety applications. Future connected and automated driving applications can require larger bandwidth and higher data rates than currently supported by sub-6GHz V2X technologies. This has triggered the interest in developing mmWave vehicular communications. However, solutions are necessary to solve the challenges resulting from the use of high-frequency bands and the high mobility of vehicles. This paper contributes to this active research area by proposing a sub-6GHz assisted mmWave MAC that decouples the mmWave data and control planes. The proposal offloads mmWave MAC control functions (beam alignment, neighbor identification and scheduling) to a sub-6GHz V2X technology, and reserves the mmWave channel for the data plane. This approach improves the operation of the MAC as the control functions benefit from the longer range, and the broadcast and omnidirectional transmissions of sub-6GHz V2X technologies. This simulation study demonstrates that the proposed sub-6GHz assisted mmWave MAC reduces the control overhead and delay, and increases the spatial sharing compared to a mmWave-only configuration (IEEE 802.11ad tailored to vehicular networks). The proposed MAC is here evaluated for V2V communications using 802.11p for the control plane and 802.11ad for the data plane. However, the proposal is not restricted to these technologies, and can be adapted to other technologies such as C-V2X and 5G NR.Comment: 8 pages, 5 figure

Beam management for vehicle-to-vehicle (V2V) communications in millimeter wave 5G

Cooperative, Connected and Automated Mobility (CCAM) is expected to leverage the full potential of wireless communications. With the growing adoption of 5G and its support for Vehicle-to-Everything (V2X) communications, beamformed vehicular communications at millimeter-wave (mmWave) bands are expected to enable the most demanding connected driving applications. Beamformed V2X links present the challenge of beam management in such a fast-changing scenario. This paper goes through the practical limitations of the 5G V2X stack to support successful beamforming procedures. Two beam management strategies are proposed. Both strategies are evaluated in terms of power performance, beam recovery time and channel usage. The results suggest that significant differences apply when the beam is more frequently updated, whereas little improvement is seen by increasing the size of the beamset. Also, the selection of a proper strategy is shown to be important to alleviate the channel from overheads, and substantial differences in required signaling can be seen depending on the beam-tracking approach.This work was partly funded by the Spanish Comisión Interministerial de Ciencia y Tecnología under projects TEC2013-47360- C3-1-P, TEC2016-78028-C3-1-P and MDM2016-0600, and Catalan Research Group 2017 SGR 219. The Spanish Ministry of Education (FPU17/05561) and Generalitat de Catalunya DI programme (2018- DI-084) also contribute with predoctoral grants for the authors.Peer ReviewedPostprint (published version

Seven Defining Features of Terahertz (THz) Wireless Systems: A Fellowship of Communication and Sensing

Wireless communication at the terahertz (THz) frequency bands (0.1-10THz) is viewed as one of the cornerstones of tomorrow's 6G wireless systems. Owing to the large amount of available bandwidth, THz frequencies can potentially provide wireless capacity performance gains and enable high-resolution sensing. However, operating a wireless system at the THz-band is limited by a highly uncertain channel. Effectively, these channel limitations lead to unreliable intermittent links as a result of a short communication range, and a high susceptibility to blockage and molecular absorption. Consequently, such impediments could disrupt the THz band's promise of high-rate communications and high-resolution sensing capabilities. In this context, this paper panoramically examines the steps needed to efficiently deploy and operate next-generation THz wireless systems that will synergistically support a fellowship of communication and sensing services. For this purpose, we first set the stage by describing the fundamentals of the THz frequency band. Based on these fundamentals, we characterize seven unique defining features of THz wireless systems: 1) Quasi-opticality of the band, 2) THz-tailored wireless architectures, 3) Synergy with lower frequency bands, 4) Joint sensing and communication systems, 5) PHY-layer procedures, 6) Spectrum access techniques, and 7) Real-time network optimization. These seven defining features allow us to shed light on how to re-engineer wireless systems as we know them today so as to make them ready to support THz bands. Furthermore, these features highlight how THz systems turn every communication challenge into a sensing opportunity. Ultimately, the goal of this article is to chart a forward-looking roadmap that exposes the necessary solutions and milestones for enabling THz frequencies to realize their potential as a game changer for next-generation wireless systems.Comment: 26 pages, 6 figure