Each day the world embraces more devices to connect everything, everywhere, and everyone. This seamless connectivity results in a huge volume of data traffic among connected devices. The newly-hyped fifth-generation (5G) paradigm is anticipated to provide the necessary impetus to carry the burden of achieving massive system capacity, reduced latency and increased energy savings. In a 5G vehicular network, the vehicles will be integrative parts of the system, not just end-nodes. In essence, vehicles will act as mobile base stations and will contribute to fill coverage holes, support local capacity needs that appear unpredictably in time and space and, ultimately, provide high quality of experience for passengers. In addition, vehicles will be able to sense its environment to support a multitude of applications. For instance, vehicles could perform real-time traffic and environmental monitoring, which in turn will enable real-time traffic management to increase the efficiency of the transport system and reduce its environmental impact.

In this context, as more and more vehicles connect wirelessly every day, it has been predicted that a double-digit increase in the available resources will be needed by year 2020 to support advanced applications in vehicular networks. For example, one can think of a scenario with a high number of vehicles located in physical proximity (relative to radio coverage ranges), generating huge amounts of real-time traffic with independent data patterns. Several alternatives could be considered to meet those requirements. On the one hand, for communication systems at frequencies below 5 GHz, the limited available bandwidth poses a major constraint on the achievable link and network capacities, even with sophisticated physical-layer solutions with very high spectral efficiencies or when utilizing advanced spectrum sharing techniques or cognitive radio mechanisms.

On the other hand, the use of higher frequency bands in the electromagnetic (EM) spectrum, such as millimeter waves (mm-Wave, from 30GHz to 300GHz) is currently gaining momentum. While this is certainly the way to go, the rather limited available consecutive bandwidth (up to 7GHz at most), poses a constraint on the maximum achievable individual and aggregate data-rates. For example, according to the Edholm’s law of bandwidth, wireless Terabit-per-second (Tbps) links will become a reality by year 2020. With 7 GHz of bandwidth, this would require the use of a modulation and coding strategy with a spectral efficiency above 100 bits/s/Hz. This is not realistic at all and has not been achieved at lower frequency bands, where the technology is much more mature.

With these results in mind, and motivated by the advanced applications of vehicular networks in what could be referred to as “beyond 5G” (5G+) networks, Terahertz (THz) band communications [1] are quickly gaining momentum. THz-band communications are envisioned as a key wireless technology to satisfy real time traffic demand for vehicular communication, by alleviating the spectrum scarcity and capacity limitations of current wireless systems. The THz band is the spectral band that spans the frequencies between 0.1THz and 10THz. While the frequency regions immediately below and above this band (the microwaves and the far infrared, respectively) have been extensively investigated, this is still one of the least explored frequency bands.

Based on these facts above, although the opportunities brought by the THz band are exciting, the challenges facing THz vehicular communication are still many. For example, the very high propagation loss at THz-band frequencies drastically limits the communication distance of individual transceivers and antennas. As a result, very large scale or massive MIMO systems might be needed for practical applications. Ultimately, to make THz-band communications a reality for 5G+ vehicular networks, there are many questions and challenges that must be addressed. These issues span the breadth of communications theory and engineering, from transceiver and antenna design and fabrication, to information theoretic modeling of THz vehicular communications and the development of new modulation, equalization, interference management techniques. Therefore, the main goal of this special issue is to explore the new ideas of THz band for vehicular communication and capture its current advancement.

[1]   I. F. Akyildiz, J. M. Jornet and C. Han, “TeraNets: Ultra-broadband Communication Networks in the Terahertz Band,” IEEE Wireless Communications Magazine, vol. 21, no. 4, pp. 130-135, August 2014.
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