Delay-Bounded Wireless Network Based on Precise Time Synchronization Using Wireless Two-Way Interferometry

Abstract

The importance of reliable information transfer in wireless networks, especially regarding communication delay, is drastically increasing to fulfill safe and high-quality communication in the 5G and post-5G era. However, conventional media access control (MAC) protocol for wireless networks, notably Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), sometimes yields unexpectedly significant delay due to its complex arbitration mechanism assuming asynchronous communication among terminals. As the delay cannot be strictly bounded by a deterministic value, this causes a vulnerability of systems relying on wireless networks. This paper utilizes precise time synchronization achieved by Wireless Two-way Interferometry (Wi-Wi), enabling all terminals to be time-synchronized via wireless signals.We show that by an appropriate periodic assignment of each terminal's data transmission timing, named Arbitration Point (AP), a simple arbitration algorithm obtains a strictly bounded maximum value for the delay while ensuring equalities among all participants. Furthermore, we demonstrate that the total number of terminals manageable in a star-topology wireless network significantly increases by densely packing AP timings, taking into account the spatial geometry information of terminals, which is another feature delivered by Wi-Wi measurement. In the meantime, we experimentally constructed a star-topology wired network where all terminals are time-synchronized via Wi-Wi to confirm the fundamental properties identified in the proposed arbitration protocol. This study paves a new way for future wireless networks where the delay is strictly bounded and provides the basis for ultra-reliable and high-quality information transfer functionalities by utilizing precise time synchronization and space localization (space-time synchronization).

Experimental Demonstration of Delay-Bounded Wireless Network Based on Precise Time Synchronization

“…B Delay-Bounded MAC Protocol: CSMA/AP Carrier Sense Multiple Access with Arbitration Point (CSMA/AP) is a contention-based media access control protocol for wireless networks, realizing collisionfree arbitration by employing precise time synchronization [14]. Thanks to the collision-freeness property and the equality of transmission opportunities among terminals, CSMA/AP can guarantee the upper boundary of communication delay.…”

“…Meanwhile, a significant error was observed with parameters being 1 µs and 3 µs; we speculate that such error may be caused by a technical issue in our current experimental setup of SDRs. Besides, exploration of much smaller AP parameters will be one of our future studies, realizing a massive number of participants as reported in [14]. Based on these results, we use 5 or 10 µs for AP duration and AP offset in the following experiments.…”

“…Concerning the abovementioned backgrounds, we consider that time synchronization is a promising resource in providing highly reliable wireless communications. Indeed, Yamasaki et al proposed a novel media access control method named Carrier Sense Multiple Access with Arbitration Point (CSMA/AP) to accomplish strictly delay-bounded wireless communication by exploiting that all devices are precisely time-synchronized [14]. In CSMA/AP, communication opportunities are specified by Arbitration Points (AP), which are periodically assigned for all devices.…”

“…The former study of CSMA/AP [14], however, has been limited to theoretical and numerical demonstrations. In [14], preliminary experimental studies were also presented, but they were based on wired connections.…”

“…The former study of CSMA/AP [14], however, has been limited to theoretical and numerical demonstrations. In [14], preliminary experimental studies were also presented, but they were based on wired connections. Thus, experimental demonstrations and verifications to examine the feasibility and the utility of time synchronization for delay-bounded communications in wireless environments are indispensable.…”