Analysis and Evaluation of Random Access Transmission for UAV-Assisted Vehicular-to-Infrastructure Communications

Abstract

In this paper, we propose a random access protocol for vehicular-to-infrastructure communications. We consider the case where an unmanned aerial vehicle (UAV) provides assistance to a roadside unit to enhance the system throughput. In a traditional carrier sense multiple access schemes (CSMA), the vehicle senses the channel first and it does not transmit the data until the channel is free. However, the CSMA has been shown to be often wasteful of resources and includes potentially unbounded channel access delays in dense networks. In this paper, we use the capture effect, where collisions can be resolved, provided the signal-to-interference-plus-noise ratio is larger than a predetermined threshold. Moreover, we show that the access probability of the vehicles can be optimized based on the known density of the network to maximize throughput. Based on the proposed random access protocol, we model the behavior of the vehicles using a two-dimensional Markov chain and derive the expression for the average system throughput. Finally, we propose two transmission power control schemes to further enhance system throughput. We present extensive simulation results to show that the UAV can provide 9%-38% improvement in throughput for variable network densities. INDEX TERMSVehicular and wireless technologies, unmanned aerial vehicles, wireless communication, wireless network, CSMA, Markov chain, random access, capture effect. I. INTRODUCTION Vehicular communication networks have received huge attention from the research community as well as the industry, for its potential to enhance road safety, traffic efficiency, and on-board information and entertainment. Some of the main communication standards developed for vehicular networks include the dedicated short range communication (DSRC) in the US [1]. DSRC is based on IEEE 802.11p [2], which is part of the wireless access in vehicular environments (WAVE) architecture. IEEE 802.11p uses carrier sense multiple access with collision avoidance (CSMA/ CA) [3], originally designed for wireless local area networks (WLAN). However, while WLAN is characterized by low mobility and low density, vehicular networks are notorious for their dynamic topology, high-mobility environment, and requirement for scalability for high density networks. Thus, researchers have recently grown skeptical of the CSMA/CA for vehicular networks [3], [4].In this regards, the 3rd Generation Partnership Project (3GPP) proposed long term evolution vehicle-to-everything (LTE V2X) [5], which offers cellular networks to vehicles, based on D2D communications. LTE V2X is still, however, a centralized approach as it relies heavily on the network for time and frequency synchronization. In general, centralized approaches are more reliable than CSMA/CA and, thus, more suitable for critical safety-related messages. However, centralized approaches incur large control overhead, require control channels and infrastructure as well as complex resource allocation algorithms. Thus, they might be unnecessarily costly for less critic...

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