Abstract
Dedicated short-range communications (DSRC) is one of the key technologies enabling safety-critical applications for intelligent transportation system (ITS). Considering the significance of such safety-of-life applications, it is of utmost importance to guarantee reliable delivery of basic safety messages (BSMs). However, in accordance with a V2X network being inherently dynamic in key aspects such as vehicle density and velocity, the networking behavior of a DSRC system is usually highly complicated to analyze. In addition, the United States Federal Communications Commission (US FCC) recently proposed the so-called “5.9 GHz band innovation,” which includes a plan to reduce bandwidth for DSRC to 10 MHz at best from 75 MHz. Motivated from these challenges, the necessity of “lightening” load of a DSRC network has become essential to keep safety-related operations from performance deterioration. To this end, this paper proposes a protocol that prioritizes transmission of a BSM from a vehicle according to the level of accident risk of the vehicle. The proposed protocol uses the distance of a vehicle from a danger source as the metric to determine the priority for transmission. Our results show that this protocol effectively prioritizes the transmission opportunity for dangerous vehicles, and hence results in higher performance in terms of key metrics–i.e., average latency, packet delivery rate ( $\mathsf {PDR}$ ), and inter-reception time ( $\mathsf {IRT}$ ).
Highlights
Distance of a vehicle to the danger source (m) Vehicle density Number of beaconing periods with failed packet delivery (EA) Number of slots spent during a backoff process (EA) Number of STAs competing for the medium (EA) Packet delivery rate Probability of a transmission Time length taken for a backoff process Time length taken for a packet collision Time length taken for a packet expiration Time length of the inter-broadcast interval Time length taken for a successful packet delivery Threshold on d→dgr for CAT i (m) often suggested to improve the performance of a vehicular communications network such as a recent work [20]
It is because of rounding the number of STAs to the nearest integer for calculation of binomial coefficients between the number of all STAs and the number of CAT 1 STAs, i.e., “Nastlal choose Ncstaat 1” in calculation of τ . (Notice that the rounding comes from A (CAT 1) / R2 where A (·) denotes the area of a space.) As such, all the subsequent quantities–viz., τ, Pcol and packet delivery rate (PDR)–are affected by the approximation since they are based on τ
This paper proposed a protocol prioritizing the transmission of a basic safety messages (BSMs) for a vehicle with a higher level of accident risk
Summary
Vehicle-to-Everything (V2X) communications have been garnering massive interest across the academic and commercial bodies thanks to their potential to significantly promote the traffic safety [1]. The universal compatibility among IEEE 802.11 technologies leads to the spectrum versatility and easy operation [4], which could strengthen DSRC in the market of connected vehicles. Based on these advantages, as of November 2018, more than 5,315 roadside units (RSUs) operating in DSRC were deployed in the United States (US) alone [5]. It has become urgent to understand how much impact of the FCC’s 5.9 GHz band reallocation will be placed on the performance of such connected vehicle infrastructure Another significant issue for DSRC is that it may need to experience coexistence with C-V2X users according to the FCC’s proposition [7]. It has become crucial to lighten the load of a DSRC network while keeping the dissemination of packets operable, in order to suit the technology into such a competitive spectrum environment
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