# Distributed Triggered Access for BSM Dissemination in 802.11 bd V2V Networks
In [26], an analytical model for delivering safety messages using prioritized Access Classes (ACs) was proposed to analyze the performance of EDCA considering virtual collisions, Arbitration Inter-frame Spacing (AIFS) differentiation, the retry limit and the difference among frame blocking probability, frame collision probability and channel busy probability into considerations. In [27], authors proposed an analytical model for DSRC networks where broadcast safety message and unicast non-safety message share the medium with different priorities. According to the past research, IEEE 802.11p can provide a decent V2V communication quality in moderate network traffic condition. As network congestion increases; however, the delay performance of channel access degrades severely because the Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA) incurs an excessive medium contention overhead in heavy traffic situation. Envisioning the future platooning environment, platooning application will require vehicles to exchange more various types of information with increased size to achieve more precise control of platoon driving. Furthermore, the adoption of platooning will possibly increase vehicle density which means that several contending nodes for channel access will also increase in the network. This rationale raises concerns that DSRC may not properly meet the requirements of future platooning. Meanwhile, IEEE Standard Association (SA) has commenced to develop the successor of IEEE 802.11p recently. As the result of a year of studies on the Next Generation Vehicle (NGV) Vehicle-to-Everything (V2X) Wireless Local Area Network (WLAN), the IEEE 802.11 bd Task Group (TG) was formed in January 2019. The main objective of IEEE 802.11 bd is to improve throughput, transmission range, and positioning performance [28]. IEEE 802.11 bd not only defines the PHY layer but also the MAC layer including congestion control. As IEEE 802.11p used to embrace many features defined in IEEE 802.11a, IEEE 802.11 bd is considering adopting some advanced features from the latest main stream WLAN standard, IEEE 802.11 ax [29]. The IEEE 802.11 ax standard has been developed since 2014. The main objective of IEEE 802.11 ax is to achieve high efficiency in dense network environment [30]. In order to solve the longstanding CSMA congestion problem, the IEEE 802.11 ax standard has adopted a new channel access scheme, namely Triggered Uplink Access (TUA), which takes advantages of scheduling-based channel access scheme in contrast to the conventional CSMA/CA scheme. In [31], an analytic model to evaluate the channel use of TUA was proposed. [PERSON] et al. proposed a Markov chain analysis of TUA Uplink Orthogonal Frequency Division Multiple Access (OFDMA) Random Access (UORA) in saturated traffic condition [32]. In [33], a V2I channel access scheme using TUA was proposed. In this paper, we propose a novel channel access scheme for V2V BSM dissemination, called Distributed Triggered Access (DTA). In the proposed scheme, each vehicle that accesses the channel using EDCA to transmit a buffered BSM may solicit simultaneous transmission of nearby vehicles. Leveraging the new PHY layer numerology of the IEEE 802.11 ax and the synchronization and instant scheduling features of TUA, the solicited vehicles can perform OFDM transmission immediately. TUA was primarily proposed to be used in a Basic Service Set (BSS) environment, where a centralized Access Point (AP) device has better understanding on the associated devices and traffic situation so that it can schedule a TUA transmission properly. Since the characteristic of BSM traffic is easy to predict and vehicles are supposed to know the presence of nearby vehicles, in the proposed scheme, TUA is used in distributed manner. To the best of our knowledge, our work is the first attempt to apply TUA to distributed V2V networks and to provide an analytic model of TUA scheme including unsaturated traffic condition.