Motivated by the need to study the performance of vehicular communication protocols as applicable to heterogeneous traffic conditions, we study the performance of IEEE 802.11p medium access protocol under such a traffic setup. We consider a setup comprising connected vehicles and human-driven Motorised Two Wheelers (MTWs), where the connected vehicles are required to move as platoon with a desired constant headway despite interruptions from the two wheelers. We invoke specific mobility models for the movement of the vehicles--car following models for connected vehicle platoons and gap-acceptance model to capture the movement of the MTWs--and use them to configure (i) the traffic setup and (ii) the rate at which data packets related to safety-critical messages need to be transmitted. A control-theoretic analysis of the car-following models yields a bound on the admissible communication delay to ensure non-oscillatory convergence of the platoon headway. We then use suitable Markov chain models to derive the distribution of the MAC access delay experienced by packets pertaining to safety-critical events as well as routine safety messages. The distribution along with the bound on the admissible delay enables us to derive the reliability of the 802.11p MAC protocol in terms of traffic and EDCA parameters. Our study highlights the need for redesign of MAC protocols for vehicular communications for safety-critical applications in heterogeneous conditions.

翻译：受限于研究适用于异构交通条件的车辆通信协议性能的需求，本文研究了IEEE 802.11p介质访问协议在此类交通环境下的表现。我们考虑由联网车辆与人类驾驶的摩托车（MTWs）组成的场景，其中联网车辆需以固定期望车头时距组成队列行驶，且不受两轮车干扰。我们采用特定车辆移动模型——联网车辆队列的跟驰模型与捕捉MTW运动的间隙接受模型——来配置：(i)交通场景；(ii)与安全关键消息相关的数据包传输速率。通过对跟驰模型进行控制理论分析，得出了确保队列车头时距非振荡收敛的可容许通信延迟边界。随后利用合适的马尔可夫链模型推导了安全关键事件数据包及常规安全消息数据包经历的MAC接入延迟分布。结合该分布与可容许延迟边界，我们根据交通参数和EDCA参数推导了802.11p MAC协议的可靠性。本研究揭示了在异构条件下为安全关键应用重新设计车辆通信MAC协议的必要性。