# Performance Analysis of the IEEE 802.11p Multichannel MAC Protocol in Vehicular Ad Hoc Networks
## 2 Related Works  
VANETs are the key components for provisioning safety-critical applications and non-safety (traffic efficient and comfort) applications on the road [13]. VANETs employ multiple channels (seven) to support these services. The transmissions of safety-related messages are employed broadcast mode on the CCH in VANETs, and there are many works studying the broadcast performance of the safety-related messages. The work in [14] explored a large parameter space to model IEEE 802.11-based 1-D VANETs, which is derived with consideration of the IEEE 802.11 Distributed Coordination Function (DCF), and to analyze the reliability performance of one-hop safety-critical broadcast services in VANETs. [PERSON] et al. [15] proposed a Markov chain model to analyze the backoff procedure of beacon and emergency message, and then the probability and throughput of packets are derived and evaluated. In [16], an analytical model for performance and reliability of safety message broadcasting was proposed. The model takes into account the vehicles' high mobility, hidden terminal problems, the transmission collisions from neighboring vehicles, and the channel fading in VANETs. The simulation and analytical results show that the model is pretty accurate in evaluating the system reliability. In [17], an analytical model for delivering DSRC safety messages within V2V communication was proposed. Two Markov chains for different priority ACs are established to analyze the delay distribution of the safety message broadcast. [PERSON] et al. [18] proposed two Markov chains to study the performance and the reliability of the IEEE 802.11p safety communication on the CCH. Safety-related messages are classified as four ACs with different priorities based on the degree of emergency. The PRR and packet delay are detailed analysis by taking virtual collisions, AIFS differentiation, the retry limit and the difference among frame blocking probability, frame collision probability and channel busy probability into considerations. Some works study the safety service performance in VANETs under multichannel conditions. [PERSON] et al. in [19; 20] analyzed the performance of periodic broadcasting of beacons and WSAs in the IEEE 802.11p by joint the feature of multichannel switch and the prioritization of messages broadcast on the CCH. The model calculates packet delivery probability as a function of CW and the number of vehicles and quantitatively characterizes the negative impact of channel switching on the performance of VANETs. An analytical model on the basis of interacting semi-Markov process which incorporates the influence of multichannel operation was designed to assess both MAC and application level performance and reliability of safety messages [21]. An optimized scheduling method was proposed to avoid synchronization collision, and channel fading is considered in the model to simulate practical communication environments. The mean transmission delay, PRR and awareness probability are derived. The work in [22] introduced a stochastic model to evaluate the delivery performance of event-driven safety messages by considering the traffic differentiation, event-drivenmessages lifetime, channel switching and channel error. Analytical and simulation results show that the larger CCHI can bring higher the successful delivery probability of event-driven messages. Nevertheless, all above performance analysis are modeled for only safety-related messages on CCH, and performance of non-safety messages is not discussed. In VANETs, driven by both safety concerns and commercial interests, one of the key services offered by VANETs is popular content distribution [23; 24]. The interval used to transmit safety messages at each synchronization interval is a critical parameter that directly impacts and limits the SCHI for transmitting non-safety messages [24].