# Performance Analysis of the IEEE 802.11p Multichannel MAC Protocol in Vehicular Ad Hoc Networks
## 2 Related Works
The unique characteristics of the VANETs, such as highly dynamic topology, ever-changing vehicle density, unstable and variable nature of wireless links, make multichannel synchronization, coordination and access particularly challenging [25]. [PERSON] and [PERSON] in [26] proposed a methodology to derive the CCHI according to requirements of safety applications, and they have analyzed the share of non-safety applications as the function of safety performance requirements and traffic density. They have found that, under high density vehicular network environments, the non-safety applications may have to be severely restricted. [PERSON] et al. [27] investigated the performance of networks built from single-channel devices in vehicular environments. Analysis and simulation results show that channel switching causes synchronization of backoff processes, which increases the frame collision probability, in particular for small sizes of contention windows. In [28], [PERSON] et al. studied the relationship among the number of vehicles, packets loss ratio on the CCH, throughput of SCHs, and the duration of CCHI and SCHI. Through simulation and analysis, they found that the switch operation between fixed CCHI and SCHI cannot satisfy reliability requirement of safety applications on the CCH and high throughput requirement of non-safety applications on the SCHs. They introduce a multichannel coordination algorithm to adaptively adjust the ratio between CCHI and SCHI to achieve better performance. However, these models do not consider the effect of combined virtual collisions, fading channel and hidden terminal problem on the performance of safety and non-safety services, and these parameters are the main factors affecting the performance of the these two applications. In this paper, we propose two analytical models for the analysis of safety and non-safety service in the IEEE 802.11p multichannel MAC protocol, taking into account virtual collisions, the retry limit, channel switch, concurrent collisions,hidden terminal problem, channel fading, unsaturated conditions, and the difference among frame collision probability, frame failure probability, frame blocking probability, and channel busy probability. We derive the transmission delay and PRR of safety-related messages to analyze the timeliness and reliability of safety-related messages transmission, and derive the throughput of non-safety messages to analyze the effectiveness of non-safety messages transmission and the utilization of SCHs. The impact of virtual collisions, channel switch, concurrent collisions, hidden terminal problem, channel fading and the length of CCHI and SCHI are evaluated by provide deeper understandings on how various factors influence safety and non-safety message delivery. The simulation and analysis results can be used to guide design of adaptive multichannel protocol in VANETs. To the best of our knowledge, this is the first attempt to model the IEEE 802.11p multichannel MAC protocol to jointly analyze the transmission delay and PRR on the CCH, and the throughput and utilization of SCHs by considering the most influential factors. The detailed comparison of different models is given in Table 1.