Performance Analysis and Improvement of SOFT MAC Scheme in 802.11p Based Vehicular Ad Hoc Networks

The development of Intelligent Transportation System (ITS) requires a more reliable and flexible network to support all kinds of neoteric applications. Meanwhile, several MAC schemes have been proposed to control channel access in Vehicular Ad-hoc Networks (VANET). In our paper, we first analyzed some prevalent MAC mechanisms by simulations. The result reveals that these MAC schemes couldn´t guarantee steady performances for multi-services in changing road environment due to the deterioration of QoS. SOFT MAC (Space, Orthogonal Frequency and Time Division Multiple Access) divides a frame into a RS and TS period, in which CSMA or TDMA is used for channel access. This new MAC scheme could provide better performance in uneven traffic density under multi-service scene according to our mathematical analysis and simulation results. The transmitting method for a packet is determined by its length. By examining the scheme, we also realize that in order to achieve better performance, the RS period length and packet threshold for choosing transmitting method should be adjusted.