# An Analytical Model for Interference Alignment in Broadcast Assisted VANETs
## 1 Introduction
### Literature Review  
Safety related information exchange is the key to the next generation of VANETs. In VANETs, vehicle is required to exchange information quickly and reliably with others within safety radius. In order to fulfill this target, some studies have designed VANETs distributed cross-layer protocols to adjust the priority of safety related information and intervene the direction of data propagation to reduce communication delay [10]. In [11], [PERSON] et al., proposed a new algorithm works on the selective distance allocation methodology for data transmission.  
As an emerging multiplexing-based interference cancellation method, IA is based on use of channel transmission features to align multiple interference streams to a specific direction at the receiving node to reduce interference. In [12], [PERSON] et al., proposed a new cellular network interference management method, which applied IA to cellular network. The simulation verified that IA can effectively improve communication rate. There is some research that studied a blind IA in cell network without full CSI information [13; 14; 15]. However, without full CSI information, the blind IA caused a large delay in direct communication and relatively large loss of effectiveness in routing.  
In [16], [PERSON] et al., proposed an intra-group IA scheme for V2V. In their research, the network is divided into two groups. One group used doppler frequency domain IA to ensure vehicles in this group are not interfered by other same group vehicles, while other groups only experience partial interference. However, because of the mobility, the vehicle cluster couldn't keep for a long time.  
In [17], [PERSON] et al., combined VANETs with CR called CR-VANETs protocol to solve spectrum scarcity problem. This method significantly increased spectrum use by equipping vehicles with a CR communication device to detect idle channel in DSRC. With the ability to capture and use available CR spectrum holes in space and time, vehicles were able to make full use of spectrum resources, thereby improving communication efficiency of VANETs [18; 19].  
In contrast to the preemptive channel exclusive method such as IEEE802.11p, i.e., in IA application, channel resources are allocated dynamically and the channel access method is time division multiple access (TDMA) [20; 21]. There are a lot of researchers that apply TDMA in VANETs and prove TDMA could overcome problems of hidden and exposed terminals. Meanwhile, TDMA makes it possible to facilitate IA in VANETs. The study in [22] verifies the feasibility of TDMA in VANETs and proves that TDMA has shorter latency and higher communication efficiency than IEEE802.11p.  
Most of the broadcast models are developed from a periodic single-hop communication. In [23], [PERSON] et al., proposed a new model to calculate a single-hop survival broadcast packet probability with a forwarding mechanism. This model accounted all possible cases of contention window assignments to all the nodes simultaneously receiving a broadcast message. Without considering characteristic of safety related information, the performance would be limited by bandwidth. For piggybacking traffic information over periodic safety related messages, [PERSON] et al., proposed a highly efficient and reliable multi-hop broadcasting protocol, Intelligent Forwarding Protocol (IFP) [24]. [PERSON] proposed a network-aware double-layer distance-dependent protocol for fast broadcasting of aggregated traffic information over multiple hops [25]. However, the hidden and exposed terminal problems still remained in these researches.