# Video Streaming in Urban Vehicular Environments: Junction-Aware Multipath Approach
## 1 Introduction  
Wireless communication between moving vehicles is increasingly becoming the focus of research for both automobile companies and academic research communities [1; 2; 3]. It is driven by the vision that the exchange of information between vehicles can be exploited to improve the safety and comfort of drivers while in motion [4; 5; 6]. One of the most valuable Vehicular Ad-Hoc Networks (VANETs) applications is video streaming [7; 8]. Which can offer more understandable and attractive on-road traffic information to drivers and passengers [9; 10]. The communicated video can be related to driving safety; for example, an accident ahead, or pedestrians or animals crossing the road [11; 12]. It can also be related to onboard communications, such as Vehicle-to-Vehicle (V2V) or Vehicle-to-Office (V2O) video conferencing [13; 14]. On-board infotainment can also offer advertisements providedby supermarkets or shopping malls along the road utilizing roadside unit Internet of Things (IoT) environments [15; 16]. Consequently, the video streaming service can reasonably improve the onboard experience of the vehicles. The daunting issues of video streaming in VANETs are packet drop, delay and bandwidth-constrained wireless network environments [17; 18]. This is due to the extremely dynamic topology of vehicles and the large size of video data packets sent across the wireless network [19]. These challenges become worse for high-quality video streaming, because of the even larger size of video data [20; 21]. Current multimedia applications require high capacity communication links to facilitate high speed data transfer rate. Video applications require stringent video quality requirements including minimum delay, packet drop, and efficient bandwidth utilization [22; 23]. Hence, there is a need for efficient video data transmission considering the characteristics of both VANETs and video streaming applications. When trying to transmit data efficiently, a path with the necessary resources to meet user requirements should be chosen. On the other hand, in conventional data networks, the routing of data is primarily concerned with an end-to-end connectivity [24; 25]. The data network protocol generally represents a network with a metric such as hop-count or delay and uses the shortest path and location algorithm for path and location estimation [26; 27]. However, in order to support the quality and delay requirements of video streaming, routing protocols usually need to take into consideration the junction area characteristics when forwarding video data [28]. The consideration of junctions on roads during transmission enhances routing decisions, achieving quality video streaming delivery [29]. A number of multipath transmission schemes have been suggested in some research studies, but few studies have considered road features such as road junctions in hop-by-hop transmission. Figure 1 presents vehicles in the junction area. Vehicle A, B and C are the candidate next forwarding vehicles, of which any one can be chosen to forward a video packet. Vehicle D is the present forwarding vehicle which needs to make a decision regarding which candidate vehicle is suitable for the data packet forwarding. When forwarding a data packet in a junction area, the vehicle after the junction area with the minimum required link quality is considered to be most suitable. Afterward, the vehicle that resides in the junction with the minimum required link quality is considered as the second-best option, while the vehicle before the junction with the minimum required link quality is the third-best option. This is because the vehicle after the junction might be closer to the targeted destination, which gives it longer connectivity and reduces the number of hops that need to be traversed. Some studies use the junction point as a forwarding area without considering the freshness of the direction of the vehicle. Figure 1: Candidate next forwarding vehicles in the junction area.