# Intersection-Based Link-Adaptive Beaconless Forwarding in Urban Vehicular Ad-Hoc Networks
## 2 Background
### Receiver-Based Data Forwarding
#### 2.4.2 Related Work  
The beacon-less routing (BLR) proposed in [47] is a receiver-based scheme, where the vehicle on reception of data packet uses location information to decide whether or not to participate in the data forwarding process. Three forwarding zones, i.e., circle, sector, and reuleaux triangle, were tested for this protocol. For the waiting time criteria, each contending vehicle assigns a dynamic forwarding delay based on its geographic progress towards destination.  
The work in [10] presented another receiver-based routing protocol called video reactive tracking-based unicast (VIRTUS) which is developed to support video streaming in vehicular environment. The forwarding zone is calculated using a forwarding angle \(\theta\), and the waiting time criteria is based on the geographic progress towards destination and link stability of the contending vehicle. The link stability is computed based on the current and future location of vehicles. Here, the future locations are predicted using Bayesian state estimation approach. However, VIRTUS requires the source and destination vehicles to periodically exchange information to update their current location coordinates to each other.  
Location-aware multipath video streaming (LIAITHON) [45] is a multipath receiver-based routing protocol developed to fulfil video streaming requirements over VANET by distributing the loads over two paths. The two paths are ensured to have the minimum route coupling effect and are selected based on the degree of closeness, geographic progress and link stability. The route coupling between the two paths is avoided by keeping them at least two times of their transmission range apart. Here, multiple paths are used to support high data rate requirements of video streaming. However, multiple paths also lead to redundant data packets flowing throughout the network, which may cause network congestion and packet collision.  
The work in [48] further enhanced LIAITHON to LIAITHON+ by increasing the number of multiple paths to three. Although having a greater number of paths may improve load distribution and support higher data rate, but it may also result in increased path length and the route coupling effect. Also, at a higher data rate, too many redundant packets may flow in the network resulting in an increased number of packet collisions.  
Besides, the distributed beaconless dissemination (DBD) [11] is a beaconless routing protocol which uses backbone-based approach to maintain robust and high quality routes, thereby enabling live video flows on multimedia highway VANETs for V2V scenarios. DBD does not use forwarding zone criterion as the transmission range of vehicles is greater than the width of the highway roads, which allows the vehicles to hear each other's data packet transmissions. Also, the vehicles that are traveling in opposite direction with respect to the vehicle broadcasting the data packet do not participate in the contention process. Another feature of DBD is the use of the link-adaptive approach. Specifically, once the contending vehicle wins the contention right, it stays in the \"winner\" state for a specific duration where it forwards any incoming data packet without setting any waiting time. The duration for which the relaying vehicle stays in the \"winner\" state is computed based on the location information of the previous and current relaying vehicles, and the wireless range of the vehicles.