# Improved Road Segment-Based Geographical Routing Protocol for Vehicular Ad-hoc Networks
## 2 Related Works
An ant colony optimization-based ad hoc demand distance vector reliability (AODV-R) routing protocol has been investigated for VANETs [20]. This protocol uses optimal route selection and data aggregation as routing parameters. This protocol is the enhanced version of ad hoc demand distance vector (AODV) routing protocol. It considers the route having the shortest distance in terms of the hop count as used in Dijkstra algorithm, and clustering methods to reduce network overhead during information dissemination. Ant colony optimization is also used as another optimization method to find the shortest route with the minimum distance and route reliability. By a combination of ant colony and clustering, this protocol claims better performance than exiting routing protocols. However, the Dijkstra algorithm only works when all routing link weights are positive, and this assumption is not always valid in VANETs scenarios. A prediction-based geographical routing (PGR) protocol has been suggested to improve the geographical routing strategy over VANET (GROOV) by using a network prediction method. It redesigned the forwarding and repairing mechanisms of GROOV protocol [21]. This protocol does not use pure routing and greedy forwarding approaches. Basically, this protocol enhances the prediction before an intersection and then saves the one hop information. It has been claimed in simulation results that the PGR performance is better in terms of hop counts, network latency, and the packet delivery ratio in both vehicular network environment including dense and sparse VANETs. However, vehicle networks are unpredictable in nature, making the network prediction method unsuitable to monitor network parameters for routing decision making. A Street-centric opportunistic Routing Protocol using Expected transmission cost (SRPE) has been investigated for vehicular traffic environments [22]. This protocol uses an expected transmission cost over a multi-hop forwarding path. In their work, the authors used winner procedure to measure the chances of link availability. An opportunist routing scheme is used for signal the fading mobility of the vehicle nodes, considering whether the vehicle state is stable or unstable according to the actions of the vehicle nodes. Routing decisions are taken at the intersection without topology information. Different combinations of the link are used to send packets to achieve a high throughput under limited-resource centric vehicular networks. However, this protocol dynamically forwards data packets by using adjacent street information. This strategy is not suitable under a vehicular network scenario with intermittent connectivity under sparse or dense vehicular networks. An analytical hierarchical process (AHP)-based multi-metric geographical routing protocol (AMGRP) has been investigated [23]. This protocol is the enhancement of the existing GPSR routing protocol. It adopts an AHP by considering multiple metrics including link lifetime, node density, and node status to find the best route in a network. However, when a protocol uses more routing metrics, it comes with more process complexities resulting in network delay and greater network overheads in VANETs scenario. Traffic-aware segment-based routing (TASR) has been explored for VANET environments [24]. This protocol considers real-time traffic information for route selection. To calculate the strength of the segment, a metric called the estimated connectivity degree (ECD) is adopted. It considers traffic density and vehicle position as major routing parameters. Routing decisions are made depending on the information of segments. Each segment has two head nodes present on its corners. Each vehicle sends hello message containing nearby traffic density and vehicle's position within the road segment which is used for making routing decision. However, the ECD cannot be recommended for higher mobility networks due to the complex and unpredictable network topologies of VANETs. Virtual backbone routing protocol (VBRP) has been suggested for VANETs [25].