Performance evaluation of probabilistic relay in ad hoc on-demand distance vector and Ad hoc on-demand multipath distance vector under highly dynamic environments

Vehicular Ad hoc Networks (VANETs) are a specific class of Mobile Ad hoc Networks (MANETs). Since vehicles tend to move in a high speed, the network topology is rapidly changed. Thus vehicle's connectivity problem is one of the interesting issues in VANETs. Ad hoc On-demand Multipath Distance Vector (AOMDV) is an extended version of ad hoc on-demand distance vector (AODV). AOMDV is designed to overcome a connectivity problem due to highly dynamic network topology. It provides multipath for data packets delivery from the source to the destination. However, AOMDV's multipath establishment and maintenance generate more control packets than those of AODV's unipath. Meanwhile, both protocols degrade their performance when the vehicle speed is increasing. Thus in this study, we added probabilistic relay, which enables adjacent vehicles to probabilistically relay unsuccessful data packet transmission into IEEE 802.11 as a MAC standard model and proposed AODV with Probabilistic Relay (AODV-PR) and AOMDV with Probabilistic Relay (AOMDV-PR). Based on our simulation results, the addition of probabilistic relay clearly helps those protocols to improve their performances especially in packet delivery ratio under highly dynamic environments. Probabilistic relay adds the number of generated beacon messages, but does not produce any additional routing messages. We evaluate those protocol performances based on several metrics such as packet delivery ratio, routing overhead, average delivery delay, hop count and number of relays under variation of vehicle speed and beacon interval. We show that beacon interval has a huge influence in the performance of AODV-PR and AOMDV-PR especially for their routing overhead.