[Paper Review] Distributed Robust Geocast Multicast Routing for Inter-Vehicle Communication

Harshvardhan P. Joshi, Mihail L. Sichitiu+1 more|arXiv (Cornell University)|Mar 31, 2022

Vehicular Ad Hoc Networks (VANETs)57 citations

TL;DR

DRG presents a completely distributed, state-less geocast routing approach for VANETs that uses distance-based backoff and angular/coverage criteria to reduce redundancy while maintaining delivery in dynamic topologies.

ABSTRACT

Numerous protocols for geocast have been proposed in literature. It has been shown that explicit route setup approaches perform poorly with VANETs due to limited route lifetime and frequent network fragmentation. The broadcast based approaches have considerable redundancy and add significantly to the overhead of the protocol. A completely distributed and robust geocast approach is presented in this paper, that is resilient to frequent topology changes and network fragmentation. A distance-based backoff algorithm is used to reduce the number of hops and a novel mechanism to reduce redundant broadcasts is introduced. The performance of the proposed protocol is evaluated for various scenarios and compared with simple flooding and a protocol based on explicit route setup.

Motivation & Objective

• Motivate the need for geocast in VANETs due to high mobility and frequent fragmentation.
• Propose a completely distributed, state-less forwarding algorithm for geocast without neighbor tables.
• Introduce a distance-based backoff and mechanisms to reduce redundant broadcasts.
• Ensure delivery to two-dimensional and one-dimensional target regions and handle network partitioning.
• Propose time-persistent geocast to deliver messages to nodes entering the region later.

Proposed method

• Use a distance-based backoff to favor farthest nodes for forwarding and reduce transmissions.
• Define Forwarding Algorithm with backoff: BO_d(R_tx,d)=MaxBO_d · S_d((R_tx−d)/R_tx).
• Incorporate burst retransmissions and long backoffs to overcome fragmentation and maintain a live message in the ZOR.
• Extend to two-dimensional scenarios by introducing angular threshold and coverage ratio concepts to govern relay selection and prevent excessive overlap.
• Adopt a time-persistent geocast scheme with periodic rebroadcasts and a persistence timer to deliver to late entrants.
• Provide evaluation using SWANS/STRAY simulations comparing DRG to flooding.

Experimental results

Research questions

• RQ1 Can a completely distributed, state-less geocast protocol achieve high delivery ratios in VANETs with frequent topology changes and fragmentation?
• RQ2 How can distance-based backoff and angular/coverage criteria be used to minimize redundancy while ensuring coverage of a target geographic region?
• RQ3 How does time-persistent geocast affect delivery to vehicles entering the ZOR after initial dissemination?
• RQ4 What is the trade-off between overhead and delivery reliability in DRG compared to simple flooding?
• RQ5 Can the forwarding algorithm work effectively in both one-dimensional highways and two-dimensional city street networks?

Key findings

• DRG achieves comparable or higher delivery ratios than flooding, especially in fragmented networks.
• End-to-end delay for DRG is less sensitive to density in well-connected networks and increases mainly due to fragmentation resolution.
• DRG incurs lower overhead than flooding in dense networks, due to the distance-based backoff reducing transmissions.
• The mechanism to live the message in the ZOR (time persistence) yields delivery to nodes entering the region after initial dissemination.
• In sparse networks, DRG maintains delivery by increasing overhead through retransmissions to overcome fragmentation.
• PDR can exceed 100% for DRG due to message persistence delivering to late entrants.