Geographic Routing Reliability Enhancement in Urban Vehicular Ad Hoc Networks

Vehicular Ad hoc Networks (VANETs) have the potential to enable various
kinds of applications aiming at improving road safety and transportation efficiency.
These applications require uni-cast routing, which remains a significant challenge due
to VANETs characteristics. Given VANET dynamic topology, geographic routing
protocols are considered the most suitable for such network due to their scalability
and low overhead. However, the optimal selection of next-hop nodes in geographic
routing is a challenging problem where the routing performance is highly affected by
the variable link quality and bandwidth availability.
In this dissertation, a number of enhancements to improve geographic routing
reliability in VANETs are proposed. To minimize packet losses, the direction and
link quality of next-hop nodes using the Expected Transmission Count (ETX) are
considered to select links with low loss ratios.
To consider the available bandwidth, a cross-layer enchantment of geographic
routing, which can select more reliable links and quickly react to varying nodes load
and channel conditions, is proposed. We present a novel model of the dynamic behavior of a wireless link. It considers the loss ratio on a link, in addition to transmission
and queuing delays, and it takes into account the physical interference e ect on the
link.
Then, a novel geographic routing protocol based on fuzzy logic systems, which
help in coordinating di erent contradicting metrics, is proposed. Multiple metrics
related to vehicles' position, direction, link quality and achievable throughput are
combined using fuzzy rules in order to select the more reliable next-hop nodes for
packet forwarding.
Finally, we propose a novel link utility aware geographic routing protocol,
which extends the local view of the network topology using two-hop neighbor information.
We present our model of link utility, which measures the usefulness of a
two-hop neighbor link by considering its minimum residual bandwidth and packet
loss rate. The proposed protocol can react appropriately to increased network tra c
and to frequent topology dis-connectivity in VANETs.
To evaluate the performance of the proposed protocols, extensive simulation
experiments are performed using network and urban mobility simulation tools. Results
confirm the advantages of the proposed schemes in increased traffic loads and
network density.