Routing protocols (Computer network protocols)

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.

Multi-hop broadcast is one of the main approaches to disseminate data in
VANET. Therefore, it is important to design a reliable multi-hop broadcast protocol,
which satis es both reachability and bandwidth consumption requirements.
In a dense network, where vehicles are very close to each other, the number of
vehicles needed to rebroadcast the message should be small enough to avoid a broad-
cast storm, but large enough to meet the reachability requirement. If the network
is sparse, a higher number of vehicles is needed to retransmit to provide a higher
reachability level. So, it is obvious that there is a tradeo between reachability and
bandwidth consumption.
In this work, considering the above mentioned challenges, we design a number
of smart broadcast protocols and evaluate their performance in various network den-
sity scenarios. We use fuzzy logic technique to determine the quali cation of vehicles
to be forwarders, resulting in reachability enhancement. Then we design a band-
width e cient fuzzy logic-assisted broadcast protocol which aggressively suppresses
the number of retransmissions. We also propose an intelligent hybrid protocol adapts
to local network density. In order to avoid packet collisions and enhance reachability, we design a cross layer statistical broadcast protocol, in which the contention window
size is adjusted based on the local density information.
We look into the multi-hop broadcast problem with an environment based
on game theory. In this scenario, vehicles are players and their strategy is either
to volunteer and rebroadcast the received message or defect and wait for others to
rebroadcast. We introduce a volunteer dilemma game inspired broadcast scheme to
estimate the probability of forwarding for the set of potential forwarding vehicles. In
this scheme we also introduce a fuzzy logic-based contention window size adjustment
system.
Finally, based on the estimated spatial distribution of vehicles, we design a
transmission range adaptive scheme with a fuzzy logic-assisted contention window
size system, in which a bloom lter method is used to mitigate overhead.
Extensive experimental work is obtained using simulation tools to evaluate the
performance of the proposed schemes. The results con rm the relative advantages of
the proposed protocols for di erent density scenarios.

A Vehicular Ad-hoc Network (VANET) is a wireless ad-hoc network that
provides communications among vehicles with on-board units and between vehicles
and nearby roadside units. The success of a VANET relies on the ability of a
routing protocol to ful ll the throughput and delivery requirements of any applications
operating on the network. Currently, most of the proposed VANET routing protocols
focus on urban or highway environments. This dissertation addresses the need for an
adaptive routing protocol in VANETs which is able to tolerate low and high-density
network tra c with little throughput and delay variation.
This dissertation proposes three Geographic Ad-hoc On-Demand Distance
Vector (GEOADV) protocols. These three GEOADV routing protocols are designed
to address the lack of
exibility and adaptability in current VANET routing protocols.
The rst protocol, GEOADV, is a hybrid geographic routing protocol. The second
protocol, GEOADV-P, enhances GEOADV by introducing predictive features. The
third protocol, GEOADV-PF improves optimal route selection by utilizing fuzzy logic
in addition to GEOADV-P's predictive capabilities.
To prove that GEOADV and GEOADV-P are adaptive their performance is demonstrated by both urban and highway simulations. When compared to existing
routing protocols, GEOADV and GEOADV-P lead to less average delay and a
higher average delivery ratio in various scenarios. These advantages allow GEOADV-
P to outperform other routing protocols in low-density networks and prove itself
to be an adaptive routing protocol in a VANET environment. GEOADV-PF is
introduced to improve GEOADV and GEOADV-P performance in sparser networks.
The introduction of fuzzy systems can help with the intrinsic demands for
exibility
and adaptability necessary for VANETs.
An investigation into the impact adaptive beaconing has on the GEOADV
protocol is conducted. GEOADV enhanced with an adaptive beacon method is
compared against GEOADV with three xed beacon rates. Our simulation results
show that the adaptive beaconing scheme is able to reduce routing overhead, increase
the average delivery ratio, and decrease the average delay.

Cognitive radio technology that enables dynamic spectrum access has been
a promising solution for the spectrum scarcity problem. Cognitive radio networks
enable the communication on both licensed and unlicensed channels, having the potential
to better solve the interference and collision issues. Channel assignment is of
great importance in cognitive radio networks. When operating on licensed channels,
the objective is to exploit spectrum holes through cognitive communication, giving
priority to the primary users. In this dissertation, we focus on the development of efficient
channel assignment algorithms and protocols to improve network performance
for cognitive radio wireless networks. The first contribution is on channel assignment
for cognitive radio wireless sensor networks aiming to provide robust topology control,
as well as to increase network throughput and data delivery rate. The approach
is then extended to specific cognitive radio network applications achieving improved
performances.

This work presents the implementations of three adaptive broadcast protocols for vehicular ad hoc networks (VANET) using the Network Simulator 3 (Ns-3). Performing real life tests for VANET protocols is very costly and risky, so simulation becomes a viable alternative technique. Ns-3 is one of the most advanced open source network simulators. Yet Ns-3 lacks implementations of broadcast protocols for VANET. We first implement the Distance to Mean (DTM) protocol, which uses the distance to mean to determine if a node should rebroadcast or not. We then implement the Distribution-Adaptive Distance with Channel Quality (DADCQ) protocol, which uses node distribution, channel quality and distance to determine if a node should favor rebroadcasting. The third protocol, Statistical Location-Assisted Broadcast protocol (SLAB), is an improvement of DADCQ which automates the threshold function design using machine learning. Our NS-3 implementations of the three protocols have been validated against their JiST/SWANS implementations.

Vehicular Ad hoc NETworks (VANETs) are a subclass of Mobile Ad hoc NETworks
and represent a relatively new and very active field of research. VANETs will enable in
the near future applications that will dramatically improve roadway safety and traffic
efficiency. There is a need to increase traffic efficiency as the gap between the traveled
and the physical lane miles keeps increasing. The Dynamic Traffic Assignment problem
tries to dynamically distribute vehicles efficiently on the road network and in accordance
with their origins and destinations. We present a novel dynamic decentralized and
infrastructure-less algorithm to alleviate traffic congestions on road networks and to fill
the void left by current algorithms which are either static, centralized, or require
infrastructure. The algorithm follows an online approach that seeks stochastic user
equilibrium and assigns traffic as it evolves in real time, without prior knowledge of the traffic demand or the schedule of the cars that will enter the road network in the future.
The Reverse Online Algorithm for the Dynamic Traffic Assignment inspired by Ant
Colony Optimization for VANETs follows a metaheuristic approach that uses reports from
other vehicles to update the vehicle’s perceived view of the road network and change route
if necessary. To alleviate the broadcast storm spontaneous clusters are created around
traffic incidents and a threshold system based on the level of congestion is used to limit
the number of incidents to be reported. Simulation results for the algorithm show a great
improvement on travel time over routing based on shortest distance. As the VANET
transceivers have a limited range, that would limit messages to reach at most 1,000 meters,
we present a modified version of this algorithm that uses a rebroadcasting scheme. This
rebroadcasting scheme has been successfully tested on roadways with segments of up to
4,000 meters. This is accomplished for the case of traffic flowing in a single direction on
the roads. It is anticipated that future simulations will show further improvement when
traffic in the other direction is introduced and vehicles travelling in that direction are
allowed to use a store carry and forward mechanism.

This work presents the development of the Context-Aware Hybrid Data Dissemination
protocol for vehicular networks. The importance of developing vehicular networking data
dissemination protocols is exemplified by the recent announcement by the U.S. Department of Transportation (DOT) National Highway Traffic Safety Administration (NHTSA) to enable vehicle-to-vehicle (V2V) communication technology. With emphasis on safety, other useful applications of V2V communication include but are not limited to traffic and routing, weather, construction and road hazard alerts, as well as advertisement and entertainment. The core of V2V communication relies on the efficient dispersion of relevant data through wireless broadcast protocols for these varied applications. The challenges of vehicular networks demand an adaptive broadcast protocol capable of handling diverse applications. This research work illustrates the design of a wireless broadcast protocol that is context-aware and adaptive to vehicular environments taking into consideration vehicle density, road topology, and type of data to be disseminated. The context-aware hybrid data dissemination scheme combines store-and-forward and multi-hop broadcasts, capitalizing on the strengths of both these categories and mitigates the weaknesses to deliver data with maximum efficiency to a widest possible reach. This protocol is designed to work in both urban and highway mobility models. The behavior and performance of the hybrid data dissemination scheme is studied by varying the broadcast zone radius, aggregation ratio, data message size and frequency of the broadcast messages. Optimal parameters are determined and the protocol is then formulated to become adaptive to node density by keeping the field size constant and increasing the number of nodes. Adding message priority levels to propagate safety messages faster and farther than non-safety related messages is the next context we add to our adaptive protocol. We dynamically
set the broadcast region to use multi-hop which has lower latency to propagate
safety-related messages. Extensive simulation results have been obtained using realistic vehicular network scenarios. Results show that Context-Aware Hybrid Data Dissemination Protocol benefits from the low latency characteristics of multi-hop broadcast and low bandwidth consumption of store-and-forward. The protocol is adaptive to both urban and highway mobility models.