17-05-2014, 02:55 PM
A Neighbor Coverage-Based Probabilistic Rebroadcast for Reducing Routing Overhead in Mobile Ad Hoc Networks
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Abstract
Due to high mobility of nodes in mobile ad hoc networks (MANETs), there exist frequent link breakages which lead to
frequent path failures and route discoveries. The overhead of a route discovery cannot be neglected. In a route discovery,
broadcasting is a fundamental and effective data dissemination mechanism, where a mobile node blindly rebroadcasts the first
received route request packets unless it has a route to the destination, and thus it causes the broadcast storm problem. In this paper,
we propose a neighbor coverage-based probabilistic rebroadcast protocol for reducing routing overhead in MANETs. In order to
effectively exploit the neighbor coverage knowledge, we propose a novel rebroadcast delay to determine the rebroadcast order, and
then we can obtain the more accurate additional coverage ratio by sensing neighbor coverage knowledge. We also define a
connectivity factor to provide the node density adaptation. By combining the additional coverage ratio and connectivity factor, we set a
reasonable rebroadcast probability. Our approach combines the advantages of the neighbor coverage knowledge and the probabilistic
mechanism, which can significantly decrease the number of retransmissions so as to reduce the routing overhead, and can also
improve the routing performance.
INTRODUCTION
MOBILE ad hoc networks (MANETs) consist of a
collection of mobile nodes which can move freely.
These nodes can be dynamically self-organized into
arbitrary topology networks without a fixed infrastructure.
One of the fundamental challenges of MANETs is the
design of dynamic routing protocols with good perfor-
mance and less overhead. Many routing protocols, such as
Ad hoc On-demand Distance Vector Routing (AODV) [1]
and Dynamic Source Routing (DSR) [2], have been
proposed for MANETs. The above two protocols are on-
demand routing protocols, and they could improve the
scalability of MANETs by limiting the routing overhead
when a new route is requested [3]. However, due to node
mobility in MANETs, frequent link breakages may lead to
frequent path failures and route discoveries, which could
increase the overhead of routing protocols and reduce the
packet delivery ratio and increasing the end-to-end delay
[4]. Thus, reducing the routing overhead in route discovery
is an essential problem.
RELATED WORK
Broadcasting is an effective mechanism for route discovery,
but the routing overhead associated with the broadcasting
can be quite large, especially in high dynamic networks [9].
Ni et al. [5] studied the broadcasting protocol analytically
and experimentally, and showed that the rebroadcast is
very costly and consumes too much network resource. The
broadcasting incurs large routing overhead and causes
many problems such as redundant retransmissions, con-
tentions, and collisions [5]. Thus, optimizing the broad-
casting in route discovery is an effective solution to improve
the routing performance. Haas et al. [10] proposed a gossip-
based approach, where each node forwards a packet with a
probability. They showed that gossip-based approach can
save up to 35 percent overhead compared to the flooding.
However, when the network density is high or the traffic
load is heavy, the improvement of the gossip-based
approach is limited [9]. Kim et al. [8] proposed a
probabilistic broadcasting scheme based on coverage area
and neighbor confirmation.
Simulation Environment
In order to evaluate the performance of the proposed NCPR
protocol, we compare it with some other protocols using the
NS-2 simulator. Broadcasting is a fundamental and effective
data dissemination mechanism for many applications in
MANETs. In this paper, we just study one of the
applications: route request in route discovery. In order to
compare the routing performance of the proposed NCPR
protocol, we choose the Dynamic Probabilistic Route
Discovery [12] protocol which is an optimization scheme
for reducing the overhead of RREQ packet incurred in
route discovery in the recent literature, and the conven-
tional AODV protocol.
CONCLUSION
In this paper, we proposed a probabilistic rebroadcast
protocol based on neighbor coverage to reduce the routing
overhead in MANETs. This neighbor coverage knowledge
includes additional coverage ratio and connectivity factor.
We proposed a new scheme to dynamically calculate the
rebroadcast delay, which is used to determine the forward-
ing order and more effectively exploit the neighbor cover-
age knowledge. Simulation results show that the proposed
protocol generates less rebroadcast traffic than the flooding
and some other optimized scheme in literatures. Because of
less redundant rebroadcast, the proposed protocol mitigates
the network collision and contention, so as to increase the
packet delivery ratio and decrease the average end-to-end
delay. The simulation results also show that the proposed
protocol has good performance when the network is in high
density or the traffic is in heavy load.