VIBRANT TOPOLOGY GOVERNOR IN MOBILE AD HOC NETWORKS WITH COOPERATIVE COMMUNICATIONS

International Journal of Technical Research and Applications e-ISSN: 2320-8163,
www.ijtra.com Volume 2, Issue 3 (May-June 2014), PP. 119-123
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VIBRANT TOPOLOGY GOVERNOR IN MOBILE
AD HOC NETWORKS WITH COOPERATIVE
COMMUNICATIONS
M.CHARLES AROCKIARAJ
HEAD, Asst.Professor, Dept. Of Computer science
Arakkonam Arts and Science College, Arakkonam-631003
Abstract: Cooperative communication has emerged as a new
dimension of diversity to emulate the strategies designed for
multiple antenna systems, since a wireless mobile device may not
be able to support multiple transmit antennas due to size, cost,
or hardware limitations. Capacity optimization of the wireless
network is performed by making changes in the physical layer of
the network. In this article, we propose a Capacity-Optimized
Cooperative (COCO) topology control scheme to improve the
network capacity in MANETs by jointly considering both upper
layer network capacity and physical layer cooperative
communications. Simulations in the network simulator are
performed to show the efficiency of the system.
Cooperative communication has received tremendous interest
for wireless networks. Most existing works on cooperative
communications are focused on link-level physical layer issues.
Consequently, the impacts of cooperative communications on
network-level upper layer issues, such as topology control,
routing and network capacity, are largely ignored. In this
article, we propose a Capacity-Optimized Cooperative (COCO)
topology control scheme to improve the network capacity in
MANETs by jointly considering both upper layer network
capacity and physical layer cooperative communications.
Through simulations, we show that physical layer cooperative
communications have significant impacts on the network
capacity, and the proposed topology control scheme can
substantially improve the network capacity in MANETs with
cooperative communications.
Key words— Capacity-Optimized Cooperative (COCO),
MANETs, topology control, MIMO (Multiple-Input, Multiple-
Output)
I. INTRODUCTION
As more and more speed of data transmission is an ever
demanding aspect of wireless network. As per previous studies
in simple wireless networks mobile agents may not be able to
support multiple transmit antennas due to the size, cost and
hardware limitations. Using cooperative communication single
antennas mobiles in multi-user environment share their
antennas in a manner that creates virtual MIMO system and
take the advantages MIMO (Multiple-Input, Multiple-
Output) systems. A problem of end-to-end delay is caused by
Fading (signal attenuation) due to multi-path effects,
shadowing and interference etc. in simple wireless networks,
in this situation some packets can be lost and needs to be
retransmitted. The transmission and spatial diversity that is
achieved by cooperative communication helps to reduce the
signal attenuation and delay .
A mobile ad hoc network (MANET) is a self-configuring
infrastructure less network of mobile devices connected by
wireless. Ad hoc is Latin and means "for this purpose. Each
device in a MANET is free to move independently in any
direction, and will therefore change its links to other devices
frequently. Each must forward traffic unrelated to its own use,
and therefore be a router. The primary challenge in building a
MANET is equipping each device to continuously maintain
the information required to properly route traffic. Such
networks may operate by themselves or may be connected to
the larger Internet. MANETs are a kind of Wireless ad hoc
network that usually has a routable networking environment
on top of a Link Layer ad hoc network.
In mobile ad hoc wireless communication, each node of
the network has a potential of varying the topology through
the adjustment of its power transmission in relation to other
nodes in the neighborhood. In contrast, wired networks have
fixed established pre-configured infrastructure with centralized
network management system structure in place. Therefore, the
fundamental reason for the topology control scheme in
MANET is to provide a control mechanism that maintains the
network connectivity and performance optimization by
prolonging network lifetime and maximizing network
throughput. A MANET topology can depend on
uncontrollable factors such as node mobility, weather,
interference, noise as well as controllable factors such as
transmission power, directional antennas and multi-channel
communications. A bad topology can impact negatively on the
network capacity by limiting spatial reuse capability of the
communication channel and also can greatly undermine the
robustness of the network. Where network capacity means
the bandwidth and ability for it to be used for communication.
A network partitioning can occur in a situation where the
network topology becomes too sparse. Similarly, a network
which is too dense is prone to interference at the medium
access
(MAC) layer, the physical layer of the network. So the
network should neither be too dense nor too sparse for
efficient communication amongst nodes to take place.
The problem identified in contemporary research literature
pertaining to topology control in MANET is that most of the
topology control algorithms do not achieve reliable and
guaranteed network connectivity.
II. TRANSMISSION IN MANETS:
With physical layer cooperative communications, there are
three transmission manners in MANETs: direct transmissions,
multi-hop transmissions and cooperative transmissions. Direct

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transmissions and multi-hop transmissions can be regarded as
special types of cooperative transmissions. A direct
transmission utilizes no relays while a multi-hop transmission
does not combine signals at the destination. In Fig. 1c, the
cooperative channel is a virtual multiple-input single-output
(MISO) channel, where spatially distributed nodes are
coordinated to form a virtual antenna to emulate multi antenna
transceivers.
Cooperative Communications:
Cooperative transmissions via a cooperative diversity
occupying two consecutive slots. The destination combines
the two signals from the source and the relay to decode the
information. Cooperative communications are due to the
increased understanding of the benefits of multiple antenna
systems. Although multiple-input multiple output (MIMO)
systems have been widely acknowledged, it is difficult for
some wireless mobile devices to support multiple antennas due
to the size and cost constraints. Recent studies show that
cooperative communications allow single antenna devices to
work together to exploit the spatial diversity and reap the
benefits of MIMO systems such as resistance to fading, high
throughput, low transmitted power, and resilient networks.
Multi-hop transmission can be illustrated using two-hop
transmission. When two-hop transmission is used, two time
slots are consumed in the first slot, messages are transmitted
from the source to the relay, and the messages will be
forwarded to the destination in the second slot. The outage
capacity of this two-hop transmission
CAPACITY-OPTIMIZED COOPERATIVE (COCO)
A Capacity-Optimized Cooperative (COCO) topology
control scheme to improve the network capacity in MANETs
by jointly optimizing transmission mode selection, relay node
selection, and interference control in MANETs with
cooperative communications. Through simulations, we show
that physical layer cooperative communications have
significant impacts on the network capacity, and the proposed
topology control scheme can substantially improve the
network capacity in MANETs with cooperative
communications.
III. PROBLEM STATEMENT
Due to the lack of centralized control, nodes in MANETs
cooperate with each other to achieve a common goal. The
major activities involved in self-organization are neighbor
discovery, topology organization, and topology reorganization.
Network topology describes the connectivity information of
the entire network, including the nodes in the network and the
connections between them. Topology control is very important
for the overall performance of a MANET
For example, to maintain reliable network connectivity,
nodes in MANETs may work at the maximum radio power,
which results in high nodal degree and long link distance, but
more interference is introduced into the network and much less
throughput per node can be obtained. Using topology control,
a node carefully selects a set of its neighbors to establish
logical data links and dynamically adjust its transmit power
accordingly, so as to achieve high throughput in the network
while keeping the energy consumption low.
Existing System
Although some works have been done on cooperative
communications, most existing works are focused on link-
level physical layer issues, such as outage probability and
outage capacity. Consequently, the impacts of cooperative
communications on network-level upper layer issues, such as
topology control, routing and network capacity, are largely
ignored. Indeed, most of current works on wireless networks
attempt to create, adapt, and manage a network on a maze of
point-to-point non-cooperative wireless links. Such
architectures can be seen as complex networks of simple links.
Proposed System
We propose a Capacity-Optimized Cooperative (COCO)
topology control scheme to improve the network capacity in
MANETs by jointly optimizing transmission mode selection,
relay node selection, and interference control in MANETs
with cooperative communications. Through simulations, we
show that physical layer cooperative communications have
significant impacts on the network capacity, and the proposed
topology control scheme can substantially improve the
network capacity in MANETs with the use of Cooperative
communications.
IV. DESIGN MODULES:
1. Network Scenario Creation
In communication networks, a topology is a usually
schematic description of the arrangement of a network,
including its nodes and connecting lines. There are two ways
of defining network geometry: the physical topology and the
logical (or signal) topology. The physical topology of a
network is the actual geometric layout of workstations.
Logical (or signal) topology refers to the nature of the paths
the signals follow from node to node. The number nodes is
going to participate in the simulation is decided. Here we
conduct experiments to a group of wireless nodes in a network
that operates on the AODV protocol. We hence use only a
logical topology as it is wireless environment.
2. Node Configuration
Node creation is nothing but the creation of the wireless
nodes in the network scenario that is decided. Node
configuration essentially consists of defining the different
node characteristics before creating them. They may consist of

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the type of addressing structure used in the simulation,
defining the network components for mobile nodes, turning on
or off the trace options at Agent/Router/MAC levels, selecting
the type of adhoc routing protocol for wireless nodes or
defining their energy model. Simulator::node-config
accommodates flexible and modular construction of different
node definitions within the same base Node class. For
instance, to create a mobile node capable of wireless
communication, one no longer needs a specialized node
creation command.
V. CO-OPERATIVE COMMUNICATIONS
The basic idea of cooperative relaying is that some nodes,
which overheard the information transmitted from the source
node, relay it to the destination node instead of treating it as
interference. Since the destination node receives multiple
independently faded copies of the transmitted information
from the source node and relay nodes, cooperative diversity is
achieved.
Relaying could be implemented using two common
strategies:
• Amplify-and-forward:
In amplify-and-forward, the relay nodes simply boost
the energy of the signal received from the sender and
retransmit it to the receiver.
• Decode-and-forward:
In decode-and-forward, the relay nodes will perform
physical-layer decoding and then forward the decoding result
to the destinations.
If multiple nodes are available for cooperation, their
antennas can employ a space-time code in transmitting the
relay signals. It is shown that cooperation at the physical layer
can achieve full levels of diversity similar to a MIMO system,
and hence can reduce the interference and increase the
connectivity of wire.
VI. TOPOLOGY CONTROL
The topology in a MANET is controllable by adjusting
some parameters such as the transmission power, channel
assignment, etc. In general, topology control is such a scheme
to determine where to deploy the links and how the links work
in wireless networks to form a good network topology, which
will optimize the energy consumption, the capacity of the
network, or end-to-end routing performance.
Topology control focuses on network connectivity with the
link information provided by MAC and physical layers. There
are two aspects in a network topology: network nodes and the
connection links among them. In general, a MANET can be
mapped into a graph G(V, E), where V is the set of nodes in
the network and E is the edge set representing the wireless
links. A link is generally composed of two nodes which are in
the transmission range of each other in classical MANETs.
The topology of such a classical MANET is parameterized by
some controllable parameters, which determine the existence
of wireless links directly. In traditional MANETs without
cooperative communications, these parameters can be transmit
power, antenna directions, etc. In MANETs with cooperative
communications, topology control also needs to determine the
transmission manner (i.e., direct transmission, multi-hop
transmission, or cooperative transmission) and the relay node
if cooperative transmission is in use. As topology control is to
determine the existence of wireless links subject to network
connectivity, the general topology control problem can be
expressed as G* = arg max f(G), (1) s.t. network connectivity.
The problem Eq. 1 uses the original network topology G,
which contains mobile nodes and link connections, as the
input. According to the objective function, a better topology
G*(V, E*) will be constructed as the output of the algorithm.
G* should contain all mobile nodes in G, and the link
connections E* should preserve network connectivity without
partitioning the network. The structure of resulting topology is
strongly related to the optimization objective function, which
is f(G) in Eq. 1. It is difficult to collect the entire network
information in MANETs. Therefore, it is desirable to design a
distributed algorithm, which generally requires only local
knowledge, and the algorithm is run at every node
independently. Consequently, each node in the network is
responsible for managing the links to all its neighbors only. If
all the neighbor connections are preserved, the end-to-end
connectivity is then guaranteed. Given a neighborhood graph
GN (VN, EN) with N neighboring nodes, we can define a
distributed topology control problem as G*N = arg max f(GN),
s.t. connectivity to all the neighbors. The objective function
f(G) in Eq. 1 is critical to topology control problems. Network
capacity is an important objective function. Our previous work
[8] shows that topology control can affect network capacity
significantly. In the following section, we present a topology
control scheme with the objective of optimizing network
capacity in MANETs with cooperative communications
VII. PERFORMANCE EVALUATION:
During simulation time the events are traced by using the
trace files. The performance of the network is evaluated by
executing the trace files. The events are recorded into trace
files while executing record procedure. In this procedure, we
trace the events like packet received, Packets lost, Last packet
received time etc. These trace values are write into the trace
files. This procedure is recursively called for every 0.05 ms.
so, trace values recorded for every 0.05 ms. The simulated
results support the performance of the system described
theoretically.
SIMULATION

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VIII. CONCLUSION
In this article, we have introduced physical layer
cooperative communications, topology control, and network
capacity in MANETs. To improve the network capacity of
MANETs with cooperative communications, we have
proposed a Capacity Optimized Cooperative (COCO)
topology control scheme that considers both upper layer
network capacity and physical layer relay selection in
cooperative communications. Simulation results have shown
that physical layer cooperative communications techniques
have significant impacts on the network capacity, and the pro-
posed topology control scheme can substantially improve the
network capacity in MANETs with cooperative
communications.
REFERENCES
[1] J. Laneman, D. Tse, and G. Wornell, “Cooperative Diver-sity
in Wireless Networks: Efficient protocols and Out-age
Behavior,” IEEE Trans. Info. Theory, vol. 50, no. 12, 2004,
pp. 3062–80.
[2] P. H. J. Chong et al., “Technologies in Multihop Cellular
Network,” IEEE Commun. Mag., vol. 45, Sept. 2007, pp. 64–
65.
[3] K. Woradit et al., “Outage Behavior of Selective Relay-ing
Schemes,” IEEE Trans. Wireless Commun., vol. 8, no. 8,
2009, pp. 3890–95.
[4] Y. Wei, F. R. Yu, and M. Song, “Distributed Optimal Relay
Selection in Wireless Cooperative Networks with Finite-State
Markov Channels,” IEEE Trans. Vehic. Tech., vol. 59, June
2010, pp. 2149–58.
[5] Q. Guan et al., “Capacity-Optimized Topology Control for
MANETs with Cooperative Communications,” IEEE Trans.
Wireless Commun., vol. 10, July 2011, pp. 2162–70.

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