12-10-2012, 01:12 PM
TOPOLOGY CONTROL IN MOBILE AD HOC NETWORKS WITH COOPERATIVE COMMUNICATIONS
[attachment=36176]
ABSTRACT
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.
INTRODUCTION
The demand for speed in wireless networks is
continuously increasing. Recently, cooperative
wireless communication has received tremendous
interests as an untapped means for improving
the performance of information transmission
operating over the ever-challenging wireless
medium. 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 [1]. By
exploiting the broadcast nature of the wireless
channel, cooperative communication allows singlsingle-
antenna radios to share their antennas to
form a virtual antenna array, and offers significant
performance enhancements. This promising
technique has been considered in the IEEE
802.16j standard, and is expected to be integrated
into Third Generation Partnership Project
(3GPP) Long Term Evolution (LTE) multihop
cellular networks [2].
COOPERATIVE COMMUNICATIONS
Cooperative communication typically refers to a
system where users share and coordinate their
resources to enhance the information transmission
quality. It is a generalization of the relay
communication, in which multiple sources also
serve as relays for each other. Early study of
relaying problems appears in the information
theory community to enhance communication
between the source and destination [7]. Recent
tremendous interests in cooperative communications
are due to the increased understanding of
the benefits of multiple antenna systems [1].
Although multiple-input multiple-output
(MIMO) systems have been widely acknowledged.
THE CAPACITY OF MANETS
As a key indicator for the information delivery
ability, network capacity has attracted tremendous
interests since the landmark paper by
Gupta and Kumar [9]. There are different definitions
for network capacity. Two types of network
capacity are introduced in [9]. The first
one is transport capacity, which is similar to the
total one-hop capacity in the network. It takes
distance into consideration and is based on the
sum of bit-meter products. One bit-meter means
that one bit has been transported to a distance
of one meter toward its destination. Another
type of capacity is throughput capacity, which is
based on the information capacity of a channel.
Obviously, it is the amount of all the data successfully
transmitted during a unit time. It has
been shown that the capacity in wireless ad hoc
networks is limited. In traditional MANETs
without cooperative communications, the capacity
is decreased as the number of nodes in the
network increases. Asymptotically, the per-node
throughput declines to zero when the number of
nodes approaches to infinity [9]. In this study,
we adopt the second type of definition.
SIMULATION RESULTS AND DISCUSSIONS
In this section, the performance of the proposed
scheme is illustrated using computer simulations.
We consider a MANET with 30 nodes randomly
deployed in a 800 × 800 m2 area. The number of
nodes is changed in the simulations. The channels
follow a Raleigh distribution. We compare
the performance of the proposed scheme with
that of an existing well-known topology control
scheme [10], called LLISE, which only considers
traditional multi-hop transmissions without
cooperative communications and preserves the
minimum interference path for each neighbor
link locally. We also show the worst network
capacity among all the topology configurations
for comparison. The original topology is shown
in Fig. 2, where links exist whenever the associated
two end nodes are within transmission
range of each other. It is clear that this topology
lacks any physical layer cooperative communications.
Figure 3 shows the resulting topology
using the proposed COCO topology control
scheme. In Fig. 3, the solid lines denote traditional
direct transmissions and multi-hop transmissions,
and the dash lines denote links
involved in cooperative communications. As we
can see from Fig. 3, to maximize the network
capacity of the MANET, many links in the network
are involved in cooperative communications.
One example of two-phase cooperative
communications is shown in the top left corner
of the figure.
[attachment=36176]
ABSTRACT
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.
INTRODUCTION
The demand for speed in wireless networks is
continuously increasing. Recently, cooperative
wireless communication has received tremendous
interests as an untapped means for improving
the performance of information transmission
operating over the ever-challenging wireless
medium. 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 [1]. By
exploiting the broadcast nature of the wireless
channel, cooperative communication allows singlsingle-
antenna radios to share their antennas to
form a virtual antenna array, and offers significant
performance enhancements. This promising
technique has been considered in the IEEE
802.16j standard, and is expected to be integrated
into Third Generation Partnership Project
(3GPP) Long Term Evolution (LTE) multihop
cellular networks [2].
COOPERATIVE COMMUNICATIONS
Cooperative communication typically refers to a
system where users share and coordinate their
resources to enhance the information transmission
quality. It is a generalization of the relay
communication, in which multiple sources also
serve as relays for each other. Early study of
relaying problems appears in the information
theory community to enhance communication
between the source and destination [7]. Recent
tremendous interests in cooperative communications
are due to the increased understanding of
the benefits of multiple antenna systems [1].
Although multiple-input multiple-output
(MIMO) systems have been widely acknowledged.
THE CAPACITY OF MANETS
As a key indicator for the information delivery
ability, network capacity has attracted tremendous
interests since the landmark paper by
Gupta and Kumar [9]. There are different definitions
for network capacity. Two types of network
capacity are introduced in [9]. The first
one is transport capacity, which is similar to the
total one-hop capacity in the network. It takes
distance into consideration and is based on the
sum of bit-meter products. One bit-meter means
that one bit has been transported to a distance
of one meter toward its destination. Another
type of capacity is throughput capacity, which is
based on the information capacity of a channel.
Obviously, it is the amount of all the data successfully
transmitted during a unit time. It has
been shown that the capacity in wireless ad hoc
networks is limited. In traditional MANETs
without cooperative communications, the capacity
is decreased as the number of nodes in the
network increases. Asymptotically, the per-node
throughput declines to zero when the number of
nodes approaches to infinity [9]. In this study,
we adopt the second type of definition.
SIMULATION RESULTS AND DISCUSSIONS
In this section, the performance of the proposed
scheme is illustrated using computer simulations.
We consider a MANET with 30 nodes randomly
deployed in a 800 × 800 m2 area. The number of
nodes is changed in the simulations. The channels
follow a Raleigh distribution. We compare
the performance of the proposed scheme with
that of an existing well-known topology control
scheme [10], called LLISE, which only considers
traditional multi-hop transmissions without
cooperative communications and preserves the
minimum interference path for each neighbor
link locally. We also show the worst network
capacity among all the topology configurations
for comparison. The original topology is shown
in Fig. 2, where links exist whenever the associated
two end nodes are within transmission
range of each other. It is clear that this topology
lacks any physical layer cooperative communications.
Figure 3 shows the resulting topology
using the proposed COCO topology control
scheme. In Fig. 3, the solid lines denote traditional
direct transmissions and multi-hop transmissions,
and the dash lines denote links
involved in cooperative communications. As we
can see from Fig. 3, to maximize the network
capacity of the MANET, many links in the network
are involved in cooperative communications.
One example of two-phase cooperative
communications is shown in the top left corner
of the figure.