31-10-2012, 03:48 PM
Cooperative routing in dynamic wireless networks
Energy-Efficient Protocol for Cooperative Networks.pdf (Size: 858.38 KB / Downloads: 25)
Abstract—
In cooperative networks, transmitting and receiving
nodes recruit neighboring nodes to assist in communication. We
model a cooperative transmission link in wireless networks as
a transmitter cluster and a receiver cluster. We then propose a
cooperative communication protocol for establishment of these
clusters and for cooperative transmission of data. We derive the
upper bound of the capacity of the protocol, and we analyze the
end-to-end robustness of the protocol to data-packet loss, along
with the tradeoff between energy consumption and error rate. The
analysis results are used to compare the energy savings and the
end-to-end robustness of our protocol with two non-cooperative
schemes, as well as to another cooperative protocol published
in the technical literature. The comparison results show that,
when nodes are positioned on a grid, there is a reduction in the
probability of packet delivery failure by two orders of magnitude
for the values of parameters considered. Up to 80% in energy
savings can be achieved for a grid topology, while for random node
placement our cooperative protocol can save up to 40% in energy
consumption relative to the other protocols. The reduction in
error rate and the energy savings translate into increased lifetime
of cooperative sensor networks.
Index Terms—Clustering, cooperative networks energy-efficient
protocols, cooperative transmission, sensor networks.
I. INTRODUCTION
I N WIRELESS sensor networks, nodes have limited energy
resources and, consequently, protocols designed for sensor
networks should be energy-efficient. One recent technology that
allows energy saving is cooperative transmission. In cooperative
transmission, multiple nodes simultaneously receive, decode,
and retransmit data packets. In this paper, as opposed to previous
works, we use a cooperative communication model with
multiple nodes on both ends of a hop and with each data packet
being transmitted only once per hop.
In our model of cooperative transmission, every node on the
path from the source node to the destination node becomes
a cluster head, with the task of recruiting other nodes in its
neighborhood and coordinating their transmissions.
RELATED WORK
The problem of energy-efficient routing in wireless networks
that support cooperative transmission was formulated in [1].
In [1], two energy-efficient approximation algorithms are presented
for finding a cooperative route in wireless networks. The
two algorithms for finding one cooperative route are designed
such that each hop consists of multiple sender nodes to one receiver
node. One of the algorithms (CAN) is used throughout
this paper for performance comparison.
The works in [2]–[5] focus on MAC layer design for networks
with cooperative transmission. In [2], when no acknowledgement
is received from the destination after timeout, the cooperative
nodes, which correctly received the data, retransmit
it. Only one cooperative node retransmits at any time, and the
other cooperative nodes flush their copy once they hear the retransmission.
Hence, this work focuses on reducing the transmission
errors, without benefiting from the energy savings of simultaneous
transmissions. In [3], high-rate nodes help low-rate
nodes by forwarding their transmissions. The work describes
how the helper nodes are discovered. Similarly to [2], only one
node can cooperate at a time, and simultaneous transmissions
are not used, hence the energy savings are not considered. Likewise,
in [4] only one node cooperates in forwarding the data.
The IEEE 802.11 protocol was extended in [5] to support multiple
antennas per node. The works in [6]–[10] use the model
with only one helper node at each hop in addition to the sender
and the receiver. The model in [11] utilizes multiple nodes to
forward the data, but only one node can transmit at any time.
Several good tutorial papers on cooperative transmission have
been published (e.g., [12] and [13]). As most of the current
works look at the cooperation from the transmitter side only, our
paper differs in that our communication model includes groups
of cooperating nodes at both sides of the transmission link with
the purpose of reduction in energy consumption.
Similar to multiple-input–multiple-output (MIMO) communications,
the main gain of cooperative transmission comes from
ELHAWARY AND HAAS: ENERGY-EFFICIENT PROTOCOL FOR COOPERATIVE NETWORKS 563
the fact that there is limited correlation between communications
from different transmitters. The increase in the degree of
freedom of signal detection decreases the bit error rate [14].
Consequently, the gain of cooperation is similar in nature to
what is achieved by MIMO techniques. Of course, there are substantial
differences in the environment and in the operation between
cooperative transmission and MIMO.