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http://hdl.handle.net/1813/3294
Title:  Distributed Cooperative Communication in LargeScale Wireless Networks 
Authors:  Sirkeci, Birsen 
Keywords:  cooperative communication distributed protocols 
Issue Date:  19Jul2006 
Abstract:  Cooperative communication employs distributed transmission resources
at the physical layer as a single radio with spatial diversity in
order to increase the performance of wireless networks. However,
node cooperation entails large communication overhead, and
distributed protocols that eliminate or reduce the communication
overhead are desirable. This dissertation proposes distributed
cooperative schemes for wireless ad hoc networks and develops new
methods to analyze their performance.
First, we study the behavior of distributed cooperative transmission
in wireless networks for both pointtopoint and broadcasting
scenarios. In particular, we analyze the effect of critical network
parameters on the number of nodes reached by cooperative
transmission. We show that there exists a phase transition in the
network behavior: if the decoding threshold is below a critical
value, the message is delivered to the intended recipient(s).
Otherwise, only a fraction of the nodes is reached. Our approach is
based on the idea of continuum approximation, which yields
closedform expressions that are accurate when the network density
is high.
We next study the optimal power allocation problem for the
cooperative broadcast in dense largescale networks. The
transmission order (schedule) and the transmission powers of the
relays are designed so that the message reaches the entire network
with the minimum possible total power consumption. In general,
finding the best scheduling in cooperative broadcast is known to be
an NPcomplete problem. We show that the optimal scheduling problem
can be solved for dense networks, which can be expressed as a
continuum of nodes.
Finally, we study the design of distributed spacetime codes for
cooperative communication. With few exceptions, most of the
literature on the subject proposes coding rules such that either
internode communication or a central control unit is required for
code assignment. We introduce novel randomized strategies that
decentralize the transmission of a space time code from a set of
distributed relays. Our simple idea is to let each node transmit an
independent random linear combination of the codewords that would
have been transmitted by all the elements of a multiantenna system.
We show that the proposed scheme achieves the optimal diversity
order. 
URI:  http://hdl.handle.net/1813/3294 
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