Cooperative Communication Networks
an abstract by Mohammad Amir Khojastepour
The primary challenge in wireless networks, unlike wireline networks,
is the existence of interference and channel variations (fading). Having
more users at higher data rates means that current point-to-po9int networks
will not scale. To engineer a scalable network, a new paradigm is needed
to exploit different network characteristics. We show that cooperation
between users in the network can effectively exchange possible interferences
from other users for useful information.
In this thesis, we explore the problem of source and channel coding over
wireless networks, ranging from theoretical information analysis to code
design and practical implementation issues. We show that significant
gains in throughput can be achieved through network coding. Despite the
importance of the problem and the work already done in this area, little
is known about network coding and the optimal choice of relaying function
in the intermediate nodes. A clear example is the problem of optimal
communication over the relay channel, the simplest form of a network,
which has been an outstanding question for the last three decades.
In this thesis, we propose a new approach to network coding that
improves upon the best-known coding schemes of many dB. Specifically,
we develop two main coding techniques: the estimate-forward and
the scale-forward coding schemes. We show that by using the new
coding techniques, higher rates than those previously achieved
are possible for the relay channel. In particular, the scale-forward
scheme provides a fresh look at the current use of linear relaying
functions. While the previous use of linear relaying functions
has never achieved significant gain over existing techniques, the
scale-forward coding scheme presents an extremely simple and implementable
choice of linear relaying function whose achievable rate surpasses
all previously known coding techniques for many cases of interest.
Furthermore, the new coding technique has proved its strength in the
presence of channel variation, i.e., in the Rayleigh fading environment,
which is the most commonly used model for the wireless channel. To this
end, we derive the exact capacity of the ergodic fading relay channel
for many channel conditions of interest, and also present a coding scheme
which nearly achieves the universal minimum bound on outage probability
for the block fading relay channel. This is the first capacity result
for the wireless fading relay channel.
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