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Title:
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Improved Achievable Rates for User Cooperation and Relay Channels |
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Author:
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Khojastepour, Mohammad; Sabharwal, Ashutosh; Aazhang, Behnaam
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Type:
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Conference Paper |
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Keywords:
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relay channel; user cooperation channel |
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Citation:
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M. Khojastepour, A. Sabharwal and B. Aazhang,"Improved Achievable Rates for User Cooperation and Relay Channels," in IEEE Symposium on Information Theory, |
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Abstract:
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In this paper, we derive a new achievable rate region for the user cooperation channel, which exceeds the
best known result for this channel [Wil83]. Since the user cooperation channel includes many other known
channels as a special case, the new rate region provides an improved achievable rates for many of the special
cases (discussed later). The most notable example is that of the Gaussian relay channel [CG79], for which
we present a new closed form inner bound higher than the only known result (Theorem 5 in [CG79]).
The basic idea of the proposed encoding and decoding scheme is easier to grasp for a simpler case, the
relay channel, by keeping in mind the following Markovian scheme from [CG79]. In Markovian encoding, the
relay decodes everything in the current block and uses it to establish a basis for common information sent
from the transmitter and relay in the next block. The fact that Markovian coding does not achieve capacity
depends on to two inter-related facts: (a) the relay decodes each codeword completely, and (b) discards the
residual after decoding; this limits the relay channel capacity to the capacity between the source and the
relay.
Our proposed encoding does not require the relay to necessarily decode the whole codeword from the
transmitter. In addition, the relay \source" encodes the whole received signal some implicit embedding of
with the decoded information. Note that the signal transmitted by the relay is not separable into a source
code and a channel code. For the user cooperation channel, the above operation is performed by both users
for each others' signal. |
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Date Published:
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2004-06-01 |
