4,957 research outputs found
Relaying for Multiuser Networks in the Absence of Codebook Information
This work considers relay assisted transmission for multiuser networks when
the relay has no access to the codebooks used by the transmitters. The relay is
called oblivious for this reason. Of particular interest is the generalized
compress-and-forward (GCF) strategy, where the destinations jointly decode the
compression indices and the transmitted messages, and their optimality in this
setting. The relay-to-destination links are assumed to be out-of-band with
finite capacity. Two models are investigated: the multiple access relay channel
(MARC) and the interference relay channel (IFRC). For the MARC with an
oblivious relay, a new outerbound is derived and it is shown to be tight by
means of achievability of the capacity region using GCF scheme. For the IFRC
with an oblivious relay, a new strong interference condition is established,
under which the capacity region is found by deriving a new outerbound and
showing that it is achievable using GCF scheme. The result is further extended
to establish the capacity region of M-user MARC with an oblivious relay, and
multicast networks containing M sources and K destinations with an oblivious
relay.Comment: submitted to IEEE Transactions on Information Theor
Using Channel Output Feedback to Increase Throughput in Hybrid-ARQ
Hybrid-ARQ protocols have become common in many packet transmission systems
due to their incorporation in various standards. Hybrid-ARQ combines the normal
automatic repeat request (ARQ) method with error correction codes to increase
reliability and throughput. In this paper, we look at improving upon this
performance using feedback information from the receiver, in particular, using
a powerful forward error correction (FEC) code in conjunction with a proposed
linear feedback code for the Rayleigh block fading channels. The new hybrid-ARQ
scheme is initially developed for full received packet feedback in a
point-to-point link. It is then extended to various different multiple-antenna
scenarios (MISO/MIMO) with varying amounts of packet feedback information.
Simulations illustrate gains in throughput.Comment: 30 page
When Can a Relay Reduce End-to-End Communication Delay?
The impact of relaying on the latency of communication in a relay channel is
studied. Both decode-forward (DF) and amplify-forward (AF) are considered, and
are compared with the point-to-point (P2P) scheme which does not use the relay.
The question as to whether DF and AF can decrease the latency of communicating
a number of bits with a given reliability requirement is addressed. Latency
expressions for the three schemes are derived. Although both DF and AF use a
block-transmission structure which sends the information over multiple
transmission blocks, they can both achieve latencies lower that P2P. Conditions
under which this occurs are obtained. Interestingly, these conditions are more
strict when compared to the conditions under which DF and AF achieve higher
information-theoretic rates than P2P.Comment: 6 pages, 4 figure
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