1,572 research outputs found
On the Noisy Feedback Capacity of Gaussian Broadcast Channels
It is well known that, in general, feedback may enlarge the capacity region
of Gaussian broadcast channels. This has been demonstrated even when the
feedback is noisy (or partial-but-perfect) and only from one of the receivers.
The only case known where feedback has been shown not to enlarge the capacity
region is when the channel is physically degraded (El Gamal 1978, 1981). In
this paper, we show that for a class of two-user Gaussian broadcast channels
(not necessarily physically degraded), passively feeding back the stronger
user's signal over a link corrupted by Gaussian noise does not enlarge the
capacity region if the variance of feedback noise is above a certain threshold.Comment: 5 pages, 3 figures, to appear in IEEE Information Theory Workshop
2015, Jerusale
Cooperative Relay Broadcast Channels
The capacity regions are investigated for two relay broadcast channels
(RBCs), where relay links are incorporated into standard two-user broadcast
channels to support user cooperation. In the first channel, the Partially
Cooperative Relay Broadcast Channel, only one user in the system can act as a
relay and transmit to the other user through a relay link. An achievable rate
region is derived based on the relay using the decode-and-forward scheme. An
outer bound on the capacity region is derived and is shown to be tighter than
the cut-set bound. For the special case where the Partially Cooperative RBC is
degraded, the achievable rate region is shown to be tight and provides the
capacity region. Gaussian Partially Cooperative RBCs and Partially Cooperative
RBCs with feedback are further studied. In the second channel model being
studied in the paper, the Fully Cooperative Relay Broadcast Channel, both users
can act as relay nodes and transmit to each other through relay links. This is
a more general model than the Partially Cooperative RBC. All the results for
Partially Cooperative RBCs are correspondingly generalized to the Fully
Cooperative RBCs. It is further shown that the AWGN Fully Cooperative RBC has a
larger achievable rate region than the AWGN Partially Cooperative RBC. The
results illustrate that relaying and user cooperation are powerful techniques
in improving the capacity of broadcast channels.Comment: Submitted to the IEEE Transactions on Information Theory, July 200
Broadcast Channels with Cooperating Decoders
We consider the problem of communicating over the general discrete memoryless
broadcast channel (BC) with partially cooperating receivers. In our setup,
receivers are able to exchange messages over noiseless conference links of
finite capacities, prior to decoding the messages sent from the transmitter. In
this paper we formulate the general problem of broadcast with cooperation. We
first find the capacity region for the case where the BC is physically
degraded. Then, we give achievability results for the general broadcast
channel, for both the two independent messages case and the single common
message case.Comment: Final version, to appear in the IEEE Transactions on Information
Theory -- contains (very) minor changes based on the last round of review
Rate Regions for the Partially-Cooperative Relay Broadcast Channel with Non-causal Side Information
In this work, we consider a partially cooperative relay broadcast channel
(PC-RBC) controlled by random parameters. We provide rate regions for two
different situations: 1) when side information (SI) S^n on the random
parameters is non-causally known at both the source and the relay and, 2) when
side information S^n is non-causally known at the source only. These achievable
regions are derived for the general discrete memoryless case first and then
extended to the case when the channel is degraded Gaussian and the SI is
additive i.i.d. Gaussian. In this case, the source uses generalized dirty paper
coding (GDPC), i.e., DPC combined with partial state cancellation, when only
the source is informed, and DPC alone when both the source and the relay are
informed. It appears that, even though it can not completely eliminate the
effect of the SI (in contrast to the case of source and relay being informed),
GDPC is particularly useful when only the source is informed.Comment: 7 pages, Proc. of IEEE International Symposium on Information theory,
ISIT 2007, Nice, Franc
Cooperative Strategies for Simultaneous and Broadcast Relay Channels
Consider the \emph{simultaneous relay channel} (SRC) which consists of a set
of relay channels where the source wishes to transmit common and private
information to each of the destinations. This problem is recognized as being
equivalent to that of sending common and private information to several
destinations in presence of helper relays where each channel outcome becomes a
branch of the \emph{broadcast relay channel} (BRC). Cooperative schemes and
capacity region for a set with two memoryless relay channels are investigated.
The proposed coding schemes, based on \emph{Decode-and-Forward} (DF) and
\emph{Compress-and-Forward} (CF) must be capable of transmitting information
simultaneously to all destinations in such set.
Depending on the quality of source-to-relay and relay-to-destination
channels, inner bounds on the capacity of the general BRC are derived. Three
cases of particular interest are considered: cooperation is based on DF
strategy for both users --referred to as DF-DF region--, cooperation is based
on CF strategy for both users --referred to as CF-CF region--, and cooperation
is based on DF strategy for one destination and CF for the other --referred to
as DF-CF region--. These results can be seen as a generalization and hence
unification of previous works. An outer-bound on the capacity of the general
BRC is also derived. Capacity results are obtained for the specific cases of
semi-degraded and degraded Gaussian simultaneous relay channels. Rates are
evaluated for Gaussian models where the source must guarantee a minimum amount
of information to both users while additional information is sent to each of
them.Comment: 32 pages, 7 figures, To appear in IEEE Trans. on Information Theor
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