37 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
Empirical Coordination with Channel Feedback and Strictly Causal or Causal Encoding
In multi-terminal networks, feedback increases the capacity region and helps
communication devices to coordinate. In this article, we deepen the
relationship between coordination and feedback by considering a point-to-point
scenario with an information source and a noisy channel. Empirical coordination
is achievable if the encoder and the decoder can implement sequences of symbols
that are jointly typical for a target probability distribution. We investigate
the impact of feedback when the encoder has strictly causal or causal
observation of the source symbols. For both cases, we characterize the optimal
information constraints and we show that feedback improves coordination
possibilities. Surprisingly, feedback also reduces the number of auxiliary
random variables and simplifies the information constraints. For empirical
coordination with strictly causal encoding and feedback, the information
constraint does not involve auxiliary random variable anymore.Comment: 5 pages, 6 figures, presented at IEEE International Symposium on
Information Theory (ISIT) 201
Capacity of 1-to-K Broadcast Packet Erasure Channels with Channel Output Feedback
This paper focuses on the 1-to-K broadcast packet erasure channel (PEC),
which is a generalization of the broadcast binary erasure channel from the
binary symbol to that of arbitrary finite fields GF(q) with sufficiently large
q. We consider the setting in which the source node has instant feedback of the
channel outputs of the K receivers after each transmission. Such a setting
directly models network coded packet transmission in the downlink direction
with integrated feedback mechanisms (such as Automatic Repeat reQuest (ARQ)).
The main results of this paper are: (i) The capacity region for general
1-to-3 broadcast PECs, and (ii) The capacity region for two classes of 1-to-K
broadcast PECs: the symmetric PECs, and the spatially independent PECs with
one-sided fairness constraints. This paper also develops (iii) A pair of outer
and inner bounds of the capacity region for arbitrary 1-to-K broadcast PECs,
which can be evaluated by any linear programming solver. For most practical
scenarios, the outer and inner bounds meet and thus jointly characterize the
capacity.Comment: 8 pages, 2 figures. Published in Allerton 2010. The journal version
of this work was submitted to IEEE Trans IT in May, 201