425 research outputs found
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
A Novel Transmission Scheme for the -user Broadcast Channel with Delayed CSIT
The state-dependent -user memoryless Broadcast Channel~(BC) with state
feedback is investigated. We propose a novel transmission scheme and derive its
corresponding achievable rate region, which, compared to some general schemes
that deal with feedback, has the advantage of being relatively simple and thus
is easy to evaluate. In particular, it is shown that the capacity region of the
symmetric erasure BC with an arbitrary input alphabet size is achievable with
the proposed scheme. For the fading Gaussian BC, we derive a symmetric
achievable rate as a function of the signal-to-noise ratio~(SNR) and a small
set of parameters. Besides achieving the optimal degrees of freedom at high
SNR, the proposed scheme is shown, through numerical results, to outperform
existing schemes from the literature in the finite SNR regime.Comment: 30 pages, 3 figures, submitted to IEEE Transactions on Wireless
Communications (revised version
The Wiretap Channel with Feedback: Encryption over the Channel
In this work, the critical role of noisy feedback in enhancing the secrecy
capacity of the wiretap channel is established. Unlike previous works, where a
noiseless public discussion channel is used for feedback, the feed-forward and
feedback signals share the same noisy channel in the present model. Quite
interestingly, this noisy feedback model is shown to be more advantageous in
the current setting. More specifically, the discrete memoryless modulo-additive
channel with a full-duplex destination node is considered first, and it is
shown that the judicious use of feedback increases the perfect secrecy capacity
to the capacity of the source-destination channel in the absence of the
wiretapper. In the achievability scheme, the feedback signal corresponds to a
private key, known only to the destination. In the half-duplex scheme, a novel
feedback technique that always achieves a positive perfect secrecy rate (even
when the source-wiretapper channel is less noisy than the source-destination
channel) is proposed. These results hinge on the modulo-additive property of
the channel, which is exploited by the destination to perform encryption over
the channel without revealing its key to the source. Finally, this scheme is
extended to the continuous real valued modulo- channel where it is
shown that the perfect secrecy capacity with feedback is also equal to the
capacity in the absence of the wiretapper.Comment: Submitted to IEEE Transactions on Information Theor
Content Delivery in Erasure Broadcast Channels with Cache and Feedback
We study a content delivery problem in a K-user erasure broadcast channel
such that a content providing server wishes to deliver requested files to
users, each equipped with a cache of a finite memory. Assuming that the
transmitter has state feedback and user caches can be filled during off-peak
hours reliably by the decentralized content placement, we characterize the
achievable rate region as a function of the memory sizes and the erasure
probabilities. The proposed delivery scheme, based on the broadcasting scheme
by Wang and Gatzianas et al., exploits the receiver side information
established during the placement phase. Our results can be extended to
centralized content placement as well as multi-antenna broadcast channels with
state feedback.Comment: 29 pages, 7 figures. A short version has been submitted to ISIT 201
Feedback-based Coding Algorithms for Braodcast Erasure Channels with Degraded Message Sets
We consider single-hop broadcast packet erasure channels (BPEC) with degraded message sets and instantaneous feedback regularly available from all receivers, and demonstrate that the main principles of the virtual-queue-based algorithms in [1], which were proposed for multiple unicast sessions, can still be applied to this setting and lead to capacity-achieving algorithms. Specifically, we propose a generic class of algorithms and intuitively describe its rationale and properties that result in its efficiency. We then apply this class of algorithms to three examples of BPEC channels (with different numbers of users and 2 or 3 degraded message sets) and show that the achievable throughput region matches a known capacity outer bound, assuming feedback availability through a separate public channel. If the feedback channel is not public, all users can still decode their messages, albeit at some overhead which results in an achievable throughput that differs from the outer bound by O(N/L), where L is the packet length. These algorithms do not require any prior knowledge of channel statistics for their operation
Cache-Enabled Broadcast Packet Erasure Channels with State Feedback
We consider a cache-enabled K-user broadcast erasure packet channel in which
a server with a library of N files wishes to deliver a requested file to each
user who is equipped with a cache of a finite memory M. Assuming that the
transmitter has state feedback and user caches can be filled during off-peak
hours reliably by decentralized cache placement, we characterize the optimal
rate region as a function of the memory size, the erasure probability. The
proposed delivery scheme, based on the scheme proposed by Gatzianas et al.,
exploits the receiver side information established during the placement phase.
Our results enable us to quantify the net benefits of decentralized coded
caching in the presence of erasure. The role of state feedback is found useful
especially when the erasure probability is large and/or the normalized memory
size is small.Comment: 8 pages, 4 figures, to be presented at the 53rd Annual Allerton
Conference on Communication, Control, and Computing, IL, US
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