43 research outputs found
On the Achievable Rate Region of Sequential Decoding for a Class of Multiaccess Channels
The achievable-rate region of sequential decoding for the class of pairwise reversible multiaccess channels is determined. This result is obtained by finding tight lower bounds to the average list size for the same class of channels. The average list size is defined as the expected number of incorrect messages that appear, to a maximum-likelihood decoder, to be at least as likely as the correct message. The average list size bounds developed here may be of independent interest, with possible applications to list-decoding schemes. © 1990 IEE
Random Access Channel Coding in the Finite Blocklength Regime
Consider a random access communication scenario over a channel whose
operation is defined for any number of possible transmitters. Inspired by the
model recently introduced by Polyanskiy for the Multiple Access Channel (MAC)
with a fixed, known number of transmitters, we assume that the channel is
invariant to permutations on its inputs, and that all active transmitters
employ identical encoders. Unlike Polyanskiy, we consider a scenario where
neither the transmitters nor the receiver know which transmitters are active.
We refer to this agnostic communication setup as the Random Access Channel, or
RAC. Scheduled feedback of a finite number of bits is used to synchronize the
transmitters. The decoder is tasked with determining from the channel output
the number of active transmitters () and their messages but not which
transmitter sent which message. The decoding procedure occurs at a time
depending on the decoder's estimate of the number of active transmitters,
, thereby achieving a rate that varies with the number of active
transmitters. Single-bit feedback at each time , enables all
transmitters to determine the end of one coding epoch and the start of the
next. The central result of this work demonstrates the achievability on a RAC
of performance that is first-order optimal for the MAC in operation during each
coding epoch. While prior multiple access schemes for a fixed number of
transmitters require simultaneous threshold rules, the proposed
scheme uses a single threshold rule and achieves the same dispersion.Comment: Presented at ISIT18', submitted to IEEE Transactions on Information
Theor
Can Negligible Cooperation Increase Network Reliability?
In network cooperation strategies, nodes work together with the aim of
increasing transmission rates or reliability. This paper demonstrates that
enabling cooperation between the transmitters of a two-user multiple access
channel, via a cooperation facilitator that has access to both messages, always
results in a network whose maximal- and average-error sum-capacities are the
same---even when those capacities differ in the absence of cooperation and the
information shared with the encoders is negligible. From this result, it
follows that if a multiple access channel with no transmitter cooperation has
different maximal- and average-error sum-capacities, then the maximal-error
sum-capacity of the network consisting of this channel and a cooperation
facilitator is not continuous with respect to the output edge capacities of the
facilitator. This shows that there exist networks where sharing even a
negligible number of bits per channel use with the encoders yields a
non-negligible benefit.Comment: 27 pages, 3 figures. Submitted to the IEEE Transactions on
Information Theor
Random Access Channel Coding in the Finite Blocklength Regime
Consider a random access communication scenario over a channel whose operation is defined for any number of possible transmitters. Inspired by the model recently introduced for the Multiple Access Channel (MAC) with a fixed, known number of transmitters by Polyanskiy, we assume that the channel is invariant to permutations on its inputs, and that all active transmitters employ identical encoders. Unlike Polyanskiy, we consider a scenario in which neither the transmitters nor the receiver know which or how many transmitters are active. We refer to this agnostic communication setup as the Random Access Channel, or RAC. Limited feedback is used to ensure that the collection of active transmitters remains fixed during each epoch. The decoder is tasked with determining from the channel output the number of active transmitters (k) and their messages but not which transmitter sent which message. The central result of this work demonstrates the achievability on a RAC of performance that is first-order optimal for the MAC in operation during each coding epoch. While prior multiple access schemes for a fixed number of transmitters require 2^k - 1 simultaneous threshold rules, the proposed scheme uses a single threshold rule and achieves the same dispersion