239 research outputs found
The Gaussian MAC with Conferencing Encoders
We derive the capacity region of the Gaussian version of Willems's two-user
MAC with conferencing encoders. This setting differs from the classical MAC in
that, prior to each transmission block, the two transmitters can communicate
with each other over noise-free bit-pipes of given capacities. The derivation
requires a new technique for proving the optimality of Gaussian input
distributions in certain mutual information maximizations under a Markov
constraint. We also consider a Costa-type extension of the Gaussian MAC with
conferencing encoders. In this extension, the channel can be described as a
two-user MAC with Gaussian noise and Gaussian interference where the
interference is known non-causally to the encoders but not to the decoder. We
show that as in Costa's setting the interference sequence can be perfectly
canceled, i.e., that the capacity region without interference can be achieved.Comment: 5 pages, To be presented at ISIT 2008 in Toront
Multiple Access Channels with Cooperative Encoders and Channel State Information
The two-user Multiple Access Channel (MAC) with cooperative encoders and
Channel State Information (CSI) is considered where two different scenarios are
investigated: A two-user MAC with common message (MACCM) and a two-user MAC
with conferencing encoders (MACCE). For both situations, the two cases where
the CSI is known to the encoders either non-causally or causally are studied.
Achievable rate regions are established for both discrete memoryless channels
and Gaussian channels with additive interference. The achievable rate regions
derived for the Gaussian models with additive interference known non-causally
to the encoders are shown to coincide with the capacity region of the same
channel with no interference. Therefore, the capacity region for such channels
is established.Comment: 8 pages, 3 figure
The Capacity Region of p-Transmitter/q-Receiver Multiple-Access Channels with Common Information
This paper investigates the capacity problem for some multiple-access
scenarios with cooperative transmitters. First, a general Multiple-Access
Channel (MAC) with common information, i.e., a scenario where p transmitters
send private messages and also a common message to q receivers and each
receiver decodes all of the messages, is considered. The capacity region of the
discrete memoryless channel is characterized. Then, the general Gaussian fading
MAC with common information wherein partial Channel State Information (CSI) is
available at the transmitters (CSIT) and perfect CSI is available at the
receivers (CSIR) is investigated. A coding theorem is proved for this model
that yields an exact characterization of the throughput capacity region.
Finally, a two-transmitter/one-receiver Gaussian fading MAC with conferencing
encoders with partial CSIT and perfect CSIR is studied and its capacity region
is determined. For the Gaussian fading models with CSIR only (transmitters have
no access to CSIT), some numerical examples and simulation results are provided
for Rayleigh fading.Comment: 29 page
Three-User Gaussian Multiple Access Channel with Partially Cooperating Encoders
Abstract—A three-user Gaussian multiple access channel (MAC) with encoders partially cooperating over a ring of finite-capacity uni-directional links is studied. The model is a simple extension of the classical two-user MAC with conferencing encoders. Upper and lower bounds on the maximum achievable common rate are derived. The lower bound is attained via a novel multi-layer cooperative strategy. The bounds are tight for a certain range of values of the inter-user link capacity. Numerical results are provided to corroborate the analysis. I
Compound Multiple Access Channels with Partial Cooperation
A two-user discrete memoryless compound multiple access channel with a common
message and conferencing decoders is considered. The capacity region is
characterized in the special cases of physically degraded channels and
unidirectional cooperation, and achievable rate regions are provided for the
general case. The results are then extended to the corresponding Gaussian
model. In the Gaussian setup, the provided achievable rates are shown to lie
within some constant number of bits from the boundary of the capacity region in
several special cases. An alternative model, in which the encoders are
connected by conferencing links rather than having a common message, is studied
as well, and the capacity region for this model is also determined for the
cases of physically degraded channels and unidirectional cooperation. Numerical
results are also provided to obtain insights about the potential gains of
conferencing at the decoders and encoders.Comment: Submitted to IEEE Transactions on Information Theor
The Compound Multiple Access Channel with Partially Cooperating Encoders
The goal of this paper is to provide a rigorous information-theoretic
analysis of subnetworks of interference networks. We prove two coding theorems
for the compound multiple-access channel with an arbitrary number of channel
states. The channel state information at the transmitters is such that each
transmitter has a finite partition of the set of states and knows which element
of the partition the actual state belongs to. The receiver may have arbitrary
channel state information. The first coding theorem is for the case that both
transmitters have a common message and that each has an additional common
message. The second coding theorem is for the case where rate-constrained, but
noiseless transmitter cooperation is possible. This cooperation may be used to
exchange information about channel state information as well as the messages to
be transmitted. The cooperation protocol used here generalizes Willems'
conferencing. We show how this models base station cooperation in modern
wireless cellular networks used for interference coordination and capacity
enhancement. In particular, the coding theorem for the cooperative case shows
how much cooperation is necessary in order to achieve maximal capacity in the
network considered.Comment: accepted for publication in IEEE Transactions on Information Theory,
Special Issue on Interference Network
On the Cost and Benefit of Cooperation (Extended Version)
In a cooperative coding scheme, network nodes work together to achieve higher
transmission rates. To obtain a better understanding of cooperation, we
consider a model in which two transmitters send rate-limited descriptions of
their messages to a "cooperation facilitator", a node that sends back
rate-limited descriptions of the pair to each transmitter. This model includes
the conferencing encoders model and a prior model from the current authors as
special cases. We show that except for a special class of multiple access
channels, the gain in sum-capacity resulting from cooperation under this model
is quite large. Adding a cooperation facilitator to any such channel results in
a network that does not satisfy the edge removal property. An important special
case is the Gaussian multiple access channel, for which we explicitly
characterize the sum-rate cooperation gain.Comment: 15 pages, 3 figures. To be presented at ISIT 201
The Classical-Quantum Multiple Access Channel with Conferencing Encoders and with Common Messages
We prove coding theorems for two scenarios of cooperating encoders for the
multiple access channel with two classical inputs and one quantum output. In
the first scenario (ccq-MAC with common messages), the two senders each have
their private messages, but would also like to transmit common messages. In the
second scenario (ccq-MAC with conferencing encoders), each sender has its own
set of messages, but they are allowed to use a limited amount of noiseless
classical communication amongst each other prior to encoding their messages.
This conferencing protocol may depend on each individual message they intend to
send. The two scenarios are related to each other not only in spirit - the
existence of near-optimal codes for the ccq-MAC with common messages is used
for proving the existence of near-optimal codes for the ccq-MAC with
conferencing encoders.Comment: 17 pages, no figure
Sending a Bivariate Gaussian Source Over a Gaussian MAC with Unidirectional Conferencing Encoders
We consider the transmission of a memoryless bivariate Gaussian source over a
two-user additive Gaussian multiple-access channel with unidirectional
conferencing encoders. Here, prior to each transmission block, Encoder 1, which
observes the first source component, is allowed to communicate with Encoder 2,
which observes the second source component, via a unidirectional noise-free
bit-pipe of given capacity. The main results of this work are sufficient
conditions and a necessary condition for the achievability of a distortion pair
expressed as a function of the channel SNR and of the source correlation. The
main sufficient condition is obtained by an extension of the vector-quantizer
scheme suggested by Lapidoth-Tinguely, for the case without conferencing, to
the case with unidirectional conference. In the high-SNR regime, and when the
capacity of the conference channel is unlimited, these necessary and sufficient
conditions are shown to agree. We evaluate the precise high-SNR asymptotics for
a subset of distortion pairs when the capacity of the conference channel is
unlimited in which case we show that a separation based scheme attains these
optimal distortion pairs. However, with symmetric average-power constraints and
fixed conferencing capacity, at high-SNR the latter separation based scheme is
shown to be suboptimal.Comment: The paper has been accepted for publication in IT Transaction
Achievable Rate Region for Multiple Access Channel with Correlated Channel States and Cooperating Encoders
In this paper, a two-user discrete memoryless multiple-access channel
(DM-MAC) with correlated channel states, each known at one of the encoders is
considered, in which each encoder transmits independent messages and tries to
cooperate with the other one. To consider cooperating encoders, it is assumed
that each encoder strictly-causally receives and learns the other encoder's
transmitted symbols and tries to cooperate with the other encoder by
transmitting its message. Next, we study this channel in a special case; we
assume that the common part of both states is known at both, hence encoders use
this opportunity to get better rate region. For these scenarios, an achievable
rate region is derived based on a combination of block-Markov encoding and
Gel'fand-Pinsker coding techniques. Furthermore, the achievable rate region is
established for the Gaussian channel, and it is shown that the capacity region
is achieved in certain circumstances.Comment: 7 pages, 2 figure
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