10 research outputs found
Channels with Cooperation Links that May Be Absent
It is well known that cooperation between users in a communication network
can lead to significant performance gains. A common assumption in past works is
that all the users are aware of the resources available for cooperation, and
know exactly to what extent these resources can be used. Unfortunately, in many
modern communication networks the availability of cooperation links cannot be
guaranteed a priori, due to the dynamic nature of the network. In this work a
family of models is suggested where the cooperation links may or may not be
present. Coding schemes are devised that exploit the cooperation links if they
are present, and can still operate (although at reduced rates) if cooperation
is not possible.Comment: Accepted for publication in the IEEE transaction on Information
Theory, June 201
Multiple Access Channels with Combined Cooperation and Partial Cribbing
In this paper we study the multiple access channel (MAC) with combined
cooperation and partial cribbing and characterize its capacity region.
Cooperation means that the two encoders send a message to one another via a
rate-limited link prior to transmission, while partial cribbing means that each
of the two encoders obtains a deterministic function of the other encoder's
output with or without delay. Prior work in this field dealt separately with
cooperation and partial cribbing. However, by combining these two methods we
can achieve significantly higher rates. Remarkably, the capacity region does
not require an additional auxiliary random variable (RV) since the purpose of
both cooperation and partial cribbing is to generate a common message between
the encoders. In the proof we combine methods of block Markov coding, backward
decoding, double rate-splitting, and joint typicality decoding. Furthermore, we
present the Gaussian MAC with combined one-sided cooperation and quantized
cribbing. For this model, we give an achievability scheme that shows how many
cooperation or quantization bits are required in order to achieve a Gaussian
MAC with full cooperation/cribbing capacity region. After establishing our main
results, we consider two cases where only one auxiliary RV is needed. The first
is a rate distortion dual setting for the MAC with a common message, a private
message and combined cooperation and cribbing. The second is a state-dependent
MAC with cooperation, where the state is known at a partially cribbing encoder
and at the decoder. However, there are cases where more than one auxiliary RV
is needed, e.g., when the cooperation and cribbing are not used for the same
purposes. We present a MAC with an action-dependent state, where the action is
based on the cooperation but not on the cribbing. Therefore, in this case more
than one auxiliary RV is needed
Successive Refinement with Decoder Cooperation and its Channel Coding Duals
We study cooperation in multi terminal source coding models involving
successive refinement. Specifically, we study the case of a single encoder and
two decoders, where the encoder provides a common description to both the
decoders and a private description to only one of the decoders. The decoders
cooperate via cribbing, i.e., the decoder with access only to the common
description is allowed to observe, in addition, a deterministic function of the
reconstruction symbols produced by the other. We characterize the fundamental
performance limits in the respective settings of non-causal, strictly-causal
and causal cribbing. We use a new coding scheme, referred to as Forward
Encoding and Block Markov Decoding, which is a variant of one recently used by
Cuff and Zhao for coordination via implicit communication. Finally, we use the
insight gained to introduce and solve some dual channel coding scenarios
involving Multiple Access Channels with cribbing.Comment: 55 pages, 15 figures, 8 tables, submitted to IEEE Transactions on
Information Theory. A shorter version submitted to ISIT 201
Cooperative Binning for Semi-deterministic Channels with Non-causal State Information
The capacity of the semi-deterministic relay channel (SD-RC) with non-causal
channel state information (CSI) only at the encoder and decoder is
characterized. The capacity is achieved by a scheme based on
cooperative-bin-forward. This scheme allows cooperation between the transmitter
and the relay without the need to decode a part of the message by the relay.
The transmission is divided into blocks and each deterministic output of the
channel (observed by the relay) is mapped to a bin. The bin index is used by
the encoder and the relay to choose the cooperation codeword in the next
transmission block. In causal settings the cooperation is independent of the
state. In \emph{non-causal} settings dependency between the relay's
transmission and the state can increase the transmission rates. The encoder
implicitly conveys partial state information to the relay. In particular, it
uses the states of the next block and selects a cooperation codeword
accordingly and the relay transmission depends on the cooperation codeword and
therefore also on the states. We also consider the multiple access channel with
partial cribbing as a semi-deterministic channel. The capacity region of this
channel with non-causal CSI is achieved by the new scheme. Examining the result
in several cases, we introduce a new problem of a point-to-point (PTP) channel
where the state is provided to the transmitter by a state encoder.
Interestingly, even though the CSI is also available at the receiver, we
provide an example which shows that the capacity with non-causal CSI at the
state encoder is strictly larger than the capacity with causal CSI