14 research outputs found
Is non-unique decoding necessary?
In multi-terminal communication systems, signals carrying messages meant for different destinations are often observed together at any given destination receiver. Han and Kobayashi (1981) proposed a receiving strategy which performs a joint unique decoding of messages of interest along with a subset of messages which are not of interest. It is now well-known that this provides an achievable region which is, in general, larger than if the receiver treats all messages not of interest as noise. Nair and El Gamal (2009) and Chong, Motani, Garg, and El Gamal (2008) independently proposed a generalization called indirect or non-unique decoding where the receiver uses the codebook structure of the messages to only uniquely decode its messages of interest. Non-unique (indirect) decoding has since been used in various scenarios. The main result in this paper is to provide an interpretation and a systematic proof technique for why indirect decoding, in all known cases where it has been employed, can be replaced by a particularly designed joint unique decoding strategy, without any penalty from a rate region viewpoint
Lattice Codes for Many-to-One Interference Channels With and Without Cognitive Messages
A new achievable rate region is given for the Gaussian cognitive many-to-one
interference channel. The proposed novel coding scheme is based on the
compute-and-forward approach with lattice codes. Using the idea of decoding
sums of codewords, our scheme improves considerably upon the conventional
coding schemes which treat interference as noise or decode messages
simultaneously. Our strategy also extends directly to the usual many-to-one
interference channels without cognitive messages. Comparing to the usual
compute-and-forward scheme where a fixed lattice is used for the code
construction, the novel scheme employs scaled lattices and also encompasses key
ingredients of the existing schemes for the cognitive interference channel.
With this new component, our scheme achieves a larger rate region in general.
For some symmetric channel settings, new constant gap or capacity results are
established, which are independent of the number of users in the system.Comment: To appear in IEEE Transactions on Information Theor
On the Compound Broadcast Channel: Multiple Description Coding and Interference Decoding
This work investigates the general two-user Compound Broadcast Channel (BC)
where an encoder wishes to transmit common and private messages to two
receivers while being oblivious to two possible channel realizations
controlling the communication. The focus is on the characterization of the
largest achievable rate region by resorting to more evolved encoding and
decoding techniques than the conventional coding for the standard BC. The role
of the decoder is first explored, and an achievable rate region is derived
based on the principle of "Interference Decoding" (ID) where each receiver
decodes its intended message and chooses to (non-uniquely) decode or not the
interfering message. This inner bound is shown to be capacity achieving for a
class of non-trivial compound BEC/BSC broadcast channels while the worst-case
of Marton's inner bound -based on "Non Interference Decoding" (NID)- fails to
achieve the capacity region. The role of the encoder is then studied, and an
achievable rate region is derived based on "Multiple Description" (MD) coding
where the encoder transmits a common as well as multiple dedicated private
descriptions to the many instances of the users channels. It turns out that MD
coding outperforms the single description scheme -Common Description (CD)
coding- for a class of compound Multiple Input Single Output Broadcast Channels
(MISO BC).Comment: 77 pages, 8 figures, Submitted to IEEE Trans. on Information Theor