724 research outputs found
On the Structure of the Capacity Region of Asynchronous Memoryless Multiple-Access Channels
The asynchronous capacity region of memoryless multiple-access channels is
the union of certain polytopes. It is well-known that vertices of such
polytopes may be approached via a technique called successive decoding. It is
also known that an extension of successive decoding applies to the dominant
face of such polytopes. The extension consists of forming groups of users in
such a way that users within a group are decoded jointly whereas groups are
decoded successively. This paper goes one step further. It is shown that
successive decoding extends to every face of the above mentioned polytopes. The
group composition as well as the decoding order for all rates on a face of
interest are obtained from a label assigned to that face. From the label one
can extract a number of structural properties, such as the dimension of the
corresponding face and whether or not two faces intersect. Expressions for the
the number of faces of any given dimension are also derived from the labels.Comment: 21 pages, 5 figures and 1 table. Submitted to IEEE Transactions on
Information Theor
On Capacity Regions of Discrete Asynchronous Multiple Access Channels
A general formalization is given for asynchronous multiple access channels
which admits different assumptions on delays. This general framework allows the
analysis of so far unexplored models leading to new interesting capacity
regions. In particular, a single letter characterization is given for the
capacity region in case of 3 senders, 2 synchronous with each other and the
third not synchronous with them.Comment: It has been presented in part at ISIT 2011, Saint Petersburg. This
extended version is accepted for publication in Kybernetik
The Strongly Asynchronous Massive Access Channel
This paper considers a Strongly Asynchronous and Slotted Massive Access
Channel (SAS-MAC) where different users transmit a randomly
selected message among ones within a strong asynchronous window
of length blocks, where each block lasts channel uses. A
global probability of error is enforced, ensuring that all the users'
identities and messages are correctly identified and decoded. Achievability
bounds are derived for the case that different users have similar channels, the
case that users' channels can be chosen from a set which has polynomially many
elements in the blocklength , and the case with no restriction on the users'
channels. A general converse bound on the capacity region and a converse bound
on the maximum growth rate of the number of users are derived.Comment: under submissio
Information theoretic analysis of LSD scheme
In this paper, the capacity region of Low Density Signature Multiple Access Channel (LDS-MAC) is calculated through information theoretic analysis. LDS Code Division Multiple Access (LDS-CDMA) uses spreading sequences of low density for spreading the data symbols in time domain. This technique benefits from a less complex Multiuser Detector (MUD) compared to conventional CDMA with optimum MUD; while keeping the performance close to the single user scenario for up to 200% loaded conditions. Also evaluated is the effect of different factors on the capacity of LDS MAC
- …