21,550 research outputs found
The Capacity Region of Restricted Multi-Way Relay Channels with Deterministic Uplinks
This paper considers the multi-way relay channel (MWRC) where multiple users
exchange messages via a single relay. The capacity region is derived for a
special class of MWRCs where (i) the uplink and the downlink are separated in
the sense that there is no direct user-to-user links, (ii) the channel is
restricted in the sense that each user's transmitted channel symbols can depend
on only its own message, but not on its received channel symbols, and (iii) the
uplink is any deterministic function.Comment: Author's final version (to be presented at ISIT 2012
The Capacity Region of the Restricted Two-Way Relay Channel with Any Deterministic Uplink
This paper considers the two-way relay channel (TWRC) where two users
communicate via a relay. For the restricted TWRC where the uplink from the
users to the relay is any deterministic function and the downlink from the
relay to the users is any arbitrary channel, the capacity region is obtained.
The TWRC considered is restricted in the sense that each user can only transmit
a function of its message.Comment: author's final version (accepted and to appear in IEEE Communications
Letters
The Suppression of Radiation Reaction and Laser Field Depletion in Laser-Electron beam interaction
The effects of radiation reaction (RR) have been studied extensively by using
the ultraintense laser interacts with the counter-propagating relativistic
electron. At the laser intensity at the order of W/cm, the
effects of RR are significant in a few laser period for a relativistic
electron. However, the laser at such intensity is tightly focused and the laser
energy is usually assumed to be fixed. Then, the signal of RR and energy
conservation cannot be guaranteed. To assess the effects of RR in a tightly
focused laser pulse and the evolution of the laser energy, we simulate this
interaction with a beam of electrons by means of Particle-in-Cell (PIC)
method. We observed that the effects of RR are suppressed due to the
ponderomotive force and accompanied by a non-negligible amount of laser field
energy reduction. This is due to the ponderomotive force that prevents the
electrons from approaching the center of the laser pulse and leads to the
interaction at weaker field region. At the same time, the laser energy is
absorbed through ponderomotive acceleration. Thus, the kinetic energy of the
electron beam has to be carefully selected such that the effects of RR become
obvious.Comment: 6 pages, 3 figure
The Capacity of Three-Receiver AWGN Broadcast Channels with Receiver Message Side Information
This paper investigates the capacity region of three-receiver AWGN broadcast
channels where the receivers (i) have private-message requests and (ii) know
the messages requested by some other receivers as side information. We classify
these channels based on their side information into eight groups, and construct
different transmission schemes for the groups. For six groups, we characterize
the capacity region, and show that it improves both the best known inner and
outer bounds. For the remaining two groups, we improve the best known inner
bound by using side information during channel decoding at the receivers.Comment: This is an extended version of the same-titled paper submitted to
IEEE International Symposium on Information Theory (ISIT) 201
Generalized Interlinked Cycle Cover for Index Coding
A source coding problem over a noiseless broadcast channel where the source
is pre-informed about the contents of the cache of all receivers, is an index
coding problem. Furthermore, if each message is requested by one receiver, then
we call this an index coding problem with a unicast message setting. This
problem can be represented by a directed graph. In this paper, we first define
a structure (we call generalized interlinked cycles (GIC)) in directed graphs.
A GIC consists of cycles which are interlinked in some manner (i.e., not
disjoint), and it turns out that the GIC is a generalization of cliques and
cycles. We then propose a simple scalar linear encoding scheme with linear time
encoding complexity. This scheme exploits GICs in the digraph. We prove that
our scheme is optimal for a class of digraphs with message packets of any
length. Moreover, we show that our scheme can outperform existing techniques,
e.g., partial clique cover, local chromatic number, composite-coding, and
interlinked cycle cover.Comment: Extended version of the paper which is to be presented at the IEEE
Information Theory Workshop (ITW), 2015 Jej
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