369 research outputs found
Achievable Rate Regions for Two-Way Relay Channel using Nested Lattice Coding
This paper studies Gaussian Two-Way Relay Channel where two communication
nodes exchange messages with each other via a relay. It is assumed that all
nodes operate in half duplex mode without any direct link between the
communication nodes. A compress-and-forward relaying strategy using nested
lattice codes is first proposed. Then, the proposed scheme is improved by
performing a layered coding : a common layer is decoded by both receivers and a
refinement layer is recovered only by the receiver which has the best channel
conditions. The achievable rates of the new scheme are characterized and are
shown to be higher than those provided by the decode-and-forward strategy in
some regions.Comment: 27 pages, 13 figures, Submitted to IEEE Transactions on Wireless
Communications (October 2013
The Multi-way Relay Channel
The multiuser communication channel, in which multiple users exchange
information with the help of a relay terminal, termed the multi-way relay
channel (mRC), is introduced. In this model, multiple interfering clusters of
users communicate simultaneously, where the users within the same cluster wish
to exchange messages among themselves. It is assumed that the users cannot
receive each other's signals directly, and hence the relay terminal in this
model is the enabler of communication. In particular, restricted encoders,
which ignore the received channel output and use only the corresponding
messages for generating the channel input, are considered. Achievable rate
regions and an outer bound are characterized for the Gaussian mRC, and their
comparison is presented in terms of exchange rates in a symmetric Gaussian
network scenario. It is shown that the compress-and-forward (CF) protocol
achieves exchange rates within a constant bit offset of the exchange capacity
independent of the power constraints of the terminals in the network. A finite
bit gap between the exchange rates achieved by the CF and the
amplify-and-forward (AF) protocols is also shown. The two special cases of the
mRC, the full data exchange model, in which every user wants to receive
messages of all other users, and the pairwise data exchange model which
consists of multiple two-way relay channels, are investigated in detail. In
particular for the pairwise data exchange model, in addition to the proposed
random coding based achievable schemes, a nested lattice coding based scheme is
also presented and is shown to achieve exchange rates within a constant bit gap
of the exchange capacity.Comment: Revised version of our submission to the Transactions on Information
Theor
Adaptive Mode Selection and Power Allocation in Bidirectional Buffer-aided Relay Networks
In this paper, we consider the problem of sum rate maximization in a
bidirectional relay network with fading. Hereby, user 1 and user 2 communicate
with each other only through a relay, i.e., a direct link between user 1 and
user 2 is not present. In this network, there exist six possible transmission
modes: four point-to-point modes (user 1-to-relay, user 2-to-relay,
relay-to-user 1, relay-to-user 2), a multiple access mode (both users to the
relay), and a broadcast mode (the relay to both users). Most existing protocols
assume a fixed schedule of using a subset of the aforementioned transmission
modes, as a result, the sum rate is limited by the capacity of the weakest link
associated with the relay in each time slot. Motivated by this limitation, we
develop a protocol which is not restricted to adhere to a predefined schedule
for using the transmission modes. Therefore, all transmission modes of the
bidirectional relay network can be used adaptively based on the instantaneous
channel state information (CSI) of the involved links. To this end, the relay
has to be equipped with two buffers for the storage of the information received
from users 1 and 2, respectively. For the considered network, given a total
average power budget for all nodes, we jointly optimize the transmission mode
selection and power allocation based on the instantaneous CSI in each time slot
for sum rate maximization. Simulation results show that the proposed protocol
outperforms existing protocols for all signal-to-noise ratios (SNRs).
Specifically, we obtain a considerable gain at low SNRs due to the adaptive
power allocation and at high SNRs due to the adaptive mode selection.Comment: arXiv admin note: substantial text overlap with arXiv:1303.373
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