1,306 research outputs found
Divide-and-conquer: Approaching the capacity of the two-pair bidirectional Gaussian relay network
The capacity region of multi-pair bidirectional relay networks, in which a
relay node facilitates the communication between multiple pairs of users, is
studied. This problem is first examined in the context of the linear shift
deterministic channel model. The capacity region of this network when the relay
is operating at either full-duplex mode or half-duplex mode for arbitrary
number of pairs is characterized. It is shown that the cut-set upper-bound is
tight and the capacity region is achieved by a so called divide-and-conquer
relaying strategy. The insights gained from the deterministic network are then
used for the Gaussian bidirectional relay network. The strategy in the
deterministic channel translates to a specific superposition of lattice codes
and random Gaussian codes at the source nodes and successive interference
cancelation at the receiving nodes for the Gaussian network. The achievable
rate of this scheme with two pairs is analyzed and it is shown that for all
channel gains it achieves to within 3 bits/sec/Hz per user of the cut-set
upper-bound. Hence, the capacity region of the two-pair bidirectional Gaussian
relay network to within 3 bits/sec/Hz per user is characterized.Comment: IEEE Trans. on Information Theory, accepte
Lattice Coding for the Two-way Two-relay Channel
Lattice coding techniques may be used to derive achievable rate regions which
outperform known independent, identically distributed (i.i.d.) random codes in
multi-source relay networks and in particular the two-way relay channel. Gains
stem from the ability to decode the sum of codewords (or messages) using
lattice codes at higher rates than possible with i.i.d. random codes. Here we
develop a novel lattice coding scheme for the Two-way Two-relay Channel: 1
2 3 4, where Node 1 and 4 simultaneously communicate with each other
through two relay nodes 2 and 3. Each node only communicates with its
neighboring nodes. The key technical contribution is the lattice-based
achievability strategy, where each relay is able to remove the noise while
decoding the sum of several signals in a Block Markov strategy and then
re-encode the signal into another lattice codeword using the so-called
"Re-distribution Transform". This allows nodes further down the line to again
decode sums of lattice codewords. This transform is central to improving the
achievable rates, and ensures that the messages traveling in each of the two
directions fully utilize the relay's power, even under asymmetric channel
conditions. All decoders are lattice decoders and only a single nested lattice
codebook pair is needed. The symmetric rate achieved by the proposed lattice
coding scheme is within 0.5 log 3 bit/Hz/s of the symmetric rate capacity.Comment: submitted to IEEE Transactions on Information Theory on December 3,
201
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
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