5,843 research outputs found
Reliable Physical Layer Network Coding
When two or more users in a wireless network transmit simultaneously, their
electromagnetic signals are linearly superimposed on the channel. As a result,
a receiver that is interested in one of these signals sees the others as
unwanted interference. This property of the wireless medium is typically viewed
as a hindrance to reliable communication over a network. However, using a
recently developed coding strategy, interference can in fact be harnessed for
network coding. In a wired network, (linear) network coding refers to each
intermediate node taking its received packets, computing a linear combination
over a finite field, and forwarding the outcome towards the destinations. Then,
given an appropriate set of linear combinations, a destination can solve for
its desired packets. For certain topologies, this strategy can attain
significantly higher throughputs over routing-based strategies. Reliable
physical layer network coding takes this idea one step further: using
judiciously chosen linear error-correcting codes, intermediate nodes in a
wireless network can directly recover linear combinations of the packets from
the observed noisy superpositions of transmitted signals. Starting with some
simple examples, this survey explores the core ideas behind this new technique
and the possibilities it offers for communication over interference-limited
wireless networks.Comment: 19 pages, 14 figures, survey paper to appear in Proceedings of the
IEE
Network Code Design for Orthogonal Two-hop Network with Broadcasting Relay: A Joint Source-Channel-Network Coding Approach
This paper addresses network code design for robust transmission of sources
over an orthogonal two-hop wireless network with a broadcasting relay. The
network consists of multiple sources and destinations in which each
destination, benefiting the relay signal, intends to decode a subset of the
sources. Two special instances of this network are orthogonal broadcast relay
channel and the orthogonal multiple access relay channel. The focus is on
complexity constrained scenarios, e.g., for wireless sensor networks, where
channel coding is practically imperfect. Taking a source-channel and network
coding approach, we design the network code (mapping) at the relay such that
the average reconstruction distortion at the destinations is minimized. To this
end, by decomposing the distortion into its components, an efficient design
algorithm is proposed. The resulting network code is nonlinear and
substantially outperforms the best performing linear network code. A motivating
formulation of a family of structured nonlinear network codes is also
presented. Numerical results and comparison with linear network coding at the
relay and the corresponding distortion-power bound demonstrate the
effectiveness of the proposed schemes and a promising research direction.Comment: 27 pages, 9 figures, Submited to IEEE Transaction on Communicatio
Reduced-Dimension Linear Transform Coding of Correlated Signals in Networks
A model, called the linear transform network (LTN), is proposed to analyze
the compression and estimation of correlated signals transmitted over directed
acyclic graphs (DAGs). An LTN is a DAG network with multiple source and
receiver nodes. Source nodes transmit subspace projections of random correlated
signals by applying reduced-dimension linear transforms. The subspace
projections are linearly processed by multiple relays and routed to intended
receivers. Each receiver applies a linear estimator to approximate a subset of
the sources with minimum mean squared error (MSE) distortion. The model is
extended to include noisy networks with power constraints on transmitters. A
key task is to compute all local compression matrices and linear estimators in
the network to minimize end-to-end distortion. The non-convex problem is solved
iteratively within an optimization framework using constrained quadratic
programs (QPs). The proposed algorithm recovers as special cases the regular
and distributed Karhunen-Loeve transforms (KLTs). Cut-set lower bounds on the
distortion region of multi-source, multi-receiver networks are given for linear
coding based on convex relaxations. Cut-set lower bounds are also given for any
coding strategy based on information theory. The distortion region and
compression-estimation tradeoffs are illustrated for different communication
demands (e.g. multiple unicast), and graph structures.Comment: 33 pages, 7 figures, To appear in IEEE Transactions on Signal
Processin
Communicating over Filter-and-Forward Relay Networks with Channel Output Feedback
Relay networks aid in increasing the rate of communication from source to
destination. However, the capacity of even a three-terminal relay channel is an
open problem. In this work, we propose a new lower bound for the capacity of
the three-terminal relay channel with destination-to-source feedback in the
presence of correlated noise. Our lower bound improves on the existing bounds
in the literature. We then extend our lower bound to general relay network
configurations using an arbitrary number of filter-and-forward relay nodes.
Such network configurations are common in many multi-hop communication systems
where the intermediate nodes can only perform minimal processing due to limited
computational power. Simulation results show that significant improvements in
the achievable rate can be obtained through our approach. We next derive a
coding strategy (optimized using post processed signal-to-noise ratio as a
criterion) for the three-terminal relay channel with noisy channel output
feedback for two transmissions. This coding scheme can be used in conjunction
with open-loop codes for applications like automatic repeat request (ARQ) or
hybrid-ARQ.Comment: 15 pages, 8 figures, to appear in IEEE Transactions on Signal
Processin
Relaying for Multiuser Networks in the Absence of Codebook Information
This work considers relay assisted transmission for multiuser networks when
the relay has no access to the codebooks used by the transmitters. The relay is
called oblivious for this reason. Of particular interest is the generalized
compress-and-forward (GCF) strategy, where the destinations jointly decode the
compression indices and the transmitted messages, and their optimality in this
setting. The relay-to-destination links are assumed to be out-of-band with
finite capacity. Two models are investigated: the multiple access relay channel
(MARC) and the interference relay channel (IFRC). For the MARC with an
oblivious relay, a new outerbound is derived and it is shown to be tight by
means of achievability of the capacity region using GCF scheme. For the IFRC
with an oblivious relay, a new strong interference condition is established,
under which the capacity region is found by deriving a new outerbound and
showing that it is achievable using GCF scheme. The result is further extended
to establish the capacity region of M-user MARC with an oblivious relay, and
multicast networks containing M sources and K destinations with an oblivious
relay.Comment: submitted to IEEE Transactions on Information Theor
Distributed Turbo-Like Codes for Multi-User Cooperative Relay Networks
In this paper, a distributed turbo-like coding scheme for wireless networks
with relays is proposed. We consider a scenario where multiple sources
communicate with a single destination with the help of a relay. The proposed
scheme can be regarded as of the decode-and-forward type. The relay decodes the
information from the sources and it properly combines and re-encodes them to
generate some extra redundancy, which is transmitted to the destination. The
amount of redundancy generated by the relay can simply be adjusted according to
requirements in terms of performance, throughput and/or power. At the
destination, decoding of the information of all sources is performed jointly
exploiting the redundancy provided by the relay in an iterative fashion. The
overall communication network can be viewed as a serially concatenated code.
The proposed distributed scheme achieves significant performance gains with
respect to the non-cooperation system, even for a very large number of users.
Furthermore, it presents a high flexibility in terms of code rate, block length
and number of users.Comment: Submitted to ICC 201
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