2,632 research outputs found
Wireless Network Information Flow: A Deterministic Approach
In a wireless network with a single source and a single destination and an
arbitrary number of relay nodes, what is the maximum rate of information flow
achievable? We make progress on this long standing problem through a two-step
approach. First we propose a deterministic channel model which captures the key
wireless properties of signal strength, broadcast and superposition. We obtain
an exact characterization of the capacity of a network with nodes connected by
such deterministic channels. This result is a natural generalization of the
celebrated max-flow min-cut theorem for wired networks. Second, we use the
insights obtained from the deterministic analysis to design a new
quantize-map-and-forward scheme for Gaussian networks. In this scheme, each
relay quantizes the received signal at the noise level and maps it to a random
Gaussian codeword for forwarding, and the final destination decodes the
source's message based on the received signal. We show that, in contrast to
existing schemes, this scheme can achieve the cut-set upper bound to within a
gap which is independent of the channel parameters. In the case of the relay
channel with a single relay as well as the two-relay Gaussian diamond network,
the gap is 1 bit/s/Hz. Moreover, the scheme is universal in the sense that the
relays need no knowledge of the values of the channel parameters to
(approximately) achieve the rate supportable by the network. We also present
extensions of the results to multicast networks, half-duplex networks and
ergodic networks.Comment: To appear in IEEE transactions on Information Theory, Vol 57, No 4,
April 201
Wireless Network Simplification: the Gaussian N-Relay Diamond Network
We consider the Gaussian N-relay diamond network, where a source wants to
communicate to a destination node through a layer of N-relay nodes. We
investigate the following question: what fraction of the capacity can we
maintain by using only k out of the N available relays? We show that
independent of the channel configurations and the operating SNR, we can always
find a subset of k relays which alone provide a rate (kC/(k+1))-G, where C is
the information theoretic cutset upper bound on the capacity of the whole
network and G is a constant that depends only on N and k (logarithmic in N and
linear in k). In particular, for k = 1, this means that half of the capacity of
any N-relay diamond network can be approximately achieved by routing
information over a single relay. We also show that this fraction is tight:
there are configurations of the N-relay diamond network where every subset of k
relays alone can at most provide approximately a fraction k/(k+1) of the total
capacity. These high-capacity k-relay subnetworks can be also discovered
efficiently. We propose an algorithm that computes a constant gap approximation
to the capacity of the Gaussian N-relay diamond network in O(N log N) running
time and discovers a high-capacity k-relay subnetwork in O(kN) running time.
This result also provides a new approximation to the capacity of the Gaussian
N-relay diamond network which is hybrid in nature: it has both multiplicative
and additive gaps. In the intermediate SNR regime, this hybrid approximation is
tighter than existing purely additive or purely multiplicative approximations
to the capacity of this network.Comment: Submitted to Transactions on Information Theory in October 2012. The
new version includes discussions on the algorithmic complexity of discovering
a high-capacity subnetwork and on the performance of amplify-and-forwar
Asymptotic Capacity of Large Relay Networks with Conferencing Links
In this correspondence, we consider a half-duplex large relay network, which
consists of one source-destination pair and relay nodes, each of which is
connected with a subset of the other relays via signal-to-noise ratio
(SNR)-limited out-of-band conferencing links. The asymptotic achievable rates
of two basic relaying schemes with the "-portion" conferencing strategy are
studied: For the decode-and-forward (DF) scheme, we prove that the DF rate
scales as ; for the amplify-and-forward (AF) scheme, we
prove that it asymptotically achieves the capacity upper bound in some
interesting scenarios as goes to infinity.Comment: submitted to IEEE Transactions on Communication
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