432 research outputs found
Beyond the Min-Cut Bound: Deterministic Network Coding for Asynchronous Multirate Broadcast
In a single hop broadcast packet erasure network, we demonstrate that it is
possible to provide multirate packet delivery outside of what is given by the
network min-cut. This is achieved by using a deterministic non-block-based
network coding scheme, which allows us to sidestep some of the limitations put
in place by the block coding model used to determine the network capacity.
Under the network coding scheme we outline, the sender is able to transmit
network coded packets above the channel rate of some receivers, while ensuring
that they still experience nonzero delivery rates. Interestingly, in this
generalised form of asynchronous network coded broadcast, receivers are not
required to obtain knowledge of all packets transmitted so far. Instead, causal
feedback from the receivers about packet erasures is used by the sender to
determine a network coded transmission that will allow at least one, but often
multiple receivers, to deliver their next needed packet.
Although the analysis of deterministic coding schemes is generally a
difficult problem, by making some approximations we are able to obtain
tractable estimates of the receivers' delivery rates, which are shown to match
reasonably well with simulation. Using these estimates, we design a fairness
algorithm that allocates the sender's resources so all receivers will
experience fair delivery rate performance
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
On Coding for Reliable Communication over Packet Networks
We present a capacity-achieving coding scheme for unicast or multicast over
lossy packet networks. In the scheme, intermediate nodes perform additional
coding yet do not decode nor even wait for a block of packets before sending
out coded packets. Rather, whenever they have a transmission opportunity, they
send out coded packets formed from random linear combinations of previously
received packets. All coding and decoding operations have polynomial
complexity.
We show that the scheme is capacity-achieving as long as packets received on
a link arrive according to a process that has an average rate. Thus, packet
losses on a link may exhibit correlation in time or with losses on other links.
In the special case of Poisson traffic with i.i.d. losses, we give error
exponents that quantify the rate of decay of the probability of error with
coding delay. Our analysis of the scheme shows that it is not only
capacity-achieving, but that the propagation of packets carrying "innovative"
information follows the propagation of jobs through a queueing network, and
therefore fluid flow models yield good approximations. We consider networks
with both lossy point-to-point and broadcast links, allowing us to model both
wireline and wireless packet networks.Comment: 33 pages, 6 figures; revised appendi
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Capacities of erasure networks
textWe have investigated, in various multiple senses, the “capacity” of several models of erasure networks. The defining characteristic of a memoryless erasure network is that each channel between any two nodes is an independent erasure channel. The models that we explore differ in the absence or presence of interference at either the transmitters, the receivers, or both; and in the availability of feedback at the transmitters. The crux of this work involves the investigation and analysis of several different performance measures for these networks: traditional information capacity (including multicast capacity and feeback capacity), secrecy capacity, and transport capacity.Electrical and Computer Engineerin
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