828 research outputs found
Further Results on Coding for Reliable Communication over Packet Networks
In "On Coding for Reliable Communication over Packet Networks" (Lun, Medard,
and Effros, Proc. 42nd Annu. Allerton Conf. Communication, Control, and
Computing, 2004), a capacity-achieving coding scheme for unicast or multicast
over lossy wireline or wireless packet networks is presented. We extend that
paper's results in two ways: First, we extend the network model to allow
packets received on a link to arrive according to any process with an average
rate, as opposed to the assumption of Poisson traffic with i.i.d. losses that
was previously made. Second, in the case of Poisson traffic with i.i.d. losses,
we derive error exponents that quantify the rate at which the probability of
error decays with coding delay.Comment: 5 pages; to appear in Proc. 2005 IEEE International Symposium on
Information Theory (ISIT 2005
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
Improved Delay Estimates for a Queueing Model for Random Linear Coding for Unicast
Consider a lossy communication channel for unicast with zero-delay feedback.
For this communication scenario, a simple retransmission scheme is optimum with
respect to delay. An alternative approach is to use random linear coding in
automatic repeat-request (ARQ) mode. We extend the work of Shrader and
Ephremides, by deriving an expression for the delay of random linear coding
over field of infinite size. Simulation results for various field sizes are
also provided.Comment: 5 pages, 3 figures, accepted at the 2009 IEEE International Symposium
on Information Theor
Performance Modelling and Optimisation of Multi-hop Networks
A major challenge in the design of large-scale networks is to predict and optimise the
total time and energy consumption required to deliver a packet from a source node to a
destination node. Examples of such complex networks include wireless ad hoc and sensor
networks which need to deal with the effects of node mobility, routing inaccuracies, higher
packet loss rates, limited or time-varying effective bandwidth, energy constraints, and the
computational limitations of the nodes. They also include more reliable communication
environments, such as wired networks, that are susceptible to random failures, security
threats and malicious behaviours which compromise their quality of service (QoS) guarantees.
In such networks, packets traverse a number of hops that cannot be determined
in advance and encounter non-homogeneous network conditions that have been largely
ignored in the literature. This thesis examines analytical properties of packet travel in
large networks and investigates the implications of some packet coding techniques on both
QoS and resource utilisation.
Specifically, we use a mixed jump and diffusion model to represent packet traversal
through large networks. The model accounts for network non-homogeneity regarding
routing and the loss rate that a packet experiences as it passes successive segments of a
source to destination route. A mixed analytical-numerical method is developed to compute
the average packet travel time and the energy it consumes. The model is able to capture
the effects of increased loss rate in areas remote from the source and destination, variable
rate of advancement towards destination over the route, as well as of defending against
malicious packets within a certain distance from the destination. We then consider sending
multiple coded packets that follow independent paths to the destination node so as to
mitigate the effects of losses and routing inaccuracies. We study a homogeneous medium
and obtain the time-dependent properties of the packet’s travel process, allowing us to
compare the merits and limitations of coding, both in terms of delivery times and energy
efficiency. Finally, we propose models that can assist in the analysis and optimisation
of the performance of inter-flow network coding (NC). We analyse two queueing models
for a router that carries out NC, in addition to its standard packet routing function. The
approach is extended to the study of multiple hops, which leads to an optimisation problem
that characterises the optimal time that packets should be held back in a router, waiting
for coding opportunities to arise, so that the total packet end-to-end delay is minimised
Random Linear Network Coding For Time Division Duplexing: Energy Analysis
We study the energy performance of random linear network coding for time
division duplexing channels. We assume a packet erasure channel with nodes that
cannot transmit and receive information simultaneously. The sender transmits
coded data packets back-to-back before stopping to wait for the receiver to
acknowledge the number of degrees of freedom, if any, that are required to
decode correctly the information. Our analysis shows that, in terms of mean
energy consumed, there is an optimal number of coded data packets to send
before stopping to listen. This number depends on the energy needed to transmit
each coded packet and the acknowledgment (ACK), probabilities of packet and ACK
erasure, and the number of degrees of freedom that the receiver requires to
decode the data. We show that its energy performance is superior to that of a
full-duplex system. We also study the performance of our scheme when the number
of coded packets is chosen to minimize the mean time to complete transmission
as in [1]. Energy performance under this optimization criterion is found to be
close to optimal, thus providing a good trade-off between energy and time
required to complete transmissions.Comment: 5 pages, 6 figures, Accepted to ICC 200
Energy-delay tradeoff in wireless network coding
A queueing model for wireless communication network in which network coding is employed is introduced. It is shown that networks with coding are closely related to queueing networks with positive and negative customers. Analytical upper and lower bounds on the energy consumption and the delay are obtained using a Markov reward approach. The tradeoff between minimizing energy consumption and minimizing delay is investigated. Exact expressions are given for the minimum energy consumption and the minimum delay attainable in a network
Scheduling of Multicast and Unicast Services under Limited Feedback by using Rateless Codes
Many opportunistic scheduling techniques are impractical because they require
accurate channel state information (CSI) at the transmitter. In this paper, we
investigate the scheduling of unicast and multicast services in a downlink
network with a very limited amount of feedback information. Specifically,
unicast users send imperfect (or no) CSI and infrequent acknowledgements (ACKs)
to a base station, and multicast users only report infrequent ACKs to avoid
feedback implosion. We consider the use of physical-layer rateless codes, which
not only combats channel uncertainty, but also reduces the overhead of ACK
feedback. A joint scheduling and power allocation scheme is developed to
realize multiuser diversity gain for unicast service and multicast gain for
multicast service. We prove that our scheme achieves a near-optimal throughput
region. Our simulation results show that our scheme significantly improves the
network throughput over schemes employing fixed-rate codes or using only
unicast communications
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