7 research outputs found
Utility Optimal Coding for Packet Transmission over Wireless Networks - Part II: Networks of Packet Erasure Channels
We define a class of multi--hop erasure networks that approximates a wireless
multi--hop network. The network carries unicast flows for multiple users, and
each information packet within a flow is required to be decoded at the flow
destination within a specified delay deadline. The allocation of coding rates
amongst flows/users is constrained by network capacity. We propose a
proportional fair transmission scheme that maximises the sum utility of flow
throughputs. This is achieved by {\em jointly optimising the packet coding
rates and the allocation of bits of coded packets across transmission slots.}Comment: Submitted to the Forty-Ninth Annual Allerton Conference on
Communication, Control, and Computing, Monticello, Illinois, US
Delay Optimal Event Detection on Ad Hoc Wireless Sensor Networks
We consider a small extent sensor network for event detection, in which nodes
take samples periodically and then contend over a {\em random access network}
to transmit their measurement packets to the fusion center. We consider two
procedures at the fusion center to process the measurements. The Bayesian
setting is assumed; i.e., the fusion center has a prior distribution on the
change time. In the first procedure, the decision algorithm at the fusion
center is \emph{network-oblivious} and makes a decision only when a complete
vector of measurements taken at a sampling instant is available. In the second
procedure, the decision algorithm at the fusion center is \emph{network-aware}
and processes measurements as they arrive, but in a time causal order. In this
case, the decision statistic depends on the network delays as well, whereas in
the network-oblivious case, the decision statistic does not depend on the
network delays. This yields a Bayesian change detection problem with a tradeoff
between the random network delay and the decision delay; a higher sampling rate
reduces the decision delay but increases the random access delay. Under
periodic sampling, in the network--oblivious case, the structure of the optimal
stopping rule is the same as that without the network, and the optimal change
detection delay decouples into the network delay and the optimal decision delay
without the network. In the network--aware case, the optimal stopping problem
is analysed as a partially observable Markov decision process, in which the
states of the queues and delays in the network need to be maintained. A
sufficient statistic for decision is found to be the network-state and the
posterior probability of change having occurred given the measurements received
and the state of the network. The optimal regimes are studied using simulation.Comment: To appear in ACM Transactions on Sensor Networks. A part of this work
was presented in IEEE SECON 2006, and Allerton 201
Utility Optimal Coding for Packet Transmission over Wireless Networks - Part I: Networks of Binary Symmetric Channels
We consider multi--hop networks comprising Binary Symmetric Channels
(s). The network carries unicast flows for multiple users. The
utility of the network is the sum of the utilities of the flows, where the
utility of each flow is a concave function of its throughput. Given that the
network capacity is shared by the flows, there is a contention for network
resources like coding rate (at the physical layer), scheduling time (at the MAC
layer), etc., among the flows. We propose a proportional fair transmission
scheme that maximises the sum utility of flow throughputs subject to the rate
and the scheduling constraints. This is achieved by {\em jointly optimising the
packet coding rates of all the flows through the network}.Comment: Submitted to Forty-Ninth Annual Allerton Conference on Communication,
Control, and Computing, Monticello, IL, US
Proportional Fair Coding for Wireless Mesh Networks
We consider multihop wireless networks carrying unicast flows for multiple users. Each flow has a specified delay deadline, and the lossy wireless links are modeled as binary symmetric channels (BSCs). Since transmission time, also called airtime, on the links is shared among flows, increasing the airtime for one flow comes at the cost of reducing the airtime available to other flows sharing the same link. We derive the joint allocation of flow airtimes and coding rates that achieves the proportionally fair throughput allocation. This utility optimization problem is nonconvex, and one of the technical contributions of this paper is to show that the proportional fair utility optimization can nevertheless be decomposed into a sequence of convex optimization problems. The solution to this sequence of convex problems is the unique solution to the original nonconvex optimization. Surprisingly, this solution can be written in an explicit form that yields considerable insight into the nature of the proportional fair joint airtime/coding rate allocation. To our knowledge, this is the first time that the utility fair joint allocation of airtime/coding rate has been analyzed, and also one of the first times that utility fairness with delay deadlines has been considered