Control of multi-node mobile Communications networks with time varying channels via stability methods

Tuesday, June 28, 2005 - 11:00am - 12:00pm
EE/CS 3-180
Harold Kushner (Brown University)
Consider a communications network consisting of mobiles, each of which can be scheduled to serve as a receiver and/or transmitter. Data from many external sources arrives at the various mobiles in some random way. Each mobile can serve as a node in the possibly multihop path from source to destination.

At each mobile the data is queued according to the source-destination pair until transmitted. Time is divided into small scheduling intervals. The connecting channels are randomly varying due to the motion of the mobiles and consequent scattering. At the beginning of the intervals, the channels are estimated via pilot signals and this information is used for scheduling.

The issues are the allocation of transmission power and/or time and bandwidth to the various queues at the various mobiles in a queue and channel-state dependent way to assure stability and good operation. Lost packets might or might not have to be retransmitted. The decisions are made at the beginning of the scheduling intervals. In a recent work, stochastic stability methods were used to develop scheduling policies for the simple system where there is a single transmitter communicating with many mobiles. The resulting controls were readily implementable and allowed a range of tradeoffs between current rates and queue lengths, under very weak conditions. Here the basic methods and results are extended to the network case. The choice of Liapunov function allows a choice of the effective performance criteria. All essential factors are incorporated into a mean rate function, so that the results cover many different systems.

Because of the non-Markovian nature of the problem, we use the perturbed Stochastic Liapunov function method, which is designed for such problems.