Channel Access Algorithms with Active Link Protection for Wireless Communication Networks with Power Control Nicholas Bambos, Shou C. Chen, Gregory J. Pottie

Agenda Overview Motivation (Problem statement) Foundation work DPC/ALP algorithm Properties of DPC/ALP algorithm Extensions to algorithm VDO and FDO Simulation results and extensions Comments

Overview: DPC/ALP DPC: An Algorithm for transmit power control –Adaptive –Distributed –On-line –Different QoS levels ALP: Admission control algorithm –Protect existing users form disruption –Method for new users to enter wireless network –“Smooth dynamics”

Motivation (Problem Statement) Power control with –Entry and –Egress from the network While maintaining QoS –For existing users Admissible?

Model QoS constraint

Foundation Work: DPC Distributed Power Control –P(k+1)=FP(k)+u –P->P* where But –Convergence path may lead to “outage” or QoS problems Alternative form: Foschini and Miljanic

DPC/ALP Algorithm Based on DPC (above) Active link protection – Ensures existing users QoS is maintained when new users are added. Distributed admission control Extended – Voluntary drop out Mechanism for “hot spots”

DPC/ALP Algorithm – continued admitted new Protection margin or buffer zone Geometric power up

Properties of DPC/ALP User is admitted when –Once admitted continuously admitted – bounded power overshoot New users –Increasing SIR’s –If admissible then admitted in bounded time But infinite power may be required Admissibility vs. admissibility

DPC/ALP/VDO Voluntary Drop-Out –When too many new users none wins –Solution is one or more links backs off Types of VDO –Coin flipping after a parameterized number of tries –Timer based

DPC/ALP/VDO/FDO Power constraint FDO – forced drop out –Active user nears max –Signals local users seeking admission to drop out –Reduces contention for resources

Simulation results VDO –Increases number of users significantly –Results in backlog of users not yet admitted Threshold effect for great enough arrival rate of new users! Clogging effect VDO and FDO –Decrease in time to admission –Higher through-put Hot spots Congestion control

Extensions Probing –Predict admissibility from two SIR samples Solve for X Y Admit after k=

Comments Dynamics of admission control –Critical to ad-hoc networks –Rapidly changing user group Results are very parameter sensitive