Optimal and Distributed Protocols for Cross-Layer Design of Physical and Transport Layers in MANETs

Abstract—We seek distributed protocols that attain the global optimum allocation of link transmitter powers and source rates in a cross-layer design of a mobile ad hoc network. Although the underlying network utility maximization is nonconvex, convexity plays a major role in our development. We provide new convexity results surrounding the Shannon capacity formula, allowing us to abandon suboptimal high-SIR approximations that have almost become entrenched in the literature. More broadly, these new re-sults can be back-substituted into many existing problems for sim-ilar benefit. Three protocols are developed. The first is based on a convexifi-cation of the underlying problem, relying heavily on our new con-vexity results. We provide conditions under which it produces a globally optimum resource allocation. We show how it may be dis-tributed through message passing for both rate- and power-alloca-tion. Our second protocol relaxes this requirement and involves a novel sequence of convex approximations, each exploiting existing TCP protocols for source rate allocation. Message passing is only used for power control. Our convexity results again provide suffi-cient conditions for global optimality. Our last protocol, motivated by a desire of power control devoid of message passing, is a near optimal scheme that makes use of noise measurements and enjoys a convergence rate that is orders of magnitude faster than existing methods. Index Terms—Congestion control, cross-layer optimization, mo-bile ad hoc network, network utility maximization, outage proba-bility, power control, Rayleigh fading. I