Cooperation techniques in cross-layer design

We explore node cooperation in a cross-layer design framework to optimize wireless network performance. We focus on the design methodology for networks with hard energy constraints, where each network node is equipped with a finite energy source that cannot be recharged. We consider network topologies where transmission distances may be small, so that transmission energy does not necessarily dominate total energy consumption. We assume that network nodes can cooperate across multiple layers of the protocol stack: in signal transmissions at the link layer, spectrum sharing at the multiple access layer, information relaying at the network layer, and information processing at the application layer. We investigate how to incorporate node cooperation at individual protocol layers into an overall cross-layer design framework using several design examples. In the first example we consider joint design of the routing, MAC, and link layer protocols to minimize total energy consumption. The joint design is posed within an optimization framework subject to given system constraints, which can be easily solved using existing convex optimization techniques. In the second example we propose a cooperative MIMO technique where multiple nodes within a cluster cooperate in signal transmission and/or reception to reduce energy and delay. By treating each cooperating cluster as a super node, the design optimization falls within the same framework as our first example. The third example considers cooperating nodes trying to jointly estimate an unknown target. In this setting we optimize link layer power control and the number of cooperating nodes to meet a desired distortion while minimizing the total power consumption. These design examples illustrate several of the key features and tradeoffs in cross-layer design of wireless networks with cooperating nodes, but they only scratch the surface of possible techniques and applications. The goal is for these design examples to motivate further exploration of cooperative techniques in cross-layer design.