Distributed Power Control 

The performance of all wireless communications systems is a function of the signal-to-interference-plus-noise-ratio (SINR).  While readily apparent at the physical layer, it is also generally true at the higher layers.  Optimal network performance is typically achieved only at a unique power vector [ref - Mike].  In a static network, it would be trivial to assign transmit powers to each node in the network to achieve this power vector.  However, wireless systems are generally mobile, or at least operate in a dynamic environment, so that any initial power vector assignment will not maintain its optimality. 

 For instance, consider a pedestrian in an urban cellular environment who rounds a corner and creates a line-of-sight (LOS) path to his base station.  This results in a significant increase in the power received at his base station, significantly improving his performance, but potentially jamming the other users in the network.  Clearly this new environment has a different ideal power vector than the original.

 In an attempt to maintain the optimum power vector, most modern communications schemes include some form of power control.  Power control is a set of real-time algorithms implemented on a network in order to maximize a performance metric.  Some common applications of power control include:

·         Ensuring proper operation in multi-user direct-sequence spread spectrum (DS-SS) systems

·         Trading off system capacity for quality of service

·         Trading off battery life versus quality of service

Every power control scheme is designed for a particular target application and anticipated devices.  These assumptions permit the network planner to maximize QoS while minimizing the use of system resources. 

In a centralized power control algorithm, all power level decisions are made by a recognized authority in the network. Some network topologies are well suited for centralized decision making, and thus are typically implemented as such.  For instance, the conceptual star topology that exists in a unicellular wireless system is a star topology with the base station (BS) forming the hub and the remaining nodes being the mobiles (MS).  In this particular situation, the BS has complete knowledge of the situation - can all mobiles.

Although some progress has been made analyzing distributed power control algorithms, no standardized approach has been formalized.  As such, many authors use radically different approaches that are difficult to generalize.  The work presented on this site adopts a game theoretic approach to analyzing distributed power control.