Adaptive communications in interference-coupled systems

In multiple access wireless systems, adaptive algorithms for power control, antenna arrays, and equalizers can all lead to significant capacity increases. However independent adaptation of these algorithms is not possible, since changes in beam pattern affect the interference power and thus the required transmitted power level and the residual multipath components, which in turn cause the equalizer to need readjustment. There is a further coupling among users due to the mutual interference. Thus care must be exercised in applying simple gradient descent methods. We describe the nature of the coupling and what modifications must be made to the distributed adaptive methods to ensure stability.