Logarithmic Feedback Control of Passive Interference

Passive intermodulation interference in wireless systems is caused by downlink radio transmissions that are nonlinearly mixed and frequency shifted in close conductive objects. This interference may jam uplink receivers. The paper proposes mitigation by logarithmic feedback control using downlink transmission power actuation. The nonlinear single downlink feedback loop is proved to be globally stable provided that a loop-gain-loop-delay stability condition holds. The multi downlink problem is then addressed by derivation of a degree greedy multiple-input-single-output controller that is proved to be optimal in a static sense. Simulations using measured data traffic illustrate the performance of the control systems.