A double loop jammer cancellation system for colocated radios

Colocation of multiple base stations on one common site may result in receiver desensitization and the generation of intermodulation products when large transmit signals overwhelm the base station receivers. The paper proposes an adaptive double loop cancellation system with two reference antennas. The system is capable of producing two nulls at different frequencies. The nulls remove transmit/jamming signals before they couple into the victim receiver, and hence, prevent nonlinearities. The paper analyzes the practicality of the system. The key challenge to stop or minimize self-cancellation of the desired signal in the primary input as a result of the reference antennas coupling in desired signal samples has been addressed. A hardware prototype has been developed. It has been configured to have a maximum desired signal self-cancellation of 1.84dB. The system achieves a commendable 30dB and 50dB cancellation of two jamming signals; sufficient to reduce the interfering third-order intermodulation products well below the receiver noise floor.