A precoder for reducing downlink interference from femtocells to macro users based on cognitive radio

This paper proposes a preprocessor for femtocell base stations to avoid the downlink interference to the macro users, where both systems are multicarrier systems. By using the concept of cognitive radio, we design a low complexity transmitter including a precoder followed by a power allocation. With the judicious design of the interference tolerant constraints, the performance degradation of the macro user is controlled to be less than a predetermined value. Simulation results show that the spectrum efficiency of the femtocell system with the presented transmitter is improved significantly.