Performance Enhancement of LTE Underlay Cognitive Femtocells System Based on Macro Users Localization

LTE overlay cognitive femtocells system can provide a satisfied throughput for the macro and the femto users. On the other hand, the femto users can assign only the vacated subcarriers from the macro users. This assignment results in a reduced throughput for the femto users. Moreover, their throughput can have a zero value when the macro users operate on all subcarriers. In this paper, an underlay cognitive femtocells operation is proposed. The femtocells can share the subcarriers with the existing macrocells in such a way that their transmission cannot affect the macro users' performance. The macro users' positions can be determined, during their uplink transmission, using the received signal strength at the femto users. Then, the femtocells adapt their emitted power to guarantee a satisfied macro users' performance. The performance of the proposed LTE underlay cognitive femtocells system is mathematically analyzed, simulated, and compared with the previous one which applies overlay cognitive femtocells. It can be observed that, the femto users' throughput is existent and has a high value in comparison with the previous LTE overlay cognitive femtocells system. Furthermore, the proposed system has a higher macro and femto users' throughput.