On the Minimum Transmit Power in Cochannel Femtocells

This letter is concerned with the transmit power minimization in co-channel femtocell networks in order to reduce the interference inflicted on the macrocell users while satisfying a target constraint on either the ergodic capacity or the average BER under Rayleigh fading. New expressions are derived for the minimum downlink femtocell transmit power in the presence of co-channel interference from the macro base station. The power minimization problem is solved under a minimum transmission rate constraint as well as under a maximum bit error rate (BER) constraint in a Rayleigh fading environment.