A method at a base station of performing Circuit Switched Fall Back, CSFB, from a serving Radio Access Technology, RAT, to a target RAT of a mobile terminal in a communications network, comprising: receiving a signal quality measure of the serving RAT from the mobile terminal, wherein said signal quality measure of the serving RAT comprising a Channel Quality Indicator, CQI, a signal strength measure, a signal-to-interference-plus-noise ratio, SINR, or a quality measurement report of the serving RAT; determining (S101) that a change is to be made from a serving RAT cell to a first target RAT since a requested service for the mobile terminal cannot be provided for in the serving RAT; estimating (S102) a signal quality measure of the first target RAT based on the signal quality measure of the serving RAT, wherein the estimation of the signal quality measure of the first target RAT comprises considering a target cell of the first target RAT to which the mobile terminal is to change to be co-located with the serving cell of the serving RAT and calculating the estimation of the signal quality measure as a function of the signal quality measure of the serving RAT and an offset function based on operating frequency of the serving RAT, transmission power of the serving cell in the serving RAT, operating frequency of the first target RAT, transmission power of the target cell in the first target RAT; instructing (S103) the mobile terminal to perform a CSFB from the serving RAT to the first target RAT if the estimated signal quality measure of the first target RAT exceeds a quality threshold value, and instructing (S104) the mobile terminal to perform a CSFB from the serving RAT to a second target RAT if the estimated signal quality measure of the first RAT does not exceed the quality threshold value, wherein the serving RAT pertains to Long Term Evolution, LTE, the first target RAT pertains to Universal Mobile Telecommunications System, UMTS, and the second target RAT pertains to Global System for Communication, GSM. receiving a signal quality measure of the serving RAT from the mobile terminal, wherein said signal quality measure of the serving RAT comprising a Channel Quality Indicator, CQI, a signal strength measure, a signal-to-interference-plus-noise ratio, SINR, or a quality measurement report of the serving RAT; determining (S101) that a change is to be made from a serving RAT cell to a first target RAT since a requested service for the mobile terminal cannot be provided for in the serving RAT; estimating (S102) a signal quality measure of the first target RAT based on the signal quality measure of the serving RAT, wherein the estimation of the signal quality measure of the first target RAT comprises considering a target cell of the first target RAT to which the mobile terminal is to change to be co-located with the serving cell of the serving RAT and calculating the estimation of the signal quality measure as a function of the signal quality measure of the serving RAT and an offset function based on operating frequency of the serving RAT, transmission power of the serving cell in the serving RAT, operating frequency of the first target RAT, transmission power of the target cell in the first target RAT; instructing (S103) the mobile terminal to perform a CSFB from the serving RAT to the first target RAT if the estimated signal quality measure of the first target RAT exceeds a quality threshold value, and instructing (S104) the mobile terminal to perform a CSFB from the serving RAT to a second target RAT if the estimated signal quality measure of the first RAT does not exceed the quality threshold value, wherein the serving RAT pertains to Long Term Evolution, LTE, the first target RAT pertains to Universal Mobile Telecommunications System, UMTS, and the second target RAT pertains to Global System for Communication, GSM. <EOS>