In this paper, we consider user equipment which is not yet connected to a given UMTS-FDD network. We propose an algorithm which allows to the user equipment to estimate bit error rate (BER) of a potential downlink in term of the spreading factor and of the power that could be allocated by a base station to this virtual link. This problem is motivated by the context of cognitive radio. Our approach is based on the estimation of the instantaneous signal-to-noise-plus-interference ratio (SINR) of the virtual link. For this, we derive a closed-form approximation of the SINR which only depends on the powers and on the channels between each active base station and the user equipment ; these parameters can be estimated easily from the pilot channels transmitted by the active base stations