In this thesis, we discuss the performance of compressed mode(CM), which enables seamless interfrequency handover with only one radio front end, in terms of acquisition of new link and Qos(Quality of service) of old link. Analysis and extensive simulation are provided for the detection probability of synchronization channel(SCH) and the bit error probability of dedicated physical channel(DPCH). Trade-off between detection probability and bit error probability is considered. Also, for the consideration of actual situation under interfrequency handover, downlink interference model is developed and applied to all simulations. Cell search in CM is basically identical to an initial cell search, but one slot cannot be used due to the switching time and the inherent feature of WCDMA. In addition, the number of decision variables in the acquisition of secondary SCH(S-SCH) can be reduced significantly. It is found that the acquisition of S-SCH is more tolerable to the variation of channel in view of little effect by larger variation of interference power. Although there exist several reasons causing loss in QoS of data in DPCH, puncturing for channel coding is dominant and other factors can be mitigated by the combining of sufficient paths. Higher detection probability for SCH can be obtained by adopting larger transmission gap, but it leads to more severe performance degradation in DPCH. So, consideration on the trade-off is taken between detection probability and bit error probability with respect to total required power to satisfy a given requirement of performance. From the simulation results, it can be said that TGL = 4 seems preferable under the environment considered.