In the mobile radio communication system where the UMTS and an another system
coexist an idle slot for observing the frequency component of another system is
inserted in one superframe of UMTS. The duration of this idle slot is at most half
of the duration of one frame that form the superframe and it is inserted at an
interval of a specified number of frames. Therefore, the frequency component of
the another system can be observed securely from the UMTS. Further, deterioration
of interleaving performance of the compressed mode frames during such observation
can be suppressed.
