Using Keyword Spotting and Utterance Verification to a Prank Call Rejection System

In this paper, a single keyword spotting and verification prototype system aiming at rejecting prank calls is reported. The system issues an announcement in Mandarin which instructs International Operator Direct Connection (IODC) customer$ to speak a keyword in Mandarin. If the system recognizes the keyword, then it switches the line to a telephone operator. If not, the call is assumed to be a prank call and the line is cut off. The underlying algorithm of this current system consists of a keyword spotter, to extract a single keyword, and a rejector, to verify whether a valid keyword or not, in each spontaneous speech utterance. The experimental results demonstrate that 97.1% of prank calls were rejected while only 2.4% of customer calls were rejected. The field-trial system was developed and has been in operation at the Chunghwa Telecom International Business Group since March 1998.