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Abstract

A user-authentication system includes an authorized user device (AUD) for transmission of dtmf tones to a user-verification system (UVS) over a telephone network, where user-verification is performed and authorized users are granted access to a desired service. In a memory module of the AUD, a plurality of passphrases and identifying data are stored for subsequent transmission to the UVS. The compensating system comprises a pair of tone devices that generate low frequency tones and high frequency tones, respective that are amplified to different amplification levels. The amplification levels compensate for the low and high frequency tone transmission characteristics associated with different microphones in use in a public telephone system. The systems further performs channel normalization with the user-activated AUD and the UVS. Tone signals representative of the access telephone number transmitted by the AUD to reach the UVS, have a reference amplitude of zero. The UVS receives the tones and a variable amplifier generates gain factors that compensate for deviations in the expected signal strength of each of the tone, caused by deficiencies in the telephone system. In another embodiment, the AUD generates a first plurality of standard tones that are representative of the portion of the frequency spectrum in which an authorized user's voice typically lies. This compensation permits the UVS to have an accurate representation of transmitted signals such as the user's voice, prior to performing user-verification.

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First Claim