Speech compensation in dual-mode telephone

• US 5,550,893 A
• Filed: 01/31/1995
• Issued: 08/27/1996
• Est. Priority Date: 01/31/1995
• Status: Expired due to Term

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Heidari, Alireza R.
• Primary Examiner(s): Bost, Dwayne D.
• Application Number:
  US08/381,314
• Time in Patent Office: 574 Days
• Field of Search: 375/216, 375/240, 379/58, 379/59, 455/33.1
• US Class Current: 455/553.1
• CPC Class Codes: H04B 1/38 Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
• CPC Class Codes: H04B 1/40 Circuits
• CPC Class Codes: H04B 1/406 with more than one transmission mode, e.g. analog and digital modes

Abstract

A dual-mode telephone has transmit and receive channels suitable for cellular telephony, and is operative in analog and digital modes of communication. Each of the channels has parallel branches of circuitry wherein the circuitry of one branch accommodates voice signals in accordance with an analog protocol and the second branch accommodates voice signals processed by digital compression and expansion circuitry. The digital compression circuitry, which is employed for outgoing voice signals, and the digital expansion circuitry, which is employed for incoming voice signals, constitute a vocoder operative under control of a microcontroller unit. Operation of the vocoder during a digital transmission mode introduces a digitally processed quality to received voice signals, this characteristic being distinguishable from the voice quality of pulse-code modulation employed in the analog communication mode. In order to introduce uniformity of voice quality during both analog and digital modes of communication, the telephone includes circuitry for inserting the vocoder circuitry into the analog branch of the receive channel as a speech compensator with the compression and expansion circuitry operated in a back-to-back arrangement. The input and output signal formats of the speech compensator are identical, but the resulting output signal of the compensator has a digitally processed voice quality. Thereby, the digitally processed voice quality is present in both analog and digital modes of communication so as to eliminate a disturbance in change of voice quality during a hand-off between the two communication modes.

Claims

1. A dual mode telephone operative in an analog mode of communication and in a digital mode of communication, the telephone having a transmit channel and a receive channel suitable for cellular telephony, the telephone comprising:

digital compression circuitry and analog protocol transmission circuitry within said transmit channel;

digital expansion circuitry and analog protocol reception circuitry within said receive channel;

selector switching means operative in said transmit channel for bypassing said digital compression circuitry by said analog protocol transmission circuitry and being operative in said receive channel for bypassing said digital expansion circuitry by said analog protocol reception circuitry for operation of the telephone in the analog communication mode, said telephone operating in the digital communication mode upon activation of said switching means to terminate said bypassing; and

means, operative during the analog communication mode, for connecting an output terminal of the digital compression circuitry to an input terminal of the digital expansion circuitry to form a speech compensator, and means for inserting said speech compensator in said receive channel during said analog communication mode for providing a digitally processed voice quality to voice signals communicated via said telephone in both said digital and said analog modes of communication.

2. A radiotelephone comprising:

a radio frequency (RF) unit enabling transmission of a voice signal to a base station and reception of a voice signal from the base station;

a voice input means and a transmit channel interconnecting the voice input means to the RF unit;

a voice output means and a receive channel interconnecting the voice output means to the RF unit;

wherein a portion of the transmit channel is bifurcated into an analog protocol signal branch and a digital protocol signal branch;

a portion of said receive channel is bifurcated into an analog protocol signal branch and a digital protocol signal branch;

said radiotelephone further comprises switching means operative to direct voice signals alternately into either the analog protocol branches of said transmit and said receive channels to effect an analog mode of communication or into the digital protocol branches of said transmit and said receive channels to effect a digital mode of communication;

said digital protocol branch of said transmit channel comprises a voice signal compressor and said digital protocol branch of said receive channel comprises a voice signal expander; and

said radiotelephone further comprises means, operative during the analog communication mode, for connecting an output terminal of the compressor to an input terminal of the expander to form a speech compensator, and means for inserting said speech compensator in

said receive channel during said analog communication mode for providing a digitally processed voice quality to voice signals communicated via said telephone in both said digital and said analog modes of communication.

3. A method of operating a dual-mode telephone in an analog mode of communication and in a digital mode of communication, the telephone having a transmit channel and a receive channel suitable for cellular telephony, the telephone further comprising analog protocol transmission circuitry within said transmit channel and analog protocol reception circuitry within said receive channel and a vocoder switchably connectable within said transmit channel and within said receive channel;

the method comprising steps of;

in said digital communication mode, switching a transmitted voice signal path away from said analog protocol transmission circuitry and into said vocoder, and switching a received voice signal path away from said analog protocol reception circuitry and into said vocoder; and

during said analog communication mode, bypassing said vocoder by said analog protocol transmission circuitry and by said analog protocol reception circuitry, and inserting said vocoder into said receive channel between said analog protocol reception circuitry and an output port of said receive channel.

4. A method of operating a radiotelephone in an analog mode of communication and in a digital mode of communication, the radiotelephone having a transmit channel and a receive channel suitable for cellular telephony, wherein a portion of the transmit channel is bifurcated into an analog protocol signal branch and a digital protocol signal branch, wherein a portion of said receive channel is bifurcated into an analog protocol signal branch and a digital protocol signal branch, wherein the radiotelephone further comprises analog protocol transmission circuitry and a digital voice signal compressor disposed respectively within the analog and the digital protocol branches of said transmit channel, and wherein the radiotelephone further comprises analog protocol reception circuitry and a digital voice signal expander disposed respectively within the analog and the digital protocol branches of said receive channel;

the method comprising steps of;

switching voice signals alternately into either the analog protocol branches of said transmit and said receive channels to effect an analog mode of communication or into the digital protocol branches of said transmit and said receive channels to effect a digital mode of communication;

during the analog communication mode, connecting an output terminal of the compressor to an input terminal of the expander to form a speech compensator; and

inserting said speech compensator in said receive channel during said analog communication mode for providing a digitally processed voice quality to voice signals communicated via said radiotelephone in both said digital and said analog modes of communication.