Mapping of digital data symbols onto one or more formant frequencies for transmission over a coded voice channel

• US 6,208,959 B1
• Filed: 12/15/1997
• Issued: 03/27/2001
• Est. Priority Date: 12/15/1997
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Swerup, Jan, Nerbrant, Per-Olof, Jonsson, Björn, Törnqvist, Krister
• Primary Examiner(s): Hudspeth, David R.
• Assistant Examiner(s): Azad, Abul K.
• Application Number:
  US08/990,773
• Time in Patent Office: 1,198 Days
• Field of Search: 704/200, 704/201, 704/203, 704/209, 704/205, 704/221, 704/207, 704/222
• US Class Current: 704/209
• CPC Class Codes: G10L 19/00 Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis in musical instruments G10H
• CPC Class Codes: H04Q 1/45 using multi-frequency signalling H04Q1/46 takes precedence

Abstract

A digital input symbol is transmitted to a receiver by determining one or more formant frequencies that correspond to the digital input symbol. In one embodiment, a pre-programmed addressable memory is used to map the set of possible digital input symbols onto a set of corresponding speech units, each comprising a superposition of one or more formant frequencies. A signal is then generated having the speech units. The signal is supplied for transmission over a voice channel. This may include supplying the signal to a voice coder prior to transmission. In another aspect of the invention, a forward error correction code (FEC) is determined for the digital input symbol, and the one or more speech units are modified as a function of the forward error correction code. In this way, the FEC may also be transmitted with the encoded input symbol. The modification may affect any of a number of attributes of the speech units, including a volume attribute and a pitch attribute.

Claims

1. A method of transmitting a digital input data symbol to a receiver, the method comprising the steps of:

mapping one or more formant frequencies that correspond to the digital input data symbol;

generating a signal having the one or more formant frequencies; and

supplying the signal for transmission over a voice channel.

2. The method of claim 1, wherein the step of supplying the signal for transmission over a voice channel comprises the step of supplying the signal to a voice coder.

3. The method of claim 1, wherein the step of determining mapping one or more formant frequencies that correspond to the digital input data symbol comprises the steps of:

supplying the digital input data symbol to an address input port of an addressable memory means, wherein the addressable memory means has formant frequency codes stored therein at addresses such that when the digital input data symbol is supplied to the address input port of the addressable memory means, a corresponding formant frequency code appears at an output port of the addressable memory means; and

using, as an indicator of the determined one or more formant frequencies, the corresponding formant frequency code appearing at the output port of the addressable memory.

4. The method of claim 3, wherein the corresponding formant frequency code indicates a plurality of formant frequencies, and

wherein the step of generating the signal having the one or more formant frequencies comprises the step of generating the plurality of formant frequencies indicated by the corresponding formant frequency code.

5. The method of claim 1, wherein the step of generating the signal having the one or more formant frequencies comprises:

determining a forward error correction code for the digital input data symbol;

generating a signal having the one or more formant frequencies; and

modifying the signal as a function of the forward error correction code.

6. The method of claim 5, wherein the step of modifying the one or more formant frequencies comprises the step of modifying a volume attribute of the one or more formant frequencies as a function of the forward error correction code.

7. The method of claim 5, wherein the step of modifying the one or more formant frequencies comprises the step of modifying a pitch attribute of the one or more formant frequencies as a function of the forward error correction code.

8. A method of transmitting both speech and digital input data symbols to a receiver, the method comprising the steps of:

transmitting the speech to the receiver by means of a voice channel;

changing to a data transmission mode by automatically generating a predetermined sequence of formant frequencies and transmitting the automatically generated formant frequencies to the receiver by means of the voice channel; and

mapping the digital input data symbols onto a corresponding formant sequence, and then transmitting a signal representing the corresponding formant sequence to the receiver by means of the voice channel.

9. The method of claim 8, wherein the step of mapping the digital input data symbols onto the corresponding formant sequence comprises the step of supplying the digital input data symbols to an input port of an addressable memory means, wherein the addressable memory means has formant frequency codes stored therein at addresses such that when one of the digital input data symbols is supplied to the address input port of the addressable memory means, a corresponding formant frequency code appears at an output port of the addressable memory means.

10. The method of claim 8, further comprising the step of returning to a speech transmission mode by automatically generating a second predetermined sequence of formant frequencies and transmitting the automatically generated second sequence of formant frequencies to the receiver by means of the voice channel.

11. A method for receiving a digital input data symbol, comprising the steps of:

receiving a signal having one or more formant frequencies that have been predefined to correspond to the digital input data symbol and modified as a function of previously transmitted digital input data symbols;

determining a received modification as a function of previously received digital input data symbols;

using the received modification to perform an inverse modification on the received signal, thereby generating an inverse modified signal;

mapping the digital input data symbol that corresponds to the one or more formant frequencies contained in the inverse modified signal; and

using the received modification to generate a signal indicative of validity of the determined digital input data signal.

12. The method of claim 11, wherein the step of mapping the digital input data symbol that corresponds to the one or more formant frequencies contained in the inverse modified signal comprises the steps of:

detecting the one or more formant frequencies that have been predefined to correspond to the digital input data symbol; and

mapping the digital input data symbol that corresponds to the detected one or more formant frequencies.

13. The method of claim 11, wherein the step of mapping the digital input data symbol that corresponds to the one or more formant frequencies contained in the inverse modified signal comprises using automated speech recognition techniques to map the digital input data symbol that corresponds to the one or more formant frequencies contained in the inverse modified signal.

14. An apparatus for transmitting a digital input data symbol to a receiver, the apparatus comprising:

means for mapping one or more formant frequencies that correspond to the digital input data symbol;

means for generating a signal having the one or more formant frequencies; and

means for supplying the signal for transmission over a voice channel.

15. The apparatus of claim 14, wherein the means for supplying the signal for transmission over a voice channel comprises means for supplying the signal to a voice coder.

16. The apparatus of claim 14, wherein the means for mapping one or more formant frequencies that correspond to the digital input data symbol comprises:

means for supplying the digital input data symbol to an address input port of an addressable memory means, wherein the addressable memory means has formant frequency codes stored therein at addresses such that when the digital input data symbol is supplied to the address input port of the addressable memory means, a corresponding formant frequency code appears at an output port of the addressable memory means; and

means for using, as an indicator of the mapped one or more formant frequencies, the corresponding formant frequency code appearing at the output port of the addressable memory.

17. The apparatus of claim 16, wherein the corresponding formant frequency code indicates a plurality of formant frequencies, and

wherein the means for generating the signal having the one or more formant frequencies comprises means for generating the plurality of formant frequencies indicated by the corresponding formant frequency code.

18. The apparatus of claim 14, wherein the means for generating the signal having the one or more formant frequencies comprises:

means for determining a forward error correction code for the digital input data symbol;

means for generating a signal having the one or more formant frequencies; and

means for modifying the signal as a function of the forward error correction code.

19. The apparatus of claim 18, wherein the means for modifying the one or more formant frequencies comprises means for modifying a volume attribute of the one or more formant frequencies as a function of the forward error correction code.

20. The apparatus of claim 18, wherein the means for modifying the one or more formant frequencies comprises means for modifying a pitch attribute of the one or more formant frequencies as a function of the forward error correction code.

21. An apparatus for transmitting both speech and digital input data symbols to a receiver, the apparatus comprising:

means for transmitting the speech to the receiver by means of a voice channel;

means for changing to a data transmission mode by automatically generating a predetermined sequence of formant frequencies and transmitting the automatically generated formant frequencies to the receiver by means of the voice channel; and

means for mapping the digital input data symbols onto a corresponding formant sequence, and then transmitting a signal representing the corresponding formant sequence to the receiver by means of the voice channel.

22. The apparatus of claim 21, wherein the means for mapping the digital input data symbols onto the corresponding formant sequence comprises means for supplying the digital input data symbols to an input port of an addressable memory means, wherein the addressable memory means has formant frequency codes stored therein at addresses such that when one of the digital input data symbols is supplied to the address input port of the addressable memory means, a corresponding formant frequency code appears at an output port of the addressable memory means.

23. The apparatus of claim 21, further comprising means for returning to a speech transmission mode by automatically generating a second predetermined sequence of formant frequencies and transmitting the automatically generated second sequence of formant frequencies to the receiver by means of the voice channel.

24. An apparatus for receiving a digital input data symbol, comprising:

means for receiving a signal having one or more formant frequencies that have been predefined to correspond to the digital input data symbol and modified as a function of previously transmitted digital input data symbols;

means for determining a received modification as a function of previously received digital input data symbols;

means for using the received modification to perform an inverse modification on the received signal, thereby generating an inverse modified signal;

means for mapping the digital input data symbol that corresponds to the one or more formant frequencies contained in the inverse modified signal; and

using the received modification to generate a signal indicative of validity of the determined digital input data signal.

25. The apparatus of claim 24, wherein the means for mapping the digital input data symbol that corresponds to the one or more formant frequencies contained in the inverse modified signal comprises:

means for detecting the one or more formant frequencies that have been predefined to correspond to the digital input data symbol; and

means for mapping the digital input data symbol that corresponds to the detected one or more formant frequencies.

26. The apparatus of claim 26, wherein the means for mapping the digital input data symbol that corresponds to the one or more formant frequencies contained in the inverse modified signal comprises speech recognition means for mapping the digital input data symbol that corresponds to the one or more formant frequencies contained in the inverse modified signal.