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

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.

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.

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.

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.

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.