Methods for in-band signaling through enhanced variable-rate codecs
View Patent ↗Improvements are disclosed for in-band signaling, i.e., transmission of data in a voice channel of a digital wireless network during a voice call session. A family of narrow-band signaling methods, some employing tapered waveforms, is disclosed to successfully pass data-carrying signals through the low-bit rate modes of the EVRC-B vocoder commonly used in CDMA wireless channels. These features can be used in cell phones or other wireless communication devices, including automotive applications.
1. A method for transmitting digital data in a voice channel connection of a digital wireless telecommunication system, the method comprising:
receiving digital input data;
encoding the digital input data into a series of audio frequency tones;
assembling the series of audio frequency tones into a data burst;
applying a selected windowing function to the data burst, the windowing function comprising a tapered leading edge followed by a substantially constant amplitude data region, so as to form a windowed waveform burst having the substantially constant amplitude data region that includes the data burst; and
inputting the windowed waveform burst to a transmission side vocoder for transmission over the voice channel connection of the digital wireless telecommunication system;
wherein the tapered leading edge of the windowing function gradually increases in amplitude from substantially zero amplitude to substantially a predetermined peak amplitude, over a first predetermined duration in a range of approximately one-half second to three seconds, so that the leading edge of the windowed waveform burst gradually increases in amplitude from substantially zero amplitude to substantially the predetermined peak amplitude, over the first predetermined duration.
2. The method of claim 1 wherein the selected windowing function also includes a tapered trailing edge, so that the windowed waveform burst includes tapered leading and trailing edges.
3. The method of claim 2 wherein each of the leading and trailing edges of the windowed waveform burst has a corresponding duration in a range of approximately one-half second to three seconds.
4. The method of claim 3 wherein the digital input data is encoded using FSK (frequency shift keying) modulation of two audio frequencies to form the data burst.
5. The method of claim 3 including inserting throw away bits into the tapered leading and trailing edges of the windowed waveform burst.
6. The method of claim 5 wherein the respective durations of the leading and trailing edges of the windowed waveform burst are substantial equal.
7. The method of claim 5 wherein the windowing function is formed using a windowing function selected from the group consisting of the Hamming, Parzen, Gaussian, Bartlett, and Kaiser window functions.
8. The method of claim 5 wherein the transmission side vocoder implements an EVRC-B vocoder.
9. An in-band signaling modem for use in a digital wireless telecommunications device to send data over a voice channel of a digital wireless telecommunications network, the in-band signaling modem comprising:
software stored in a memory in the digital wireless telecommunications device, the software executable in a processor in the digital wireless telecommunications device;
the software configured to control the processor to
receive digital input data;
encode the digital input data into a series of audio frequency tones;
assemble the series of audio frequency tones into a data burst;
apply a selected windowing function to the data burst, the windowing function comprising a tapered leading edge followed by a substantially constant amplitude data region, so as to form a windowed waveform burst having the substantially constant amplitude data region that includes the data burst; and
output the windowed waveform burst to a transmission side vocoder for transmission over the voice channel connection of a digital wireless telecommunication system;
wherein the tapered leading edge of the windowing function gradually increases in amplitude from substantially zero amplitude to substantially a predetermined peak amplitude, over a first predetermined duration in a range of approximately one-half second to three seconds, so that the leading edge of the windowed waveform burst gradually increases in amplitude from substantially zero amplitude to substantially the predetermined peak amplitude, over the first predetermined duration.
10. The in-band signaling modem according to claim 9 wherein:
the selected windowing function also includes a tapered trailing edge, so that the windowed waveform burst includes tapered leading and trailing edges; and
each of the leading and trailing edges of the windowed waveform burst has a corresponding duration in a range of approximately one-half second to three seconds.
11. The in-band signaling modem according to claim 10 wherein the digital wireless telecommunications device comprises a cell phone or smart phone.
12. The in-band signaling modem according to claim 10 wherein the digital wireless telecommunications device is integrated into a motor vehicle and arranged for automatic operation to send data responsive to an emergency over said voice channel of the digital wireless telecommunications network.