In-band signaling for data communications over digital wireless telecommunications networks
View Patent ↗An inband signaling modem communicates digital data over a voice channel of a wireless telecommunications network. An input receives digital data. An encoder converts the digital data into audio tones that synthesize frequency characteristics of human speech. The digital data is also encoded to prevent voice encoding circuitry in the telecommunications network from corrupting the synthesized audio tones representing the digital data. An output then outputs the synthesized audio tones to a voice channel of a digital wireless telecommunications network.
1. A synchronizer, comprising:
an input that samples first and second audio tones;
a demodulator that generates a synchronization value by comparing the samples of the first audio tone with the samples of the second audio tone; and
a synchronizer that synchronizes the demodulator by shifting a start time for the samples of the first and second audio tones until the demodulator generates an optimum synchronization value.
2. A synchronizer according to claim 1 including a tuner coupled to the input that shifts the first and second audio tones to a baseband frequency.
3. A synchronizer according to claim 1 wherein the demodulator includes:
a first integrator for summing the samples of the first audio tone;
a second integrator for summing the samples of the second audio tone; and
a summer generating the synchronization value by comparing the output of the first integrator with the output of the second integrator.
4. A synchronizer according to claim 3 including:
a first rectifier coupled between the first integrator and the summer; and
a second rectifier coupled between the second integrator and the summer.
5. A synchronizer according to claim 3 including a comparator coupled to the summer for generating binary bit values.
6. A synchronizer according to claim 1 wherein the first and second audio tones are transmitted over a voice channel of a digital telecommunications network.
7. A synchronizer according to claim 1 wherein a number of samples of the first tone and a number of samples of the second tone compared by the demodulator represents an amount of time the first and second tones are generated for one bit of the digital data.
8. A synchronizer according to claim 1 wherein the demodulator takes a running sum of The samples and compares the running sum for the first and second tones to generate a binary “1” value or a binary “0” value.
9. A synchronizer according to claim 8 including a synchronization pattern correlator that identities the optimum synchronization value by correlating the binary “1” and binary “0” values with a synchronization pattern.