Data delivery using acoustic transmissions
Systems, methods, and computer program products for delivering information to an individual, group, or device. The information is carried by audio signals beyond the audible frequency range of human hearing, but within the frequency range of an audio system. The information is modulated onto an ultrasonic frequency and embedded into an audio signal transmitted by the audio system. Each individual, group member, or device may have or be coupled to a receiver configured to receive an acoustic signal transmitted by the audio system that includes the modulated ultrasonic frequency. The receiver extracts the information from the modulated ultrasonic frequency and provides the information to the individual, group member, or device.
1. An apparatus comprising a device configured to:
receive an acoustic signal including a communication signal generated by modulating a transmitter carrier frequency using a sequence of symbols including a pilot sequence;
synchronize the sequence of symbols using the pilot sequence; and
recover a data signal by decoding the synchronized sequence of symbols.
2. The apparatus of claim 1 , wherein synchronizing the sequence of symbols using the pilot sequence includes:
sampling the acoustic signal at a sampling rate to produce a discrete received signal;
demodulating the discrete received signal using a demodulator carrier frequency to produce a baseband demodulated signal including a plurality of baseband demodulated signal samples; and
finding a sequence of the baseband demodulated signal samples that locks onto the pilot sequence.
3. The apparatus of claim 2 , wherein the device is further configured to:
determine a frequency mismatch between the transmitter carrier frequency and the demodulator carrier frequency;
adjust the demodulator carrier frequency by the frequency mismatch; and
re-synchronize the sequence of symbols using the pilot sequence and the adjusted demodulator carrier frequency.
4. The apparatus of claim 3 , wherein the device is further configured to:
iteratively determine the frequency mismatch between the transmitter carrier frequency and the demodulator carrier frequency, adjust the demodulator carrier frequency by the frequency mismatch, and re-synchronize the sequence of symbols using the pilot sequence and the adjusted demodulator carrier frequency until a start sample for the pilot sequence remains the same for two iterations in a row.
5. The apparatus of claim 2 , wherein the communication signal has a symbol rate, and the sampling rate is greater than the symbol rate.
6. The apparatus of claim 2 , wherein synchronizing the sequence of symbols using the pilot sequence includes:
identifying the pilot sequence by performing a cross-correlation between one or more known pilot sequences and the communication signal.
7. The apparatus of claim 2 , wherein finding the sequence of the baseband demodulated signal samples that locks onto the pilot sequence includes processing the baseband demodulated signal through a matched filter.
8. The apparatus of claim 1 , wherein the device is further configured to:
detect a transmit frame comprising one or more symbols of the synchronized sequence of symbols.
9. The apparatus of claim 8 , wherein the device is further configured to:
estimate a distortion in the communication signal based on where the detected transmit frame starts and ends.
10. The apparatus of claim 8 , wherein the device is further configured to activate an audio circuit in response to detecting the transmit frame.
11. A method comprising:
receiving an acoustic signal including a communication signal generated by modulating a transmitter carrier frequency using a sequence of symbols including a pilot sequence;
synchronizing the sequence of symbols using the pilot sequence; and
recovering a data signal by decoding the synchronized sequence of symbols.
12. The method of claim 11 , wherein synchronizing the sequence of symbols using the pilot sequence includes:
sampling the acoustic signal at a sampling rate to produce a discrete received signal;
demodulating the discrete received signal using a demodulator carrier frequency to produce a baseband demodulated signal including a plurality of baseband demodulated signal samples; and
finding a sequence of the baseband demodulated signal samples that locks onto the pilot sequence.
13. The method of claim 12 , further comprising:
determining a frequency mismatch between the transmitter carrier frequency and the demodulator carrier frequency;
adjusting the demodulator carrier frequency by the frequency mismatch; and
re-synchronizing the sequence of symbols using the pilot sequence and the adjusted demodulator carrier frequency.
14. The method of claim 13 , further comprising:
iteratively determining the frequency mismatch between the transmitter carrier frequency and the demodulator carrier frequency, adjusting the demodulator carrier frequency by the frequency mismatch, and re-synchronizing the sequence of symbols using the pilot sequence and the adjusted demodulator carrier frequency until a start sample for the pilot sequence remains the same for two iterations in a row.
15. The method of claim 12 , wherein the communication signal has a symbol rate, and the sampling rate is greater than the symbol rate.
16. The method of claim 12 , wherein synchronizing the sequence of symbols using the pilot sequence includes:
identifying the pilot sequence by performing a cross-correlation between one or more known pilot sequences and the communication signal.
17. The method of claim 12 , wherein finding the sequence of the baseband demodulated signal samples that locks onto the pilot sequence includes processing the baseband demodulated signal through a matched filter.
18. The method of claim 11 , further comprising:
detecting a transmit frame comprising one or more symbols of the synchronized sequence of symbols.
19. The method of claim 18 , further comprising:
estimating a distortion in the communication signal based on where the detected transmit frame starts and ends.
20. A computer program product, comprising:
a non-transitory computer-readable storage medium; and
program code stored on the non-transitory computer-readable storage medium that, when executed by one or more processors, causes the one or more processors to:
receive an acoustic signal including a communication signal generated by modulating a transmitter carrier frequency using a sequence of symbols including a pilot sequence;
synchronize the sequence of symbols using the pilot sequence; and
recover a data signal by decoding the synchronized sequence of symbols.