Timing and time information extraction from a phase modulated signal in a radio controlled clock receiver
A system and method for a radio controlled clock receiver adapted to extract timing and time information from a phase modulated signal. The official time signal is broadcast from a central location using a modulation scheme that adds phase modulation to legacy pulse width modulated/amplitude modulation that allows for greatly improved performance. The information modulated onto the phase contains a known synchronization sequence having good autocorrelation properties, error-correcting coding for the time information and notifications of daylight-saving-time (DST) transitions that are provided months in advance. The modulation scheme is based on a form of phase modulation, such as binary-phase-shift-keying (BPSK) or phase reversal keying (PRK). A superframe comprising multiple frames with repeated information allows for the accumulation of received energy over multiple frames to provide for a corresponding gain in the receiver.
1. A radio receiver, comprising:
a receiver circuit operative to receive a phase modulated (PM), pulse width modulation (PWM)/amplitude shift keyed (ASK) broadcast signal encoded with timing information separate from time information, said timing information based on a known synchronization sequence spanning multiple seconds; and
a circuit operative to extract said timing and time information from the phase of said received signal;
wherein said phase modulation comprises pulse width modulation/amplitude shift keyed modulated data transmitted with and without a phase reversal; and
wherein information represented by said phase modulation is independent of the information represented by said pulse width modulation/amplitude shift keyed modulation.
2. The device according to claim 1 , wherein said phase modulation comprises antipodal binary phase shift keying (BPSK) modulation.
3. The device according to claim 1 , wherein said phase modulation comprises non-antipodal binary phase shift keying (BPSK) modulation.
4. The device according to claim 1 , wherein said phase modulation comprises discontinuous binary phase shift keying (BPSK) modulation.
5. The device according to claim 1 , wherein said extraction circuit is operative to correlate said phase modulated received signal against a known synchronization sequence to recover said timing information.
6. The device according to claim 1 , wherein said timing information is used to determine bit boundaries (symbol timing) and frame timing (minute boundaries).
7. The device according to claim 1 , wherein said circuit is operative to limit phase demodulation to the last 0.5 second of each bit of a legacy PWM/ASK modulation scheme.
8. The device according to claim 1 , wherein said circuit is operative to limit phase demodulation to those portions of each bit that are at high amplitude in accordance with a legacy PWM/ASK modulation scheme.
9. The device according to claim 1 , wherein said circuit performs phase demodulation on the low as well as high portions of each bit of a legacy PWM/ASK modulation scheme.
10. A radio receiver method, said method comprising:
receiving a phase modulated (PM), pulse width modulated (PWM)/amplitude shift keyed (ASK) broadcast signal encoded with timing information separate from time information, said timing information based on a known synchronization sequence spanning multiple seconds; and
extracting said timing and time information from the phase of said received signal;
wherein said phase modulation comprises pulse width modulation/amplitude shift keyed modulated data transmitted with and without a phase reversal; and
wherein information represented by said phase modulation is independent of the information represented by said pulse width modulation/amplitude shift keyed modulation.
11. The method according to claim 10 , wherein said phase modulation comprises antipodal binary phase shift keying (BPSK) modulation.
12. The method according to claim 10 , wherein said phase modulation comprises non-antipodal binary phase shift keying (BPSK) modulation.
13. The method according to claim 10 , wherein said phase modulation comprises discontinuous binary phase shift keying (BPSK) modulation.
14. The method according to claim 10 , wherein said phase modulated received signal is correlated against a known synchronization sequence to recover said timing information.
15. The method according to claim 10 , wherein extracting said timing and time information comprises limiting phase demodulation to the last 0.5 second of each bit of a legacy PWM/ASK modulation scheme.
16. The method according to claim 10 , wherein extracting said timing and time information comprises limiting phase demodulation to those portions of each bit that are at high amplitude in accordance with a legacy PWM/ASK modulation scheme.
17. The method according to claim 10 , wherein extracting said timing and time information comprises performing phase demodulation on the low as well as high portions of each bit of a legacy PWM/ASK modulation scheme.
18. A radio receiver method for use in a timekeeping device, said method comprising:
receiving a phase modulated (PM), pulse width modulated (PWM)/amplitude shift keyed (ASK) broadcast signal encoded with timing information separate from time information, said timing information based on a known synchronization sequence spanning multiple seconds;
extracting said timing and time information from the phase of said received signal; and
correlating said timing information against a known synchronization sequence so as to establish frame and symbol timing;
wherein said phase modulation comprises pulse width modulation/amplitude shift keyed modulated data transmitted with and without a phase reversal; and
wherein information represented by said phase modulation is independent of the information represented by said pulse width modulation/amplitude shift keyed modulation.
19. The method according to claim 18 , further comprising applying averaging filtering whereby the timing information extracted from the received signal is weighted against the local currently assumed time in said timekeeping device.
20. The method according to claim 19 , wherein said averaging and weighting are adaptive and performed using coefficients adapted to consider the level of confidence in the received signal, based on the reception conditions, against the level of confidence in the current time, based on the time that has elapsed since the last timing correction and the monitored statistics of historical timing adjustments.
21. The method according to claim 18 , further comprising determining a current time as a nonlinear threshold-comparison function of the timing and time information extracted from a received frame, said threshold-comparison function adapted to determine whether the distance between said extracted information and the local currently assumed time in said timekeeping device is greater than a predefined threshold.
22. The method according to claim 18 , wherein the time information extracted from a received frame is compared against local assumed time allowing the device to validate said local assumed time or replace it with said extracted time information based on whether or not the reception conditions suggest high confidence in the corresponding received information.
23. The method according to claim 22 , wherein the time information extracted from a received frame is validated against successive receptions obtained in one or more subsequent frames before being used in place of the local assumed time in said timekeeping device.
24. The method according to claim 18 , further comprising accumulating received energy over multiple one-minute frames thereby providing a corresponding gain in reception.
25. The method according to claim 18 , further comprising receiving superframes consisting of sets of 60 frames used to extract hourly timing information.
26. The method according to claim 18 , wherein synchronization sequence fields in the frames of a superframe are phase modulated in accordance with a known pattern.
27. A radio receiver method, said method comprising:
receiving a phase modulated (PM) broadcast signal encoded with timing information separate from time information, said timing information based on a known synchronization sequence spanning multiple seconds, wherein said timing and time information, intended for synchronization and time reference purposes, is conveyed in the phase of the carrier portion of said broadcast signal; and
extracting said timing and time information from the phase of said received signal;
wherein said phase modulation comprises pulse width modulation/amplitude shift keyed modulated data transmitted with and without a phase reversal; and
wherein information represented by said phase modulation is independent of the information represented by said pulse width modulation/amplitude shift keyed modulation.
28. The method according to claim 27 , wherein said phase modulation comprises antipodal binary phase shift keying (BPSK) modulation.
29. The method according to claim 27 , wherein said phase modulation comprises non-antipodal binary phase shift keying (BPSK) modulation.
30. The method according to claim 27 , wherein said phase modulation comprises discontinuous binary phase shift keying (BPSK) modulation.