Subcarrier signal for synchronization in macro network
View Patent ↗Disclosed herein are methods and systems that may help a WiMAX base station function without a GPS signal by providing a high-stability reference signal via a subcarrier of a broadcast signal, such as an FM radio signal. An exemplary broadcast station may therefore be configured to phase-lock a subcarrier signal to a GPS signal, and include this subcarrier in its broadcast signal, thereby providing the subcarrier signal for use by a base station as a high-stability reference signal for local-oscillator stabilization at the base station. The broadcast station may further modulate a timing signal onto the subcarrier signal. An exemplary base station may therefore receive the broadcast signal, decode the broadcast signal to acquire the subcarrier signal, and use the subcarrier signal to stabilize its local oscillator, rather than using a GPS signal. The base station may further demodulate the subcarrier to acquire the timing signal, which the base station may use for frame-start synchronization, instead of a GPS signal.
1. A method comprising:
at a terrestrial broadcast station, receiving a GPS signal;
the terrestrial broadcast station generating a frequency shift keying (FSK) timing signal comprising timing information, wherein the FSK timing signal is phase-locked to the GPS signal;
the terrestrial broadcast station modulating the FSK timing signal onto a subcarrier signal; and
the terrestrial broadcast station transmitting a terrestrial broadcast signal that includes the subcarrier signal, thereby providing the timing information for use by the base station to determine a time-of-flight delay between the broadcast station and the base station, wherein the base station uses the timing information provided by the FSK timing signal and the time-of-flight delay to determine timing with which to transmit data frames for frame-start synchronization and wherein the timing information provided by the FSK timing signal provides for (i) detection of transitions in the FSK timing signal by the base station, and (ii) transmission of data from the base station with a timing that is based at least in part on when the transitions in the FSK timing signal occur.
2. The method of claim 1 , further comprising the terrestrial broadcast station using the GPS signal to generate the subcarrier signal.
3. The method of claim 2 , wherein using the GPS signal to generate the subcarrier signal comprises:
phase-locking a local oscillator to the GPS signal; and
using the local oscillator to generate the subcarrier signal, thereby phase-locking the subcarrier signal to the GPS signal.
4. The method of claim 3 , further comprising the terrestrial broadcast station periodically interrupting the timing information in the FSK timing signal, waiting a predetermined period of time, and then inserting time-of-day information in the FSK timing signal.
5. The method of claim 3 , wherein the subcarrier signal is a 92 kHz subcarrier of an FM radio signal, and wherein the FSK timing signal comprises a 200 Hz FSK timing signal.
6. A method comprising:
at a base station, receiving a terrestrial broadcast signal that was generated by a terrestrial broadcast station, wherein the broadcast signal comprises a subcarrier signal having a frequency shift keying (FSK) timing signal modulated thereon, and wherein the FSK timing signal comprises timing information;
decoding the terrestrial broadcast signal to acquire the subcarrier signal;
demodulating the subcarrier signal to acquire the FSK timing signal;
determining a time-of-flight delay between the terrestrial broadcast station and the base station; and
using the timing information provided by the FSK timing signal and the time-of-flight delay to determine timing with which to transmit data frames for frame-start synchronization, wherein using the timing information provided by the FSK timing signal as a basis for frame-start synchronization comprises (i) detecting when transitions in the FSK timing signal occur and (ii) based at least in part on when the transitions in the FSK timing signal occur, determining the timing with which to transmit data frames.
7. The method of claim 6 , wherein the subcarrier signal has been phase-locked to a GPS signal by the terrestrial broadcast station, the method further comprising:
the base station using the subcarrier signal to stabilize a local oscillator at the base station, wherein the local oscillator is used by the base station to maintain signal stability for wireless communications.
8. The method of claim 6 , wherein the received signal comprises an FM radio signal, wherein the subcarrier signal is a 92 kHz subcarrier, and wherein the FSK timing signal comprises a 200 Hz FSK timing signal.
9. The method of claim 6 , wherein using the time-of-flight delay to determine the timing with which to transmit the data frames comprises:
detecting transitions in the FSK timing signal; and
each time a transition in the FSK timing signal is detected, delaying for a period of time to compensate for the time-of-flight delay before transmitting a next data frame.
10. The method of claim 6 , further comprising:
detecting periodic interruptions in the timing information that is included in the FSK timing signal; and
after detecting each interruption in the timing information, acquiring time-of-day information from the FSK timing signal.
11. A system comprising:
a GPS receiver configured to acquire a GPS signal;
a timing signal generator that is configured to generate a frequency shift keying (FSK) timing signal comprising timing information, wherein the FSK timing signal is phase-locked to the GPS signal;
a subcarrier generator that is configured to generate a subcarrier signal, wherein the FSK timing signal is modulated onto the subcarrier signal; and
a transmitter configured to transmit a terrestrial broadcast signal that includes the subcarrier signal, thereby providing the timing information for use by the base station to determine a time-of-flight delay between the broadcast station and the base station, wherein the base station uses the timing information provided by the FSK timing signal and the time-of-flight delay to determine timing with which to transmit data frames for frame-start synchronization and wherein the timing information provided by the FSK timing signal provides for (i) detection of transitions in the FSK timing signal by the base station, and (ii) transmission of data from the base station with a timing that is based at least in part on when the transitions in the FSK timing signal occur.
12. The system of claim 11 , further comprising a local oscillator, wherein the local oscillator is phase-locked to the GPS signal, wherein the subcarrier generator is further configured to phase-lock the subcarrier signal to the GPS signal via use of the local oscillator, such that the subcarrier signal provides a high-stability reference signal for use for use by the base station for local-oscillator stabilization at the base station.
13. The system of claim 11 , wherein the timing-signal generator is further configured to periodically interrupt the timing information in the FSK timing signal, wait for a predetermined period of time, and then insert time-of-day information in the FSK timing signal.
14. A system comprising:
a receiver configured to receive a terrestrial broadcast signal that was generated by a terrestrial broadcast station, wherein the broadcast signal comprises a subcarrier signal having a frequency shift keying (FSK) timing signal modulated thereon, and wherein the FSK timing signal comprises timing information;
a decoder configured to decode the terrestrial broadcast signal to acquire the subcarrier signal;
a demodulator configured to demodulate the subcarrier signal to acquire the FSK timing signal;
means for determining a time-of-flight delay between the terrestrial broadcast station and the base station; and
a signal generator configured to use the timing information provided by the FSK timing signal and the time-of-flight delay to determine timing with which to transmit data frames for frame-start synchronization, and wherein using the timing information provided by the timing signal as a basis for frame-start synchronization comprises (i) means for detecting when transitions in the FSK timing signal occur and (ii) means for, based at least in part on when the transitions in the FSK timing signal occur, determining the timing with which to transmit data frames.
15. The system of claim 14 , further comprising means for using the subcarrier signal to stabilize a local oscillator at the base station, wherein the local oscillator is used by the base station to maintain signal stability for wireless communications.
16. The system of claim 14 , wherein the signal generator is further configured to, each time a transition in the FSK signal is detected, delay for a period of time to compensate for the time-of-flight delay before transmitting a next data frame.
17. The system of claim 14 , further comprising:
means for detecting periodic interruptions in the timing information, and after detecting each interruption in the timing information, acquiring time-of-day information from the FSK timing signal.