Edge-QAM and M-CMTS core timing lock
Systems and methods can provide for Edge-QAM and M-CMTS timing lock. In some implementations, an Edge-QAM can provide for timing lock with an M-CMTS core by observing DOCSIS-SYNC MAC messages. In other implementations, an Edge-QAM can provide for timing lock with an M-CMTS core by observing per-modem ranging MAC messages. In other implementations, an EQAM can provide for timing lock with an M-CMTS core by performing timing lock check and adjustment. Using existing protocol messages defined in the M-CMTS architecture, the EQAM can intercept, snoop, and extract timing values from the M-CMTS core thereby reducing or even eliminating the need for a DTI server.
1. A system, comprising:
a broadband communication system configured to transmit digital data and receive radio frequency (RF) modulated data, the broadband communication system being further configured to use a first local clock signal;
one or more modulator systems, executed on a processing device, configured to receive digital data, modulate the digital data, and transmit the RF modulated data, the one or more modulator systems being further configured to use a second local clock signal;
a communication path for connecting the broadband communication system to the one or more modulator systems;
the broadband communication system including a media access control module configured to provide media access control for data transmissions;
the media access control module configured to transmit a plurality of media access control messages with a first time value, the first time value being based on the first local clock signal;
the one or more modulator systems being configured to replace the first time value in the plurality of media access control messages with a second time value based on the second local clock signal and transmit the media access control messages as the RF modulated data to one or more customer premise devices;
the one or more modulator systems being configured to adjust the second local clock based on a computation derived from the one or more first time values, track a divergence of the first time values in the plurality of media access control messages, and, when the divergence reaches a threshold, adjusting the second local clock based on the divergence, wherein the adjustment to the second local clock is made without feedback from the broadband communication system; and
the one or more modulator systems being configured to further adjust the second local clock based on a plurality of ranging media access control messages.
2. The system of claim 1 , wherein the computation comprises using the first time value from one of the media access control messages as the second local clock value.
3. The system of claim 1 , wherein the computation comprises periodically updating the second time value with the first time value using a plurality of media access control messages.
4. The system of claim 1 , wherein a moving average is used as the computation of the divergence.
5. The system of claim 1 , wherein an alarm is issued if the divergence reaches a threshold.
6. The system of claim 1 , wherein the broadband communication system is based on DOCSIS.
7. The system of claim 6 , wherein the communication path comprises ethernet.
8. The system of claim 7 , wherein the modulation comprises quadrature amplitude modulation.
9. The system of claim 1 , wherein the modulator system is further configured to adjust the second local clock, and the system further comprises:
the plurality of customer premise equipment devices each configured to transmit and receive RF signals;
a communication path for connecting the broadband communication system and the one or more modulator systems to the plurality of customer premise equipment devices;
the plurality of customer premise equipment devices configured to transmit a plurality of ranging burst media access control messages;
the broadband communication system being further configured to receive the ranging burst media access control messages, compute third time values for each respective customer premise equipment device based on a timing divergence, and transmit a plurality of ranging media access control messages with the third time values to the modulator system; and
the modulator system being further configured to receive the third time values and adjust the second local clock based on the third time value.
10. The system of claim 9 , wherein the modulator system is configured to adjust the second local clock based on a subset of the ranging media access control messages selected from a sample population of the customer premise equipment devices.
11. The system of claim 10 , wherein the modulator system is further configured to adjust said second local clock based on the timing divergence associated with the third time values.