Compensation of reference frequency drift in system requiring critical upstream timing
View Patent ↗Systems and methods are disclosed for to compensating reference frequency drift in a communications system having a plurality of modems and a headend, where the system requires critical upstream timing. One embodiment of the method includes learning or determining the relative delay of each modem and reporting each modem's unique delay (relative to the closest modem) to the headend. The method further includes the headend monitoring its own reference for frequency drift, the modem broadcasting pertinent frequency drift information to the modems and adjusting the modems' upstream timing to account for each modem's unique distance (i.e., delay) combined with the broadcast stream of frequency drift information.
1. A communication system adapted to mitigate timing offset in return transmissions, comprising:
at least one modem, said at least one modem adapted to report its delay relative to a delay associated with a particular one of a plurality of modems that is the closest one of the plurality of modems to a head end; and
a headend adapted to determine relative delay of said at least one modem and monitor its own reference for frequency drift,
wherein said at least one modem is adapted to adjust its upstream timing to account for said delay.
2. A headend for mitigating timing off set in a system having critical timing synchronization of return transmissions, comprising:
a first circuit for receiving reported relative delays from a plurality of modems, wherein relative delays comprise at least one of the plurality of modems' delays relative to a particular one of the plurality of modems that is the closest one of the plurality of modems to a headend;
a second circuit for monitoring frequency drift;
a third circuit for broadcasting information on said frequency drift; and
wherein broadcasting said information on said frequency drift comprises broadcasting said information to each of the plurality of modems using actual frequency normalized by nominal frequency.
3. The head end of claim 2 , wherein receiving reported relative delay further comprises receiving proprietary messaging.
4. The head end of claim 2 , wherein monitoring said frequency drift further comprises monitoring frequency drift relative to a stable reference.
5. The head end of claim 2 , wherein monitoring said frequency drift comprises building a delay at the headend in the system and measuring a frequency a delayed reference.
6. The head end of claim 2 , wherein the second circuit for monitoring said frequency drift a frequency discriminator.