Fast channel scanning and acquisition system and method for cable modem applications
View Patent ↗A programmable channel scanning and acquisition method for a cable modem first performs a fast scan and then a slow scan to identify channels supporting cable modem services. The fast scan involves only a check of the cable modem AGC lock. A list of potentially operational channels is assembled and scanned. The list includes, in order of preference, the last known good channel, golden channels that are likely to support cable modem services, “learned” golden channels consisting of previous last known good channels, and other channels within the frequency plan range. The list omits channels on a “black list” known not to be operational and channels outside of the frequency range, except during registration. The method may be optimized by the setting of various parameters for operation in a DOCSIS or EuroDOCSIS environment.
1. A cable modem channel scanning and acquisition method comprising:
performing a fast scan of each channel in a list of candidate channels for supporting cable modem services, the fast scan including the steps of
identifying potentially valid channels by considering a first operating state of the cable modem; and
attempting to acquire at least one potentially valid channel that has been identified by the fast scan; and,
in response to not acquiring at least one valid channel during the fast scan, performing a slow scan of each channel in the list, the slow scan of each channel in the list including the steps of
identifying potentially valid channels by considering a plurality of additional operating states of the cable modem; and
attempting to acquire at least one potentially valid channel that has been identified by the slow scan.
2. A method as claimed in claim 1 , wherein the first operating state is AGC lock state.
3. A method as claimed in claim 1 , wherein the first channel considered is the last known good channel, and wherein, during the same acquisition attempt, the method periodically returns to and attempts to acquire the last known good channel.
4. A method as claimed in claim 3 , wherein the frequency of attempts to acquire the last known good channel is determined by a programmable channel hop depth that is less than the number of channels in the list of candidate channels.
5. A method as claimed in claim 1 , wherein the method first attempts to acquire channels on a golden list of channels that are likely to support cable modem services.
6. A method as claimed in claim 5 , wherein the golden list is adaptively updated by adding the previous last known good channel to the golden list whenever the last known good channel is updated.
7. A method as claimed in claim 5 , wherein the method does not attempt to acquire channels on a black list of channels that are not likely to support cable modem services.
8. A method as claimed in claim 7 , wherein the method does not attempt to acquire channels outside the range of the applicable frequency plan.
9. A method as claimed in claim 8 , and comprising an initial scanning and acquisition procedure performed prior to first registration of the modem wherein channels on the black list and outside the range of the applicable frequency plan are scanned, but are not scanned thereafter.
10. The method as claimed in claim 1 , wherein the slow scan step comprises considering both the first operating state and a second operating state of the cable modem, wherein the second operating state indicates the presence of a valid channel and is different from the first operating state.
11. The method as claimed in claim 1 , wherein the slow scan scans at a slower speed than the fast scan to acquire the channel.
12. The method as claimed in claim 1 , wherein the plurality of additional operating states of the modem includes a lock state of a demodulator and a PLL lock of a PLL.
13. The method as claimed in claim 1 , wherein the slow scan mode scans the plurality of operating states even when the first operating state does not indicate the presence of a valid channel.