Method and apparatus for channel determination through power measurements
First Claim
1. In a cable telecommunications system in which a transmitter transmits a signal over a cable network to a receiver, said signal comprising a plurality of signal components, each one of said signal components being defined by a distinct frequency range,a method for selectively receiving a target signal component from among said plurality of signal components, said method comprising the steps of:
- obtaining a first plurality of power measurements for a first signal component of said signal, said first signal component being defined by a first frequency range, said first plurality of power measurements including a first power measurement and a second power measurement, wherein obtaining a plurality of power measurements includes the steps of;
(a) tuning a first frequency selection system to a first center frequency, said first center frequency being within said first frequency range;
(b) said first frequency selection system providing a first filtered signal from a first band of frequencies of said signal centered about said first center frequency;
(c) measuring the power of said first filtered signal to obtain said first power measurement;
(d) tuning said first frequency selection system to a second center frequency, said second center frequency being within said first frequency range;
(e) said first frequency selection system providing a second filtered signal from a second band of frequencies of said signal centered about said second center frequency; and
(f) measuring the power of said second filtered signal to obtain said second power measurement; and
if said first plurality of power measurements satisfy predetermined criteria, identifying said first signal component as being said target signal component.
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Accused Products
Abstract
In a data-over-cable system, a cable head-end transmits a signal that includes a plurality of analog television signal components an at least one quadrature amplitude modulated (QAM) digital signal component, the signal components being defined by frequency channels. A cable modem has a tunable frequency selection system, operable at a first bandwidth, corresponding to the bandwidth of the frequency channels, and at a second, substantially narrower bandwidth, that provides a filtered signal and a power measurement system that measures the power level of the filtered signal. The frequency selection system scans through the channels, operating at its second bandwidth, and, in each channel, tunes to a first frequency and a second frequency. The power levels of the filtered signals from the first and second frequencies are measured and compared to distinguish the QAM digital signal components from the other signal components.
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Citations
37 Claims
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1. In a cable telecommunications system in which a transmitter transmits a signal over a cable network to a receiver, said signal comprising a plurality of signal components, each one of said signal components being defined by a distinct frequency range,
a method for selectively receiving a target signal component from among said plurality of signal components, said method comprising the steps of: -
obtaining a first plurality of power measurements for a first signal component of said signal, said first signal component being defined by a first frequency range, said first plurality of power measurements including a first power measurement and a second power measurement, wherein obtaining a plurality of power measurements includes the steps of;
(a) tuning a first frequency selection system to a first center frequency, said first center frequency being within said first frequency range;
(b) said first frequency selection system providing a first filtered signal from a first band of frequencies of said signal centered about said first center frequency;
(c) measuring the power of said first filtered signal to obtain said first power measurement;
(d) tuning said first frequency selection system to a second center frequency, said second center frequency being within said first frequency range;
(e) said first frequency selection system providing a second filtered signal from a second band of frequencies of said signal centered about said second center frequency; and
(f) measuring the power of said second filtered signal to obtain said second power measurement; and
if said first plurality of power measurements satisfy predetermined criteria, identifying said first signal component as being said target signal component. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
if said first plurality of power measurements do not satisfy said predetermined criteria, obtaining a second plurality of power measurements for a second signal component, said second signal component being defined by a second frequency range.
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3. The method of claim 2, further comprising the step of:
if said second plurality of power measurements satisfy said predetermined criteria, identifying said second signal component as being said target signal component.
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4. The method of claim 1, wherein said first plurality of power measurements satisfies said predetermined criteria if said first and second power measurements are both greater than a threshold power level.
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5. The method of claim 1, wherein said target signal component comprises a carrier modulated by a digital signal using quadrature amplitude modulation (QAM).
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6. The method of claim 5, wherein at least one of said plurality of signal components comprises a carrier modulated by a visual signal using amplitude modulation (AM).
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7. The method of claim 1, wherein said first frequency selection system has a bandwidth substantially less than the width of said frequency range of said first signal component.
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8. The method of claim 7, further comprising the steps of:
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tuning a second frequency selection system to a working center frequency, said working center frequency being within the frequency range of said target signal component; and
said second frequency selection system providing a filtered target signal from a working band of frequencies of said signal centered about said working center frequency, said working band of frequencies corresponding to the frequency range of said target signal component.
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9. The method of claim 8, further comprising the step of:
demodulating said filtered target signal.
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10. In a data-over-cable system in which a signal is transmitted over a cable network to a cable modem, said signal comprising a plurality of signal components defined by a plurality of predetermined frequency channels, said frequency channels having a channel bandwidth, said frequency channels including at least one analog channel and at least one digital channel, said signal components including at least one analog signal component having a first spectral profile and at least one digital signal component having a second spectral profile, said analog signal components being defined by analog channels, said digital signal components being defined by digital channels,
a method for selectively receiving one of said digital signal components, said method comprising the step of: -
classifying a first channel based on the spectral profile of any signal component present in said first channel, said first channel being one of said plurality of frequency channels, wherein classifying said first channel comprises the steps of;
(a) tuning a first frequency selection system to a first center frequency being within said first channel, said first frequency selection system having a bandwidth substantially less than said channel bandwidth;
(b) said first frequency selection system providing a first filtered signal from a first band of frequencies of said signal centered about said first center frequency;
(c) measuring the power of said first filtered signal to obtain a first power measurement;
(d) tuning said first frequency selection system to a second center frequency, said second center frequency being within said first channel;
(e) said second frequency selection system providing a second filtered signal from a second band of frequencies of said signal centered about said second frequency;
(f) measuring the power of said second filtered signal to obtain a second power measurement; and
(g) identifying said first channel as a digital channel if said first and second power measurements are both greater than a first threshold power level. - View Dependent Claims (11, 12, 13, 14, 15)
identifying said first channel as an analog channel if said first power measurement exceeds said second power measurement by a predetermined amount.
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12. The method of claim 11, further comprising the step of:
identifying said first channel as inactive if said first and second power measurements are both less than a second threshold power level.
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13. The method of claim 10, further comprising the step of:
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if said first channel is identified as a digital channel, tuning a second frequency selection system to said first channel to selectively receive the digital signal component defined by said first channel, said second frequency selection system having a bandwidth compatible with said channel bandwidth, otherwise;
classifying a second channel based on the spectral profile of any signal component present in said second channel, said second channel being one of said plurality of frequency channels.
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14. The method of claim 10, wherein said one digital signal component comprises a carrier modulated by a digital signal using quadrature amplitude modulation (QAM).
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15. The method of claim 14, wherein said at least one analog signal component comprises a carrier modulated by a visual signal using amplitude modulation (AM).
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16. A cable modem for selectively receiving a digital component from a signal transmitted over a cable network, said signal having a plurality of signal components, said cable modem comprising:
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a tunable frequency selection system for providing a filtered signal from a selected band of frequencies of said signal, said frequency selection system being operable at a first bandwidth and at a second bandwidth, said second bandwidth being narrower than said first bandwidth, said frequency selection system including a first band-pass filter and a second band-pass filter, said first band-pass filter defining said first bandwidth and said second band-pass filter defining said second bandwidth;
a demodulator for obtaining a digital signal by demodulating said filtered signal from said frequency selection system; and
a power measurement system for providing a power level signal indicative of a power level associated with said filtered signal from frequency selection system. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25)
(a) causing said frequency selection system to operate at said second bandwidth;
(b) tuning said frequency selection system to a first center frequency;
(c) obtaining a first power level from a first power level signal from said power measurement system; and
(d) tuning said frequency selection system to a second center frequency;
(e) obtaining a second power level from a second power level signal from said power measurement system.
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23. The cable modem of claim 22, wherein said set of machine language
instructions are executable by said central processing unit for: determining whether said first and second power levels are both greater than a first threshold power level.
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24. The cable modem of claim 23, wherein said set of machine language instructions are executable by said central processing unit for:
determining whether said first power levels exceeds said second power level by a predetermined amount.
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25. The cable modem of claim 24, wherein said set of machine language instructions are executable by said central processing unit for:
determining whether said first and second power levels are both less than a second threshold power level.
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26. A method of initializing a cable modem, said cable modem being disposed for receiving a signal transmitted over a cable network, said method comprising the steps of:
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selectively receiving a first band of frequencies centered about a first center frequency, said first band of frequencies having a first bandwidth;
selectively receiving a second band of frequencies centered about a second center frequency, said second band of frequencies having a second bandwidth substantially equal to said first bandwidth;
selectively receiving a third band of frequencies centered about a third center frequency, said third band of frequencies having a third bandwidth substantially greater than said first bandwidth, said third band of frequencies including frequencies from said first band of frequencies and from said second band of frequencies;
demodulating said third band of frequencies to obtain a digital signal; and
said cable modem synchronizing with said digital signal. - View Dependent Claims (27, 28, 29)
obtaining a first power measurement indicative of the power level of said first band of frequencies; and
obtaining a second power measurement indicative of the power level of said second band of frequencies.
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28. The method of claim 26, wherein said third band of frequencies comprises a quadrature amplitude modulated (QAM) digital signal.
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29. The method of claim 28, wherein said signal includes a plurality of signal components, said signal components including said quadrature amplitude modulated (QAM) digital signal and at least one analog television signal.
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30. In a data-over-cable system in which the signal is transmitted over a cable network to a cable modem, said signal comprising a plurality of signal components defined by a plurality of frequency channels, said cable modem having a tunable frequency selection system operable at a wide bandwidth and at a narrow bandwidth,
a method for selectively receiving a target signal component from among said plurality of signal components, said method comprising the steps of: -
tuning said frequency selection system to a first frequency in one of said predetermined frequency channels, said frequency selection system operating at said narrow bandwidth, said frequency selection system providing a first filtered signal from a first band of frequencies of said signal centered about said first frequency;
measuring the power of said first filtered signal to obtain a first power measurement;
tuning said frequency selection system to a second frequency in said one of said predetermined frequency channels, said frequency selection system operating at said narrow bandwidth, said frequency selection system providing a second filtered signal from a second band of frequencies of said signal centered about said second frequency;
measuring the power of said second filtered signal to obtain am second power measurement; and
if said first and second power measurements both exceed a predetermined level, operating said frequency selection system at said wide bandwidth to provide a third filtered signal from a third band of frequencies in said one of said predetermined frequency channels. - View Dependent Claims (31, 32, 33, 34, 35)
said cable modem demodulating said third filtered signal to obtain a digital signal.
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32. The method of claim 31, further comprising the step of:
said cable modem synchronizing with said digital signal.
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33. The method of claim 30, wherein said first frequency substantially corresponds to an expected frequency for a visual carrier if said one of said predetermined frequency channels defined an analog television signal.
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34. The method of claim 33, wherein said second frequency exceeds said first frequency by about 1 to 3 MHz.
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35. The method of claim 30, wherein said narrow bandwidth is in the range of 100 kHz to 1 MHz.
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36. In a cable telecommunications system in which a transmitter transmits a signal over a cable network to a receiver, said signal comprising a plurality of signal components defined by a plurality of predetermined frequency channels, said frequency channels having a channel bandwidth, a method for identifying a possible channel plan, said method comprising the steps of:
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tuning a frequency selection system to a first frequency, said first frequency corresponding to an expected frequency for a visual carrier in a first channel plan, said frequency selection system providing a first filtered signal from a first band of frequencies of said signal centered about said first frequency;
measuring the power of said first filtered signal to obtain a first power measurement;
tuning said frequency selection system to a second frequency, said second frequency corresponding to an expected frequency for a visual carrier in a second channel plan, said frequency selection system providing a second filtered signal from a second band of frequencies of said signal centered about said second frequency;
measuring the power of said second filtered signal to obtain a second power measurement;
if said first power measurement exceeds said second power measurement by at least a predetermined amount, identifying said first channel plan as said possible channel plan; and
if said second power measurement exceeds said first power measurement by at least said predetermined amount, identifying said second channel plan as said possible channel plan. - View Dependent Claims (37)
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Specification