 Device for selecting and controlling a plurality of signal sources in a television system |
| Accordingly, it is a primary object of the invention to provide a television-based device that ... |
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| Wireless music and data transceiver system |
| OF THE INVENTION With reference first to FIG. 1, a system is illustrated therein for local ... |
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| Distribution of television signals to workstations |
| It is therefore an object of the present invention to provide a video server that provides a ... |
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| Webcam-based interface for initiating two-way video communication and providing access to cached video |
| OF THE PREFERRED EMBODIMENTS The present invention solves the foregoing problems and disadvantages ... |
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| Apparatus for decoding video signals encoded in different formats |
| In accordance with the present invention it is recognized that a signal processing network can ... |
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| Information-signal recording apparatus and recording mode inquiring/specifying method |
| It is an object of the present invention to control the audio recording mode of a VTR with a ... |
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| Device control with topology map in a digital network |
| Accordingly, in one embodiment, a topology map for a digital system is generated and displayed on a ... |
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| Signal selector |
| In accordance with one aspect of the present invention, there is provided a DBS receiving system ... |
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Fast and reliable data carrier detection by a cable modem in a cable television plant
| Details |
Inventors: Roeck, Guenter E.; Chen, Wei-Sing; Naegeli, Charles J.;
Assignee: Cisco Technology, Inc. (San Jose, CA)
Primary Examiner: Miller; John
Assistant Examiner: Rouvas; Nikolaos
Attorney, Agent or Firm: Beyer Weaver & Thomas, LLP
Apparatus, methods, and computer program products are disclosed for detecting or locating a viable data carrier in a downstream channel by a cable modem. When a cable modem is first installed by a cable operator or powered up by a user, it must first locate or tune in to the correct downstream channel in order to receive data from the headend of the cable plant. This time-consuming process can be shortened by performing two matches between the selected, potential downstream data carrier and constellation diagrams of certain modulation schemes. Through this method, potential channels for data carriers can be eliminated quickly by going through a "screening" process (the first constellation diagram match) thereby preventing those potential channels from going through a significantly more time-consuming second constellation match. The process begins with selecting a potential frequency channel from the downstream band. It is then determined whether the potential channel contains a signal modulated in a particular modulation scheme where the modulation scheme is one not normally used on signals in the downstream channel, such as QPSK. If the signal in the potential frequency channel is not modulated according to the particular modulation scheme, the cable modem determines whether the signal in the potential channel is modulated according to another particular modulation scheme, such as QAM64 or QAM256. These particular modulation schemes, however, are ones normally used on signals in the downstream channel. The determination of whether the signal in the potential channel is modulated according to the first particular modulation scheme is done rapidly and only potential channels containing a signal likely to be modulated according to the second particular modulation scheme are examined for the second determination step. |
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DETAILED DESCRIPTION According to the present invention, methods, apparatus, and computer program products are disclosed for a cable modem to detect a viable data carrier on the downstream channel in a cable plant.
In one aspect of the invention, a method of detecting a data carrier in a downstream channel in a cable television plant is disclosed.
A potential or possible frequency channel from the downstream band is selected.
It is then determined whether the potential channel contains a signal modulated in a particular modulation scheme where the modulation scheme is one not normally used on signals in the downstream channel, such as QPSK.
If the signal in the potential frequency channel is not modulated according to the particular modulation scheme, the cable modem determines whether the signal in the potential channel is modulated according to another particular modulation scheme.
This particular modulation scheme, however, is one normally used on signals in the downstream channel.
The determination of whether the signal in the potential channel is modulated according to the first particular modulation scheme is done rapidly and only potential channels containing a signal likely to be modulated according to the second particular modulation scheme are examined for the second determination step.
In one embodiment, the first particular modulation scheme is QPSK and the second modulation scheme is either QAM64 or QAM256.
In another embodiment, the potential channel is the frequency channel most recently used by the cable modem.
In yet another embodiment, a signal from the potential frequency channel is matched against a constellation diagram corresponding to the first particular modulation scheme.
Similarly, in yet another embodiment, the signal from the potential frequency channel is matched against a constellation diagram corresponding to the second particular modulation scheme.
In yet another embodiment, it is determined whether the signal-to-noise ratio associated with the potential frequency channel is less than a particular preset signal-to-noise ratio threshold after the potential channel is matched against the first particular modulation scheme
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Television 
