The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jun. 03, 2003
Filed:
Jan. 08, 1999
Guenter E. Roeck, San Jose, CA (US);
Wei-Sing Chen, Fremont, CA (US);
Charles J. Naegeli, Montara, CA (US);
Cisco Technology, Inc., San Jose, CA (US);
Abstract
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.