Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Reexamination Certificate
2000-12-11
2004-06-29
Nguyen, Lee (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
C455S423000, C725S107000
Reexamination Certificate
active
06757522
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to data networks, and more specifically to a technique for determining the signal-to-noise ratio value on one or more channels of an access network.
2. Background
Broadband access technologies such as cable, fiber optic, and wireless have made rapid progress in recent years. Recently there has been a convergence of voice and data networks which is due in part to US deregulation of the telecommunications industry. In order to stay competitive, companies offering broadband access technologies need to support voice, video, and other high-bandwidth applications over their local access networks. For networks that use a shared access medium to communicate between subscribers and the service provider (e.g., cable networks, wireless networks, etc.), providing reliable high-quality voice/video communication over such networks is not an easy task.
One type of broadband access technology relates to cable modem networks. A cable modem network or “cable plant” employs cable modems, which are an improvement of conventional PC data modems and provide high speed connectivity. Cable modems are therefore instrumental in transforming the cable system into a full service provider of video, voice and data telecommunications services. Digital data on upstream and downstream channels of the cable network is carried over radio frequency (“RF”) carrier signals. Cable modems convert digital data to a modulated RF signal for upstream transmission and convert downstream RF signal to digital form. The conversion is done at a subscriber's facility. At a Cable Modem Termination System (“CMTS”), located at a Head End of the cable network, the conversions are reversed. The CMTS converts downstream digital data to a modulated RF signal, which is carried over the fiber and coaxial lines to the subscriber premises. The cable modem then demodulates the RF signal and feeds the digital data to a computer. On the return path, the digital data is fed to the cable modem (from an associated PC for example), which converts it to a modulated RF signal. Once the CMTS receives the upstream RF signal, it demodulates it and transmits the digital data to an external source.
FIG. 1
is a block diagram of a typical two-way hybrid fiber-coaxial (HFC) cable network system. It shows a Head End
102
(essentially a distribution hub) which can typically service about 40,000 homes. Head End
102
contains a CMTS
104
that is needed when transmitting and receiving data using cable modems. Primary functions of the CMTS include (1) receiving baseband data inputs from external sources
100
and converting the data for transmission over the cable plant (e.g., converting Ethernet or ATM baseband data to data suitable for transmission over the cable system); (2) providing appropriate Media Access Control (MAC) level packet headers for data received by the cable system, and (3) modulating and demodulating the data to and from the cable system.
Head End
102
connects through pairs of fiber optic lines
106
(one line for each direction) to a series of fiber nodes
108
. Each Head End can support normally up to 80 fiber nodes. Pre-HFC cable systems used coaxial cables and conventional distribution nodes. Since a single coaxial cable was capable of transmitting data in both directions, one coaxial cable ran between the Head End and each distribution node. In addition, because cable modems were not used, the Head End of pre-HFC cable systems did not contain a CMTS. Returning to
FIG. 1
, each of the fiber nodes
108
is connected by a coaxial cable
110
to two-way amplifiers or duplex filters
112
, which permit certain frequencies to go in one direction and other frequencies to go in the opposite direction (different frequency ranges are used for upstream and downstream paths). Each fiber node
108
can normally service up to
2000
subscribers. Fiber node
108
, coaxial cable
110
, two-way amplifiers
112
, plus distribution amplifiers
114
along with trunk line
116
, and subscriber taps, i.e. branch lines
118
, make up the coaxial distribution system of an HFC system. Subscriber tap
118
is connected to a cable modem
120
. Cable modem
120
is, in turn, connected to a network device
122
, such as a subscriber computer.
In order for data to be able to be transmitted effectively over a wide area network such as HFC or other broadband computer networks, a common standard for data transmission is typically adopted by network providers. A commonly used and well known standard for transmission of data or other information over HFC networks is the Data Over Cable System Interface Specification (DOCSIS). The DOCSIS standard has been publicly presented by Cable Television Laboratories, Inc. (Louisville, Colo.), in a document entitled, DOCSIS 1.1 RF Interface Specification (document control number SP-RFIv1.1-I04-000407, Apr. 7, 2000). That document is incorporated herein by reference in its entirety for all purposes.
In conventional DOCSIS systems, the CMTS may include a plurality of physically distinct line cards having appropriate hardware for communicating with cable modems in the network. Each line card is typically assigned to a separate DOCSIS domain, which is a collection of downstream and upstream channels for which a single MAC Allocation and Management protocol operates. Typically, each DOCSIS domain includes a single downstream channel and one or more upstream channels. The downstream channel is used by the CMTS to broadcast data to all cable modems (CMs) within that particular domain. Only the CMTS may transmit data on the downstream. In order to allow the cable modems of a particular DOCSIS domain to transmit data to the CMTS, the cable modems share one or more upstream channels within that domain.
Channel Quality Detection
It will be appreciated that the performance of data communication in a conventional cable network may be dependent upon channel conditions of the upstream and/or downstream channels in the cable network. For this reason, it is desirable to monitor conditions of the upstream channels of the cable network in order to provide for effective management and use of each of the upstream channels. For example, if it is determined that conditions on a particular upstream channel are below acceptable quality levels, the CMTS may instruct cable modems on that channel to hop to a second upstream channel and begin using the second upstream channel for communicating with the CMTS.
One indicator which is typically used to evaluate channel conditions of a selected channel is the signal-to-noise ratio (SNR) associated with that channel. Typically, in most HFC networks, the SNR value for each upstream channel is measured and calculated using an off-the-shelf component such as, for example, the ASIC chip BCM3137, manufactured by Broadcom Corporation of Irvine, Calif.
Conventional techniques for determining the SNR value of a selected upstream channel are typically based upon Error Vector Magnitude (EVM) calculations, which are generally known to one having ordinary skill in the art. For example, a conventional ASIC chip configured to measure SNR on a particular upstream channel of an HFC network continuously monitors the upstream channel for received signals. When a signal is detected, the ASIC analyzes the signal to determine codes or symbols which may be embedded therein according to a predetermined format or protocol. For each symbol detected in the received signal, the ASIC determines the Error Vector Magnitude (EVM) for that symbol. The EVM value represents the amount of deviation that exists between the vector position of the detected symbol and the theoretically ideal position of that symbol. Once the EVM value for a particular symbol has been determined, a SNR value may then be calculated using a predetermined formula generally known to one having ordinary skill in the art. Additionally, it is typically the case that the ASIC computes an average SNR value for the selected upstream channel using the EVM values associated wit
Azarakhsh Nozar
Chen Hungsan
de Jesus Leano Chrisanto
Mahesh Harihara
Naegeli Charles
Beyer Weaver & Thomas LLP
Cisco Technology Inc.
Nguyen Lee
LandOfFree
Technique for determining carrier-to-noise ratio of selected... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Technique for determining carrier-to-noise ratio of selected..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Technique for determining carrier-to-noise ratio of selected... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3353541