Multichannel, multimode DOCSIS headend receiver

Details Multichannel, multimode DOCSIS headend receiver Multichannel, multimode DOCSIS headend receiver

2002-06-13

2004-09-14

Kizou, Hassan (Department: 2662)

Multiplex communications

Channel assignment techniques

Combined time and frequency assignment

C370S447000, C370S462000, C370S538000, C725S117000, C725S144000

Reexamination Certificate

active

06791995

ABSTRACT:

FIELD OF USE
The invention finds use in the digital data receivers of cable modem termination systems (hereafter CMTS) of DOCSIS enabled cable television distribution systems. The DOCSIS 1.0 systems used time division multiplexed (hereafter TDMA) bursts only. However, the desire for higher speeds for transmission of digital data led to the development of DOCSIS 1.1 systems which were also TDMA systems but faster.
Upstream noise is a major problem in any system where digital data is transmitted upstream over a cable television hybrid fiber coaxial (hereafter HFC) cable distribution system to a cable modem termination system (hereafter CMTS). Privacy can also be a problem with TDMA bursts. One way of overcoming these noise problems and insuring privacy is to use code division multiplexing (hereafter CDMA) for upstream bursts. The code gain of CDMA systems helps overcome the noise and the spread spectrum nature of the signal prevents evesdropping by those without access to the spreading codes used in the transmitters. Terayon Communication Systems, Inc. of Santa Clara, Calif. has been a leader in bringing spread spectrum cable modems to the market. Terayon's modems enjoy a further noise advantage because they use sychronous code division multiplexing (hereafter SCDMA) to cut down on intersymbol interference. SCDMA requires all remote modems to perform a ranging process to determine a delay which is proper for their distance from the CMTS such that frames of spread spectrum data transmitted from the remote modems all arrive at the CMTS with their frame boundaries aligned in time. This minimizes intersymbol interference caused by transmissions from other modems.
DOCSIS cable modem termination system receivers are under development by Terayon which are capable of receiving both TDMA and SCDMA bursts on different channels as well as both TDMA and SCDMA bursts in separate time intervals (with different MAP messages applying to each) on the same frequency channel. DOCSIS defines a sub-channels as bursts with frequencies and symbol rates such that there is overlapping bandwidth. Sub-channel bursts cannot be transmitted with overlap in time. Different type bursts with different multiplexing and/or different symbol rates can be transmitted during different time intervals on the same carrier, and because there is overlapping bandwidth, each interval would be a sub-channel. The term sub-channel, as it is used herein means bursts transmitted on the same or different frequencies with symbol rates and center frequencies of the RF carrier on which they are transmitted such that there is an overlap in the bandwidth, but multiplexed in time such that there is no overlap in time. Channels or frequency channel, as the terms are used herein means transmissions on carriers of different frequencies and at symbol rates such that there is no overlap in bandwidth. Because there is no overlap in bandwidth, transmissions on different channels may overlap in time.
A prior art receiver that could not receive two sub-channels or channels at different center frequencies referred to as the Jasper I was developed by the assignee of the present invention and is currently on sale. A United States patent application Ser. No. 09/792,815 filed by the assignee of the present invention on Feb. 23, 2001 describes circuitry of Jasper I, and that patent application is hereby incorporated by reference. The receiver of the above identified patent application is capable of receiving 15 different SCDMA and TDMA burst types by adjusting the operation of its circuitry using burst parameter data that define the burst to be received. The differences in the various burst types relate to the symbol rate, type of multiplexing, type of modulation, function of the burst such as initial ranging or periodic station maintenance or data, etc.
When deploying new cable modems (hereafter CMs) capable of higher speed TDMA transmissions and high speed SCDMA bursts into a system with existing slower DOCSIS 1.0 or DOCSIS 1.1 modems, there arises a backward compatibility problem. Cable operators devote a certain portion of the bandwidth of the HFC to upstream digital data transmissions and there is no other available bandwidth upon which the higher speed TDMA or SCDMA upstream bursts can be transmitted. The bandwidth of a channel is related to its symbol rate. The symbol rate of DOCSIS 1.0 and 1.1 modems is slower (1.28 or 2.56 Msps) than the new advanced PHY TDMA and SCDMA modems (5.12 Msps), so the new modem channels have wider bandwidth when transmitting at the faster symbol rates. Thus, it is frequently necessary for wide-bandwidth, high-speed TDMA and SCDMA advanced PHY channels to overlap in bandwidth with lower-speed, more narrow bandwidth channels on which the older DOCSIS 1.0 and 1.1 modems transmit. This is because of the bandwidth and frequency band limit restrictions on upstream transmissions imposed on digital data delivery services by the cable operators.
The Jasper I receiver chip cannot receive mixed mode signals, i.e., two different sub-channels at different symbol rates and/or different multiplexing types which have overlapping bandwidth and the same center frequency. Further, it could not receive two different sub-channels having overlapping bandwidth and different center frequencies. The Jasper I receiver also cannot receive different channels at different RF center frequencies. Further, the Jasper I receiver was capable of receiving bursts at a maximum of 5.12 Msps, so when it was receiving DOCSIS 1.0 or 1.1 bursts at 1.28 or 2.56 Msps, the digital circuitry was idle most of the time.
Therefore, there is a need for a receiver that can receive bursts on multiple different RF inputs to keep the shared back end digital circuitry busy all the time. Further, there is a need for a CMTS receiver that can receive, on each RF input, mixed mode transmissions, that is having multiple sub-channels with overlapping bandwidth and either the same or different center frequencies. The receiver should be able to receive sub-channels of any type on the same frequency channel such as DOCSIS 1.0, Advanced PHY TDMA or advanced PHY SCDMA, and the different sub-channels may have different symbol rates. The receiver should be able to receive different sub-channels having overlapping bandwidth and the same center frequency or different center frequencies. Further, the receiver should be able to receive, multiple different channels without overlapping bandwidth and having the same or different symbol rates and/or multiplexing types and different center frequencies which are spread far enough apart given the symbol rate that there is no overlap in bandwidth. For example, there is a need for a receiver that can receive a single advanced PHY SCDMA channel having a symbol rate of 5.12 megasymbols per second (Msps) and a center frequency of F
1
transmitted with its bandwidth overlapping the bandwidths of multiple separate other channels of DOCSIS 1.0 bursts having symbol rates of 1.28 Msps or 2.56 Msps and center frequencies on both sides of F
1
and spaced apart so that the DOCSIS 1.0 channel bandwidths do not overlap each other. The receiver must be able to receive a different UCD message for each sub-channel type and switch between sub-channels on the fly during a guardtime between bursts on different sub-channels or different channels.
Channels with overlapping bandwidth and different burst types are typically multiplexed in time so that two different burst types with overlapping bandwidth are not transmitted at the same time, but there is also a need for a receiver that can simultaneously receive two or more sub-channels with overlapping bandwidth and overlapping in time. To receive overlapping bandwidth bursts of different types which are time division multiplexed, the circuitry of the needed CMTS receiver has to be adjusted using burst parameter data that defines the burst to be received during any particular time on a sub-channel or channel.
The Jasper I receiver could only receive one channel of RF signals at a time, i.e., it only had one RF

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