Multiplex communications – Channel assignment techniques – Combining or distributing information via time channels...
Reexamination Certificate
1999-06-21
2002-10-01
Vincent, David (Department: 2732)
Multiplex communications
Channel assignment techniques
Combining or distributing information via time channels...
C370S441000
Reexamination Certificate
active
06459703
ABSTRACT:
FIELD OF USE
The invention finds application in the field of digital data delivery over cable TV systems and possibly in cellular and satellite communications systems.
In the emerging field of digital data delivery over media such as hybrid fiber coaxial cable systems of cable television plants and wireless modems etc. there exists the problem of backward compatibilty. Some existing systems have time division multiplexed (TDMA) cable modems or other types of TDMA modems already installed, but newer technology makes faster TDMA modems possible and also makes synchronous code division multiplexed modems possible. It is desirable to be able to use these newer modems in existing systems without rendering the older modems obsolete or requiring them to operate on a different frequency band (hereafter referred to as a physical channel). For example, in all-TDMA systems, slower symbol rate modems such as DOCSIS 1.0 modems exist which can only transmit at a maximum symbol rate of 2.56 million symbols per second. However, faster TDMA modems are now available that can transmit TDMA bursts at 5.12 million symbols per second. Thus, a need has arisen for a method of allowing TDMA modems with different maximum symbol rates to coexist and function on the same shared transmission medium.
As another example of this problem, consider the existing DOCSIS digital data delivery systems for delivery of digital data over cable TV systems. In these prior art DOCSIS 1.0 systems, digital data delivery is made across the hybrid fiber/coax media of cable television systems bidirectionally using TDMA only at a maximum symbol rate of 2.56 Msymbols/sec. These systems used frequency division multiplexing to keep the digital data separate from the cable television signals. Multiple different physical frequency channels are used within the band of frequencies used for digital data delivery. Within each frequency channel, multiple DOCSIS 1.0 modems transmitted their data by modulating it onto a carrier having the same center frequency as the carrier used by all the other modems assigned to the same channel. Within each channel, time division multiple access multiplexing or TDMA was used to keep the data from each of the plurality of different DOCSIS 1.0 modems separate for transmission upstream to the CMTS (CMTS stands for Cable Modem Termination System and is the headend cable modem to which all remote unit cable modems transmit or head end.
This system works well, however, a movement is now underway to define a new national standard where synchronous code division multiplexed communication of digital data across cable television networks can be accomplished. The advantages of such a system are numerous including increased privacy, the ability of all modems with upstream traffic that have been awarded bandwidth to transmit at once, etc. This new proposed standard is publicly available as the IEEE 802.14a standard entitled “High-capacity physical layer specification, Draft 1, Revision 3” which was published Mar. 30, 1999 and will hereafter be referred to as the advanced PHY specification and modems which comply with it will be referred to as advanced PHY modems or advanced PHY transceivers. Although the IEEE 802.14a unapproved standards draft is in flux, its current state will be used for purposes of explaining this invention. advanced PHY modems currently must be capable of transmitting TDMA bursts at a faster maximum symbol rate than the DOCSIS 1.0 modems as well as to transmit SCDMA bursts. The advanced PHY proposal thus defines two modes of operation: (1) a TDMA mode which is defined both under the advanced PHY and the DOCSIS 1.0 standards; and (2) an SCDMA mode which is defined in advanced PHY only. An apparatus for transmitting digital data upstream using SCDMA with a chip clock rate derived from the arbitrary clock rate of an MCNS (MCNS is the acronym for a consortium of cable operators that backed the standardization of the DOCSIS specifications that define standards digital cable modems have, to meet in DOCSIS cable systems) or IEEE 802.14 downstream is defined in U.S. patent application Ser. No. 09/074,036, filed May 6, 1998 entitled APPARATUS AND METHOD FOR SYNCHRONIZING AN SCDMA UPSTREAM OR ANY OTHER TYPE UPSTREAM TO AN MCNS DOWNSTREAM OR ANY OTHER TYPE OF DOWNSTREAM WITH A DIFFERENT CLOCK RATE THAN THE UPSTREAM, which is hereby incorporated by reference. An earlier PCT publication WO97/08861 published Mar. 6, 1997 teaches the details of SCDMA transmitters and receivers for transmitting SCDMA frames on cable television systems, and is hereby incorporated by reference as are all the prior art publications incorporated by reference into this PCT publication including PCT publication WO97/34421, published Sep. 18, 1997 teaching methods and apparatus for using SCDMA to establish virtual links for use in transmitting ATM cells. A method of two dimension interleaving of data between minislots and spreading codes for the SCDMA upstream in the advanced PHY SCDMA bursts is taught in U.S. patent application Ser. No. 09/152,643, filed Sep. 14, 1998, which is hereby incorporated by reference. A method of using a bank of filters for excision of narrow-band interference to SCDMA signals is taught in U.S. patent application Ser. No. 09/152,645, filed Sep. 14, 1998, which is hereby incorporated by reference.
The downstream in MCNS systems for digital data delivery through cable TV systems breaks MAC layer packets down into MPEG packets. These are 64-QAM or 256-QAM modulated and sent as a continuous stream after FEC encoding. The upstream SCDMA transmitters in all the remote units derive their chip clocks from the downstream master clock and all transmit their SCDMA multiplexed data upstream in frames on the same frequency using the same chip clock. Alignment of the frame boundaries at the CMTS is achieved by doing a frame alignment offset calculation prior to carrying out the ranging process described in the PCT publications cited above to speed up the ranging process. The offset calculation determines the degree of offset of the minislot counter in each remote unit (hereafter RU) from the upstream minislot counter in the CMTS. This offset calculation is done using the timestamp messages normally sent in the downstream by sampling a local kiloframe counter in the RU each time a downstream sync message is received and performing a particular mathematical calculation.
While the advanced PHY SCDMA upstream is better, there is the problem of backward compatibility of the CMTS needed to implement advanced PHY transmissions with older systems populated by DOCSIS 1.0 TDMA only modems. If a CMTS head end apparatus is installed in a cable television system populated by a mixture of DOCSIS 1.0 TDMA only modems and the newer advanced PHY modems which can transmit in either TDMA or SCDMA, the older 1.0 TDMA only modems will not successfully communicate with the CMTS if they transmit on the same frequency as the newer modems and will have to operate on a different frequency band. Thus, a need has arisen for a new CMTS structure and process which can receive and process bandwidth requests and accomodate transmissions from both DOCSIS 1.0 TDMA only modems as well as advanced PHY TDMA or SCDMA modems on the same frequency channel and without requiring any changes to the DOCSIS 1.0 TDMA modems.
SUMMARY OF THE INVENTION
The basic idea underlying the process and apparatus of the invention is to provide a method by which multiple upstream channels having different symbol rates and/or multiplexing types can coexist on the same system and be transmitted using the same center frequency or the same PHYSICAL channel. For example, two sets of TDMA modems with a newer set of modems operating at higher maximum TDMA symbol rates than older modems can share the same PHYSICAL channel without the need for any change to the older modems or requiring them to transmit on a different frequency. Likewise, TDMA modems can coexist with another set of modems sharing the same PHYSICAL channel using SCDMA multiplexing. Further, two different sets of modems
Grimwood Michael
Lind Paul Alan
Rakib Selim Shlomo
Fish Ronald C.
Ronald Craig Fish, a Law Corporation
Sam Phirin
Terayon Communication Systems, Inc.
Vincent David
LandOfFree
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