WO2005002143A1 - Hybrid docsis configuration in a cable modem - Google Patents

Abstract

A data over cable device (300) includes a diplexer (315) having a downstream frequency range of about 112 megahertz to about 858 megahertz and an upstream frequency range of about 5 megahertz to about 65 megahertz; a low-pass filter (345) in signal communication with the diplexer, the low-pass filter having a cut-off frequency of about 65 megahertz; and a surface acoustic wave filter (360) in signal communication with the diplexer, the surface acoustic wave filter having a channel bandwidth of about 6 megahertz; and a corresponding method (300) for transmitting data over a cable device includes providing (315) a downstream frequency range of about 112 megahertz to about 858 megahertz; providing (315) an upstream frequency range of about 5 megahertz to about 65 megahertz; passing (345) the portion of the upstream frequency range falling below about 65 megahertz; and passing (360) a portion of the downstream frequency range falling within a 6 megahertz channel bandwidth.

Description

HYBRID DOCSIS CONFIGURATION IN A CABLE MODEM

CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit of U.S. Provisional Application Serial No. 60/480,729 (Attorney Docket No. PU030172), filed June 23, 2003, and entitled

"HYBRID DOCSIS CONFIGURATION IN A CABLE MODEM", which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION The present invention is directed towards data modems, and more particularly, towards data modems for cable communications systems.

BACKGROUND OF THE INVENTION Cable modem service providers typically use devices compliant with the Data- Over-Cable Service Interface Specification (DOCSIS). Providers in Europe are currently using North American DOCSIS (NA-DOCSIS) cable modems, where the downstream channels are compliant with ITU J83.b Digital Video and Cable Modem Standard (IEEE 802.14/DOCSIS), hereafter referred to as Annex B. Unfortunately, some of these providers are running out of bandwidth for the upstream spectrum, which has a range of only 5-42 MHz edge-to-edge for NA-DOCSIS. The Euro-

DOCSIS specification, on the other hand, has an upstream frequency range of 5-65 MHz edge-to-edge, but the downstream performance would be significantly compromised with an Annex B downstream channel. Therefore, what is needed is a hybrid cable modem with the upstream bandwidth capacity of a Euro-DOCSIS cable modem and the downstream performance of an NA-DOCSIS cable modem.

SUMMARY OF THE INVENTION These and other drawbacks and disadvantages of the prior art are addressed by a hybrid DOCSIS cable modem with the upstream bandwidth capacity of a Euro- DOCSIS cable modem and the downstream performance of an NA-DOCSIS cable modem. An exemplary data over cable device includes a diplexer having a downstream frequency range of about 112 megahertz to about 858 megahertz and an upstream frequency range of about 5 megahertz to about 65 megahertz; a low-pass filter in signal communication with the diplexer, the low-pass filter having a cut-off frequency of about 65 megahertz; and a surface acoustic wave filter in signal communication with the diplexer, the surface acoustic wave filter having a channel bandwidth of about 6 megahertz; and a corresponding method for transmitting data over a cable device includes providing a downstream frequency range of about 112 megahertz to about 858 megahertz; providing an upstream frequency range of about 5 megahertz to about 65 megahertz; passing the portion of the upstream frequency range falling below about 65 megahertz; and passing a portion of the downstream frequency range falling within a 6 megahertz channel bandwidth. These and other aspects, features and advantages of the present invention will become apparent from the following description of exemplary embodiments, which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention may be better understood with reference to the following exemplary figures, in which: Figure 1 shows a block diagram for a typical North American Data-Over-Cable

Service Interface Specification (NA-DOCSIS) data over cable device; Figure 2 shows a block diagram for a typical Euro-DOCSIS data over cable device; and Figure 3 shows a block diagram for a hybrid data over cable device in accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The Data-Over-Cable Service Interface Specification (DOCSIS) has several annexes. North American DOCSIS (NA-DOCSIS) cable modems are typically used where the downstream channels are to be compliant with Annex B of the DOCSIS specification. Many service providers in Europe use downstream channels that are compliant with Annex B. Unfortunately, some of these service providers are running out of bandwidth for the upstream spectrum, which has a range of only 5-42 MHz edge-to-edge for NA-DOCSIS. The Euro-DOCSIS specification, on the other hand, has an upstream frequency range of 5-65 MHz edge-to-edge, but the downstream performance would be significantly compromised with an Annex B downstream channel. Accordingly, the present disclosure provides a hybrid cable modem with the upstream bandwidth capacity of a Euro-DOCSIS cable modem and the downstream performance of a NA-DOCSIS cable modem. A "dual mode" Euro-DOCSIS cable modem has been offered to allow European service providers a way to use Annex B DOCSIS channels (6MHz) in Europe. That solution was practical as long as the provider was willing to sacrifice some downstream performance when using 6 MHz channels, or to use 6 MHz channels while keeping the center frequencies of the downstream carriers spaced at 8 MHz. If the downstream frequencies are Annex B and spaced at 6 MHz on center, full North American DOCSIS compliance is not achieved. Embodiments of the present invention address a market niche by providing a hybrid modem having full North American DOCSIS downstream performance, while extending the upstream spectral range. Embodiments provide a hybrid data over cable device, such as a cable modem (CM), Voice over Internet Protocol (VOIP) Mail Transport Agent (MTA), Set Top Box (STB), or like device. The purpose is to extend the return bandwidth up to 65 MHz, similar to the Euro-DOCSIS standard. As a consequence, this modem uses the frequency bands of 108-862MHz instead of 88- 862MHz in the downstream, and 5-65MHz instead of 5-42MHz in the upstream. Other embodiments may also be Euro-DOCSIS compliant in the upstream direction. The instant description illustrates the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. Thus, for example, it will be appreciated by those skilled in the art that the block diagrams presented herein represent conceptual views of illustrative circuitry embodying the principles of the invention. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudocode, and the like represent various processes which may be substantially represented in computer readable media and so executed by a computer or processor, whether or not such computer or processor is explicitly shown. The functions of the various elements shown in the figures may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term "processor" or "controller" should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor ("DSP") hardware, read-only memory ("ROM") for storing software, random access memory ("RAM"), and non-volatile storage. Other hardware, conventional and/or custom, may also be included. Similarly, any switches shown in the figures are conceptual only. Their function may be carried out through the operation of program logic, through dedicated logic, through the interaction of program control and dedicated logic, or even manually, the particular technique being selectable by the implementer as more specifically understood from the context. In the claims hereof, any element expressed as a means for performing a specified function is intended to encompass any way of performing that function including, for example, a) a combination of circuit elements that performs that function or b) software in any form, including, therefore, firmware, microcode or the like, combined with appropriate circuitry for executing that software to perform the function. The invention as defined by such claims resides in the fact that the functionalities provided by the various recited means are combined and brought together in the manner which the claims call for. Applicant thus regards any means that can provide those functionalities as equivalent to those shown herein. As shown in Figure 1 , a North American Data-Over-Cable Service Interface Specification (NA-DOCSIS) data over cable device is indicated generally by the reference numeral 100. The NA-DOCSIS device 100 includes a diplexer 110 having a downstream range of about 91-857 MHz and an upstream range of about 5-42 MHz. The diplexer 110 is in signal communication with a balun 120 via an upstream channel. The balun 120, in turn, is in signal communication with an upstream amplifier 130 via dual channels. The amplifier 130 is in signal communication with a low pass filter 140 via dual channels, where the low pass filter 140 has a cut-off frequency of about 42 MHz. The low pass filter 140, in turn, is in signal communication with a DOCSIS physical layer 150 via dual channels, where the physical layer 150 may be implemented in silicon. The physical layer 150 is in signal communication with a 6 MHz SAW filter 160 via dual channels, which, in turn, is in signal communication with one or more mixer blocks 170 via dual channels to reach a final intermediate frequency (IF), where the mixer blocks 170 may include an IF amplifier (not shown). The mixer blocks 170 are in signal communication with a low noise amplifier (LNA) 180 via dual channels, and the LNA is in signal communication with the diplexer 110 via dual channels. Turning to Figure 2, a Euro-DOCSIS data over cable device is indicated generally by the reference numeral 200. The Euro-DOCSIS device 200 includes a diplexer 215 having a downstream range of about 112-858 MHz and an upstream range of about 5-65 MHz. The diplexer 215 is in signal communication with a balun 220 via an upstream channel. The balun 220, in turn, is in signal communication with an upstream amplifier 230 via dual channels. The amplifier 230 is in signal communication with a low pass filter 245 via dual channels, where the low pass filter 245 has a cut-off frequency of about 65 MHz. The low pass filter 245, in turn, is in signal communication with a DOCSIS physical layer 250 via dual channels, where the physical layer 250 may be implemented in silicon. The physical layer 250 is in signal communication with an 8 MHz SAW filter 265 via dual channels, which, in turn, is in signal communication with one or more mixer blocks 270 via dual channels to reach a final IF, where the mixer blocks 270 may include an IF amplifier (not shown). The mixer blocks 270 are in signal communication with an LNA 280 via dual channels, and the LNA is in signal communication with the diplexer 215 via dual channels. Turning now to Figure 3, a hybrid data over cable device is indicated generally by the reference numeral 300. The hybrid device 300 includes a diplexer 315 having a downstream range of about 112-858 MHz and an upstream range of about 5-65 MHz. The diplexer 315 is in signal communication with a balun 320 via an upstream channel. The balun 320, in turn, is in signal communication with an upstream amplifier 330 via dual channels. The amplifier 330 is in signal communication with a low pass filter 345 via dual channels, where the low pass filter 345 has a cut-off frequency of about 65 MHz. The low pass filter 345, in turn, is in signal communication with a physical layer 350 via dual channels, where the physical layer 350 may be implemented in silicon. The physical layer 350 is in signal communication with a 6 MHz SAW filter 360 via dual channels, which, in turn, is in signal communication with one or more mixer blocks 370 via dual channels to reach a final IF, where the mixer blocks 370 may include an IF amplifier (not shown). The mixer blocks 370 are in signal communication with an LNA 380 via dual channels, and the LNA is in signal communication with the diplexer 315 via dual channels. Thus, Figures 1 , 2, and 3 show block diagrams of various RF front-end architectures for various data over cable devices. Figure 1 shows a typical architecture for a North American DOCSIS data over cable device, while Figure 2 shows a typical architecture for a Euro-DOCSIS data over cable device. Figure 3, which incorporates principles of the present invention, shows a hybrid data over cable device RF front-end. This embodiment starts with a Euro- DOCSIS architecture, but then changes the standard 8 MHz surface acoustic wave (SAW) filter to a 6 MHz SAW filter. The advantage of this approach is that the hybrid data over cable device has full North American DOCSIS performance in the downstream physical (PHY) layer while benefiting from an extended upstream frequency range that meets the Euro-DOCSIS standard. In operation, downstream performance measurements were made for a preferred embodiment cable modem to compare the architectures outlined in Figures 2 and 3. The results of these measurements are outlined in Table 1. The parameters of the tests were as follows: All testing was performed at a desired carrier frequency of 603 MHz; All adjacent channel testing was performed with adjacent channel frequencies of 597 MHz and 609 MHz; The upper and lower adjacent channel signals were always the same power; The adjacent channels used were 64 QAM, Annex B signals; and All test data was taken when the CM reached a bit error rate (BER) of 1x10e-8.

Table 1 , The collected data clearly demonstrates that significant adjacent channel performance is gained over the dual-mode approach. This architecture embodiment is intended for 6 MHz, Annex B, downstream signals. The embodiment of Figure 3 is using differential signals in the upstream, and thus has two signal connections. As will be recognized by those of ordinary skill in the pertinent art, this can also be achieved using a single-ended architecture having one connection in the upstream channel. In such an embodiment, the balun would no longer be needed. In other embodiments, the optional balun need not be limited to a 2:1 type, since it is only that way because of the exemplary architecture of Figure 3. Thus, alternate embodiments may use a 1 :1 type or other balun, depending on the upstream amplifier used. In addition, the downstream need not be differential throughout the entire downstream change. Alternate embodiments may use single-ended IF amplifiers as well, for example. These and other features and advantages of the present invention may be readily ascertained by one of ordinary skill in the pertinent art based on the teachings herein. It is to be understood that the principles of the present invention may be implemented in various forms of hardware, software, firmware, special purpose processors, or combinations thereof. Most preferably, the principles of the present invention are implemented as a combination of hardware and software. Moreover, the software is preferably implemented as an application program tangibly embodied on a program storage unit. The application program may be uploaded to, and executed by, a machine comprising any suitable architecture. Preferably, the machine is implemented on a computer platform having hardware such as one or more central processing units ("CPU"), a random access memory ("RAM"), and input/output ("I/O") interfaces. The computer platform may also include an operating system and microinstruction code. The various processes and functions described herein may be either part of the microinstruction code or part of the application program, or any combination thereof, which may be executed by a CPU. In addition, various other peripheral units may be connected to the computer platform such as an additional data storage unit and a printing unit. It is to be further understood that, because some of the constituent system components and methods depicted in the accompanying drawings are preferably implemented in software, the actual connections between the system components or the process function blocks may differ depending upon the manner in which the present invention is programmed. Given the teachings herein, one of ordinary skill in the pertinent art will be able to contemplate these and similar implementations or configurations of the present invention. Although the illustrative embodiments have been described herein with reference to the accompanying drawings, it is to be understood that the present invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one of ordinary skill in the pertinent art without departing from the scope or spirit of the present invention. All such changes and modifications are intended to be included within the scope of the present invention as set forth in the appended claims.

Claims

1. A data over cable device (300) comprising: a diplexer (315) having a downstream frequency range of about 112 megahertz to about 858 megahertz and an upstream frequency range of about 5 megahertz to about 65 megahertz; a low-pass filter (345) in signal communication with the diplexer, the low-pass filter having a cut-off frequency of about 65 megahertz; and a surface acoustic wave filter (360) in signal communication with the low-pass filter, the surface acoustic wave filter having a channel bandwidth of about 6 megahertz.

2. A data over cable device as defined in Claim 1 , further comprising a balun (320) in signal communication with the diplexer via an upstream channel.

3. A data over cable device as defined in Claim 2, further comprising an upstream amplifier (330) in signal communication with the balun.

4. A data over cable device as defined in Claim 3 wherein the upstream amplifier (330) is in signal communication with the low-pass filter (345).

5. A data over cable device as defined in Claim 1 , further comprising a DOCSIS physical layer (350) in signal communication with each of the low-pass filter and the surface acoustic wave filter.

6. A data over cable device as defined in Claim 5 wherein the DOCSIS physical layer is implemented in silicon.

7. A data over cable device as defined in Claim 1 , further comprising a low noise amplifier (380) in signal communication with the diplexer via a downstream channel.

8. A data over cable device as defined in Claim 7, further comprising at least one mixer block (370) in signal communication with the linear amplifier.

9. A data over cable device as defined in Claim 8 wherein the at least one mixer block (370) is in signal communication with the surface acoustic wave filter

(360).

10. A data over cable device (300) comprising: diplexing means for providing a downstream frequency range of about 112 megahertz to about 858 megahertz, and providing an upstream frequency range of about 5 megahertz to about 65 megahertz; first filtering means for passing the portion of the upstream frequency range falling below about 65 megahertz; and second filtering means for passing a portion of the downstream frequency range falling within a 6-megahertz channel bandwidth.

11. A method for transmitting data over a cable device, the method comprising: providing a downstream frequency range of about 112 megahertz to about 858 megahertz; providing an upstream frequency range of about 5 megahertz to about 65 megahertz; passing the portion of the upstream frequency range falling below about 65 megahertz; and passing a portion of the downstream frequency range falling within a 6- megahertz channel bandwidth.

12. A method for transmitting data over a cable device as defined in Claim

11 , further comprising balancing the impedance for the upstream frequency range.

13. A method for transmitting data over a cable device as defined in Claim

12, further comprising amplifying the upstream frequency range.

14. A method for transmitting data over a cable device as defined in Claim 11 , further comprising frequency converting between the upstream and the downstream channels.

15. A method for transmitting data over a cable device as defined in Claim 11 , further comprising amplifying the downstream frequency range.

16. A method for transmitting data over a cable device as defined in Claim 15, further comprising mixing the downstream frequency range.

17. A program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform program steps for transmitting data over a cable device, the program steps comprising: providing a downstream frequency range of about 112 megahertz to about 858 megahertz; providing an upstream frequency range of about 5 megahertz to about 65 megahertz; passing the portion of the upstream frequency range falling below about 65 megahertz; and passing a portion of the downstream frequency range falling within a 6- megahertz channel bandwidth.

18. A program storage device for transmitting data over a cable device as defined in Claim 17, further comprising the program step of balancing the impedance for the upstream frequency range.

19. A program storage device for transmitting data over a cable device as defined in Claim 17, further comprising the program step of frequency converting between the upstream and the downstream channels.

20. A program storage device for transmitting data over a cable device as defined in Claim 17, further comprising the program step of amplifying the downstream frequency range.