Efficient transmission of digital return path data in cable television return path

• US 20030154496A1
• Filed: 11/08/2002
• Published: 08/14/2003
• Est. Priority Date: 02/12/2002
• Status: Active Grant

• Current Assignee: II-VI Delaware, Inc. (Coherent Corp.)
• Original Assignee: Finisar Corporation (II-VI Incorporated)
• Inventors: Oyadomari, Randy Ichiro, Sage, Gerald F.
• Granted Patent: US 7,725,036 B2
• Time in Patent Office: Days
• US Class Current: 725/121
• CPC Class Codes: H04N 21/437 Interfacing the upstream path of the transmission network, e.g. for transmitting client requests to a VOD server flow control in data networks H04L47/10; streaming protocols, e.g. RTP or RTCP, H04L65/65; scheduling or organising the servicing of application requests in data packet switching networks H04L67/60
• CPC Class Codes: H04N 21/6168 involving cable transmission, e.g. using a cable modem
• CPC Class Codes: H04N 7/17309 Transmission or handling of upstream communications

Abstract

An efficient means for transmitting digitized return path signals over a cable television return path is disclosed. In one embodiment of the invention, the cable television return path includes a node that receives an analog return signal from a subtree of the cable television system and generates a digital transport signal representative of the analog return path signal. The digital transport signal, however, is not a digitized form of the analog return signal. Rather, the digital transport signal is encoded such that fewer bits are used to represent the analog return signal without substantially impacting the accuracy and dynamic range of the signal. At the hub, the digital transport signal is decoded and converted to produce an analog signal that is a close approximation of the analog return signal.

Claims

1. A signal encoder for use in a cable television return path, comprising:

an input configured to receive an N-bit digital input sample from an analog-to-digital converter;

logic configured to determine a size of the N-bit digital sample, selected from a plurality of distinct possible sizes of an N-bit value, the logic further configured to generate one or more selection output bits indicative of the determined size of the N-bit digital sample;

logic configured to produce a digital output sample representative of the N-bit digital input sample, the digital output sample including a subset of the N-bits of the digital input sample selected from among a plurality of possible subsets for the N-bits, the subset of the N bits being selected in accordance with the one or more selection output bits, the digital output sample further including the one or more selection output bits, but fewer total bits than N; and

an output, coupled to the logic, configured to provide the digital output sample to an optical transmitter.

2. The signal encoder of claim 1, wherein the one or more selection output bits comprise two selection output bits.

3. The signal encoder of claim 1, wherein the one or more selection output bits correspond to a number of zeros that will be added to the selected subset of the N-bits by a decoder to regenerate an approximation of the N-bit digital sample.

4. The signal encoder of claim 1, wherein the N-bit digital sample is in offset-binary format.

5. The signal encoder of claim 1, wherein the logic configured to determine a size of the N-bit digital sample determines the size based at least in part on one or more prefix bits of the digital sample.

6. A signal decoder for use in a cable television return path, comprising:

an input configured to receive an M-bit digital sample from an optical receiver, the M-bit digital sample having M bits that include one or more selection bits and a plurality of non-selection bits;

logic to generate a representation of the one or more selection bits;

logic to combine the representation of the one or more selection bits, and one or more non-selection bits of the plurality of non-selection bits, to create a digital output sample;

logic to optionally insert one or more padding bits into the digital output sample, based at least in part on the one or more selection bits;

wherein the digital output sample is representative of the M-bit digital sample, but has more bits than the M-bit digital sample; and

a digital-to-analog converter coupled to the logic, the digital-to-analog converter configured to provide an analog signal corresponding to the digital output sample.

7. The decoder of claim 6, wherein the one or more selection bits comprise a binary-coded value, and further wherein the representation of the one or more selection bits is an unencoded version of the binary-coded value.

8. The decoder of claim 7, wherein the representation corresponds to a size of the M-bit digital sample.

9. The decoder of claim 6, wherein the one or more non-selection bits that are combined with the representation include all of the plurality of non-selection bits, as determined by the one or more selection bits.

10. The decoder of claim 6, wherein the one or more non-selection bits that are combined with the representation are a subset of the plurality of non-selection bits, as determined by the one or more selection bits.

11. The decoder of claim 6, wherein the logic to optionally insert one or more padding bits is configured to insert the one or more padding bits as the least significant bits of the digital output sample.

12. The decoder of claim 6, wherein the M-bit digital sample is in offset-binary format.

13. A cable television return path of a cable television system, comprising:

an analog-to-digital converter configured to receive an analog return signal from a subtree of the cable television system and configured to generate a first digital signal representative of the analog return signal, the first digital signal having a stream of first digital samples each having N bits;

an encoder configured to receive the first digital signal and to generate a second digital signal that includes a stream of second digital samples each having a fewer number of bits than N, each of the second digital samples including one or more selection bits and a subset of the N-bits of a corresponding one of the first digital samples, determined by the one or more selection bits;

an optical transmitter configured to convert the second digital signal into an optical signal;

an optical receiver configured to receive the optical signal and to convert the optical signal into a replica of the second digital signal;

a decoder configured to recover a third digital signal from the replica of the second digital signal, the third digital signal including a stream of third digital samples, wherein each of the third digital samples includes N bits; and

a digital-to-analog converted configured to convert the third digital signal to an analog signal that is substantially equivalent to the analog return signal.

14. The cable television return path of claim 13, wherein the encoder comprises:

an input configured to receive a digital sample of the first digital signal from the analog-to-digital converter;

logic configured to determine a size of the N-bit digital sample, selected from a plurality of distinct possible sizes of an N-bit value, the logic further configured to generate one or more selection output bits indicative of the determined size of the N-bit digital sample; and

logic configured to produce a digital output sample representative of the N-bit digital input sample, the digital output sample including a subset of the N-bits of the digital input sample selected from among a plurality of possible subsets for the N-bits, the subset of the N bits being selected in accordance with the one or more selection output bits, the digital output sample further including the one or more selection output bits, but having fewer total bits than N.

15. The cable television return path of claim 14, wherein the one or more selection output bits generated by the encoder comprise two selection output bits.

16. The cable television return path of claim 14, wherein the one or more selection output bits generated by the encoder correspond to a number of padding bits that will be added to a corresponding third digital sample recovered by the decoder.

17. The cable television return path of claim 13, wherein the decoder comprises:

an input configured to receive a digital sample from an optical receiver, the digital sample having fewer bits than N bits but includes one or more selection bits and a plurality of non-selection bits;

logic to generate a representation of the one or more selection bits;

logic to combine the representation of the one or more selection bits, and one or more non-selection bits of the plurality of non-selection bits, to create a digital output sample; and

logic to optionally insert one or more padding bits into the digital output sample, based at least in part on the one or more selection bits;

wherein the digital output sample is representative of the N-bit digital sample, but has more bits than the N-bit digital sample.

18. The cable television return path of claim 17, wherein the one or more selection bits of the digital sample comprise a binary-coded value, and further wherein the representation of the one or more selection bits is an unencoded version of the binary-coded value.

19. The cable television return path of claim 17, wherein the representation generated by the decoder corresponds to a size of the M-bit digital sample.

20. The cable television return path of claim 17, wherein the one or more non-selection bits that are combined with the representation generated by the decoder include all of the plurality of non-selection bits, as determined by the one or more selection bits.

21. The cable television return path of claim 17, wherein the one or more non-selection bits that are combined with the representation generated by the decoder are a subset of the plurality of non-selection bits, as determined by the one or more selection bits.

22. The cable television return path of claim 17, wherein the logic to optionally insert one or more padding bits in the decoder is configured to insert the one or more padding bits as the least significant bits of the digital output sample.