Upstream data transmission system for cable television

• US 5,535,206 A
• Filed: 02/07/1995
• Issued: 07/09/1996
• Est. Priority Date: 11/14/1994
• Status: Expired due to Term

• Current Assignee: LG Electronics, Inc. (LG Corporation)
• Original Assignee: Zenith Electronics Corporation (LG Corporation)
• Inventors: Bestler, Caitlin B., Rabii, Khosro M.
• Primary Examiner(s): MARCELO, MELVIN C
• Application Number:
  US08/385,242
• Time in Patent Office: 518 Days
• Field of Search: 370/79, 370/82, 370/83, 370/85.1, 370/85.7, 370/85.8, 370/95.1, 370/95.2, 348/12, 455/5.1
• US Class Current: 370/458
• CPC Class Codes: H04J 3/1694 Allocation of channels in TDM/TDMA networks, e.g. distributed multiplexers Passive Optical Networks H04Q11/0062
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• 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 21/6118 involving cable transmission, e.g. using a cable modem
• 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

A cable television upstream data transmission system provides a plurality of time slots synchronized to the downstream symbol clock for use by subscriber terminals in upstream data transmission. The width and number of time slots are controlled by a pair of downloadable values to accommodate dynamic changes of the cable system. A transmission modulator used within the subscriber terminal produces an upstream transmission carrier having a frequency locked to the symbol clock. The frequency of the carrier signal produced by the transmission modulator is programmably controlled by a plurality of program values which are selected to provide frequency and phase lock of the modulator'"'"'s carrier to the symbol clock.

Claims

1. An upstream data transmission system for use in a cable television system in which downstream data transmission is carried out using data frames and a periodic data frame synchronization signal via a cable network from a headend to a plurality of subscriber terminals, said upstream data transmission system comprising:

time slot means for dividing said data frames into a plurality of time slots in response to a downloadable slot width signal;

superframe means for combining one or more of said data frames into a superframe interval in which each data frame is sequentially numbered in response to a downloadable superframe signal;

means for assigning a time slot to a subscriber terminal expressed as a time slot identifier having a frame number within said superframe and a slot number within said numbered frame; and

timing means for transmitting upstream data from a subscriber terminal to said headend during said assigned time slot.

2. An upstream data transmission system as set forth in claim 1 wherein said downstream data frames comprise a plurality of N-level symbols occurring at a predetermined symbol rate, said upstream data transmission system including means for generating a symbol clock signal having a frequency corresponding to said predetermined rate, said time slot means and said superframe means comprising counting means synchronously operated in response to said symbol clock signal.

3. An upstream data transmission system as set forth in claim 1 wherein said plurality of time slots are substantially equal and wherein said time slot means includes a repetitive down counter and means for loading said down counter with a numeric value of said slot width signal.

4. An upstream data transmission system as set forth in claim 3 wherein said means for loading said down counter includes means responsive to said data frame synchronization signal.

5. An upstream data transmission system as set forth in claim 4 wherein said down counter produces an output signal each time a predetermined count is reached and wherein said time slot means includes a slot counter responsive to said output signal to count said time slots between said data frame synchronization signals and output a slot count number.

6. An upstream data transmission system as set forth in claim 5 wherein said superframe means includes a frame counter for counting said data frame synchronizing signals between each superframe signal and outputting a frame count number.

7. An upstream data transmission system as set forth in claim 6 wherein said timing means includes:

comparator means coupled to said slot counter and said frame counter; and

first memory means for storing said time slot identifier for said subscriber terminal together with an upstream data message;

said comparator means comparing said frame count and slot count numbers to said stored time slot identifier and causing said timing means to initiate upstream transmission of said data message when a match is found.

8. An upstream data transmission system as set forth in claim 7 wherein said timing means further includes a second memory means for storing said time slot identifier together with an upstream data message.

9. An upstream data transmission system as set forth in claim 7 wherein said frame count number corresponds to the most significant bits of said time slot identifier and said slot count number corresponds to the least significant bits of said time slot identifier.

10. An upstream data transmission system as set forth in claim 9 wherein said comparator means includes a register coupled to said first memory means and wherein said most significant bits of said time slot identifier is initially stored in said register for match to said frame count number and said least significant bits of said time slot identifier are stored in said register once a frame number match is detected and thereafter said least significant bits of said time slot identifier are compared to said slot count number to detect a match.

11. In a cable television system in which a plurality of subscriber terminals are coupled to a headend by a network and in which a plurality of data frames, each comprising a plurality of N-level data symbols occurring at a predetermined symbol rate and a periodic data frame synchronization signal, are transmitted downstream from said headend to said subscriber terminals, an upstream data transmission method comprising the steps of:

generating a symbol clock having a frequency corresponding to said predetermined rate;

dividing each of said data frames into a plurality of time slots synchronously with said symbol clock, each of said time slots having a duration corresponding to a downloadable slot width value;

forming a superframe synchronously with said symbol clock composed of one or more sequential data frames corresponding to a downloadable superframe value;

assigning a time slot to a subscriber terminal for upstream data communication expressed as a time slot identifier having a frame number within said superframe and a slot number therein; and

timing upstream data communication from a subscriber terminal to said headend to occur during said assigned time slot.

12. The upstream data transmission method set forth in claim 11 wherein said forming step includes the steps of:

providing a periodic superframe synchronizing signal synchronously with said data frame synchronizing signal and having a period equal to an integer multiple of the period of said data frame synchronizing signal; and

counting sequential data frames between said superframe synchronizing signals to establish frame count numbers in each superframe.

13. The upstream data transmission method set forth in claim 12 wherein said dividing step includes the step of sequentially numbering said time slots within each data frame to establish slot count numbers.

14. The upstream data transmission method set forth in claim 13 wherein said timing step includes the steps of:

first comparing the frame number of said assigned time slot of a subscriber terminal to said frame count numbers until a match is detected;

second comparing the slot number of said assigned time slot of a subscriber terminal to said slot count numbers within said matching frame of downstream data until a match is detected; and

initiating upsteam data transmission during the matching slot.

15. In a cable television system in which a plurality of subscriber terminals are coupled to a headend by a network and in which a plurality of data frames, each comprising a plurality of N-level data symbols occurring at a predetermined rate and a periodic data frame synchronization signal, are transmitted downstream from said headend to said subscriber terminals, an upstream data transmission system comprising:

means for generating a symbol clock signal having a frequency corresponding to said predetermined rate;

means responsive to said symbol clock signal for dividing each data frame into a plurality of time slots having a duration corresponding to a downloadable width value;

means responsive to said symbol clock signal for forming a superframe composed of one or more sequential data frames corresponding to a downloadable superframe value;

means for assigning a time slot to a subscriber terminal for upstream data communication expressed as a time slot identifier having a frame number within said superframe and a slot number therein; and

means for timing upstream data communications from a subscriber terminal to said headend to occur during the assigned time slot for the transmitting subscriber terminal.

16. The upstream data transmission system set forth in claim 15 wherein said means for forming includes:

means for providing a periodic superframe synchronizing signal synchronously with said data frame synchronizing signal and having a period equal to an integer multiple of the period of said data frame synchronizing signal; and

means for counting sequential data frames between said superframe synchronizing signals to establish frame count numbers in each superframe.

17. The upsteam data transmission system set forth in claim 16 wherein said means for dividing includes means for sequentially numbering said time slots within each data frame to establish slot count numbers.

18. The upstream data transmission system set forth in claim 17 wherein said frame count number corresponds to the most significant bits of said time slot identifier and said slot count number corresponds to the least significant bits of said time slot identifier.

19. The upstream data transmission system set forth in claim 18 wherein said means for timing includes:

first means for comparing the frame number of said assigned time slot of a subscriber terminal to each of said frame count numbers until a match is detected;

second means responsive to the first comparing means for comparing the slot number of said assigned time slot of a subscriber terminal to each of said slot count numbers until a match is detected; and

means responsive to said second comparing means for initiating upstream data transmission during the matching time slot.

20. In a cable television system in which a plurality of subscriber terminals are coupled to a headend by a network and in which data is transferred to said subscriber terminals using N-level symbols at a symbol clock rate within a plurality of data frames and periodic data frame synchronization signals are transmitted downstream from said headend to said subscriber terminals, an upstream data transmission method comprising the steps of:

dividing each data frame into a plurality of time slots each synchronized to said symbol clock and each having a duration corresponding to a programmable width value;

generating an upstream carrier synchronized to said symbol clock;

forming a superframe synchronized to said symbol clock composed of one or more sequential data frames corresponding to a programmable superframe value;

assigning a time slot to a subscriber terminal for upstream data communication expressed as a time slot identifier having a frame number within said superframe and a slot number therein; and

timing upstream data communication from a subscriber terminal to said headend to occur during the assigned time slot for the transmitting subscriber terminal.