Method and apparatus for synchronizing timing of components of a telecommunication system

• US 5,793,772 A
• Filed: 11/29/1995
• Issued: 08/11/1998
• Est. Priority Date: 11/29/1995
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Bahary, Rob, Burke, Timothy M., Mannette, Michael
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): PHILLIPS, MATTHEW
• Application Number:
  US08/564,606
• Time in Patent Office: 986 Days
• Field of Search: 370/17, 370/29, 370/79, 370/84, 370/85.1, 370/85.2, 370/85.7, 370/85.11, 370/95.1, 370/95.3, 370/507, 370/508, 370/509, 370/513, 370/514, 370/503, 370/516, 370/517 , 370/519, 455/33.1, 455/33.2, 455/33.3, 455/34.1, 455/34.2, 375/356, 375/357, 375/358
• US Class Current: 370/508
• CPC Class Codes: H04H 60/94 Telephonic networks for accessing the Internet H04H60/84
• CPC Class Codes: H04H 60/97 using uplink of the CATV systems
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 12/2801 Broadband local area networks

Abstract

A method for synchronizing timing of signal transmissions in a telecommunication system (100) determines a "fixed portion" (222) of the propagation delay between the central unit (102) and subscribers (206, 208) in a particular node (202). Additionally, the method determines a `variable portion` (226) of the propagation delay that accounts for the variation of spacing of different subscribers (e.g., homes (206, 208)) on a particular node (202). The preferred method offsets the control unit'"'"'s (102) receiving window (410) in accordance with the fixed portion, and directs the various subscriber units (206, 208) to offset the timing of signals (314, 322) (i.e., bursts of data) that they transmit by the variable portion (226).

Claims

1. A method for synchronizing timing of components of a telecommunication system comprising the steps of:

receiving, at a subscriber equipment, a signal indicative of a receiving window of a control unit that routes information provided by the subscriber equipment;

in response to the step of receiving, transmitting, from the subscriber equipment to the control unit, a signal burst which is sampled at the control unit during the receiving window, the receiving window being adjusted in time by a fixed portion of a propagation delay from the subscriber equipment to the control unit;

receiving, at the subscriber equipment, time alignment information indicative of a variable portion of the propagation delay from the subscriber equipment to the control unit calculated from a timing of arrival of the signal burst at the control unit; and

transmitting, from the subscriber equipment, an information burst positioned in time in accordance with the time alignment information.

2. The method of claim 1 wherein the receiving window has a first-duration, wherein the step of transmitting the signal burst comprises transmitting the signal burst having a second duration which is less than or equal to about half of the first duration.

3. The method of claim 1, the fixed portion of the propagation delay being calculated by the control unit determining a delay between a global probe signal sent to a node associated with at least one subscriber equipment and detection of a received signal at the control unit sent by the at least one subscriber equipment in response to the global probe signal.

4. The method of claim 3, wherein the received signal is detected at the control unit by comparing a strength of the received signal to a predetermined threshold.

5. In a telecommunication system transmitting over coaxial cable and using a communication scheme wherein bursts of information from a subscriber equipment must be received at a control unit during a receiving window having a first duration and wherein an unspecified propagation delay exists between the subscriber equipment and the control unit, a method for synchronizing an arrival of the bursts of information with the receiving window comprising the steps of:

receiving, at the subscriber equipment, a receive time slot signal indicative of a timing of the receiving window;

transmitting, from the subscriber equipment to the control unit, a short burst signal timed in a predetermined relationship to the receive time slot signal, the short burst signal being received at the control unit during the receiving window which is positioned in time in accordance with a common portion of the unspecified propagation delay;

receiving, at the subscriber equipment, time alignment information indicative of the unspecified propagation delay between the subscriber equipment and the control unit; and

transmitting, from the subscriber equipment, a plurality of information burst signals each being advanced in time, compared to the short burst signal, relative to the receive time slot signal.

6. The method of claim 5 wherein the step of transmitting the short burst signal comprises transmitting the short burst signal having a second duration which is less than or equal to about half of the first duration.

7. The method of claim 5, the fixed portion of the unspecified propagation delay being calculated by the control unit determining a delay between a global probe signal sent to a node associated with one or more subscriber equipment and detection of a received signal at the control unit sent by the one or more subscriber equipment in response to the global probe signal.

8. In a telecommunication system that requires bursts of information from a subscriber equipment to be received at a control unit during a timing window having a first duration and wherein an undetermined timing delay exists between the subscriber equipment and the control unit, a method for synchronizing an arrival of the bursts of information at the control unit comprising the steps of:

receiving a time slot signal from the control unit at the subscriber equipment;

transmitting, from the subscriber equipment, a subscriber equipment timing burst having a second duration less than half the first duration, the subscriber equipment timing burst being transmitted at a predetermined amount of time following reception of the time slot signal;

receiving, at the subscriber equipment, time alignment information indicative of a variable portion of the undetermined timing delay between the subscriber equipment and the control unit; and

transmitting, from the subscriber equipment, a plurality of information burst signals each being positioned in time in accordance with the time alignment information, the timing window being shifted in time by an amount correlating to a fixed portion of the undetermined timing delay between the subscriber equipment and the control unit.

9. The method of claim 8, the fixed portion of the undetermined timing delay being calculated by the control unit determining a delay between a global probe signal sent to a node associated with one or more subscriber equipment and detection of a received signal at the control unit sent by the one or more subscriber equipment in response to the global probe signal.

10. A method for synchronizing a timing of information transmission in a telecommunication system comprising the steps of:

transmitting a time slot signal from a control unit to a subscriber unit;

receiving, at the control unit, a propagation delay measurement signal during a receiving window of the control unit which is positioned in time in accordance with a common portion of a control unit to subscriber unit propagation delay;

determining at what point during the receiving window the propagation delay measurement signal arrives at the control unit;

generating time alignment information in response to the step of determining;

transmitting the time alignment information to the subscriber unit; and

receiving, at the control unit, subsequent subscriber signals positioned in time in accordance with the time alignment information.

11. The method of claim 10, wherein the step of receiving the propagation delay measurement signal comprises receiving the propagation delay measurement signal having a duration less than or equal to about one half of a duration of the receiving window.

12. The method of claim 10, the fixed portion of the control unit to subscriber unit propagation delay being calculated by the control unit determining a delay between a global probe signal sent to a node associated with one or more subscriber units and detection of a received signal at the control unit sent by the one or more subscriber units in response to the global probe signal.

13. The method of claim 12, wherein the received signal is detected at the control unit by integrating the received signal to provide an integrated value and further, identifying a predetermined increase in the integrated value.

14. In a telecommunication system wherein an undetermined propagation delay exists between a subscriber equipment and a control unit that routes signals from the subscriber equipment, and wherein the signals from the subscriber equipment must be received during a predetermined time slot at the control unit, a method for synchronizing a timing of reception of the signals from the subscriber equipment comprising the steps of:

transmitting a global probe signal to a plurality of different ones of the subscriber equipment;

receiving a received signal comprising combined response signals from the plurality of different ones of the subscriber equipment;

determining a fixed portion of the undetermined propagation delay by calculating a timing difference between the step of transmitting and the step of receiving; and

offsetting a position of the predetermined time slot by the fixed portion of the undetermined propagation delay.

15. A method for synchronizing timing of components of a telecommunication system comprising the steps of:

transmitting a global probe signal from a first unit to a plurality of subscriber units, the first unit receiving signals during a predetermined time slot;

receiving a received signal comprising combined response signals from the plurality of subscriber units;

determining a fixed portion of an undetermined propagation delay between the first unit and the plurality of subscriber units by calculating a timing difference between transmitting the global probe signal and receiving the received signal; and

offsetting a position of the predetermined time slot by the fixed portion of the undetermined propagation delay.

16. In a telecommunication system utilizing coaxial cable as a transmission medium and wherein an undetermined propagation delay exists between a subscriber equipment and a control unit that routes signals from the subscriber equipment, and wherein the signals from the subscriber equipment must be received during a predetermined time slot at the control unit, the predetermined time slot having a first duration, a method for synchronizing a timing of reception of the signals from the subscriber equipment comprising the steps of:

offsetting in time the predetermined time slot by an amount correlating to a fixed portion of the undetermined propagation delay;

transmitting a time slot signal from the control unit to the subscriber equipment;

receiving, at the control unit, a propagation delay measurement signal transmitted from the subscriber equipment, the propagation delay measurement signal having a second duration less than or equal to one half of the first duration, the propagation delay measurement signal being received following a beginning of the predetermined time slot;

determining a variable portion of the undetermined propagation delay by measuring an amount of time following the beginning of the predetermined time slot that the propagation delay measurement signal is received; and

transmitting to the subscriber equipment time alignment information indicative of the variable portion of the undetermined propagation delay.

17. The method of claim 16, the fixed portion of the undetermined propagation delay being calculated by the control unit determining a delay between a global probe signal sent to a node associated with one or more subscriber units and detection of a received signal at the control unit sent by the one or more subscriber units in response to the global probe signal.

18. In a telecommunication system that requires bursts of information from a subscriber equipment to be received at a control unit during a timing window having a first duration and wherein an undetermined timing delay exists between the subscriber equipment and the control unit, an article of manufacture comprising a program memory directing the subscriber equipment, the program memory comprising:

instructions directing the subscriber equipment to receive a time slot signal from the control unit at the subscriber equipment;

instructions directing the subscriber equipment to transmit a subscriber equipment timing burst having a second duration less than half the first duration, the subscriber equipment timing burst being transmitted at a predetermined amount of time following reception of the time slot signal;

instructions directing the subscriber equipment to receive time alignment information indicative of a variable portion of the undetermined timing delay between the subscriber equipment and the control unit; and

instructions directing the subscriber equipment to transmit a plurality of information burst signals each being positioned in time in accordance with the time alignment information, the timing window being shifted in time by an amount correlating to a fixed portion of the undetermined timing delay between the subscriber equipment and the control unit.

19. In a telecommunication system wherein an undetermined propagation delay exists between a subscriber equipment and a control unit that routes signals from the subscriber equipment, and wherein the signals from the subscriber equipment must be received during a predetermined time slot at the control unit, an article of manufacture comprising a program memory directing the control unit, the program memory comprising:

instructions directing the control unit to transmit a time slot signal to the subscriber equipment, the time slot signal indicative of a timing of the predetermined time slot;

instructions directing the control unit to receive, from the subscriber equipment, a propagation delay measurement signal during the predetermined time slot, the predetermined time slot positioned in time in accordance with a common portion of the undetermined propagation delay; and

instructions directing the control unit to determine an amount of time after a beginning of the predetermined time slot that the propagation delay measurement signal is received.

20. A method for synchronizing timing of components of a telecommunication system comprising the steps of:

providing signal information to a control unit from a subscriber unit, the signal information having a beginning position and an end position;

producing an energy profile of the signal information, the profile including a value representing the total energy of the signal information;

determining where the approximate half-sum value of the total energy is located within the energy profile;

setting a start position within the signal information based upon the location of the half-sum value;

locating at least one SYNC word within the signal information; and

transmitting an offset value to the subscriber unit that compensates for substantially all of the delay between the start position and the beginning position.

21. The method of claim 20, wherein the step of providing comprises the steps of:

receiving an analog signal;

converting the analog signal into a digital signal by sampling the analog signal, the digital signal being divided into symbols with each symbol being represented by at least one sample, a predetermined number of symbols being representative of a complete time slot of information; and

loading the complete slot of information into a main memory.

22. The method of claim 21, wherein the step of converting produces digital signals that are loaded into a buffer memory and the step of loading loads the complete slot of information from the buffer memory to the main memory.

23. The method of claim 21, wherein each symbol is represented by at least one sample and the step of producing comprises the steps of:

calculating a value of sample energy for each symbol based on at least one sample of each symbol; and

integrating a set of the sample energy calculations over the complete slot of information to produce the energy profile.

24. The method of claim 23, wherein each symbol is represented by four samples and the step of calculating calculates samples energy for each symbol based on every other sample.

25. The method of claim 24, wherein the set of energy calculations integrated in the step of integrating only includes every fourth energy calculation.

26. The method of claim 21, further comprising the step of processing the complete slot of information in a timing detection program to determine the optimum sample, the step of processing occurring between the steps of setting and locating.

27. The method of claim 26, further comprising the step of extracting data from the complete slot by processing the complete slot in a detection program based on the optimum sample to remove noise from the signal information, the step of extracting occurring between the steps of processing and locating.

28. The method of claim 20, wherein the step of determining comprises the steps of:

dividing the value of total energy by two to produce the half-sum value; and

searching the energy profile to find a location within the profile that most closely matches the half-sum value.

29. The method of claim 20, wherein the step of locating searches the signal information for three SYNC words.

30. The method of claim 29, wherein the three SYNC words are located adjacent to each other within the signal information.

31. The method of claim 30, wherein at least one of the three SYNC words is equivalent to "1F53A0."

32. A control unit for use in a synchronous telecommunication system that connects a plurality of subscriber units to the control unit, the control unit comprising:

an RF transceiver that provides an interface between the control unit and the telecommunication system, the RF transceiver providing digital signals to the control unit, a predetermined number of digital signals comprising a complete time slot;

main memory coupled to the RF transceiver to receive the complete time slot;

processing circuitry coupled to the main memory to process the time slot to at least determine any time delay between the control unit and each of the subscriber units by first estimating where signal information is located within the time slot before extracting the signal information, the processing circuitry providing to each subscriber unit an offset value that compensates for the delay determined for each respective subscriber unit; and

the RF transceiver provides digital signals by sampling the RF signals received from the subscriber units and the processing circuitry calculates total energy for a plurality of the samples, integrates the total energy calculation over the complete time slot, determines a half-sum value of the total energy and determines where the closest match of the half-sum value exists within the time slot.

33. The control unit of claim 32 further comprising program memory coupled to the processing circuitry that contains programs for the processing circuitry to execute.

34. A control unit for use in a synchronous telecommunication system that connects a plurality of subscriber units to the control unit, the control unit comprising:

an RF transceiver that provides an interface between the control unit and the telecommunication system, the RF transceiver providing digital signals to the control unit a predetermined number of digital signals comprising a complete time slot;

main memory coupled to the RF transceiver to receive the complete time slot;

processing circuitry coupled to the main memory to process the time slot to at least determine any time delay between the control unit and each of the subscriber units by first estimating where signal information is located within the time slot before extracting the signal information, the processing circuitry providing to each subscriber unit an offset value that compensates for the delay determined for each respective subscriber unit; and

the processing circuitry searches the time slot in main memory for at least one SYNC word.

35. The control unit of claim 34, wherein "1F53A0" is at least one of the SYNC words the processing circuitry searches for.

36. A method for synchronizing timing of components of a telecommunication system, the telecommunication system including downlink transmissions from a control unit to at least one subscriber unit and uplink transmissions from the at least one subscriber unit to the control unit, each transmission having a transmission length, the method comprising the steps of:

receiving a downlink trigger from the control unit;

offsetting the next uplink transmission by a delay common to the at least one subscriber unit representative of worst case propagation delay between the control unit and a selected one of the at least one subscriber unit;

turning on an RF transceiver in the selected subscriber unit to a transmission power setting;

setting the transmission length to correspond to a short burst;

formatting at least one SYNC word within a signal corresponding to the next uplink transmission; and

transmitting the signal corresponding to the next uplink transmission.

37. The method of claim 36, wherein the step of turning on an RF transceiver includes the steps of:

turning on the transceiver at a low power setting; and

increasing power of the RF transceiver from the low power setting to a transmitting power setting.

38. The method of claim 36, wherein the step of formatting includes formatting three consecutive SYNC words within the signal corresponding to the next uplink transmission.

39. The method of claim 38, wherein at least one of the SYNC words formatted in the step of formatting is formatted to a bit pattern corresponding to "1F53A0."

40. The method of claim 39, wherein the three consecutive SYNC words have a bit pattern corresponding to "1F53A0."

41. The method of claim 36 further comprising the steps of:

decreasing power of the RF transceiver from the transmitting power setting to a low power setting after the step of transmitting the signal; and

turning off the transceiver.

42. The method of claim 36, further comprising the steps of:

receiving a propagation delay offset value from the control unit at a time after the step of transmitting the signal;

modifying the offset of the next uplink to the delay offset value; and

resetting the transmission length to correspond to a normal burst.

43. A plurality of subscriber access units for use in a synchronous telecommunication system that connects a control unit to the plurality of subscriber access units based on the control unit receiving transmissions from the subscriber units within a predetermined receiving window, wherein the predetermined receiving window for each of the plurality of subscriber units is determined by offsetting a timing of the window by a delay common to the subscriber access units, at least one of the subscriber access units comprising:

an RF transceiver that provides an interface between the subscriber access unit and the telecommunication system, the RF transceiver providing digital signals to the subscriber access unit, a predetermined number of digital signals comprising a complete time slot;

a plurality of temporary registers that store values for at least a delay offset value and a transmission frame length;

specialized processing circuitry coupled to the RF transceiver that receives the digital signals from the RF transceiver and provides digital signals to the RF transceiver;

main memory coupled to the specialized processing circuitry; and

a processor coupled to the main memory and to the plurality of registers, the processor responding to receiving a downlink trigger by providing a short burst uplink signal to the specialized processing circuitry until a delay offset value is received from the control unit, at which time normal uplink bursts are provided at a time such that the uplink burst is received by the control unit aligned with the time of the receiving window.

44. The subscriber access unit of claim 43, wherein the specialized processing circuitry is an application specific integrated circuit (ASIC).

45. The subscriber access unit of claim 44, wherein the ASIC and the plurality of registers are formed from a single integrated circuit.

46. The subscriber access unit of claim 43, wherein the plurality of registers further includes registers that stores a value corresponding to a timing trigger to turn the RF transceiver on.

47. The subscriber access unit of claim 46, wherein the plurality of registers further includes registers that stores a value corresponding to a timing trigger to increases power to the RF transceiver from an initial power setting to transmit power.

48. A method for providing synchronous transmissions in a telecommunication system having a plurality of subscriber units and a control unit that communicate based on the control unit receiving information during a predetermined receiving window, the method comprising the steps of:

system initialization including the steps of;

establishing a fixed portion propagation delay; and

compensating for the fixed portion; and

individual two way communication initialization including the steps of;

receiving a complete slot of information that represents a short burst at the control unit from a selected subscriber unit, the short burst including at least one SYNC word;

estimating the location of the average power of the information within the complete slot in the control unit;

extracting data from the complete slot based on the estimate in the control unit;

searching the extracted data for the at least one SYNC word in the control unit;

providing from the control unit to the selected subscriber unit an offset delay value such that subsequent transmission from the selected subscriber unit are time aligned with the appropriate receiving window;

adjusting transmission timing of the selected subscriber unit based on the received offset delay value; and

changing, at the selected subscriber unit, from a short burst length to normal burst length.

49. The method of claim 48, wherein the short burst includes three consecutive SYNC words.

50. The system of claim 49, wherein at least one of the three consecutive SYNC words corresponds to a bit pattern of "1F53A0."