Method and system for synchronising stations within communications networks and stations for use therein

• US 8,488,518 B2
• Filed: 06/30/2004
• Issued: 07/16/2013
• Est. Priority Date: 08/04/2003
• Status: Expired due to Fees

• Current Assignee: Barrett Communications Pty., Ltd. (Motorola Solutions, Inc.)
• Original Assignee: Barrett Communication Pty Limited
• Inventors: Bradshaw, Phillip
• Primary Examiner(s): Phan, Tri H
• Application Number:
  US10/567,110
• Publication Number:
  US 20110122980A1
• Time in Patent Office: 3,303 Days
• Field of Search: 370310-350, 370203-211, 370498-529, 375132-149
• US Class Current: 370/324
• CPC Class Codes: H04B 1/713 using frequency hopping
• CPC Class Codes: H04B 1/7156 Arrangements for sequence synchronisation
• CPC Class Codes: H04B 2001/7154 with means for preventing interference
• CPC Class Codes: H04W 56/0035 detecting errors in frequency or phase

Abstract

A system for synchronizing stations in a communications network comprising: at least one airborne or space-based vehicle; and at least two stations, each station having receiver means in data communication with the at least one airborne or space-based vehicle and control means in data communication with the receiver means and in control communication with a communication means. When each receiver means receives a synchronization signal from the at least one airborne or space-based vehicle each receiver means forwards the synchronization signal to its respective control means. The respective control means processes the synchronization signal to determine the operational frequency required by its respective communication means to maintain or establish communication with the other station. The respective control means also operates to control its respective communication means to change to the determined operational frequency.

Claims

1. A system for synchronising stations in a wireless communications network comprising:

at least one airborne or space-based vehicle; and

at least two stations, each station having receiver means in data communication with the at least one airborne or space-based vehicle and control means in data communication with the receiver means and in control communication with a communication means,

wherein, when each receiver means receives a synchronisation signal from the at least one airborne or space-based vehicle;

each receiver means forwards the synchronisation signal to its respective control means;

each control means processes the synchronisation signal to determine an operational frequency required by its respective communication means to maintain or establish communication with the other station; and

each control means controls its respective communication means to change to the determined operational frequency,

the system being characterized in that each station also has a real-time clock for emitting a time pulse, the clock being coupled to the control means of the station, the synchronisation signal comprising a time and position sentence, the control means parses the sentence to determine a time of a timing pulse that immediately precedes the sentence, and in that a rising edge of the timing pulse is used to synchronise the clock.

2. The system for synchronising stations in a wireless communications network according to claim 1, the system being further characterized in that processing of the synchronisation signal includes iterating a pseudo-random algorithm on receipt of the synchronisation signal and determining the operational frequency based on the iterated value of the pseudo-random algorithm.

3. The system for synchronising stations in a wireless communications network according to claim 2, the system being further characterized in that a frequency range of each communication means is determined from at least a part of an initial code, the initial code being an initial value of the pseudo-random algorithm.

4. The system for synchronising stations in a wireless communications network according to claim 3, the system being further characterized in that an operable frequency spectrum of each communication means is divided into a set of hopping bands, a start frequency of each hopping band being stored in a reference table.

5. The system for synchronising stations in a wireless communications network according to claim 4, the system being further characterized in that processing of the synchronisation signal includes iterating a pseudo-random algorithm on receipt of the synchronisation signal and determining the operational frequency based on the iterated value of the pseudo-random algorithm, wherein a frequency range of each communication means is determined from at least part of an initial code, the initial code being the initial value of the pseudo-random algorithm, and wherein each hopping band has a range equal to the determined frequency range.

6. The system for synchronising stations in a wireless communications network according to claim 4, the system being further characterized in that the operational frequency required by the communication means to maintain or establish communication with the other station is determined according to the formula:

F=Fb+(C×

Fr)/Y

wherein;

F=the operational frequency

Fb=the start frequency of the hopping band currently being used for transmission, as determined by values stored in the reference table;

C=a present value of the pseudo-random algorithm, or a part thereof;

Fr=a maximum allowable range of frequency hop in Hz; and

Y=2^{(the number of bits used by C)}.

7. The system for synchronising stations in a wireless communications network according to claim 6, the system being further characterized in that Y=256.

8. The system for synchronising stations in a wireless communications network according to claim 4, the system being further characterized in that the control means operates to avoid determining an operational frequency falling within at least one predetermined hopping band.

9. The system for synchronising stations in a wireless communications network according to claim 4, each hopping band has a range equal to the determined frequency range.

10. The system for synchronising stations in a wireless communications network according to claim 2, the system being further characterized in that the iterated value of the pseudo-random algorithm is cross-referenced with a frequency table to determine the operational frequency required to maintain or establish communication with the other station.

11. The system for synchronising stations in a wireless communications network according to claim 2, the system being further characterized in that the pseudo-random algorithm is iterated on receipt of each time pulse.

12. The system for synchronising stations in a wireless communications network according to claim 11, the system being further characterized in that the real-time clock emits a predetermined number of time pulses (R) a second.

13. The system for synchronising stations in a wireless communications network according to claim 12, the system being further characterized in that R is in the range 5 [R [10.

14. The system for synchronising stations in a wireless communications network according to claim 13, the system being further characterized in that R=5.

15. The system for synchronising stations in a wireless communications network according to claim 12, the system being further characterized in that when a new station joins the communications network, synchronisation of the new station with existing stations is attained by setting the value of the pseudo-random algorithm to an initial code and iterating the pseudo-random algorithm according to the formula:

I=S×

R

wherein;

I=number of iterations of the pseudo-random algorithm to be performed;

S=number of seconds that have passed since a predetermined amount of time elapsed; and

R=the predetermined number of time pulses a second.

16. The system for synchronising stations in a wireless communications network according to claim 12, the system being further characterized in that the pseudo-random algorithm performs at least 86400×

R iterations before repeating.

17. The system for synchronising stations in a wireless communications network according to claim 2, the system being further characterized in that after a predetermined amount of time the pseudo-random algorithm resets its value to equal an initial code, the initial code being an initial value of the pseudo-random algorithm.

18. The system for synchronising stations in a wireless communications network according to claim 17, the system being further characterized in that the predetermined amount of time is 24 hours.

19. The system for synchronising stations in a wireless communications network according to claim 2, the system being further characterized in that the pseudo-random algorithm is at least a 31 bit algorithm.

20. The system for synchronising stations in a wireless communications network according to claim 2, the system being further characterized in that when the pseudo-random algorithm has a value equal to an initial code, the initial code being an initial value of the pseudo-random algorithm, the control means operates to iterate the pseudo-random algorithm a predetermined number of times.

21. The system for synchronising stations in a wireless communications network according to claim 2, the system being further characterized in that the pseudo-random algorithm is based on the Digital Encryption Standard algorithm.

22. The system for synchronising stations in a wireless communications network according to claim 2, the system being further characterized in that each station includes a data input means, data input using the data input means being operable to seed the pseudo-random algorithm with an initial value.

23. The system for synchronising stations in a wireless communications network according to claim 1, the system being further characterized in that time information is cross-referenced with a frequency table to determine the operational frequency required to maintain or establish communication with the other station.

24. The system for synchronising stations in a wireless communications network according to claim 1, the system being further characterized in that the communication means is a transceiver.

25. The system for synchronising stations in a wireless communications network according to claim 1, the system being further characterized in that the communication means of at least one station is a transmitter or transceiver and the communication means of at least one station is a receiver.

26. The system for synchronising stations in a wireless communications network according to claim 1, the system being further characterized in that the at least one airborne or space-based vehicle comprises the global positioning system network of satellites.

27. The system for synchronising stations in a wireless communications network according to claim 1, the system being further characterized in that the at least one airborne or space-based vehicle comprises a geosynchronous satellite.

28. The system for synchronising stations in a wireless communications network according to claim 1, the system being further characterized in that each station also has a unique identification code and wherein, when one station, a calling station, communicates with another station, a receiving station:

the calling station transmits a communication message including the unique identification codes of the calling station and receiving station on each frequency in a predetermined set of frequencies, commencing with the operational frequency;

the receiving station records a value of at least one attribute in respect of a transmission signal encapsulating the communication message for each frequency in the predetermined set of frequencies;

the receiving station sends a reply communication message including the unique identification codes of the calling station and receiving station on the frequency having the best recorded value or best combination of recorded values; and

the calling station scans each frequency in the predetermined set of frequencies until the frequency on which the reply communication message has been sent is received,

communications between calling station and receiving station thereafter continuing on that frequency.

29. The system for synchronising stations in a wireless communications network according to claim 28, the system being further characterized in that the calling station transmits a communication message including the unique identification codes of the calling station and receiving station on each frequency in a predetermined set of frequencies twice and where the receiving station records the best value of the at least one attribute in respect of the two transmission signals encapsulating the communication message for each frequency in the predetermined set of frequencies.

30. The system for synchronising stations in a wireless communications network according to claim 28, the system being further characterized in that the at least one attribute includes at least one of the following:

signal strength;

bit error rate.

31. A station for use in a system for synchronising stations in a wireless communications, comprising:

at least one airborne or space-based vehicle; and

at least two of the stations, each station having receiver means in data communication with the at least one airborne or space-based vehicle, and control means in data communication with the receiver means and in control communication with a communication means;

wherein, when each receiver means receives a synchronisation signal from the at least one airborne or space-based vehicle;

each receiver means forwards the synchronisation signal to its respective control means;

each control means processes the synchronisation signal to determine an operational frequency required by its respective communication means to maintain or establish communications with another station; and

each control means controls its respective communication means to change to the determined operational frequency,

the system being characterised in that each station also has a real-time clock for emitting a time pulse, the clock being coupled to the control means of the station, the synchronisation signal comprising a time and position sentence, the control means parses the sentence to determine a time of a timing pulse that immediately precedes the sentence, and in that a rising edge of the timing pulse is used to synchronise the clock.

32. A method of synchronising stations in a wireless communications network, the method comprising:

receiving, at each station of the communications network, a synchronisation signal from at least one airborne or space-based vehicle;

processing the synchronisation signal to determine an operational frequency required by a communication means of each station to maintain or establish communication with another station; and

changing a frequency of the communication means to communicate on the operational frequency,

the method being characterised in that a control means of each station parses a time and position sentence of the synchronisation signal to determine a time of a timing pulse that immediately precedes the sentence, and in that a rising edge of the timing pulse is used to synchronise a real-time clock of each station, the clock being for emitting a time pulse, and the clock being coupled to the control means of the station.

33. The method of synchronising stations in a wireless communications network according to claim 32, the method being further characterized in that it includes the step of iterating a pseudo-random algorithm on receipt of the synchronisation signal, and in that the step of processing the synchronisation signal determines the operational frequency based on the iterated value of the pseudo-random algorithm.

34. The method of synchronising stations in a wireless communications network according to claim 33, the method being further characterized in that it includes the step of determining a frequency range for the communication means from at least a part of an initial code, the initial code being an initial value of the pseudo-random algorithm.

35. The method of synchronising stations in a wireless communications network according to claim 34, the method being further characterized in that it includes the steps of dividing an operable frequency spectrum of each communication means into a set of hopping bands and storing a start frequency of each hopping band in a reference table.

36. The method of synchronising stations in a wireless communications network according to claim 35, the method being further characterized in that it includes the steps of iterating a pseudo-random algorithm on receipt of the synchronisation signal wherein the step of processing the synchronisation signal determines the operational frequency based on the iterated value of the pseudo-random algorithm;

and determining a frequency range for the communication means from at least a part of an initial code, the initial code being the initial value of the pseudo-random algorithm, wherein the step of dividing the operable frequency spectrum into a set of hopping bands involves dividing the operable frequency spectrum into a set of hopping bands each having a range equal to the determined frequency range.

37. The method of synchronising stations in a wireless communications network according to claim 35, the method being further characterized in that the step of determining the operational frequency is determined according to the formula:

F=Fb+(C×

Fr)/Y

wherein;

F=the operational frequency

Fb=the start frequency of the hopping band currently being used for transmission, as determined by values stored in the reference table;

C=a present value of the pseudo-random algorithm, or a part thereof;

Fr=a maximum allowable range of frequency hop in Hz; and

Y=2^{(the number of bits used by C)}.

38. The method of synchronising stations in a wireless communications network according to claim 35, the method being further characterized in that it includes the step of avoiding determining an operational frequency falling within at least one predetermined hopping band.

39. The method of synchronising stations in a wireless communications network according to claim 35, the method being further characterised in that the step of dividing the operable frequency spectrum into a set of hopping bands involves dividing the operable frequency spectrum into a set of hopping bands having a range equal to the determined frequency range.

40. The method of synchronising stations in a wireless communications network according to claim 33, the method being further characterized in that the step of determining the operational frequency includes the sub-step of cross-referencing the iterated value of the pseudo-random algorithm with a frequency table.

41. The method of synchronising stations in a wireless communications network according to claim 33, the method being further characterized in that it includes the step of iterating the pseudo-random algorithm on receipt of the time pulse emitted by the real time clock.

42. The method of synchronising stations in a wireless communications network according to claim 41, the method being further characterized in that it includes the step of emitting a predetermined number of time pulses (R) a second.

43. The method of synchronising stations in a wireless communications network according to claim 42, the method being further characterized in that R is in the range 5≦

R≦

10.

44. The method of synchronising stations in a wireless communications network according to claim 43, the method being further characterized in that R=5.

45. The method of synchronising stations in a wireless communications network according to claim 33, the method being further characterized in that it includes the step of synchronising a new station with existing stations in the communications network by setting the value of the pseudo-random algorithm to an initial code and iterating the pseudo-random algorithm according to the formula:

I=S×

R

wherein;

I=number of iterations of the pseudo-random algorithm to be performed;

S=number of seconds that have passed since a predetermined amount of time elapsed; and

R=the predetermined number of time pulses a second.

46. The method of synchronising stations in a wireless communications network according to claim 33, the method being further characterized in that it includes the step of resetting the value of the pseudo-random algorithm to equal an initial code, the initial code being the initial value of the pseudo-random algorithm, after a predetermined amount of time.

47. The method of synchronising stations in a wireless communications network according to claim 46, the method being further characterized in that the predetermined amount of time is 24 hours.

48. The method of synchronising stations in a wireless communications network according to claim 33, the method being further characterized in that it includes the step of iterating the pseudo-random algorithm a predetermined number of times when the pseudo-random algorithm has a value equal to an initial code, the initial code being an initial value of the pseudo-random algorithm.

49. The method of synchronising stations in a wireless communications network according to claim 33, the method being further characterized in that it includes the step of seeding the pseudo-random algorithm with an initial value using data input means.

50. The method of synchronising stations in a wireless communications network according to claim 32, the method being further characterized in that the step of determining the operational frequency includes the sub-step of cross-referencing time information included in the time and position sentence with a frequency table.

51. The method of synchronising stations in a wireless communications network according to claim 32, the method being further characterized in that it includes the steps of:

transmitting a communication message including a unique identification code of a calling station and of a receiving station on each frequency in a predetermined set of frequency frequencies, commencing with the operational frequency;

scanning each frequency in the predetermined set of frequencies for a reply communication message including the unique identification codes of the calling station and receiving station;

receiving the reply communication message on a frequency having the best recorded value or best combination of recorded values, as determined by a value recorded by the receiving station of at least one attribute in respect of a transmission signal encapsulating the communication message for each frequency in the predetermined set of frequencies; and

communicating with the receiving station on the frequency having the best recorded value or best combination of recorded values.

52. The method of synchronising stations in a wireless communications network according to claim 51, the method being further characterized in that the step of transmitting a communication message including a unique identification code of a calling station and of a receiving station on each frequency in a predetermined set of frequencies, commencing with the operational frequency, is repeated twice.

53. The method of synchronising stations in a wireless communications network according to claim 51, the method being further characterized in that the at least one attribute includes at least one of the following:

signal strength;

bit error rate.

54. The method of synchronising stations in a wireless communications network according to claim 32, the method being further characterized in that it includes the steps of:

receiving a communication message including a unique identification code of a calling station and of a receiving station on each frequency in a predetermined set of frequencies, commencing with the operational frequency;

recording a value of at least one attribute in respect of a transmission signal encapsulating the communication message for each frequency in the predetermined set of frequencies;

sending a reply communication message including the unique identification codes of the calling station and receiving station on the frequency having the best recorded value or best combination of recorded values; and

communicating with the calling station on the frequency having the best recorded value or best combination of recorded values.

55. The method of synchronising stations in a wireless communications network according to claim 54, the method being further characterized in that the step of receiving a communication message including a unique identification code of a calling station and of a receiving station on each frequency in a predetermined set of frequencies, commencing with the operational frequency, is repeated twice, and in that the step of recording a value of at least one attribute in respect of the transmission signal encapsulating the communication message for each frequency in the predetermined set of frequencies operates to record the best of the two values.

56. The method of synchronising stations in a wireless communications network according to claim 55, the method being further characterized in that the at least one attribute includes at least one of the following:

signal strength;

bit error rate.