Method and apparatus for receiving an amplitude modulated radiosignal

• US 20040041692A1
• Filed: 06/20/2003
• Published: 03/04/2004
• Est. Priority Date: 12/20/2000
• Status: Active Grant

• Current Assignee: Land Rover (TATA Motors Limited), Hi-Key Ltd. (Valeo SE)
• Original Assignee: Land Rover (TATA Motors Limited), Hi-Key Ltd. (Valeo SE)
• Inventors: Lyons, Patrick J., Greenwood, Jeremy J.
• Granted Patent: US 7,099,638 B2
• Time in Patent Office: Days
• US Class Current: 340/5.64
• CPC Class Codes: B60R 25/24 using electronic identifiers containing a code not memorised by the user
• CPC Class Codes: G07C 2009/00238 the transmittted data signal containing a code which is changed
• CPC Class Codes: G07C 2009/00555 comprising means to detect or avoid relay attacks
• CPC Class Codes: G07C 2009/00793 by Hertzian waves
• CPC Class Codes: G07C 2209/61 Signal comprising different frequencies, e.g. frequency hopping
• CPC Class Codes: G07C 9/00182 operated with unidirectional data transmission between data carrier and locks
• CPC Class Codes: H03J 1/0091 provided with means for scanning over a band of frequencies H03J1/0058 takes precedence

Abstract

Receiving apparatus (1) for receiving an amplitude modulated signal which may be transmitted on a plurality of frequency channels within a predetermined frequency bandwidth comprises a tuner (3) for sequentially scanning through the channels under the control of a microprocessor (6) which determines the presence of a signal on a channel to which the tuner (3) is tuned. A first validation circuit (10) determines if the received signal is a valid type signal, and if so the microprocessor (6) counts the channels from the channel on which the signal is first detected to the channel on which the signal can no longer be detected is reached. The microprocessor (6) determines the middle one of the channels in which the signal is detected, and the microprocessor (6) locks the tuner (3) onto the frequency of the middle channel, and simultaneously operates a gate circuit (11) for outputting at least one complete signal to security apparatus of a motor vehicle for switching the state of the security apparatus from one of an armed and a disarmed state to the other of the armed and disarmed state. A noise suppressing circuit (9) is responsive to a noise analysing circuit (8) under the control of the microprocessor (6) for suppressing noise in the received signal.

Claims

1. A method for receiving an AM radio signal which may be transmitted in any one of a plurality of frequency channels within a predetermined frequency bandwidth, the method comprising operating a tuning means (3) of a radio receiver to scan the channels of the predetermined frequency bandwidth for detecting a signal, characterised in that on detecting a signal in a frequency channel the tuning means (3) is operated to scan a frequency bandwidth adjacent the channel in which the signal is detected for determining the number of channels in which the signal can be detected, and operating the tuning means (3) at the frequency of a middle one of the channels in which the signal can be detected.

2. A method as claimed in claim 1 characterised in that the tuning means (3) is locked onto the frequency of the middle one of the channels in which the signal can be detected for a period sufficient for allowing at least one complete signal to be received.

3. A method as claimed in claim 2 characterised in that the tuning means (3) is locked onto the frequency of the middle one of the channels in which the signal can be detected for a predetermined time period.

4. A method as claimed in any preceding claim characterised in that the frequency bandwidths of the respective frequency channels are similar.

5. A method as claimed in any preceding claim characterised in that each time a signal is detected in a frequency channel in a scan the received signal is analysed for determining if the signal is of a valid type.

6. A method as claimed in claim 5 characterised in that each received signal is analysed for determining if the signal is of a valid type format.

7. A method as claimed in any preceding claim characterised in that the tuning means (3) is operated for scanning the frequency channels within the predetermined frequency bandwidth sequentially from one end of the predetermined bandwidth to the other.

8. A method as claimed in claim 6 characterised in that the tuning means (3) is operated for scanning the frequency channels within the predetermined frequency bandwidth from the channel of lowest frequency to the channel of highest frequency.

9. A method as claimed in claim 7 or 8 characterised in that the tuning means (3) is operated for scanning the predetermined frequency bandwidth by sequentially altering the scanned frequency in frequency steps.

10. A method as claimed in claim 9 characterised in that the frequency steps are of similar value.

11. A method as claimed in claim 9 or 10 characterised in that the frequency bandwidth of each frequency step is similar to the frequency bandwidth of the respective frequency channels.

12. A method as claimed in any preceding claim characterised in that on detecting a signal in one of the frequency channels, the tuning means (3) is operated to sequentially scan the channels from the channel in which the signal is first detected until a channel in which the signal can no longer be detected has been reached for determining the middle one of the channels in which the signal can be detected.

13. A method as claimed in claim 12 characterised in that a count is recorded of the number of frequency channels through which the tuning means (3) is stepped from the channel in which the signal is first detected to the channel in which the signal can no longer be detected has been reached for determining the middle one of the channels in which the signal can be detected.

14. A method as claimed in claim 13 characterised in that the number of frequency steps through which the tuning means (3) is stepped after the channel in which the signal is first detected is limited to a predetermined number of steps.

15. A method as claimed in claim 14 characterised in that the predetermined number of steps through which the tuning means (3) is stepped after the channel in which the signal is first detected does not exceed ten steps.

16. A method as claimed in claim 15 characterised in that the predetermined number of steps through which the tuning means (3) is stepped after the channel in which the signal is first detected does not exceed seven steps.

17. A method as claimed in claim 16 characterised in that the predetermined number of steps through which the tuning means (3) is stepped after the channel in which the signal is first detected does not exceed five steps.

18. A method as claimed in any of claims 12 to 16 characterised in that when the channel in which the signal can no longer be detected has been reached or the tuning means (3) has been stepped through the predetermined number of steps from the channel in which the signal is first detected, the frequency at which the tuning means (3) is operating is altered by approximately half the number of frequency steps through which the tuning means (3) had been operated from the channel in which the signal is first detected.

19. A method as claimed in any preceding claim characterised in that the received signal in each frequency channel is passed through a variable level noise suppressing means (9), and the received signal from the noise suppressing means (9) from each frequency channel is analysed for the presence of noise, and on noise being present in the signal, the level of suppression at which the noise suppressing means (9) is being operated for the frequency channel to which the tuning means (3) is tuned is incremented by one level up to a maximum predetermined number of suppression levels.

20. A method as claimed in claim 19 characterised in that when the noise suppressing means (9) is being operated at the maximum level for the frequency channel to which the tuning means (3) is tuned, and noise is still present in the signal from that channel, a flag means is set for that channel, and that channel is skipped on each scan of the frequency bandwidth for a predetermined number of scans.

21. A method as claimed in claim 19 or 20 characterised in that on no noise being present in the signal from the noise suppressing means (9) on the channel to which the tuning means (3) is tuned, the suppression level at which the noise suppressing means (9) is being operated is decremented by one suppression level for that channel until the suppression level at which the noise suppressing means (9) is being operated for that channel is reduced to a zero level of suppression.

22. A method as claimed in any of claims 19 to 21 characterised in that each time the level of suppression of the noise suppressing means (9) is altered for each channel, the new level of suppression to which the noise suppressing means (9) has been altered is recorded.

23. A method as claimed in any of claims 19 to 22 characterised in that each time noise is detected in a signal on a channel, that channel is assigned an integer of a first value which is summed to already assigned integers to that channel to determine a current integer value for that channel, and on the current integer value for any channel reaching one of a number of predetermined first current integer values which correspond to levels of suppression after an integer of the first value has been summed to the already assigned integers to that channel, the level of suppression at which the suppressing means (9) is being operated for that channel is altered to the corresponding level of suppression.

24. A method as claimed in any of claims 19 to 23 characterised in that each time no noise is detected in a signal on a channel, that channel is assigned an integer of a second value which is deducted from already assigned integers to that channel to determine a current integer value for that channel, and on the current integer value of any channel falling to one of a number of predetermined second current integer values which correspond to levels of suppression after an integer of the second value has been deducted from the already assigned integers to that channel, the level of suppression at which the suppressing means (9) is being operated for that channel is altered to the corresponding level of suppression.

25. A method as claimed in claim 23 or 24 characterised in that the first value of the integer is greater than the second value of the integer for introducing a sufficient level of hysteresis for avoiding excessive cycling of the suppressing means (9) between respective adjacent levels of suppression.

26. A method as claimed in any of claims 23 to 25 characterised in that the first current integer values are less than the second current integer values corresponding to each level of suppression for introducing a sufficient level of hysteresis for avoiding excessive cycling of the suppressing means (9) between the respective adjacent levels of suppression.

27. A receiving apparatus for receiving an amplitude modulated radio signal which may be transmitted in any one of a plurality of frequency channels within a predetermined frequency bandwidth, the apparatus (1) comprising a receiving means (1) for receiving the AM. radio signal, a tuning means (3) for sequentially tuning the receiving means (1) to the plurality of frequency channels, a detecting means (6) for detecting the presence of a signal, and a control means (6) for controlling the tuning means (3) for scanning the frequency bandwidth for detecting a signal in a frequency channel, characterised in that the control means (6) is responsive to the detecting means (6) detecting a signal in a frequency channel for controlling the tuning means (3) to scan a frequency bandwidth adjacent the frequency channel in which the signal is detected for determining the number of channels in which the signal can be detected, and for further operating the tuning means (3) at the frequency of a middle one of the channels in which the signal can be detected.

28. Apparatus as claimed in claim 27 characterised in that the control means (6) locks the tuning means (3) onto the frequency of the middle one of the channels in which the signal can be detected for a period sufficient for allowing at least one complete signal to be received.

29. Apparatus as claimed in claim 28 characterised in that the control means (6) locks the tuning means (3) onto the frequency of the middle one of the channels in which the signal can be detected for a predetermined time period.

30. Apparatus as claimed in any of claims 27 to 29 characterised in that a first signal analysing means (10) is provided for analysing each received signal for determining if the signal is of a valid type.

31. Apparatus as claimed in claim 30 characterised in that the first signal analysing means (10) analyses each received signal for determining if the signal is of a valid type format.

32. Apparatus as claimed in any of claims 27 to 31 characterised in that the control means (6) operates the tuning means (3) for scanning the frequency channels of the predetermined frequency bandwidth sequentially from one end of the predetermined bandwidth to the other.

33. Apparatus as claimed in claim 32 characterised in that the control means (6) operates the tuning means for scanning the frequency channels of the predetermined frequency bandwidth sequentially from the end of lowest frequency to the end of highest frequency.

34. Apparatus as claimed in any of claims 27 to 33 characterised in that the control means (6) operates the tuning means (3) for scanning the predetermined frequency bandwidth by sequentially altering the scanned frequency in respective frequency steps.

35. Apparatus as claimed in claim 34 characterised in that the control means (6) operates the tuning means (3) for scanning the predetermined frequency bandwidth by altering the scanned frequency in frequency steps of predetermined frequency.

36. Apparatus as claimed in claim 35 characterised in that the control means (6) operates the tuning means (3) for scanning the predetermined frequency bandwidth in predetermined frequency steps of similar frequency bandwidth.

37. Apparatus as claimed in any of claims 34 to 36 characterised in that each frequency step corresponds to the frequency bandwidth of each channel.

38. Apparatus as claimed in any of claims 27 to 37 characterised in that the control means (6) is responsive to the detecting means (6) detecting a signal in one of the channels for operating the tuning means (3) to sequentially scan the channels from the channel in which the signal is first detected until a channel in which the signal can no longer be detected has been reached for determining the middle one of the channels in which the signal can be detected.

39. Apparatus as claimed in any of claims 27 to 38 characterised in that the control means (6) stores a count of the number of channels through which the tuning means (3) is stepped from the first channel in which a signal is detected to the channel in which the signal can no longer be detected has been reached.

40. Apparatus as claimed in claim 39 characterised in that the control means (6) is responsive to the count of the number of channels in which the signal can be detected exceeding a predetermined number or to the channel in which the signal can no longer be detected being reached for altering the frequency at which the tuning means (3) is operating to a frequency which is at least one frequency step towards the channel in which the signal is first detected for determining the middle one of the channels in which the signal can be detected.

41. Apparatus as claimed in any of claims 27 to 40 characterised in that a variable level noise suppressing means (9) is provided for suppressing noise in the received signal under the control of the control means (6), the received signal on each frequency channel being passed through the noise suppressing means (9), and a noise analysing means (8) being provided for analysing the received signal on each channel for noise after the signal has been passed through the noise suppressing means (9), the control means being responsive to the noise analysing means (8) detecting the presence of noise in a channel to which the tuning means (3) is tuned for incrementing the level of suppression at which the noise suppressing means (9) is being operated by one level up to a maximum predetermined number of suppression levels.

42. Apparatus as claimed in claim 41 characterised in that the control means (6) records the level of suppression at which the noise suppressing means (9) is being operated for each channel in a storing means.

43. Apparatus as claimed in claim 41 or 42 characterised in that the control means (6) is responsive to the noise suppressing means (9) being operated at the maximum noise suppression level in a frequency channel to which the tuning means is tuned for setting a flag means for that channel, and the control means (6) is responsive to a flag means being set for operating the tuning means (3) for skipping any channel for which a flag means has been set for a predetermined number of scans.

44. Apparatus as claimed in any of claims 41 to 43 characterised in that the control means (6) is responsive to the noise analysing means (8) failing to detect noise in the signal from a channel to which the tuning means (3) is tuned for reducing the level of suppression to which the noise suppressing means (9) is set for that channel by one level to a minimum of zero levels of suppression.

45. Apparatus as claimed in any of claims 27 to 44 characterised in that a gate means (11) is provided which is responsive to a valid type signal being detected for gating the valid type signal from the apparatus.

46. Apparatus as claimed in any of claims 27 to 45 characterised in that the apparatus (1) is adapted for use in a security apparatus (2) of a motor vehicle, and a received valid type signal is gated to the security apparatus.

47. Apparatus as claimed in claim 46 characterised in that the apparatus (1) is adapted for controlling an immobilising means for immobilising the vehicle.

48. Apparatus as claimed in claim 46 or 47 characterised in that the apparatus (1) is adapted for controlling a means for controlling a central locking system of the motor vehicle.

49. Apparatus as claimed in any of claims 46 to 48 characterised in that the apparatus (1) is adapted for controlling an alarm circuit of the motor vehicle.

50. Security apparatus for a motor vehicle characterised in that the security apparatus comprises the receiving apparatus (1) as claimed in any of claims 27 to 49, and a second analysing means (10) for analysing each valid type signal gated from the receiving apparatus (1) for determining if the valid type signal is a valid signal for the security apparatus.

51. Security apparatus as claimed in claim 50 characterised in that an immobilising means is provided for immobilising the vehicle, the immobilising means being responsive to a valid signal being received.

52. Security apparatus as claimed in claim 50 or 51 characterised in that an alarm circuit is provided, and the alarm circuit is armed or disarmed in response to a valid signal being received.

53. Security apparatus as claimed in any of claims 50 to 52 characterised in that the security apparatus (2) is responsive to a valid signal being received for operating a central locking system of the vehicle.