Random access in a mobile telecommunications system

• US 6,606,313 B1
• Filed: 10/05/1998
• Issued: 08/12/2003
• Est. Priority Date: 10/05/1998
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Dahlman, Erik, Beming, Per, Gustafsson, Maria
• Primary Examiner(s): Ton, Dang
• Assistant Examiner(s): Phan, Tri H.
• Application Number:
  US09/166,679
• Time in Patent Office: 1,772 Days
• Field of Search: 370/329, 370/335, 370/336, 370/337, 370/346, 370/347, 370/441, 370/328, 370/321, 370/327, 370/342, 370/503, 370/322, 370/515, 370/528, 370/324, 455/522, 714/748, 714/749, 714/750, 375/200, 375/130, 375/142-145, 375/150-152, 375/211, 375/140
• US Class Current: 370/347
• CPC Class Codes: H04L 1/1867 Arrangements specially adapted for the transmitter end
• CPC Class Codes: H04W 36/16 Performing reselection for specific purposes
• CPC Class Codes: H04W 74/006 in the downlink, i.e. towards the terminal
• CPC Class Codes: H04W 74/0833 Random access procedures, e.g. with 4-step access

Abstract

A method for processing multiple random access requests is disclosed in which a base station transmits an acquisition indicator signal, which indicates that the base station has detected the presence of a random access transmission. The acquisition indicator can be generated based on the amount of energy received on the random access channel (e.g., as opposed to the correct/incorrect decoding of a random access message). Consequently, the delay between the beginning of the random access transmission and the beginning of the acquisition indicator transmission is significantly shorter than the delay to the beginning of an acknowledgment transmission based on the reception of a correctly decoded random access message. If a mobile station does not receive a positive acquisition indicator, it should interrupt the present transmission and start to re-transmit the random access burst in the next time slot, while modifying the transmission power level accordingly between the successive re-transmissions.

Claims

1. A method for improving the performance of a random access mobile communications system, comprising the steps of:

a mobile station transmitting a random access request, said random access request comprising a preamble, said preamble being modulated with a signature pattern randomly selected from a set of patterns; and

a base station detecting a presence of said random access request, generating an indicator signal indicating said presence of said random access request, and transmitting said indicator signal to the mobile station prior to decoding of the random access request, wherein said indicator signal is associated with the selected signature.

2. The method of claim 1, wherein said transmitting step comprises transmitting said indicator signal at a predetermined instant of time.

3. The method of claim 1, wherein said indicator signal comprises an ON portion of an ON-OFF signal.

4. The method of claim 1, further comprising the steps of:

if said mobile station receives said indicator signal, said mobile station continuing said transmitting of said random access request; and

if said mobile station does not receive said indicator signal by a predetermined instant of time, said mobile station discontinuing said transmitting of said random access request.

5. The method of claim 1, wherein said step of detecting a presence of said random access request comprises detecting a power level equal to or exceeding a predetermined threshold level.

6. The method of claim 1, wherein said random access mobile communications system comprises a spread spectrum mobile communications system.

7. The method of claim 1, wherein said random access mobile communications system comprises a wideband CDMA system.

8. The method of claim 1, wherein said indicator signal comprises an acquisition indicator signal.

9. The method of claim 1, wherein said indicator signal is transmitted on a physical channel.

10. The method of claim 4, wherein said step of discontinuing said transmitting of said random access request further comprises the step of re-transmitting said random access request in a subsequent time slot.

11. The method of claim 10, wherein the step of re-transmitting said random access request includes re-transmitting the preamble.

12. The method of claim 11, wherein the step of re-transmitting comprises re-transmitting said preamble with a different spreading code.

13. The method of claim 11, wherein the step of re-transmitting comprises re-transmitting said preamble with a different signature.

14. The method of claim 12, further comprising the step of said mobile station reducing a negative power offset for said random access request prior to said re-transmitting step.

15. The method of claim 9, wherein said physical channel is a downlink channel that is orthogonal to other downlink physical channels.

16. The method of claim 9, wherein said physical channel is a downlink physical channel that is non-orthogonal to other downlink physical channels.

17. The method of claim 1, wherein said indicator signal is associated with a unique signature.

18. The method of claim 1, wherein said indicator signal is associated with a set of unique signatures.

19. The method of claim 17, wherein said indicator signal comprises an orthogonal code word associated with said unique signature.

20. The method of claim 17 or 18, wherein said indicator signal comprises an ON part of an ON-OFF signal.

39. The method of claim 1, wherein the step of transmitting is performed prior to completion of the decoding of said random access request.

21. A random access communications system, comprising:

a mobile station, said mobile station including a transmitter for transmitting a random access request, said random access request comprising a preamble, said preamble being modulated with a signature pattern randomly selected from a set of patterns; and

a base station coupled to said mobile station via an air interface, said base station configured to detect a presence of said random access request, generate an indicator signal indicating said presence of said random access request, and transmit said indicator signal to the mobile station prior to decoding of the random access request, wherein said indicator signal is associated with the selected signature.

22. The system of claim 21, wherein said means for transmitting comprises means for transmitting said indicator signal at a predetermined instant of time.

23. The system of claim 21, further comprising:

said mobile station including means for receiving said indicator signal, and determining if said mobile station has received said indicator signal, and if so, said mobile station continuing said transmitting of said random access request; and

if said mobile station does not receive said indicator signal by a predetermined instant of time, said mobile station discontinuing said transmitting of said random access request.

24. The system of claim 21, wherein said means for detecting a presence of said random access request comprises means for detecting a power level equal to or exceeding a predetermined threshold level.

25. The system of claim 21, wherein said random access communications system comprises a spread spectrum mobile communications system.

26. The system of claim 21, wherein said random access communication system comprises a wideband CDMA system.

27. The system of claim 21, wherein said indicator signal comprises an acquisition indicator signal.

28. The system of claim 21, wherein said indicator signal is transmitted on a physical channel.

29. The system of claim 23, further comprising means for re-transmitting said random access request in a subsequent time slot.

30. The system of claim 29, wherein said means for re-transmitting said random access request includes means for re-transmitting the preamble.

31. The system of claim 30, wherein said means for re-transmitting comprises means for re-transmitting said preamble with a different spreading code.

32. The system of claim 30, wherein said means for re-transmitting comprises means for re-transmitting said preamble with a different signature.

33. The system of claim 29, further comprising means for reducing a negative power offset for said random access request prior to said re-transmitting.

34. The system of claim 28, wherein said physical channel is a downlink channel that is orthogonal to other downlink physical channels.

35. The system of claim 28, wherein said physical channel is a downlink physical channel that is non-orthogonal to other downlink physical channels.

36. The system of claim 21, wherein said indicator signal is associated with a unique signature.

37. The system of claim 21, wherein said indicator signal is associated with a set of unique signatures.

38. The system of claim 36 or 37, wherein said indicator signal comprises an ON part of an ON-OFF signal.

40. The system of claim 21, wherein base station transmits said indicator signal prior to the completion of the decoding of said random access request.

41. A method for improving the performance of a random access mobile communications system, said method comprising the steps of:

detecting a presence of a random access request from a mobile station at a base station, wherein said step of detecting a presence of said random access request comprises detecting a power level equal to or exceeding a predetermined threshold level;

generating an indicator signal indicating said presence of said random access request; and

transmitting said indicator signal to the mobile station prior to decoding of said random access request, wherein said indicator signal is associated with a selected signature.

42. The method of claim 41, wherein the step of transmitting is performed prior to completion of the decoding of said random access request.

43. A method for improving the performance of a random access mobile communication system, said method comprising the steps of:

transmitting, by a mobile station, said random access request comprising a preamble, said preamble being modulated with a signature pattern randomly selected from a set of patterns;

detecting, by a base station, a presence of the random access burst prior to decoding of the random access burst;

generating an acquisition indicator signal indicating the presence of the random access burst, wherein said indicator signal is associated with the selected signature; and

transmitting, by the base station, the acquisition indicator signal to the mobile station.

44. The method of claim 43, wherein the step of transmitting the acquisition indicator signal associated with the at least one unique signature indicates the reception of the random access burst having the at least one unique signature from the mobile station.

45. The method of claim 43, wherein the at least one unique signature comprises a set of unique signatures.

46. The method of claim 43, wherein the acquisition indicator signal is associated with a plurality of unique signatures.

47. The method of claim 43, wherein the acquisition indicator signal comprises an orthogonal code word.

48. The method of claim 43, wherein the at least one unique signature is located in a control part of the random access burst.

49. The method of claim 43, wherein the at least one unique signature is located in a preamble of the random access burst.

50. A base station within a mobile communication system comprising:

an antenna for receiving a random access burst, said random access request comprising a preamble, said preamble being modulated with a signature pattern randomly selected from a set of patterns, and

wherein said base station is configured to generate an acquisition indicator indicating the receipt of the random access burst, wherein said indicator signal is associated with the selected signature, and transmit the acquisition indicator signal to the mobile station prior to decoding of the random access burst.

51. The base station of claim 50, wherein the acquisition indicator signal transmitted by the base station indicates to the mobile station reception of the random access burst having the at least one unique signature.

52. The base station of claim 50, wherein the at least one unique signature comprises a set of unique signatures.

53. The base station of claim 50, wherein the acquisition indicator signal is associated with a plurality of unique signatures.

54. The base station of claim 50, wherein the at least one unique signature is located in a control part of the random access burst.

55. The base station of claim 50, wherein the at least one unique signature is located in a preamble of the random access burst.

56. The base station of claim 50, further comprising:

a matched filter for detecting the presence of the random access burst and despreading a preamble part of the random access burst;

a plurality of accumulators for accumulating the energy received over the duration of the preamble part of the random access burst, each one of the plurality of accumulators being tuned to a different unique signature;

a plurality of detectors for detecting the energy in the plurality of accumulators and selecting the accumulators that have the energy exceeding a determined threshold; and

a plurality of acquisition indicator generation circuits coupled to the plurality of detectors for receiving the input signal from an associated one of the detectors and outputting the acquisition indicator signal associated with one of the accumulators having its energy exceeding the determined threshold and tuned to the unique signature.