Subscriber station, network control means and method for triggering inter-frequency measurements in a mobile communication system

• US 6,567,670 B1
• Filed: 08/30/2000
• Issued: 05/20/2003
• Est. Priority Date: 08/31/1999
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Petersson, Justus
• Primary Examiner(s): Chin, Vivian
• Assistant Examiner(s): Afshar, Kamran
• Application Number:
  US09/651,012
• Time in Patent Office: 993 Days
• Field of Search: 455/436, 455/437, 455/443, 455/438, 455/444, 455/447, 455/525, 370/331, 370/332, 370/333, 370/329, 370/318, 379/59
• US Class Current: 455/522
• CPC Class Codes: H04W 36/00837 Determination of triggering parameters for hand-off
• CPC Class Codes: H04W 36/0085 Hand-off measurements
• CPC Class Codes: H04W 36/12 Reselecting a serving backbone network switching or routing node
• CPC Class Codes: H04W 52/12 Outer and inner loops
• CPC Class Codes: H04W 52/24 using SIR [Signal to Interference Ratio] or other wireless path parameters
• CPC Class Codes: H04W 52/36 with a discrete range or set of values, e.g. step size, ramping or offsets
• CPC Class Codes: H04W 52/40 during macro-diversity or soft handoff
• CPC Class Codes: H04W 52/44 in connection with interruption of transmission

Abstract

A quality measurement means (QMM) provided in a network control means (RNC) of a communication system (T1) monitors the transmission quality on the down link (DL) of a communication connection (CC) between the subscriber station (MS) and the base transceiver station (RBS). A network IF handover means generates a network IF measurement trigger signal (NIFTS) when the transmission quality drops under a predetermined quality measure (QoS-MS). The generated network (IF) measurement trigger signal (NIFTS) is sent to the subscriber station (MS) and an IF measurement means (IFMM) in the subscriber station (MS) starts the IF measurements in response to a receipt of the network IF measurement trigger signal (NIFTS). One example of evaluating the quality on the down link of the communication connection (CC) is to monitor the transmitted output power on the down link. Thus, the network control means (RNC) can independently generate the trigger signal without the need of measurements from the subscriber station (MS) and without an additional interference on the up link due to a transmission of such measurements and without an unnecessary reduction of the lifetime of the battery of the subscriber station (MS).

Claims

1. A subscriber station of a mobile communication system having at least one base transceiver station and a network control unit operable to establish at least one communication connection with said subscriber station, said subscriber station comprising:

an inter-frequency measurement unit operable to perform inter-frequency measurements;

a network inter-frequency measurement trigger signal transmitted and generated by a network handover unit of said network control unit; and

a quality measurement unit determining that the transmission quality on a down-link of said at least one communication connection drops below a predetermined quality measure, said inter-frequency measurement unit performing said inter-frequency measurements in response to reception of said network inter-frequency measurement trigger signal, said inter-frequency measurement trigger signal generated and transmitted in response to said transmission quality dropping below said predetermined quality measure.

2. The subscriber station according to claim 1, wherein said network inter-frequency measurement trigger signal indicates that a transmitted output power measured on the down-link by a power measurement unit exceeds a predetermined power limit value.

3. The subscriber station according to claim 2, wherein said network inter-frequency measurement trigger signal indicates that said transmitted output power measured on the down-link by said power measurement unit exceeds said predetermined power limit value at least for a predetermined measurement interval.

4. The subscriber station according to claim 2, further comprising a power adjustment unit operable to preset at least one of a predetermined power offset value, an upper threshold value and a lower threshold value for the downlink within which said measured down-link power is allowed to vary.

5. The subscriber station according to claim 4, wherein said power offset value is dependent on a slow power control, said upper and lower threshold values are dependent on a fast power control, said slow power control and said fast power control carried out by said network control unit including a calibration unit operable to calibrate at least one power step to predetermined values within a range determined by the upper and lower threshod values and said power offset value.

6. The subscriber station according to claim 1, wherein at least two communication connections are established between a plurality of base station transceivers and said subscriber station, said network inter-frequency measurement trigger signal generated by said network handover unit when said quality measurement unit determines that the transmission quality on all down-links of all said communication connections drops below a respective predetermined quality measure.

7. The subscriber station according to claim 1, further comprising a subscriber handover unit operable to perform measurements made within said subscriber station for generating a subscriber inter-frequency measurement trigger signal, said inter-frequency measurement unit operable to start said inter-frequency measurements when said network trigger signal and said subscriber trigger signal are generated.

8. The subscriber station according to claim 7, wherein said subscriber handover unit transmits to said network control unit said subscriber inter-frequency measurement trigger signal, said network handover unit generates and transmits said network inter-frequency measurement signal when said measurements in said subscriber inter-frequency measurement trigger signal indicate the necessity for a handover and said quality measurement unit determines that the transmission quality on the down-link of said at least one communication connection has dropped below said predetermined quality threshold.

9. The subscriber station according to claim 8, wherein said network inter-frequency measurement trigger signal is generated when said measurements made within said subscriber station and reported in said subscriber inter-frequency measurement trigger signal from said subscriber station indicate a handover, said quality measurement unit determines that the transmission quality on the down-link of said at least one communication connection has dropped below said predetermined quality threshold, and system information provided in the network control unit indicates a handover.

10. The subscriber station according to claim 7, wherein said subscriber handover unit is operable to perform measurements by an average filtering of a pilot channel during a predetermined time.

11. The subscriber station according to claim 9, wherein said system information includes at least one of a total uplink interference level of the communication connection and a total down-link output power.

12. The subscriber station according to claim 7, wherein said network handover unit is operable to determine the necessity for a handover on the basis of a supervision of loads at all of said at least one base transceiver stations in the communication system.

13. The subscriber station according to claim 7, wherein at least one of said subscriber handover unit and said network handover unit are operable to determine the necessity for a handover on the basis of a supervision of the distance between said at least one base transceiver station and the subscriber station.

14. The subscriber station according to claim 7, wherein at least one of said subscriber handover unit and said network handover unit are operable to determine the necessity for a handover on the basis of a supervision of a measured pilot signal strength falling below a predetermined power threshold.

15. The subscriber station according to claim 7, further comprising a subscriber station power adjustment module, at least one of said subscriber handover unit and said network handover unit operable to determine the necessity for a handover on the basis of said subscriber station power adjustment module failing to further increase its power on an uplink of said at least one communication connection in response to a power increase command by at least one of said base transceiver station.

16. The subscriber station according to claim 1, further comprising:

a data transmission determining unit operable to determine a predetermined time interval in which said at least one base transceiver station will not direct to said subscriber station a data transmission, said inter-frequency measurement unit operable to perform said inter-frequency measurements in a predetermined time interval after said network inter-frequency measurement trigger signal is received.

17. The subscriber station according to claim 16, wherein a transmission of data is carried out on said at least one communication connection via at least one transmission frame including a control portion and a data portion, said data transmission determining unit operable to determine a power ratio of the information contained in the data portion to the information contained in the control portion, said data transmission determining unit including a power estimation unit operable to determine that no data transmission will take place in a time interval corresponding to a predetermined number of data slots following the output of said inter-frequency measurement trigger signal if said power ratio is below a predefined power ratio.

18. The subscriber station according to claim 16, further comprising:

a non-active mode operation unit operable to hold the subscriber station in a non-active operation mode in which at least a signalling communication is established between said subscriber station and said at least one base transceiver station; and

a paging flag monitoring unit operable to monitor a transmission of a paging flag from said at least one base transceiver station to said subscriber station, said paging flag monitoring unit operable to determine that no transmission of said paging flag has been made, said data transmission determining unit operable to determine that a data transmission will not take place in a time interval corresponding to a predetermined number of data slots after detecting said paging flag.

19. The subscriber station according to claim 17, further comprising a compression-mode detection unit, said data transmission between said subscriber station and said at least one base transceiver station occurring in a compressed mode by compression of said data transmission in said data portion in at least one time slot such that an idle time interval is provided in said time slot where no data transmission occurs, said compression-mode detection unit operable to detect data transmission in said compressed mode, said predetermined time interval corresponding to a plurality of data slots where no data transmission takes place and a number of idle time portions of data slots where data transmission is made in a compressed mode.

20. The subscriber station according to claim 1, wherein at least one of said network inter-frequency measurement trigger signal and a control signal from the network control unit indicates a time interval in which said subscriber station is to carry out said inter-frequency measurements.

21. A method for triggering inter-frequency measurements in a subscriber station of a mobile communication system including at least one base transceiver station and a network control unit operable to establish at least one communication connection with said subscriber station, said subscriber station including an inter-frequency measurement unit operable to perform said inter-frequency measurements, said method comprising the steps of:

monitoring, in said network control unit, the transmission quality on a down-link of said at least one communication connection;

generating a network inter-frequency measurement trigger signal when said transmission quality drops below a predetermined quality measure;

sending said generated network inter-frequency measurement trigger signal to said subscriber station; and

performing said inter-frequency measurements by said inter-frequency measurement unit in said subscriber station in response to said network inter-frequency measurement trigger signal.

22. The method according to claim 21, further comprising the step of measuring a transmitted output power on the down-link by a power measurement unit, said generating step occurring when said transmitted output power on the down-link exceeds a predetermined power limit value.

23. The method according to claim 22, wherein said step of generating occurs when said transmitted output power measured on the down-link by said power measurement unit exceeds said predetermined power offset value longer than a predetermined measurement interval.

24. The method according to claim 22, further comprising the step of presetting, by a quality measurement unit, said predetermined power offset value, an upper threshold value and a lower threshold value within which said measured down-link power is allowed to vary.

25. The method according to claim 24, wherein said power offset value is dependent on a slow power control, said upper and lower power thresholds are variable dependent on a fast power control, said slow power control and said fast power control carried out by a power adjustment unit of said network control unit, a calibration unit calibrating each power step within a range determined by the upper and lower thresholds and said power offset value to predetermined values.

26. The method according to claim 21, further comprising the step of establishing a plurality of communication connections between a plurality of base transceiver stations and said subscriber station, said generating step occurring when said quality measurement unit determines that the transmission quality on all down-links of all said communication connections drop below a respective predetermined quality threshold.

27. The method according to claim 21, further comprising the step of generating a subscriber inter-frequency measurement trigger signal by making measurements in said subscriber station, said inter-frequency measurement unit operable to start said inter-frequency measurements when said network trigger signal and said subscriber trigger signal are generated.

28. The method according to claim 27, further comprising the step of transmitting said subscriber inter-frequency measurement trigger signal to said network control unit, said subscriber measurement trigger signal indicating said measurements performed in said subscriber station, said network handover unit generating and transmitting said network inter-frequency measurement signal when said measurements included in said subscriber inter-frequency measurement trigger signal indicate the necessity for a handover and said quality measurement unit determines that the transmission quality on the down-link of said communication connection has dropped below said predetermined quality measure.

29. The method according to claim 28, wherein said network inter-frequency measurement trigger signal is generated if said measurements included in said subscriber inter-frequency measurement trigger signal from said subscriber station indicate a handover, said quality measurement unit determines that the transmission quality on the down-link of said communication connection has dropped below said predetermined quality measure, and system information provided in the network control unit indicates a handover.

30. The method according to claim 27, further comprising the step of performing, by a subscriber handover unit, measurements by an average filtering of a pilot channel during a predetermined time.

31. The method according to claim 29, wherein said system information includes at least one of a total uplink interference level of the communication connection and a total down-link output power.

32. The method according to claim 28, wherein said network handover unit is operable to determine the necessity for a handover on the basis of a supervision of loads at all of said at least one base transceiver stations in the communication system.

33. The method according to claim 28, wherein at least one of said subscriber handover unit and said network handover unit determines the necessity for a handover on the basis of a supervision of the distance between said at least one base transceiver station and the subscriber station.

34. The method according to claim 28, wherein at least one of said subscriber handover unit and said network handover unit determines the necessity for a handover on the basis of a supervision of a measured pilot signal strength falling below a predetermined power threshold.

35. The method according to claim 28, wherein at least one of said subscriber handover unit and said network handover unit determines the necessity for a handover on the basis of a supervision that, in response to a power increase command by a base station, a subscriber station power adjustment module is unable to further increase its power on the uplink of said communication connection.

36. The method according to claim 21, wherein at least one of said network inter-frequency measurement trigger signal and a control signal from the network control unit indicates a time interval in which said subscriber station is to carry out said inter-frequency measurements.

37. A mobile communication system including at least one subscriber station having an inter-frequency measurement unit operable to perform said inter-frequency measurements, at least one base transceiver station, and a network control unit operable to establish at least one communication connection with said subscriber station, said system comprising:

a quality measurement unit in said network control unit, said quality measurement unit operable to monitor the transmission quality on a down-link of said at least one communication connection; and

a network handover unit operable to generate a network inter-frequency measurement trigger signal when said transmission quality drops below a predetermined quality measure, said network handover unit sending said generated network inter-frequency measurement trigger signal to said subscriber station, said inter-frequency measurement unit operable to perform said inter-frequency measurements in said subscriber station in response to said network inter-frequency measurement trigger signal.

38. The system according to claim 37, further comprising a subscriber handover unit operable to perform measurements for generating a subscriber measurement trigger signal in said subscriber station, said inter-frequency measurement unit operable to start said inter-frequency measurements when said network trigger signal and said subscriber trigger signal are generated.

39. The system according to claim 38, wherein said subscriber handover unit is operable to transmit said subscriber inter-frequency measurement trigger signal to said network control unit, said subscriber inter-frequency signal indicating said measurements made by said subscriber handover unit, said network handover unit generating and transmitting said network inter-frequency measurement signal when said measurements in said subscriber inter-frequency measurement trigger signal indicate the necessity for a handover and said quality measurement unit determines that the transmission quality on the down-link of said at least one communication connection has dropped below said predetermined quality measure.

40. The system according to claim 39, wherein said network inter-frequency measurement trigger signal is generated by said network handover unit if said measurements in said subscriber inter-frequency measurement trigger signal from said subscriber station indicate a handover, said quality measurement unit determines that the transmission quality on the down-link of said at least one communication connection has dropped below said predetermined quality measure, and system information provided in the network control unit also indicates a handover.

41. The system according to claim 38, wherein said subscriber handover unit performs measurements by an average filtering of a pilot channel during a predetermined time.

42. The system according to claim 40, wherein said system information includes at least one of a total uplink interference level of the at least one communication connection and the total down-link output power.

43. The system according to claim 38, wherein said network handover unit is operable to determine the necessity for a handover on the basis of a supervision of loads at all of said at least one base transceiver stations in the communication system.

44. The system according to claim 38, wherein at least one of said subscriber handover unit and said network handover unit determines the necessity for a handover on the basis of a supervision of the distance between said at least one base transceiver station and the subscriber station.

45. The system according to claim 38, wherein at least one of said subscriber handover unit and said network handover unit determines the necessity for a handover on the basis of a supervision of a measured pilot signal strength falling below a predetermined power threshold.

46. The system according to claim 38, wherein at least one of said subscriber handover unit and said network handover unit determines the necessity for a handover on the basis of an output by a network power supervision unit, said output indicating that in response to a power increase command by said at least one base transceiver station a subscriber station power adjustment module is unable to further increase its power on the uplink of said at least one communication connection.

47. The system according to claim 37, wherein at least one of said network measurement trigger signal and a control signal from the network control unit indicates a time interval in which said subscriber station is to carry out said inter-frequency measurements.

48. A network control unit of a mobile communication system, said communication system having at least one subscriber station including an inter-frequency measurement unit operable to perform inter-frequency measurements, said communication system further including at least one base transceiver station operable to establish at least one communication connection with said subscriber station, said network control unit comprising:

a quality measurement unit operable to monitor the transmission quality on a down-link of said at least one communication connection; and

a network handover unit operable to generate a network inter-frequency measurement trigger signal when said transmission quality drops below a predetermined quality measure, said network handover unit sending said generated network inter-frequency measurement trigger signal to said subscriber station, said inter-frequency measurement unit operable to perform said inter-frequency measurements in said subscriber station in response to said network inter-frequency measurement trigger signal.

49. A network control unit according to claim 48, further comprising a power measurement unit operable to measure a transmitted output power on the down-link, said network inter-frequency measurement trigger signal generated by said network handover unit when said transmitted output power on the downlink exceeds a predetermined power limit value.

50. The network control unit according to claim 49, wherein said network inter-frequency measurement trigger signal is generated by said network handover unit if said transmitted output power measured on the down-link by said power measurement unit exceeds said predetermined power limit value longer than a predetermined measurement interval.

51. The network control unit according to claim 49, wherein said quality measurement unit presets for the downlink a predetermined power offset value, an upper threshold value and a lower threshold value within which said measured down-link power is allowed to vary.

52. The network control unit according to claim 51, further comprising a calibration unit, said power offset value is variable dependent on a slow power control, said upper threshold value and said lower thresholds threshold value are dependent on a fast power control, said fast power control and said slow power control carried out by a power control unit of said network control unit, said calibration unit operable to calibrate to predetermined values at least one power step within a range determined by the upper threshold value, the lower threshold value and said variable power offset value.

53. The network control unit according to claim 48 wherein a plurality of communication connections are established between a plurality of base transceiver stations and said subscriber station, said network inter-frequency measurement trigger signal generated by said network handover unit when said quality measurement unit determines that the transmission quality on all down-links of all said communication connections drops below a respective predetermined quality measure.