System and method for selecting a serving base station according to a drop of a mobile subscriber station in a broadband wireless access communication system

• US 7,693,520 B2
• Filed: 04/06/2007
• Issued: 04/06/2010
• Est. Priority Date: 09/04/2003
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Koo, Chang-Hoi, Lee, Sung-Jin, Son, Yeong-Moon, Kim, So-Hyun, Kang, Hyun-Jeong, Son, Jung-Je
• Primary Examiner(s): Kincaid; Lester
• Assistant Examiner(s): SHEDRICK, CHARLES TERRELL
• Application Number:
  US11/784,532
• Publication Number:
  US 20070249353A1
• Time in Patent Office: 1,096 Days
• Field of Search: 455436-443
• US Class Current: 455/436
• CPC Class Codes: H04W 36/0079 in case of hand-off failure or rejection
• CPC Class Codes: H04W 36/302 due to low signal strength
• CPC Class Codes: H04W 36/305 Handover due to radio link failure control signalling for hand-off failure H04W36/0079

Abstract

Disclosed are a system and a method for selecting a new serving base station when a drop occurs in a mobile subscriber station in a broadband wireless access communication system including the mobile subscriber station, a serving base station communicating with the mobile subscriber station, and a plurality of neighbor base stations, different from the serving base station. The mobile subscriber station receives information related to the neighbor base stations from the serving base station communicating with the mobile subscriber station. The mobile subscriber station monitors the frequency bands of the neighbor base stations included in the information related to the neighbor base stations if the drop is detected in order to detect target base stations capable of serving as a new serving base station for communicating with the mobile subscriber station when the drop occurs in the mobile subscriber station according to a monitoring result for the frequency bands of the neighbor base stations. The mobile subscriber station selects the new serving base station from the detected target base stations so that the it is possible for the mobile subscriber station to reestablish the communication with regard to the new serving base station within a short period of time.

Claims

1. A method of selecting a new serving base station when a drop occurs in a mobile subscriber station in a broadband wireless access communication system including the mobile subscriber station, a serving base station communicating with the mobile subscriber station, and a plurality of neighbor base stations, different from the serving base station, the method comprising the steps of:

i) detecting the drop after receiving information related to the neighbor base stations transmitted from the serving base station communicating with the mobile subscriber station;

ii) monitoring frequency bands of the neighbor base stations included in the information related to the neighbor base stations, if the drop is detected;

iii) detecting target base stations capable of serving as the new serving base station for communicating with the mobile subscriber station when the drop occurs in the mobile subscriber station according to a monitoring result for the frequency bands of the neighbor base stations;

iv) selecting the new serving base station from the detected target base stations; and

v) controlling the new serving base station by performing drop ranging in relation to the new serving base station using a predetermined drop ranging code after selecting the new serving base station in such a manner that the new serving base station recognizes that the mobile subscriber station is attempting to reestablish a communication with regard to the new base station due to the drop occurring in the mobile subscriber station.

2. The method as claimed in claim 1, wherein step i) comprises the substeps of repeatedly transmitting a ranging request message to the serving base station if a ranging response message is not received within a predetermined period of time in response to the ranging request message after transmitting the ranging request message to the serving base station, and detecting the drop if a ranging response message is not received within a predetermined period of time after repeatedly transmitting the ranging request message to the serving base station.

3. The method as claimed in claim 1, wherein step i) comprises a substep of detecting the drop if a channel quality of a downlink signal transmitted from the serving base station is less than a reference channel quality during a predetermined interval.

4. The method as claimed in claim 3, wherein the channel quality is determined based on a result of a cyclic redundancy check for the downlink signal.

5. The method as claimed in claim 1, wherein, in step ii), a carrier to interference and noise ratio of a reference channel signal is measured at each frequency band of the neighbor base stations.

6. The method as claimed in claim 5, wherein, in step iii), neighbor base stations transmitting reference channel signals having a carrier to interference and noise ratio greater than a reference carrier to interference and noise ratio are detected as target base stations.

7. The method as claimed in claim 6, further comprising the steps of:

a) monitoring all of the frequency bands preset in the mobile subscriber station when the target base station is not detected after monitoring frequency bands of the neighbor base stations;

b) detecting the target base stations corresponding to a monitoring result for all of the frequency bands; and

c) selecting the new serving base station from the target base stations detected in step b).

8. The method as claimed in claim 7, wherein, in step a), a carrier to interference and noise ratio of a reference channel signal is measured at all frequency bands.

9. The method as claimed in claim 8, wherein, in step b), neighbor base stations transmitting reference channel signals having a carrier to interference and noise ratio greater than a reference carrier to interference and noise ratio and being received through all frequency bands are detected as target base stations.

10. The method as claimed in claim 1, wherein the drop ranging is used for reestablishing a communication with regard to the new serving base station when the drop occurs in the mobile subscriber station.

11. A method of selecting a new serving base station when a drop occurs in a mobile subscriber station in a broadband wireless access communication system including the mobile subscriber station, a serving base station communicating with the mobile subscriber station, and a plurality of neighbor base stations, different from the serving base station, the method comprising the steps of:

i) detecting the drop after receiving information related to the neighbor base stations transmitted from the serving base station communicating with the mobile subscriber station;

ii) monitoring frequency bands of the neighbor base stations included in the information related to the neighbor base stations, if the drop is detected;

iii) detecting target base stations capable of serving as the new serving base station for communicating with the mobile subscriber station when the drop occurs in the mobile subscriber station according to a monitoring result for the frequency bands of the neighbor base stations;

iv) selecting the new serving base station from the detected target base stations; and

v) controlling the new serving base station by performing drop ranging in relation to the new serving base station at a predetermined drop ranging time slot after selecting the new serving base station in such a manner that the new serving base station recognizes that the mobile subscriber station is attempting to reestablish a communication with regard to the new base station due to the drop occurring in the mobile subscriber station.

12. The method as claimed in claim 11, wherein the drop ranging is used for reestablishing a communication with regard to the new serving base station when the drop occurs in the mobile subscriber station.

13. A method of selecting a new serving base station when a drop occurs in a mobile subscriber station during a handover operation of the mobile subscriber station from a serving base station to a neighbor base station in a broadband wireless access communication system including the mobile subscriber station, the serving base station communicating with the mobile subscriber station, and n neighbor base stations different from the serving base station, the method comprising the steps of:

i) receiving information related to the n neighbor base stations transmitted from the serving base station communicating with the mobile subscriber station and monitoring frequency bands of the n neighbor base stations included in the information related to the n neighbor base stations;

ii) determining by the serving base station the handover operation and detecting m neighbor base stations, where m≦

n, capable of serving as a new serving station according to a monitoring result for the frequency bands of the n neighbor base stations;

iii) sending a signal requesting a handover to the serving base station based on information about the m neighbor base stations;

iv) monitoring frequency bands of the m neighbor base stations if the drop occurs after requesting the handover;

v) detecting target base stations capable of serving as a new serving station according to a monitoring result for the frequency bands of the m neighbor base stations;

vi) selecting the new serving station from the target base stations detected in step v); and

v) controlling the new serving base station by performing drop ranging in relation to the new serving base station using a predetermined drop ranging code after selecting the new serving base station in such a manner that the new serving base station recognizes that the mobile subscriber station is attempting to reestablish communication with regard to the new base station due to the drop occurring in the mobile subscriber station.

14. The method as claimed in claim 13, wherein the drop is detected by repeatedly transmitting a ranging request message to the serving base station if a ranging response message is not received within a predetermined period of time in response to the ranging request message after transmitting the ranging request message to the serving base station, and detecting the drop if a ranging response message is not received within a predetermined period of time after repeatedly transmitting the ranging request message to the serving base station.

15. The method as claimed in claim 13, wherein the drop is detected if channel quality of a downlink signal transmitted from the serving base station is less than reference channel quality during a predetermined interval.

16. The method as claimed in claim 15, wherein the channel quality is determined based on a result of a cyclic redundancy check for the downlink signal transmitted from the serving base station.

17. The method as claimed in claim 13, wherein, in step i), a carrier to interference and noise ratio of a reference channel signal is measured at each of the frequency band of the neighbor base stations.

18. The method as claimed in claim 17, wherein step iv) comprises the substeps of sequentially ordering the m neighbor base stations according to a value of the carrier to interference and noise ratio of the reference channel signal transmitted from the m neighbor base stations and detected when requesting the handover, and detecting the carrier to interference and noise ratio of the reference channel signal received at each of the frequency band of the m ordered neighbor base stations.

19. The method as claimed in claim 17, wherein, in step v), neighbor base stations transmitting reference channel signals having a carrier to interference and noise ratio greater than a reference carrier to interference and noise ratio are detected as target base stations.

20. The method as claimed in claim 13, further comprising the steps of:

a) monitoring all of the frequency bands preset in the mobile subscriber station when the target base station is not detected after monitoring frequency bands of the m neighbor base stations;

b) detecting the target base stations corresponding to a monitoring result for all frequency bands; and

c) selecting the new serving base station from the target base stations detected in step b).

21. The method as claimed in claim 20, wherein, in step a), a carrier to interference and noise ratio of a reference channel signal is measured at all of the frequency bands.

22. The method as claimed in claim 21, wherein, in step b), neighbor base stations transmitting reference channel signals having a carrier to interference and noise ratio greater than a reference carrier to interference and noise ratio and received through all of the frequency bands are detected as target base stations.

23. The method as claimed in claim 13, wherein the drop ranging is used for reestablishing a communication with regard to the new serving base station when the drop occurs in the mobile subscriber station.

24. A method of selecting a new serving base station when a drop occurs in a mobile subscriber station during a handover operation of the mobile subscriber station from a serving base station to a neighbor base station in a broadband wireless access communication system including the mobile subscriber station, the serving base station communicating with the mobile subscriber station, and n neighbor base stations different from the serving base station, the method comprising the steps of:

i) receiving information related to the n neighbor base stations transmitted from the serving base station communicating with the mobile subscriber station and monitoring frequency bands of the n neighbor base stations included in the information related to the n neighbor base stations;

ii) determining by the serving base station the handover operation and detecting m neighbor base stations, where m≦

n, capable of serving as a new serving station according to a monitoring result for the frequency bands of the n neighbor base stations;

iii) sending a signal requesting a handover to the serving base station based on information about the m neighbor base stations;

iv) monitoring frequency bands of the m neighbor base stations if the drop occurs after requesting the handover;

v) detecting target base stations capable of serving as a new serving station according to a monitoring result for the frequency bands of the m neighbor base stations;

vi) selecting the new serving station from the target base stations detected in step v); and

v) controlling the new serving base station by performing drop ranging in relation to the new serving base station at a predetermined drop ranging time slot after selecting the new serving base station in such a manner that the new serving base station recognizes that the mobile subscriber station is attempting to reestablish communication with regard to the new base station due to the drop occurring in the mobile subscriber station.

25. The method as claimed in claim 24, wherein the drop ranging is used for reestablishing a communication with regard to the new serving base station when the drop occurs in the mobile subscriber station.

26. A method of selecting a new serving base station when a drop occurs in a mobile subscriber station during a handover operation of the mobile subscriber station from a serving base station to a neighbor base station in a broadband wireless access communication system including the mobile subscriber station, the serving base station communicating with the mobile subscriber station, and n neighbor base stations, different from the serving base station, the method comprising the steps of:

i) receiving information related to the neighbor base stations transmitted from the serving base station communicating with the mobile subscriber station and monitoring frequency bands of the neighbor base stations included in the information about the neighbor base stations;

ii) monitoring each of the frequency band of neighbor base stations if the drop is detected after monitoring the frequency bands of the neighbor base stations;

iii) detecting target base stations capable of serving as the new serving base station according to a monitoring result for each frequency band of neighbor base stations;

iv) selecting the new serving base station from the target base stations detected in step iii); and

v) controlling the new serving base station by performing drop ranging in relation to the new serving base station using a predetermined drop ranging code after selecting the new serving base station in such a manner that the new serving base station recognizes that the mobile subscriber station is attempting to reestablish a communication with regard to the new base station due to the drop occurring in the mobile subscriber station.

27. The method as claimed in claim 26, wherein the drop is detected by repeatedly transmitting a ranging request message to the serving base station if a ranging response message is not received within a predetermined period of time in response to the ranging request message after transmitting the ranging request message to the serving base station, and detecting the drop if a ranging response message is not received within a predetermined period of time after repeatedly transmitting the ranging request message to the serving base station.

28. The method as claimed in claim 26, wherein the drop is detected if a channel quality of a downlink signal transmitted from the serving base station is less than a reference channel quality during a predetermined interval.

29. The method as claimed in claim 28, wherein the channel quality is determined based on a result of a cyclic redundancy check for the downlink signal transmitted from the serving base station.

30. The method as claimed in claim 26, wherein step ii) comprises the substeps of sequentially ordering the neighbor base stations according to a value of the carrier to interference and noise ratio of the reference channel signal transmitted from the neighbor base stations and detected before the drop occurs, and measuring the carrier to interference and noise ratio of the reference channel signal at each of the frequency band of the ordered neighbor base stations.

31. The method as claimed in claim 30, wherein, in step iii), neighbor base stations transmitting reference channel signals having a carrier to interference and noise ratio greater than a reference carrier to interference and noise ratio are detected as target base stations.

32. The method as claimed in claim 26, further comprising the steps of:

a) monitoring all of the frequency bands preset in the mobile subscriber station when the target base station is not detected after monitoring the frequency bands of the neighbor base stations;

b) detecting the target base stations corresponding to a monitoring result for all frequency bands; and

c) selecting the new serving base station from the target base stations detected in step b).

33. The method as claimed in claim 32, wherein, in step a), a carrier to interference and noise ratio of a reference channel signal is measured at all of the frequency bands.

34. The method as claimed in claim 33, wherein, in step b), neighbor base stations transmitting reference channel signals having a carrier to interference and noise ratio greater than a reference carrier to interference and noise ratio and received through all of the frequency bands are detected as target base stations.

35. The method as claimed in claim 26, wherein the drop ranging is used for reestablishing communication with regard to the new serving base station when the drop occurs in the mobile subscriber station.

36. A method of selecting a new serving base station when a drop occurs in a mobile subscriber station during a handover operation of the mobile subscriber station from a serving base station to a neighbor base station in a broadband wireless access communication system including the mobile subscriber station, the serving base station communicating with the mobile subscriber station, and n neighbor base stations, different from the serving base station, the method comprising the steps of:

i) receiving information related to the neighbor base stations transmitted from the serving base station communicating with the mobile subscriber station and monitoring frequency bands of the neighbor base stations included in the information about the neighbor base stations;

ii) monitoring each of the frequency band of neighbor base stations if the drop is detected after monitoring the frequency bands of the neighbor base stations;

iii) detecting target base stations capable of serving as the new serving base station according to a monitoring result for each frequency band of neighbor base stations;

iv) selecting the new serving base station from the target base stations detected in step iii); and

v) controlling the new serving base station by performing drop ranging in relation to the new serving base station at a predetermined drop ranging time slot after selecting the new serving base station in such a manner that the new serving base station recognizes that the mobile subscriber station is attempting to reestablish a communication with regard to the new base station due to the drop occurring in the mobile subscriber station.

37. The method as claimed in claim 36, wherein the drop ranging is used for reestablishing communication with regard to the new serving base station when the drop occurs in the mobile subscriber station.

38. A method of selecting a new serving base station when a drop occurs in a mobile subscriber station during a handover operation of the mobile subscriber station from a serving base station to a neighbor base station in a broadband wireless access communication system including the mobile subscriber station, the serving base station communicating with the mobile subscriber station, and n neighbor base stations, different from the serving base station, the method comprising the steps of:

i) receiving information related to the n neighbor base stations transmitted from the serving base station communicating with the mobile subscriber station and monitoring frequency bands of the n neighbor base stations included in the information related to the n neighbor base stations;

ii) determining by the serving base station the handover operation and detecting m neighbor base stations, where m≦

n, capable of serving as a new serving station according to a monitoring result for the frequency bands of the n neighbor base stations;

iii) sending a signal requesting a handover to the serving base station based on information related the m neighbor base stations;

iv) receiving a handover response including information about k recommended neighbor base stations, where k≦

m, to which the mobile subscriber station is handed-over from the serving base station, according to a request for the handover;

v) monitoring frequency bands of the k recommended neighbor base stations if the drop occurs after the request for the handover;

vi) detecting target base stations capable of serving as a new serving station according to a monitoring result for the frequency bands of the k recommended neighbor base stations;

vii) selecting the new serving station from the target base stations detected in step vi); and

viii) controlling the new serving base station by performing drop ranging in relation to the new serving base station using a predetermined drop ranging code after selecting the new serving base station in such a manner that the new serving base station recognizes that the mobile subscriber station is attempting to reestablish a communication with regard to the new base station due to the drop occurring in the mobile subscriber station.

39. The method as claimed in claim 38, wherein the drop is detected by repeatedly transmitting a ranging request message to the serving base station if a ranging response message is not received within a predetermined period of time in response to the ranging request message after transmitting the ranging request message to the serving base station, and detecting the drop if a ranging response message is not received within a predetermined period of time after repeatedly transmitting the ranging request message to the serving base station.

40. The method as claimed in claim 39, wherein the drop is detected if channel quality of a downlink signal transmitted from the serving base station is less than reference channel quality during a predetermined interval.

41. The method as claimed in claim 40, wherein the channel quality is determined based on a result of a cyclic redundancy check for the downlink signal transmitted from the serving base station.

42. The method as claimed in claim 38, wherein, in step i), a carrier to interference and noise ratio of a reference channel signal is measured at each of the frequency bands of the neighbor base stations.

43. The method as claimed in claim 40, wherein step v) comprises the substeps of sequentially ordering the k recommended neighbor base stations in an order of a service level detected when requesting the handover, and detecting the carrier to interference and noise ratio of the reference channel signal received at each of the frequency bands of the k recommended neighbor base stations.

44. The method as claimed in claim 43, wherein, in step vi), the recommended neighbor base stations transmitting reference channel signals having the carrier to interference and noise ratio greater than a reference carrier to interference and noise ratio are detected as target base stations.

45. The method as claimed in claim 38, further comprising the steps:

a) monitoring all of the frequency bands preset in the mobile subscriber station when the target base station is not detected after monitoring frequency bands of the k recommended neighbor base stations;

b) detecting the target base stations corresponding to a monitoring result for all frequency bands; and

c) selecting the new serving base station from the target base stations detected in step b).

46. The method as claimed in claim 45, wherein, in step a), a carrier to interference and noise ratio of a reference channel signal is measured at all of the frequency bands.

47. The method as claimed in claim 46, wherein, in step b), neighbor base stations transmitting reference channel signals having a carrier to interference and noise ratio greater than a reference carrier to interference and noise ratio and received through all frequency bands are detected as target base stations.

48. The method as claimed in claim 38, further comprising the steps of:

a) selecting a final neighbor base station from the k recommended base stations after receiving the handover response such that the mobile subscriber station is handed-over to the final neighbor base station and sending a signal requesting the handover and including information about the selected final neighbor base station to the serving base station;

b) monitoring a frequency band of the final neighbor base station if the drop is detected in step a); and

c) selecting the final neighbor base station as a new serving base station if the final neighbor base station is detected as the target base station in step b).

49. The method as claimed in claim 48, further comprising the steps of:

d) monitoring all of the frequency bands preset in the mobile subscriber station if the final neighbor base station is not detected as the target station;

e) detecting target base stations corresponding to a monitoring result of step d); and

f) selecting the new serving base station from the target neighbor base stations detected in step e).

50. The method as claimed in claim 38, wherein the drop ranging is used for reestablishing a communication with regard to the new serving base station when the drop occurs in the mobile subscriber station.

51. A method of selecting a new serving base station when a drop occurs in a mobile subscriber station during a handover operation of the mobile subscriber station from a serving base station to a neighbor base station in a broadband wireless access communication system including the mobile subscriber station, the serving base station communicating with the mobile subscriber station, and n neighbor base stations, different from the serving base station, the method comprising the steps of:

i) receiving information related to the n neighbor base stations transmitted from the serving base station communicating with the mobile subscriber station and monitoring frequency bands of the n neighbor base stations included in the information related to the n neighbor base stations;

ii) determining by the serving base station the handover operation and detecting m neighbor base stations, where m≦

n, capable of serving as a new serving station according to a monitoring result for the frequency bands of the n neighbor base stations;

iii) sending a signal requesting a handover to the serving base station based on information related the m neighbor base stations;

iv) receiving a handover response including information about k recommended neighbor base stations, where k≦

m, to which the mobile subscriber station is handed-over from the serving base station, according to a request for the handover;

v) monitoring frequency bands of the k recommended neighbor base stations if the drop occurs after the request for the handover;

vi) detecting target base stations capable of serving as a new serving station according to a monitoring result for the frequency bands of the k recommended neighbor base stations;

vii) selecting the new serving station from the target base stations detected in step vi); and

viii) controlling the new serving base station by performing drop ranging in relation to the new serving base station at a predetermined drop ranging time slot after selecting the new serving base station in such a manner that the new serving base station recognizes that the mobile subscriber station is attempting to reestablish a communication with regard to the new base station due to the drop occurring in the mobile subscriber station.

52. The method as claimed in claim 51, wherein the drop ranging is used for reestablishing a communication with regard to the new serving base station when the drop occurs in the mobile subscriber station.

53. A system for selecting a new serving base station when a drop occurs in a mobile subscriber station in a broadband wireless access communication system including the mobile subscriber station, a serving base station communicating with the mobile subscriber station, and a plurality of neighbor base stations, different from the serving base station, the system comprising:

the mobile subscriber station for receiving information related neighbor base stations from the serving base station communicating with the mobile subscriber station, monitoring frequency bands of the neighbor base stations included in the information related to the neighbor base stations if the drop is detected in order to detect target base stations capable of serving as the new serving base station, selecting the new serving base station from the detected target base stations, and notifying the new serving base station of a reestablishment of a communication caused by the drop occurring in the mobile subscriber station; and

the new serving base station assigning channel resources to the mobile subscriber station when the new serving base station receives a notification of the reestablishment of the communication from the mobile subscriber station,

wherein the mobile subscriber station controls the new serving base station by performing drop ranging in relation to the new serving base station using a predetermined drop ranging code after selecting the new serving base station in such a manner that the new serving base station recognizes that the mobile subscriber station is attempting to reestablish a communication with regard to the new base station due to the drop occurring in the mobile subscriber station.

54. The system as claimed in claim 53, wherein mobile subscriber station repeatedly transmits a ranging request message to the serving base station if a ranging response message is not transmitted thereto within a predetermined period of time in response to the ranging request message after transmitting the ranging request message to the serving base station, and detects the drop if a ranging response message is not received within a predetermined period of time after repeatedly transmitting the ranging request message to the serving base station.

55. The system as claimed in claim 53, wherein the mobile subscriber station detects the drop if a channel quality of a downlink signal transmitted from the serving base station is less than a reference channel quality during a predetermined interval.

56. The system as claimed in claim 55, wherein mobile subscriber station determines the channel quality based on a result of a cyclic redundancy check for the downlink signal transmitted thereto from the serving base station.

57. The system as claimed in claim 53, wherein the mobile subscriber station detects a carrier to interference and noise ratio of a reference channel signal at each frequency band of the neighbor base stations in order to monitor the frequency bands of the neighbor base stations.

58. The system as claimed in claim 57, wherein the mobile subscriber station selects neighbor base stations transmitting reference channel signals having a carrier to interference and noise ratio greater than a reference carrier to interference and noise ratio as target base stations.

59. The system as claimed in claim 58, wherein the mobile subscriber station detects the target base stations by monitoring all of the frequency bands preset in the mobile subscriber station if the target base station is not detected after monitoring frequency bands of the neighbor base stations, and selects the new serving base station from the detected target base stations.

60. The system as claimed in claim 53, wherein the drop ranging is used for reestablishing the communication with regard to the new serving base station when the drop occurs in the mobile subscriber station.

61. A system for selecting a new serving base station when a drop occurs in a mobile subscriber station in a broadband wireless access communication system including the mobile subscriber station, a serving base station communicating with the mobile subscriber station, and a plurality of neighbor base stations, different from the serving base station, the system comprising:

the mobile subscriber station for receiving information related neighbor base stations from the serving base station communicating with the mobile subscriber station, monitoring frequency bands of the neighbor base stations included in the information related to the neighbor base stations if the drop is detected in order to detect target base stations capable of serving as the new serving base station, selecting the new serving base station from the detected target base stations, and notifying the new serving base station of a reestablishment of a communication caused by the drop occurring in the mobile subscriber station; and

the new serving base station assigning channel resources to the mobile subscriber station when the new serving base station receives a notification of the reestablishment of the communication from the mobile subscriber station,

wherein the mobile subscriber station controls the new serving base station by performing drop ranging in relation to the new serving base station at a predetermined drop ranging time slot after selecting the new serving base station in such a manner that the new serving base station recognizes that the mobile subscriber station is attempting to reestablish a communication with regard to the new base station due to the drop occurring in the mobile subscriber station.

62. The system as claimed in claim 61, wherein the drop ranging is used for reestablishing the communication with regard to the new serving base station when the drop occurs in the mobile subscriber station.