CDMA type mobile radio communication system capable of realizing an effective system operation without excess and deficiency of radio base stations simultaneously connected

• US 6,400,953 B1
• Filed: 05/29/1998
• Issued: 06/04/2002
• Est. Priority Date: 08/11/1997
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Furukawa, Hiroshi
• Primary Examiner(s): MAUNG, NAY AUNG
• Application Number:
  US09/087,080
• Time in Patent Office: 1,467 Days
• Field of Search: 370/320, 370/331, 370/332, 370/333, 370/335, 455/436, 455/437, 455/440, 455/441, 455/442, 455/443, 455/444
• US Class Current: 455/442
• CPC Class Codes: H04B 7/2628 using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA] H04B7/2618 takes precedence
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

In a code division multiple access (CDMA) cellular type mobile radio communication system, in order to realize effective system operation with neither more nor less of radio base stations which are simultaneously communicated with a mobile station on carrying out soft handoff, it is possible for the mobile station to communicate with the radio base stations having proper numbers in accordance with propagation environment and a moving speed of the mobile station by changing threshold levels for selection of the radio base stations and a hysteresis margin therefor on the basis of a variation rate in a propagation loss estimated by a reception level of a pilot signal.

Claims

1. A method of selecting radio base stations in a single mobile station of a code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to said single mobile station, said method comprising the steps of:

selecting the radio base stations to be connected so as to become more by increasing a connection threshold level when a level of propagation loss in said single mobile station changes rapidly, the connection threshold level being given by a function of a variation rate of a relative propagation loss; and

selecting the radio base stations to be connected to so as to become less by decreasing the connection threshold level when the level of the propagation loss in said single mobile station changes slowly,

thereby ensuring connection of the radio base station having a minimum propagation loss.

2. A method of setting a hysteresis margin in a single mobile station of a code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to said single mobile station, the hysteresis margin defining release connection of said radio base stations and the hysteresis margin being equal to a difference between a connection threshold level and a disconnection threshold level, said method comprising the steps of:

setting the hysteresis margin so as to become larger with the connection threshold level increased when a level of propagation loss in said single mobile station changes rapidly, increasing radio base stations simultaneously connected to said single mobile station, the connection threshold level being given by a function of a variation rate of a relative propagation loss; and

setting the hysteresis margin so as to become smaller with the connection threshold level decreased when the level of the propagation loss in said signal mobile station changes slowly, decreasing radio base stations simultaneously connected to said single mobile station,

thereby ensuring connection of the radio base station having a minimum propagation loss.

3. A method of selecting radio base stations in a single mobile station of a code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to said single mobile station, said method comprising the steps of:

determining, in said single mobile station, relative propagation losses for said radio base stations on the basis of a minimum propagation loss for said radio base stations;

calculating, in said single mobile station, variation rates of the relative propagation losses;

determining, in said single mobile station, whether of not said single mobile station is connected to each radio base station;

producing, in said single mobile station, determined result indicative of connection or disconnection for radio base station; and

when the determined result indicates that a particular radio base station is not connected to said single mobile station and when the relative propagation loss for said particular radio base station is lower than a connection threshold level which is given by a function of the variation rate such that an increase in the variation rate causes the connection threshold level to increase, starting, in said single mobile station, connection of said mobile station of said particular radio base station,

thereby ensuring connection of the radio base station having the minimum propagation loss.

4. A method as claimed in claim 3, wherein said method further comprises the step of maintaining a disconnection condition for said particular radio base station when the determined result indicates that said particular radio base station is not connected to said mobile station and when the relative propagation loss for said particular radio base station is not lower than the connection threshold level.

5. A method as claimed in claim 3, wherein said method further comprises the step of, when the determined result indicates that a specific radio base station is connected to said mobile station and when the relative propagation loss for said specific radio base station is higher than a disconnection threshold level which is obtained by adding a hysteresis margin to the connection threshold level, disconnecting of said mobile station to said specific radio base station.

6. A method as claimed in claim 5, wherein the hysteresis margin being given by the function of the variation rate as an argument, the faster the variation rate being, the larger the hysteresis margin being.

7. A method as claimed in claim 5, wherein said method further comprises the step of maintaining a connection condition for said specific radio base station when said determining result indicates that said specific radio base station is connected to said mobile station and when the relative propagation loss for said specific radio base station is not higher than the disconnection threshold level.

8. A method as claimed in claim 7, wherein the hysteresis margin being given by the function of the variation rate as an argument, the faster the variation rate being, the larger the hysteresis margin being.

9. A method of selecting radio base stations in a single mobile station of a code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to said single mobile station, said method comprising the steps of:

selecting the radio base stations to be connected so as to become more by increasing a connection threshold level when a moving speed of said single mobile station is fast, the connection threshold level being given by a function of the moving speed measured at said single mobile station; and

selecting the radio base stations to be connected so as to become less by decreasing the connection threshold level when the moving speed of said single mobile station is slow,

thereby ensuring connection of the radio base station having a minimum propagation loss.

10. A method of setting a hysteresis margin in a single mobile station of a code division multiple access (CDMA) mobile ratio communication system in which several radio base stations are simultaneously connected to said single mobile station, the hysteresis margin defining release from connection of said radio base stations and the hysteresis margin being equal to a difference between a connection threshold level and a disconnection threshold level, said method comprising the steps of:

setting the hysteresis margin so as to become larger with the connection threshold level increased when a moving speed of said mobile station is fast, increasing radio base stations simultaneously connected to said single mobile station, the connection threshold level being given by a function of the moving speed measured at said single mobile station; and

setting the hysteresis margin so as to become smaller with the connection threshold level decreased when the moving speed of said mobile station is slow, decreasing radio base stations simultaneously connected to said single mobile station,

thereby ensuring connection of the radio base station having a minimum propagation loss.

11. A method of selecting radio base stations in a single mobile station of a code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to said single mobile station, said method comprising the steps of:

detecting, in said single mobile station, a moving speed of said single mobile station;

determining, in said single mobile station, relative propagation losses for said radio base stations on the basis of a minimum propagation loss for said radio base stations;

determining, in said single mobile station, whether or not said single mobile station is connected to each radio base station;

producing, in said single mobile station, a determined result indicative of connection or disconnection for each radio base station; and

when the determined result indicates that a particular radio base station is not connected to said mobile station and when the relative propagation loss for said particular radio base station is lower than a connection threshold level which is given by a function of the moving speed such that an increase in the moving speed causes the connection threshold level to increase, starting, in said single mobile station, connection of said mobile station of said particular radio base station,

thereby ensuring connection of the radio base station having the minimum propagation loss.

12. A method as claimed in claim 11, wherein said method further comprises the step of maintaining a disconnection condition for said particular radio base station when the determined result indicates that said particular radio base station is not connected to said mobile station and when the relative propagation loss for said particular radio base station is not lower than the connection threshold level.

13. A method as claimed in claim 11, wherein said method further comprises the step of, when the determined result indicates that a specific radio base station is connected to said mobile station and when the relative propagation loss for said specific radio base station is higher than a disconnection threshold level which is obtained by adding a hysteresis margin to the connection threshold level, disconnecting of said mobile station to said specific radio base station.

14. A method as claimed in claim 13, wherein the hysteresis margin being given by the function of the moving speed as an argument, the faster the moving speed being, the larger the hysteresis margin being.

15. A method as claimed in claim 13, wherein said method further comprises the step of maintaining a connection condition for said specific radio base station when said determining result indicates that said specific radio base station is connected to said mobile station and when the relative propagation loss for said specific radio base station is not higher than the disconnection threshold level.

16. A method as claimed in claim 15, wherein the hysteresis margin being given by the function of the moving speed as an argument, the faster the moving speed being, the larger the hysteresis margin being.

17. A code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to a mobile station, said mobile station comprising:

a propagation loss measurement unit for measuring a propagation loss from said mobile station to each of the radio base stations; and

a soft handoff radio base station selection unit, connected to said propagation loss measurement unit, for determining the radio base stations to be connected or to be disconnected on the basis of the propagation loss with reference to a connection threshold level which is given by a function of a variation rate of a relative propagation loss, said soft handoff radio base station selection unit selecting the radio base stations to be connected so as to become more by increasing the connection threshold level when a level of the propagation loss changes rapidly, said soft handoff radio base station selection unit selecting the radio base stations to be connected so as to become less by decreasing the connection threshold level when the level of the propagation loss changes slowly,

thereby ensuring connection of the radio base station having a minimum propagation loss.

18. A code division multiple access (CDMA) cellular type mobile radio communication system in which several radio base stations are simultaneously connected to a mobile station, said mobile station comprising:

a propagation loss measurement unit for measuring a propagation loss from said mobile station to each of the radio base stations; and

a soft handoff radio base station selection unit, connected to said propagation loss measurement unit, for determining the radio base stations to be connected or to be connected on the basis of the propagation loss with reference to a connection threshold level and a disconnection threshold level which is higher than the connection threshold level by a hysteresis margin,

wherein said soft handoff radio base station selection unit increasing the hysteresis margin with the connection threshold level increased when a level of the propagation loss changes rapidly, increasing radio base stations simultaneously connected to said mobile station, the connection threshold level being given by a function at a variation rate of a relative propagation loss, and

wherein said soft handoff radio base station selection unit decreases the hysteresis margin with the connection threshold level decreased when the level of the propagation loss changes slowly,

thereby ensuring connection of the radio base station having a minimum propagation loss.

19. A code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to a mobile station, said mobile station comprising:

a propagation loss measurement unit for measuring a propagation loss from said mobile station to each of the radio base stations; and

a soft handoff radio base station selection unit, connected to said propagation loss measurement unit, for determining the radio base stations to be connected or to be disconnected on the basis of the propagation loss with reference to a connection threshold level and a disconnection threshold level which is higher than the connection threshold level by a hysteresis margin;

said soft handoff radio base station selection unit comprising;

means for determining relative propagation losses for said radio base stations on the basis of a minimum propagation loss for said radio base stations;

calculation means for calculating variation rates of the relative propagation losses;

determining means for determining whether or not said mobile station is connected to each radio base station to produce determined result indicative of connection or disconnection for radio base station; and

connection starting means, when the determined result indicates that a particular radio base station is not connected to said mobile station and when the relative propagation loss for said particular radio base station is lower than a connection threshold level which is given by a function of the variation rate such that an increase in the variation rate causes the connection threshold level to increase, for starting connection of said mobile station to said particular radio base station,

thereby ensuring connection of the radio base station having the minimum propagation loss.

20. A CDMA mobile radio communication system as claimed in claim 19, wherein said soft handoff radio base station selection unit further comprises means for maintaining a disconnection condition for said particular radio base station when the determined result indicates that said particular radio base station is not connected to said mobile station and when the relative propagation loss for said particular radio base station is not lower than the connection threshold level.

21. A CDMA mobile radio communication system as claimed in claim 19, wherein said soft handoff radio base station selection unit further comprises disconnecting means, when the determined result indicates that a specific radio base station is connected to said mobile station and when the relative propagation loss for said specific radio base station is higher than the disconnection threshold level, disconnecting said mobile station from said specific radio base station.

22. A CDMA mobile radio communication system as claimed in claim 21, wherein the connection threshold level is given by the function of the variation rate as an argument, the faster the variation rate being, the higher the connection threshold level being, the hysteresis margin being given by the function of the variation rate as an argument, the faster the variation rate being, the larger the hysteresis margin being.

23. A CDMA mobile radio communication system as claimed in claim 21, wherein said soft handoff radio base station selection unit further comprises means for maintaining a connection condition for said specific radio base station when said determining result indicates that said specific radio base station is connected to said mobile station and when the relative propagation loss for said specific radio base station is not higher than the disconnection threshold level.

24. A CDMA mobile radio communication system as claimed in claim 23, wherein the hysteresis margin being given by the function of the variation rate as an argument, the faster the variation rate being, the larger the hysteresis margin being.

25. A code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to a mobile station, said mobile station comprising:

a propagation loss measurement unit for measuring a propagation loss from said mobile station to each of the radio base stations;

a moving speed detection unit for detecting a moving speed of said mobile station; and

a soft handoff radio base station selection unit, connected to said propagation loss measurement unit and said moving speed detection unit, for determining the radio base stations to be connected or to be disconnected on the basis of the propagation loss with reference to a connection threshold level which is given by a function of the moving speed, said soft handoff radio base station selection unit selecting the radio base stations to be connected so as to become more by increasing the connection threshold level when the moving speed is fast, said soft handoff radio base station selection unit selecting the radio base stations to be connected so as to become less by decreasing the connection threshold level when the moving speed is slow,

thereby ensuring connection of the radio base station having a minimum propagation loss.

26. A code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to a mobile station, said mobile station comprising:

a propagation loss measurement unit for measuring a propagation loss from said mobile station to each of the radio base stations;

a moving speed detection unit for detecting a moving speed of said mobile station; and

a soft handoff radio base station selection unit, connected to said propagation loss measurement unit and said moving speed detection unit, for determining the radio base stations to be connected or to be disconnected on the basis of the propagation loss with reference to a connection threshold level and a disconnection threshold level which is higher than the connection threshold level by a hysteresis margin,

wherein said soft handoff radio base station selection unit increases the hysteresis margin with the connection threshold level increased when the moving speed is fast, increasing radio base stations simultaneously connected to said mobile station, the connection threshold level being given by a function of the moving speed, and

wherein said soft handoff radio base station selection unit decreases the hysteresis margin with the connection threshold level decreased when the moving speed is slow, decreasing radio base stations simultaneously connected to said mobile station,

thereby ensuring connection of the radio base station having a minimum propagation loss.

27. A code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to a mobile station, said mobile station comprising:

a propagation loss measurement unit for measuring a propagation loss from said mobile station to each of the radio base stations;

a moving speed detection unit for detecting a moving speed of said mobile station; and

a soft handoff radio base station selection unit, connected to said propagation loss measurement unit and said moving speed detection unit, for determining the radio base stations to be connected or to be disconnected on the basis of the propagation loss with reference to a connection threshold level and a disconnection threshold level which is higher than the connection threshold level by a hysteresis margin;

said soft handoff radio base station selection unit comprising;

means for determining relative propagation losses for said radio base stations on the basis of a minimum propagation loss for said radio base stations;

determining means for determining whether or not said mobile station is connected to each radio base station;

means for producing a determined result indicative of connection or disconnection for radio base station; and

connection starting means, when the determined result indicates that a particular radio base station is not connected to said mobile station and when the relative propagation loss for said particular radio base station is lower than a connection threshold level which is given by a function of the moving speed such that an increase in the moving speed causes the connection level to increase, for starting connection of said mobile station to said particular radio base station,

thereby ensuring connection of the radio base station having the minimum propagation loss.

28. A CDMA mobile radio communication system as claimed in claim 27, wherein said soft handoff radio base station selection unit further comprises means for maintaining a disconnection condition for said particular radio base station when the determined result indicates that said particular radio base station is not connected to said mobile station and when the relative propagation loss for said particular radio base station is not lower than the connection threshold level.

29. A CDMA mobile radio communication system as claimed in claim 27, wherein said soft handoff radio base station selection unit further comprises disconnecting means, when the determined result indicates that a specific radio base station is connected to said mobile station and when the relative propagation loss for said specific radio base station is higher than the disconnection threshold level, disconnecting said mobile station from said specific radio base station.

30. A CDMA mobile radio communication system as claimed in claim 29, wherein the hysteresis margin being given by the function of the moving speed as an argument, the faster the moving speed being, the larger the hysteresis margin being.

31. A CDMA mobile radio communication system as claimed in claim 29, wherein said soft handoff radio base station selection unit further comprises means for maintaining a connection condition for said specific radio base station when said determining result indicates that said specific radio base station is connected to said mobile station and when the relative propagation loss for said specific radio base station is not higher than the disconnection threshold level.

32. A CDMA mobile radio communication system as claimed in claim 31, wherein the hysteresis margin being given by the function of the moving speed as an argument, the faster the moving speed being, the larger the hysteresis margin being.

33. A mobile station for use in a code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to said mobile station, said mobile station comprising:

a propagation loss measurement unit for measuring a propagation loss from said mobile station to each of the radio base stations; and

a soft handoff radio base station selection unit, connected to said propagation loss measurement unit, for determining the radio base stations to be connected or to be disconnected on the basis of the propagation loss with reference to a connection threshold level which in given by a function of a variation rata of a relative propagation loss, said soft handoff radio base station selection unit selecting the radio base stations to be connected so as to become more by increasing the connection threshold level when a level of the propagation loss changes rapidly, said soft handoff radio base station selection unit selecting the radio base stations to be connected so as to become less by decreasing the connection threshold level when the level of the propagation loss changes slowly,

thereby ensuring connection of the radio base station having a minimum propagation loss.

34. A mobile station for use in a code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to said mobile station, said mobile station comprising:

a propagation loss measurement unit for measuring a propagation loss from said mobile station to each of the radio base stations; and

a soft handoff radio base station selection unit, connected to said propagation loss measurement unit, for determining the radio base stations to be connected or to be disconnected on the basis of the propagation loss with reference to a connection threshold level and a disconnection threshold level which is higher than the connection threshold level by a hysteresis margin,

wherein said soft handoff radio base station selection unit increases the hysteresis margin with the connection threshold level increased when a level of the propagation loss changes rapidly, increasing radio base stations simultaneously connected to said mobile stations, the connection threshold level being given by a function of a variation rate of a relative propagation loss, and

wherein said soft handoff radio base station selection unit decreases the hysteresis margin with the connection threshold level decreased when the level of the propagation loss changes slowly, decreasing radio base stations simultaneously connected to said mobile station,

thereby ensuring connection of the radio base station having a minimum propagation loss.

35. A mobile station for use in a code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to said mobile station, said mobile station comprising:

a propagation loss measurement unit for measuring a propagation loss from said mobile station to each of the radio base stations; and

a soft handoff radio base station selection unit, connected to said propagation loss measurement unit, for determining the radio base stations to be connected or to be disconnected on the basis of the propagation loss with reference to a connection threshold level and a disconnection threshold level which is higher than the connection threshold level by a hysteresis margin;

said soft handoff radio base station selection unit comprising;

means for determining relative propagation losses for said radio base stations on the basis of a minimum propagation loss for said radio base stations;

calculation means for calculating variation rates of the relative propagation losses;

determining means for determining whether or not said mobile station is connected to each radio base station;

means for producing determined result indicative of connection or disconnection for radio base station; and

connection starting means, when the determined result indicates that a particular radio base station is not connected to said mobile station and when the relative propagation loss for said particular radio base station is lower than the connection threshold level which is given by a function of the variation rate such that an increase in the variation rate causes the connection threshold level to increase, for starting connection of said mobile station to said particular radio base station,

thereby ensuring connection of the radio base station having the minimum propagation loss.

36. A mobile station as claimed in claim 35, wherein said soft handoff radio base station selection unit further comprises means for maintaining a disconnection condition for said particular radio base station when the determined result indicates that said particular radio base station is not connected to said mobile station and when the relative propagation loss for said particular radio base station is not lower than the connection threshold level.

37. A mobile station as claimed in claim 35, wherein said soft handoff radio base station selection unit further comprises disconnecting means, when the determined result indicates that a specific radio base station is connected to said mobile station and when the relative propagation loss for said specific radio base station is higher than the disconnection threshold level, disconnecting said mobile station from said specific radio base station.

38. A mobile station as claimed in claim 37, wherein the hysteresis margin being given by the function of the variation rate as an argument, the faster the variation rate being, the larger the hysteresis margin being.

39. A mobile station as claimed in claim 37, wherein said soft handoff radio base station selection unit further comprises means for maintaining a connection condition for said specific radio base station when said determining result indicates that said specific radio base station is connected to said mobile station and when the relative propagation loss for said specific radio base station is not higher than the disconnection threshold level.

40. A mobile station as claimed in claim 39, wherein the hysteresis margin being given by the function of the variation rate as an argument, the faster the variation rate being, the larger the hysteresis margin being.

41. A mobile station for use in a code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to said mobile station, said mobile station comprising:

a propagation loss measurement unit for measuring a propagation loss from said mobile station to each of the radio base stations;

a moving speed detection unit for detecting a moving speed of said mobile station; and

a soft handoff radio base station selection unit, connected to said propagation loss measurement unit and said moving speed detection unit, for determining the radio base stations to be connected or to be disconnected on the basis of the propagation loss with reference to a connection threshold level which is given by a function of the moving speed, said soft handoff radio base station selection unit selecting the radio base stations to be connected so as to become more by increasing the connection threshold level when the moving speed is fast, said soft handoff radio base station selection unit selecting the radio base stations to be connected so as to become less by decreasing the connection threshold level when the moving speed is slow,

thereby ensuring connection of the radio base station having a minimum propagation loss.

42. A mobile station for use in a code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to said mobile station, said mobile station comprising:

a propagation loss measurement unit for measuring a propagation loss from said mobile station to each of the radio base stations;

a moving speed detection unit for detecting a moving speed of said mobile station; and

a soft handoff radio base station selection unit, connected to said propagation loss measurement unit and said moving speed detection unit, for determining the radio base stations to be connected or to be disconnected on the basis of the propagation loss with reference to a connection threshold level and a disconnection threshold level which is higher than the connection, threshold level by a hysteresis margin,

wherein said soft handoff radio base station selection unit increases the hysteresis margin with the connection threshold level increased when the moving speed is fast, increasing radio base stations simultaneously connected to said mobile station, the connection threshold level being given by a function of the moving speed, and

wherein said soft handoff radio base station selection unit decreases the hysteresis margin with the connection threshold level decreased when the moving speed is slow, decreasing radio base stations simultaneously connected to said mobile station,

thereby ensuring connection of the radio base station having a minimum propagation loss.

43. A mobile station for use in a code division multiple access (CDMA) mobile radio communication system in which several radio base stations are simultaneously connected to said mobile station, said mobile station comprising:

a propagation loss measurement unit for measuring a propagation loss from said mobile station to each of the radio base stations;

a moving speed detection unit for detecting a moving speed of said mobile station; and

a soft handoff radio base station selection unit, connected to said propagation loss measurement unit and said moving speed detection unit, for determining the radio base stations to be connected or to be disconnected on the basis of the propagation loss with reference to a connection threshold level and a disconnection threshold level which is higher than the connection threshold level by a hysteresis margin;

said soft handoff radio base station selection unit comprising;

means for determining relative propagation losses for said radio base stations on the basis of a minimum propagation loss for said radio base stations;

determining means for determining whether or not said mobile station is connected to each radio base station to produce a determined result indicative of connection or disconnection for radio base station; and

connection starting means, when the determined result indicates that a particular radio base station is not connected to said mobile station and when the relative propagation loss for said particular radio base station is lower than the connection threshold level which is given by a function of the moving speed such that an increase in the moving speed causes the connection threshold level to increase, for starting connection of said mobile station of said particular radio base station,

thereby ensuring connection of the radio base station having the minimum propagation loss.

44. A mobile station as claimed in claim 43, wherein said soft handoff radio base station selection unit further comprises means for maintaining a disconnection condition for said particular radio base station when the determined result indicates that said particular radio base station is not connected to said mobile station and when the relative propagation loss for said particular radio base station is not lower than the connection threshold level.

45. A mobile station as claimed in claim 43, wherein said soft handoff radio base station selection unit further comprises disconnecting means, when the determined result indicates that a specific radio base station is connected to said mobile station and when the relative propagation loss for said specific radio base station is higher than the disconnection threshold level, disconnecting said mobile station from said specific radio base station.

46. A mobile station as claimed in claim 45, wherein the hysteresis margin being given by the function of the moving speed as an argument, the faster the moving speed being, the larger the hysteresis margin being.

47. A mobile station as claimed in claim 45, wherein said soft handoff radio base station selection unit further comprises means for maintaining a connection condition for said specific radio base station when said determining result indicates that said specific radio base station is connected to said mobile station and when the relative propagation loss for said specific radio base station is not higher than the disconnection threshold level.

48. A mobile station as claimed in claim 47, wherein the hysteresis margin being given by the function of the moving speed as an argument, the faster the moving speed being, the larger the hysteresis margin being.