Method and system in a mobile radio system

• US 20010001762A1
• Filed: 01/16/2001
• Published: 05/24/2001
• Est. Priority Date: 08/15/1997
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Olofsson, Hakan, Almgren, Magnus, Frodigh, Magnus
• Granted Patent: US 6,640,102 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04W 36/302 due to low signal strength

Abstract

The invention relates to a method of performing handover in a mobile radio system. The mobile radio system performs quality measurements on signals transmitted (300) between a mobile terminal and predetermined radio base stations. Handover is performed (301, 302, 303) when some of the measured signal strengths exceeds the signal strength for the radio base station to which the mobile terminal for the moment is set up, added to a handover value. The handover value is dependent on measured signal strengths and neighboring cell relation values. The neighboring cell relation values depend on a probability for handover to be performed from one radio base station to another radio base station in the mobile radio system.

Claims

1. A method of handover in a mobile radio system having radio base stations (RBS1, RBS2, . . .) with associated cells, and at least one mobile terminal (MS1), comprising the steps of:

measuring a quality measure (SS_C1, SS_C2, . . .) of radio signals transferred between at least some of the radio base stations (RBS1, RBS2, . . .) and the mobile terminal (MS1), performing handover of the mobile terminal (MS1) from a first radio base station (RBS1) to a second radio base station (RBS2),

characterized in that

said handover is performed utilizing a handover value depending on said measured quality measure (SS_C1, SS_C2. . .) and relation values (q₁₁, q₁₂, . . .) between said cells, said relation values being essentially independent of said measuring of quality measures.

2. Method according to

claim 1

, characterized in that said relation values (q11, q12, . . .) are dependent on the number of times handover has been performed between the respective radio base stations during a predetermined period of time.

3. Method according to

claim 1

or

2

, characterized in that said relation values (q11, q12, . . .) are dependent on a measured or calculated radio wave transmission condition in the cells, preferably the attenuation of radio waves between different points in the cells.

4. Method according to any of claims 1-3, characterized in that said relation values (q11, q12, . . .) are dependent on a geometric relationship between said cells, preferably a distance relationship between the respective radio base stations.

5. Method according to any of claims 1-4, characterized in that said quality measure is a signal strength measure.

6. Method according to any of claims 1-4, characterized in that said quality measure is a bit error ratio.

7. Method according to any of claims 1-4, characterized in that said quality measure is a signal/interference relation.

8. Method according to

claim 5

, characterized in that said handover value is decreasing function of measured signal strength (SS_C1, SS_C2, . . .).

9. Method according to any of claims 5 or 8, characterized in that said handover value is a non-increasing function of said relation values (q11, q12, . . .).

10. Method according to any of claims 5, 8 or 9, characterized in that said handover value depends on a sum of quotients $(\frac{{\mathrm{SS}}_{\mathrm{C3}}}{\mathrm{q32}},\dots$

),

where the numerator in the respective quotient is formed by said measured signal strenqth from a radio base station in question whose associated cell is a neighbouring cell to the cell of the first radio base station and where the denominator in the respective quotient is formed by the relation value between the second radio base station and the radio base station in question.

11. Method according to

claim 10

, characterized in that said handover value is formed by means of the following steps:

generating quotients between at least one measured signal strength (SS_C1, SS_C2, . . .) and each of a respective relation value (q1m, q2m, . . .)

transforming each quotient to a corresponding value within a defined first area by means of a first saturation function,

summing the transformed quotients whereby some is obtained,

generating a first standardized value by multiplying said sum by a predetermined factor;

transforming a first standardized value to said handover value within a defined second area by means of a second saturation function.

12. Method according to

claim 11

, characterized in that the defined area for said first saturation function is independent on which radio base station the mobile radio system that is the first radio base station.

13. Method according to

claim 11

, characterized in that the defined area for said first saturation function is dependent on which radio base station in the mobile radio system that is the first radio base station.

14. Method according to any of claims 11-13, characterized in that said first saturation function is a first tangent hyperbolicus function.

16. Method according to any of claims 11-15, characterized in that the defined area for said second saturation function is independent on which radio base station in the mobile radio system that is the first radio base station.

17. Method according to any of claims 11-15, characterized in that the defined area for said second saturation function is dependent on which radio base station in the mobile radio system is the first radio base station.

18. Method according to any of claims 11-17, characterized in that said saturation function is a second tangent hyperbolicus function.

15. Method according to any of claim I1-14, characterized in that said predetermined factor is inversely proportional to the number of generated quotients.

19. System for mobile radio, comprising radio base stations (RBS1, RBS2, . . .) having associated cells, and a mobile terminal (MS1), the system comprising

measurement means adapted to measure a quality measure (SS_C1, SS_C2, . . .) of radio signals transmitted between at least some of the radio base stations (RBS1, RBS2, . . .) and the mobile terminal (MS1),

handover means adapted to perform handover of the mobile terminal (MS1) from a first radio base station (RBS1) to a second radio base station (RBS2),

characterized by

storage means adapted to store relation values (q11, q12, . . .) between at least some of said cells,

calculating means adapted to form a handover value which is dependent on said measured quality measure and said relation values, and

said handover means being adapted to perform handover utilizing said handover value.

20. System according to

claim 19

, characterized in that said stored relation values are dependent on the number of times handover has been performed between the respective radio base stations during a predetermined period of time.

21. System according to

claim 19

or

20

, characterized in that said relation values are dependent on a measured or calculated radio wave transmitting condition within the cells, preferably the attenuation of radio signals between different points in the cells.

22. System according to any of claims 19-21, characterized in that said relation values are dependent on a geometric relation between said cells, preferably a distance relation between said radio base stations.

23. System according to any of claims 19-22, characterized in that said measurement means are adapted to measure a signal strength.

24. System according to any of claims 19-22, characterized in that said measurement means are adapted to measure a bit error ratio.

25. System according to any of claims 19-22, characterized in that said measurement means are adapted to measure a signal/interference relation.

26. System according to

claim 23

, characterized in that said calculating means are adapted to form said handover value as a non-decreasing function of said measured signal strengths.

27. System according to any of claims 23 or 26, characterized in that said calculating means are adapted to form said handover value as a non-increasing function of said relation values.

28. System according to any of claims 23, 26 or 27, characterized in that said calculating means are adapted to form said handover value utilizing a sum of quotients $(\frac{{\mathrm{SS}}_{\mathrm{C3}}}{\mathrm{q32}},\dots$

),

wherein the respective quotient is formed by said measured signal strength from a radio base station in question whose associated cell is a neighbouring cell to the cell of the first radio base station, and the relation value between the second radio base station and the radio base station in question.

29. System according to

claim 28

, characterized in that said calculating means are adapted to carry out the following steps:

generate quotients between at least one measured signal strength (SS_C1, SS_C2, . . .) and each of a respective relation value (q11, q12, . . .),

transform each quotients into a corresponding value within a defined first area by means of a first saturation function,

sum the transformed quotients to obtain a sum,

generate a first standardized value by multiplying said sum by a predetermined factor,

transform said first standardized value to said handover value within a defined second area by means of second saturation function.

30. System according to

claim 29

, characterized in that the defined area for said first saturation function is independent of which radio base station in the mobile radio system is a first radio base station.

31. System according to

claim 29

, characterized in that the defined area for said first saturation function is dependent on which radio base station in the mobile radio system is the first radio base station.

32. System according to any of claims 29-31, characterized in that said first saturation function is a first tangent hyperbolicus function.

33. System according to any of claims 29-32, characterized in that said predetermined factor is inversely proportional to the number of generated quotients.

34. System according to any of claims 29-33, characterized in that the defined area for said second saturation function is independent of which radio base station in the mobile radio system is the first radio base station.

35. System according to any of claims 29-33, characterized in that the defined area for said second saturation function is dependent of which radio base station in the mobile radio system is the first radio base station.

36. System according to any of claims 29-35, characterized in that said second saturation function is a second tangent hyperbolic function.

37. Mobile terminal included in a system according to any of claims 19-36, characterized in that it comprises said measurement means.

38. Mobile terminal according to

claim 37

, characterized in that it comprises said calculating means.

39. Radio base station included in a system according to any of claims 19-36, characterized in that it comprises said calculating means.

40. Radio base station included in a system according to any of claims 19-36, characterized in that it comprises said storage means.