Cell selection

• US 20030083069A1
• Filed: 07/31/2002
• Published: 05/01/2003
• Est. Priority Date: 08/16/2001
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Vadgama, Sunil Keshavji
• Granted Patent: US 7,277,709 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 36/22 for handling the traffic
• CPC Class Codes: H04W 36/302 due to low signal strength

Abstract

Cell selection techniques for use in cellular communications systems are disclosed. A decision as to whether to use a cell for data transmission is made in dependence on a measure of a congestion level in the cell. The decision may either be part of a cell selection decision, or used to override a cell selection decision. The techniques may be used in fast cell site selection.

Claims

1. A cellular communications system for carrying out a site selection diversity method, the system comprising:

a user equipment comprising a processor operable periodically to select a cell for data transmission from a plurality of cells, and a transmitter operable to transmit a result of the selection to a base station; and

a plurality of base stations, each of which comprises a receiver operable to receive a result of a selection, a transmitter operable to transmit data to the user equipment, and a controller operable to determine whether or not the base station is a selected base station and to control the transmission of data to the mobile unit in dependence on whether or not it is determined that the base station is a selected base station;

wherein the processor in the user equipment is operable to select a cell for data transmission based on measures of congestion levels in the cells.

2. A system according to claim 1 wherein the processor in the user equipment is operable to select a cell for data transmission based additionally on measures of signal qualities in the cells.

3. A system according to claim 2 wherein the processor is operable to select a cell which has the lowest congestion level when the difference in measures of signal qualities between two cells is below a certain threshold.

4. A system according to claim 1, wherein each base station comprises a measurement unit operable to measure congestion levels and the transmitter is operable to transmit measures of congestion levels to the user equipment.

5. A system according to claim 4 wherein the measurement unit is operable to determine an amount of data which is to be transmitted by the base station over a predetermined time period.

6. A system according to claim 4 wherein the measurement unit is operable to measure congestion levels based on the occupancy of a buffer containing data to be transmitted.

7. A system according to claim 4, wherein the transmitter is operable to transmit the measures of congestion levels in a broadcast channel.

8. A system according to claim 1 wherein the user equipment comprises a measurement unit operable to measure congestion levels.

9. A system according to claim 8 wherein the measurement unit is operable to measure congestion levels based on the usage of a shared transmission channel.

10. A system according to claim 1 wherein the controller in a base station is operable to control the transmission of data to the user equipment additionally in dependence on a quality of a signal containing the result of a selection which is received by the base station from the user equipment.

11. A system according to claim 1 wherein the processor in the user equipment is operable to select a base station based additionally on a command transmitted by a base station to the user equipment instructing the user equipment not to select that base station.

12. A system according to claim 1 wherein the processor in a user equipment is operable to select a base station based additionally on whether a signal is received by the user equipment from the selected base station within a certain time from the transmission of a result of a selection.

13. A system according to claim 1 wherein the processor in the user equipment is operable to select a base station based additionally on a priority of data which is to be transmitted.

14. A system according to claim 1 wherein the controller in a base station is arranged to control the transmission of data to the user equipment additionally in dependence on a priority of data to be transmitted.

15. A system according to claim 1 wherein the result of a selection comprises an identification number of the selected base station.

16. A system according to claim 1 wherein the user equipment is operable to select a cell for data transmission and to transmit a result of the selection at a rate of more than once per superframe, and the controller in a base station is arranged to determine whether or not the base station is a selected base station at a rate of more than once per superframe.

17. A system according to claim 1, the system being operable to perform fast cell site selection.

18. A base station which carries out a site selection diversity method in a cellular communications system, the base station comprising:

a measurement unit operable to measure a congestion level in a cell served by the base station;

a transmitter operable to transmit a measure of a congestion level to a user equipment;

a receiver operable to receive a result of a selection from the user equipment, the result of a selection indicating a base station to be used for data transmission; and

a controller operable to determine whether or not the base station is a selected base station, and to control transmission of data to the mobile unit in dependence on whether or not it is determined that the base station is a selected base station.

19. A user equipment which carries out a site selection diversity method in a cellular communications system, the user equipment comprising:

a measurement unit operable to measure congestion levels in a plurality of cells;

a processor operable to select a cell from the plurality of cells based on measures of congestion levels in the cells; and

a transmitter operable to transmit a result of the selection to a base station.

20. A base station which carries out a site selection diversity method in a cellular communications system, the base station comprising:

a measurement unit operable to produce a measure of a congestion level in a cell served by the base station;

a receiver operable to receive a result of a selection from a user equipment, the result of a selection indicating a base station to be used for data transmission;

a transmitter operable to transmit data to a user equipment; and

a controller operable to determine whether or not the base station is a selected base station, and to control the transmission of data to the user equipment in dependence on whether or not it is determined that the base station is a selected base station and in dependence on the measure of a congestion level in the cell.

21. A base station according to claim 20, wherein the controller is operable to suppress data transmission to the user equipment if the measure of a congestion level is above a certain threshold.

22. A base station according to claim 20 wherein the receiver is operable to receive an indication of the degree of marginality of the result of a selection, and the controller is operable to control the transmission of data to the user equipment additionally in dependence on the indication of the degree of marginality.

23. A base station according to claim 20 wherein the controller is operable to control the transmission of data to the user equipment additionally in dependence on a quality of a signal containing the result of the selection which is received by a base station from the user equipment.

24. A base station according to claim 20 wherein the controller is operable to control the transmission of data to the user equipment additionally in dependence on a priority of data to be transmitted.

25. A base station according to claim 20 wherein the transmitter is operable to transmit a command instructing a user equipment not to select that base station.

26. A cellular communications system for carrying out a site selection diversity method, the system comprising a base station and a user equipment, the base station comprising:

a measurement unit operable to produce a measure of a congestion level in a cell served by the base station;

a receiver operable to receive a result of a selection from the user equipment, the result of a selection indicating a base station to be used for data transmission;

a transmitter operable to transmit data to the user equipment; and

a controller operable to determine whether or not the base station is a selected base station, and to control the transmission of data to the user equipment in dependence on whether or not it is determined that the base station is a selected base station and in dependence on the measure of a congestion level in the cell;

and the user equipment comprising;

a receiver operable to receive transmission signals from a plurality of base stations;

a processor operable to produce measures of qualities of signals received from the base stations, and to select a cell based on measures of signal qualities; and

a transmitter operable to transmit a result of a cell selection decision to the base stations.

27. A system according to claim 26 wherein the processor in the user equipment is operable to select a base station based additionally on whether a signal is received by the user equipment from the selected base station within a certain time from the transmission of a result of a selection.

28. A system according to claim 26 wherein the processor in the user equipment is operable to determine a degree of marginality of a cell selection decision, and the transmitter in the user equipment is operable to transmit an indication of the degree of marginality to the base station.

29. A cellular communications system for carrying out a site selection diversity method, the system comprising:

a user equipment comprising means for periodically selecting a cell for data transmission from a plurality of cells, and means for transmitting a result of the selection to a base station; and

a plurality of base stations, each of which comprises means for receiving a result of a selection, means for determining whether or not the base station is a selected base station, and means for controlling transmission of data to the mobile unit in dependence on whether or not it is determined that the base station is a selected base station;

wherein the selecting means in the user equipment is arranged to select a cell for data transmission based on measures of congestion levels in the cells.

30. A base station for carrying out a site selection diversity method in a cellular communications system, the base station comprising:

means for measuring a congestion level in a cell served by the base station;

means for transmitting a measure of a congestion level to a user equipment;

means for receiving a result of a selection from the user equipment, the result of a selection indicating a base station to be used for data transmission;

means for determining whether or not the base station is a selected base station; and

means for controlling transmission of data to the mobile unit in dependence on whether or not it is determined that the base station is a selected base station.

31. A user equipment for carrying out a site selection diversity method in a cellular communications system, the user equipment comprising:

means for measuring congestion levels in a plurality of cells;

means for selecting a cell from the plurality of cells based on measures of congestion levels in the cells; and

means for transmitting a result of the selection to a base station.

32. A base station for carrying out a site selection diversity method in a cellular communications system, the base station comprising:

means for producing a measure of a congestion level in a cell served by the base station;

means for receiving a result of a selection from a user equipment, the result of a selection indicating a base station to be used for data transmission;

means for determining whether or not the base station is a selected base station; and

means for controlling transmission of data to the user equipment in dependence on whether or not it is determined that the base station is a selected base station and in dependence on the measure of a congestion level in the cell.

33. A site selection diversity method for use in a cellular communications network, the method comprising the steps of:

in a user equipment, periodically selecting a cell for data transmission from a plurality of cells and transmitting a result of the selection to a base station; and

in a base station, receiving a result of a selection, determining whether or not the base station is a selected base station, and controlling transmission of data to the mobile unit in dependence on whether or not it is determined that the base station is a selected base station;

wherein a cell for data transmission is selected based on measures of congestion levels in the cells.

34. A site selection diversity method for use in a base station of a cellular communications network, the method comprising the steps of, in the base station:

producing a measure of a congestion level in a cell served by the base station;

receiving a result of a selection from a user equipment, the result of a selection indicating a base station to be used for data transmission;

determining whether or not the base station is a selected base station; and

controlling transmission of data to the mobile unit in dependence on whether or not it is determined that the base station is a selected base station.

35. A site selection diversity method for use in a user equipment of a cellular communications network, the method comprising the steps of, in the user equipment:

measuring congestion levels in a plurality of cells;

selecting a cell from the plurality of cells based on measures of congestion levels in the cells; and

transmitting a result of the selection to a base station.

36. A site selection diversity method for use in a cellular communications network, the method comprising the steps of:

producing a measure of a congestion level in a cell served by the base station;

receiving a result of a selection from a user equipment, the result of a selection indicating a base station to be used for data transmission;

determining whether or not the base station is a selected base station; and

controlling transmission of data to the user equipment in dependence on whether or not it is determined that the base station is a selected base station and in dependence on the measure of a congestion level in the cell.