Methods and apparatus in a wireless communication system
The present invention relates to methods and apparatus in a RBS and a UE for reference signal (RS) measurements in an OFDM system, that enable having a configurable RS transmission bandwidth which is smaller than the system bandwidth. This allows for better interference coordination of RS, which in turn improves the UE RS measurements used for different services such as positioning. The RBS retrieves the RS transmission bandwidth, determines a RS measurement bandwidth based on this RS transmission bandwidth, and transmits the determined bandwidth to the UE. The UE receives the RS measurement bandwidth and measures the RS in a bandwidth determined based on the received measurement bandwidth and the UE capability.
1. A method implemented by a controlling network node for reference signal, RS, measurements in an OFDM system, wherein the OFDM system comprises a radio base station configured to transmit to a user equipment over a defined system bandwidth, the method comprising:
retrieving a RS transmission bandwidth for a cell, said RS transmission bandwidth being smaller than the system bandwidth,
determining a RS measurement bandwidth based on the RS transmission bandwidth, and
transmitting the RS measurement bandwidth to a user equipment when said RS measurement bandwidth is smaller than the RS transmission bandwidth, in order for the user equipment to measure the RS of the cell.
2. The method of claim 1 , wherein the RS transmission bandwidth is statically configured in the controlling network node.
3. The method of claim 1 , wherein the RS transmission bandwidth is dynamically configured based on a first algorithm in the controlling network node.
4. The method of claim 1 , wherein the RS transmission bandwidth is dynamically configured based on coordination with a neighbouring radio base station.
5. The method of claim 1 , wherein the controlling network node is a serving mobile location center.
6. The method of claim 1 , wherein the RS transmission bandwidth corresponds to a contiguous part of the system bandwidth.
7. The method of claim 1 , wherein the RS measurement bandwidth is cell specific.
8. The method of claim 1 , wherein the RS measurement bandwidth is user equipment specific.
9. The method of claim 1 , wherein transmitting the RS measurement bandwidth comprises including the RS measurement bandwidth in assistance data transmitted to the user equipment.
10. The method of claim 1 , further comprising suppressing data transmission in a sub frame over a first low interference bandwidth for the cell serving the user equipment, said first low interference bandwidth being smaller than the system bandwidth, and wherein determining a RS measurement bandwidth comprises determining a RS measurement bandwidth also based on said first low interference bandwidth and on a second low interference bandwidth of a neighbouring cell.
11. The method of claim 10 , wherein said first and second low interference bandwidth are statically configured in the controlling network node.
12. The method of claim 10 , wherein said first and second low interference bandwidth are dynamically configured based on a second algorithm in the controlling network node.
13. The method of claim 10 , wherein said first and second low interference bandwidth are dynamically configured based on coordination with a neighbouring radio base station.
14. The method of claim 10 , wherein said first and second low interference bandwidth correspond to contiguous parts of the system bandwidth.
15. The method of claim 1 , wherein determining a RS measurement bandwidth comprises determining a RS measurement bandwidth also based on interference statistics.
16. The method of claim 1 , wherein the RS measurements are used for positioning in an LTE system.
17. A controlling network node for an OFDM system, wherein the OFDM system comprises a radio base station that is configured to transmit to a user equipment over a defined system bandwidth, the controlling network node comprising a processor and a memory, said memory containing instructions executable by said processor whereby said controlling network node is configured to:
retrieve a RS transmission bandwidth for a cell, said RS transmission bandwidth being smaller than the system bandwidth,
determine a RS measurement bandwidth for the cell based on the RS transmission bandwidth, and
transmit the RS measurement bandwidth to a user equipment when said RS measurement bandwidth is smaller than the RS transmission bandwidth, in order for the user equipment to measure the RS of the cell.
18. The controlling network node of claim 17 , wherein the RS transmission bandwidth is statically configured in the controlling network node.
19. The controlling network node of claim 17 , wherein the RS transmission bandwidth is dynamically configured based on a first algorithm in the controlling network node.
20. The controlling network node of claim 17 , wherein the RS transmission bandwidth is dynamically configured based on coordination with a neighbouring radio base station.
21. The controlling network node of claim 17 , wherein the controlling network node is a serving mobile location center.
22. The controlling network node of claim 17 , wherein the RS measurement bandwidth is cell specific.
23. The controlling network node of claim 17 , wherein the RS measurement bandwidth is user equipment specific.
24. The controlling network node of claim 17 , wherein the RS transmission bandwidth corresponds to a contiguous part of the system bandwidth.
25. The controlling network node of claim 17 , wherein the controlling network node is configured to transmit the RS measurement bandwidth by including the RS measurement bandwidth in assistance data transmitted to the user equipment.
26. The controlling network node of claim 17 , wherein the controlling network node is configured to suppress data transmission in a sub frame over a first low interference bandwidth for the cell serving the user equipment, said first low interference bandwidth being smaller than the system bandwidth, and wherein the controlling network node is further configured to determine the RS measurement bandwidth also based on said first low interference bandwidth and on a second low interference bandwidth of a neighbouring cell.
27. The controlling network node of claim 26 , wherein said first and second low interference bandwidth are statically configured in the controlling network node.
28. The controlling network node of claim 26 , wherein said first and second low interference bandwidth are dynamically configured based on a second algorithm in the controlling network node.
29. The controlling network node of claim 26 , wherein said first and second low interference bandwidth are dynamically configured based on coordination with a neighbouring radio base station.
30. The controlling network node of claim 26 , wherein said first and second low interference bandwidth correspond to contiguous parts of the system bandwidth.
31. The controlling network node of claim 17 , wherein the controlling network node is further configured to determine the RS measurement bandwidth also based on interference statistics.
32. The controlling network node of claim 17 , wherein the RS measurements are used for positioning in an LTE system.