Point-dependent resource symbol configuration in a wireless cell
A high-power point and one or more low-power points transmit signals associated with the same cell-identifier in a heterogeneous cell deployment. Coverage areas corresponding to the low-power points fall at least partly within the coverage area for the high-power point, so that mobile stations within range of a low-power point are also within range of the high-power point. Channel-state-information reference symbols, CSI-RS, are transmitted using different CSI-RS resources on different transmission points within the cell, while configuration of CSI-RS measurement resources is conducted on a UE-specific basis. The choice of measurement resources to be used is determined by the network, based on the properties of the channels from the transmission points to the UE. As the UE moves around within the cell, the network tracks the channel properties and reconfigures the CSI-RS resources measured by the UE, to correspond to the resource of the closest transmission point or points.
1. A method in a network node for collecting channel-state-information (CSI) feedback in a wireless network that comprises a plurality of geographically separated transmission points sharing a cell identifier, the method comprising:
receiving CSI feedback from a mobile station, based on measurements of first CSI reference symbols (CSI-RS) transmitted on a first CSI-RS resource from a first one of the transmission points;
detecting that the mobile station has approached a second one of the transmission points, differing from the first one of the transmission points;
reconfiguring the mobile station, in response to said detecting, by transmitting a reconfiguration message to the mobile station, to measure CSI-RS on a second CSI-RS resource transmitted from the second one of the transmission points; and
receiving CSI feedback from the mobile station, based on measurements of second CSI-RS transmitted on the second CSI-RS resource from the second one of the transmission points.
2. The method of claim 1 , wherein the transmission points include a primary, high-power transmission point, having a first coverage area, and one or more secondary, low-power, transmission points, each having a coverage area that is within or substantially within the first coverage area.
3. The method of claim 1 , wherein detecting that the mobile station has approached a second one of the transmission points comprises measuring an uplink transmission from the mobile station at the second one of the transmission points and assessing channel strength based on said measuring.
4. The method of claim 3 , wherein the measured uplink transmission comprises at least one of a Sounding Reference Signal (SRS), a Physical Uplink Control Channel (PUCCH) transmission, and a Physical Uplink Shared Channel (PUSCH) transmission.
5. The method of claim 1 , further comprising:
configuring the mobile station, by transmitting a configuration message to the mobile station, to also measure CSI-RS on a third CSI-RS resource transmitted from a third one of the transmission points; and
transmitting third CSI-RS on the third CSI-RS resource, from the third one of the transmission points, simultaneously with said transmitting of second CSI-RS from the second one of the transmission points;
wherein the CSI feedback received from the mobile station is further based on measurements of the third CSI-RS.
6. The method of claim 1 , further comprising:
transmitting CSI-RS from each of the transmission points, using at least one distinct CSI-RS resource for each of the transmission points;
selecting a subset of the CSI-RS resources for CSI feedback from a mobile station, based on channel strength measurements corresponding to the mobile station and the transmission points; and
configuring the mobile station, by transmitting a configuration message to the mobile station, to provide CSI feedback for the selected CSI-RS resources.
7. The method of claim 6 , wherein selecting the subset of the CSI-RS resources is based on measurements of an uplink transmission at one or more of the transmission points.
8. The method of claim 7 , wherein the measured uplink transmission comprises at least one of a Sounding Reference Signal (SRS), a Physical Uplink Control Channel (PUCCH) transmission, and a Physical Uplink Shared Channel (PUSCH) transmission.
9. The method of claim 6 , wherein selecting the subset of the CSI-RS resources is based on measurement data sent by the mobile station to the wireless network.
10. A control unit in a network node in a wireless network having a wireless network cell that comprises a plurality of geographically separated transmission points sharing a cell identifier, the control unit comprising:
a network communication circuit configured to transmit and receive control information to and from a plurality of transmission points; and
a processing circuit configured to:
receive channel state information (CSI) feedback from a mobile station, based on measurements of first CSI reference symbols (CSI-RS) transmitted on a first CSI-RS resource from a first one of the transmission points;
detect that the mobile station has approached a second one of the transmission points, differing from the first one of the transmission points;
reconfigure the mobile station, in response to said detecting, by sending a reconfiguration message to the mobile station, to measure CSI-RS on a second CSI-RS resource transmitted from the second one of the transmission points; and
receive CSI feedback from the mobile station, based on measurements of second CSI-RS transmitted on the second CSI-RS resource from the second one of the transmission points.
11. The control unit of claim 10 , wherein the processing circuit is configured to detect that the mobile station has approached a second one of the transmission points by using measurements of an uplink transmission from the mobile station made at the second one of the transmission points and assessing channel strengths based on said measurements.
12. The control unit of claim 11 , wherein the measured uplink transmission comprises at least one of a Sounding Reference Signal (SRS), a Physical Uplink Control Channel (PUCCH) transmission, and a Physical Uplink Shared Channel (PUSCH) transmission.
13. The control unit of claim 10 , wherein the processing circuit is further configured to:
configure the mobile station, by sending a configuration message to the mobile station, to also measure CSI-RS on a third CSI-RS resource transmitted from a third one of the transmission points; and
control the third one of the transmission points to transmit third CSI-RS on the third CSI-RS resource, simultaneously with the transmitting of second CSI-RS from the second one of the transmission points;
wherein the CSI feedback received from the mobile station is further based on measurements of the third CSI-RS.
14. The control unit of claim 10 , wherein the processing circuit is further configured to:
control all of the transmission points to transmit CSI-RS, wherein at least one distinct CSI-RS resource is used by each of the transmission points;
select a subset of the CSI-RS resources for CSI feedback from a mobile station, based on channel strength measurements corresponding to the mobile station and the transmission points; and
configure the mobile station, by sending a configuration message to the mobile station, to provide CSI feedback for the selected CSI-RS resources.
15. The control unit of claim 14 , wherein the processing circuit is configured to select the subset of the CSI-RS resources based on measurements of an uplink transmission at one or more of the transmission points.
16. The control unit of claim 15 , wherein the measured uplink transmission comprises at least one of a Sounding Reference Signal (SRS), a Physical Uplink Control Channel (PUCCH) transmission, and a Physical Uplink Shared Channel (PUSCH) transmission.
17. The control unit of claim 14 , wherein the processing circuit is configured to select the subset of the CSI-RS resources based on measurement data sent by the mobile station to one or more of the transmission points.
18. The control unit of claim 10 , wherein the control unit is part of a primary transmission node corresponding to the first one of the transmission points.
19. The control unit of claim 10 , wherein the control unit is part of a secondary transmission node corresponding to the second one of the transmission points, and wherein the network communication circuit is further configured to transmit and receive control information to and from a primary transmission node corresponding to the first one of the transmission points.