Distribution of cell-common downlink signals in a hierarchical heterogeneous cell deployment

• US 9,300,450 B2
• Filed: 11/02/2011
• Issued: 03/29/2016
• Est. Priority Date: 02/09/2011
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Jngren, George, Lindbom, Lars, Parkvall, Stefan
• Primary Examiner(s): LY, ANH VU H
• Application Number:
  US13/389,501
• Publication Number:
  US 20120201164A1
• Time in Patent Office: 1,609 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: H04L 1/1812 Hybrid protocols; Hybrid automatic repeat request [HARQ]
• CPC Class Codes: H04L 25/03898 codebook-based design selection of codebook or precoding matrix for MIMO diversity systems H04B7/0456
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04W 16/32 Hierarchical cell structures
• CPC Class Codes: H04W 72/23 in the downlink direction of a wireless link, i.e. towards a terminal
• CPC Class Codes: H04W 88/06 adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A high-power point (110) and one or more low-power points (120) transmit signals that are associated with the same cell-identifier in a heterogeneous cell deployment. The coverage areas corresponding to the low-power points (120) fall at least partly within the coverage area for the high-power point (110), so that mobile stations (130) within range of a low-power point are also within range of the high-power point (110), from a downlink perspective. The same CRS signals are transmitted by both the high-power (macro) point (110) and some or all of the low-power (pico) points (120). At the same time, the network transmits CRS-based PDSCH for a particular UE on both the high-power point (110) as well as on some or all of the low-power points (120). In some embodiments only a subset of the points, e.g., those points that the UE hears sufficiently well, participate in the PDSCH transmission using CRS for channel estimation.

Claims

1. A method for transmitting data to a mobile station, the method comprising

transmitting cell-specific reference symbol (CRS) signals from a primary, high-power, transmitting node having a first coverage area;

transmitting the same CRS signals from each of two or more secondary, low-power, transmitting nodes, each of the secondary transmitting nodes having a coverage area that is within or substantially within the first coverage area;

simultaneously transmitting a physical downlink data channel to a mobile station from the primary, high-power, transmitting node and from at least one of but fewer than all of the two or more secondary, low-power, transmitting nodes, wherein said at least one but fewer than all of the two or more secondary, low-power, transmitting nodes is selected based on a determination of whether the physical downlink data channel transmissions from each secondary transmitting node could be received by the mobile station with adequate signal strength; and

monitoring traffic load at each of said secondary transmitting nodes; and

selectively powering on and powering off transmissions of the CRS signals at each secondary transmitting node, based on the corresponding traffic load.

2. The method of claim 1, wherein said determination is made by measuring uplink transmissions from the mobile station at one or more of the secondary transmitting nodes, or by monitoring channel-state-information feedback from the mobile station, or both.

3. The method of claim 1, wherein the CRS signals comprises a series of CRS symbol transmissions, and wherein selectively powering on and powering off transmissions of the CRS signals at each secondary transmitting node comprises ramping up and ramping down, respectively, the power level of CRS signal transmissions over a plurality of CRS symbol transmissions.

4. The method of claim 1, further comprising transmitting a same synchronization channel from all of said secondary transmitting nodes.

5. A system of transmitting nodes in a wireless network, the system comprising:

a primary, high-power, transmitting node configured to transmit cell-specific reference symbol (CRS) signals over a first coverage area, and;

two or more secondary, low-power, transmitting nodes, each configured to transmit the same CRS signals over a coverage area that is within or substantially within the first coverage area;

wherein said primary transmitting node and at least one of but fewer than all of said two or more secondary transmitting nodes are configured to simultaneously transmit a physical downlink data channel to a first mobile station;

wherein the system further comprises a control element configured to select said at least one but fewer than all of the two or more secondary transmitting nodes for transmitting the physical downlink data channel to the mobile station, based on whether physical downlink data channel transmissions from each secondary transmitting node could be received by the mobile station with adequate signal strength, to monitor traffic load at each of the secondary transmitting nodes, and to selectively cause each secondary transmitting node to power on and power off transmissions of the CRS signals, based on the corresponding traffic load.

6. The system of claim 5, wherein the control element is configured to select said at least one but fewer than all of the two or more secondary transmitting nodes based on measurements of uplink transmissions from the mobile station at one or more of the secondary transmitting nodes, or based on monitoring of channel-state-information feedback from the mobile station, or both.

7. The system of claim 5, wherein each of the secondary transmitting nodes is configured to power on and power off transmissions of the CRS signal by ramping up and ramping down, respectively, the power level of CRS signal transmissions over a time interval selected so that the change in CRS power level is slower than channel variations due to fading.

8. The system of claim 5, wherein all of said two or more secondary transmitting nodes are configured to transmit a same synchronization signal.

9. A control unit for use in a wireless network having a primary, high-power, transmitting node with a first coverage area and a plurality of secondary, low-power, transmitting nodes, each having a coverage area that is within or substantially within the first coverage area, the control unit comprising:

a network communication circuit configured to transmit and receive control information to and from said secondary transmitting nodes; and

a processing circuit configured to configure said primary transmitting node to transmit cell-specific reference symbol (CRS) signals over the first coverage area;

wherein the processing circuit is further configured to;

configure two or more of said secondary transmitting nodes to transmit the same CRS signals;

configure said primary transmitting node and at least one of but fewer than all of said two or more secondary transmitting nodes to simultaneously transmit a physical downlink data channel to a mobile station, wherein the processing circuit is further configured to select said at least one but fewer than all of said two or more secondary transmitting nodes based on a determination of whether physical downlink data channel transmissions from each secondary transmitting node could be received by the mobile station with adequate signal strength;

monitor traffic load at each of the secondary transmitting nodes; and

selectively configure each of the secondary transmitting nodes to power on and power off transmissions of the CRS signals, based on the corresponding traffic load.

10. The control unit of claim 9, wherein the processing circuit is configured to configure all of said secondary transmitting nodes in the first coverage area to transmit the same CRS signals.

11. The control unit of claim 9, wherein the processing circuit is configured to select said at least one but fewer than all of said two or more secondary transmitting nodes based on measurements of uplink transmissions from the mobile station at one or more of the secondary transmitting nodes, or based on monitoring channel-state-information feedback from the mobile station, or both.

12. The control unit of claim 9, wherein the control unit is part of the primary transmitting node.

13. The control unit of claim 9, wherein the control unit is part of one of the secondary transmitting nodes, and wherein the network communication circuit is further configured to transmit and receive control information to and from the primary transmitting node.