IN A RADIO NETWORK ENVIRONMENT, REDUCING INTERFERENCE AMONG OVERLAPPING CELLS

• US 20110034174A1
• Filed: 08/04/2009
• Published: 02/10/2011
• Est. Priority Date: 08/04/2009
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Xu, Ning, Yang, Jin
• Granted Patent: US 8,160,591 B2
• Time in Patent Office: Days
• US Class Current: 455/447
• CPC Class Codes: H04W 16/02 Resource partitioning among network components, e.g. reuse partitioning
• CPC Class Codes: H04W 72/0453 Resources in frequency domain, e.g. a carrier in FDMA
• CPC Class Codes: H04W 72/27 between access points
• CPC Class Codes: H04W 72/541 using the level of interference
• CPC Class Codes: H04W 84/045 using private Base Stations, e.g. femto Base Stations, home Node B

Abstract

Disclosed is a method for a femtocell to reduce interference with an overlapping macrocell. The femtocell determines soft-frequency-reuse (“SFR”) information of the macrocell. From that information, the femtocell determines which frequency sub-channels are assigned by the macrocell for its cell-center users and which frequency sub-channels are assigned for cell-edge users. (Cell-edge users are given a higher transmission power profile in order to overcome potential interference with neighboring macrocells.) Then, the femtocell selects from the cell-center user frequency sub-channels for transmission to the femtocell'"'"'s users. By transmitting on the cell-center user frequency sub-channels, the femtocell reduces interference with the overlapping macrocell. The femtocell continues to update its knowledge of the macrocell'"'"'s SFR information and re-assigns frequency sub-channels as the SFR changes. If the macrocell detects that one of its cell-center users is “close enough” to the femtocell, then the macrocell re-assigns the cell-center user as a cell-edge user to overcome interference.

Claims

1. A method for a femtocell to reduce signal interference with a macrocell that overlaps the femtocell, the method comprising:

obtaining, by the femtocell, soft-frequency-reuse (SFR) information of the overlapping macrocell;

analyzing, by the femtocell, the obtained SFR information to distinguish between frequency sub-channels to be assigned to cell-center users of the macrocell and frequency sub-channels to be assigned to cell-edge users of the macrocell;

giving, by the femtocell, high schedule priority for femtocell-downlink transmissions to frequency sub-channels to be assigned to cell-center users of the macrocell; and

transmitting, by the femtocell to a user of the femtocell, on a high-schedule-priority frequency sub-channel.

2. The method of claim 1 wherein the SFR information is selected from the group consisting of:

SFR pattern and power profile.

3. The method of claim 1 wherein obtaining SFR information comprises obtaining the SFR information via backhaul communications.

4. The method of claim 3 wherein the backhaul communications comprise an X2 interface supporting Relative-Narrowband-TX-Power-Indicator messaging.

5. The method of claim 1 wherein obtaining SFR information comprises obtaining the SFR information via measurement of a downlink reference signal of the macrocell.

6. The method of claim 1 further comprising:

giving, by the femtocell, low schedule priority for femtocell-downlink transmissions to frequency sub-channels to be assigned to cell-edge users of the macrocell; and

transmitting, by the femtocell to a user of the femtocell, on a low-schedule-priority frequency sub-channel.

7. The method of claim 1 further comprising:

detecting, by the femtocell, a change in the SFR information of the overlapping macrocell; and

repeating, by the femtocell, the obtaining, analyzing, giving, and transmitting steps.

8. The method of claim 1 further comprising:

periodically performing, by the femtocell, the obtaining step; and

if the SFR information of the overlapping macrocell has changed, then repeating, by the femtocell, the analyzing, giving, and transmitting steps.

9. A controller for controlling a femtocell, the controller comprising:

a transceiver; and

a processor operatively connected to the transceiver and configured for obtaining soft-frequency-reuse (SFR) information of a macrocell overlapping the femtocell, for analyzing the obtained SFR information to distinguish between frequency sub-channels to be assigned to cell-center users of the macrocell and frequency sub-channels to be assigned to cell-edge users of the macrocell, for giving high schedule priority for femtocell-downlink transmissions to frequency sub-channels to be assigned to cell-center users of the macrocell, and for transmitting, via the transceiver, to a user of the femtocell on a high-schedule-priority frequency sub-channel.

10. The controller of claim 9 further comprising:

an X2 interface, operatively connected to the processor and configured for supporting Relative-Narrowband-TX-Power-Indicator messaging.

11. The controller of claim 9 wherein the processor is further configured for obtaining the SFR information via measurement of a downlink reference signal of the macrocell received via the transceiver.

12. A method for a macrocell to reduce signal interference with a femtocell that overlaps the macrocell, the method comprising:

assigning, by the macrocell, a first set of frequency sub-channels to be used by cell-center users of the macrocell;

assigning, by the macrocell, a second set of frequency sub-channels to be used by cell-edge users of the macrocell;

detecting, by the macrocell, that a cell-center user of the macrocell is close enough to the femtocell; and

scheduling, by the macrocell, the cell-center user as a cell-edge user.

13. The method of claim 12 wherein detecting that the cell-center user of the macrocell is close enough to the femtocell comprises:

receiving, by the macrocell from the cell-center user, a neighbor list, the neighbor list comprising the femtocell; and

receiving, by the macrocell from the cell-center user, an indication that a strength of a signal received from the femtocell is above a threshold.

14. A method for a macrocell to reduce signal interference with a femtocell that overlaps the macrocell, the method comprising:

assigning, by the macrocell, a first set of frequency sub-channels to be used by cell-center users of the macrocell;

assigning, by the macrocell, a second set of frequency sub-channels to be used by cell-edge users of the macrocell;

detecting, by the macrocell, that a cell-center user of the macrocell is close enough to the femtocell; and

assigning, by the macrocell, higher schedule priority for the cell-center user of the macrocell that is close enough to the femtocell to a subset of the first set of frequency sub-channels than to frequency sub-channels in the first set but not in the subset.

15. The method of claim 14 wherein detecting that the cell-center user of the macrocell is close enough to the femtocell comprises:

receiving, by the macrocell from the cell-center user, a neighbor list, the neighbor list comprising the femtocell; and

receiving, by the macrocell from the cell-center user, an indication that a strength of a signal received from the femtocell is above a threshold.

16. The method of claim 14 further comprising:

setting, by the macrocell, a staged power profile wherein a power assigned for the subset of the first set of frequency sub-channels is higher than a power assigned for frequency sub-channels in the first set but not in the subset.

17. A controller for controlling a macrocell, the controller comprising:

a transceiver; and

a processor operatively connected to the transceiver and configured for assigning a first set of frequency sub-channels to be used by cell-center users of the macrocell, for assigning a second set of frequency sub-channels to be used by cell-edge users of the macrocell, for detecting that a cell-center user of the macrocell is close enough to the femtocell, and for scheduling the cell-center user as a cell-edge user.

18. The controller of claim 17 wherein the processor is further configured for receiving, via the transceiver from the cell-center user, a neighbor list, the neighbor list comprising the femtocell, and for receiving, via the transceiver from the cell-center user, an indication of a strength of a signal received from the femtocell.

19. A controller for controlling a macrocell, the controller comprising:

a transceiver; and

a processor operatively connected to the transceiver and configured for assigning a first set of frequency sub-channels to be used by cell-center users of the macrocell, for assigning a second set of frequency sub-channels to be used by cell-edge users of the macrocell, for detecting that a cell-center user of the macrocell is close enough to the femtocell, and for assigning higher schedule priority for the cell-center user of the macrocell that is close enough to the femtocell to a subset of the first set of frequency sub-channels than to frequency sub-channels in the first set but not in the subset.

20. The controller of claim 19 wherein the processor is further configured for receiving, via the transceiver from the cell-center user, a neighbor list, the neighbor list comprising the femtocell, and for receiving, via the transceiver from the cell-center user, an indication of a strength of a signal received from the femtocell.