Methods For Synchronizing Macro Cell And Small Cell Systems

• US 20120236977A1
• Filed: 03/18/2011
• Published: 09/20/2012
• Est. Priority Date: 03/18/2011
• Status: Active Grant

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Alcatel-Lucent USA, Inc. (Nokia Corporation)
• Inventors: Zou, Jialin, Vasudevan, Subramanian
• Granted Patent: US 9,357,514 B2
• Time in Patent Office: Days
• US Class Current: 375/354
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 7/042 Detectors therefor, e.g. correlators, state machines digital correlators in general G06F17/15
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others

Abstract

Example embodiments are directed to a method including transmitting, by a small cell, a pilot signal to a user equipment (UE) based on a first training signal received from the UE, and receiving, by the small cell, a second training signal from the UE. The second training signal is offset by a time based on the pilot signal transmitted by the small cell. The time offset represents a difference in time between the UE receiving a reference signal transmitted by a macro cell and the UE receiving the pilot signal transmitted by the small cell. The small cell adjusts a local reference timing based on the second training signal.

Claims

1. A method comprising:

transmitting, by a small cell, a pilot signal to a user equipment (UE) based on a first training signal received from the UE;

receiving, by the small cell, a second training signal from the UE, the second training signal being offset by a time based on the pilot signal transmitted by the small cell, the time offset representing a difference in time between the UE receiving a reference signal transmitted by a macro cell and the UE receiving the pilot signal transmitted by the small cell; and

adjusting a reference timing of the small cell based on the second training signal.

2. The method of claim 1, wherein the first receiving receives the first training signal while in a sleep mode.

3. The method of claim 1, wherein the adjusting includes,

shifting the reference timing of the small cell to synchronize with a timing of the macro cell.

4. The method of claim 1, wherein the second training signal is based on a round trip delay from the UE to the small cell.

5. The method of claim 1, wherein the second training signal is based on a propagation delay between the macro cell and the UE.

7. The method of claim 1, wherein the time offset is based on a round trip delay from the UE to the small cell.

8. The method of claim 7, wherein the time offset is one half of the round trip delay.

6. The method of 1, wherein the transmitting transmits the pilot signal based on a reference timing of the small cell.

9. A method, comprising:

transmitting, by a small cell, a first signal to a user equipment (UE); and

receiving, by the small cell, time offset information from a macro cell configured to communicate with the UE, the time offset information representing a difference in time between the UE receiving a reference signal transmitted by the macro cell and the UE receiving the pilot signal.

10. The method of claim 9, wherein the transmitting transmits the first signal if the UE is within a threshold distance of the small cell.

11. The method of claim 9, wherein the first signal is a pilot signal.

12. The method of claim 9, further comprising:

transmitting, by the small cell, a second signal to the UE, the transmitting the second signal being synchronized with transmissions by the macro cell to the UE.

13. The method of claim 9, further comprising:

transmitting, by the small cell, a second signal offset in time, the offset based on the time offset information.

14. The method of claim 9, wherein the time offset information includes a difference in time between frame boundaries of the first signal received at the UE and frame boundaries of the signal transmitted by the macro cell received at the UE.

15. The method of claim 14, wherein the time offset information includes a frame offset, the frame offset is a difference between a system frame number (SFN) of the first signal and an SFN of the signal transmitted by the macro cell.

16. The method of claim 15, further comprising:

resetting, by the small cell, a SFN counter based on the frame offset.

17. The method of claim 9, wherein the receiving receives the time offset information in a network message.

18. The method of claim 17, further comprising:

transmitting, by the UE, the time offset information to the macro cell.

19. The method of claim 9, wherein the receiving receives the time offset information if at least one of the following occur, a measured power of the small cell is above a threshold, the difference in time between the UE receiving the signal transmitted by the macro cell and the UE receiving the pilot signal exceeds a time threshold and if a period of time ends.

20. A small cell comprising:

a transceiver configured to,

transmit a pilot signal to a user equipment (UE) based on a first training signal received from the UE,

receive a second training signal from the UE, the second training signal being offset by a time offset based on the pilot signal transmitted by the small cell, the time offset representing a difference in time between the UE receiving a signal transmitted by a macro cell and the UE receiving the pilot signal transmitted by the small cell; and

adjust a local reference timing of the small cell based on the second training signal.

21. A user equipment (UE) configured to receive a reference signal from a macro cell, receive a pilot signal from a small and determine time offset information based on the reference signal and the pilot signal, the time offset information representing a difference in time between the receiving the reference signal and receiving the pilot signal.