UPLINK SYNCHRONIZATION MAINTENANCE PRINCIPLES IN WIRELESS NETWORKS

• US 20080267165A1
• Filed: 04/29/2008
• Published: 10/30/2008
• Est. Priority Date: 04/30/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Shen, Zukang, Bertrand, Pierre, Muharemovic, Tarik
• Granted Patent: US 8,218,526 B2
• Time in Patent Office: Days
• US Class Current: 370/350
• CPC Class Codes: H04J 3/06 Synchronising arrangements for television systems H04N5/04; bit-synchronisation H04L7/00
• CPC Class Codes: H04W 56/0005 synchronizing of arrival of multiple uplinks
• CPC Class Codes: H04W 56/0045 compensating for timing error by altering transmission time

Abstract

A cell within cellular network includes user equipments (UEs) that transmit data to a base station (eNB). UEs are synchronized to the eNB upon entry to the cell. If a particular UE has data to transmit, it will be placed in a connected state and scheduled for transmission. Over a period of time, not all of the UEs will have data to transmit. The UEs are tracked as a scheduled portion and an unscheduled portion, wherein a UE is included in the scheduled portion in response to receiving a scheduling request from the UE. Synchronization is maintained between the eNB and each UE in the scheduled portion by sending a timing adjustment (TA) command if needed in response to receiving a scheduled transmission from each respective UE in the scheduled portion; Synchronization is maintained between the eNB and each UE in the unscheduled portion by allocating a periodic reference signal (sync-RS) to each UE in the unscheduled portion and by sending a respective timing adjustment (TA) command if needed to each respective UE in the unscheduled portion in response to a respective sync-RS received from each UE in the unscheduled portion.

Claims

1. A method for maintaining synchronization in a cellular network between a plurality of user equipment (UE) in a cell and a base station (eNB) serving the cell, comprising:

tracking the plurality of UE as a scheduled portion and an unscheduled portion, wherein a UE is included in the scheduled portion in response to receiving a scheduling request from the UE;

maintaining synchronization of each UE in the scheduled portion with the eNB by sending a timing adjustment (TA) command if needed in response to receiving a scheduled transmission from each respective UE in the scheduled portion; and

maintaining synchronization of each UE in the unscheduled portion with the eNB by allocating a periodic reference signal (sync-RS) to each UE in the unscheduled portion and by sending a respective TA command if needed in response to a respective sync-RS received from each UE un the unscheduled portion.

2. The method of claim 1, further comprising determining a maximum TA rate expected for the cell, and wherein the sync-RS period is configured by the eNB to be approximately equal to the maximum TA rate expected in the cell.

3. The method of claim 1, further comprising determining a maximum TA accuracy targeted in the cell, and wherein the sync-RS bandwidth is configured by the eNB to be approximately equal to the inverse of the maximum TA accuracy targeted in the cell.

4. The method of claim 1, wherein each sync-RS is allocated every n sub-frames in a symbol slot not used by a demodulation reference signal (DMRS) or by data transmission.

5. The method of claim 4, wherein the sync-RSs are orthogonally multiplexed in code division multiplexing (CDM), in frequency division multiplexing (FDM), and in time division multiplexing (TDM).

6. The method of claim 4, wherein the sync-RSs are orthogonally multiplexed in code division multiplexing (CDM) and in frequency division multiplexing (FDM) in the same OFDM symbol with other sounding reference signals (SRS) used by scheduled UEs.

7. The method of claim 5, further comprising performing CDM multiplexing of the sync-RS by cyclic shifting a constant amplitude zero autocorrelation (CAZAC)-like sequence.

8. The method of claim 1, further comprising:

transmitting to a UE in the unscheduled portion on a downlink (DL) channel; and

receiving an autonomous TA request from the UE in the unscheduled portion in response to a timing variation beyond a threshold observed by the UE in the DL channel transmission from the eNB.

9. The method of claim 8 where the timing variation observed by the UE in the DL channel transmission from the eNB is a time shift of the received delay profile.

10. The method of claim 8 where the timing variation observed by the UE in the DL channel transmission from the eNB is a variation of the delay spread of the received delay profile.

11. The method of claim 8, wherein the autonomous TA request is conveyed by a scheduling request indicator (SRI), an uplink (UL) channel used to transmit new scheduling requests.

12. The method of claim 1, wherein the cellular network is a discrete Fourier Transform (DFT)-spread orthogonal frequency division multiple access (OFDMA) system.

16. The method of claim 1, wherein each sync-RS is allocated every n sub-frames in a symbol slot not used by a demodulation reference signal (DMRS) or by data transmission.

17. The method of claim 16, wherein the sync-RSs are orthogonally multiplexed in code division multiplexing (CDM), in frequency division multiplexing (FDM), and in time division multiplexing (TDM).

18. The method of claim 16, wherein the sync-RSs are orthogonally multiplexed in code division multiplexing (CDM) and in frequency division multiplexing (FDM) in the same OFDM symbol with other sounding reference signals (SRS) used by scheduled UEs.

19. The method of claim 17, further comprising performing CDM multiplexing of the sync-RS by cyclic shifting a constant amplitude zero autocorrelation (CAZAC)-like sequence.

13. A method for maintaining synchronization in a cellular network between a user equipment (UE) in a cell and a base station (eNB) serving the cell, comprising:

placing the UE in a low power standby mode (DRX) while the UE has no data to transmit;

receiving an allocation for a periodic reference signal (sync-RS);

transmitting the sync-RS to the eNB periodically while in DRX mode; and

receiving a timing adjust (TA) command, if needed, from the eNB in response to the sync-RS.

14. The method of claim 13, further comprising determining a maximum TA rate expected for the cell, and wherein the sync-RS period is configured by the eNB to be approximately equal to the maximum TA rate expected in the cell.

15. The method of claim 13, further comprising determining a maximum TA accuracy targeted in the cell, and wherein the sync-RS bandwidth is configured by the eNB to be approximately equal to the inverse of the maximum TA accuracy targeted in the cell.

20. The method of claim 13, further comprising receiving a transmission at the UE from the eNB on a downlink (DL) channel;

and

transmitting an autonomous TA request from the UE in response to a timing variation beyond a threshold observed by the UE in the DL channel transmission from the eNB.

21. The method of claim 20, wherein the autonomous TA request is conveyed by a scheduling request indicator (SRI), an uplink (UL) channel used to transmit new scheduling requests.

22. A cellular telephone for use in a cellular network, comprising:

a receiver connected to an antenna operable to receive information from a base station (eNB) within a given cell that provides information via a downlink (DL) channel;

a processor connected to a storage memory holding instructions for execution by the processor and coupled to the receiver, wherein the processor is operable to place the cellular telephone in a low power mode (DRX) during which the cellular telephone is not expected to transmit data to the serving eNB, wherein the processor is operable to receive an allocation for a periodic reference signal (sync-RS) via the DL channel;

a transmitter coupled to the processor operable to transmit the sync-RS to the eNB periodically while in DRX mode; and

wherein the processor is operable to receive via the DL channel a timing adjust (TA) command, if needed, from the eNB in response to the sync-RS.

23. A user equipment (UE) for use in a cellular network, comprising:

means for placing the UE in a low power standby mode (DRX) while the UE has no data to transmit;

means for receiving an allocation for a periodic reference signal (sync-RS);

means for transmitting the sync-RS to a base station (eNB) periodically while in DRX mode; and

means for receiving a timing adjust (TA) command, if needed, from the eNB in response to the sync-RS, whereby synchronization is maintained between the UE in a cell and the eNB serving the cell,

24. A base station apparatus (eNB) for use in a cellular network, comprising:

a receiver connected to an antenna operable to receive transmissions from user equipment (UE)in a cell served by the eNB;

a transmitter coupled to an antenna operable to transmit to the UE served by the eNB;

a processor connected to a storage memory holding instructions for execution by the processor and coupled to the receiver and to the transmitter, wherein the processor is operable to track a plurality of UE as a scheduled portion and an unscheduled portion, wherein a UE is included in the scheduled portion in response to receiving a scheduling request from the UE;

wherein the processor is operable to maintain synchronization of each UE in the scheduled portion with the eNB by sending a timing adjustment (TA) command if needed in response to receiving a scheduled transmission from each respective UE in the scheduled portion; and

wherein the processor is operable to maintain synchronization of each UE in the unscheduled portion with the eNB by allocating a periodic reference signal (sync-RS) to each UE in the unscheduled portion and by sending a respective TA command if needed in response to a respective sync-RS received from each UE un the unscheduled portion.