Uplink Synchronization Maintenance Principles in Wireless Networks

• US 20130242973A1
• Filed: 06/22/2012
• Published: 09/19/2013
• Est. Priority Date: 04/30/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Bertrand, Pierre, Muharemovic, Tarik, Shen, Zukang
• Granted Patent: US 9,166,717 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). 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. 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

1-14. -14. (canceled)

25. 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, wherein the UE having scheduled uplink communications comprise a scheduled portion, and the UE in discontinuous reception mode (DRX) comprise an unscheduled portion:

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

26. The method of claim 25, 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.

27. The method of claim 25, 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.

28. The method of claim 25, wherein the sync-RS is allocated every n sub-frames in a symbol slot not used by a demodulation reference signal (DMRS) or by data transmission.

29. The method of claim 28, wherein the sync-RSs are orthogonally multiplexed in code division multiplexing (CDM), in frequency division multiplexing (FDM), and in time division multiplexing (TDM).

30. The method of claim 28, 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.

31. The method of claim 29, further comprising performing CDM multiplexing of the sync-RS by cyclic shifting a constant amplitude zero autocorrelation (CAZAC)-like sequence.

32. The method of claim 25, 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.

33. The method of claim 32 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.

34. The method of claim 32 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.

35. The method of claim 32, wherein the autonomous TA request is conveyed by a scheduling request indicator (SRI), an uplink (UL) channel used to transmit new scheduling requests.

36. The method of claim 25, wherein the cellular network is a discrete Fourier Transform (DFT)-spread orthogonal frequency division multiple access (OFDMA) system.

40. The method of claim 25, wherein the sync-RS is allocated every n sub-frames in a symbol slot not used by a demodulation reference signal (DMRS) or by data transmission.

41. The method of claim 40, wherein the sync-RSs are orthogonally multiplexed in code division multiplexing (CDM), in frequency division multiplexing (FDM), and in time division multiplexing (TDM).

42. The method of claim 40, 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.

43. The method of claim 41, further comprising performing CDM multiplexing of the sync-RS by cyclic shifting a constant amplitude zero autocorrelation (CAZAC)-like sequence.

44. The method of claim 41, 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.

45. The method of claim 44, wherein the autonomous TA request is conveyed by a scheduling request indicator (SRI), an uplink (UL) channel used to transmit new scheduling requests.

37. 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.

38. The method of claim 37, 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.

39. The method of claim 37, 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.