METHODS AND APPARATUS FOR CYCLIC PREFIX REDUCTION IN MMWAVE MOBILE COMMUNICATION SYSTEMS

• US 20130315321A1
• Filed: 04/04/2013
• Published: 11/28/2013
• Est. Priority Date: 04/09/2012
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Rajagopal, Sridhar, Abu-Surra, Shadi, Gupta, Ankit, Ramakrishna, Sudhir, Josiam, Kaushik, Pi, Zhouyue, Li, Ying
• Granted Patent: US 9,531,573 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04B 7/0695 using beam selection
• CPC Class Codes: H04J 13/0062 Zadoff-Chu
• CPC Class Codes: H04L 1/0031 Multiple signaling transmission H04L1/1664, F15 take precedence
• CPC Class Codes: H04L 27/2607 Cyclic extensions
• CPC Class Codes: H04L 27/261 Details of reference signals

Abstract

To reduce the duration of a cyclic prefix used for a multiple input, multiple output (MIMO) communications channel, delay spread variations for different transmit/receive beam pair combination is estimated and used for fast beam switching and to support single user MIMO (SU-MIMO) even when the CP difference between two beams is large. Beam switching reference signals are employed to estimate delay spread exceeding current CP, and to support beam switching. CP covering sub-clusters within clusters for the MIMO channel are exploited to reduce the CP requirement and improve efficiency. Any one of a number of different CP durations may be selected for each different mobile station, using one of a finite set of subframe configurations for which the CP durations of different symbol locations within the subframe are predefined. Dynamically switching subframe configurations by the system accommodates high mobility.

Claims

1. A method, comprising:

including a beam switching reference signal in an Orthogonal Frequency Division Multiplexing (OFDM) signal transmitted from a base station to a mobile station in a Multiple Input, Multiple Output (MIMO) wireless communications system; and

using the beam switching reference signal to estimate delay spread exceeding a cyclic prefix of the OFDM signal.

2. The method according to claim 1, wherein the beam switching reference signal is a non-OFDM signal.

3. The method according to claim 1, wherein a beam width, a band width and power of the beam switching reference signal are comparable to a Physical Downlink Shared CHannel (PDSCH) transmission.

4. The method according to claim 3, wherein the beam width, band width and power of the beam switching reference signal are selected to allow estimation of a power delay profile (PDP) during data transmission.

5. The method according to claim 1, wherein the beam switching reference signal has characteristics allowing synchronization in addition to delay spread estimation.

6. The method according to claim 1, wherein the beam switching reference signal comprises one of a Zadoff Chu (ZC) sequence and an M-sequence.

7. The method according to claim 1, wherein the beam switching reference signal comprises a plurality of sequences inserted between each of a plurality of sets of contiguous resource blocks in time and frequency within the OFDM signal.

11. The method according to claim 1, wherein the beam switching reference signal comprises a plurality of different time domain Zadoff Chu (ZC) sequences each based on one of a plurality of different sequence roots, wherein ZC sequences based on different sequence roots are inserted between sets of contiguous resource blocks in time and frequency within the OFDM signal.

12. The method according to claim 11, wherein the ZC sequences are interleaved over an entire band of the OFDM signal.

13. The method according to claim 12, wherein one of guard tones and active interference cancellation (AIC) tones are inserted between the ZC sequences and OFDM tones formed by the sets of contiguous resource blocks.

8. The method according to claim wherein the beam switching reference signal comprises a plurality of different time domain sequences based from a single sequence root.

9. The method according to claim 8, wherein the beam switching reference signal comprises cyclically shifted versions of a Zadoff Chu (ZC) sequence that are orthogonal to one another.

10. The method according to claim 9, wherein the beam switching reference signal comprises a sequence that is orthogonal to a sequence within a beam switching reference signal used in one of an adjacent sector and an adjacent cell.

14. A system, comprising:

a transmitter configured to transmit an Orthogonal Frequency Division Multiplexing (OFDM) signal from a base station to a mobile station in a Multiple Input, Multiple Output (MIMO) wireless communications system,

wherein the transmitter is configured to insert a beam switching reference signal in the OFDM signal, the beam switching reference signal structured to estimate delay spread exceeding a cyclic prefix of the OFDM signal.

15. The system according to claim 14, wherein the beam switching reference signal is a non-OFDM signal.

16. The system according to claim 14, wherein a beam width, a band width and power of the beam switching reference signal are comparable to a Physical Downlink Shared CHannel (PDSCH) transmission.

17. The system according to claim 16, wherein the beam width, band width and power of the beam switching reference signal are selected to allow estimation of a power delay profile (PDP) during data transmission.

18. The system according to claim 14, wherein the beam switching reference signal has characteristics allowing synchronization in addition to delay spread estimation.

19. The system according to claim 14, wherein the beam switching reference signal comprises one of a Zadoff Chu (ZC) sequence and an M-sequence.

20. The system according to claim 14, wherein the beam switching reference signal comprises a plurality of sequences inserted between each of a plurality of sets of contiguous resource blocks in time and frequency within the OFDM signal.

21. The system according to claim 14, wherein the beam switching reference signal comprises a plurality of different time domain sequences based from a single sequence root.

22. The system according to claim 21, wherein the beam switching reference signal comprises cyclically shifted versions of a Zadoff Chu (ZC) that are orthogonal to one another.

23. The system according to claim 22, wherein the beam switching reference signal comprises a sequence that is orthogonal to a sequence within a beam switching reference signal used in one of an adjacent sector and an adjacent cell.

24. The system according to claim 14, wherein the beam switching reference signal comprises a plurality of different time domain Zadoff Chu (ZC) sequences each based on one of a plurality of different sequence roots, wherein ZC sequences based on different ones of the sequence roots are inserted between sets of contiguous resource blocks in time and frequency within the OFDM signal.

25. The system according to claim 24, wherein the ZC sequences are interleaved over an entire band of the OFDM signal.

26. The system according to claim 24, wherein one of guard tones and active interference cancellation (AIC) tones are inserted between the ZC sequences and OFDM tones formed by the sets of contiguous resource blocks.

27. A system, comprising:

one of a transmitter configured to transmit an Orthogonal Frequency Division Multiplexing (OFDM) signal from a base station to a mobile station in a Multiple Input, Multiple Output (MIMO) wireless communications system and a receiver configured to receive the OFDM signal from the base station,

wherein the OFDM signal includes a beam switching reference signal, the beam switching reference signal having one of;

a power corresponding to a single Physical Downlink Shared CHannel (PDSCH) symbol spread over a plurality Q OFDM symbols, and

frequency domain signal characteristics enabling a receiver to estimate a power delay profile (PDP).

28. The system according to claim 27, wherein a sequence employed in the beam switching reference signal is a very long pseudo-random noise (PN) sequence.

29. The system according to claim 27, wherein a cyclic prefix for symbols within the OFDM signal covers a delay spread for all beams between the base station and the mobile station.

30. A method, comprising:

for a base station transmitting data to a first mobile station in a Multiple Input, Multiple Output (MIMO) wireless communications system using a first beam pair (i,j), using a beam switching reference signal within an Orthogonal Frequency Division Multiplexing (OFDM) signal carrying the data to determine a delay for each of a plurality of different beams between the base station and the first mobile station; and

one of;

based on one or more determined delays, selecting another beam pair (m,n) of the plurality of beams on which subsequent frames of the data are transmitted from the base station to the first mobile station, and

setting a cyclic prefix to exceed each of the delays determined for the different beams.

31. The method according to claim 30, wherein the beam pair (m,n) has a delay greater than a delay of the beam pair (i,j).

32. The method according to claim 30, further comprising one of:

scheduling a second mobile station having a delay greater than a delay difference between the beam pair (i,j) and the beam pair (m,n) for receiving data on the beam pair (i,j) after the base station switches transmitting data to the first mobile station from the beam pair (i,j) to the beam pair (m,n);

inserting a quiet time for the beam pair (i,j) after the base station switches transmitting data to the first mobile station from the beam pair (i,j) to the beam pair (m,n); and

inserting a large cyclic prefix for symbol transmitted on the beam pair (i,j) after the base station switches transmitting data to the first mobile station from the beam pair (i,j) to the beam pair (m,n).

33. The method according to claim 30, wherein switching transmission of data from the base station to the first mobile station from the beam pair (i,j) to the beam pair (m,n) occurs at a slot boundary.

34. The method according to claim 30, wherein the beam pair (m,n) has a delay greater than a cyclic prefix of the beam pair (i,j).

36. A method, comprising:

for a base station transmitting data to at least one mobile station in a Multiple Input, Multiple Output (MIMO) wireless communications system, selecting one of a plurality of predetermined subframe configurations for use during a subframe,

wherein each of the subframe configurations employs one of a plurality of predetermined durations for a cyclic prefix, and

wherein a number of Orthogonal Frequency Division Multiplexing (OFDM) symbols included within each subframe configuration is based on the cyclic prefix duration employed, to produce a total subframe transmission time that is identical for all of the subframe configurations.

35. The method according to claim 40, wherein a duration of the cyclic prefix is selected from a plurality of predetermined durations for the cyclic prefix.

37. The method according to claim 36, wherein the selected subframe configuration is periodically updated.

38. The method according to claim 36, wherein the at least one mobile station requests use of one of the predetermined cyclic prefix durations by the base station based on a worst case delay across a plurality of different beams.

39. The method according to claim 36, wherein the selected subframe configuration is configured at a cell planning stage.

40. The method according to claim 36, wherein the selected subframe configuration is initially set to a longest one of the predetermined cyclic prefix durations for each of a plurality of mobile stations including the at least one mobile station, then subsequently set to a shorter one of the predetermined cyclic prefix durations for one or more of the plurality of mobile stations based on measurements and/or feedback from the mobile station.

41. A method, comprising:

for a subframe received by a mobile station from a base station in a Multiple Input, Multiple Output (MIMO) wireless communications system, one of;

(1) trying each of a plurality of predetermined durations for a cyclic prefix in decoding a first symbol within the received subframe, and decoding symbols subsequent to the first symbol based upon allowed subframe cyclic prefix configuration indicated in a successfully decoded first symbol of the received subframe; and

(2) using a predetermined one of the plurality of predetermined durations for the cyclic prefix in decoding the first symbol within the received subframe, and, based on one of a plurality of predetermined subframe configurations indicated by the decoded first symbol, decoding a remainder of the received subframe;

(3) decoding the received subframe using one of the plurality of predetermined subframe configurations, the one predetermined subframe configuration indicated by a last symbol within a subframe preceding the received subframe;

(4) decoding a synchronization channel within the received subframe using a longest one of a plurality of predetermined cyclic prefix durations, and, based on one of a plurality of predetermined subframe configurations indicated by the decoded synchronization channel, decoding a remainder of the received subframe; and

(5) decoding the subframe using one of a plurality of predetermined subframe configurations indicated in a message from the base station to the mobile station.

42. The method according to claim 41, wherein the subframe configuration is selected based on a delay spread reported by the mobile station.

43. The method according to claim 42, wherein the delay spread is reported by the mobile station using a table of cyclic prefix durations supported by the base station.

44. The method according to claim 43, wherein a cyclic prefix index reported by the mobile station is determined based on a worst case delay among a plurality of transmit-receive beam pairs between the base station and the mobile station.

45. The method according to claim 42, wherein the mobile stations reports either one of a plurality of predetermined cyclic prefix durations or one of a plurality of quantized delay spreads to the base station either on a periodic feedback channel or during a channel quality information (CQI) feedback reporting instance.

46. The method according to claim 45, wherein the CQI feedback reporting instance one of recurs periodically and dynamically replaces CQI reporting based on changes detected by the mobile station.

47. The method according to claim 42, wherein the mobile stations reports either one of a plurality of predetermined cyclic prefix durations or one of a plurality of quantized delay spreads to the base station using an uplink control channel request.