Adaptive pilot insertion for a MIMO-OFDM system

• US 20060018287A1
• Filed: 07/20/2004
• Published: 01/26/2006
• Est. Priority Date: 07/20/2004
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Walton, Jay Rodney, Wallace, Mark S.
• Granted Patent: US 8,000,221 B2
• Time in Patent Office: Days
• US Class Current: 370/334
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04L 1/0001 Systems modifying transmission characteristics according to link quality, e.g. power backoff adaptive data allocation for multicarrier modulation H04L5/0044; controlling transmission power for radio systems H04W52/04
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 27/261 Details of reference signals

Abstract

A transmitting entity transmits a “base” pilot in each protocol data unit (PDU). A receiving entity is able to derive a sufficiently accurate channel response estimate of a MIMO channel with the base pilot under nominal (or most) channel conditions. The transmitting entity selectively transmits an additional pilot if and as needed, e.g., based on channel conditions and/or other factors. The additional pilot may be adaptively inserted in almost any symbol period in the PDU. The receiving entity is able to derive an improved channel response estimate with the additional pilot. The transmitting entity sends signaling to indicate that additional pilot is being sent. This signaling may be embedded within pilot symbols sent on a set of pilot subbands used for a carrier pilot that is transmitted across most of the PDU. The signaling indicates whether additional pilot is being sent and possibly other pertinent information.

Claims

1. A method of transmitting pilot in a multiple-input multiple-output (MIMO) communication system, comprising:

transmitting in each protocol data unit (PDU) a first pilot suitable for deriving an estimate of a response of a MIMO channel between a transmitting entity and a receiving entity; and

selectively transmitting in each PDU an additional pilot suitable for deriving an improved estimate of the MIMO channel response.

2. The method of claim 1, further comprising:

determining whether to transmit the additional pilot based on one or more factors including condition of the MIMO channel.

3. The method of claim 1, further comprising:

transmitting signaling to indicate the additional pilot being transmitted.

4. The method of claim 3, wherein the signaling for the additional pilot is transmitted concurrently with the additional pilot.

5. The method of claim 3, wherein the additional pilot is sent on a first set of frequency subbands in a symbol period selected for additional pilot transmission, and wherein the signaling is sent on a second set of frequency subbands in the symbol period.

6. The method of claim 5, wherein the second set of frequency subbands is for a carrier pilot suitable for tracking a phase of a carrier signal used by the transmitting entity.

7. The method of claim 1, wherein the first pilot and the additional pilot are unsteered MIMO pilots sent from a plurality of antennas at the transmitting entity and without spatial processing by the transmitting entity.

8. The method of claim 1, wherein the first pilot and the additional pilot are steered MIMO pilots sent on orthogonal spatial channels of the MIMO channel.

9. The method of claim 1, wherein the additional pilot is sent on all subbands usable for data transmission.

10. The method of claim 1, wherein the additional pilot is sent on a subset of subbands usable for data transmission.

11. The method of claim 1, wherein each PDU spans a plurality of symbol periods designated for data transmission, and wherein the additional pilot is selectively transmitted in each of the plurality of symbol periods.

12. The method of claim 1, wherein the MIMO system utilizes orthogonal frequency division multiplexing (OFDM).

13. An apparatus in a multiple-input multiple-output (MIMO) communication system, comprising:

a transmitter unit to transmit in each protocol data unit (PDU) a first pilot suitable for deriving an estimate of a response of a MIMO channel between a transmitting entity and a receiving entity and to selectively transmit in each PDU an additional pilot suitable for deriving an improved estimate of the MIMO channel response; and

a controller to direct selective transmission of the additional pilot in each PDU.

14. The apparatus of claim 13, wherein the controller further directs transmission of signaling to indicate the additional pilot being transmitted.

15. The apparatus of claim 14, wherein the additional pilot is sent on a first set of frequency subbands in a symbol period selected for additional pilot transmission, and wherein the signaling is sent on a second set of frequency subbands in the symbol period.

16. The apparatus of claim 13, wherein each PDU spans a plurality of symbol periods designated for data transmission, and wherein the additional pilot is selectively transmitted in each of the plurality of symbol periods.

17. An apparatus in a multiple-input multiple-output (MIMO) communication system, comprising:

means for transmitting in each protocol data unit (PDU) a first pilot suitable for deriving an estimate of a response of a MIMO channel between a transmitting entity and a receiving entity; and

means for selectively transmitting in each PDU an additional pilot suitable for deriving an improved estimate of the MIMO channel response.

18. The apparatus of claim 17, further comprising:

means for transmitting signaling to indicate the additional pilot being transmitted.

19. The apparatus of claim 18, wherein the additional pilot is sent on a first set of frequency subbands in a symbol period selected for additional pilot transmission, and wherein the signaling is sent on a second set of frequency subbands in the symbol period.

20. The apparatus of claim 17, wherein each PDU spans a plurality of symbol periods designated for data transmission, and wherein the additional pilot is selectively transmitted in each of the plurality of symbol periods.

21. A method of transmitting signaling in a multiple-input multiple-output (MIMO) communication system utilizing orthogonal frequency division multiplexing (OFDM), comprising:

selecting a signaling value from among a plurality of signaling values;

selecting a set of pilot symbols from among a plurality of sets of pilot symbols, wherein each of the plurality of sets of pilot symbols corresponds to a different one of the plurality of signaling values, and wherein the selected set of pilot symbols corresponds to the selected signaling value; and

multiplexing the selected set of pilot symbols on a first set of frequency subbands used for a carrier pilot.

22. The method of claim 21, wherein the carrier pilot is suitable for use by a receiving entity to track a phase of a carrier signal used by a transmitting entity.

23. The method of claim 21, wherein the plurality of signaling values include a first signaling value indicating additional pilot symbols are being transmitted on a second set of frequency subbands.

24. The method of claim 23, wherein the selected set of pilot symbols is transmitted on the first set of frequency subbands and the additional pilot symbols are concurrently transmitted on the second set of frequency subbands in a symbol period.

25. The method of claim 23, wherein the plurality of signaling values further include a second signaling value indicating data symbols are being transmitted on the second set of frequency subbands.

26. The method of claim 21, wherein the selected signaling value indicates a type of an additional pilot being transmitted.

27. The method of claim 21, wherein the selected signaling value indicates a set of frequency subbands used to transmit an additional pilot.

28. The method of claim 21, wherein the selected signaling value indicates a mode of transmission for an additional pilot being transmitted.

29. An apparatus in a multiple-input multiple-output (MIMO) communication system utilizing orthogonal frequency division multiplexing (OFDM), comprising:

a controller to select a signaling value from among a plurality of signaling values;

a processor to select a set of pilot symbols from among a plurality of sets of pilot symbols, wherein each of the plurality of sets of pilot symbols corresponds to a different one of the plurality of signaling values, and wherein the selected set of pilot symbols corresponds to the selected signaling value; and

a multiplexer to multiplex the selected set of pilot symbols on a first set of frequency subbands used for a carrier pilot.

30. The apparatus of claim 29, wherein the plurality of signaling values include a first signaling value indicating additional pilot symbols are being transmitted on a second set of frequency subbands.

31. The apparatus of claim 30, wherein the selected set of pilot symbols is transmitted on the first set of frequency subbands and the additional pilot symbols are concurrently transmitted on the second set of frequency subbands in a symbol period.

32. The apparatus of claim 29, wherein the selected signaling value indicates a set of frequency subbands used to transmit an additional pilot.

33. An apparatus in a multiple-input multiple-output (MIMO) communication system utilizing orthogonal frequency division multiplexing (OFDM), comprising:

means for selecting a signaling value from among a plurality of signaling values;

means for selecting a set of pilot symbols from among a plurality of sets of pilot symbols, wherein each of the plurality of sets of pilot symbols corresponds to a different one of the plurality of signaling values, and wherein the selected set of pilot symbols corresponds to the selected signaling value; and

means for multiplexing the selected set of pilot symbols on a first set of frequency subbands used for a carrier pilot

34. The apparatus of claim 33, wherein the plurality of signaling values include a first signaling value indicating additional pilot symbols are being transmitted on a second set of frequency subbands.

35. The apparatus of claim 34, wherein the selected set of pilot symbols is transmitted on the first set of frequency subbands and the additional pilot symbols are concurrently transmitted on the second set of frequency subbands in a symbol period.

36. The apparatus of claim 33, wherein the selected signaling value indicates a set of frequency subbands used to transmit an additional pilot.

37. A method of receiving pilot in a multiple-input multiple-output (MIMO) communication system, comprising:

receiving a first pilot transmitted in each protocol data unit (PDU) and suitable for deriving an estimate of a response of a MIMO channel between a transmitting entity and a receiving entity; and

receiving an additional pilot selectively transmitted in each PDU and suitable for deriving an improved estimate of the MIMO channel response.

38. The method of claim 37, further comprising:

receiving signaling indicating whether the additional pilot is being transmitted in each PDU.

39. The method of claim 38, wherein the signaling is received on a first set of frequency subbands and the additional pilot is received on a second set of frequency subbands.

40. The method of claim 38, wherein the signaling and the additional pilot are transmitted concurrently in a symbol period by the transmitting entity.

41. The method of claim 37, wherein each PDU spans a plurality of symbol periods designated for data transmission, and wherein the additional pilot is selectively transmitted in each of the plurality of symbol periods.

42. The method of claim 37, wherein the first pilot and the additional pilot are unsteered MIMO pilots sent from a plurality of antennas at the transmitting entity and without spatial processing by the transmitting entity.

43. The method of claim 37, wherein the first pilot and the additional pilot are steered MIMO pilots sent on orthogonal spatial channels of the MIMO channel.

44. An apparatus in a multiple-input multiple-output (MIMO) communication system, comprising:

a receiver unit to receive a first pilot transmitted in each protocol data unit (PDU) and suitable for deriving an estimate of a response of a MIMO channel between a transmitting entity and a receiving entity and to receive an additional pilot selectively transmitted in each PDU and suitable for deriving an improved estimate of the MIMO channel response.

45. The apparatus of claim 44, further comprising:

a controller to receive signaling indicating whether the additional pilot is being transmitted in each PDU.

46. The apparatus of claim 45, wherein the signaling is received on a first set of frequency subbands and the additional pilot is received on a second set of frequency subbands.

47. The apparatus of claim 45, wherein the signaling and the additional pilot are transmitted concurrently in a symbol period by the transmitting entity.

48. An apparatus in a multiple-input multiple-output (MIMO) communication system, comprising:

means for receiving a first pilot transmitted in each protocol data unit (PDU) and suitable for deriving an estimate of a response of a MIMO channel between a transmitting entity and a receiving entity; and

means for receiving an additional pilot selectively transmitted in each PDU and suitable for deriving an improved estimate of the MIMO channel response.

49. The apparatus of claim 48, further comprising:

means for receiving signaling indicating whether the additional pilot is being transmitted in each PDU.

50. The apparatus of claim 49, wherein the signaling is received on a first set of frequency subbands and the additional pilot is received on a second set of frequency subbands.

51. The apparatus of claim 49, wherein the signaling and the additional pilot are transmitted concurrently in a symbol period by the transmitting entity.