Velocity enhancement for OFDM systems

• US 6,904,550 B2
• Filed: 12/30/2002
• Issued: 06/07/2005
• Est. Priority Date: 12/30/2002
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Enami, Shahriar, Sibecas, Salvador, Stratis, Glafkos, Rasor, Gregg, Corral, Celestino, Gorday, Robert
• Primary Examiner(s): Lamarre, Guy J.
• Assistant Examiner(s): BRITT, CYNTHIA H
• Application Number:
  US10/331,692
• Publication Number:
  US 20040128605A1
• Time in Patent Office: 890 Days
• Field of Search: 714/701, 714/703, 714/712, 714/715, 714/746, 714/758, 714/776, 714/786, 714/714, 375/224, 375/225, 375/265, 375/341, 375362-365, 375/368, 370/522, 370/525, 370527-529
• US Class Current: 714/714
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 25/0232 by interpolation between sounding signals
• CPC Class Codes: H04L 27/34 Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

An orthogonal frequency division multiplexing (OFDM) transmitter method, consistent with certain embodiments of the present invention arranges OFDM data symbols representing data bits for transmission in a packet. A prescribed pattern of OFDM data symbols are removed (212) and replaced (216) with pilot symbols. The packet is then transmitted (220) to an OFDM receiver that receives the packet (224) and determines a channel correction factor from the pilot pattern. The receiver then estimates a plurality of channel correction factors, one for each of the plurality of OFDM symbols representing data (228) and uses these correction factors to correct the OFDM symbols representing data (232). Arbitrary data are then inserted in place of the pilot symbols (236). The OFDM symbols representing data along with the arbitrary data are then decoded using an error correction decoder that corrects the errors induced by substitution of the pilot symbols for data symbols (240).

Claims

1. An orthogonal frequency division multiplexing (OFDM) transmitter method, comprising:

arranging OFDM data symbols representing data bits for transmission in a packet;

removing at least one data symbol and replacing the removed data symbol with a pilot symbol; and

transmitting the packet.

2. An orthogonal frequency division multiplexing transmitter method in accordance with claim 1, wherein the removing and replacing introduces the likelihood of a data error.

3. An orthogonal frequency division multiplexing transmitter method in accordance with claim 1, wherein the removing comprises removing a plurality of data symbols in a prescribed pattern, and wherein the replacing comprises replacing the plurality of data symbols with a plurality of pilot symbols.

4. An orthogonal frequency division multiplexing transmitter method in accordance with claim 3, wherein the prescribed pattern comprises a linear pattern.

5. An orthogonal frequency division multiplexing transmitter method in accordance with claim 3, further comprising:

encoding the data bits with an error correction coding,

wherein the prescribed pattern is selected to produce no more errors than the error correction code can correct.

6. An orthogonal frequency division multiplexing transmitter method in accordance with claim 3, further comprising transmitting information conveying the prescribed pattern.

7. An orthogonal frequency division multiplexing transmitter method in accordance with claim 3, wherein the prescribed pattern is selected by a receiver receiving transmitted packets from the transmitter.

8. An orthogonal frequency division multiplexing transmitter method in accordance with claim 3, wherein the pilot symbols in the prescribed pattern of pilot symbols have a minimum spacing in time given by:

$M_t<<br><br>\frac{1}{2<br><br>f_{\mathrm{Drel}}<br><br>\left(1+\frac{T_G}{T}\right)}$

where;

T=the effective symbol length=NT_S,

T_S is the sampling period of the system,

N is the number of subcarriers,

T_G is the length of cyclic prefix,

The total symbol length=T+T_G, and

F_Drel=a relative Doppler frequency.

9. An orthogonal frequency division multiplexing transmitter method in accordance with claim 3, wherein the pilot symbols in the prescribed pattern of pilot symbols have a minimum spacing in subchannels given by:

$M_f<<br><br>\frac{T}{T_G}$

where;

T=the effective symbol length=NT_S,

T_S is the sampling period of the system,

N is the number of subcarriers,

T_G is the length of cyclic prefix, and

the total symbol length=T+T_G.

10. An orthogonal frequency division multiplexing (OFDM) receiver method, comprising:

receiving a packet containing a plurality of OFDM symbols representing data, wherein at least one of the OFDM data symbols has been replaced with a pilot symbol of a pilot pattern comprising at least one pilot symbol;

determining a channel correction factor from the pilot pattern;

estimating a plurality of channel correction factors, one for each of the plurality of OFDM symbols representing data;

correcting the OFDM symbols representing data using the plurality of channel correction factors; and

decoding the OFDM symbols representing data using an error correction decoder.

11. An orthogonal frequency division multiplexing receiver method in accordance with claim 10, further comprising replacing the pilot pattern with arbitrary data prior to decoding.

12. An orthogonal frequency division multiplexing receiver method in accordance with claim 10, wherein a plurality of OFDM data symbols have been replaced with pilot symbols in a prescribed pattern.

13. An orthogonal frequency division multiplexing receiver method in accordance with claim 12, wherein the prescribed pattern comprises a linear pattern.

14. An orthogonal frequency division multiplexing receiver method in accordance with claim 12, wherein the OFDM data symbols represent data bits that have been encoded with an error correction coding, and wherein the prescribed pattern is selected to produce no more errors than the error correction decoder can correct.

15. An orthogonal frequency division multiplexing receiver method in accordance with claim 12, further comprising receiving information conveying the prescribed pattern.

16. An orthogonal frequency division multiplexing receiver method in accordance with claim 10, wherein the estimating comprises applying coherent time approximations to the plurality of channel correction factors for time periods shorter than a length of the packet.

17. An orthogonal frequency division multiplexing receiver method in accordance with claim 10, wherein the estimating comprises applying coherent frequency approximations to the plurality of correction factors for frequencies within two subcarrier frequencies of a frequency occupied by one of the at least one pilot symbols of the pilot pattern.

18. An orthogonal frequency division multiplexing receiver method in accordance with claim 10, further comprising selecting the pilot pattern and transmitting a signal indicative of the selected pilot pattern for use by a transmitter that transmits the packet containing the plurality of OFDM symbols.

19. An orthogonal frequency division multiplexing (OFDM) transmitter, comprising:

a binary data to complex symbol mapper that maps a binary input representing a packet of information to a stream of constellation symbols;

a serial to parallel converter that converts the stream of constellation symbols to a parallel collection of data symbols;

a pilot substitutor that removes at least one data symbol and replaces the removed data symbol with a pilot symbol; and

an inverse Fast Fourier Transformer (FFT) that receives the collection of data symbols and the pilot symbol as inputs and produces an OFDM output signal.

20. An orthogonal frequency division multiplexing transmitter in accordance with claim 19, wherein the pilot substitutor removes a plurality of data symbols in a prescribed pattern and replaces the data symbols with pilot symbols.

21. An orthogonal frequency division multiplexing transmitter in accordance with claim 20, wherein the prescribed pattern comprises a linear pattern.

22. An orthogonal frequency division multiplexing transmitter in accordance with claim 21, further comprising an error correction encoder that encodes the binary input with an error correction code and produces an output to the binary data to complex symbol mapper.

23. An orthogonal frequency division multiplexing transmitter in accordance with claim 22, wherein the prescribed pattern is selected to produce no more errors than the error correction code can correct.

24. An orthogonal frequency division multiplexing transmitter in accordance with claim 20, wherein the prescribed pattern is selected by a receiver receiving transmitted packets from the transmitter.

25. An orthogonal frequency division multiplexing transmitter in accordance with claim 22, further comprising an interleaver that interleaves the output of the error correction encoder and sends the interleaved output to the binary data to complex symbol mapper.

26. An orthogonal frequency division multiplexing transmitter in accordance with claim 20, further comprising means for transmitting information conveying the prescribed pattern.

27. An orthogonal frequency division multiplexing transmitter in accordance with claim 20, wherein the pilot symbols in the prescribed pattern of pilot symbols have a minimum spacing in time given by:

$M_t<<br><br>\frac{1}{2<br><br>f_{\mathrm{Drel}}<br><br>\left(1+\frac{T_G}{T}\right)}$

where;

T=the effective symbol length=NT_S,

T_S is the sampling period of the system,

N is the number of subcarriers,

T_G is the length of cyclic prefix,

The total symbol length=T+T_G, and

F_Drel=a relative Doppler frequency.

28. An orthogonal frequency division multiplexing transmitter in accordance with claim 20, wherein the pilot symbols in the prescribed pattern of pilot symbols have a minimum spacing in subchannels given by:

$M_f<<br><br>\frac{T}{T_G}$

where;

T=the effective symbol length=NT_S,

T_S is the sampling period of the system,

N is the number of subcarriers,

T_G is the length of cyclic prefix, and

the total symbol length=T+T_G.

29. An orthogonal frequency division multiplexing (OFDM) receiver, comprising:

an OFDM receiver that receives a packet containing a plurality of OFDM symbols representing data, wherein at least one of the OFDM data symbols has been replaced with a pilot symbol of a pilot pattern comprising at least one pilot symbol;

a Fast Fourier Transformer receiving the OFDM symbols;

a channel estimator that estimates a channel correction factor from the pilot pattern and estimates a plurality of channel correction factors, one for each of the plurality of OFDM symbols representing data;

a channel corrector that corrects the OFDM symbols representing data using the plurality of channel correction factors; and

a decoder that decodes the OFDM symbols representing data using an error correction decoder.

30. An orthogonal frequency division multiplexing receiver in accordance with claim 29, further comprising a pilot to arbitrary data substitutor that replaces the pilot pattern with arbitrary data prior to the decoder.

31. An orthogonal frequency division multiplexing receiver in accordance with claim 29, wherein a plurality of OFDM data symbols have been replaced with pilot symbols in a prescribed pattern.

32. An orthogonal frequency division multiplexing receiver in accordance with claim 31, wherein the prescribed pattern comprises a linear pattern.

33. An orthogonal frequency division multiplexing receiver in accordance with claim 31, wherein the OFDM data symbols represent data bits that have been encoded with an error correction coding, and wherein the prescribed pattern is selected to produce no more errors than the error correction decoder can correct.

34. An orthogonal frequency division multiplexing receiver in accordance with claim 29, further comprising means for receiving information conveying the prescribed pattern.

35. An orthogonal frequency division multiplexing receiver in accordance with claim 34, wherein the information conveying the prescribed pattern is conveyed as service data within an OFDM packet structure.

36. An orthogonal frequency division multiplexing receiver in accordance with claim 29, wherein the channel estimator estimates the channel correction factors by applying coherent time approximations to the correction factors for time periods shorter than a length of the packet.

37. An orthogonal frequency division multiplexing receiver in accordance with claim 29, wherein the channel estimator estimates the channel correction factors by applying coherent frequency approximations to plurality of the correction factors for frequencies within two subcarrier frequencies of a frequency occupied by one of at least one pilot symbols of the pilot pattern.

38. An orthogonal frequency division multiplexing (OFDM) communication method, comprising:

at an OFDM transmitter, establishing a pattern of pilot symbols to substitute for data symbols in a transmitted OFDM data packet;

identifying the pattern of pilot symbols by a code; and

transmitting the code to an OFDM receiver.

39. The orthogonal frequency division multiplexing communication method according to claim 38, wherein the code is embedded in a packet SERVICE code.

40. The orthogonal frequency division multiplexing communication method according to claim 38, wherein the code forms a part of a packet length code.

41. The orthogonal frequency division multiplexing communication method according to claim 39, wherein the pattern of pilot symbols comprises a linear pattern.

42. An orthogonal frequency division multiplexing (OFDM) communication method, comprising:

at an OFDM receiver, receiving a code that identifies a pattern of pilot symbols substituted for data symbols in a transmitted OFDM data packet;

translating the code to the pattern of pilot symbols;

substituting arbitrary data symbols for pilot symbols received according to the pattern of pilot symbols; and

decoding the data symbols.

43. The orthogonal frequency division multiplexing communication method according to claim 42, wherein the code is embedded in a packet SERVICE code.

44. The orthogonal frequency division multiplexing communication method according to claim 42, wherein the code forms a part of a packet length code.

45. The orthogonal frequency division multiplexing communication method according to claim 42, wherein the pattern of pilot symbols comprises a linear pattern.

46. An orthogonal frequency division multiplexing (OFDM) carrier wave, comprising:

a plurality of OFDM data symbols;

a pattern of pilot symbols substituted for data symbols; and

a segment of code identifying the pattern of pilot symbols.

47. The orthogonal frequency division multiplexing carrier wave according to claim 46, wherein the plurality of OFDM data symbols, the pattern of pilot symbols and the segment of code are arranged in a packet.

48. The orthogonal frequency division multiplexing carrier wave according to claim 47, wherein the segment of code is embedded in a packet SERVICE code.

49. The orthogonal frequency division multiplexing carrier wave according to claim 47, wherein the segment of code forms a part of a packet length code.

50. The orthogonal frequency division multiplexing carrier wave according to claim 46, wherein the pattern of pilot symbols comprises a linear pattern.

51. A transmitter method, comprising:

arranging data symbols representing data bits for transmission in a packet;

removing at least one data symbol and replacing the removed data symbol with a pilot symbol and thus introducing a likelihood of a data error; and

transmitting the packet.

52. A transmitter method in accordance with claim 51, wherein the removing comprises removing a plurality of data symbols in a prescribed pattern, and wherein the replacing comprises replacing the plurality of data symbols with a plurality of pilot symbols.

53. A transmitter method in accordance with claim 52, further comprising transmitting information conveying the prescribed pattern.

54. A transmitter method in accordance with claim 52, wherein the prescribed pattern is selected by a receiver receiving transmitted packets from the transmitter.

55. A receiver method, comprising:

receiving a packet containing a plurality of data symbols, wherein at least one of the data symbols has been replaced with a pilot symbol of a pilot pattern comprising at least one pilot symbol;

determining a channel correction factor from the pilot pattern;

estimating a plurality of channel correction factors;

correcting the data symbols using the plurality of channel correction factors; and

decoding the data symbols using an error correction decoder.

56. A receiver method in accordance with claim 55, further comprising replacing the pilot pattern with arbitrary data prior to decoding.

57. A receiver method in accordance with claim 55, wherein the data symbols represent data bits that have been encoded with an error correction coding, and wherein the pilot pattern is selected to produce no more errors than the error correction decoder can correct.

58. A receiver method in accordance with claim 55, further comprising receiving information conveying the pilot pattern.

59. A receiver method in accordance with claim 55, further comprising selecting the pilot pattern and transmitting a signal indicative of the pilot pattern for use by a transmitter transmitting the packet containing the plurality of data symbols.