CA2553746A1 - Pilot transmission and channel estimation for an ofdm system with excess delay spread - Google Patents

Pilot transmission and channel estimation for an ofdm system with excess delay spread Download PDF

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Publication number
CA2553746A1
CA2553746A1 CA002553746A CA2553746A CA2553746A1 CA 2553746 A1 CA2553746 A1 CA 2553746A1 CA 002553746 A CA002553746 A CA 002553746A CA 2553746 A CA2553746 A CA 2553746A CA 2553746 A1 CA2553746 A1 CA 2553746A1
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Prior art keywords
impulse response
channel impulse
response estimate
initial
estimates
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CA002553746A
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French (fr)
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CA2553746C (en
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Dhananjay Ashok Gore
Avneesh Agrawal
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Qualcomm Inc
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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H04L25/0226—Channel estimation using sounding signals sounding signals per se
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0212—Channel estimation of impulse response
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2602—Signal structure
    • H04L27/2605—Symbol extensions, e.g. Zero Tail, Unique Word [UW]
    • H04L27/2607—Cyclic extensions
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/0001—Arrangements for dividing the transmission path
    • H04L5/0003—Two-dimensional division
    • H04L5/0005—Time-frequency
    • H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

Pilot transmission and channel estimation techniques for an OFDM system with excess delay spread are described. To mitigate the deleterious effects of excess delay spread, the number of pilot subbands is greater than the cyclic prefix length. This "oversampling" may be achieved by using more pilot subbands in each symbol period or different sets of pilot subbands in different symbol periods. In one channel estimation technique, first and second groups of received pilot symbols are obtained for first and second pilot subband sets, respectively, and used to derive first and second frequency response estimates, respectively. First and second impulse response estimates are derived based on the first and second frequency response estimates, respectively, and used to derive a third impulse response estimate having more taps than the number of pilot subbands in either set.

Claims (39)

1. ~A method of estimating a frequency response of a wireless channel in a wireless communication system, comprising:
obtaining at least two groups of received pilot symbols for at least two sets of pilot subbands, one group of received pilot symbols for each set of pilot subbands, wherein each of the at least two sets of pilot subbands is used for pilot transmission in a different symbol period;
obtaining at least two initial frequency response estimates based on the at least two groups of received pilot symbols, one initial frequency response estimate for each group of received pilot symbols;
deriving an overall channel impulse response estimate based on the at least two initial frequency response estimates, wherein the overall channel impulse response estimate comprises more taps than the number of pilot subbands in each of the at least two sets of pilot subbands; and deriving an overall frequency response estimate for the wireless channel based on the overall channel impulse response estimate.
2. ~The method of claim 1, wherein the deriving an overall channel impulse response estimate based on the at least two initial frequency response estimates includes deriving at least two initial channel impulse response estimates based on the at least two initial frequency response estimates, one initial impulse response estimate for each initial frequency response estimate, and deriving the overall channel impulse response estimate based on the at least two initial channel impulse response estimates.
3. ~The method of claim 1, wherein the deriving an overall channel impulse response estimate based on the at least two initial frequency response estimates includes deriving an intermediate frequency response estimate based on the at least two initial frequency response estimates, and deriving the overall channel impulse response estimate based on the intermediate frequency response estimate.
4. ~The method of claim 1, wherein the overall channel impulse response estimate comprises N T taps, where N T is a length of the overall channel impulse response estimate and is equal to total number of pilot subbands in the at least two sets of pilot subbands.
5. ~The method of claim 1, wherein the pilot subbands in each set are uniformly distributed across N F total subbands and are offset from the pilot subbands in remaining ones of the at least two sets of pilot subbands, where N F is an integer greater than one.
6. ~The method of claim 1, wherein received pilot symbols are obtained on a first set of pilot subbands in odd-numbered symbol periods, and wherein received pilot symbols are obtained on a second set of pilot subbands in even-numbered symbol periods.
7. ~The method of claim 1, wherein the at least two sets of pilot subbands include equal number of pilot subbands.
8. ~The method of claim 1, wherein the at least two sets of pilot subbands include different numbers of pilot subbands.
9. ~The method of claim 2, wherein the deriving an overall channel impulse response estimate further includes repeating each of the at least two initial channel impulse response estimates at least once to obtain at least two instances of the initial channel impulse response estimate, forming an extended channel impulse response estimate for each initial channel impulse response estimate based on the at least two instances of the initial channel impulse response estimate, and deriving the overall channel impulse response estimate based on at least two extended channel impulse response estimates for the at least two initial channel impulse response estimates.
10. ~The method of claim 9, wherein the deriving an overall channel impulse response estimate further includes selectively adjusting phase of the at least two instances of each initial channel impulse response estimate, and wherein the extended channel impulse response estimate for each initial channel impulse response estimate is formed based on at least two selectively phase adjusted instances of the initial channel impulse response estimate.
11. ~The method of claim 9, wherein the deriving an overall channel impulse response estimate further includes scaling each of the at least two extended channel impulse response estimates with a respective set of coefficients to obtain a corresponding scaled channel impulse response estimate, wherein at least two scaled channel impulse response estimates are obtained for the at least two extended channel impulse response estimates with at least two sets of coefficients, and combining the at least two scaled channel impulse response estimates to obtain the overall channel impulse response estimate.
12. ~The method of claim 11, wherein the at least two sets of coefficients are for a finite impulse response (FIR) filter.
13. ~The method of claim 11, wherein the at least two sets of coefficients are for an infinite impulse response (IIR) filter.
14. ~The method of claim 11, wherein each set of coefficients include N cp coefficients of a first value and N L coefficients of a second value, wherein the N cp coefficients of the first value are for first N cp taps of the overall channel impulse response estimate, and wherein the N L coefficients of the second value are for remaining taps of the overall channel impulse response estimate, where N cp and N L are integers greater than one.
15. ~The method of claim 1, wherein each of the at least two initial channel impulse response estimates is derived by performing an inverse fast Fourier transform (IFFT) on a respective one of the at least two initial frequency response estimates.
16. ~The method of claim 1, wherein the overall frequency response estimate is derived by performing a fast Fourier transform (FFT) on the overall channel impulse response estimate.
17. ~The method of claim 1, further comprising:
setting selected ones of N T taps of the overall channel impulse response estimate to zero, where N T is a length of the overall channel impulse response estimate and is an integer greater than one.
18. ~The method of claim 17, wherein last N Z of the N T taps of the overall channel impulse response estimate are set to zero, where N Z is less than N T.
19. ~The method of claim 18, wherein N Z is equal to N T - N cp, where N cp is a cyclic prefix length for the system and is an integer greater than one.
20. ~The method of claim 1, further comprising:~
determining energy of each of N T taps of the overall channel impulse response estimate, where N T is a length of the overall channel impulse response estimate and is an integer greater than one; and setting each of the N T taps to zero if the energy of the tap is less than a threshold.
21. ~The method of claim 20, wherein the threshold is derived based on total energy of the N T taps.
22. ~The method of claim 1, further comprising:
determining energy of each of N T taps of the overall channel impulse response estimate, where N T is a length of the overall channel impulse response estimate and is an integer greater than one;
retaining N X taps with largest energy among the N T taps of the overall channel impulse response estimate, where N X is an integer one or greater; and setting N T - N X remaining taps of the overall channel impulse response estimate to zero.
23. ~The method of claim 1, further comprising:
performing detection on received data symbols with the overall frequency response estimate.
24. ~The method of claim 1, wherein the wireless communication system utilizes orthogonal frequency division multiplexing (OFDM).
25. ~The method of claim 1, wherein the wireless communication system utilizes discrete mufti tone (DMT).
26. ~The method of claim 24, wherein each OFDM symbol transmitted in the wireless communication system includes a cyclic prefix, and wherein the overall channel impulse response estimate comprises more taps than a length of the cyclic prefix.
27. ~An apparatus in a wireless communication system, comprising:
a demodulator operative to obtain at least two groups of received pilot symbols for at least two sets of pilot subbands, one group of received pilot symbols for each set of pilot subbands, wherein each of the at least two sets of pilot subbands is used for pilot transmission in a different symbol period;
a pilot detector operative to obtain at least two initial frequency response estimates for a wireless channel based on the at least two groups of received pilot symbols, one initial frequency response estimate for each group of received pilot symbols;
a combiner unit operative to derive an overall channel impulse response estimate based on the at least two initial frequency response estimates, wherein the overall channel impulse response estimate comprises more taps than the number of pilot subbands in each of the at least two sets of pilot subbands; and a first transform unit operative to derive an overall frequency response estimate for the wireless channel based on the overall channel impulse response estimate.
28. ~The apparatus of claim 27, further comprising:
a second transform unit operative to derive at least two initial channel impulse response estimates based on the at least two initial frequency response estimates, one initial channel impulse response estimate for each initial frequency response estimate, and wherein the combiner unit is operative to derive the overall channel impulse response estimate based on the at least two initial channel impulse response estimates.
29. ~The apparatus of claim 27, wherein the combiner unit is operative to derive an intermediate frequency response estimate based on the at least two initial frequency response estimates and to derive the overall channel impulse response estimate based on the intermediate frequency response estimate.
30. ~The apparatus of claim 28, wherein the combiner unit is operative to repeat each of the at least two initial channel impulse response estimates at least once to obtain at least two instances of the initial channel impulse response estimate, form an extended channel impulse response estimate for each initial channel impulse response estimate based on the at least two instances of the initial channel impulse response estimate, and derive the overall channel impulse response estimate based on at least two extended channel impulse response estimates for the at least two initial channel impulse response estimates.
31. ~The apparatus of claim 30, wherein the combiner unit is further operative to scale each of the at least two extended channel impulse response estimates with a respective set of coefficients to obtain a corresponding scaled channel impulse response estimate, wherein at least two scaled channel impulse response estimates are obtained for the at least two extended channel impulse response estimates with at least two sets of coefficients, and combine the at least two scaled channel impulse response estimates to obtain the overall channel impulse response estimate.
32 32.~The apparatus of claim 27, further comprising:
a thresholding unit operative to set selected ones of N T taps of the overall channel impulse response estimate to zero, where N T is a length of the overall channel impulse response estimate and is an integer greater than one.
33. ~The apparatus of claim 27, wherein the wireless communication system utilizes orthogonal frequency division multiplexing (OFDM), wherein each OFDM symbol transmitted in the wireless communication system includes a cyclic prefix, and wherein the overall channel impulse response estimate comprises more taps than a length of the cyclic prefix.
34. ~An apparatus in a wireless communication system, comprising:
means for obtaining at least two groups of received pilot symbols for at least two sets of pilot subbands, one group of received pilot symbols for each set of pilot subbands, wherein each of the at least two sets of pilot subbands is used for pilot transmission in a different symbol period;
means for obtaining at least two initial frequency response estimates for a wireless channel based on the at least two groups of received pilot symbols, one initial frequency response estimate for each group of received pilot symbols;
means for deriving an overall channel impulse response estimate based on the at least two initial frequency response estimates, wherein the overall channel impulse response estimate comprises more taps than the number of pilot subbands in each of the at least two sets of pilot subbands; and~~
means for deriving an overall frequency response estimate for the wireless channel based on the overall channel impulse response estimate.
35. ~The apparatus of claim 34, wherein the means for deriving an overall channel impulse response estimate based on the at least two initial frequency response estimates~~
includes means for deriving at least two initial channel impulse response estimates based on the at least two initial frequency response estimates, one initial channel impulse response estimate for each initial frequency response estimate, and means for deriving the overall channel impulse response estimate based on the at least two initial channel impulse response estimates.
36. ~The apparatus of claim 34, wherein the means for deriving an overall channel impulse response estimate based on the at least two initial frequency response estimates includes means for deriving an intermediate frequency response estimate based on the at least two initial frequency response estimates, and means for deriving the overall channel impulse response estimate based on the intermediate frequency response estimate.
37. ~The apparatus of claim 35, further comprising:
means for repeating each of the at least two initial channel impulse response estimates at least once to obtain at least two instances of the initial channel impulse response estimate;
means for forming an extended channel impulse response estimate for each initial channel impulse response estimate based on the at least two instances of the initial channel impulse response estimate; and means for deriving the overall channel impulse response estimate based on at least two extended channel impulse response estimates for the at least two initial channel impulse response estimates.
38. ~The apparatus of claim 34, further comprising:
means for scaling each of the at least two extended channel impulse response estimates with a respective set of coefficients to obtain a corresponding scaled channel impulse response estimate, wherein at least two scaled channel impulse response estimates are obtained for the at least two extended channel impulse response estimates with at least two sets of coefficients, and means for combining the at least two scaled channel impulse response estimates to obtain the overall channel impulse response estimate.
39. ~The apparatus of claim 34, further comprising:
means for setting selected ones of N T taps of the overall channel impulse response estimate to zero, where N T is a length of the overall channel impulse response estimate and is an integer greater than one.
CA002553746A 2004-01-21 2004-12-07 Pilot transmission and channel estimation for an ofdm system with excess delay spread Active CA2553746C (en)

Applications Claiming Priority (5)

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US53821004P 2004-01-21 2004-01-21
US60/538,210 2004-01-21
US10/821,706 US7339999B2 (en) 2004-01-21 2004-04-09 Pilot transmission and channel estimation for an OFDM system with excess delay spread
US10/821,706 2004-04-09
PCT/US2004/040959 WO2005076558A1 (en) 2004-01-21 2004-12-07 Pilot transmission and channel estimation for an ofdm system with excess delay spread

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EP (2) EP1714452B1 (en)
JP (2) JP2007519368A (en)
KR (1) KR100831126B1 (en)
CN (2) CN101040503B (en)
AR (1) AR047452A1 (en)
AU (1) AU2004315369C1 (en)
BR (1) BRPI0418430B1 (en)
CA (1) CA2553746C (en)
IL (1) IL176989A (en)
RU (1) RU2348120C2 (en)
TW (1) TWI353147B (en)
WO (1) WO2005076558A1 (en)

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