US9270494B2 - Channel estimation method and associated device for estimating channel for OFDM system - Google Patents
Channel estimation method and associated device for estimating channel for OFDM system Download PDFInfo
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- US9270494B2 US9270494B2 US14/298,956 US201414298956A US9270494B2 US 9270494 B2 US9270494 B2 US 9270494B2 US 201414298956 A US201414298956 A US 201414298956A US 9270494 B2 US9270494 B2 US 9270494B2
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- 238000012545 processing Methods 0.000 claims abstract description 15
- 239000011159 matrix material Substances 0.000 claims abstract description 12
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- 238000010586 diagram Methods 0.000 description 12
- 230000004044 response Effects 0.000 description 5
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000004891 communication Methods 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
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- 230000015556 catabolic process Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
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- 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
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- 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
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- 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
- H04L25/0204—Channel estimation of multiple channels
-
- 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
- H04L25/022—Channel estimation of frequency response
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- 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
- H04L25/0228—Channel estimation using sounding signals with direct estimation from sounding signals
- H04L25/023—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols
- H04L25/0232—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols by interpolation between sounding signals
- H04L25/0234—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols by interpolation between sounding signals by non-linear interpolation
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- 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
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- 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
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- 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
- H04L25/024—Channel estimation channel estimation algorithms
- H04L25/0242—Channel estimation channel estimation algorithms using matrix methods
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- 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
Definitions
- the present invention relates to a channel estimation method, and more particularly, to a channel estimation method and associated device for estimating both the pilot channel and data channel of data resource element.
- LTE Long Term Evolution
- variations in phase and amplitude are introduced into signals transmitted along the channel. These variations can be realized as channel response.
- the channel response is usually frequency-dependent and time-dependent. If the receiver can correctly detect the channel response, channel degradation in the received signal can be compensated. Detection of the channel response is called channel estimation.
- a number of resource elements (REs) are chosen to carry pilot signals for channel estimation purposes.
- the pilot signals contain useful information which facilitates the channel estimator in order to detect the channel response of a specific frequency and time. These resource elements carrying the pilot signals are also called pilot resource elements.
- FIG. 1 is a diagram illustrating a prior art channel estimation method performed upon a time-frequency domain 100 , wherein the x-axis represents the time domain, and the y-axis represents the frequency domain.
- the time-frequency domain 100 includes a plurality of pilot resource elements represented by the time-frequency grids H 0 -H 17 aligned in both the time direction and the frequency direction.
- the pilot resource elements H 0 -H 17 are utilized to estimate the data channel of the data resource element (i.e. the grid RE 1 ) by performing a two-dimensional (2D) channel estimation, wherein the data resource element RE 1 is calculated by interpolating all of the pilot channels H 0 -H 17 .
- 2D two-dimensional
- each data resource element is estimated by performing a plurality of multiplication operations (18 multiplication operations are required for estimating each data resource element), which thereby increases the computational complexity thereof.
- An object of the present invention is to provide a channel estimation method and an associated device to solve the aforementioned problem.
- Another object of the present invention is to provide a channel estimation method and an associated device for performing channel estimations with low computational complexity and a small ROM/RAM size.
- An embodiment of the present invention provides a channel estimation method arranged for estimating a data channel of a data resource element.
- the channel estimation method comprises obtaining a plurality of pilot channels for pilot resource elements in a time-frequency domain, respectively; utilizing a processing circuit to apply a transformation matrix to the pilot channels, to obtain a plurality of transformed pilot channels corresponding to the pilot resource elements, respectively; and estimating the data channel of the data resource element by performing a plurality of one-dimensional channel estimations according to the transformed pilot channels.
- the channel estimation device comprises a pilot channel estimator, a processing circuit and a data channel estimator.
- the pilot channel estimator is arranged to obtain a plurality of pilot channels for pilot resource elements in a time-frequency domain, respectively.
- the processing circuit is arranged to apply a transformation matrix to the pilot channels, to obtain a plurality of transformed pilot channels corresponding to the pilot resource elements, respectively.
- the data channel estimator is arranged to estimate the data channel of the data resource element by performing a plurality of one-dimensional channel estimations according to the transformed pilot channels.
- the channel estimation method comprises: obtaining a plurality of pilot channels for pilot resource elements in a time-frequency domain, respectively; utilizing a processing circuit to use the plurality of pilot channels for pilot resource elements to obtain a plurality of reference channels corresponding to the pilot resource elements, respectively; and estimating the data channel of the data resource element by performing a one-dimensional (1D) channel estimations according to the reference pilot channels.
- the channel estimation device comprises a pilot channel estimator, a processing circuit and a data channel estimator.
- the pilot channel estimator is arranged to obtain a plurality of pilot channels for pilot resource elements in a time-frequency domain, respectively.
- the processing circuit is arranged to use the plurality of pilot channels for pilot resource elements to obtain a plurality of reference channels corresponding to the pilot resource elements, respectively.
- the data channel estimator arranged to estimate the data channel of the data resource element by performing a one-dimensional (1D) channel estimations according to the reference pilot channels.
- FIG. 1 is a diagram illustrating a prior art channel estimation method performed upon a time-frequency domain.
- FIG. 2 is a diagram illustrating a channel estimation device arranged for estimating a data channel of a data resource element.
- FIG. 3 is a diagram illustrating a scenario of performing channel estimation upon the time-frequency domain shown in FIG. 1 according to an embodiment of the present invention.
- FIG. 4 is a diagram illustrating a scenario of performing channel estimation upon the time-frequency domain shown in FIG. 1 according to another embodiment of the present invention.
- FIG. 5 is a flowchart illustrating a channel estimation method according to an embodiment of the present invention.
- FIG. 6 is a diagram illustrating a scenario of performing channel estimation upon the time-frequency domain shown in FIG. 1 according to yet another embodiment of the present invention.
- FIG. 7 is a diagram illustrating a scenario of performing channel estimation upon the time-frequency domain shown in FIG. 1 according to still another embodiment of the present invention.
- FIG. 2 is a diagram illustrating a channel estimation device 200 arranged for estimating a data channel of a data resource element.
- FIG. 3 is a diagram illustrating a scenario of performing channel estimation upon the time-frequency domain 100 shown in FIG. 1 according to an embodiment of the present invention.
- the channel estimation device 200 includes a pilot channel estimator 210 , a processing circuit 220 and a data channel estimator 230 .
- the pilot channel estimator 210 is arranged to obtain a plurality of pilot channels for pilot resource elements (e.g. the pilot channels H 0 -H 17 as shown in FIG. 1 ) in the time-frequency domain 100 , respectively. After the pilot channels H 0 -H 17 are obtained, the data resource element RE 1 may be estimated accordingly.
- pilot resource elements e.g. the pilot channels H 0 -H 17 as shown in FIG. 1
- the data resource element RE 1 may be estimated accordingly.
- the present invention is not limited to the pattern, and the number of the pilot channels is also not limited.
- pilot channel estimation accuracy can be enhanced with the assistance of other pilots, since the original pilot channel is raw generally derived by a least square estimator for each pilot resource element independently.
- the processing circuit 220 is arranged to apply a transformation matrix T to the pilot channels H 0 -H 17 , for obtaining a plurality of transformed pilot channels x 0 -x 17 corresponding to the pilot channels H 0 -H 17 , respectively.
- each of the pilot channels H 0 -H 17 maybe stacked as a vector h′.
- a minimum mean-square error (MMSE) interpolation may be utilized to mitigate the influence of the noise vector ⁇ and improve the performance of the channel estimation.
- the transformation matrix can be some classical transformation matrices, some coefficient matrices, or an identity matrix.
- the present invention does not limit the type of transformation matrix.
- the MMSE interpolation may be replaced with other mathematical computations (e.g. the least-square (LS) estimation, linear interpolation and averaging operation) as long as similar results can be achieved.
- the present invention is not limited to the MMSE interpolation.
- the data channel estimator 230 is arranged to estimate the data channel of the data resource element by performing a plurality of one-dimensional (1D) channel estimations according to the transformed pilot channels x 0 -x 17 . More specifically, the 1D channel estimations include a first interpolation operation in a first direction and a second interpolation operation in a second direction, wherein the second interpolation operation is performed after the first interpolation operation.
- the first direction is the time direction
- the second direction is the frequency direction. This is merely for illustrative purposes, however. In some modifications of this embodiment, the first direction may be the frequency direction, and the second direction may be the time direction. In short, the 1D channel estimation will be performed once for each of the time and frequency domains.
- the transformed pilot channels x 0 -x 8 of the same symbol may be utilized (e.g. interpolated or multiplied) to generate a temporary pilot channel M 1 on the subcarrier where the data resource element RE 1 is located.
- the transformed pilot channels x 9 -x 17 of the same symbol may be utilized (e.g. interpolated or multiplied) to generate another temporary pilot channel M 2 on the subcarrier where the data resource element RE 1 and the temporary pilot channel M 1 are located.
- the temporary pilot channels M 1 and M 2 may be interpolated to generate the estimated data channel of the data resource element RE 1 .
- the data channel of the data resource element RE 1 may be estimated by performing 1D channel estimations twice according to the transformed pilot channels x 0 -x 17 .
- the whole channel estimation operation is performed with two 1D channel estimation operations instead of the 2D channel estimation operation of the conventional method illustrated in FIG. 1 .
- the computational complexity is therefore greatly reduced. Since the pilot channels H 0 -H 17 are further transformed into the transformed pilot channels x 0 -x 17 , the detected noise can be mitigated by applying the MMSE interpolation, and the channel estimation performance is improved.
- the temporary pilot channel M 1 requires performing 9 multiplications with the transformed pilot channels x 0 -x 8 to be generated.
- the temporary pilot channel M 2 requires performing 9 multiplications with the transformed pilot channels x 9 -x 17 to be generated.
- the data resource element RE 1 requires performing 2 multiplications with the temporary pilot channels M 1 -M 2 to be generated. If neglecting the complexity for calculating x, the first data resource element RE 1 requires a total of 20 multiplications, the following estimation upon each of the data resource elements on the same subcarrier (column) where the data resource element RE 1 is located requires only 2 multiplications, since x and the time (frequency) direction interpolation results can be reused.
- the estimations upon each of the data resource elements on the same subcarrier where the data resource element RE 1 is located therefore require about 3.3 multiplications on average.
- the aforementioned conventional 2D channel estimation method requires 18 multiplication operations on average for each of data resource element.
- the embodiment of the present invention is capable of reducing the computational complexity, and thereby reducing the hardware loading.
- this embodiment can be implemented with two steps.
- the first step is to perform channel estimation for the reference resource elements (e.g. temporary pilot channels M 1 and M 2 ), so as to use the calculated reference resource elements to estimate the data resource element (e.g. the data resource element RE 1 ).
- the second step is to reuse the calculated reference resource elements to calculate other data resource elements on the same subcarrier where the first data resource element (e.g. the data resource element RE 1 ) is located. That is, a one-dimensional interpolation is performed with the help of reference resource elements to obtain a next data resource element, thus reducing the computational complexity.
- the x does not need to be recalculated.
- FIG. 4 is a diagram illustrating a scenario of performing channel estimation upon the time-frequency domain 100 shown in FIG. 1 according to another embodiment of the present invention.
- the frequency directional interpolation operation is performed first.
- the transformed pilot channels x 8 and x 17 of the same subcarrier may be utilized (e.g. interpolated or multiplied) to generate a temporary pilot channel M 1 on the symbol where the data resource element RE 1 is located, and the transformed pilot channels x 7 and x 16 of the same subcarrier may be utilized (e.g.
- the temporary pilot channels M 1 -M 9 may be interpolated to generate the estimated data channel of the data resource element RE 1 .
- the data channel of the data resource element RE 1 may be estimated by performing a plurality of 1D channel estimations according to the transformed pilot channels x 0 -x 17 .
- This embodiment is also capable of improving the channel estimation performance without increasing the computational complexity, and thereby reducing the hardware loading. Compared with the conventional channel estimation method, this embodiment requires less multiplication operations to obtain the precise channel estimation result.
- this embodiment can be implemented with two steps.
- the first step is to perform channel estimation for the reference resource elements (e.g. temporary pilot channels M 1 -M 9 ), so as to use the calculated reference resource elements to estimate the data resource element (e.g. the data resource element RE 1 ).
- the second step is to reuse the calculated reference resource elements to calculate other data resource elements on the same symbol where the first data resource element (e.g. the data resource element RE 1 ) is located. That is, a one-dimensional interpolation is performed with the help of reference resource elements to obtain a next data resource element, thus reducing the computational complexity.
- the y does not need to be recalculated.
- the first direction interpolation results do not need to be re-calculated as well.
- FIG. 5 is a flowchart illustrating a channel estimation method according to an embodiment of the present invention. Please note that, if the result is substantially the same, the steps are not required to be executed in the exact order shown in FIG. 5 .
- the flowchart can be briefly summarized as follows.
- Step 502 Start.
- Step 504 Obtain a plurality of pilot channels for pilot resource elements in a time-frequency domain, respectively.
- Step 506 Utilize a processing circuit to apply a transformation matrix to the pilot channels for obtaining a plurality of transformed pilot channels corresponding to the pilot resource elements, respectively.
- Step 508 Estimate the data channel of the data resource element by performing a plurality of one-dimensional channel estimations according to the transformed pilot channels.
- Step 510 End.
- pilot channel estimation accuracy can be enhanced as well with the assistance of other pilots, since the aforementioned pilot channels are considered as raw data that may be jointly utilized to obtain the desired RE 1 .
- FIG. 6 is a diagram illustrating a scenario of performing channel estimation upon the time-frequency domain shown in FIG. 1 according to yet another embodiment of the present invention
- FIG. 7 is a diagram illustrating a scenario of performing channel estimation upon the time-frequency domain shown in FIG. 1 according to still another embodiment of the present invention.
- the entire channel estimation can be divide into two steps:
- Step- 1 Utilize a processing circuit of a channel estimation device to estimate the channels (such as ⁇ ref-1 and ⁇ ref-2 in FIG. 6 or ⁇ ref-1 ⁇ ref-9 in FIG. 7 , but not the intermediate calculation results M 1 , M 2 , . . . shown in the FIGS. 3-4 ) for reference REs in the same subcarrier or same symbol as the desired RE 1 ; and
- Step- 2 Interpolate the channel for the desired RE with the assistance of the reference REs.
- the pilot channels H 0 , H 1 and H 2 may be jointly utilized to obtain the reference channel ⁇ ref-1
- the pilot channels H 9 , H 10 and H 11 may be jointly utilized to obtain the reference channel ⁇ ref-2
- the present invention is not limited thereto.
- the reference channel ⁇ ref-2 may be obtained by jointly utilizing the pilot channels H 0 , H 1 , H 9 and H 10 , or even all pilot channels.
- the exemplary scenario in FIG. 6 estimates channels ⁇ ref-1 and ⁇ ref-2 for reference REs in the same subcarrier, and then interpolate the reference REs to obtain the desired RE 1
- the exemplary scenario in FIG. 7 estimates channels ⁇ ref-1 - ⁇ ref-9 for reference REs in the same symbol, and then interpolate the reference REs to obtain the desired RE 1 .
- the reference REs do not necessarily to be aligned with pilot RE's.
- the reference RE number could be equal to/less than/greater than the pilot RE number in the same subcarrier (or symbol).
- the aforementioned transformation matrix T may be applied to the exemplary embodiment shown in FIGS. 6 and 7 , to obtain the reference channel estimation results. Since similar schemes are introduced in the embodiments of FIGS. 3 and 4 , the detailed descriptions are omitted here for brevity.
- the present invention is capable of improving the channel estimation performance with low computational complexity, thereby solving the problems of the prior art.
Abstract
Description
h′=h+η (1)
x=T·h′
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US20120213315A1 (en) * | 2009-09-17 | 2012-08-23 | St-Ericsson Sa | Process for estimating the channel in a ofdm communication system, and receiver for doing the same |
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2014
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US6654429B1 (en) * | 1998-12-31 | 2003-11-25 | At&T Corp. | Pilot-aided channel estimation for OFDM in wireless systems |
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