Publication number | US20080095256 A1 |

Publication type | Application |

Application number | US 11/978,841 |

Publication date | Apr 24, 2008 |

Filing date | Oct 30, 2007 |

Priority date | Oct 18, 2006 |

Also published as | US7830994, US8761277, US20080095275, US20110103450, US20110103453, US20110182340, US20110182374, WO2008048630A2, WO2008048630A3 |

Publication number | 11978841, 978841, US 2008/0095256 A1, US 2008/095256 A1, US 20080095256 A1, US 20080095256A1, US 2008095256 A1, US 2008095256A1, US-A1-20080095256, US-A1-2008095256, US2008/0095256A1, US2008/095256A1, US20080095256 A1, US20080095256A1, US2008095256 A1, US2008095256A1 |

Inventors | Haim Primo, Yosef Stein, Wei An |

Original Assignee | Haim Primo, Yosef Stein, Wei An |

Export Citation | BiBTeX, EndNote, RefMan |

Patent Citations (28), Non-Patent Citations (1), Referenced by (14), Classifications (15), Legal Events (1) | |

External Links: USPTO, USPTO Assignment, Espacenet | |

US 20080095256 A1

Abstract

Channel estimation for high mobility OFDM channels is achieved by identifying a set of channel path delays from an OFDM symbol stream including carrier data, inter-channel interference noise and channel noise; determining the average channel impulse response for the identified set of channel path delays in each symbol; generating a path delay curvature for each channel path delay in each symbol based on stored average channel impulse responses for the identified channel path delays; estimating the carrier data in the symbols in the OFDM symbol stream in the presence of inter-channel interference noise and channel noise from the OFDM symbol steam and the average impulse responses for the identified channel path delays; reconstructing the inter-channel interference noise in response to the path delay curvature, the identified set of channel path delays and estimated carrier data to produce a symbol stream of carrier data and channel noise with suppressed inter-channel interference noise.

Claims(30)

a threshold setting circuit for setting a local predetermined threshold for sets of channel path delays in each said window in accordance with their energy levels; and

a threshold circuit for selecting channel path delays in each said window meeting their local predetermined threshold and combining the selected channel path delays, from all said windows, to determine the total channel path delays.

an estimator circuit for determining average path gains based on least squares and known noise.

a selection circuit for selecting from storage the average channel gains of neighboring OFDM symbols;

a rate determining circuit for determining the rate of change of the neighboring average channel gains;

a model selection circuit for identifying a best fit average free curve for the stored channel impulse responses.

a vector generating circuit for creating a vector with zeros and inserting average path gains in associated delay locations; and

an equalization circuit for calculating equalization coefficients.

local OFDM symbol generator, responsive to estimated carrier data to generate locally OFDM symbol replicas; and

an ICI distortion generator for shifting an OFDM symbol replica by each associated channel path delay, multiplying it by the associated path delay curvature and summing the shifted, multiplied symbol replicas to produce local inter-channel interference noise.

setting a threshold for groups of channel path delays in accordance with their energy levels; and

selecting channel path delays meeting a predetermined threshold.

averaging the channel gains of neighboring OFDM symbols;

determining the rate of change of the neighboring average channel gains; and

identifying a best fit average free curve for the stored channel impulse responses.

creating a vector with zeros and inserting average path gains in associated delay locations; and

calculating equalization coefficients in response to an FT and applying them to the associated symbol.

generating locally OFDM symbol replicas from said estimated carrier data; and

shifting an OFDM symbol replica by each associated channel path delay, multiplying it by the associated path delay curvature and summing the shifted, multiplied symbol replicas to produce local inter-channel interference noise.

a threshold setting circuit for setting a local predetermined threshold for sets of channel path delays in each said window in accordance with their energy levels; and

a threshold circuit for selecting channel path delays in each said window meeting their local predetermined threshold and combining the selected channel path delays, from all said windows, to determine the total channel path delays.

setting a local predetermined threshold for sets of channel path delays in each said window in accordance with their energy levels; and

selecting channel path delays in each said window meeting their local predetermined threshold and combining the selected channel path delays, from all said windows, to determine the total channel path delays.

Description

- [0001]This application is a continuation-in-part of U.S. patent application Ser. No. 11/789,180 filed Apr. 24, 2007 which claims benefit of and priority to U.S. Provisional Application Ser. No. 60/852,607 filed Oct. 18, 2006 each of which are incorporated herein by this reference.
- [0002]This invention relates to channel estimator system and method components for high mobility OFDM channels.
- [0003]Binary phase shift keying (BPSK) is a conventional data modulation scheme that conveys data by changing, the phase of a reference carrier signal, for example, during each BPSK symbol period carrier data in the form of either a positive or negative sine wave is transmitted. A positive sine wave represents a data “1”, a negative sine wave a data “0”. When the symbol stream arrives at the receiver it is decoded by multiplying with a positive sine wave. The multiplying of it by another positive sine wave produces a average positive level; if the symbol period contains a negative sine wave the multiplexing by a positive sine wave produces an average negative level. Orthogonal Frequency Division Multiplexing (OFDM) employs the same idea but instead of one carrier wave per bit, the bit stream to be transmitted is split into several parallel low-rate bit streams, two, ten or any number; presently over 8k (8192). Each low-rate bit stream is transmitted over one sub-channel by modulating a sub-carrier using a standard modulation scheme, for example BPSK. The sub-carrier frequencies are chosen so that the modulated data streams are orthogonal to each other. The demodulation at the receiver is done in the same way with the symbol period sine waves being multiplied selectively by a positive sine wave of each of the frequencies transmitted. By virtue of orthogonality it is possible to distinguish between the various carrier sine waves. OFDM is thus a much higher density data encoding technique. OFDM has shortcomings but works well especially where the transmitter and received are fixed or not moving fast with respect to each other and so the transmitter channel between them remains constant or fairly constant. That is, the amplitude and phase of the various sine waves transmitted over that channel within a symbol period do not vary significantly over the symbol period. However in high mobility situations where the channel does change over the time of a symbol period, e.g. video streaming to a receiver on a moving vehicle or train, different sine waves can experience different channel paths resulting in variations in their phase and/or amplitude. Such variations referred to as inter-carrier or inter-channel interference (ICI) noise interferes with the orthogonality of the sine waves and can cause errors in the data decoding causing “1”s to appear to be “0”s and “0”s to appear as “1”s. This ICI noise accompanies but is different then the conventional channel noise that accompanies the carrier data.
- [0004]It is therefore an object of this invention to provide improved OFDM estimator system and method components for high mobility OFDM channels.
- [0005]It is a further object of this invention to provide such improved OFDM estimator system and method components which make efficient use of memory and power.
- [0006]It is a further object of this invention to provide such improved OFDM estimator system and method components which are power adaptive to channel conditions.
- [0007]The invention results from the realization that a channel estimation for high mobility OFDM channels can be achieved with improved system and method components for identifying a set of channel path delays from an OFDM symbol stream including carrier data, inter-channel interference noise and channel noise; for determining the average channel impulse response for the identified set of channel path delays in each symbol; for generating a path delay curvature for each channel path delay in each symbol from the stored average channel impulse responses for the identified channel path delays; for estimating the carrier data in the symbols in the OFDM symbol stream in the presence of inter-channel interference noise from the OFDM symbol stream and said average impulse responses for the identified channel path delays; for reconstructing the inter-channel interference noise in response to the identified set of channel path delays and estimated carrier data to produce a symbol stream of carrier data and channel noise with suppressed inter-channel interference noise.
- [0008]The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives.
- [0009]This invention features a path delay estimator circuit responsive to an OFDM symbol stream including carrier data, inter-channel interference noise and channel noise for identifying a set of channel path delays in a group of non-overlapping windows which are above a predetermined energy threshold including a threshold setting circuit for setting a local predetermined threshold for sets of channel path delays in each window in accordance with their energy levels and a threshold circuit for selecting channel path delays in each window meeting their local predetermined threshold and combining the selected channel path delays, from all the windows, to determine the total channel path delays.
- [0010]In a preferred embodiment the path delay estimator circuit may include a Fourier transform circuit for performing Fourier transform on an OFDM symbol. The path delay estimator circuit may include a normalizing circuit for extracting the channel frequency response for known carriers and inserting zeros for unknown carriers. The path delay estimator circuit may include an inverse Fourier transform for performing inverse Fourier transform on the channel frequency response. The path delay estimator circuit may include a noise estimator circuit for determining the channel noise level.
- [0011]This invention also features an average channel estimator circuit, responsive to the OFDM symbol stream and an identified set of channel path delays, for determining the average channel impulse response for the identified set of channel path delays in each symbol including an estimator circuit for determining average path gains based on least squares and known noise.
- [0012]In a preferred embodiment the channel estimator circuit may include a normalizing circuit for extracting the channel frequency response for known carriers. The channel estimator circuit may include a Fourier transform circuit for performing a Fourier transform on an OFDM symbol
- [0013]This invention also features a curve generator circuit, responsive to stored average impulse responses, for generating a path delay curvature for required channel path delay in each symbol. There is a selection circuit for selecting from storage the average channel gains of neighboring OFDM symbols, a rate determining circuit for determining the rate of change of the neighboring average channel gains and a model selection circuit for identifying a best fit average free curve for the stored channel impulse responses.
- [0014]This invention also features a carrier data estimator circuit, responsive to an OFDM symbol stream and average impulse responses from an average channel estimator circuit, for estimating the carrier data in the symbols in the OFDM symbol stream in the presence of inter-channel interference and channel noise including a vector generating circuit for creating a vector with zeros and inserting average path gains in associated delay locations and an equalization circuit for calculating equalization coefficients.
- [0015]In a preferred embodiment the carrier data estimator circuit may include a Fourier transform circuit for performing a Fourier transform on the vector. The carrier data estimator circuit may include an averaging circuit for calculating noise level. The carrier data estimator circuit may include a slicer circuit for matching the equalized symbols to a predefined grid of levels.
- [0016]This invention also features a regenerator circuit, responsive to a curve generator, path delay estimator circuit and carrier data estimation circuit, for reconstructing inter-channel interference noise including a local OFDM symbol generator, responsive to estimated carrier data to generate locally OFDM symbol replicas and an ICI distortion generator for shifting an OFDM symbol replica by each associated channel path delay, multiplying it by the associated path delay curvature and summing the shifted, multiplied symbol replicas to produce local inter-channel interference noise.
- [0017]This invention also features a method for identifying a set of channel path delays from an OFDM symbol stream including carrier data, inter-channel interference noise and channel noise including setting a threshold for groups of channel path delays in accordance with their energy levels and selecting channel path delays meeting a predetermined threshold.
- [0018]In a preferred embodiment the method may include performing a Fourier transform on an OFDM symbol. The method may include extracting the channel frequency response for known carriers and inserting zeros for unknown carriers. The method may include performing IFT on the channel frequency response. The method may include determining the channel noise level.
- [0019]This invention also features a method for determining the average channel impulse response for an identified set of channel path delays in each symbol including determining average path gains based on least squares and known noise.
- [0020]In a preferred embodiment the method may include extracting the channel frequency response for known carriers. The method may include performing a FT on an OFDM symbol.
- [0021]This invention also features a method for generating a path delay curvature for each channel path delay in each symbol based on stored average channel impulse responses for the identified channel path delays including averaging the channel gains of neighboring OFDM symbols, determining the rate of change of the neighboring average channel gains, and identifying a best fit average free curve for the stored channel impulse responses.
- [0022]This invention also features a method for estimating the carrier data in the symbols in the OFDM symbol stream in the presence of inter-channel interference noise and channel noise from the OFDM symbol stream and average impulse responses for the identified channel path delays including creating a vector with zeros and inserting average path gains in associated delay locations and calculating equalization coefficients in response to an FT and applying them to the associated symbol.
- [0023]In a preferred embodiment the method may include performing FT on the vector. The method may include calculating noise level. The method may include matching the equalized symbols to a predefined grid of levels.
- [0024]This invention also features a method of reconstructing the inter-channel interference noise in response to the path delay curvature, the identified set of channel path delays and estimated carrier data including generating locally OFDM symbol replicas from the estimated carrier data and shifting an OFDM symbol replica by each associated channel path delay, multiplying it by the associated path delay curvature and summing the shifted, multiplied symbol replicas to produce local inter-channel interference noise.
- [0025]This invention also features a system for identifying a set of channel path delays from an OFDM symbol stream including carrier data, inter-channel interference noise and channel noise for identifying a set of channel path delays in a group of non-overlapping windows which are above a predetermined energy threshold including a threshold setting circuit for setting a local predetermined threshold for sets of channel path delays in each window in accordance with their energy levels and a threshold circuit for selecting channel path delays in each window meeting their local predetermined threshold and combining the selected channel path delays, from all windows, to determine the total channel path delays.
- [0026]This invention also features a method for identifying a set of channel path delays from an OFDM symbol stream including carrier data, inter-channel interference noise and channel noise for identifying a set of channel path delays in a group of non-overlapping windows which are above a predetermined energy threshold including setting a local predetermined threshold for sets of channel path delays in each window in accordance with their energy levels and selecting channel path delays in each window meeting their local predetermined threshold and combining the selected channel path delays, from all windows, to determine the total channel path delays.
- [0027]Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:
- [0028]
FIG. 1 is a schematic, time domain, representation of two OFDM symbols; - [0029]
FIG. 2 is a schematic, frequency domain, representation of the OFDM symbols ofFIG. 1 ; - [0030]
FIG. 3 is a schematic diagram showing an example of multiple paths occurring in a channel between a transmitter and receiver; - [0031]
FIG. 3A is a graphical illustration of the gain and delay associated with each path inFIG. 3 ; - [0032]
FIG. 4 is a schematic block diagram of one embodiment of a channel estimator system according to this invention; - [0033]
FIG. 5 is a diagram of a flow chart of the path delay estimator circuit ofFIG. 4 ; - [0034]
FIG. 5A is a graphical illustration of the forcing of zeros in the unknown data carriers, referred to inFIG. 5 ; - [0035]
FIG. 5B is a graphical illustration of the windowing and thresholding of the channel impulse responses, referred to inFIG. 5 ; - [0036]
FIG. 6 is a diagram of a flow chart of the average channel estimator circuit ofFIG. 4 ; - [0037]
FIG. 7 is a diagram of a flow chart of the carrier data estimator circuit ofFIG. 4 ; - [0038]
FIG. 7A is a graphical illustration of the insertion of average path gains and zeros for unknown carriers in an N size vector, referred to inFIG. 5 ; - [0039]
FIG. 7B is a graphical illustration of the slicing of equalized data to set thresholds, referred to inFIG. 7 ; - [0040]
FIG. 8 is a diagram of a flow chart of the curve generator estimator circuit ofFIG. 4 ; - [0041]
FIG. 8A is a graphical illustration of curve modeling and filtering operation, referred to inFIG. 8 ; - [0042]
FIG. 9 is a diagram of a flow chart of the regenerator ICI circuit ofFIG. 4 ; - [0043]
FIG. 9A a graphical illustration of the building of an N size vector and insertion of carrier data estimation, pilots and zeros, referred to inFIG. 9 ; and - [0044]
FIG. 9B is a graphical illustration of the distortion or adjusting of an OFDM symbol according to the associated delay and gain referred to inFIG. 9 . - [0045]Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.
- [0046]There is shown in
FIG. 1 an OFDM symbol stream**10**including two symbols**12**and**14**each of which includes a cyclical prefix section**16**and carrier data section**18**. Each carrier data section**18**,FIG. 2 , includes a plurality of carrier data a_{0}, a_{1}, a_{2}, a_{3- }- - - a_{n-1}, a_{n }where the filled circles represent pilot carrier data whose amplitude and phase are known and the empty circles represent unknown carrier data. The OFDM symbol stream is typically propagated along a channel from a transmitter**20**,FIG. 3 , to a receiver**22**. Because of reflection from objects**24**in the area the channel may have multiple paths, the most direct path**28**with a phase of m_{0 }and additional paths**30**,**32**, and**34**having phases of m_{1}, m_{2}, m_{3}, respectively. Each path has its own gain or attenuation as shown inFIG. 3A , where each path has associated it with it a gain or amplitude h_{0}, h_{1}, h_{2}, h_{3}, and an associated phase shift m_{0}, m_{1}, m_{2}, m_{3}. If the transmitter**20**and**22**move relatively fast with respect to one another, inter-channel interference (ICI) noise develops due to the loss of orthogonality because the carrier data sine wave arrives at the receiver**22**along four paths with different phases and different amplitudes. This can result in inaccuracies in determining the nature of the data, possibly reading ones as zeros and zeros as ones. - [0047]In accordance with this invention the inter-channel interference (ICI) noise is suppressed by generating a replica ICI noise function and subtracting it from the signal in channel noise: thus where the incoming signal is represented by S+f(S)+n where S is the OFDM carrier data, f(S) is the ICI noise and n is the general channel noise this invention contemplates the generation of a replica ICI noise f′ h(S) and subtracting it from the incoming signal S+f(S)+n resulting in an output of simply S+n
- [0048]One embodiment of a channel estimation system
**36**having improved components: average channel estimation circuit**44**, curve generation circuit**48**, carrier data estimation circuit**50**, path delays estimation circuit**40**and regenerator ICI circuit**42**according to this invention is shown inFIG. 4 . Path delay estimator circuit**40**which responds to OFDM symbol stream**38**and estimates the path delays m_{0}-m_{n}; the certain identified ones of the estimated path delays are delivered both to ICI regenerator circuit**42**and average channel estimator circuit**44**. Average channel estimator circuit**44**responds to the identified set of channel path delays from path delay estimator circuit**40**and the OFDM symbol stream on line**38**and determines the average channel impulse responseh _{0},h _{1}, . . . ,h _{n }for the identified set of channel path delays in each symbol. Those average channel impulse responses for the identified channel path delays are stored in storage circuit**46**and then used by curve generator circuit**48**to generate a path delay curvature for each channel path delay in each symbol. Carrier data estimator circuit**50**also responds to the average impulse responses from the average channel estimator circuit and the OFDM symbol stream on input line**38**to locally estimate the carrier data (a**0**,a**1**, . . . an) in the OFDM symbol stream in the presence of inter-channel interference and channel noise. Regenerator ICI circuit**42**responds to the locally produced estimated carrier data from carrier data estimator circuit**50**and the path delay curvature for each channel path delay for curve generator circuit**48**and adjusts their phase in accordance with the path delay estimator circuit output**40**to reconstruct a replica ICI noise. This replica ICI noise on line**52**is then subtracted from the incoming OFDM symbol stream on line**38**in subtraction circuit**54**resulting in a symbol stream of carrier data and channel noise with suppressed inter-channel interference noise. - [0049]Channel estimator system
**36**in one embodiment may be constructed using a programmable device such as a Digital Signal Processor (DSP) programmed to operate as indicated inFIGS. 5-9 . - [0050]Path delay estimator circuit
**40**.FIG. 5 , first extracts the next OFDM symbol**60**and a Fourier Transform (FT)**62**(typically an FFT) is performed. The results are then normalized in a normalizing circuit using the known carriers. Thus, where, for example, a known carrier data a_{0 }is known and its frequency response H_{0 }can be determined, the carrier can be normalized by dividing a_{0}H_{0 }by the known a_{0 }to obtain the channel frequency response H_{o }alone**64**. Zero's are now forced in positions of all the unknown carriers**66**as shown graphically inFIG. 5A ; the known or pilot carriers are shown as filled circles**70**; the empty circles**72**represent the unknown carriers in which the zeros are forced, and the inverse Fourier transform (IFT)**68**(typically an inverse FFT or IFFT) is performed. This is done for a number of iterations, K, over a number of symbols to obtain an average H_{0 }and successively an average H_{1}, H_{2}, H_{3}. The noise level is then estimated in a noise estimator circuit**78**to determine the channel noise level. After the Kth iteration,**76**, the noise level**78**is estimated and then a window including a group of channel impulse responses are monitored to determine their energy level and accordingly a local threshold is set for the particular group**80**of that window. Then those channel impulse responses above the threshold level are identified and become the identified set of channel path delays**82**. This is shown more graphically inFIG. 5B where, for example, channel impulse responses**90**,**92**,**94**and**96**are viewed in window**98**to determine the energy level of that group of impulse responses**90**-**96**. Based on that energy level a first local threshold level**100**is set. The noise level is shown at**102**. Anything above threshold**100**is then selected as the identified channel path delays and the delays m_{o}, m_{1}, m_{2}, m_{3 }can be determined. In a second group**104**,**106**,**108**,**110**, viewed through a second window**112**, a lower energy is detected resulting in a second lower local threshold**114**being set. - [0051]Average channel estimator
**44**,FIG. 6 , begins by extracting the OFDM symbol**120**and then performing FFT on it,**122**. The results are normalized by known carriers, step**124**, in the same way as previously, where the known carrier, a_{0}, accompanied by the frequency response, H_{0}, is normalized by being divided by a_{0 }to obtain the frequency response H_{0}. The average path gains such as**90**-**96**shown inFIG. 5B are then estimated**126**using the Least Squares (LS) model and the known noise. Carrier data estimator circuit**50**,FIG. 7 , may be implemented by performing an FFT**130**on a received OFDM signal, then building a vector size N with zeros**132**and average path gains**134**inserted in the proper delay locations. This is shown in greater detail inFIG. 7A where the average path gains are shown at**138**and the unknown carriers which receive the zero insertions are shown at**140**. Following the insertion of the average path gains FFT is performed**136**to obtain the channel frequency response H_{0}, H_{1 }. . . . The noise level is again calculated**138**using an averaging circuit based on H_{0}, H_{1}, H_{2 }. . . and the pilot carriers. After this the equalization coefficients - [0000]
$\frac{1}{{H}_{0}},\frac{1}{{H}_{1}},\dots \ue89e\phantom{\rule{0.6em}{0.6ex}}\ue89e\frac{1}{{H}_{n}}$ - [0000]are calculated using an equalization circuit and equalization is performed
**140**. This can be done using the minimum mean square error (MMSE) method which is well known in the art. After this, slicing is performed**142**to match the equalized values to a predefined grid of level. For example, as shown inFIG. 7B , there are a grid of levels +1, +2, +3, −1, −2, −3, and the equalized data**144**are assigned to thresholds consistent with their levels: equalized data**144***a*is assigned level three, while equalized data**144***b*is assigned level 1, equalized data**144***c*is assigned level −2. - [0052]Curve generator circuit
**48**may be implemented as shown inFIG. 8 . Initially the average channel gains of the selected symbol P and neighboring symbols P+1, P+2. P−1, P−2 . . . are retrieved, selected using a selection or addressing circuit**170**from storage**46**. The curvature model is then determined using an FFT operation**172**and an estimation model is built**174**to estimate the tap function parameters. For example, if the best estimate is a line the model would be ax+b, if it were a parabola it would be ax^{2}+bx+c, a third order curve it would be ax^{3}+bx^{2}+cx+d. After the estimation the system returns to inquire whether the last path delay in the set has been processed**176**. If it has the routine is finished. If not it returns to retrieve average channel gain symbols**170**from storage**46**. A selection circuit performs the retrieving of the average channel gains in**170**and the FFT operation**172**functions as a rate determining circuit for determining the rate of change of the neighboring average channel gains. Model selection is accomplished by building the estimation model**174**. The operation is shown graphically inFIG. 8A where the instant symbol P has average channel response ĥ_{0 }along with the neighboring symbols P+1, P+2, P+3 . . . P−1, P−2 . . . in order to obtain an indication of the best fit average free curve**180**. In this case a first order or straight line best fit is indicated. InFIG. 8B , however, the curve**180***b*changes at a much higher rate and so it requires a higher order best fit average free curve, for example, a parabolic shape**182**whose average should be equal to the average channel response of the symbol P. The order of the best fit curve thus depends upon the rate of change of the average channel gain as determined by the FFT operation**172**. - [0053]Regenerator ICI circuit
**42**may be implemented,FIG. 9 , by building a vector size N with zeros**190**and then inserting carrier data a_{0 }estimation**192**and inserting the pilot data**194**. This is shown graphically inFIG. 9A where the inserted carrier data estimation and pilots are shown at**198**along with carrier data labeled a_{0}-a_{n-3 }and null carriers**200**indicated by zeros. After thisFIG. 9 , FFT is performed**202**and then ICI distortion is accomplished**204**and the results are summed**206**. The ICI distortion is accomplished by a local OFDM symbol replica generator**209**as shown inFIG. 9B . OFDM symbol**210**represented as OFDM symbol sine wave**212**is multiplied by the ICI average free gain curve**214**associated path delay curvature. Each of the phases m_{0 }through m_{3 }is shifted. The shifted forms of OFDM symbol are multiplied**212**by each of the ICI average free gains h_{0}, h_{1}, h_{2}, h_{3}, represented as one curve at**214**. The multiplication occurs in multiplier**212**and each of the waves, phase shifted by their phase m_{0}-m_{3 }is presented at**210***a,***210***b,***210***c,***210***d,*respectively. These are then summed**216**to generate the ICI replica**218**. - [0054]Although the preferred embodiment herein is shown with the Fourier transform operation being fast Fourier transforms (FFT's) or IFFT's, Fourier transforms (FT) of any type e.g., DFT, IDFT could be used.
- [0055]Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments.
- [0056]In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended.
- [0057]Other embodiments will occur to those skilled in the art and are within the following claims.

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US7995688 * | Aug 9, 2011 | Her Majesty The Queen In Right Of Canada, As Represented By The Minister Of Industry, Through The Communications Research Centre Canada | Channel estimation and ICI cancellation for OFDM | |

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Classifications

U.S. Classification | 375/260 |

International Classification | H04K1/10 |

Cooperative Classification | H04L27/2647, H04L25/03159, H04L25/03038, H04L25/025, H04L2025/03414, H04L2025/03783, H04B17/364, H04L25/0218, H04L25/0228, H04B17/345 |

European Classification | H04L25/03B1A5, H04B17/00B1D, H04B17/00B1F |

Legal Events

Date | Code | Event | Description |
---|---|---|---|

Oct 30, 2007 | AS | Assignment | Owner name: ANALOG DEVICES, INC., MASSACHUSETTS Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:STEIN, YOSEF;AN, WEI;PRIMO, HAIM;REEL/FRAME:020089/0213;SIGNING DATES FROM 20070731 TO 20071022 |

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