Source: http://www.google.com/patents/US7881237?dq=5,583,822
Timestamp: 2014-07-10 04:46:34
Document Index: 319099476

Matched Legal Cases: ['Application No. 60', 'art 16', 'art 16', 'art 16', 'art 11', 'art 11', 'art 11']

Patent US7881237 - Compensation for residual frequency offset, phase noise and I/Q imbalance in ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsA method and apparatus for processing a radio frequency signal. The method includes compensating a digital in-phase signal and a digital quadrature signal for any imbalance; converting the compensated digital in-phase signal and the compensated digital quadrature signal into a frequency domain digital...http://www.google.com/patents/US7881237?utm_source=gb-gplus-sharePatent US7881237 - Compensation for residual frequency offset, phase noise and I/Q imbalance in OFDM modulated communicationsAdvanced Patent SearchPublication numberUS7881237 B1Publication typeGrantApplication numberUS 12/645,678Publication dateFeb 1, 2011Filing dateDec 23, 2009Priority dateAug 19, 2002Also published asUS7433298, US7643405, US8488442Publication number12645678, 645678, US 7881237 B1, US 7881237B1, US-B1-7881237, US7881237 B1, US7881237B1InventorsRavi NarasimhanOriginal AssigneeMarvell International Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (15), Non-Patent Citations (6), Classifications (19) External Links: USPTO, USPTO Assignment, EspacenetCompensation for residual frequency offset, phase noise and I/Q imbalance in OFDM modulated communicationsUS 7881237 B1Abstract A method and apparatus for processing a radio frequency signal. The method includes compensating a digital in-phase signal and a digital quadrature signal for any imbalance; converting the compensated digital in-phase signal and the compensated digital quadrature signal into a frequency domain digital OFDM symbol; generating a plurality of channel estimates, wherein each channel estimate corresponds to an estimate of the channel for a corresponding sub-carrier of the frequency domain digital OFDM symbol; and generating (i) a most likely estimate of the imbalance between the digital in-phase signal and the digital quadrature signal and (ii) a most likely estimate of a common phase error in the plurality of channel estimates. The most likely estimate of the imbalance is used to compensate the digital in-phase signal and the digital quadrature signal, and the most likely estimate of the common phase error is used to compensate the plurality of channel estimates.
RELATED APPLICATIONS This application is a continuation of U.S. patent application Ser. No. 12/287,199, filed Oct. 7, 2008, which is a continuation of U.S. patent application Ser. No. 10/316,806 (now U.S. Pat. No. 7,433,298), filed Dec. 10, 2002, which claims priority benefit under 35 U.S.C. �119(e)(1) to U.S. Provisional Application No. 60/404,655, filed Aug. 19, 2002. The disclosures of the above applications are incorporated herein by reference in their entirety.
x ⁡ ( t ) = 1 N ⁢ ∑ k = 0 N - 1 ⁢ X k ⁢ ⅇ j ⁢ 2 ⁢ ⁢ nkt NT ( 1 ) where Xk are the frequency-domain data symbols. In other words, the N values Xk represent the respective values of the discretely-varying (e.g. QPSK or QAM) signals modulating the OFDM carriers.
Referring still to FIG. 5, the preamble field 502 is followed by a signal field 504 which consists of one OFDM symbol. This contains the rate and length fields as requested by the MAC interface 125. The rate field conveys information about the type of modulation and the coding rate as used in the rest of the packet. The encoding of the SIGNAL single OFDM symbol is performed with BPSK modulation of the sub-carriers and again using convolutional coding at R=�. The SIGNAL field is composed of 24 bits, with bits 0 to 3 encoding the rate, bit 4 reserved, and bits 5-16 encoding the length of the packet, with the LSB being transmitted first. A single parity bit and 6-bit tail field complete the SIGNAL symbol. Finally, the SIGNAL field 504 is followed by the data 506 comprising a variable number of OFDM symbols including the SERVICE field still forming part of the PLCP Header, consistent with the length specified in the SIGNAL field 504.
z ⁡ ( t ) ≈ y ⁡ ( t ) + y * ⁡ ( t ) ⁡ [ ɛ 2 - j ⁢ θ 2 ] + v ⁡ ( t ) ( 3 ) Let Φn, yn, zn, vn denote the discrete-time versions of Φ(t), y(t), z(t), v(t), respectively, sampled at the rate 1/Ts. Let Yk, Zk, Vk denote the N-point FFT's of yn, zn, vn, respectively. Also, let α=(ε−jθ)/2, which represents the I/Q imbalance in the frequency domain, and Λk, phase noise and residual frequency offset, denote the FFT of ejΦn (the residual frequency offset and phase noise in the frequency domain). The FFT output Zk is given by
H k = ∫ h ⁡ ( τ ) ⁢ ⅇ - j ⁢ 2 ⁢ ⁢ nk ⁢ ⁢ τ NTs ⁢ ⅆ τ is the FFT of the channel impulse response and Wk represents intercarrier interference and noise (also known as Additive White Gaussian Noise or AWGN). The common phase error (CPE) is given by Λo. Let Ak=HkXk/N. Therefore,
Λ o , ML = c 1 ⁢ r 2 - c 2 * ⁢ r 1 c 1 2 -  c 2  2 ⁢ ⁢ and ( 6 ) α ML = c 1 ⁢ r 1 - c 2 ⁢ r 2 c 1 ⁢ r 2 * - c 2 ⁢ r 1 * ( 7 ) where
c 1 = ∑ i = 1 M ⁢ (  A ^ k i  2 +  A ^ - k i  2 ) , ( 8 ) c ⁢ ⁢ 2 = 2 ⁢ ⁢ ∑ i = 1 M ⁢ A ^ k i ⁢ A ^ - k i , ( 9 ) r 1 = ∑ i = 1 M ⁢ ( Z k i ⁢ A ^ - k i + Z - k i ⁢ A ^ k i , and ( 10 ) r 2 = ∑ i = 1 M ⁢ ( Z k i ⁢ A ^ k i * + Z - k i ⁢ A ^ - k i * ) . ( 11 ) The most likely estimates Λ0,ML and αML are in fact here derived from a maximum likelihood estimation expression:
λ 0 , α min ⁡ [ ∑ i = 1 M ⁢ [  Z ki - Λ o ⁢ A ki - Λ o * ⁢ α ⁢ ⁢ A - ki *  2 +  Z - ki - Λ o ⁢ A - ki - Λ o * k ⁢ ⁢ 1 ⁢ α ⁢ ⁢ A ki *  2 ] ] , based on a likelihood function for equation (5) listed above for pilot subcarriers at �k1, . . . , �kM, distributed according to multi dimensional Gaussian distribution. To find Λ0,ML and αML from this expression, this expression is differentiated with respect to α and Λ0, the results are set to 0 and solved for these variables.
εML=2 (αML) (13)ΛML=−2 (αML) (14)Let In, Qn denote the I and Q components of the output of the analog to digital converter, namely ADC 210 in FIG. 2 which define the nth OFDM symbol in the inbound PLCP frame. The I/Q imbalance is compensated by the I/Q imbalance compensation unit 220 by forming Ĩn, {tilde over (Q)}n where
α ML = ∑ i = 1 M ⁢ [ ( Z k i - A ^ k i ) ⁢ A ^ - k i + ( Z - k i - A ^ - k i ) ⁢ A ^ k i ] ∑ i = 1 M ⁢ [  A ^ - k i  2 +  A ^ k i  2 ] , ( 17 ) where �k=ĤkXk|N. Here, the common phase error Λo,ML is deemed to be negligible and so no adaptive compensation of the channel estimates accounting for Λo,ML need occur. In comparison to the previously described embodiments, this results in a less complex I/Q imbalance calculation unit (which only needs to calculate αML per equation (17), as well as εML and θML in light thereof, as presented in equations (13) and (14) if, for example, an I/Q imbalance compensation unit such as unit 220 (FIG. 2) is employed. However, this potentially result in reduced receiver performance in comparison with previously described embodiments, particularly where effective data throughput approaches 802.11a/g maximum rates or orthogonality of the sub-carriers is substantially comprised by ambient noise.
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS5949821Aug 5, 1996Sep 7, 1999Motorola, Inc.Method and apparatus for correcting phase and gain imbalance between in-phase (I) and quadrature (Q) components of a received signal based on a determination of peak amplitudesUS6035003Dec 1, 1997Mar 7, 2000Daewoo Electronics Co., Ltd.Apparatus for correcting frequency offset in OFDM receiving systemUS6097776Feb 12, 1998Aug 1, 2000Cirrus Logic, Inc.Maximum likelihood estimation of symbol offsetUS6363084Aug 12, 1998Mar 26, 2002Daewoo Electronics Co. Ltd.Method for estimating coarse frequency offset in OFDM receiver and apparatus employing the sameUS6414936Nov 18, 1998Jul 2, 2002Korea Electronics Technology InstituteMethod of estimating carrier frequency offset in an orthogonal frequency division multiplexing systemUS6549561Aug 21, 2001Apr 15, 2003Magis Networks, Inc.OFDM pilot tone tracking for wireless LANUS6892060Jun 28, 2002May 10, 2005Institute Of MicroelectronicsFully integrated self-tuned image rejection downconversion systemUS6950483Mar 8, 2001Sep 27, 2005Proxim, Inc.Timing misalignment estimationUS7012882Jul 30, 2001Mar 14, 2006Sony International (Europe) GmbhChannel estimator for OFDM systemUS7020226Apr 4, 2002Mar 28, 2006Nortel Networks LimitedI/Q distortion compensation for the reception of OFDM signalsUS7088672Dec 6, 2001Aug 8, 2006Samsung Electronics Co., Ltd.Device for receiving OFDM signal, and method for restoring signal by channel estimationUS7433298Dec 10, 2002Oct 7, 2008Marvell International Ltd.Compensation for residual frequency offset, phase noise and I/Q imbalance in OFDM modulated communicationsWO2001080509A1Apr 10, 2001Oct 25, 2001Mitsubishi Electric CorpCompensation of sampling frequency offset and local oscillator frequency offset in a ofdm receiverWO2002023844A1 Title not availableWO2002045387A2Nov 15, 2001Jun 6, 2002Rpm PartnershipSynchronization, channel estimation and pilot tone tracking systemNon-Patent CitationsReference1IEEE P802.16a/D2-2002, Sponsor LAN MAN Standards Committee of IEEE Computer Society, "Local and Metropolitan Area Networks-Part 16: Air Interface for Fixed Broadband Wireless Access Systems," Feb. 7, 2002, pp. 1-253.2IEEE P802.16a/D2-2002, Sponsor LAN MAN Standards Committee of IEEE Computer Society, "Local and Metropolitan Area Networks�Part 16: Air Interface for Fixed Broadband Wireless Access Systems," Feb. 7, 2002, pp. 1-253.3IEEE std 802.16-2004, (Revision of IEEE std. 802.16-2001), IEEE Standard for Local and metropolitan area networks, Part 16; Air Interface for Fixed Broadband Wireless Access Systems, IEEE Computer Society and the IEEE Microwave Theory and Techniques Society, Sponsored by the LAN/MAN Standards Committee, 893 pages.4IEEE std. 802.11a-1999, Sponsor LAN MAN Standards Committee of IEEE Computer Society, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, High-Speed Physical Layer Extension in the 5 GHz Band," Sep. 1999, pp. 1-83.5International Standard, ANSI/IEEE std. 802.11, first edition, Sponsor LAN MAN Standards Committee of IEEE Computer Society, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications," 1999.6LAN/MAN Standards Committee of the IEEE Computer Society (May 2002). "DRAFT Supplement to STANDARD (for) Information Technology-Telecommunications and Information Exchange Between Systems-Local and Metropolitan area Networks-Specific Requirements-Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Further Higher-Speed Physical Layer Extension in the 2.4 GHz Band," IEEE Std. 802.11g/D2.8 (Supplement to ANSI/IEEE Std. 802.11, 1999 Edition) 48 pages total.Classifications U.S. Classification370/280, 375/376, 375/373, 370/206, 370/210, 370/503, 370/516, 375/371International ClassificationH04J11/00Cooperative ClassificationH04L27/2665, H04L27/2695, H04L25/022, H04L25/0228, H04L27/3863, H04L25/023European ClassificationH04L25/02C7C, H04L27/38N2A, H04L27/26M5, H04L27/26M5C3RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google