WO2004025916A1 - Estimation iterative et correction d'asymetries entre une branche en phase et une branche en quadrature dans des systemes de transmission a porteuses multiples - Google Patents

Estimation iterative et correction d'asymetries entre une branche en phase et une branche en quadrature dans des systemes de transmission a porteuses multiples Download PDF

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Publication number
WO2004025916A1
WO2004025916A1 PCT/DE2003/002849 DE0302849W WO2004025916A1 WO 2004025916 A1 WO2004025916 A1 WO 2004025916A1 DE 0302849 W DE0302849 W DE 0302849W WO 2004025916 A1 WO2004025916 A1 WO 2004025916A1
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WO
WIPO (PCT)
Prior art keywords
channel
data symbols
new
distortion parameters
received data
Prior art date
Application number
PCT/DE2003/002849
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German (de)
English (en)
Inventor
Lars BRÖTJE
Karl-Dirk Kammeyer
Volker Kühn
Sven Vogeler
Original Assignee
Infineon Technologies Ag
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Infineon Technologies Ag filed Critical Infineon Technologies Ag
Priority to EP03794799A priority Critical patent/EP1537710A1/fr
Publication of WO2004025916A1 publication Critical patent/WO2004025916A1/fr
Priority to US11/075,310 priority patent/US20050180534A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
    • H04L27/36—Modulator circuits; Transmitter circuits
    • H04L27/362—Modulation using more than one carrier, e.g. with quadrature carriers, separately amplitude modulated
    • H04L27/364—Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels
    • 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
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L25/03159—Arrangements for removing intersymbol interference operating in the frequency domain
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0016—Stabilisation of local oscillators
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0024—Carrier regulation at the receiver end

Definitions

  • the present invention relates to a method for estimating and correcting the distortion of radio signals caused by transmitter or receiver IQ asymmetries and by channel distortion, which are transmitted in a multicarrier transmission method, and an apparatus for carrying out the method.
  • DVB-S Digital Video Broadcasting
  • DVD-C digital transmission systems for cable
  • DVD-T terrestrial digital radio transmission
  • OFDM transmission method orthogonal freguency division multiplexing
  • Another important area of application of the OFDM transmission method is high-speed wireless data transmission networks such as LAN (Wireless Local Area Network), in particular the transmission methods specified in the standards IEEE802.11a and 11g and HIPERLAN / 2.
  • LAN Wireless Local Area Network
  • the OFDM transmission method is a multicarrier transmission method in which the data stream is divided into a number of parallel (orthogonal) subcarriers, each of which is modulated with a correspondingly low data rate. As shown in Fig. 1, are on the Frequency scale within a transmission bandwidth K (sub)
  • Carrier frequencies arranged at an equidistant distance from each other.
  • the carrier frequencies are on both sides and symmetrical to a center frequency f c .
  • an OFDM symbol results from the superposition of all K carrier frequencies.
  • the data transmission takes place in the form of frames or bursts, one frame containing a constant number of OFDM symbols.
  • OFDM radio signals can be received and demodulated using conventional reception concepts, which are based on the principle of heterodyne reception with subsequent digital quadrature mixing. Mainly for reasons of lower power consumption and the avoidance of external filters for image frequency suppression, however, increasingly advanced reception concepts are preferred, in which direct mixing methods are used.
  • direct-mixing receiver concepts the radio signal received and amplified via an antenna is split into an in-phase (I) and a quadrature (Q) branch and mixed in both branches with the output frequency of a local oscillator, the oscillator frequencies fed to the mixers being controlled by a phase shifter are mutually displaced by 90 °.
  • Quadrature demodulation for the recovery of the information-carrying baseband signals in this reception concept is carried out in analog circuit technology.
  • IQ asymmetries or IQ distortions, ie amplitude and phase asymmetries between the quadrature components.
  • the real and imaginary parts of the complex baseband signal are not exactly 90 ° out of phase with each other and also occur Amplitude deviations between the I and Q branches.
  • Such IQ asymmetries can occur in both the transmitter and the receiver. In the receiver, the IQ asymmetries in the case of OFDM-based transmission systems in the frequency domain, i.e.
  • each data symbol transmitted on the subcarrier n generates a signal contribution on the subcarrier with the index -n (image frequency) due to the IQ asymmetry added in the time domain.
  • the superimposition leads to distortions of the useful signals at positions n and -n.
  • Circuit arrangements of the two methods shown have a relatively large number of function blocks and are therefore characterized by a high level of implementation effort.
  • Another method is known from WO 02/056523, with which IQ asymmetries on the transmitter and receiver side can be eliminated. This method is based on the fact that compensation signals corresponding to the IQ errors are generated and used for the compensation.
  • the present invention relates to methods for estimating and correcting the distortion of radio signals caused by transmitter or receiver IQ asymmetries and by channel distortion, which are transmitted in a multi-carrier transmission method in the form of frames or bursts.
  • the method can be used in all areas in which multicarrier
  • Transmission methods can be used, for example in the area of wireless data transmission networks (WLAN) or in the area of digital terrestrial video or audio signal transmission.
  • a known multi-carrier transmission method is, for example, the OFDM method already described above.
  • the spectrum of the multicarrier transmission method contains and to subcarriers Subcarriers arranged spectrally with respect to a center frequency f c .
  • the frames each contain a number of symbols, each of which is composed of the data symbols d n sent on the subcarriers.
  • the distortion relevant to the invention consists in interference between subcarriers which are mirror-symmetrical on both sides of the center frequency of the multicarrier spectrum. This distortion is mainly caused by transmitter and receiver IQ asymmetries. Furthermore, the multipath propagation of the radio channel leads to linear distortions of the subcarrier under consideration.
  • the total distortion composed of the IQ distortion and the channel distortion can be modeled using the following equation:
  • d (i) are the distorted symbols received on subcarrier n at time i
  • d n (i) the undistorted transmitted symbols
  • a ⁇ x forms the transmitter-side IQ distortion matrix
  • C contains the channel coefficients one Multi-way channel.
  • the invention is based on the fact that either the transmitter-side or the receiver-side IQ asymmetry is already known. If one of the IQ distortion matrices ⁇ A or A ⁇ x ) is already known, then the coefficients of the other IQ distortion matrix and the channel coefficients C can be iteratively estimated and at the same time the received symbols can be equalized and decided.
  • the received multicarrier is processed in blocks. Data symbols (e.g. OFDM symbols).
  • a data block consisting of a group of OFDM symbols is thus processed in each iteration loop and the channel coefficients and IQ distortion parameters determined at the end of the iteration run are applied to this group of data symbols.
  • This group of data symbols hereinafter referred to as a data block, can be a subset of the frame or burst. However, depending on the definition of the burst length in the respective standard, it is also conceivable that the data block corresponds to the frame.
  • a first method according to the invention for estimating and correcting the IQ asymmetry on the transmitter side can be carried out.
  • the received data symbols of a first data block are equalized with the channel coefficients determined from the previous data block.
  • the data symbols in a method step b. equalized with the IQ distortion parameters determined from a previous data block.
  • the data symbols rectified in this way are then processed in a method step c. subjected to a symbol decision process.
  • the reference symbols provided by the symbol decision process and the received data symbols are provided for a channel estimation to generate new channel coefficients.
  • the new IQ distortion parameters are estimated.
  • the data block of received data symbols referred to as the first data block is, by definition, any data block of the radio signal transmission.
  • the designation of the first data block is only used for linguistic identification and differentiation from the second data block that follows in time.
  • the actually first data block of the radio transmission is referred to here as the initialization data block.
  • the method according to the invention cannot initially be carried out in the same way as with all subsequent data blocks, since a previous data block does not yet exist.
  • the received data symbols contained in the initialization data block can be carried out in method steps a. and b. are equalized in such a way that a channel estimation is carried out on the basis of pilot signals as are usually contained in a preamble of the corresponding data burst, that of the
  • Initialization data block listened.
  • the received data symbols are in step a. with those from the Channel estimate equalized channel coefficients determined and in method step b. the IQ distortion parameters are set to zero.
  • step f. with the in process steps d. and e. determined new channel coefficients and new IQ
  • Distortion parameters the process steps a. to e. are repeated for the received data symbols of the first data block.
  • This iteration step and further iteration steps for updating the channel coefficients and the IQ distortion parameters can thus optionally be carried out on the basis of the first data block or the data blocks which follow in time.
  • Channel coefficients and IQ distortion parameters can optionally be followed by further iteration steps, in each of which the method steps a. to e. be run through. After the end of the last intended iteration step, the received data symbols are equalized with the channel coefficients and IQ distortion parameters last updated, the Subjected symbol decision process and the decided data symbols delivered to a next processing unit of the recipient.
  • the new channel coefficients are generated in that the channel coefficients determined from a channel estimate on the basis of the reference symbols supplied by the symbol decision process and the received data symbols are weighted averaged with the old values of
  • Channel coefficients are subjected so that on the basis of these averaged channel coefficients, the reference symbols and the received data symbols in method step e. the IQ error according to Eq. (2.2) can be estimated again (IQ tracking or IQ tracking).
  • the new IQ distortion parameters are generated by averaging the IQ distortion parameters determined on the basis of the new channel coefficients determined in the channel estimation, the reference symbols and the received data symbols using the IQ distortion parameters determined in one or more previous iteration steps.
  • IQ predistortion of the reference symbols provided by the symbol decision process is carried out on the basis of the updated IQ distortion parameters. This IQ predistortion of the reference symbols can significantly reduce the estimation error due to the IQ distortion.
  • a second method according to the invention is used to estimate and correct the receiver-side IQ asymmetry. Again starting from Eq. In this case (1) it is assumed that the transmitter-side IQ distortion matrix (A ⁇ x ) has already been estimated and corrected beforehand by suitable measures. With the approximation a x , a TM 1 and d with knowledge of the channel coefficients C n , C_ n , the remaining variables of the IQ distortion matrix A 1 ⁇ can be passed through
  • a second method according to the invention for estimating and correcting the IQ asymmetry on the receiver side can be carried out.
  • this second method according to the invention in its most general form, a. the received data symbols of a first data block are equalized with the IQ distortion parameters determined from a previous data block. Then the data symbols in a method step b. provided for a channel estimate for generating new channel coefficients and then in a method step c. equalized with the determined channel coefficients. The data symbols equalized in this way are then processed in a method step d. subjected to a symbol decision process. Then in a process step e. on the basis of the reference symbols supplied by the symbol decision process and the channel coefficients provided by the channel estimate, an IQ estimate is carried out and the determined IQ distortion parameters are supplied to the IQ correction circuit.
  • Fig. 2 shows a receiver-side block circuit arrangement for
  • Fig. 3 shows a receiver-side block circuit arrangement for
  • the exemplary embodiment shown in FIG. 2 and the variables used therein relate to the case of estimating and correcting an IQ asymmetry on the transmitter side, both channel coefficients C n , C_ n being used to determine the IQ distortion parameters b ⁇ X and b TM also the transmitted symbols d n (i) or d. n (i) are required (see Eq. (2.2)).
  • Received data symbols d ⁇ , d n are fed to the device contained in a receiver and shown in FIG. 2, the data symbols being contained in data blocks.
  • Several data blocks form a frame, each frame having preamble symbols d ⁇ '.
  • the data symbols which in the exemplary embodiment are represented by OFDM
  • Symbols are formed are fed to a channel equalizer 2, in which they are equalized with the channel coefficients C n determined from the previous data block.
  • the equalized data symbols are then fed to an IQ error correction circuit 3, in which an IQ Error correction is carried out with the IQ distortion parameters —b n X, —b_X n determined from the previous data block.
  • the equalized and IQ-corrected data symbols are then fed to a symbol decision maker 4, which has two outputs. After the symbol decision, new reference symbols are available for all subcarriers n / -n, which are delivered to a first output of the symbol decision maker 4.
  • a new channel estimation can be carried out in a carial estimator 6, to which the received data symbols d n are also fed. Previously, those of the
  • Symbol decision maker 4 supplied reference symbols are fed to an IQ predistorter 5, to which the updated IQ distortion parameters —bTX are also fed.
  • the IQ predistortion reduces the estimation error due to the IQ distortion.
  • the channel coefficients calculated in the channel estimator 6 are subjected to a weighted averaging with the old values, so that on the basis of these averaged channel coefficients, the reference symbols and the received values, the IQ errors in an IQ tracking unit 7, to which the received symbols d n are also fed, can be estimated again.
  • the values can be averaged in the time direction to reduce noise
  • a next iteration can then be carried out with the updated values of the channel coefficients and the IQ distortion parameters supplied to the channel equalizer 2 and the IQ correction circuit 3 be performed. This can be carried out using the data block of received OFDM symbols following the current data block. However, it is also possible to improve the estimated values by multiple iterations based on the same received data block.
  • reference data such as, for example, the symbols d ⁇ sent in a preamble, as indicated in FIG.
  • the exemplary embodiment shown in FIG. 3 and the variables used therein relate to the case of the estimation and correction of an IQ asymmetry on the receiver side, with the determination of the IQ distortion parameters £ * and b ⁇ Eq. (3.1) serves as the basis.
  • Received data symbols d ⁇ , d n are fed to the device contained in a receiver and shown in FIG. 3.
  • the data symbols are first fed to an IQ correction circuit 10, in which an IQ correction is carried out on the basis of IQ distortion parameters, as had been determined on the basis of a previous iteration run using an earlier group of data symbols.
  • the IQ-corrected data symbols are then fed to a channel estimator 11 for determining channel coefficients and then in a channel equalizer 12 equalized on the basis of the channel coefficients determined by the channel estimator 11.
  • the channel-equalized receive symbols are then fed to a symbol decision maker 13, in which a
  • the symbol decider 13 has two outputs. After the symbol decision, new reference symbols are available for all subcarriers n / -n, which are delivered to a first output of the symbol decision maker 13.
  • the reference symbols are supplied to an IQ estimator 14, in which, based on the reference symbols and the channel coefficients provided by the channel estimator 11, one
  • Estimation of the IQ distortion parameters is performed.
  • Distortion parameters are supplied to the IQ correction circuit 10, so that a new iteration can be carried out on the basis of the current data block or a next data block.
  • the present invention is generally applicable to those receiver concepts in which the received input signal is branched to an I and Q branch in the analog circuit part of the receiver.
  • the most important application of the invention thus relates to a so-called direct-mixing receiver known per se, as is shown, for example, in Fig. 3.5 of the Schuchert thesis cited at the beginning.
  • the invention can also be applied to an overlay receiver with direct mixing of the second stage, which is also known per se, as shown, for example, in FIG. 3.6 of the thesis mentioned and described in the associated text.
  • Such an overlay receiver with direct mixing second stage is a modification of a heterodyne receiver. gers, in which the second mixer stage is designed as a direct-mixing analog quadrature receiver. Even with such a receiver, the IQ errors described at the outset can occur, which can be estimated and corrected using the method according to the invention.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Abstract

Le procédé selon l'invention sert à estimer et à corriger des distorsions, provoquées par des asymétries IQ côté émetteur ou côté récepteur et par des distorsions de canal, de signaux radio transmis sous forme de blocs ou de paquets de données selon un procédé de transmission à porteuses multiples, par exemple selon le procédé OFDM. Des distorsions linéaires de la sous-porteuse considérée se produisent également en raison de la propagation par trajets multiples du canal radio. Ledit procédé repose sur le principe que soit l'asymétrie IQ côté émetteur soit l'asymétrie IQ côté récepteur est déjà connue. Si une des matrices de distorsion IQ est déjà connue, il est possible d'estimer de façon itérative les coefficients de l'autre matrice de distorsion IQ ainsi que les coefficients de canaux et, simultanément, de corriger les symboles reçus et de leur faire subir un processus de décision. Selon ce procédé, le traitement des symboles de données de modulation à porteuses multiples reçus s'effectue par bloc.
PCT/DE2003/002849 2002-09-09 2003-08-26 Estimation iterative et correction d'asymetries entre une branche en phase et une branche en quadrature dans des systemes de transmission a porteuses multiples WO2004025916A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP03794799A EP1537710A1 (fr) 2002-09-09 2003-08-26 Estimation iterative et correction d'asymetries entre une branche en phase et une branche en quadrature dans des systemes de transmission a porteuses multiples
US11/075,310 US20050180534A1 (en) 2002-09-09 2005-03-08 Iterative estimation and equalization of asymmetries between inphase and quadrature branches in multicarrier transmission systems

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE2002141679 DE10241679A1 (de) 2002-09-09 2002-09-09 Iterative Schätzung und Entzerrung von Unsymmetrien zwischen Inphase-und Quadraturzweig in Mehrtäger-Übertragungssystemen
DE10241679.6 2002-09-09

Related Child Applications (1)

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US11/075,310 Continuation US20050180534A1 (en) 2002-09-09 2005-03-08 Iterative estimation and equalization of asymmetries between inphase and quadrature branches in multicarrier transmission systems

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EP (1) EP1537710A1 (fr)
CN (1) CN1682508A (fr)
DE (1) DE10241679A1 (fr)
WO (1) WO2004025916A1 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2878393B1 (fr) * 2004-11-23 2007-01-12 Commissariat Energie Atomique Procede et dispositif de compensation de desequilibres d'un recepteur
US8656243B2 (en) * 2010-01-13 2014-02-18 Intel Mobile Communications GmbH Radio receiver and method for channel estimation

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998032221A1 (fr) * 1997-01-17 1998-07-23 Ericsson Inc. Procede et dispositif pour compenser les desequilibres entre signaux en quadrature
US6442217B1 (en) * 2000-05-22 2002-08-27 Sicom, Inc. Digital communication receiver with digital, IF, I-Q balancer

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998032221A1 (fr) * 1997-01-17 1998-07-23 Ericsson Inc. Procede et dispositif pour compenser les desequilibres entre signaux en quadrature
US6442217B1 (en) * 2000-05-22 2002-08-27 Sicom, Inc. Digital communication receiver with digital, IF, I-Q balancer

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
ANDREAS SCHUCHERT: "Verfahren der digitalen Kompensation von Unsymmetrien der analogen Quadraturmischung in OFDM-Empfängern", DISSERTATION, 2001, Bergische Universität - Gesamthochschule Wuppertal, pages 1 - 141, XP002266752, Retrieved from the Internet <URL:http://elpub.bib.uni-wuppertal.de/edocs/dokumente/fb13/diss2001/schuchert;internal&action=buildframes.action> [retrieved on 20040113] *
L. BRÖTJE, S. VOGELER, K.-D. KAMMEYER: "Estimation and Correction of transmitter-caused I/Q Imbalance in OFDM Systems", 7TH INTERNATIONAL OFDM WORKSHOP, 10 September 2002 (2002-09-10) - 11 September 2002 (2002-09-11), Hamburg, XP002266751 *

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EP1537710A1 (fr) 2005-06-08
DE10241679A1 (de) 2004-03-18
CN1682508A (zh) 2005-10-12

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