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WO2002009375A1 - Evaluation de la voie de liaison descendante appliquee au systeme universel de telecommunications mobiles - Google Patents

Evaluation de la voie de liaison descendante appliquee au systeme universel de telecommunications mobiles Download PDF

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Publication number
WO2002009375A1
WO2002009375A1 PCT/IB2001/001303 IB0101303W WO0209375A1 WO 2002009375 A1 WO2002009375 A1 WO 2002009375A1 IB 0101303 W IB0101303 W IB 0101303W WO 0209375 A1 WO0209375 A1 WO 0209375A1
Authority
WO
WIPO (PCT)
Prior art keywords
channel
receiver
vector
estimation
active users
Prior art date
Application number
PCT/IB2001/001303
Other languages
English (en)
Inventor
Umberto Mengali
Michele Morelli
Alessandro Masciarelli
Original Assignee
Telit Mobile Terminals S.P.A.
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.)
Filing date
Publication date
Application filed by Telit Mobile Terminals S.P.A. filed Critical Telit Mobile Terminals S.P.A.
Priority to AU2002224589A priority Critical patent/AU2002224589A1/en
Publication of WO2002009375A1 publication Critical patent/WO2002009375A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7097—Interference-related aspects
    • H04B1/7103—Interference-related aspects the interference being multiple access interference
    • H04B1/7105—Joint detection techniques, e.g. linear detectors

Definitions

  • the present invention relates to a method for estimating channels in a receiver for the downlink of the TDD (Time Division Duplex) component of the UMTS (Universal Mobile Telecommunication System) and a receiver thereof.
  • TDD Time Division Duplex
  • UMTS Universal Mobile Telecommunication System
  • ISI inter symbol interference
  • the receiver needs to identify this channel distortion and equalize it.
  • Classical system identification techniques require the use of both system input and output, which leads to the transmission of a training sequence, i.e. a set of fixed data (that do not carry information) that are known to both transmitter and receiver.
  • the use of a training sequence reduces the transmission rate, especially when the training sequence has to be retransmitted often, due to the possibly fast channel variations that occur in mobile communications.
  • blind equalizers adapt without using a training sequence.
  • the channel estimation is based on the transmission of training sequences known at the receiver in every data packet.
  • the problem of channel estimation by means of training sequences in receiver of mobile terminals has received much attention in the literature over the past years.
  • Some algorithms operate in the time-domain and are based on a least-square approach .
  • Other schemes operate in the frequency domain and are based on Discrete Fourier Transform (DFT) techniques.
  • DFT Discrete Fourier Transform
  • a reduced complexity search for the optimum training sequences has been proposed.
  • channel estimation is performed without taking into account a priori knowledge (Side Information) of the transmit shaping filter.
  • Side Information Priori knowledge
  • a few time-domain schemes exploiting side information have been recently investigated and it has been shown that side information can improve the estimation accuracy with respect to conventional methods.
  • each active user is associated with a cyclically shifted version of a basic code with good autocorrelation properties.
  • This model allows estimation of the channel impulse responses in the uplink by means of standard techniques. In the downlinlc the problem of channel estimation is quite different with respect to the uplink, since all users arrive at the mobile station MS through the same channel. Consequently, the channel impulse responses of the users only differ for a scalar factor that depends on the user's power. In particular, if a user is not active in the link then its scalar factor is zero. Thus, in contrast to the uplink situation where N ut different channels must be estimated (one for each active user), a single channel impulse response must be estimated in the downlink.
  • the received signal is given by
  • P represents the length of the midamble expressed in chip intervals T
  • h(f) is the channel impulse response with support in (0, WT)
  • ⁇ (/) ⁇ a ⁇
  • the parameters P We N ut satisfy the following relation
  • *(») *(0L B r/2 + w(n) ⁇ n ⁇ 2P - l (5)
  • ⁇ h(k); 0 ⁇ k ⁇ 2W - 1 ⁇ are the samples of h(t) taken at kT / 2
  • b® is related to the th training sequence by the relation
  • the UMTS-TDD standard employs orthogonal spreading codes to provide intrinsic protection against multiaccess interference.
  • the conventional code-matched filter receiver is optimum for transmission over the additive white Gaussian noise (AWGN) channel.
  • AWGN additive white Gaussian noise
  • signals undergo frequency-selective fading and the spreading codes lose their orthogonality.
  • the matched filter detector suffers severe performance degradation due to multiaccess interference.
  • multiuser detection equalization techniques can be resorted to. As the complexity of the optimum multiuser detector is unrealistically high, suboptimum schemes based on block equalization have been proposed which provide a reasonable trade-off between performance and complexity.
  • the equalizer coefficients can be computed by separately minimizing the mean squared error between the samples at the equalizer output and the data of each active user. This technique represents a suboptimum joint detection strategy and can be used with both linear or decision feedback equalizers (DFE).
  • DFE decision feedback equalizers
  • the DFE implementation is rather complex and has not been used for the downlink.
  • Scheme based on linear equalization have been recently proposed and some of them are still investigated. It is worth noting that all these reduced- complexity multiuser detectors require knowledge of the channel impulse response and identification of the active users in the slot.
  • a further object of the present invention is to provide a channel estimation accuracy superior to that achieved with other existing methods.
  • a further object of the present invention is to accurately identify whether a given user is active or not. .In order to achieve such aims, it is the object of the present invention to provide a method for estimating channels in a receiver and/or a receiver incorporating the features of the annexed claims, which form an integral part of the description herein.
  • - Fig. 1 shows the slot structure of the UMTS-TDD component to be used in association with the method according to the invention.
  • the key idea of the method for estimating channels according to invention is of jointly estimating channel response and signal amplitudes starting from signal amplitudes. This approach has the following advantages: i) The channel estimation accuracy is superior to that achieved with other existing methods because we exploit the aggregate of all the active users' signals rather than a single signal, i ⁇ ) It is possible to accurately identify whether a given user is active or not.
  • h s Ph s + w (12) where h s is a 2N U/ W -dimensional vector containing scaled versions of the channel response h
  • the noise-vector w [w(Q),w( ⁇ ),...,w(2P - l)] ⁇ is zero-mean and Gaussian, with covariance matrix
  • [y] n represents the nth entry ofy
  • X(m) is the 2 -point TDF of the observed vector ⁇ ; 2P-1
  • Equation (21) indicates that v is an unbiased estimate of h s and is normally exploited in the uplink of the UMTS-TDD component as an estimate of the channel impulse responses associated to the active users.
  • w t is the z ' th subvector of w . It is worth noting that y t represents an estimate of the channel ⁇ ji associated to the z ' th user.
  • the key idea of the invention is of jointly estimating vectors h and ⁇ starting fromj ⁇ With this approach the channel estimation accuracy is superior to that achieved with other existing methods because we exploit the aggregate of all the active users' signals rather than a single signal, and further, z ' t is possible to accurately identify whether a given user is active or not. To this end we resort to the least square criterion
  • Joz?t estimation ofh and ⁇ Equations (27) and (29) can be used to jointly estimate vectors A and ⁇ in an iterative fashion. Denoting by A (c) and ⁇ w the estimates of A and ⁇ at the Mi iteration, the next estimates are computed as
  • Tables I and II are normalized to MSE std and have been obtained with the channel model 3 as standardized by 3 -GPP [3 -Generation Partnership Project] assuming that all users have equal power. It is seen that the accuracy of the proposed method is close to the bound and is much better than that achieved by the ad hoc scheme, at least at signal-to-noise ratio of practical interest (6-8 dB).
  • the proposed algorithm (30)-(31) can be used to decide whether a given user is active or not. Identification of the active users is an open problem in the standardization process, as clearly indicated in several 3 -GPP documents where it is proposed the use of a separated channel to transmit information about the active users in the slot in order to minimize the probability of false codes' detection.
  • a simple data detector for the downlink is based on the fact that the spreading codes are perfectly orthogonal and all user signals arrive at the mobile station through the same channel. In a frequency-selective environment the spreading codes lose their orthogonality. To mitigate this problem we may resort to a standard linear equalizer (to restore codes' orthogonality), followed by a single-user receiver.
  • This detector is much simpler than those described previously and its performance is only 1.5 dB worse if the equalizer coefficients are computed according to the MMSE criterion and the channel selectivity is not too severe. Obviously, the choice of the equalizer's taps requires knowledge of the channel impulse response. It is found that if the proposed channel estimator is used, the performance of the reduced complexity data detector is superior to that achieved with other more complex schemes operating with traditional channel estimation methods.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
  • Transmitters (AREA)
  • Time-Division Multiplex Systems (AREA)
  • Circuits Of Receivers In General (AREA)

Abstract

La présente invention concerne un procédé itératif d'évaluation de voie dans la liaison descendante d'un composant en mode duplex à répartition dans le temps (Time Division Duplex : TDD) du système universel de télécommunications mobiles (Universal Mobile Telecommunication System : UMTS). Outre la réponse en impulsion de la voie, l'algorithme fournit également des évaluations des capacités de l'utilisateur, qui sont nécessaires pour réaliser une détection multi-utilisateur. La complexité de calcul limitée permet la mise en oeuvre du plan selon cette invention dans un récepteur de station mobile (Mobile Station : MS).
PCT/IB2001/001303 2000-07-21 2001-07-20 Evaluation de la voie de liaison descendante appliquee au systeme universel de telecommunications mobiles WO2002009375A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2002224589A AU2002224589A1 (en) 2000-07-21 2001-07-20 Estimation of the downlink channel for umts

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ITTS2000A000004 2000-07-21
IT2000TS000004A ITTS20000004A1 (it) 2000-07-21 2000-07-21 Stima del canale e delle potenze degli utenti nel downlink standard umts in modalita' tdd

Publications (1)

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WO2002009375A1 true WO2002009375A1 (fr) 2002-01-31

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AU (1) AU2002224589A1 (fr)
IT (1) ITTS20000004A1 (fr)
WO (1) WO2002009375A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2004059865A1 (fr) * 2002-12-30 2004-07-15 Koninklijke Philips Electronics N.V. Programme et dispositif de detection d'une sequence d'entrainement dans un systeme tdd/cdma de liaison descendante
WO2006125365A1 (fr) * 2005-05-24 2006-11-30 Shanghai Ultimate Power Communications Technology Co., Ltd. Procede permettant de determiner la reponse impulsionnelle du canal utilisateur dans les systemes amrc synchrones temporels
DE102006017296A1 (de) * 2006-04-12 2007-10-18 Benq Mobile Gmbh & Co. Ohg Verfahren zum Erzeugen und Verwenden von Trainingssequenzen und Kommunikazionssystem
US8111641B2 (en) 2005-05-26 2012-02-07 Shanghai Ultimate Power Communications Technology Co., Ltd. Joint detection (jd) method for adjacent cells in TDD/CDMA system

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* Cited by examiner, † Cited by third party
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EP1077551A1 (fr) * 1999-03-06 2001-02-21 Matsushita Electric Industrial Co., Ltd. Elimination de signaux parasites

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Publication number Priority date Publication date Assignee Title
EP1077551A1 (fr) * 1999-03-06 2001-02-21 Matsushita Electric Industrial Co., Ltd. Elimination de signaux parasites

Non-Patent Citations (6)

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Title
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LATVA-AHO, JUNTTI: "Modified adaptive LMMSE receiver for DS-CDMA systems in fading channels", IEEE INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, 1 September 1997 (1997-09-01) - 4 September 1997 (1997-09-04), New York, US, pages 554 - 558, XP002178852, ISBN: 0-7803-3871-5 *
LEI SONG, HOLTZMAN: "CDMA dynamic downlink power control", IEEE VEHICULAR TECHNOLOGY CONFERENCE, 18 May 1998 (1998-05-18) - 21 May 1998 (1998-05-21), New York, US, pages 1101 - 1105, XP000895069, ISBN: 0-7803-4321-2 *
MUDULODU, PAULRAJ: "A blind multiuser receiver for the CDMA downlink", IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH, AND SIGNAL PROCESSING. PROCEEDINGS, 5 June 2000 (2000-06-05) - 9 June 2000 (2000-06-09), Piscataway, US, pages 2933 - 2936 vol.5, XP002178854, ISBN: 0-7803-6293-4 *
STEINER, JUNG: "Optimum and suboptimum channel estimation for the uplink of CDMA mobile radio systems with joint detection", EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS AND RELATED TECHNOLOGIES, vol. 5, no. 1, January 1994 (1994-01-01), MILAN, IT, pages 39 - 50, XP000445714, ISSN: 1120-3862 *
WEISS, FRIEDLANDER: "Channel estimation for synchronous DS-CDMA downlink", IEEE SIGNAL PROCESSING WORKSHOP ON STATISTICAL SIGNAL AND ARRAY PROCESSING, 14 September 1998 (1998-09-14) - 16 September 1998 (1998-09-16), New York, US, pages 284 - 287, XP002178851 *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2004059865A1 (fr) * 2002-12-30 2004-07-15 Koninklijke Philips Electronics N.V. Programme et dispositif de detection d'une sequence d'entrainement dans un systeme tdd/cdma de liaison descendante
WO2006125365A1 (fr) * 2005-05-24 2006-11-30 Shanghai Ultimate Power Communications Technology Co., Ltd. Procede permettant de determiner la reponse impulsionnelle du canal utilisateur dans les systemes amrc synchrones temporels
US7899014B2 (en) 2005-05-24 2011-03-01 Shanghai Ultimate Power Communications Technology Co., Ltd. Method for determining user channel impulse response in TD-SCDMA system
US8111641B2 (en) 2005-05-26 2012-02-07 Shanghai Ultimate Power Communications Technology Co., Ltd. Joint detection (jd) method for adjacent cells in TDD/CDMA system
DE102006017296A1 (de) * 2006-04-12 2007-10-18 Benq Mobile Gmbh & Co. Ohg Verfahren zum Erzeugen und Verwenden von Trainingssequenzen und Kommunikazionssystem

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Publication number Publication date
ITTS20000004A1 (it) 2002-01-21
AU2002224589A1 (en) 2002-02-05
ITTS20000004A0 (it) 2000-07-21

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