WO2001050694A1 - Procede et systeme recepteur wcdma-utra/fdd - Google Patents

Procede et systeme recepteur wcdma-utra/fdd Download PDF

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Publication number
WO2001050694A1
WO2001050694A1 PCT/IT2000/000531 IT0000531W WO0150694A1 WO 2001050694 A1 WO2001050694 A1 WO 2001050694A1 IT 0000531 W IT0000531 W IT 0000531W WO 0150694 A1 WO0150694 A1 WO 0150694A1
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WO
WIPO (PCT)
Prior art keywords
receiver
filter
coefficients
wcdma
estimate
Prior art date
Application number
PCT/IT2000/000531
Other languages
English (en)
Inventor
Lorenzo Vangelista
Nevio Benvenuto
Elena Costa
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 AU23958/01A priority Critical patent/AU2395801A/en
Publication of WO2001050694A1 publication Critical patent/WO2001050694A1/fr

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Classifications

    • 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
    • H04B1/709—Correlator structure
    • H04B1/7093—Matched filter type
    • 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
    • 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
    • H04L25/025—Channel estimation channel estimation algorithms using least-mean-square [LMS] method
    • 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

Definitions

  • the present invention refers to a channel estimation method and to a receiver for the downlink of wireless communication systems.
  • extensive research and standardization activities have been parallely carried out in Europe, Japan and North America on third-generation cellular systems.
  • UTRA Universal Mobile Telecommunication Systems
  • WCDMA Wideband Code Division Multiple Access
  • the major source of impairment in digital wireless communication systems is represented by the phenomenon of multipath propagation, or multipath fading.
  • Wideband signals are subject to a frequency-selective fading.
  • the CDMA technology is based on the direct sequence spread spectrum (DS-SS) modulation technique, according to which a high chip-rate pseudo-random sequence, ⁇ c ⁇ ° ⁇ , referred to as spreading sequence, modulates the user information data symbols ⁇ " ⁇ at the transmitter end .
  • DS-SS direct sequence spread spectrum
  • the modulated signal bandwidth is typically larger than the channel coherence bandwidth, so that DS-SS systems are generally associated to frequency-selective fading.
  • the spreading sequences exhibit an auto-correlation function which is an ideal Kronecker delta function and zero cross-correlation when they are just one chip out of sync.
  • multipath signal components with relative delays larger than one chip turn out to be uncorrelated and, at the receiver, after despreading, they represent just independently attenuated multiple replicas of the transmitted information signal.
  • the most widely adopted receiver in the CDMA systems is the RAKE receiver or matched filter receiver, which exploits the inherent time-diversity of the multipath channel.
  • a RAKE receiver separately tracks and conveniently recombines the multipath signal components through a bank of synchronous correlators, each of which decorrelates a different delayed version (of t, ) of the received signal.
  • the output of the single correlator is then properly weighed by a factor , .
  • the weights are computed according to the Maximum Ratio Combining criterion: if h i ⁇ ,) is the (I -1 )-th channel path amplitude and h e ⁇ l) its estimate, then
  • This solution requires initially an accurate estimate of the multipath channel delays and amplitudes to properly set the RAKE fingers to the positions of the strongest multipath components.
  • a circuit is used for each finger for the tracking of the optimum values of ⁇ t ; ⁇ and ⁇ a, ⁇ .
  • the most widely used channel estimation method for the design of a RAKE receiver in the WCDMA-UTRA FDD systems is the pilot symbol-assisted method.
  • Such method exploits the availability of a known sequence of pilot symbols that is periodically transmitted time-multiplexed with the information symbols in the user dedicated physical channel.
  • a field of N P ii ot bits is placed at the end of each slot.
  • the auto-correlation of x p / is expected to be a Kronecker delta function and the sequence may be therefore used to sound the channel according to the correlation method.
  • the accuracy of the estimate obtained with this method is tightly related to the properties of auto-correlation of the sequence x pf .
  • the general scope of the present invention is to obviate to the above mentioned drawbacks, by producing a method of channel estimation at the receiver that firstly takes into account the non ideal properties of auto-correlation of x pf and then compensates them.
  • a further purpose of the present invention is to produce a receiver realized according to such method while exhibiting a reduced complexity.
  • the coefficients of h eq are estimated through a Least-Squares method.
  • despreading, channel estimation and receiving filtering are implemented through a tapped delay line with delays of Tc/2.
  • a receiver in a WCDMA-UTRA/FDD transmission system comprising a reduced matched filter obtained by setting to zero a prearranged number of coefficients of the channel matched filter among those which, according to a Least-Squares estimate, have less significant amplitude.
  • the invention concerns a WCDMA-UTRA/FDD transmission system with the receiver realized according to the method described above .
  • -figure 1 represents a simplified model of the known DS-CDMA transmission system.
  • -figure 2 represents a receiver structure according to the invention;
  • FIG. 1 the simplified model of a complete UTRA-FDD transmission system is shown, where the spreading operation by c, (1) is represented within the symbol period [[mT s ,(m + l)T s ⁇ ⁇ ] by an interpolation filter with impulse response:
  • the cascade of the transmitter pulse shaping filter, the channel filter and the receive front-end filter may be modeled by the equivalent channel filter with impulse response h eq .
  • the receive filter impulse response is denoted as g Rc .
  • the despreading operation may be represented by a filter with impulse response:
  • the model for the Rayleigh fading channel that is typically adopted in the literature is the wide-sense-stationary-uncorrelated scattering (WSSUS) model , according to which the signal at the channel output is given by the sum of delayed replicas of the transmitted signal weighed by time-varying complex Gaussian processes, which are uncorrelated and have zero mean. Moreover, the channel introduces a noise, that is denoted as w(t) at the output of the receive front-end filter in figure 1.
  • the most widely used receiver in the known technique is the RAKE receiver, characterized by the drawbacks outlined above.
  • a receiver architecture is proposed, that differs from that illustrated in figure 1 for the order in which the receive filter, the despreading and the sampler are implemented.
  • the despreading filter with impulse response As shown in figure 2, according to the invention, in the receiver, the despreading filter with impulse response
  • the matched filter is implemented, in an innovative way, through a tapped delay line, with delays of T c /2 (rather than of Tc as in the known technique), from which the name chip-matched filter (CMF).
  • Each delayed input is weighed by the complex conjugate value of the estimated channel amplitude at that delay.
  • the matched filter contrary to what claimed in the known technique, succeds in collecting the overall multipath signal energy, provided that the signal processing at the receiver is performed at a rate which is at least twice the chip- rate. In fact, if the estimation is performed with period T c /2 , a perfect reconstruction of the channel impulse response can be achieved.
  • the LS method does not lend itself to be used in an architecture of the RAKE type, but it has been found that it can be used with great advantage in a receiver architecture of the "matched-filter” type as that described above.
  • the Least Squares (LS) method can be adopted to separately estimate the two impulse responses h 0 ⁇ p) and at T c .
  • the number N palh of coefficients to be estimated is determined by a trade-off between the need to solve the highest number of channel paths and the need to have a noise-free estimate.
  • the signal-to-estimation error ratio increases by reducing N path .
  • the estimation error is defined as
  • the coefficients are determined so as to minimize the cost function ⁇ defined as
  • ⁇ is the correlation matrix of the inputs and ⁇ is the vector of the cross- correlations between the inputs and the desired response.
  • a receiver for the WCDMA-UTRA/FDD transmission system in which a Least Square method is applied for the channel estimation, may compensate the non ideality of the auto-correlation of the employed chip pilot sequence, in the case of low processing gains (SF ⁇ 64).
  • a receiver structure that includes a single despreader, matched to the intended user, followed by a reduced version of the matched filter, the reduced chip matched filter (RCMF), obtained by setting to zero a certain number of coefficients of the filter matched to the channel, between those that according to a Least Squares estimate result to have less significant amplitude.
  • This receiver structure definitely outperforms a conventional matched filter, since in its design the coefficient estimates which are more affected by the noise effect are discarded.
  • the RCMF performs significantly better than a RAKE receiver with the same number of fingers. This is due the higher accuracy of the LS estimate as compared to the estimate obtained by means of the correlation method.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Radio Relay Systems (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

Abstract

L'invention concerne un procédé d'estimation de la réponse impusionnelle de canal heq dans un système de transmission WCDMA, selon lequel les coefficients de heq sont estimés par une méthode des moindres carrés. L'invention concerne également une architecture innovatrice d'un récepteur WCDMA dont la complexité est réduite, dans lequel l'opération de désétalement précède le filtre de réception et dans lequel le désétalement, l'estimation de canal et le filtrage de réception sont mis en oeuvre via une ligne à retard à dérivations avec des retards de Tc/2. L'invention concerne en outre un récepteur produit par un filtre adapté réduit, obtenu en remettant à zéro un certain nombre de coefficients d'un filtre adapté parmi ceux qui, selon l'estimation des moindres carrés, possèdent la plus petite amplitude significative. L'invention concerne enfin un système de transmission WCDMA-UTRA/FDD doté d'un tel récepteur.
PCT/IT2000/000531 1999-12-30 2000-12-19 Procede et systeme recepteur wcdma-utra/fdd WO2001050694A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU23958/01A AU2395801A (en) 1999-12-30 2000-12-19 Wcdma-utra/fdd method and receiver system

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ITMI99A002745 1999-12-30
IT1999MI002745A IT1314344B1 (it) 1999-12-30 1999-12-30 Metodo ricevitore e sistema di trasmissione wcdma-utra/fdd

Publications (1)

Publication Number Publication Date
WO2001050694A1 true WO2001050694A1 (fr) 2001-07-12

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PCT/IT2000/000531 WO2001050694A1 (fr) 1999-12-30 2000-12-19 Procede et systeme recepteur wcdma-utra/fdd

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AU (1) AU2395801A (fr)
IT (1) IT1314344B1 (fr)
WO (1) WO2001050694A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2370469A (en) * 2000-09-07 2002-06-26 Nec Corp Improvements in CDMA receivers
US9258149B2 (en) 2004-09-10 2016-02-09 Mstar Semiconductor, Inc. Refinement of channel response calculation

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5251233A (en) * 1990-12-20 1993-10-05 Motorola, Inc. Apparatus and method for equalizing a corrupted signal in a receiver
US5490165A (en) * 1993-10-28 1996-02-06 Qualcomm Incorporated Demodulation element assignment in a system capable of receiving multiple signals
WO1998038772A1 (fr) * 1997-02-25 1998-09-03 Nokia Telecommunications Oy Estimation de la reponse impulsionnelle d'un canal au moyen de la decomposition d'une valeur singuliere
WO1999050969A2 (fr) * 1998-03-27 1999-10-07 Telefonaktiebolaget Lm Ericsson Egaliseur utile dans des systemes de modulation a porteuses multiples

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5251233A (en) * 1990-12-20 1993-10-05 Motorola, Inc. Apparatus and method for equalizing a corrupted signal in a receiver
US5490165A (en) * 1993-10-28 1996-02-06 Qualcomm Incorporated Demodulation element assignment in a system capable of receiving multiple signals
WO1998038772A1 (fr) * 1997-02-25 1998-09-03 Nokia Telecommunications Oy Estimation de la reponse impulsionnelle d'un canal au moyen de la decomposition d'une valeur singuliere
WO1999050969A2 (fr) * 1998-03-27 1999-10-07 Telefonaktiebolaget Lm Ericsson Egaliseur utile dans des systemes de modulation a porteuses multiples

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2370469A (en) * 2000-09-07 2002-06-26 Nec Corp Improvements in CDMA receivers
GB2370469B (en) * 2000-09-07 2004-10-27 Nec Corp Improvements in CDMA receivers
US9258149B2 (en) 2004-09-10 2016-02-09 Mstar Semiconductor, Inc. Refinement of channel response calculation

Also Published As

Publication number Publication date
ITMI992745A0 (it) 1999-12-30
ITMI992745A1 (it) 2001-06-30
AU2395801A (en) 2001-07-16
IT1314344B1 (it) 2002-12-09

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