EP0985280A1 - Sondage a ponderation temporelle d'un canal de transmission - Google Patents
Sondage a ponderation temporelle d'un canal de transmissionInfo
- Publication number
- EP0985280A1 EP0985280A1 EP98920611A EP98920611A EP0985280A1 EP 0985280 A1 EP0985280 A1 EP 0985280A1 EP 98920611 A EP98920611 A EP 98920611A EP 98920611 A EP98920611 A EP 98920611A EP 0985280 A1 EP0985280 A1 EP 0985280A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- matrix
- channel
- estimate
- impulse response
- estimation
- Prior art date
- Legal status (The legal status 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 status listed.)
- Withdrawn
Links
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
- H04L25/024—Channel estimation channel estimation algorithms
- H04L25/0242—Channel estimation channel estimation algorithms using matrix methods
-
- 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
- H04B1/76—Pilot transmitters or receivers for control of transmission or for equalising
-
- 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
- H04L25/0224—Channel estimation using sounding signals
Definitions
- the present invention relates to a method for probing a transmission channel.
- the invention proposes a method for estimating the impulse response of a transmission channel.
- a transmitter transmits a signal in a transmission channel intended for a receiver.
- the transmitted signal undergoes amplitude and phase fluctuations in the transmission channel, so that the signal received by the receiver is not identical to it.
- the signal fluctuations are mainly due to what the skilled person calls intersymbol interference. This interference can come from the modulation law used for the transmission and it is also due to the multipath propagation in the channel.
- the received signal generally comes from a large number of reflections in the channel, the different paths taken by the transmitted signal thus leading to various delays at the level of the receiver.
- the impulse response of the channel represents all of these fluctuations, to which the transmitted signal is subjected. This is therefore the fundamental characteristic representing the transmissions between the transmitter and the receiver.
- the impulse response of the channel is used in particular by an equalizer which precisely has the function of correcting the intersymbol interference in the receiver.
- a conventional method for making an estimate of this impulse response consists in having in the transmitted signal a training sequence formed of known symbols. This sequence is chosen according to the modulation law and the dispersion of the channel, dispersion which should be understood here as the delay of an emitted symbol taking the longest path of the channel with respect to this same symbol using the shortest route.
- the dispersion is commonly expressed as a multiple of the duration which separates two successive transmitted symbols, ie a number of "symbol duration".
- two known techniques will be cited for estimating the impulse response of a transmission channel.
- the first technique uses specific training sequences known as CAZAC sequences, for the Anglo-Saxon expression “Constant Amplitude Zero Autocorrelation”. Such sequences are described in the article by A. MILEWSKI: "Periodic sequences with optimal properties for channel estimation and fast start-up equalization", IBM Journal of Research and Development, vol.27, N ° 5, Sept.83, pages 426-431.
- the GSM digital cellular radiocommunication system uses TS training sequences formed by 26 symbols noted a 0 to a25 taking the value +1 or -1. These sequences have the following properties:
- the estimation of the impulse response takes the form of a vector X with 5 components denoted x 0 to X4.
- the sequence of symbols received S corresponding to the learning sequence TS is also formed of 26 symbols denoted s 0 to S25. It is naturally assumed here that the transmitter and the receiver are perfectly synchronized and in this case the estimate of the impulse response X is given by the following expression: 20
- the CAZAC technique has the advantage of great simplicity of implementation. However, we note that each component of the impulse response is established from only 16 symbols received. Since the training sequence includes 26 symbols and the dispersion of the channel is equal to 4, there is information in the received signal which is not taken into account and this leads to a reduction in performance compared to 1 theoretical ideal.
- the second known technique uses the least squares criterion. It is described in particular in patent applications FR 2 696 604 and EP 0 564 849. In terms of recall, this technique uses a measurement matrix A constructed from the learning sequence TS of length n. This matrix includes (n-d) rows and (d + 1) columns, d always representing the dispersion of the channel. The element appearing in the ith row and in the j th column is the (d + i-j) th symbol of the learning sequence:
- the learning sequence is chosen such that the matrix A ⁇ A is invertible where the operator. * - represents the transposition. This is naturally the case for CAZAC sequences but it is also the case for other sequences.
- the first four s ⁇ to s 3 are not taken into account because they also depend on unknown symbols transmitted before the learning sequence, since the dispersion of the channel is 4.
- the received signal By a abuse of language we will henceforth define the received signal as a vector S having as components the symbols received, S4, S5, s 6 , ..., s 2 5.
- the present invention thus relates to a method of probing a transmission channel which has better resistance to additive noise or, in other words, which leads to a reduced error compared to the estimation error of known techniques.
- the method for probing a transmission channel requires a signal received by this channel, this received signal corresponding to a transmitted learning sequence, and it comprises the following steps: acquisition of a statistic of this channel transmission, establishment of an estimate of the impulse response of this channel weighted by this statistic of the channel by means of the signal received.
- the channel statistic represents a value of the impulse response prior to the acquisition of the received signal.
- the aforementioned weighting introduces the fact that the impulse response relating to the received signal has a value probably closer to this previous value than a value which would be very far from it. Thus, statistically, the estimation error is reduced.
- this statistic corresponds to an estimate of the covariance of said impulse response.
- the method comprises the following steps: smoothing of the impulse response and orthonormalization by means of a transformation matrix W to obtain the estimate of the covariance which then takes the form of a matrix L - search for eigenvectors VJ_ 'and associated eigenvalues ⁇ i' of this matrix L ',
- N Q is a strictly positive real number representing an additive noise.
- the additive noise is chosen equal to the smallest of the eigenvalues ⁇ i '.
- each of these eigenvalues is forced to the value of the additive noise. The complexity is reduced accordingly.
- the estimation of the covariance taking the form of a matrix R, by noting A to the measurement matrix associated with the learning sequence, the establishment of the weighted estimate is thus carried out:
- N S - A.X, - normalization of the energy of this instantaneous noise estimate.
- the method of probing a transmission channel provides for the acquisition of a statistic of this channel.
- statistic we mean a set of data reflecting the behavior of this channel over an analysis period. It is therefore a representation of the average behavior of the channel during the analysis period.
- This statistic can be established by any means whatsoever and anywhere. Indeed, in the current case where the sounding process is implemented in a receiver, the establishment of the statistics can take place in another equipment of the radiocommunication network. What matters is that the receiver can acquire this statistic. By way of example, such a statistic can be obtained in the following manner.
- an estimate X of the impulse response is calculated according to a known method. If we take the least squares technique this estimate X is worth:
- the transmitter and the receiver are supposed to be synchronized better than a half symbol near, in which case the reception signal is formed by the vector S whose components are the symbols received S4 to S25 symbols a4 to a25 of the TS training sequence. If such synchronization was not acquired, several solutions are available to acquire it and two will be cited as an example.
- smoothing matrix L by smoothing the various estimates X obtained during the analysis period to obtain an estimate of the covariance associated with this impulse response.
- smoothing in a very general sense, that is to say any operation making it possible to smooth or average the impulse response over the analysis period. This gives a statistical representation of the behavior of the transmission channel.
- a first example of smoothing consists in carrying out the average of the matrix XX n over the analysis period assumed to include m learning sequences: m
- the initialization can be done by any means, in particular by means of the first estimate X obtained or else by an average obtained as above for a small number of learning sequences.
- the measurement matrix A is well conditioned, that is to say that the eigenvalues of the matrix A ⁇ are very close to each other. In this case, it is advantageous to carry out the orthonormalization of the vectors constituted by the columns of the measurement matrix A, but one should not see there a limitation of 1 invention.
- noise estimation step will be described later to make the presentation clearer, although this step precedes the one which will now be explained.
- the method according to the invention therefore comprises a step of searching for couples (eigenvalue, eigenvector) for one or the other of the matrices L ′ or R ′.
- This step will not be more detailed since it is well known to those skilled in the art.
- the next step consists in estimating the instantaneous impulse response X established according to any of the known techniques from the received signal corresponding to the last training sequence received.
- X WX '
- this last estimate is weighted by the following method to obtain an Xp weighting of the instantaneous impulse response:
- a first solution consists in assigning N ⁇ to a predetermined value which reflects a threshold below which it is unlikely that the additive noise can fall. This value could be determined by a measurement of signal-to-noise ratio, or by receiver performance, as an example.
- a third solution which is undoubtedly the most efficient consists in directly estimating the additive noise from the received signal S and from the measurement matrix A.
- N the noise vector affecting the received signal
- N 0 (-) (S - AX) h (S - AX)
- the Xp weighting of the estimate of the instantaneous impulse response can then be carried out as mentioned above.
- the weighted estimate Xp is established directly as follows:
- the weighting matrix P is not necessarily calculated at the time of each new learning sequence transmitted. It can be calculated at a slower rate because it varies substantially at the same rate as R 'and therefore slower than the received signal S. It will also be noted that the weighted estimate is carried out without having recourse to the instantaneous impulse response. It is produced directly from the signal received S.
Landscapes
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- Mathematical Physics (AREA)
- Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
- Filters That Use Time-Delay Elements (AREA)
- Small-Scale Networks (AREA)
- Noise Elimination (AREA)
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR9704933 | 1997-04-14 | ||
FR9704933A FR2762164B1 (fr) | 1997-04-14 | 1997-04-14 | Sondage a ponderation temporelle d'un canal de transmission |
PCT/FR1998/000734 WO1998047239A1 (fr) | 1997-04-14 | 1998-04-10 | Sondage a ponderation temporelle d'un canal de transmission |
Publications (1)
Publication Number | Publication Date |
---|---|
EP0985280A1 true EP0985280A1 (fr) | 2000-03-15 |
Family
ID=9506161
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP98920611A Withdrawn EP0985280A1 (fr) | 1997-04-14 | 1998-04-10 | Sondage a ponderation temporelle d'un canal de transmission |
Country Status (7)
Country | Link |
---|---|
US (1) | US6671313B1 (fr) |
EP (1) | EP0985280A1 (fr) |
CN (1) | CN1256814A (fr) |
BR (1) | BR9808543A (fr) |
CA (1) | CA2286556A1 (fr) |
FR (1) | FR2762164B1 (fr) |
WO (1) | WO1998047239A1 (fr) |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR2821502A1 (fr) * | 2001-02-27 | 2002-08-30 | Thomson Csf | Procede et dispositif d'estimation d'un canal de propagation a partir de ses statistiques |
US7058147B2 (en) * | 2001-02-28 | 2006-06-06 | At&T Corp. | Efficient reduced complexity windowed optimal time domain equalizer for discrete multitone-based DSL modems |
KR100615889B1 (ko) * | 2001-12-29 | 2006-08-25 | 삼성전자주식회사 | 송/수신 다중 안테나를 포함하는 이동 통신 장치 및 방법 |
US7065371B1 (en) * | 2003-02-20 | 2006-06-20 | Comsys Communication & Signal Processing Ltd. | Channel order selection and channel estimation in wireless communication system |
Family Cites Families (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5263026A (en) * | 1991-06-27 | 1993-11-16 | Hughes Aircraft Company | Maximum likelihood sequence estimation based equalization within a mobile digital cellular receiver |
US5432816A (en) * | 1992-04-10 | 1995-07-11 | International Business Machines Corporation | System and method of robust sequence estimation in the presence of channel mismatch conditions |
FR2696604B1 (fr) * | 1992-10-07 | 1994-11-04 | Alcatel Radiotelephone | Dispositif d'estimation d'un canal de transmission. |
FR2708162B1 (fr) * | 1993-07-20 | 1995-09-01 | Alcatel Mobile Comm France | Procédé pour déterminer la longueur optimale d'un bloc de données dans un système de communication à accès multiple à répartition dans le temps (AMRT). |
FR2715488B1 (fr) * | 1994-01-21 | 1996-03-22 | Thomson Csf | Procédé et dispositif permettant à un modem de se synchroniser sur un transmetteur de données numériques par voie hertzienne en présence de brouilleurs. |
FR2718306B1 (fr) * | 1994-03-31 | 1996-04-26 | Alcatel Mobile Comm France | Procédé d'adaptation de l'interface air, dans un système de radiocommunication vers des mobiles. |
FR2719961B1 (fr) * | 1994-05-11 | 1996-06-21 | Alcatel Mobile Comm France | Dispositif d'estimation de la qualité d'un canal de transmission et utilisation correspondante. |
US5513221A (en) * | 1994-05-19 | 1996-04-30 | Hughes Aircraft Company | Doppler bandwidth dependent estimation of a communications channel |
US6101399A (en) * | 1995-02-22 | 2000-08-08 | The Board Of Trustees Of The Leland Stanford Jr. University | Adaptive beam forming for transmitter operation in a wireless communication system |
-
1997
- 1997-04-14 FR FR9704933A patent/FR2762164B1/fr not_active Expired - Fee Related
-
1998
- 1998-04-10 US US09/402,956 patent/US6671313B1/en not_active Expired - Lifetime
- 1998-04-10 CA CA002286556A patent/CA2286556A1/fr not_active Abandoned
- 1998-04-10 EP EP98920611A patent/EP0985280A1/fr not_active Withdrawn
- 1998-04-10 BR BR9808543-3A patent/BR9808543A/pt not_active IP Right Cessation
- 1998-04-10 CN CN98805137.0A patent/CN1256814A/zh active Pending
- 1998-04-10 WO PCT/FR1998/000734 patent/WO1998047239A1/fr not_active Application Discontinuation
Non-Patent Citations (1)
Title |
---|
See references of WO9847239A1 * |
Also Published As
Publication number | Publication date |
---|---|
CA2286556A1 (fr) | 1998-10-22 |
WO1998047239A1 (fr) | 1998-10-22 |
US6671313B1 (en) | 2003-12-30 |
FR2762164B1 (fr) | 1999-09-24 |
CN1256814A (zh) | 2000-06-14 |
BR9808543A (pt) | 2001-06-19 |
FR2762164A1 (fr) | 1998-10-16 |
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