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
  • H04L25/0224—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 a person skilled in the art calls intersymbol interference. This interference can come from the modulation law used for transmission; it is also due to 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 temporal dispersion of the channel, dispersion which should be understood here as the delay of an emitted symbol taking the longest path of the channel compared to this same symbol taking the path most short.
• the temporal dispersion is commonly expressed as a multiple of the duration which separates two successive transmitted symbols, ie a number of "symbol duration".
• the present invention thus relates to a method of probing a transmission channel which has significantly improved performance in a mobile environment.
• a transmission channel affected by a time dispersion d is probed from a training sequence and from a reception signal corresponding to this sequence, this by means of a matrix.
• measurement established from the learning sequence taking into account this temporal dispersion; the method comprises a step for producing the dynamic impulse response of this channel using the least squares technique such as the combination of a static response r with (d + 1) components and a time drift r 'which therefore depends on time.
• the method comprises a step for weighting this coefficient by the expression ⁇ / ( ⁇ + No) where N Q represents the modulus of the reception noise.
• N Q represents the modulus of the reception noise.
• reception noise modulus may be obtained by normalizing the energy of the instantaneous noise.
• the method comprises a step for finding the eigenvector rg associated with the largest eigenvalue of the covariance of the static response, the reception signal being defined by the expression drift coefficients.
• FIG. 1 a block diagram of the method according to the invention
• FIG. 2 a block diagram of a first variant of implementation of the invention
• FIG. 3 a block diagram of a second variant of implementation of the invention.
• FIG. 4 a block diagram of a third embodiment of one invention.
• the elements common to several figures are assigned a single reference.
• This system uses TS training sequences made up of 26 symbols noted an to a25 taking the value +1 or -1. These symbols coming from the transmitter are known to the receiver and one will thus include under the term "training sequence” any sequence of bits which are known a priori of this receiver by any means whatsoever.
• the sequence s of symbols received by the receiver corresponding to the training sequence TS transmitted by the transmitter is also formed by 26 symbols denoted SQ to s 25-
• estimation techniques use a measurement matrix M constructed from the learning sequence TS of length n.
• This matrix includes (nd) rows and (d + 1) columns, d always representing the temporal dispersion of the channel.
• the element appearing in the ith row and in the jth column is the (d + i- j) th symbol of the learning sequence: a4 a 3 & 2 ai ao as 4 a3 & 2 ai a6 as a4 a 3 a2
• the learning sequence is chosen such that the matrix M ⁇ is invertible where the operator represents the transposition.
• T is a diagonal matrix of dimension 22, the element of which appears in the ith row and in the ith column represents the time which corresponds to the (d + i) th symbol of the training sequence, that is to say the origin of time being arbitrarily fixed between the fifteenth and sixteenth symbols.
• equation (1) is expressed by the following two expressions:
• the dynamic impulse response CIR therefore appears as a vector with 10 components formed by the five components of the static response r and the five components of the time drift r '. It follows a relative complexity of the computations necessary by comparison with the traditional methods.
• a smoothing matrix L is constructed by smoothing the different responses obtained for the successively transmitted learning sequences, this in order to obtain an estimate of the covariance associated with this static response. Smoothing is understood here in a very general sense, that is to say any operation making it possible to smooth or to average the static response.
• a first example of smoothing consists in carrying out the average of the matrix rr n over a period supposed to include m learning sequences, the operator.
• a second smoothing example consists in updating, at the ith training sequence received, the smoothing matrix obtained in the (il) th training sequence by means of a multiplicative coefficient ⁇ , this factor being generally known under the name smoothing forget factor and being between 0 and 1:
• Li (rr h ) ⁇ riri h + (l- ⁇ ) Li_ ⁇ (rr h )
• Initialization can be done by any means, in particular by means of the first estimate r obtained or by an average obtained as above for a low number of learning sequences.
• a first solution consists in assigning Nn with 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 signal-to-noise ratio measurement, or by the performance of the receiver, this by way of example.
• a second solution consists in considering that the last eigenvalue, (the weakest) of the smoothing matrix L is equal to NQ.
• N 0 () (s - Mr - ⁇ 0 Tu 0 ) n (s - Mr - ⁇ 0 Tu 0 )
• the additive noise is therefore obtained by normalizing the energy of the instantaneous noise.
• weighted coefficient ⁇ pp tends to zero when the transmission channel is stationary because the variance ⁇ 2 also tends to zero.
• a dynamic impulse response with seven components is adopted, including five components for the static response and two for the time drift.
• the static response r is calculated by any of the known techniques.
• Equation (3) Equation (3) then results in the following expression:
• the time drift here corresponds to the term ⁇ ⁇ ⁇ ri.
• the dynamic impulse response is presented as a vector with 15 components formed by the five components of the static response r and the ten components of the time drift (five for r 'and five for r ").

Landscapes

• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Filters That Use Time-Delay Elements (AREA)
• Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
• Dc Digital Transmission (AREA)
• Testing, Inspecting, Measuring Of Stereoscopic Televisions And Televisions (AREA)

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• 1998
  • 1998-08-04 FR FR9810225A patent/FR2782212B1/fr not_active Expired - Fee Related
• 1999
  • 1999-08-04 WO PCT/FR1999/001933 patent/WO2000008815A1/fr not_active Application Discontinuation
  • 1999-08-04 JP JP2000564343A patent/JP2002522963A/ja active Pending
  • 1999-08-04 BR BR9913358-0A patent/BR9913358A/pt not_active Application Discontinuation
  • 1999-08-04 CA CA002340017A patent/CA2340017A1/fr not_active Abandoned
  • 1999-08-04 EP EP99936689A patent/EP1101334A1/de not_active Withdrawn

Non-Patent Citations (1)

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