EP1358728A1 - Method for extracting a variable reference pattern - Google Patents

Method for extracting a variable reference pattern

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Publication number
EP1358728A1
EP1358728A1 EP02702465A EP02702465A EP1358728A1 EP 1358728 A1 EP1358728 A1 EP 1358728A1 EP 02702465 A EP02702465 A EP 02702465A EP 02702465 A EP02702465 A EP 02702465A EP 1358728 A1 EP1358728 A1 EP 1358728A1
Authority
EP
European Patent Office
Prior art keywords
transmission channel
channel
extracting
estimate
sequence
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Withdrawn
Application number
EP02702465A
Other languages
German (de)
French (fr)
Inventor
Michel Alard
Nathalie Goudard
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sierra Wireless SA
Original Assignee
Wavecom SA
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 Wavecom SA filed Critical Wavecom SA
Publication of EP1358728A1 publication Critical patent/EP1358728A1/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
    • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0006—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission format
    • H04L1/0007—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission format by modifying the frame length

Definitions

  • the field of the invention is that of the transmission of digital data. More specifically, the invention relates to the estimation of the transfer function of a transmission channel, and the maintenance of the synchronization of a radiocommunication device exchanging digital data via this channel with a remote station.
  • reference symbols In conventional digital communication systems, a sequence of reference symbols, known to the receiver, is frequently used in the data stream sent by the transmitter, called reference symbols or pilot symbols. These reference symbols allow a receiver to properly estimate the transmission channel and thus guarantee a good demodulation of the received signals. It has been envisaged, for communication systems implementing time-varying transmission channels, to distribute reference symbols at different positions within a train of exchanged data.
  • the structure and characteristics of the reference symbols of a radiocommunication device are determined according to the worst case of propagation. Such a constraint is indeed essential to ensure a correct channel estimation whatever the propagation conditions.
  • the radiocommunication terminal When the initial synchronization phase is completed, the radiocommunication terminal is allocated a dedicated resource, and then implements a possible phase of maintaining synchronization, and an estimation of the transmission channel.
  • the reference structure is chosen so as to allow a correct channel estimation in all cases, and even in the worst case of communication, that is to say for the maximum level of multi-route and the maximum speed of the communication terminal considered.
  • the reference structure is dimensioned so as to be adapted to the worst case of Doppler and spread time propagation (in English "delay spread").
  • a drawback of this dimensioning of the worst case reference structure is that it induces a statistical loss of useful transmission capacity and / or of protection against errors, in cases where the characteristics of the transmission channel are favorable.
  • the inventors have detected and analyzed this problem. They deduced therefrom that a drawback of this technique of the prior art is that the reference structure is fixed once and for all for a given physical transmission channel.
  • the invention therefore aims in particular to overcome these drawbacks of the prior art.
  • an objective of the invention is to optimize the useful bit rate for transmitting digital data between a radiocommunication device and a remote station, in particular, but not exclusively, in a multicarrier system.
  • Another objective of the invention is to implement a communication system, and in particular radiocommunication, of high spectral efficiency.
  • the invention also aims to provide a communication system making it possible to achieve a good compromise between quality and bit rate of digital data transmission.
  • Yet another objective of the invention is to implement a radiocommunication system making it possible to limit the losses of useful transmission capacity when the channel has favorable characteristics.
  • the invention also aims to allow a good estimate of the transfer function of a channel, even when the transmission channel considered is disturbed.
  • a secondary objective of the invention is to provide a technique for reducing the envelope fluctuations of the transmitted signal.
  • the structure of such a reference pattern is variable, as a function of at least one characteristic of the transmission channel.
  • the invention is based on a completely new and inventive approach to the estimation of the transfer function of a transmission channel.
  • the invention is based in particular on the implementation of an adaptive reference structure, as a function of one or more characteristics of the transmission channel. The invention therefore goes against the prejudices of those skilled in the art, for whom the reference symbols which are used to estimate the channel must be frozen in the worst case of propagation.
  • the said characteristic or characteristics of the transmission channel include the maximum Doppler frequency and / or the spreading of the response impulse of the maximum delay spread.
  • such a method of extracting a sequence of pilot symbols making it possible to estimate the transfer function of a transmission channel comprises a step of allocating at least one channel to a communication, said allocated channels being functionally identical, but based on distinct waveforms in terms of synchronization, as a function of said characteristics of the transmission channel.
  • the most suitable reference structure is chosen, and making it possible to achieve the best compromise between the quality of the channel estimation and the data transmission capacity.
  • said step of allocating a traffic channel to a communication between said radiocommunication device and said remote station comprises a step of exchanging data representative of the characteristic or characteristics of the transmission channel.
  • the remote station or any other decision-making entity of the radiocommunication network considered, can choose the reference structure most suited to the communication starting between the radiocommunication device and the remote station.
  • said exchange step also allows the transmission of signaling data and / or control data relating to said communication.
  • the duration of the symbols forming the multicarrier signal is variable, depending on the one or more characteristics of the transmission channel.
  • multicarrier modulation systems are particularly advantageous in the case of transmission channels affected by strong fading and multiple paths.
  • a broadband channel which is highly frequency selective is transformed into a large number of non-selective narrowband channels, frequency multiplexed.
  • the transmission channel is estimated by a network of reference carriers, also called pilots.
  • a multicarrier modulation is characterized by the density of its network of subcarriers, consisting of all of the reference carriers and useful carriers, this density being defined by (7 0 v 0 ) ⁇ , where ⁇ 0 corresponds at symbol time, and where v 0 corresponds to the spacing between subcarriers. According to the invention, it is therefore possible to optimize the symbol time as a function of one or more characteristics of the transmission channel.
  • said duration of the symbols is chosen so that it makes the maximum Doppler frequency and the maximum "delay spread" in standard units substantially identical.
  • Such a symbol duration indeed corresponds to the optimal symbol duration.
  • such a method of extracting a sequence of pilot symbols making it possible to estimate the transfer function of a transmission channel being applied to a system offering two channels, a permanent signaling channel and a channel operating in burst mode (by bursts), said characteristics of the transmission channel are measured on said permanent channel, said channel in burst mode starting directly with an optimal reference pattern.
  • said permanent channel uses CDMA modulation (in English “Code Division Multiple Access”, and said channel in "burst” mode uses multicarrier modulation (OFDM / IOTA).
  • the synchronization of the mobile terminal obtained from the WCDMA type channel is used for the IOTA type channel (in “Wideband Code Division Multiple Access” for “multiple access by broadband distribution code”) and it is assumed that the information characterizing the transmission channel (maximum Doppler spreading and maximum time spreading) is known, which makes it possible to start directly with the optimal reference network.
  • the IOTA prototype function described for example in patent document No. FR 2 733 869, exhibits a rapid decrease in time and frequency and is identical to its Fourier transform.
  • said structure of the reference pattern can be modified during communication, when said characteristics of the transmission channel vary.
  • This structure of the reference pattern therefore does not vary over the duration of a block, but may vary from one block relative to the other.
  • the modification of said structure of the reference pattern is carried out using a procedure of the "intra handover" type, used in cellular networks.
  • the term "handover" designates a switching of the transmission means used by a communication without interruption of the latter.
  • said reference pattern is constructed so as to limit the envelope fluctuations of the transmitted signal.
  • the energy dissymmetry between reference carriers and useful carriers can cause significant fluctuations in the average power profile of the transmitted signal. It will be recalled that such an energy asymmetry results from the fact that the symbols transmitted on the reference carriers have a higher energy than that of the useful symbols, in order to allow a better estimation of the transmission channel. It is therefore particularly advantageous to condition the geometry of the network of pilots as a function of the constraint of reduction of the signal envelope fluctuations, so as to limit the degradations due to the non-linearities of the power amplifiers implemented on transmission. of the signal.
  • said reference pattern is formed of drivers, of value and of location in time-frequency space known from said device and regularly distributed in said time-frequency space.
  • said pilots define a parallelogram in time-frequency space.
  • the implementation of a parallelogram pilot network in time-frequency space makes it possible to limit the temporal and / or frequency fluctuations of the transmitted power.
  • the transmission of at least certain data between said device and said remote station is a block transmission.
  • such a method comprises a step of maintaining the synchronization of said device with said remote station, implementing a comparison of the energy associated with said pilots and the energy associated with frequencies carriers known as informative of the signal emitted.
  • a technique is implemented when the network of reference symbols is of rectangular shape.
  • such a method of extracting a sequence of pilot symbols making it possible to estimate the transfer function of a transmission channel comprises a step of adapting the duration of said blocks in function of said characteristics of the transmission channel, so that said channel meets a stationarity criterion during said duration.
  • Such an adaptation of the duration of the blocks as a function of the characteristics of the channel allows in particular that the initial synchronization acquired for example via a channel of the WCDMA type remains valid over the entire duration of a block.
  • the duration of a block is too long for the channel to be considered as quasi-stationary on the whole block, and therefore to be able to ensure good synchronization of the receiver, and a good estimate of the channel on the whole block.
  • Such a modification of the size of the blocks can notably consist in increasing the size of the block in frequency, and in decreasing the duration of the block, so as to obtain a block of reduced duration but without reduction of the amount of information transmitted by this block. .
  • said structure of the reference pattern is variable as a function of said duration of a block.
  • said blocks form time-frequency parallelograms, at least one edge and / or at least one corner of which is identified by a of said pilots.
  • edges of said parallelograms are entirely defined by pilots.
  • such a method of extracting a sequence of pilot symbols making it possible to estimate the transfer function of a transmission channel also comprises a step of adapting the time density and / or frequency of said pilots as a function of said characteristic or characteristics of the transmission channel.
  • the invention also relates to a radiocommunication signal exchanged between a remote station and a radiocommunication device, comprising a reference pattern whose structure is variable as a function of at least one characteristic of the transmission channel.
  • the invention also relates to a receiver, a base station, a transmission system, methods of synchronization, transmission and reception of a radiocommunication signal as described above.
  • FIG. 1 illustrates an example of multi-path data transmission between a fixed transmitter and a moving radio terminal
  • FIG. 2 shows a block diagram of the steps implemented to allocate a reference pattern to a communication of the type illustrated in FIG. 1
  • FIG. 3 illustrates the steps implemented during a data transmission in blocks, to adapt the duration of a block and the reference pattern associated with it as a function of the characteristics of the transmission channel
  • FIG. 4 shows an example of a reference pattern adapted to the "worst case" of the transmission channel illustrated in FIG.
  • FIG. 5 illustrates an example of a reference pattern of a multicarrier communication system in which the pilots form parallelograms in time-frequency space
  • - Figure 6 shows a simplified block diagram of a transmitter according to the invention.
  • the general principle of the invention is based on the adaptability of the reference structure of the signal exchanged between a radiocommunication device and a remote station, depending on the characteristics of the transmission channel.
  • FIGS. 1 and 2 We present, in relation to FIGS. 1 and 2, an example of multi-path data transmission between a fixed transmitter and a mobile radio terminal, as well as the allocation mechanism of a reference structure adapted to such a transmission.
  • a transmitter 1 transmits digital data to a mobile radiocommunication terminal 2.
  • a terminal 2 can, for example, be carried in the moving vehicle of a user.
  • the signal emitted by the station 1 can follow different paths before reaching the terminal 2. It undergoes in particular a plurality of reflections on the reflectors 3, 4 and 5. It can also be diffracted by an obstacle 7, and undergo local dispersion in zone 6, near the terminal 2.
  • the mobile terminal 2 therefore receives a plurality of identical signals, emitted by the fixed station 1, but offset in time, depending on the path followed to reach the mobile terminal 2.
  • the transmission channel established between the transmitter 1 and the terminal 2 is notably characterized by the maximum "delay spread”, that is to say by the maximum spreading of the propagation time, associated with the longest of the paths represented by Figure 1 between transmitter 1 and terminal 2.
  • the transmission channel is also characterized by the maximum Doppler frequency, associated with the speed of terminal 2.
  • these characteristics of the transmission channel are exchanged in the form of a message during a step referenced 20 between the radiocommunication device 2 and the remote station 1.
  • station 1 of the radio network considered decides to allocate to the communication between the device 2 and station 1 a frequency channel having a reference pattern adapted to the characteristics of the transmission channel.
  • the different frequency channels that can be allocated are functionally identical, but have different waveforms in terms of distribution of the reference symbols.
  • the more favorable the characteristics of the transmission channel i.e. the more favorable the transmission environment
  • the characteristics of the transmission channel may vary (22) over time, due to changes in the environment of the terminal 2, or a change in its speed of movement, for example.
  • the station 1 can then modify, after consultation with the device 2, the reference structure implemented, during a step referenced 23. (Such a reference structure does not vary over the duration of a block but can vary d 'one block to another). Such a modification can for example be carried out in real time according to a “handover intra” type procedure. It will be recalled that, in a cellular radiocommunication system with mobiles, the term "handover" designates a switching of the transmission means used by a communication without interruption of the latter.
  • the transmission channel transmission can be considered as quasi-stationary over the duration of a sub-block.
  • a block is too long in duration for the initial synchronization acquired via the WCDMA channel for example to be considered as valid over the entire duration of a block
  • the reference pattern to be associated with each of the successively transmitted sub-blocks is then determined, so as to make a good estimate of the channel.
  • the size of the blocks can be adapted according to any suitable method, taking particular account of the stationarity of the channel. It is also possible to envisage implementing a mechanism for tracking synchronization between the station 1 and the device 2, in particular by exploiting the energy asymmetry between useful subcarriers and reference subcarriers.
  • a step 30 of channel estimation is implemented, making it possible to determine the characteristics of the transmission.
  • an evolution 31 of the maximum duration during which the transmission channel can be considered as quasi-stationary one can consider modifying 32 the duration of the data blocks transmitted, so that the initial synchronization acquired via the type channel WCDMA remains valid for the entire duration of a block.
  • the structure of the reference pattern adapted to each of the data blocks is then determined (34).
  • the invention can in particular be used within the framework of the transmission system described in French patent n ° FR 2 777 407, in the name of the same applicants as the present application, and concerning a "Cellular radiotelephony signal with additional channel assigned to the meaning corresponding descendant, method, system, mobile and base station ".
  • multicarrier systems are of particular interest in the case of transmissions affected by fading and multiple paths, in particular when they are associated with error correcting coding and with interleaving.
  • a main characteristic of OFDM modulation is the density of the carrier network, which is equal to 2 for OFDM / OQAM type modulation (in English "Orthogonal Frequency Division Multiplex / Offset Quadrature Amplitude Modulation") such as IOTA.
  • the density of the carrier network is defined by ( ⁇ 0 v 0 ), where ⁇ 0 corresponds to the symbol time, and where v 0 corresponds to the spacing between subcarriers.
  • the effects of the transmission channel on the transmitted signal are symmetrical.
  • the degradations relating to the Doppler spreading and to the delay in propagation are both equivalent to a convolution or to a filtering in direct space, therefore to a multiplication or an attenuation in reciprocal space.
  • the transmission channel and the prototype function being symmetrical, we can therefore use a basic signal localized in time and frequency with the same time-frequency scale as the channel. We therefore make the maximum Doppler and the Maximum "delay spread", in standard units, by optimizing the symbol duration.
  • This condition ensures that none of the dimensions, time and frequency, are privileged during transmission, and the signal emitted is therefore the least altered possible.
  • N the time spacing between two pilots and N f the frequency spacing.
  • the set of parameters ( ⁇ 0 , v 0 , N t , N f ) defines a physical channel. A propagation channel therefore corresponds to a single physical channel.
  • the transmitted block is bordered by a guard band, in order to reduce the interference between adjacent transmitted blocks and to take into account the rise time of the amplifiers.
  • the reference symbols are distributed uniformly over the channel estimation window, in order to best characterize and estimate significant variations in the channel. These symbols are separated as far as possible from each other in order to obtain the maximum of information therefrom while maximizing the useful throughput.
  • T slot is the duration of a slot.
  • N f the pilot sampling step according to the frequency dimension.
  • T max is the maximum propagation delay, or in English "maximum delay spread”.
  • N t and N f are therefore determined, and the distribution of the pilots within the resulting carrier network, so that the two above equations are verified. 1.2.3. Determining the size of the estimation window
  • the transmission system presented in this particular embodiment ensures the sharing of a high speed transmission resource between several users.
  • a transmission system implementing a packet transmission Such a system therefore allows the transmission of packets of a priori arbitrary size for a given frequency band.
  • This diversity in the size of the blocks transmitted leads in particular to the use of estimation windows of reduced size, fixing the minimum size of a data block.
  • Figure 4 illustrates the distribution of pilots in the estimation window.
  • the reference symbols 41 are distributed regularly within the carrier network 40, respecting a time spacing N t and a frequency spacing N x .
  • the energy dissymmetry between reference carriers and useful carriers can cause significant fluctuations in the average power profile of the transmitted signal.
  • the geometry of the pilot network can therefore be conditioned by the constraint of reducing signal envelope fluctuations, in order to limit the degradations due to the non-linearities of the power amplifiers implemented on transmission.
  • FIG. 5 thus represents an example of a network of information symbols 50 in time-frequency space, in which reference symbols 51 are regularly distributed, so as to form a parallelogram pattern 52.
  • Figure 6 shows a simplified block diagram of a signal transmitter according to the invention.
  • binary source is meant a series of data elements corresponding to one or more source signals of all types (sound, image, data) sampled digital or analog.
  • This binary data is subjected to a binary-to-binary channel coding 61 adapted to channels exhibiting fading.
  • a trellis code possibly concatenated with a Reed-Solomon code (the convolutional code then playing the role of internal code), or use Turbo Codes.
  • this data is distributed (62) in time-frequency space, so as to bring the necessary diversity, and to decorrelate the fading (in English "fading") of Rayleigh affecting the symbols emitted. More generally, a first binary to binary coding is performed, an interleaving in time and frequency and a binary coding with coefficients (in English "mapping").
  • the framing block 63 performs the insertion of the pilots into the carrier network.
  • the reason for inserting the pilots depends on the characteristics of the channel and the size of the block transmitted, which are parameters known to the receiver.
  • a signal receiver according to the invention has a structure similar to that of conventional receivers, comprising in particular means for detecting an overshoot of the correlation of the samples received with those of a sequence known to the receiver , used for synchronization, and means for estimating the transfer function of the transmission channel. According to the invention, such receivers further comprise means for adapting to a reference pattern of variable structure.
  • such receivers can operate according to one of the modes described below: according to a first operating mode, the receiver implements means for receiving, via a signaling channel, relative information the structure of the reference pattern used during the communication; according to a second operating mode, the receiver determines the structure of the desired reference pattern implemented during the communication, as a function of transmission characteristics measured beforehand.
  • the signaling and control information (in particular the information for locating the time / frequency blocks) is transmitted on the WCDMA type channel.
  • this information is toggled on the IOTA channel for the duration of transmission of the block.
  • the synchronization obtained from the WCDMA type channel is used and the maximum frequency and time spreads are assumed to be known.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Quality & Reliability (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Monitoring And Testing Of Transmission In General (AREA)
  • Detection And Prevention Of Errors In Transmission (AREA)

Abstract

The invention concerns a method for extracting a sequence of pilot symbols enabling to estimate the transfer function of a transmission channel, at least a radiocommunication device communicating through said channel with a remote station, the latter regularly delivering to said radiocommunication device a reference pattern. The invention is characterised in that the structure of said reference pattern is variable, depending on at least one characteristic of said transmission channel.

Description

PROCEDE D'EXTRACTION D'UN MOTIF DE REFERENCE VARIABLE METHOD FOR EXTRACTING A VARIABLE REFERENCE PATTERN
Le domaine de l'invention est celui de la transmission de données numériques. Plus précisément, l'invention concerne l'estimation de la fonction de transfert d'un canal de transmission, et le maintien de la synchronisation d'un dispositif de radiocommunication échangeant des données numériques par l'intermédiaire de ce canal avec une station distante.The field of the invention is that of the transmission of digital data. More specifically, the invention relates to the estimation of the transfer function of a transmission channel, and the maintenance of the synchronization of a radiocommunication device exchanging digital data via this channel with a remote station.
Dans les systèmes de communication numérique conventionnels, on utilise fréquemment une séquence de symboles de référence, connus du récepteur, dans le train de données envoyé par l'émetteur, appelés symboles de référence ou symboles pilotes. Ces symboles de référence permettent à un récepteur d'estimer convenablement le canal de transmission et ainsi de garantir un bon déroulement de la démodulation des signaux reçus. On a envisagé, pour les systèmes de communication mettant en œuvre des canaux de transmission variables dans le temps, de répartir des symboles de référence en différentes positions au sein d'un train de données échangées.In conventional digital communication systems, a sequence of reference symbols, known to the receiver, is frequently used in the data stream sent by the transmitter, called reference symbols or pilot symbols. These reference symbols allow a receiver to properly estimate the transmission channel and thus guarantee a good demodulation of the received signals. It has been envisaged, for communication systems implementing time-varying transmission channels, to distribute reference symbols at different positions within a train of exchanged data.
Dans ces différents systèmes de communication, la structure et les caractéristiques des symboles de référence d'un dispositif de radiocommunication sont déterminés en fonction du pire cas de propagation. Une telle contrainte est en effet indispensable pour assurer une estimation de canal correcte quelles que soient les conditions de propagation.In these different communication systems, the structure and characteristics of the reference symbols of a radiocommunication device are determined according to the worst case of propagation. Such a constraint is indeed essential to ensure a correct channel estimation whatever the propagation conditions.
Lorsque la phase de synchronisation initiale est terminée, le terminal de radiocommunication se voit allouer une ressource dédiée, et met alors en œuvre une éventuelle phase de maintien de la synchronisation, et une estimation du canal de transmission.When the initial synchronization phase is completed, the radiocommunication terminal is allocated a dedicated resource, and then implements a possible phase of maintaining synchronization, and an estimation of the transmission channel.
Selon cette technique de l'art antérieur, la structure de référence est choisie de façon à permettre une estimation de canal correcte dans tous les cas, et même dans le pire cas de communication, c'est-à-dire pour le niveau maximal de multitrajet et la vitesse maximale du terminal de communication considéré.According to this technique of the prior art, the reference structure is chosen so as to allow a correct channel estimation in all cases, and even in the worst case of communication, that is to say for the maximum level of multi-route and the maximum speed of the communication terminal considered.
En d'autres termes, la structure de référence est dimensionnée de façon à être adaptée au pire cas de Doppler et d'étalement du temps de propagation (en anglais "delay spread").In other words, the reference structure is dimensioned so as to be adapted to the worst case of Doppler and spread time propagation (in English "delay spread").
Un inconvénient de ce dimensionnement de la structure de référence au pire cas est qu'il induit une perte statistique de capacité utile de transmission et/ou de protection contre les erreurs, dans les cas où les caractéristiques du canal de transmission sont favorables. Les inventeurs ont détecté et analysé ce problème. Ils en ont déduit qu'un inconvénient de cette technique de l'art antérieur est que la structure de référence est figée une fois pour toutes pour un canal de transmission physique donné.A drawback of this dimensioning of the worst case reference structure is that it induces a statistical loss of useful transmission capacity and / or of protection against errors, in cases where the characteristics of the transmission channel are favorable. The inventors have detected and analyzed this problem. They deduced therefrom that a drawback of this technique of the prior art is that the reference structure is fixed once and for all for a given physical transmission channel.
Par conséquent, un autre inconvénient de cette technique de l'art antérieur est que la séquence de symboles de référence retenue ne dépend pas des caractéristiques du canal de transmission, liées d'une part à l'environnement du terminal de communication considéré, et d'autre part à la vitesse de déplacement de ce dernier.Consequently, another drawback of this technique of the prior art is that the sequence of reference symbols chosen does not depend on the characteristics of the transmission channel, linked on the one hand to the environment of the communication terminal considered, and d on the other hand at the speed of movement of the latter.
Il convient de noter que le fait de se poser ce problème est nouveau et inventif pour l'homme du métier, ce dernier ayant toujours considéré que, pour obtenir une bonne estimation de canal, la structure de référence devait être figée et unique, car adaptée au pire cas de propagation du signal.It should be noted that posing this problem is new and inventive for those skilled in the art, the latter having always considered that, in order to obtain a good channel estimate, the reference structure should be fixed and unique, since it is adapted in the worst case of signal propagation.
L'invention a donc notamment pour objectif de pallier ces inconvénients de l'art antérieur.The invention therefore aims in particular to overcome these drawbacks of the prior art.
Plus précisément, un objectif de l'invention est d'optimiser le débit utile de transmission de données numériques entre un dispositif de radiocommunication et une station distante, notamment, mais non exclusivement, dans un système multiporteuse.More specifically, an objective of the invention is to optimize the useful bit rate for transmitting digital data between a radiocommunication device and a remote station, in particular, but not exclusively, in a multicarrier system.
Un autre objectif de l'invention est de mettre en œuvre un système de communication, et notamment de radiocommunication, d'efficacité spectrale élevée. L'invention a également pour objectif de fournir un système de communication permettant de réaliser un bon compromis entre qualité et débit de transmission de données numériques.Another objective of the invention is to implement a communication system, and in particular radiocommunication, of high spectral efficiency. The invention also aims to provide a communication system making it possible to achieve a good compromise between quality and bit rate of digital data transmission.
Encore un autre objectif de l'invention est de mettre en œuvre un système de radiocommunication permettant de limiter les pertes de capacité utile de transmission lorsque le canal présente des caractéristiques favorables.Yet another objective of the invention is to implement a radiocommunication system making it possible to limit the losses of useful transmission capacity when the channel has favorable characteristics.
L'invention a encore pour objectif de permettre une bonne estimation de la fonction de transfert d'un canal, même lorsque le canal de transmission considéré est perturbé. Un objectif secondaire de l'invention est de fournir une technique de réduction des fluctuations d'enveloppe du signal émis.The invention also aims to allow a good estimate of the transfer function of a channel, even when the transmission channel considered is disturbed. A secondary objective of the invention is to provide a technique for reducing the envelope fluctuations of the transmitted signal.
Ces objectifs, ainsi que d'autres qui apparaîtront par la suite, sont atteints à l'aide d'un procédé d'extraction d'une séquence de symboles pilotes nécessaire à l'estimation de la fonction de transfert d'un canal de transmission, au moins un dispositif de radiocommunication communiquant par ledit canal avec une station distante, cette dernière délivrant régulièrement audit dispositif de radiocommunication un motif de référence.These objectives, as well as others which will appear subsequently, are achieved using a method of extracting a sequence of pilot symbols necessary for the estimation of the transfer function of a transmission channel. , at least one radiocommunication device communicating by said channel with a remote station, the latter regularly delivering to said radiocommunication device a reference pattern.
Selon l'invention, la structure d'un tel motif de référence est variable, en fonction d'au moins une caractéristique du canal de transmission. Ainsi, l'invention repose sur une approche tout à fait nouvelle et inventive de l'estimation de la fonction de transfert d'un canal de transmission. En effet, l'invention repose notamment sur la mise en œuvre d'une structure de référence adaptative, en fonction d'une ou plusieurs caractéristiques du canal de transmission. L'invention va donc à l'encontre des préjugés de l'homme du métier, pour qui les symboles de référence qui servent à l'estimation du canal doivent être figés au pire cas de propagation.According to the invention, the structure of such a reference pattern is variable, as a function of at least one characteristic of the transmission channel. Thus, the invention is based on a completely new and inventive approach to the estimation of the transfer function of a transmission channel. Indeed, the invention is based in particular on the implementation of an adaptive reference structure, as a function of one or more characteristics of the transmission channel. The invention therefore goes against the prejudices of those skilled in the art, for whom the reference symbols which are used to estimate the channel must be frozen in the worst case of propagation.
Avantageusement, la ou lesdites caractéristiques du canal de ttansmission comprennent la fréquence Doppler maximale et/ou l'étalement de la réponse impulsionnelle du canal ("delay spread") maximal.Advantageously, the said characteristic or characteristics of the transmission channel include the maximum Doppler frequency and / or the spreading of the response impulse of the maximum delay spread.
Ces caractéristiques sont liées notamment à la vitesse de déplacement du dispositif de communication et à l'environnement dans lequel ce dernier évolue.These characteristics are linked in particular to the speed of movement of the communication device and the environment in which it operates.
Selon une caractéristique avantageuse de l'invention, un tel procédé d'extraction d'une séquence de symboles pilotes permettant d'estimer la fonction de transfert d'un canal de transmission comprend une étape d'allocation d'au moins un canal à une communication, lesdits canaux alloués étant identiques fonctionnellement, mais basés sur des formes d'ondes distinctes en termes de synchronisation, en fonction desdites caractéristiques du canal de transmission. On choisit ainsi, en fonction des caractéristiques du canal de transmission, la structure de référence la plus adaptée, et permettant de réaliser le meilleur compromis entre la qualité de l'estimation de canal et la capacité de transmission de données.According to an advantageous characteristic of the invention, such a method of extracting a sequence of pilot symbols making it possible to estimate the transfer function of a transmission channel comprises a step of allocating at least one channel to a communication, said allocated channels being functionally identical, but based on distinct waveforms in terms of synchronization, as a function of said characteristics of the transmission channel. Thus, according to the characteristics of the transmission channel, the most suitable reference structure is chosen, and making it possible to achieve the best compromise between the quality of the channel estimation and the data transmission capacity.
Préférentiellement, ladite étape d'allocation d'un canal de trafic à une communication entre ledit dispositif de radiocommunication et ladite station distante comprend une étape d'échange de données représentatives de la ou desdites caractéristiques du canal de transmission.Preferably, said step of allocating a traffic channel to a communication between said radiocommunication device and said remote station comprises a step of exchanging data representative of the characteristic or characteristics of the transmission channel.
À l'issue de cet échange de données, la station distante, ou toute autre entité décisionnelle du réseau de radiocommunication considéré, peut choisir la structure de référence la plus adaptée à la communication débutant entre le dispositif de radiocommunication et la station distante.At the end of this data exchange, the remote station, or any other decision-making entity of the radiocommunication network considered, can choose the reference structure most suited to the communication starting between the radiocommunication device and the remote station.
Avantageusement, ladite étape d'échange permet en outre la transmission de données de signalisation et/ou de données de contrôle relatives à ladite communication.Advantageously, said exchange step also allows the transmission of signaling data and / or control data relating to said communication.
Selon une technique avantageuse de l'invention, un tel procédé d'extraction d'une séquence de symboles pilotes permettant d'estimer la fonction de transfert d'un canal de transmission étant mis en œuvre dans un système multiporteuse, la durée des symboles formant le signal multiporteuse est variable, en fonction de la ou desdites caractéristiques du canal de transmission. On rappelle que les systèmes de modulation multiporteuse sont particulièrement intéressants dans le cas de canaux de transmission affectés de forts évanouissements et de trajets multiples. Dans un tel système de communication multiporteuse, un canal large bande fortement sélectif en fréquence est transformé en un grand nombre de canaux à bande étroite non sélectifs, multiplexes en fréquence. L'estimation du canal de transmission, est assurée par un réseau de porteuses de référence, encore appelées pilotes. On rappelle qu'une modulation multiporteuse est caractérisée par la densité de son réseau de sous-porteuses, constitué par l'ensemble des porteuses de référence et des porteuse utiles, cette densité étant définie par (70v0)~ , oùτ0 correspond au temps symbole, et où v0 correspond à l'espacement entre sous-porteuses. Selon l'invention, il est donc possible d'optimiser le temps symbole en fonction d'une ou plusieurs caractéristiques du canal de transmission.According to an advantageous technique of the invention, such a method of extracting a sequence of pilot symbols making it possible to estimate the transfer function of a transmission channel being implemented in a multicarrier system, the duration of the symbols forming the multicarrier signal is variable, depending on the one or more characteristics of the transmission channel. It will be recalled that multicarrier modulation systems are particularly advantageous in the case of transmission channels affected by strong fading and multiple paths. In such a multicarrier communication system, a broadband channel which is highly frequency selective is transformed into a large number of non-selective narrowband channels, frequency multiplexed. The transmission channel is estimated by a network of reference carriers, also called pilots. Recall that a multicarrier modulation is characterized by the density of its network of subcarriers, consisting of all of the reference carriers and useful carriers, this density being defined by (7 0 v 0 ) ~ , whereτ 0 corresponds at symbol time, and where v 0 corresponds to the spacing between subcarriers. According to the invention, it is therefore possible to optimize the symbol time as a function of one or more characteristics of the transmission channel.
Avantageusement, ladite durée des symboles est choisie de façon qu'elle rende sensiblement identique la fréquence Doppler maximale et le "delay spread" maximal en unités normalisées.Advantageously, said duration of the symbols is chosen so that it makes the maximum Doppler frequency and the maximum "delay spread" in standard units substantially identical.
Une telle durée symbole correspond en effet à la durée symbole optimale.Such a symbol duration indeed corresponds to the optimal symbol duration.
Selon un mode de réalisation particulier, un tel procédé d'extraction d'une séquence de symboles pilotes permettant d'estimer la fonction de transfert d'un canal de transmission étant appliqué à un système offrant deux canaux, un canal permanent de signalisation et un canal fonctionnant en mode "burst" (par salves), lesdites caractéristiques du canal de transmission sont mesurées sur ledit canal permanent, ledit canal en mode "burst" démarrant directement avec un motif de référence optimal.According to a particular embodiment, such a method of extracting a sequence of pilot symbols making it possible to estimate the transfer function of a transmission channel being applied to a system offering two channels, a permanent signaling channel and a channel operating in burst mode (by bursts), said characteristics of the transmission channel are measured on said permanent channel, said channel in burst mode starting directly with an optimal reference pattern.
Selon une variante de réalisation particulière, ledit canal permanent utilise une modulation CDMA (en anglais "Code Division Multiple Access", accès multiple par code de répartition), et ledit canal en mode "burst" utilise une modulation multiporteuse (OFDM/IOTA).According to a particular variant embodiment, said permanent channel uses CDMA modulation (in English "Code Division Multiple Access", and said channel in "burst" mode uses multicarrier modulation (OFDM / IOTA).
Ainsi, dans un mode de réalisation particulier de l'invention s'appuyant sur le standard UMTS (en anglais "Universal Mobile Télécommunication System") défini par 3GPP (en anglais "Third Génération Partnership Project"), on utilise pour le canal de type IOTA, la synchronisation du terminal mobile obtenue à partir du canal de type WCDMA (en anglais "Wideband Code Division Multiple Access" pour "accès multiple par code de répartition large bande") et on suppose que les informations caractérisant le canal de transmission (étalement Doppler maximal et étalement en temps maximal) sont connues, ce qui permet de démarrer directement avec le réseau de référence optimal. On rappelle que la fonction prototype IOTA, décrite par exemple dans le document de brevet n° FR 2 733 869, présente une décroissance rapide en temps et en fréquence et est identique à sa transformée de Fourier.Thus, in a particular embodiment of the invention based on the UMTS standard (in English "Universal Mobile Telecommunications System") defined by 3GPP (in English "Third Generation Partnership Project"), the synchronization of the mobile terminal obtained from the WCDMA type channel is used for the IOTA type channel (in "Wideband Code Division Multiple Access" for "multiple access by broadband distribution code") and it is assumed that the information characterizing the transmission channel (maximum Doppler spreading and maximum time spreading) is known, which makes it possible to start directly with the optimal reference network. It is recalled that the IOTA prototype function, described for example in patent document No. FR 2 733 869, exhibits a rapid decrease in time and frequency and is identical to its Fourier transform.
On peut récupérer la synchronisation du terminal mobile à partir du canalWe can recover the synchronization of the mobile terminal from the channel
WCDMA car les structures de trame des deux canaux sont supposées synchrones.WCDMA because the frame structures of the two channels are assumed to be synchronous.
L'intérêt d'un tel procédé est que le canal WCDMA met en œuvre une technique permettant une récupération de la synchronisation simple et rapide, ainsi qu'exposé par exemple dans le document de brevet n° FR 2777407.The advantage of such a method is that the WCDMA channel implements a technique allowing simple and rapid synchronization recovery, as explained for example in patent document No. FR 2777407.
Avantageusement, ladite structure du motif de référence peut être modifiée en cours de communication, lorsque lesdites caractéristiques du canal de transmission varient.Advantageously, said structure of the reference pattern can be modified during communication, when said characteristics of the transmission channel vary.
Cette structure du motif de référence ne varie donc pas sur la durée d'un bloc, mais peut varier d'un bloc par rapport à l'autre.This structure of the reference pattern therefore does not vary over the duration of a block, but may vary from one block relative to the other.
Selon une autre caractéristique avantageuse de l'invention, la modification de ladite structure du motif de référence est effectuée à l'aide d'une procédure du type "handover intra", utilisée dans les réseaux cellulaires.According to another advantageous characteristic of the invention, the modification of said structure of the reference pattern is carried out using a procedure of the "intra handover" type, used in cellular networks.
On rappelle que, dans un système cellulaire de radiocommunication avec les mobiles, le terme "handover" désigne une commutation des moyens de transmission utilisés par une communication sans interruption de cette dernière. En mettant en œuvre une telle procédure, on peut ainsi modifier le type du canal en temps réel, en cours de communication entre le dispositif de radiocommunication et la station distante.It will be recalled that, in a cellular radiocommunication system with mobiles, the term "handover" designates a switching of the transmission means used by a communication without interruption of the latter. By implementing such a procedure, it is thus possible to modify the type of channel in real time, during communication between the radiocommunication device and the station. remote.
De manière préférentielle, ledit motif de référence est construit de façon à limiter les fluctuations d'enveloppe du signal émis.Preferably, said reference pattern is constructed so as to limit the envelope fluctuations of the transmitted signal.
En effet, dans le cas d'un système de modulation multiporteuse, la dissymétrie énergétique entre porteuses de référence et porteuses utiles peut provoquer des fluctuations importantes du profil de puissance moyenne du signal émis. On rappelle qu'une telle dissymétrie énergétique résulte de ce que les symboles transmis sur les porteuses de référence possèdent une énergie plus importante que celle des symboles utiles, afin de permettre une meilleure estimation du canal de transmission. Il est donc particulièrement avantageux de conditionner la géométrie du réseau des pilotes en fonction de la contrainte de réduction des fluctuations d'enveloppe du signal, de manière à limiter les dégradations dues aux non-linéarités des amplificateurs de puissance mis en œuvre à l'émission du signal.Indeed, in the case of a multicarrier modulation system, the energy dissymmetry between reference carriers and useful carriers can cause significant fluctuations in the average power profile of the transmitted signal. It will be recalled that such an energy asymmetry results from the fact that the symbols transmitted on the reference carriers have a higher energy than that of the useful symbols, in order to allow a better estimation of the transmission channel. It is therefore particularly advantageous to condition the geometry of the network of pilots as a function of the constraint of reduction of the signal envelope fluctuations, so as to limit the degradations due to the non-linearities of the power amplifiers implemented on transmission. of the signal.
De façon avantageuse, ledit motif de référence est formé de pilotes, de valeur et d'emplacement dans l'espace temps-fréquence connus dudit dispositif et répartis régulièrement dans ledit espace temps-fréquence.Advantageously, said reference pattern is formed of drivers, of value and of location in time-frequency space known from said device and regularly distributed in said time-frequency space.
Selon une technique avantageuse de l'invention, lesdits pilotes définissent un parallélogramme dans l'espace temps-fréquence.According to an advantageous technique of the invention, said pilots define a parallelogram in time-frequency space.
Dans un système de modulation multiporteuse, la mise en œuvre d'un réseau de pilotes en parallélogramme dans l'espace temps-fréquence permet en effet de limiter les fluctuations temporelles et/ou fréquentielles de la puissance émise.In a multi-carrier modulation system, the implementation of a parallelogram pilot network in time-frequency space makes it possible to limit the temporal and / or frequency fluctuations of the transmitted power.
Avantageusement, la transmission d'au moins certaines données entre ledit dispositif et ladite station distante est une transmission par blocs.Advantageously, the transmission of at least certain data between said device and said remote station is a block transmission.
Selon une variante de réalisation avantageuse de l'invention, un tel procédé comprend une étape de maintien de la synchronisation dudit dispositif avec ladite station distante, mettant en œuvre une comparaison de l'énergie associée auxdits pilotes et de l'énergie associée à des fréquences porteuses dites informatives du signal émis. Une telle technique est mise en œuvre lorsque le réseau de symboles de référence est de forme rectangulaire.According to an advantageous alternative embodiment of the invention, such a method comprises a step of maintaining the synchronization of said device with said remote station, implementing a comparison of the energy associated with said pilots and the energy associated with frequencies carriers known as informative of the signal emitted. Such a technique is implemented when the network of reference symbols is of rectangular shape.
Selon un mode de réalisation particulier de l'invention, un tel procédé d'extraction d'une séquence de symboles pilotes permettant d'estimer la fonction de transfert d'un canal de transmission comprend une étape d'adaptation de la durée desdits blocs en fonction desdites caractéristiques du canal de transmission, de façon que ledit canal respecte un critère de stationnarité pendant ladite durée.According to a particular embodiment of the invention, such a method of extracting a sequence of pilot symbols making it possible to estimate the transfer function of a transmission channel comprises a step of adapting the duration of said blocks in function of said characteristics of the transmission channel, so that said channel meets a stationarity criterion during said duration.
Une telle adaptation de la durée des blocs en fonction des caractéristiques du canal permet notamment que la synchronisation initiale acquise par exemple via un canal de type WCDMA reste valable sur toute la durée d'un bloc.Such an adaptation of the duration of the blocks as a function of the characteristics of the channel allows in particular that the initial synchronization acquired for example via a channel of the WCDMA type remains valid over the entire duration of a block.
En effet, lors d'une transmission par blocs, il peut arriver que la durée d'un bloc soit trop importante pour que le canal puisse être considéré comme quasi - stationnaire sur l'ensemble du bloc, et donc pour pouvoir assurer une bonne synchronisation du récepteur, et une bonne estimation du canal sur l'ensemble du bloc. On peut donc envisager d'adapter la taille des blocs transmis, de façon que le canal vérifie un critère de stationnarité pendant la durée d'un bloc. Dans ce dessein, on peut segmenter les blocs en sous-blocs, ou modifier la taille des blocs si la ressource en fréquence le permet. Une telle modification de la taille des blocs peut notamment consister à augmenter la taille du bloc en fréquence, et à diminuer la durée du bloc, de façon à obtenir un bloc de durée réduite mais sans réduction de la quantité d'informations transmises par ce bloc.Indeed, during a block transmission, it may happen that the duration of a block is too long for the channel to be considered as quasi-stationary on the whole block, and therefore to be able to ensure good synchronization of the receiver, and a good estimate of the channel on the whole block. We can therefore consider adapting the size of the transmitted blocks, so that the channel satisfies a stationarity criterion during the duration of a block. For this purpose, we can segment the blocks into sub-blocks, or modify the size of the blocks if the frequency resource allows. Such a modification of the size of the blocks can notably consist in increasing the size of the block in frequency, and in decreasing the duration of the block, so as to obtain a block of reduced duration but without reduction of the amount of information transmitted by this block. .
Selon une variante de réalisation avantageuse, ladite structure du motif de référence est variable en fonction de ladite durée d'un bloc.According to an advantageous alternative embodiment, said structure of the reference pattern is variable as a function of said duration of a block.
On peut ainsi envisager de déterminer, pour chacun des blocs transmis, une structure de motif de référence adaptée. On rappelle qu'une telle structure de référence ne varie pas sur la durée d'un bloc, mais peut varier d'un bloc à l'autre.It is thus possible to envisage determining, for each of the transmitted blocks, a suitable reference pattern structure. It is recalled that such a reference structure does not vary over the duration of a block, but can vary from one block to another.
Préférentiellement, lesdits blocs forment des parallélogrammes dans l'espace temps-fréquence, dont au moins un bord et/ou au moins un coin est repéré par un desdits pilotes.Preferably, said blocks form time-frequency parallelograms, at least one edge and / or at least one corner of which is identified by a of said pilots.
De façon avantageuse, les bords desdits parallélogrammes sont intégralement définis par des pilotes.Advantageously, the edges of said parallelograms are entirely defined by pilots.
Selon une caractéristique avantageuse de l'invention, un tel procédé d'extraction d'une séquence de symboles pilotes permettant d'estimer la fonction de transfert d'un canal de transmission comprend en outre une étape d'adaptation de la densité temporelle et/ou fréquentielle desdits pilotes en fonction de la ou lesdites caractéristiques du canal de transmission.According to an advantageous characteristic of the invention, such a method of extracting a sequence of pilot symbols making it possible to estimate the transfer function of a transmission channel also comprises a step of adapting the time density and / or frequency of said pilots as a function of said characteristic or characteristics of the transmission channel.
L'invention concerne également un signal de radiocommunication échangé entre une station distante et un dispositif de radiocommunication, comprenant un motif de référence dont la structure est variable en fonction d'au moins une caractéristique du canal de transmission.The invention also relates to a radiocommunication signal exchanged between a remote station and a radiocommunication device, comprising a reference pattern whose structure is variable as a function of at least one characteristic of the transmission channel.
L'invention concerne encore un récepteur, une station de base, un système de transmission, des procédés de synchronisation, d'émission et de réception d'un signal de radiocommunication tel que décrit précédemment.The invention also relates to a receiver, a base station, a transmission system, methods of synchronization, transmission and reception of a radiocommunication signal as described above.
D'autres caractéristiques et avantages de l'invention apparaîtront plus clairement à la lecture de la description suivante d'un mode de réalisation préférentiel, donné à titre de simple exemple illustratif et non limitatif, et des dessins annexés, parmi lesquels : - la figure 1 illustre un exemple de transmission de données multi-trajets entre un émetteur fixe et un terminal de radiocommunication en mouvement ; la figure 2 présente un synoptique des étapes mises en œuvre pour allouer un motif de référence à une communication du type illustrée en figure 1 ; la figure 3 illustre les étapes mises en œuvre lors d'une transmission de données par blocs, pour adapter la durée d'un bloc et le motif de référence qui lui est associé en fonction des caractéristiques du canal de transmission ; la figure 4 présente un exemple de motif de référence adapté au "pire cas" de canal de transmission illustré en figure 1 dans le cas d'une modulation multiporteuse ; la figure 5 illustre un exemple de motif de référence d'un système de communication multiporteuse dans lequel les pilotes forment des parallélogrammes dans l'espace temps-fréquence ; - la figure 6 présente un synoptique simplifié d'un émetteur selon l'invention.Other characteristics and advantages of the invention will appear more clearly on reading the following description of a preferred embodiment, given by way of simple illustrative and nonlimiting example, and of the appended drawings, among which: - the figure 1 illustrates an example of multi-path data transmission between a fixed transmitter and a moving radio terminal; FIG. 2 shows a block diagram of the steps implemented to allocate a reference pattern to a communication of the type illustrated in FIG. 1; FIG. 3 illustrates the steps implemented during a data transmission in blocks, to adapt the duration of a block and the reference pattern associated with it as a function of the characteristics of the transmission channel; FIG. 4 shows an example of a reference pattern adapted to the "worst case" of the transmission channel illustrated in FIG. 1 in the case of a modulation multicarrier; FIG. 5 illustrates an example of a reference pattern of a multicarrier communication system in which the pilots form parallelograms in time-frequency space; - Figure 6 shows a simplified block diagram of a transmitter according to the invention.
Le principe général de l'invention repose sur l'adaptabilité de la structure de référence du signal échangé entre un dispositif de radiocommunication et une station distante, en fonction des caractéristiques du canal de transmission.The general principle of the invention is based on the adaptability of the reference structure of the signal exchanged between a radiocommunication device and a remote station, depending on the characteristics of the transmission channel.
On présente, en relation avec les figures 1 et 2, un exemple de transmission de données multi-trajets entre un émetteur fixe et un terminal de radiocommunication en mouvement, ainsi que le mécanisme d'allocation d'une structure de référence adaptée à une telle transmission.We present, in relation to FIGS. 1 and 2, an example of multi-path data transmission between a fixed transmitter and a mobile radio terminal, as well as the allocation mechanism of a reference structure adapted to such a transmission.
Un émetteur 1 transmet des données numériques à destination d'un terminal de radiocommunication mobile 2. Un tel terminal 2 peut, par exemple, être embarqué dans le véhicule en mouvement d'un utilisateur. Le signal émis par la station 1 peut suivre différents trajets avant d'atteindre le terminal 2. Il subit notamment une pluralité de réflexions sur les réflecteurs 3, 4 et 5. Il peut également être diffracté par un obstacle 7, et subir une dispersion locale dans la zone 6, à proximité du terminal 2. Le terminal mobile 2 reçoit donc une pluralité de signaux identiques, émis par la station fixe 1, mais décalés dans le temps, en fonction du chemin suivi pour atteindre le terminal mobile 2.A transmitter 1 transmits digital data to a mobile radiocommunication terminal 2. Such a terminal 2 can, for example, be carried in the moving vehicle of a user. The signal emitted by the station 1 can follow different paths before reaching the terminal 2. It undergoes in particular a plurality of reflections on the reflectors 3, 4 and 5. It can also be diffracted by an obstacle 7, and undergo local dispersion in zone 6, near the terminal 2. The mobile terminal 2 therefore receives a plurality of identical signals, emitted by the fixed station 1, but offset in time, depending on the path followed to reach the mobile terminal 2.
Le canal de transmission établi entre l'émetteur 1 et le terminal 2 est notamment caractérisé par le "delay spread" maximal, c'est-à-dire par l'étalement maximal du temps de propagation, associé au plus long des trajets représenté en figure 1 entre l'émetteur 1 et le terminal 2.The transmission channel established between the transmitter 1 and the terminal 2 is notably characterized by the maximum "delay spread", that is to say by the maximum spreading of the propagation time, associated with the longest of the paths represented by Figure 1 between transmitter 1 and terminal 2.
Le canal de transmission est également caractérisé par la fréquence Doppler maximale, associée à la vitesse du terminal 2.The transmission channel is also characterized by the maximum Doppler frequency, associated with the speed of terminal 2.
Ainsi qu'illustré en figure 2, ces caractéristiques du canal de transmission (Doppler maximal et "delay spread" maximal) sont échangées sous forme de message au cours d'une étape référencée 20 entre le dispositif de radiocommunication 2 et la station distante 1.As illustrated in Figure 2, these characteristics of the transmission channel (Maximum Doppler and maximum delay spread) are exchanged in the form of a message during a step referenced 20 between the radiocommunication device 2 and the remote station 1.
En fonction des informations échangées, la station 1 du réseau de radiocommunication considéré décide d'allouer à la communication entre le dispositif 2 et la station 1 un canal de fréquence présentant un motif de référence adapté aux caractéristiques du canal de transmission. Les différents canaux de fréquence pouvant être alloués sont fonctionnellement identiques, mais présentent des formes d'onde différentes en termes de répartition des symboles de référence. Ainsi, plus les caractéristiques du canal de transmission sont favorables (c'est-à-dire plus l'environnement de la transmission est favorable), moins le système de communication consommera de la capacité du canal à des fins d'estimation de la fonction de transfert du canal de transmission, et, le cas échéant, à des fins de maintien de la synchronisation, au profit de la capacité de transmission et/ou de la capacité de protection contre les erreurs.Based on the information exchanged, station 1 of the radio network considered decides to allocate to the communication between the device 2 and station 1 a frequency channel having a reference pattern adapted to the characteristics of the transmission channel. The different frequency channels that can be allocated are functionally identical, but have different waveforms in terms of distribution of the reference symbols. Thus, the more favorable the characteristics of the transmission channel (i.e. the more favorable the transmission environment), the less the communication system will consume the capacity of the channel for the purpose of estimating the function. transmission channel transfer, and, where appropriate, for the purpose of maintaining synchronization, for the benefit of the transmission capacity and / or the error protection capacity.
Il est possible que les caractéristiques du canal de transmission varient (22) au cours du temps, en raison de l'évolution de l'environnement du terminal 2, ou d'un changement intervenu dans sa vitesse de déplacement par exemple.The characteristics of the transmission channel may vary (22) over time, due to changes in the environment of the terminal 2, or a change in its speed of movement, for example.
La station 1 peut alors modifier, après concertation du dispositif 2, la structure de référence mise en œuvre, au cours d'une étape référencée 23. (Une telle structure de référence ne varie pas sur la durée d'un bloc mais peut varier d'un bloc à l'autre). Une telle modification peut par exemple s'effectuer en temps réel selon une procédure de type "handover intra". On rappelle que, dans un système cellulaire de radiocommunication avec les mobiles, le terme "handover" désigne une commutation des moyens de transmission utilisés par une communication sans interruption de cette dernière.The station 1 can then modify, after consultation with the device 2, the reference structure implemented, during a step referenced 23. (Such a reference structure does not vary over the duration of a block but can vary d 'one block to another). Such a modification can for example be carried out in real time according to a “handover intra” type procedure. It will be recalled that, in a cellular radiocommunication system with mobiles, the term "handover" designates a switching of the transmission means used by a communication without interruption of the latter.
Dans le cas d'une transmission par blocs, on peut aussi envisager de mettre en œuvre une segmentation des blocs en plusieurs sous-blocs, de façon que le canal de transmission puisse être considéré comme quasi-stationnaire sur la durée d'un sous- bloc. Ainsi, si un bloc est de durée trop grande pour que la synchronisation initiale acquise via le canal WCDMA par exemple puisse être considérée comme valable sur toute la durée d'un bloc, on peut envisager de segmenter le bloc en sous-blocs pour lesquels les motifs de référence sont a priori différents. On détermine alors le motif de référence à associer à chacun des sous-blocs successivement transmis, de manière à réaliser une bonne estimation du canal. Plus généralement, la taille des blocs peut être adaptée selon toute méthode adéquate, en tenant compte notamment de la stationnarité du canal. On peut encore envisager de mettre en œuvre un mécanisme de poursuite de synchronisation entre la station 1 t le dispositif 2, notamment en exploitant la dissymétrie énergétique entre sous-porteuses utiles et sous-porteuses de référence.In the case of a block transmission, it is also possible to envisage implementing a segmentation of the blocks into several sub-blocks, so that the transmission channel transmission can be considered as quasi-stationary over the duration of a sub-block. Thus, if a block is too long in duration for the initial synchronization acquired via the WCDMA channel for example to be considered as valid over the entire duration of a block, it is possible to consider segmenting the block into sub-blocks for which the Reference patterns are a priori different. The reference pattern to be associated with each of the successively transmitted sub-blocks is then determined, so as to make a good estimate of the channel. More generally, the size of the blocks can be adapted according to any suitable method, taking particular account of the stationarity of the channel. It is also possible to envisage implementing a mechanism for tracking synchronization between the station 1 and the device 2, in particular by exploiting the energy asymmetry between useful subcarriers and reference subcarriers.
Ainsi qu'illustré en figure 3, on met en œuvre une étape 30 d'estimation du canal, permettant de déterminer les caractéristiques de la transmission. En cas d'évolution 31 de la durée maximale pendant laquelle le canal de transmission peut être considéré comme quasi-stationnaire, on peut envisager de modifier 32 la durée des blocs de données transmis, de façon que la synchronisation initiale acquise via le canal de type WCDMA reste valable sur toute la durée d'un bloc.As illustrated in FIG. 3, a step 30 of channel estimation is implemented, making it possible to determine the characteristics of the transmission. In the event of an evolution 31 of the maximum duration during which the transmission channel can be considered as quasi-stationary, one can consider modifying 32 the duration of the data blocks transmitted, so that the initial synchronization acquired via the type channel WCDMA remains valid for the entire duration of a block.
En fonction de l'évolution 33 des caractéristiques du canal de transmission (par exemple en fonction du changement d'environnement d'une communication), on détermine ensuite (34) la structure du motif de référence adaptée à chacun des blocs de données.Depending on the evolution 33 of the characteristics of the transmission channel (for example as a function of the change in the environment of a communication), the structure of the reference pattern adapted to each of the data blocks is then determined (34).
On présente désormais, en relation avec les figures 3 à 5, un exemple de mise en œuvre du procédé d'extraction d'une séquence de symboles pilotes permettant d'estimer la fonction de transfert du canal de transmission selon l'invention, dans le cadre d'un système de transmission utilisant une modulation de type OFDM/OQAM/IOTA. L'invention s'applique bien sûr également à tout autre système de transmission de données dans lequel une estimation de canal est nécessaire, et notamment aux systèmes de transmission mettant en œuvre une modulation de type monoporteuse.We now present, in relation to FIGS. 3 to 5, an example of implementation of the method of extracting a sequence of pilot symbols making it possible to estimate the transfer function of the transmission channel according to the invention, in the part of a transmission system using OFDM / OQAM / IOTA modulation. The invention is of course also applicable to any other data transmission system in which a channel estimation is necessary, and in particular to transmission systems implementing a single carrier type modulation.
L'invention peut notamment être utilisée dans le cadre du système de transmission décrit dans le brevet français n° FR 2 777 407, au nom des mêmes déposants que la présente demande, et concernant un "Signal de radiotéléphonie cellulaire à canal supplémentaire affecté au sens descendant, procédé, système, mobile et station de base correspondants".The invention can in particular be used within the framework of the transmission system described in French patent n ° FR 2 777 407, in the name of the same applicants as the present application, and concerning a "Cellular radiotelephony signal with additional channel assigned to the meaning corresponding descendant, method, system, mobile and base station ".
On rappelle que les systèmes multiporteuses présentent un intérêt particulier dans le cas de transmissions affectées d'évanouissements et de trajets multiples, notamment lorsqu'elles sont associées à un codage correcteur d'erreur et à un entrelacement.It will be recalled that multicarrier systems are of particular interest in the case of transmissions affected by fading and multiple paths, in particular when they are associated with error correcting coding and with interleaving.
Une caractéristique principale de la modulation OFDM est la densité du réseau de porteuses, qui est égale à 2 pour les modulations de type OFDM/OQAM (en anglais "Orthogonal Frequency Division Multiplex/Offset Quadrature Amplitude Modulation") telle que IOTA. On rappelle que la densité du réseau de porteuses est définie par (τ0v0) , oùτ0 correspond au temps symbole, et où v0 correspond à l'espacement entre sous-porteuses.A main characteristic of OFDM modulation is the density of the carrier network, which is equal to 2 for OFDM / OQAM type modulation (in English "Orthogonal Frequency Division Multiplex / Offset Quadrature Amplitude Modulation") such as IOTA. Recall that the density of the carrier network is defined by (τ 0 v 0 ), whereτ 0 corresponds to the symbol time, and where v 0 corresponds to the spacing between subcarriers.
Pour un canal caractérisé par les paramètres de fréquence Doppler et de "delay spread", les effets du canal de transmission sur le signal émis sont symétriques. En effet, les dégradations relatives à l'étalement Doppler et au retard à la propagation sont toutes deux équivalentes à une convolution ou à un filtrage dans l'espace direct, donc à une multiplication ou une atténuation dans l'espace réciproque. En outre, la fonction prototype IOTA présente une parfaite symétrie temps-fréquence pour les variables normalisées τ0 = Vr~ et 0 = V r - Le canal de transmission et la fonction prototype étant symétriques, on peut donc utiliser un signal de base localisé en temps et en fréquence avec la même échelle temps-fréquence que le canal. On rend donc identiques le Doppler maximal et le "delay spread" maximal, en unités normalisées, en optimisant la durée symbole.For a channel characterized by the Doppler frequency and "delay spread" parameters, the effects of the transmission channel on the transmitted signal are symmetrical. Indeed, the degradations relating to the Doppler spreading and to the delay in propagation are both equivalent to a convolution or to a filtering in direct space, therefore to a multiplication or an attenuation in reciprocal space. In addition, the IOTA prototype function has perfect time-frequency symmetry for the normalized variables τ 0 = Vr ~ and 0 = V r - The transmission channel and the prototype function being symmetrical, we can therefore use a basic signal localized in time and frequency with the same time-frequency scale as the channel. We therefore make the maximum Doppler and the Maximum "delay spread", in standard units, by optimizing the symbol duration.
Cette condition assure qu'aucune des dimensions, temps et fréquence, n'est privilégiée durant la transmission, et le signal émis est donc le moins altéré possible.This condition ensures that none of the dimensions, time and frequency, are privileged during transmission, and the signal emitted is therefore the least altered possible.
1.1. Structure du réseau de pilotes Soit N, l'espacement temporel entre deux pilotes et Nf l'espacement fréquentiel. Le jeu de paramètres (τ0,v0,Nt,Nf) définit un canal physique. Un canal de propagation correspond donc à un canal physique unique.1.1. Structure of the pilot network Let N be the time spacing between two pilots and N f the frequency spacing. The set of parameters (τ 0 , v 0 , N t , N f ) defines a physical channel. A propagation channel therefore corresponds to a single physical channel.
L'insertion des pilotes, en fonction des paramètres du canal de propagation, est gérée dynamiquement. Selon le mode de réalisation particulier décrit dans la suite du document, le bloc transmis est bordé par une bande de garde, afin de réduire l'interférence entre blocs transmis adjacents et prendre en compte le temps de montée des amplificateurs.The insertion of the pilots, according to the parameters of the propagation channel, is managed dynamically. According to the particular embodiment described in the following document, the transmitted block is bordered by a guard band, in order to reduce the interference between adjacent transmitted blocks and to take into account the rise time of the amplifiers.
Les symboles de référence sont répartis uniformément sur la fenêtre d'estimation de canal, pour caractériser et estimer au mieux les variations significatives du canal. Ces symboles sont éloignés autant que possible les uns des autres pour en tirer le maximum d'information tout en maximisant le débit utile.The reference symbols are distributed uniformly over the channel estimation window, in order to best characterize and estimate significant variations in the channel. These symbols are separated as far as possible from each other in order to obtain the maximum of information therefrom while maximizing the useful throughput.
1.2. Adaptation du réseau de porteuses de référence et du temps symbole 7.2J. Adaptation du temps symbole1.2. Adaptation of the network of reference carriers and symbol time 7.2J. Adaptation of symbol time
On considère un mode de réalisation particulier de l'invention s'appuyant sur le standard UMTS défini par 3GPP. On utilise la synchronisation obtenue à partir du canal de type WCDMA et on suppose acquises les informations sur le type de canal de propagation. On bascule ensuite sur un canal mettant en œuvre une modulation de type OFDM/IOTA. À partir des informations concernant le Doppler maximal et le retard maximal pour chaque type de canal de propagation, la densité du réseau étant fixée à 2 (1), on détermine le temps symbole et l'espacement entre sous-porteuses, tels que le rapport des supports des filtres modélisant le canal soit proportionnel au rapport entre τ0 et v0 (2) : (DWe consider a particular embodiment of the invention based on the UMTS standard defined by 3GPP. The synchronization obtained from the WCDMA type channel is used and the information on the type of propagation channel is assumed to be acquired. We then switch to a channel implementing OFDM / IOTA type modulation. From the information concerning the maximum Doppler and the maximum delay for each type of propagation channel, the density of the network being fixed at 2 (1), the symbol time and the spacing between sub-carriers are determined, such as the ratio filter supports modeling the channel is proportional to the ratio between τ 0 and v 0 (2): (D
T0 _ '' max (2) T 0 _ '' max (2)
2fD 2f D
Le temps symbole doit alors respecter la structure de trame du système (3)The symbol time must then respect the frame structure of the system (3)
Lslol p, p entier (3) τo où Tslot est la durée d'un slot. L slol p, p integer (3) τ o where T slot is the duration of a slot.
Les différentes valeurs de τ0 et v0 issues de l'analyse de canaux de type UMTS, spécifiés par l'ETSI (on peut se référer par exemple au document TR 101 112 N3.2.0 Annexe B.l), sont répertoriées dans le tableau ci-dessousThe different values of τ 0 and v 0 from the analysis of UMTS type channels, specified by ETSI (we can refer for example to the document TR 101 112 N3.2.0 Annex Bl), are listed in the table below. -Dessous
On rappelle que, pour un système de transmission reposant sur une modulation OFDM classique, une telle adaptation du temps symbole n'est pas envisagée sous cette forme. 1.2.2. Détermination de la répartition des pilotes Détermination de Nt : It will be recalled that, for a transmission system based on a conventional OFDM modulation, such adaptation of the symbol time is not envisaged in this form. 1.2.2. Determination of the distribution of pilots Determination of N t :
Soit N„ le pas d'échantillonnage des pilotes selon la dimension temporelle. D'après le théorème d'échantillonnage (dit théorème de Shannon), la période d'échantillonnage des pilotes selon la dimension temporelle, Ntτ0, doit vérifier :Let N „be the pilot sampling step according to the time dimension. According to the sampling theorem (known as Shannon's theorem), the pilot sampling period according to the time dimension, N t τ 0 , must verify:
où BD est la bande de fréquence Doppler [-FD, +FD] avec FD la fréquence Doppler maximale et BD=2*FD. where B D is the Doppler frequency band [-F D , + F D ] with F D the maximum Doppler frequency and B D = 2 * F D.
Détermination de N£ :. Soit Nf, le pas d'échantillonnage des pilotes selon la dimension fréquentielle.Determination of N £ :. Let N f be the pilot sampling step according to the frequency dimension.
La période d'échantillonnage des pilotes selon la dimension fréquentielle,The pilot sampling period according to the frequency dimension,
NfV0, doit vérifier :N f V 0 , must check:
où Tmax est le retard maximal de propagation, ou en anglais "delay spread" maximal. On détermine donc les paramètres Nt et Nf, et la répartition des pilotes au sein du réseau de porteuses qui en résulte, de sorte que les deux équations ci-dessus soient vérifiées. 1.2.3. Détermination de la taille de la fenêtre d'estimation where T max is the maximum propagation delay, or in English "maximum delay spread". The parameters N t and N f are therefore determined, and the distribution of the pilots within the resulting carrier network, so that the two above equations are verified. 1.2.3. Determining the size of the estimation window
On considère que le système de transmission présenté dans ce mode de réalisation particulier assure le partage d'une ressource de transmission à haut débit entre plusieurs utilisateurs. On considère notamment un système de transmission mettant en œuvre une transmission par paquets. Un tel système permet donc la transmission de paquets de taille a priori quelconque pour une bande de fréquence donnée. Cette diversité dans la taille des blocs transmis conduit notamment à l'utilisation de fenêtres d'estimation de taille réduite, fixant la taille minimale d'un bloc de données. La figure 4 illustre la répartition des pilotes dans la fenêtre d'estimation. Les symboles de référence 41 sont répartis régulièrement au sein du réseau de porteuses 40, en respectant un espacement temporel Nt et un espacement fréquentiel Nx.It is considered that the transmission system presented in this particular embodiment ensures the sharing of a high speed transmission resource between several users. We consider in particular a transmission system implementing a packet transmission. Such a system therefore allows the transmission of packets of a priori arbitrary size for a given frequency band. This diversity in the size of the blocks transmitted leads in particular to the use of estimation windows of reduced size, fixing the minimum size of a data block. Figure 4 illustrates the distribution of pilots in the estimation window. The reference symbols 41 are distributed regularly within the carrier network 40, respecting a time spacing N t and a frequency spacing N x .
On peut également envisager une répartition des pilotes en parallélogramme dans la fenêtre d'estimation, ainsi qu'illustré en figure 5.It is also possible to envisage a distribution of the pilots in parallelogram in the estimation window, as illustrated in FIG. 5.
En effet, la dissymétrie énergétique entre porteuses de référence et porteuses utiles peut provoquer des fluctuations importantes du profil de puissance moyenne du signal émis. La géométrie du réseau de pilotes peut donc être conditionnée par la contrainte de réduction des fluctuations d'enveloppe du signal, en vue de limiter les dégradations dues aux non-linéarités des amplificateurs de puissance mis en œuvre à l'émission.Indeed, the energy dissymmetry between reference carriers and useful carriers can cause significant fluctuations in the average power profile of the transmitted signal. The geometry of the pilot network can therefore be conditioned by the constraint of reducing signal envelope fluctuations, in order to limit the degradations due to the non-linearities of the power amplifiers implemented on transmission.
On représente ainsi en figure 5 un exemple de réseau de symboles d'information 50 dans l'espace temps-fréquence, dans lequel sont répartis régulièrement des symboles de référence 51, de manière à former un motif en parallélogramme 52.FIG. 5 thus represents an example of a network of information symbols 50 in time-frequency space, in which reference symbols 51 are regularly distributed, so as to form a parallelogram pattern 52.
1.3. Principe d'un émetteur1.3. Principle of a transmitter
La figure 6 présente un synoptique simplifié d'un émetteur d'un signal selon l'invention.Figure 6 shows a simplified block diagram of a signal transmitter according to the invention.
On considère une source binaire 60 à haut débit. Par source binaire, on entend une série d'éléments de données correspondant à un ou plusieurs signaux source de tous types (son, image, données) numériques ou analogiques échantillonnées. Ces données binaires sont soumises à un codage canal 61 binaire à binaire adapté à des canaux présentant des évanouissements. On pourra par exemple utiliser un code en treillis, concatené éventuellement avec un code de Reed-Solomon (le code convolutif jouant alors le rôle de code interne), ou utiliser des Turbo Codes.We consider a binary source 60 at high speed. By binary source is meant a series of data elements corresponding to one or more source signals of all types (sound, image, data) sampled digital or analog. This binary data is subjected to a binary-to-binary channel coding 61 adapted to channels exhibiting fading. We could for example use a trellis code, possibly concatenated with a Reed-Solomon code (the convolutional code then playing the role of internal code), or use Turbo Codes.
Ensuite, on répartit (62) ces données dans l'espace temps-fréquence, de façon à apporter la diversité nécessaire, et à décorréler l'évanouissement (en anglais "fading") de Rayleigh affectant les symboles émis. Plus généralement, on effectue un premier codage binaire à binaire, un entrelacement en temps et en fréquence et un codage binaire à coefficients (en anglais "mapping").Then, this data is distributed (62) in time-frequency space, so as to bring the necessary diversity, and to decorrelate the fading (in English "fading") of Rayleigh affecting the symbols emitted. More generally, a first binary to binary coding is performed, an interleaving in time and frequency and a binary coding with coefficients (in English "mapping").
À l'issue de cette opération de codage, on dispose des symboles réels à émettre, am π, qui sont ultérieurement modulés à l'aide d'un modulateur OFDM/OQAM/IOTA 64.At the end of this coding operation, there are the real symbols to be transmitted, a m π , which are subsequently modulated using an OFDM / OQAM / IOTA 64 modulator.
Le bloc de mise en trame 63 effectue l'insertion des pilotes dans le réseau de porteuses. Le motif d'insertion des pilotes (nombre de pilotes en temps et en fréquence, espacement entre les pilotes) dépend des caractéristiques du canal et de la taille de bloc transmis, qui sont des paramètres connus du récepteur.The framing block 63 performs the insertion of the pilots into the carrier network. The reason for inserting the pilots (number of pilots in time and frequency, spacing between the pilots) depends on the characteristics of the channel and the size of the block transmitted, which are parameters known to the receiver.
Le signal complexe généré à l'issue du modulateur 64 est alors converti (65) sous forme analogique, puis transposé à la fréquence finale par un modulateur 66 à deux voies en quadrature (I et Q), et enfin amplifié (67) avant d'être émis (68). 1.4. Principe d'un récepteur Un récepteur de signal selon l'invention est de structure similaire à celle des récepteurs classiques, comprenant notamment des moyens de détection d'un dépassement de seuil de la corrélation des échantillons reçus avec ceux d'une séquence connue du récepteur, utilisée pour la synchronisation, et des moyens d'estimation de la fonction de transfert du canal de transmission. Selon l'invention, de tels récepteurs comprennent en outre des moyens d'adaptation à un motif de référence de structure variable. Notamment, de tels récepteurs peuvent fonctionner selon l'un des modes décrits ci-dessous : selon un premier mode de fonctionnement, le récepteur met en œuvre des moyens de réception, par l'intermédiaire d'un canal de signalisation, d'informations relatives à la structure du motif de référence utilisé au cours de la communication ; selon un second mode de fonctionnement, le récepteur détermine la structure du motif de référence souhaité mis en œuvre au cours de la communication, en fonction de caractéristiques de transmission mesurées préalablement.The complex signal generated at the end of the modulator 64 is then converted (65) into analog form, then transposed to the final frequency by a two-way modulator 66 in quadrature (I and Q), and finally amplified (67) before d 'be issued (68). 1.4. Principle of a receiver A signal receiver according to the invention has a structure similar to that of conventional receivers, comprising in particular means for detecting an overshoot of the correlation of the samples received with those of a sequence known to the receiver , used for synchronization, and means for estimating the transfer function of the transmission channel. According to the invention, such receivers further comprise means for adapting to a reference pattern of variable structure. In particular, such receivers can operate according to one of the modes described below: according to a first operating mode, the receiver implements means for receiving, via a signaling channel, relative information the structure of the reference pattern used during the communication; according to a second operating mode, the receiver determines the structure of the desired reference pattern implemented during the communication, as a function of transmission characteristics measured beforehand.
Selon une autre approche, dans un premier mode de fonctionnement, les informations de signalisation et de contrôle (notamment les informations de repérage des pavés temps/fréquence) sont transmises sur le canal de type WCDMA. Dans un deuxième mode de fonctionnement, ces informations sont basculées sur le canal IOTA pendant la durée de transmission du bloc. Dans tous les cas, on utilise la synchronisation obtenue à partir du canal de type WCDMA et les étalements fréquentiel et temporel maximaux sont supposés connus. According to another approach, in a first operating mode, the signaling and control information (in particular the information for locating the time / frequency blocks) is transmitted on the WCDMA type channel. In a second operating mode, this information is toggled on the IOTA channel for the duration of transmission of the block. In all cases, the synchronization obtained from the WCDMA type channel is used and the maximum frequency and time spreads are assumed to be known.

Claims

REVENDICATIONS
1. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission, au moins un dispositif de radiocommunication communiquant par ledit canal avec une station distante, cette dernière délivrant régulièrement audit dispositif de radiocommunication un motif de référence, caractérisé en ce que la structure dudit motif de référence est variable, en cours de communication, en fonction d'au moins une caractéristique du canal de transmission appartenant au groupe comprenant la fréquence Doppler maximale et/ou l'étalement de la réponse impulsionnelle du canal ("delay spread") maximal.1. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel, at least one radiocommunication device communicating by said channel with a remote station, the latter regularly delivering to said device of a reference pattern radiocommunication, characterized in that the structure of said reference pattern is variable, during communication, as a function of at least one characteristic of the transmission channel belonging to the group comprising the maximum Doppler frequency and / or the spread of the maximum impulse response of the channel ("delay spread").
2. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon la revendication 1, caractérisé en ce qu'il comprend une étape d'allocation d'au moins un canal à une communication, lesdits canaux alloués étant identiques fonctionnellement, mais basés sur des formes d'ondes distinctes en termes de structure dudit motif de référence, en fonction desdites caractéristiques du canal de transmission.2. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to claim 1, characterized in that it comprises a step of allocating at least one communication channel, said allocated channels being functionally identical, but based on distinct waveforms in terms of the structure of said reference pattern, as a function of said characteristics of the transmission channel.
3. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon l'une quelconque des revendications 1 et 2, caractérisé en ce que ladite étape d'allocation d'un canal de trafic à une communication entre ledit dispositif de radiocommunication et ladite station distante comprend une étape d'échange de données représentatives de la ou desdites caractéristiques du canal de transmission. 3. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to any one of claims 1 and 2, characterized in that said step of allocating a traffic channel for communication between said radiocommunication device and said remote station comprises a step of exchanging data representative of the characteristic or characteristics of the transmission channel.
4. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon la revendication 3, caractérisé en ce que ladite étape d'échange permet en outre la transmission de données de signalisation et/ou de données de contrôle relatives à ladite communication. 4. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to claim 3, characterized in that said exchange step also allows the transmission of data from signaling and / or control data relating to said communication.
5. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission d'un signal multiporteuse selon l'une quelconque des revendications 1 à 4, ledit signal multiporteuse étant constitué d'une succession de symboles formés chacun d'une pluralité de fréquences porteuses, caractérisé en ce que l'intervalle de temps et/ou l'intervalle de fréquence entre deux fréquences porteuses consécutives est variable, en fonction de la ou desdites caractéristiques dudit canal.5. Method for extracting a sequence of pilot symbols allowing in particular to estimate the transfer function of a transmission channel of a multicarrier signal according to any one of claims 1 to 4, said multicarrier signal consisting of a succession of symbols each formed from a plurality of carrier frequencies , characterized in that the time interval and / or the frequency interval between two consecutive carrier frequencies is variable, as a function of the said characteristic or characteristics of said channel.
6. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon la revendication 5, caractérisé en ce que l'intervalle de temps entre deux fréquences ^ porteuses consécutives est choisi de façon qu'il rende sensiblement identiques la fréquence Doppler maximal et le "delay spread" maximal en unités normalisées.6. A method of extracting a sequence of pilot symbols to include estimating the transfer function of a transmission channel according to claim 5, characterized in that the time interval between two consecutive carrier frequencies ^ is selected so that it makes the maximum Doppler frequency and the maximum delay spread in standard units substantially identical.
7. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon l'une quelconque des revendications 5 et 6, appliqué à un système offrant deux canaux, un canal permanent de signalisation et un canal fonctionnant en mode "burst" (par salves), caractérisé en ce que lesdites caractéristiques dudit canal de transmission sont mesurées sur ledit canal permanent, ledit canal en mode "burst" démarrant directement avec un motif de référence optimal.7. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to any one of claims 5 and 6, applied to a system offering two channels, a permanent channel signaling and a channel operating in "burst" mode (by bursts), characterized in that said characteristics of said transmission channel are measured on said permanent channel, said channel in "burst" mode starting directly with an optimal reference pattern.
8. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon la revendication 7, caractérisé en ce que ledit. canal permanent utilise une modulation CDMA (en anglais "Code Division Multiple Access"), et ledit canal en mode "burst" utilise une modulation multiporteuse (OFDM/IOTA).8. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to claim 7, characterized in that said. permanent channel uses CDMA modulation (in English "Code Division Multiple Access"), and said channel in "burst" mode uses multicarrier modulation (OFDM / IOTA).
9. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon l'une quelconque des revendications 1 à 8, caractérisé en ce que la modification de ladite structure du motif de référence est effectuée à l'aide d'une procédure du type "handover intra", utilisée dans les réseaux cellulaires.9. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to any one of claims 1 to 8, characterized in that the modification of said pattern structure of reference is carried out using a procedure of the "intra handover" type, used in cellular networks.
10. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon l'une quelconque des revendications 1 à 9, caractérisé en ce que ledit motif de référence est construit de façon à limiter les fluctuations d'enveloppe du signal émis.10. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to one any one of claims 1 to 9, characterized in that said reference pattern is constructed so as to limit the envelope fluctuations of the transmitted signal.
11. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon l'une quelconque des revendications 1 à 10, caractérisé en ce que ledit motif de référence est formé de fréquences porteuses de référence, appelées pilotes, de valeur et d'emplacement dans l'espace temps-fréquence connus dudit dispositif et répartis régulièrement dans ledit espace temps-fréquence.11. Method of extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to any one of claims 1 to 10, characterized in that said reference pattern is formed of reference carrier frequencies, called pilots, of value and location in time-frequency space known to said device and regularly distributed in said time-frequency space.
12. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon la revendication 11, caractérisé en ce que lesdits pilotes définissent un parallélogramme dans l'espace temps-fréquence.12. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to claim 11, characterized in that said pilots define a parallelogram in time-frequency space.
13. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon l'une quelconque des revendications 10 et 12, caractérisé en ce que la transmission d'au moins certaines données entre ledit dispositif et ladite station distante est une transmission par blocs.13. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to any one of claims 10 and 12, characterized in that the transmission of at least certain data between said device and said remote station is a block transmission.
14. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon l'une quelconque des revendications 5 à 13, caractérisé en ce qu'il comprend une étape de maintien, de la synchronisation dudit dispositif avec ladite station distante, mettant en œuvre une comparaison de l'énergie associée auxdits pilotes et de l'énergie associée à des fréquences porteuses dites informatives du signal émis.14. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to any one of claims 5 to 13, characterized in that it comprises a holding step , synchronization of said device with said remote station, implementing a comparison of the energy associated with said pilots and the energy associated with carrier frequencies called informative of the transmitted signal.
15. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon la revendication 14, caractérisé en ce qu'il comprend une étape d'adaptation de la durée desdits blocs en fonction desdites caractéristiques du canal de transmission, de façon que ledit canal respecte un critère de stationnarité pendant ladite durée.15. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to claim 14, characterized in that it comprises a step of adapting the duration of said blocks according to said characteristics of the transmission channel, so that said channel meets a stationarity criterion during said duration.
16. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon la revendication 15, caractérisé en ce que ladite structure du motif de référence est variable en fonction de ladite durée d'un bloc.16. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to the claim 15, characterized in that said structure of the reference pattern is variable as a function of said duration of a block.
17. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon les revendications 13 à 16, caractérisé en ce que lesdits blocs forment des parallélogrammes dans l'espace temps-fréquence, dont au moins un bord et/ou au moins un coin est repéré par un desdits pilotes.17. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to claims 13 to 16, characterized in that said blocks form parallelograms in time space- frequency, at least one edge and / or at least one corner of which is identified by one of said pilots.
18. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon la revendication 17, caractérisé en ce que les bords desdits parallélogrammes sont intégralement définis par des pilotes.18. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to claim 17, characterized in that the edges of said parallelograms are entirely defined by pilots.
19. Procédé d'extraction d'une séquence de symboles pilotes permettant notamment d'estimer la fonction de transfert d'un canal de transmission selon l'une quelconque des revendications 12 à 18, caractérisé en ce qu'il comprend en outre une étape d'adaptation de la densité temporelle et/ou fréquentielle desdits pilotes en fonction de la ou lesdites caractéristiques dudit canal de transmission.19. Method for extracting a sequence of pilot symbols making it possible in particular to estimate the transfer function of a transmission channel according to any one of claims 12 to 18, characterized in that it further comprises a step adaptation of the time and / or frequency density of said pilots as a function of the said characteristic or characteristics of said transmission channel.
20. Procédé de synchronisation d'au moins un dispositif de radiocommunication avec une station distante, cette dernière délivrant régulièrement audit dispositif de radiocommunication un motif de référence, caractérisé en ce que la structure dudit motif de référence est variable, en cours de communication, en fonction d'au moins une caractéristique du canal de transmission appartenant au groupe comprenant la fréquence Doppler maximale et/ou l'étalement de la réponse impulsionnelle du canal ("delay spread") maximal20. Method for synchronizing at least one radiocommunication device with a remote station, the latter regularly delivering to said radiocommunication device a reference pattern, characterized in that the structure of said reference pattern is variable, during communication, by function of at least one characteristic of the transmission channel belonging to the group comprising the maximum Doppler frequency and / or the spreading of the maximum impulse response of the channel ("delay spread")
21. Signal de radiocommunication échangé entre une station distante et un dispositif de radiocommunication, caractérisé en ce qu'il comprend un motif de référence dont la structure est variable, en cours de communication, en fonction d'au moins une caractéristique du canal de transmission appartenant au groupe comprenant la fréquence Doppler maximale et/ou l'étalement de la réponse impulsionnelle du canal ("delay spread") maximal. 21. Radiocommunication signal exchanged between a remote station and a radiocommunication device, characterized in that it comprises a reference pattern whose structure is variable, during communication, according to at least one characteristic of the transmission channel belonging to the group comprising the maximum Doppler frequency and / or the spreading of the maximum impulse response of the channel ("delay spread").
22. Récepteur d'un signal de radiocommunication selon la revendication 21, caractérisé en ce qu'il comprend des moyens d'estimation de la fonction de transfert du canal de transmission capables de traiter un motif de référence dont la structure est variable, en cours de communication, en fonction d'au moins une caractéristique dudit canal appartenant au groupe comprenant la fréquence Doppler maximale et/ou l'étalement de la réponse impulsionnelle du canal ("delay spread") maximal.22. Receiver of a radiocommunication signal according to claim 21, characterized in that it comprises means for estimating the transfer function of the transmission channel capable of processing a reference pattern whose structure is variable, during communication, as a function of at least one characteristic of said channel belonging to the group comprising the maximum Doppler frequency and / or the spreading of the maximum impulse response of the channel ("delay spread").
23. Station de base émettant un signal de radiocommunication selon la revendication 21, caractérisé en ce qu'elle comprend des moyens pour modifier la structure d'un motif de référence, en cours de communication, en fonction d'au moins unej aractéristique du canal de transmission appartenant au groupe comprenant la fréquence Doppler maximale et/ou l'étalement de la réponse impulsionnelle du canal ("delay spread") maximal.23. Base station transmitting a radiocommunication signal according to claim 21, characterized in that it comprises means for modifying the structure of a reference pattern, during communication, as a function of at least one characteristic of the channel. transmission belonging to the group comprising the maximum Doppler frequency and / or the spreading of the maximum impulse response of the channel ("delay spread").
24. Procédé d'émission d'un signal de radiocommunication selon la revendication 21. 24. Method for transmitting a radiocommunication signal according to claim 21.
25. Procédé de réception d'un signal de radiocommunication selon la revendication 21.25. The method of receiving a radiocommunication signal according to claim 21.
26. Système de transmission d'un signal selon la revendication 21, entre au moins un émetteur et au moins un récepteur. 26. A signal transmission system according to claim 21, between at least one transmitter and at least one receiver.
EP02702465A 2001-02-08 2002-02-07 Method for extracting a variable reference pattern Withdrawn EP1358728A1 (en)

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FR0101751A FR2820574B1 (en) 2001-02-08 2001-02-08 METHOD FOR EXTRACTING A REFERENCE SYMBOL PATTERN FOR ESTIMATING THE TRANSFER FUNCTION OF A TRANSMIT CHANNEL, SIGNAL, DEVICE AND CORRESPONDING METHODS
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PCT/FR2002/000486 WO2002065685A1 (en) 2001-02-08 2002-02-07 Method for extracting a variable reference pattern

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