WO2002065685A1 - Procede d'extraction d'un motif de reference variable - Google Patents

Procede d'extraction d'un motif de reference variable Download PDF

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Publication number
WO2002065685A1
WO2002065685A1 PCT/FR2002/000486 FR0200486W WO02065685A1 WO 2002065685 A1 WO2002065685 A1 WO 2002065685A1 FR 0200486 W FR0200486 W FR 0200486W WO 02065685 A1 WO02065685 A1 WO 02065685A1
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WO
WIPO (PCT)
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.)
Ceased
Application number
PCT/FR2002/000486
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English (en)
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
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Filing date
Publication date
Application filed by Wavecom SA filed Critical Wavecom SA
Priority to KR1020037010498A priority Critical patent/KR100914021B1/ko
Priority to BRPI0207123-1A priority patent/BR0207123A/pt
Priority to CN02806251.5A priority patent/CN1496622B/zh
Priority to JP2002564876A priority patent/JP4150591B2/ja
Priority to US10/467,571 priority patent/US7313174B2/en
Priority to EP02702465A priority patent/EP1358728A1/fr
Publication of WO2002065685A1 publication Critical patent/WO2002065685A1/fr
Anticipated expiration legal-status Critical
Ceased 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)
PCT/FR2002/000486 2001-02-08 2002-02-07 Procede d'extraction d'un motif de reference variable Ceased WO2002065685A1 (fr)

Priority Applications (6)

Application Number Priority Date Filing Date Title
KR1020037010498A KR100914021B1 (ko) 2001-02-08 2002-02-07 가변의 기준 패턴의 추출방법
BRPI0207123-1A BR0207123A (pt) 2001-02-08 2002-02-07 método para extrair um padrão de referência variável
CN02806251.5A CN1496622B (zh) 2001-02-08 2002-02-07 可变参考模式提取方法及装置
JP2002564876A JP4150591B2 (ja) 2001-02-08 2002-02-07 可変の基準パターンを抽出する方法
US10/467,571 US7313174B2 (en) 2001-02-08 2002-02-07 Method for extracting a variable reference pattern
EP02702465A EP1358728A1 (fr) 2001-02-08 2002-02-07 Procede d'extraction d'un motif de reference variable

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR01/01751 2001-02-08
FR0101751A FR2820574B1 (fr) 2001-02-08 2001-02-08 Procede d'extraction d'un motif de symboles de reference servant a estimer la fonction de transfert d'un canal de transmission, signal, dispositif et procedes correspondants

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WO2002065685A1 true WO2002065685A1 (fr) 2002-08-22

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PCT/FR2002/000486 Ceased WO2002065685A1 (fr) 2001-02-08 2002-02-07 Procede d'extraction d'un motif de reference variable

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US (1) US7313174B2 (enExample)
EP (1) EP1358728A1 (enExample)
JP (1) JP4150591B2 (enExample)
KR (1) KR100914021B1 (enExample)
CN (1) CN1496622B (enExample)
BR (1) BR0207123A (enExample)
FR (1) FR2820574B1 (enExample)
WO (1) WO2002065685A1 (enExample)

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FR2820574A1 (fr) 2002-08-09
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US7313174B2 (en) 2007-12-25
JP2004530319A (ja) 2004-09-30
CN1496622A (zh) 2004-05-12
JP4150591B2 (ja) 2008-09-17
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US20040131110A1 (en) 2004-07-08
BR0207123A (pt) 2006-03-01

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