FR2851383A1 - Wireless data transmitting process for universal mobile telecommunication system, involves estimating response of transmission channel of data transmission signal by taking into account simple carrier pilot signal - Google Patents

Abstract

Transmission of wireless data between a transmitter and a receiver involves implementing a simple carrier pilot signal (CPICH) and a first data transmission signal transmitted in accordance with multiple carrier modulation. The response of the transmission channel of the data transmission signal is estimated by an estimation unit (60), where the estimation process takes into account the simple carrier pilot signal. The frequency band utilized for the pilot signal on the transmission channel includes the frequency band utilized for the transmission signal. Independent claims are also included for the following: (a) a wireless data receiving device (b) a wireless data transmitting device (c) a wireless data transmission signal (d) a cellular telecommunication system.

Description

Method for transmitting radio data, signal, system and devices

corresponding.

  The present invention relates to the field of telecommunications, and in particular, the invention relates to the transmission and processing of data, in particular in a cellular network, in particular at high bit rates.

  More specifically, the invention relates to a channel response estimate and the use of this estimate to equalize data in a received signal.

  The third generation radio systems, and the following, 10 offer or allow many services and applications involving the transmission of data at very high rates. The resources allocated to data transfers (for example files containing sound and / or still or animated images), in particular via the Internet or similar networks, will represent a preponderant part of the available resource and will probably be greater than 15 In the long run, the resources allocated to voice communications, which should remain substantially constant.

  However, the total throughput offered to users of radiotelephony equipment is limited in particular by the width of the available frequency band. In order to increase the available resources, we have traditionally used 20, in particular, a densification of cells in a given territory. This creates a network infrastructure divided into "micro-cells" which are relatively small cells. A disadvantage of this technique is that it requires a multiplication of fixed stations (base station or BS from the English "Base Station" called "Node B" from the English "Node B" according to the UMTS standard), which are relatively complex and expensive items. In addition, the data rate, although high, is not optimal. In addition, at the higher level, it is clear that the more cells, and therefore the fixed stations, the more complex the management.

  In radio telecommunication systems, the transmitted signals are generally subject to echoes resulting in the presence of multiple paths having different amplitudes and delays. The combination of these paths can cause fading (or "fading" in English) at the level of the receiver, which can very disturb reception. In addition, the environment and / or the receiver being mobile, the channel changes over time. It is therefore necessary to provide in such systems effective means for counteracting disturbances on the signals and in particular to estimate the response of the channel and to ensure equalization of the data received by taking this estimate into account. This supposes the emission of reference data (pilots in particular). Of course, this reference data is transmitted at the expense of the useful data, which leads to a reduction in the useful throughput. This is particularly the case in third generation UMTS networks (from the English "Universal Mobile Telecommunication System" or "Universal Mobile Telecommunication System").

  Furthermore, the third generation systems under development are based, like the existing radiotelephone systems, on a symmetrical structure. Thus, the UMTS standard defined at 3GPP (from the English "Third Generation Partnerchip Project" or "Third generation partnership project") provides, for the main link FDD (from the English "Frequency Division Duplex" or "duplex par frequency distribution "), a symmetrical distribution between the downlink (base station to terminal) and the uplink (terminal to base station). There is also a TDD link (from the English "Time Division Duplex" or "time division duplex") allowing a certain asymmetry. However, the asymmetry thus offered is limited when faced with the needs of users for broadband Internet-type services, with or without mobility, on the downlink.

  Also, it is planned to add a broadband downlink (known as HSDPA) which provides additional throughput in order to meet increased needs in terms of throughput for, in particular, multimedia applications. This link is based on a packet data transmission using: either a single-carrier modulation (also called single-carrier) of spread spectrum type (CDMA of English "Code Division Multiple Access" or "Multiple Access by Distribution by Code " in French); - Or a modulation with multiple carriers (or subcarriers) (also called multicarriers), for example of the OFDM type (from the English "Orthogonal Frequency Division Multiplex" or "Multiplexing by orthogonal frequency division"). In the second case, a CDMA channel (for the "basic" symmetrical link) and an OFDM channel (for an additional data transmission link) will therefore be used jointly, the two channels having to be processed (in particular demodulated and equalized) separately.

  In order to correctly decode the data received on an OFDM channel, in particular in a noisy environment and generating multiple echoes of the radio signal, an estimation of the channel is implemented from pilots inserted in the OFDM signal in order to allow equalization. of the received signal.

  The principle of OFDM (illustrated with regard to FIGS. 1 and 2) consists in dividing a frequency band into a sufficiently large number of passband subbands 20 so that a channel subjected to multiple paths, and therefore frequency selective becomes non selective in each subband. The channel then becomes multiplicative on each sub-band, which facilitates equalization and effectively combats the selectivity of the propagation channel.

  FIG. 1 shows an OFDM signal known per se in a time / frequency plane. This signal comprises a succession of OFDM symbols 1641 to 164p corresponding respectively to instants tl to tp. Each of the OFDM symbols 1641 to 164p comprises several sub-carriers symbolized by solid or non-ellipses, each associated with a frequency. Thus, the symbol 1641 includes a first subcarrier 111 associated with the frequency F1, a second subcarrier associated with a frequency F2 and so on up to a 64th subcarrier associated with a frequency F64. frequencies (the corresponding subcarriers being represented in the form of solid ellipses) are reserved for transmitting a pilot while others are reserved for the transport of data (the corresponding subcarriers being represented in the form of 5 empty ellipses). , for example, the subcarriers 111, 112, 11p associated with the frequency F1 allow the transport of data while the subcarriers 121, 122, 12p associated with the frequency F2 corresponding to pilots.

  FIG. 2 illustrates a processing (known per se) of a signal 20 comprising OFDM symbols 1641 to 164p presented opposite FIG. 1.

  The signal 20 is first presented in baseband to a demodulator 21 which is responsible for converting the received signal into a succession of samples which will be processed subsequently. The OFDM signal comprises a sum of several symbols each modulating a subcarrier over a duration corresponding to an OFDM symbol. Since the subcarriers are orthogonal to each other, the OFDM demodulator 21 projects the signal received on all of the subcarriers, thus making it possible to extract information symbols.

  The demodulator 20 then supplies means 22 for extracting the pilot symbols and an equalizer 24.

  The means 22 extract the pilot symbols from the demodulated OFDM signal 20 in order to supply channel values at the time / frequency positions corresponding to interpolation means 23.

  The interpolation means 23 estimate the channel in the entire time / frequency plane from the channel values supplied by the means 22 and supply the equalizer 24 with the channel estimation thus obtained.

  The equalizer 24 equalizes the information symbols transmitted by the demodulator 21 on the basis of the channel estimation supplied by the means 23 by presenting at output 25 a succession of equalized information.

  The equalization processing of a CDMA signal is relatively different from that described above for a signal corresponding to a modulation with 30 multiple carriers.

  Indeed, to equalize a CDMA signal within the framework of the UMTS standard and more generally a single-carrier signal subjected to a multipath channel, it is possible to autocorrelate a dedicated pilot signal transmitted continuously (called CPICH channel ). A multi-path channel includes multiple paths, each with delay and attenuation.

  Thus, after determining the delays zi undergone by the transmitted pilot signal, an autocorrelation of this signal is carried out. The transmission channel comprising L paths can be modeled in the form of the following transfer function h (t): L-1 h (t) = la, (t) ô (t- Ti) i = O or: a, (t) represents a coefficient of the channel along the file path; - T. a delay associated with the journey; - t time; and - ô the distribution of Dirac.

  The invention according to its various aspects aims in particular to overcome these drawbacks of the prior art.

  More specifically, an objective of the invention is to provide a method and devices for transmitting data through a radio channel (and therefore capable of being subjected to multiple paths) which are relatively technically simple to implement, and therefore inexpensive, and suitable for the reception of different types of data (for example voice and multimedia data at low or high speed).

  Another objective of the invention is to propose such a data transmission technique improving the use of the available resources, and which is particularly suitable for the transmission of data at low or high speeds (for example of several Mbits / s ).

  The invention also aims to improve the use of an allocated frequency band while maintaining reliable and efficient data transmission.

  An additional objective of the invention is to provide such a technique allowing the reception of data (in particular at high speed), even under unfavorable reception conditions (high travel speed and multiple paths in particular).

  Yet another objective of the invention is to provide such a technique, which allows an improved allocation of the transmission resource, between one or more mobiles, at a given time. In particular, an objective of the invention is to allow the sharing of the high speed transmission resource.

  In addition, the invention aims to improve the robustness vis-à-vis the radio-mobile propagation conditions and in particular an improvement in data transmission performance and / or the mobility of communication terminals.

  To this end, the invention provides a method of transmitting radio data between a transmitter and a receiver, using at least one pilot signal with single carrier and at least one first signal for transmitting data transmitted according to carrier modulation. multiple, remarkable in that it comprises a step of estimating the response of the transmission channel of the first data transmission signal transmitted according to a multi-carrier modulation, the estimation taking into account the pilot single-carrier signal. A pilot signal is in particular a predetermined signal whose temporal, frequency and / or amplitude characteristics during transmission are known to the receiver, which makes it possible to estimate a transmission channel.

  According to a particular characteristic, the method is remarkable in that the frequency band used for the pilot signal on a transmission channel 25 includes the frequency band used for the first transmission signal.

  Thus, the entire frequency band used for the first transmission signal based on multi-carrier modulation, making it possible, in particular, to obtain a fine estimate of the channel over the entire band, is taken into account for equalization. Indeed, if the frequency band used for said pilot signal on a transmission channel does not completely encompass the frequency band used for the first transmission signal, an extrapolation is necessary to obtain information on the entire band corresponding to the first multicarrier transmission signal, this extrapolation giving less reliable results than an estimate over the entire band.

  According to a particular characteristic, the method is remarkable in that it comprises an equalization of the data transmitted according to a multi-carrier modulation, the equalization taking into account the estimation of the response of the transmission channel of the first transmission signal.

  Thus, the implementation of the equalization of the first signal does not require the use of pilots inserted in the signal with multiple carriers which makes it possible to save bandwidth.

  According to a particular characteristic, the method is remarkable in that the estimation takes into account at least one autocorrelation performed on the pilot signal.

  According to a particular characteristic, the method is remarkable in that each of the autocorrelations is associated with a delay corresponding to a path on the transmission channel.

  According to a particular characteristic, the method is remarkable in that the autocorrelations are performed for each of the paths between the transmitter and the receiver on the transmission channel and corresponding to delays less than a determined maximum terminal.

  Thus, the entire transmission channel can be finely estimated and an echo determination is not necessary.

  According to a particular characteristic, the method is remarkable in that it comprises a step of selecting paths between the transmitter and the receiver on the transmission channel and in that the autocorrelations are carried out for each of the paths selected during the selection step.

  Thus, the implementation of the method is simplified, which in particular makes it possible to save material resources (electronic components, silicon surface or CPU time) and / or energy (in particular supplied by battery with limited autonomy in the mobile terminals).

  A path selection based on the determination of echoes is moreover generally implemented in a single-carrier mobile system. Thus, this step does not consume additional resources.

  According to a particular characteristic, the method is remarkable in that it comprises a step of determining a frequency response taking into account the autocorrelations.

  Thus, both time and frequency channel estimation can be provided, which is particularly well suited to equalization of data transmitted over a multi-carrier signal.

  According to a particular characteristic, the method is remarkable in that it comprises a Fourier transform step providing at least one coefficient associated with each subcarrier of a symbol of the first signal for the transmission of data transmitted according to a multi-carrier modulation. .

  According to a particular characteristic, the method is remarkable in that the pilot signal is of the spread spectrum type.

  Thus, the invention allows compatibility with spread spectrum systems (in particular of the UMTS type), elements dedicated to the processing of 20 spread spectrum signals which can advantageously be used for equalization of data transmitted on a carrier channel. multiple.

  In addition, the implementation of the data transmission method is simplified since it is not necessary to manage (insertion of pilots, channel estimation, etc.) two independent transmission channels: only the single channel 25 carrier includes pilots.

  According to a particular characteristic, the method is remarkable in that the first data transmission signal transmitted according to a multi-carrier modulation does not include a pilot symbol.

  Thus, the method allows an economy of bandwidth and, in particular, an improvement in the overall transmission rate (or data rate of useful data).

  It also allows an improvement in the energy allocated to information symbols for a given maximum transmission power.

  In addition, the envelope fluctuation of the multi-carrier signal is reduced.

  According to a particular characteristic, the method is remarkable in that the first transmission signal is of the OFDM type.

  According to a particular characteristic, the method is remarkable in that the first transmission signal is of the IOTA type.

  The use of the method when the multi-carrier signal is of type IOTA is particularly advantageous since in this case, a so-called first ring processing aiming at eliminating pilot interference in the multi-carrier signal IOTA is not used. implemented here. Thus, the invention makes it possible to take advantage of the advantages of IOTA modulation (in particular the absence of a guard interval thus making it possible to increase the data transmission rate) while having a simple implementation.

  It is recalled that the modulation of the IOTA type (from the English "Isotropic Orthogonal Transform Algorithm") is defined in patent FR-95 05455 filed on May 2, 1995. The IOTA modulation is notably based on a multicarrier signal intended to be transmitted to a digital receiver, corresponding to the frequency multiplexing of several elementary sub-carriers each corresponding to a series of symbols, two consecutive symbols being separated by a symbol time t0, the spacing v0 between two neighboring sub-carriers being equal to the half of the inverse of the symbol time To, and each subcarrier undergoing shaping filtering of its spectrum having a bandwidth strictly greater than twice the spacing between subcarriers v0, the filtering being chosen so that each symbol is strongly concentrated in the time domain and in the frequency domain.

  According to a particular characteristic, the method is remarkable in that, in addition, the transmitter transmits a second data transmission signal on a single carrier channel to the receiver, the signal being equalized from a channel estimate determined based on the pilot signal.

  Thus, a single carrier channel can be used for the transmission of information and / or signaling data, the channel estimation from the pilot single carrier signal making it possible both to equalize the data transmitted on a single carrier signal and data transmitted on a multi-carrier signal. The invention therefore allows a wide variety of applications, in particular data transmission, for example, at low speed on a single carrier channel and at high speed on a multi-carrier channel, as well as compatibility with existing standards. radio communication (notably the UMTS standard and more generally the mobile network standards based on the use of single carrier channels).

  According to a particular characteristic, the method is remarkable in that the transmitter and the receiver belong to a mobile communication network.

  Thus, the method is particularly well suited to the conditions of transmission to mobile terminals and / or in a mobile environment. It allows in particular to take into account an unstable channel with multiple echoes.

  It is also particularly suitable for the use of communication between a base station and a terminal. In particular, an advantageous implementation comprises two downlink channels between a base station and a terminal, one of the channels being of the single carrier with pilot type and the other with multiple unmanned carrier.

  According to a particular characteristic, the method is remarkable in that the transmitter belongs to a base station of the mobile communication network and the receiver belongs to a terminal, the base station transmitting the pilot signal and the first transmission signal of data in multi-carrier, high-speed modulation when necessary.

  Thus, the method is particularly well suited to a transmission between a base station and a mobile network terminal and more precisely, but not exclusively, to a high speed transmission (in particular for data transmissions at a speed greater than 1 Mbit / s) on a downlink channel between the base station and the terminal using multicarrier modulation. In this context, a bidirectional link can be provided between the base station and the terminal: - the base station transmitting data on a multicarrier channel and a pilot signal and possibly signaling and / or information data to low speed on a single carrier channel, - the terminal transmitting signaling data and / or information to the base station on a single carrier channel.

  The invention also relates to a device for receiving radio data using at least one pilot signal with single carrier and at least one signal for transmitting data transmitted according to a multicarrier modulation, remarkable in that the device comprises means estimating the response of the transmission channel of the data transmission signal transmitted according to a multi-carrier modulation, the estimation taking account of the pilot single-carrier signal.

  The invention further relates to a radio data transmission device implementing at least one single carrier pilot signal and at least one data transmission signal transmitted according to a multi-carrier modulation, remarkable in that the device comprises means for modulating the unmanned transmission signal, the pilot signal being intended to allow an estimation of the response of the transmission channel of the transmission signal of data transmitted according to a multicarrier modulation, the estimation taking account of the pilot signal to simple carrier.

  Furthermore, the invention relates to a radio data transmission signal comprising at least one single-carrier pilot channel and a multi-carrier data transmission channel, remarkable in that the multi-carrier transmission channel is unmanned, the single-carrier pilot channel being intended to allow an estimation of the response of the transmission channel of data transmitted according to a multi-carrier modulation, the estimation taking account of the single-carrier pilot signal.

  The invention also relates to a cellular telecommunication system of the type implementing at least one single-carrier pilot channel and one multi-carrier data transmission channel remarkable in that the multi-carrier transmission channel is unmanned, the channel single-carrier pilot being intended to allow an estimate of the response of the transmission channel of data transmitted according to a multi-carrier modulation, the estimate taking account of the single-carrier pilot signal.

  The advantages of the devices, the data transmission signal and the system are the same as those of the data transmission method, they are not described in more detail.

  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 shows an example of an OFDM signal known per se; FIG. 2 shows a block diagram of equalization of the OFDM signal according to FIG. 1; - Figure 3 illustrates a mobile communication network according to the invention according to a particular embodiment; - Figure 4 describes a transceiver module associated with a fixed station implemented in the network of Figure 3; - Figure 5 describes a transceiver module associated with a terminal implemented in the network of Figure 3; FIG. 6 illustrates equalization means implemented in the transmitter / receiver of FIG. 5; - Figure 7 illustrates equalization means according to a variant of the invention; and - Figure 8 shows a communication protocol in the mobile communication network of Figure 3.

  The technique known per se and illustrated with reference to FIG. 1 consisting in demodulating and separately equalizing a single carrier channel and a multicarrier channel has several drawbacks.

  In particular, the overall transmission rate (or bit rate of useful data) is not optimized.

  This technique also results in a reduction of the energy allocated to the information symbols for a given maximum transmission power.

  In addition, it is relatively complex to implement both in transmission and in reception since it is necessary in particular to manage two independent channels.

  In addition, in the context of OFDM modulation, an additional envelope fluctuation is generated due in particular to the fact that the energy of the pilot symbols is higher than that of the other OFDM symbols and that the pilot symbols are distributed by a discontinuously in the time / frequency plane, which generates an increase in energy of the OFDM symbols containing pilot symbols.

  Another disadvantage of the prior art is that, in the case of the use of certain other types of modulation (in particular OFDMIOQAM), additional processing is required. Indeed, in this case, the channel introduces interference between the sub-carriers and an estimate of the channel cannot be obtained directly.

  On the other hand, the general principle of the invention is based on the transmission of a single carrier pilot signal (for example of the CPICH type as used in the context of UMTS) associated with the transmission of data on a channel multiple carriers (for example OFDM type). In order to equalize the channel with 30 multiple carriers, the channel estimate provided by the pilot signal is used.

  Preferably, the pilot signal undergoes an auto-correlation over a length corresponding to that of an OFDM symbol and then this estimate is transposed in the frequency domain by applying to it, for example, a Fourier transform (discrete or fast) in order to feed equalization of the demodulated OFDM signal.

  According to a variant of the invention, the pilot signal is processed in a simplified manner by considering only the most relevant delays.

  There is presented, in relation to FIG. 3, a block diagram of a mobile radio network implementing the invention.

  The network is for example a network partially compatible with the UMTS standard ("Universal Mobile Telecommunication System") defined by the 3GPP committee.

  The network includes a cell 30 which is managed by a base station 31 (BS).

  The cell 30 itself comprises the base station 31 and terminals (UE) 32, 33 and 34.

  The terminals 32, 33 and 34 can exchange data (for an application type layer) and / or signaling with the base station 31 via uplink and downlink channels. Thus, the terminal 32 and the base station 31 20 are connected in communication by: - a downlink channel 310 with single carrier allowing the transport of signaling and / or control data of the communication with the terminal 32 as well as the transmission of 'a pilot signal; - an uplink channel 311 with single carrier also allowing the transport of signaling and / or communication control data; and a downlink channel 312 with multiple unmanned carriers, for example of the OFDM type, allowing high speed data transfer from the base station 31 to the terminal 32.

  By default, the terminals are in standby mode, that is to say in a mode where they are not in communication mode but present and available for communication. In a first mode of communication, these terminals are in particular listening to signals transmitted by the base station 31 on a downlink channel using a simple carrier modulation. These signals are transmitted on: - common transport channels corresponding to the services offered to the upper layers of the communication protocol, in particular on BCH (or "broadcast channel") and PCH (or "mobile search channel" from English "Paging CHannel"); and - common transport channels corresponding to the physical layer of the communication protocol, in particular on CPICH channels (or "pilot common channel" from the English "Common PIlot CHannel").

  The single carrier channels used by third generation (or 3G) mobile networks are well known to those skilled in the art of mobile networks and are in particular specified in the standard "3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical Channels and mapping of transport channels onto physical channels (FDD) release 1999 "of reference 3GPP TS25.211 and distributed by the publications office of 3GPP. These channels will therefore not be described more fully.

  FIG. 4 illustrates a transceiver module 40 belonging to the base station 31 implemented in the network 30.

  The module 40 comprises in particular: - a single or multiple antenna 43; - a duplexer 47; - A reception chain 41; and - a broadcast channel 42.

  The antenna 43 is connected to each of the reception 41 and transmission 42 chains via the duplexer 47.

  The reception chain 41 is suitable for processing the uplink channel 311 with single carrier and provides on an output 44 decoded data received by the antenna 43. This chain 41 whose implementation is well known to those skilled in the art does not will not be described further.

  The transmission chain 42 is suitable for transmitting: a pilot signal 4211 as well as signaling and / or control data for a communication on the downlink channel 310 with single carrier; and - data 46 at low or high speed on the downlink channel with 10 multiple carriers 312.

  The transmission chain 42 comprises: - a modulator 429 adapted to generate a CPICH pilot signal 4211 from a reference code 45; a modulator 4210 adapted to modulate data 46 according to an OFDM multi-carrier modulation; - a signal processing processor (or DSP from the English "Digital Signal Processor") 428; - a digital to analog converter 426, 427 on each of the channels I (channel in phase) and Q (channel in quadrature of phase); A modulator 424 in intermediate frequency controlled by a synthesizer 427; - a bandpass filter 423; a mixer 421 and an agile synthesizer 422 making it possible to transpose the signals at intermediate frequency into the transmission band; and - a power amplifier 420. The DSP 428 is associated with a "hardware" accelerator for the combination of: - single carrier signals to be transmitted (including the pilot channel 30 CPICH 4211 and possibly signals carrying data from control, signaling and / or useful information to be transmitted on a single carrier channel); and multi-carrier signals 4212 of the OFDM type representative of the useful information 46 to be transmitted.

  Unlike the frame illustrated with reference to FIG. 1, the OFDM channel here carries only useful information data and does not include subcarriers associated with pilots.

  Furthermore, preferably, the pilot channel 4211 and the multi-carrier signals 4212 are combined synchronously (the OFDM symbols coinciding with the CPICH code symbols). Alternatively, the pilot channel 4211 and the multi-carrier signals 4212 are combined asynchronously.

  FIG. 5 illustrates a transceiver module 50 belonging to one of the terminals 32 to 34 implemented in the network 30. The module 50 is adapted to communicate with the module 40 illustrated with reference to FIG. 4.

  The module 50 comprises in particular: - a single or multiple antenna 53; - a duplexer 57; - A reception chain 51; and 20 - a broadcast channel 52.

  The antenna 53 is connected to each of the reception 51 and transmission 52 chains via the duplexer 57.

  The transmission chain 52 is adapted to process the uplink channel 311 with single carrier. It provides a single carrier modulated signal to the antenna 53 for transmission on the uplink channel 311 from the data presented on an input 54. This chain 52, the implementation of which is well known to those skilled in the art. will not be described further.

  The reception chain 51 is adapted to receive: a pilot signal as well as signaling and / or control data for a communication on the downlink channel 310 with single carrier; and - high-speed data on the downlink multicarrier channel 312.

  The reception chain 51 comprises: - a low noise amplifier 510 - a mixer 511 and an agile synthesizer 512 making it possible to transpose the signal received in the transmission band into a signal 10 at intermediate frequency; a bandpass filter 423 centered around the intermediate frequency and a bandwidth corresponding to the width used for the transmission of the signal; - a baseband I / Q converter 514 controlled by a synthesizer 515; - a digital analog converter 516, 517 on each of the channels I (channel in phase) and Q (channel in quadrature of phase); - a signal processing processor (or DSP) 518 making it possible to separate single-carrier signals and signals with 20 multiple carriers; and - equalization means 519 adapted to demodulate and equalize the single-carrier and multi-carrier signals supplied by the DSP 518.

  FIG. 6 illustrates the equalization means 519 which comprise: a CPICH input accepting baseband signals modulated in single carrier and supplied by the DSP 518; - an OFDM input accepting baseband signals modulated in multiple carriers (OFDM type) and supplied by the DSP 518.

  The CPICH input notably includes a CPICH type signal making it possible to estimate the transmission channel.

  The equalization means 519 further comprise: - estimation means 60 adapted to estimate a channel from a pilot signal with single carrier; - OFDM demodulation means 64; and an OFDM equalization unit 66. The means 60 accept as input a CPICH type signal in single carrier and comprises in particular: - auto-correlation means 600; and Fourier transform means 602. The autocorrelation means 600 perform an estimation of the channel as a function of the signal CPICH and more precisely an autocorrelation of the signal CPICH for each of the delays zl to zn, rl corresponding to the direct path, r2 to a second path and mrn to the longest path (each of the paths selected corresponding to a direct path or to a relevant echo). n autocorrelations are thus calculated.

  In general, rk is equal to the product of a factor k by the chip period Tc of the CPICH code (equal to 1/3840000 s or approximately 0.26 gts within the framework of the UMTS standard), k being preferably a integer or a multiple of 0.5.

  The coefficient of the channel corresponding to a delay rk is obtained according to the following autocorrelation equation: h (rk) = h (kTc) = TCPICH (r) .CPICH (tkTc) dt If we consider a length of CDMA code equal to 256, the signal being preferably digitally processed, the sampled version of the previous autocorrelation equation 25 is written: h (k) - 256, CPICH (i) .CPICH (n - i) 256 i = o According to a mode preferred of the invention, the OFDM symbols are transmitted synchronously with the CPICH symbols. In this case, the autocorrelation function is implemented on a window corresponding to a CPICH code symbol (or equivalent in the case of synchronization between the different signals, to an OFDM symbol).

  According to another embodiment of the invention, the OFDM symbols and the CPCIHC code symbols are transmitted asynchronously. In this case, several variants can be implemented: - according to a first variant, autocorrelations of the CPICH symbol are calculated closest in time to the OFDM symbol considered (which allows great simplicity of implementation, this autocorrelation generally being 10 necessary for other use within the framework of a network partly CDMA); - according to a second variant, autocorrelations are calculated on CPICH symbols which at least partially overlap with the OFDM symbol considered and an interpolation is carried out of the 15 autocorrelations obtained in order to supply an operation of frequency estimation of the channel; - according to a third variant (which allows the most reliable channel estimation for a considered OFDM symbol), the autocorrelations are calculated on the end of a first CPICH code and the start of a second CPICH code, the autocorrelations retained coinciding synchronously with the OFDM symbol considered.

  In all cases, the duration of the proposed correlations is the same as that of the OFDM symbol considered.

  The autocorrelation means 600 transmit to the means 602, on n outputs 601, the n results of autocorrelations performed, each of the n results being associated with one of the outputs 601.

  Then, the means 602 carry out a Fourier transform of length n over all of the n autocorrelation results, thus making it possible to obtain the corresponding frequency response. n is chosen to be greater than or equal to the number of subcarriers used in the OFDM channel. Thus, if each sub-carrier of the OFDM channel uses a band of 3.75 kHz, and if each OFDM symbol is modulated on 1024 sub-carriers, a useful band of 3.84 MHz is obtained. In this case, the means 602 implement a transform of 5 fast Fourrier (or PFT from the English "Fast Fourrier Transform") of length 1024 which makes it possible to obtain 1024 channel coefficients on the considered band of 3.84 MHz .

  As a variant, if the number of OFDM subcarriers is not a power of 2, the means 602 preferentially implement a discrete Fourrier transform (or DFT from the English "Discrete Fourrier Transform") of suitable length. Thus, if each sub-carrier of the OFDM channel has a bandwidth equal to 3.75 kHz, and if each OFDM symbol is modulated on 600 subcarriers, a useful band of the order of 2 MHz is obtained and the means 602 put implements a DFT of length 600 providing 600 coefficients.

  This gives an estimate of the frequency channel which can be used for OFDM equalization. According to a preferred embodiment, the correlation of the CPICH signal is made over the duration of a corresponding OFDM symbol. A new correlation (and therefore a new channel estimate) is thus made for each OFDM symbol. According to a variant, in particular when the receiver 20 considers that the channel is sufficiently stable, a single estimate can be considered to be valid for several OFDM symbols (which in particular makes it possible to save resources (CPU time, batteries, etc.) of the receiving terminal).

  In parallel, the means 64 demodulate the input OFDM signal and 25 supply demodulated OFDM symbols to the OFDM equalization unit 66.

  Receiving in parallel the estimate of the channel and of the demodulated OFDM symbols communicated respectively by the means 602 and by the means 64, the equalization unit equalizes the OFDM symbols as a function of the estimate of the channel and provide the data d information corresponding to the 30 OFDM symbols processed. The equalization can be carried out according to different methods taking into account a channel estimation. A first relatively simple equalization method comprises a multiplication of the OFDM symbols received by the conjugate of the channel (which allows phase correction).

  According to another equalization method, the OFDM symbols are divided by the 5 channel. According to yet another method, the equalization of the data originating from the OFDM symbols is of the MMSE type (from the English "Minimum Mean Square Error" or "Error with minimum variance").

  FIG. 7 illustrates equalization means 79 according to a variant of the invention making it possible to simplify their implementation.

  The essential difference between the equalization means 79 and 519 (illustrated with reference to FIG. 6) is based on the determination of the paths associated with an autocorrelation determination. The elements common to the equalization means 79 and 519 bear the same references and will not be described further.

  In fact, according to this variant, the receiver implements an echo detection and an estimation of r delays r] to rr corresponding (for example from a primary synchronization channel ("Primary SCH" according to the UMTS standard). )).

  The equalization means 79 comprise: - estimation means 70 adapted to estimate a channel from a pilot signal with single carrier; - OFDM demodulation means 64; and an OFDM equalization unit 66. The estimation means 70 accept as input a signal of the CPICH type in single carrier, as well as a list of the r delays rI to rr to be taken into account and comprises in particular: - auto-correlation means 700; and - Fourier transform means 602. The autocorrelation means 700 carry out an estimation of the channel as a function of the signal CPICH and more precisely an autocorrelation of the signal CPICH for each of the delays T1 to rr to be taken into account (according to a method or variants similar to those implemented in the autocorrelation means 600).

  The auto-correlation means 700 transmit to the Fourier transform means 602, on n outputs 601: - the r results of autocorrelations carried out corresponding to the delays rI to vr; and - (n-r) zero autocorrelation values corresponding to the (n-r) delays not retained.

  each of the n values transmitted being associated with one of the outputs 601.

  According to a variant, the auto-correlation means 700 carry out an estimation of the channel as a function of the CPICH signal and more precisely an autocorrelation of the CPICH signal for each of the delays vi to mz equal or close to the delays ri to rr. According to this variant, a delay is close to a delay, i, if it differs by at most P chip periods Tc from the delay Ti considered, P preferably being equal to 2 (but being able to take other values, for example 1 or 3).

  Thus, if the delay i corresponds to an identified echo, an autocorrelation will preferably be carried out by the means 700 for the delays Ti-2Tc, zTc, vi, vi + Tc and vi + 2Tc. The larger the value of P, the finer the estimate.

  On the other hand, the smaller the value of P, the simpler the implementation of the autocorrelation means 700.

  According to other variants, the delays taken into account and obtained, for example, by interpolation of the signal CPICH are non-integer multiples of the chip time Tc.

  FIG. 8 illustrates a communication protocol between the base station 31 and the terminal 32 during a communication using the channels 310 to 312. This protocol comprises two phases: a phase 80 of communication establishment essentially comprising signaling data exchanges and a communication phase 81 implementing high speed data transmission using an OFDM channel and a CPCIH channel 30 for estimating the transmission channel.

  During the phase 80 of establishing a communication, the base station 31 transmits a signal 800 on the downlink SCH intended for the terminals present in the cell 30 and in particular for the terminal 32. Thus, the terminal 32 is synchronized on the SCH channel of the base station 31.

  It is noted that this signal SCH is transmitted regularly by the base station 31 and that as soon as the synchronization of the terminal 32 degrades beyond a certain predetermined threshold, it is again synchronized with the base station 31.

  The base station 31 also transmits a signal 801 on the BCH channel. This downlink signal indicates to terminal 32 which PCH channel it should listen to. Thus, after receiving this signal, the terminal 32 listens to the PCH channel indicated by the signal 802.

  Then, the base station 31 transmits a signal to the terminal 32 on the PCH channel indicated by the signal 801, this signal making it possible to detect an incoming call.

  Then, assuming that the terminal 32 wishes to initiate a communication, it transmits a signal 803 on the RACH channel (from the English "Random Access CHannel" which is a common channel corresponding to a high layer service of access to the channel) , this signal 803 indicating to the base station 31 that the terminal 32 requests the establishment of a communication.

  Then, the base station 31 transmits a communication channel allocation signal 804 on the FACH channel (from the English "Fast Access CHannel" which is also a common channel corresponding to a high layer service) according to the first mode communication (single carrier).

  The signals corresponding to the first mode of communication are compatible with the first two layers (physical and link) defined by the UMTS standard. According to the invention, at level 3, the base station indicates where, when and how to listen to the OFDM.

  Then, the terminal 32 listens to the pilot channel 805 CPICH which, according to the invention, makes it possible in particular to estimate the transmission channel. The pilot channel 30 805 CPICH is transmitted continuously by the base station 31.

  Then, communication is established between the terminal 32 and the base station 31.

  The mobile sends a request via the uplink channel PRACH 806 (physical channel corresponding to the RACH channel) while listening to the 5 channel FACH 804, for the network response, as provided by the current UMTS - FDD standard. If the network decides that the information to be transmitted to the mobile is large, in particular if the speed offered by the FACH channel is not enough, the base station 31 indicates to the terminal 32 via the FACH channel 804 corresponding to the first mode to listen to the associated OFDM channel 10 for data transmission.

  Thus, according to the invention, the use of a common channel, called OFDM channel, using OFDM modulation is coupled with the common RACH / FACH channels (that is to say the terminal transmits a RACH request and the station base responds with a FACH frame which indicates to the terminal 32 that the data transmission between the base station 31 and the terminal 32 is carried out according to a second mode of communication with multiple carriers) without changing the physical characteristics of transmission of the RACH ( up channel) and FACH (down channel).

  The FACH channel carries the signaling information allowing the mobile to correctly listen to the OFDM channel. The FACH indicates when (i.e. when the block intended for the terminal starts and ends), o (in the frequency band, the transmission does not necessarily use all the available frequency band) and how (format of coding, interleaving, ...) listen to the OFDM channel to receive the data block concerned. By default, the base station uses OFDM modulation with predetermined characteristics (symbol times, spacings between the subcarriers and distribution of the reference symbols or pilot symbols). According to a variant, these characteristics will be optimized dynamically by the base station and adapted as a function of the characteristics of the propagation channel.

  Thus, the communication between the base station 31 and the terminal 32 switches to a second communication mode (phase 81) which uses unmanned multi-carrier modulation, the transmission of a single carrier CPICH pilot channel being maintained. Thus, the base station 31 transmits data on the common OFDM channel by means of successive signals 810, 811 and following, the pilot signal CPICH with single carrier being transmitted by the base station 31 continuously allowing the terminal 32 to correctly estimate the transmission channel.

  Level 2 acknowledgments can then be sent by the terminal 10 32 on the RAC channel.

  At the end of the communication, the terminal 32 and / or the base station 31 indicate via the FACH channel that the communication ends.

  Of course, the invention is not limited to the embodiments mentioned above.

  In particular, the person skilled in the art can make any variant in the definition of single carrier or multiple carrier modulations used. Single carrier modulation may in particular be of the phase modulation type (for example of the PSK (or "Phase Shift Keying"), GMSK (or "Gaussian Minimum Shift Keying")) or of amplitude (in particular of the FSK 20 type (or Frequency Shift Keying), QAM (or "Quadrature Amplitude Modulation")) Likewise, a person skilled in the art can make any variant in the type of multi-carrier modulation used. Thus, the modulation could for example be of the OFDM type as described in particular in patent FR-98 04883 filed on April 10, 1998 by the company Wavecom or a modulation of IOTA 25 type defined in patent FR-95 05455 filed on May 2 1995 and included here by reference.

  The invention is not limited to UMTS or 3G networks, but extends to communications between a fixed or mobile transmitter and fixed or mobile receiver, (corresponding for example to two terminals, to a network infrastructure station and a terminal or two network infrastructure stations) especially when high spectral efficiency and / or bandwidth savings are desired. Thus, the possible supports of the invention are, for example, digital terrestrial broadcasting systems, whether they are images, sounds and / or data or digital communication systems 5 to high speed mobiles (in mobile networks, local radio networks or for transmissions to or from satellites) or even for submarine transmissions using an acoustic transmission channel.

  The applications of the invention are varied and in particular allow broadband services of the internet type (in the case of the application of the invention to 10 UMTS, the low speed of the RACH channel, although much stronger than in GSM coupled with the very high speed of the OFDM channel, corresponds well to the needs of such services).

  In addition to estimating the channel, the invention makes it possible to use the single-carrier channel to carry out processing specific to the OFDM channel, in particular: initial synchronization and monitoring of synchronization in time or in frequency, measurement of the quality the channel and the modulation adaptation, ...

Claims (20)

  1. Method for transmitting radio data between a transmitter (40, 31) and a receiver (50, 32, 34, 33), using at least one single carrier pilot signal (805, CPICH) and at least one first signal (810, 811) for transmitting data transmitted according to a multicarrier modulation, characterized in that said method comprises a step of estimating (60) the response of the transmission channel of said first signal for transmitting data transmitted according to multi-carrier modulation, said estimate taking into account said single carrier pilot signal.   2. Method according to claim 1, characterized in that the frequency band used for said pilot signal on a transmission channel includes the frequency band used for said first transmission signal.   3. Method according to any one of claims 1 and 2, characterized in that it comprises an equalization (66) of said data transmitted according to a multi-carrier modulation, said equalization taking into account said estimation of the response of the transmission of said first transmission signal.   4. Method according to any one of claims 1 to 3, characterized in that said estimation takes into account at least one autocorrelation (600) carried out on said pilot signal.   5. Method according to claim 4, characterized in that each of said autocorrelations is associated with a delay (X1, x2, ..) corresponding to a path on said transmission channel.   6. Method according to claim 5, characterized in that said autocorrelations are performed for each of the paths between said transmitter and said receiver on said transmission channel and corresponding to delays less than a determined maximum terminal (tn).   7. Method according to claim 5, characterized in that it comprises a step of selecting paths (X1, .. tr) between said transmitter and said receiver on said transmission channel and in that said autocorrelations are performed for each of the routes selected during said selection step.   8. Method according to any one of claims 4 to 7, characterized in that it comprises a step of determining a frequency response taking into account said autocorrelations.   9. Method according to claim 8, characterized in that it comprises a Fourrier transform step (602) providing at least one coefficient associated with each subcarrier of a symbol of said first data transmission signal transmitted according to a modulation. with multiple carriers.   10. Method according to any one of claims 1 to 9, characterized in that said pilot signal is of the spread spectrum type (CDMA).   11. Method according to any one of claims 1 to 10, characterized in that said first data transmission signal transmitted according to a multicarrier modulation does not include a pilot symbol.   12. Method according to any one of claims 1 to 11, characterized in that said first transmission signal is of the OFDM type.   13. Method according to any one of claims 1 to 11, characterized in that said first transmission signal is of the IOTA type.   14. Method according to any one of claims 1 to 13, characterized in that, in addition, said transmitter transmits a second data transmission signal on a single carrier channel to said receiver, said signal being equalized from a channel estimate determined as a function of said pilot signal.   15. Method according to any one of claims 1 to 14, characterized in that said transmitter and said receiver belong to a mobile communication network.   16. The method of claim 15, characterized in that said transmitter belongs to a base station of said mobile communication network and said receiver belongs to a terminal, said base station transmitting said pilot signal and said first data transmission signal according to multi-carrier, high-speed modulation when necessary.   17. Device (50, 32, 33, 34) for receiving radio data using at least one single carrier pilot signal (805) and at least one transmission signal (810, 811) of data transmitted according to a modulation multi-carrier, characterized in that said device comprises means for estimating (60) the response of the transmission channel of said data transmission signal transmitted according to a multi-carrier modulation, said estimation taking account of said single pilot signal carrier.   18. Device (42, 31) for transmitting radio data using at least one single-carrier pilot signal (805) and at least one transmission signal (810; 811) of data transmitted according to a multi-carrier modulation, characterized in that said device comprises means (42) for modulating said unmanned transmission signal, said pilot signal being intended to allow an estimation of the response of the transmission channel of said data transmission signal transmitted according to a multi-carrier modulation , said estimate taking into account said single carrier pilot signal.   19. Radio data transmission signal comprising at least one single-carrier pilot channel (311) and one multi-carrier data transmission channel (312), characterized in that said multi-carrier transmission channel is unmanned, said single carrier pilot channel being intended to allow an estimation (60) of the response of the data transmission channel 25 transmitted according to a multicarrier modulation, said estimation taking into account said single carrier pilot signal.   20. Cellular telecommunication system of the type using at least one single carrier pilot channel (311) and one multi-carrier data transmission channel (312), characterized in that said multi-carrier transmission channel is without pilot, said single-carrier pilot channel being intended to allow an estimation (60) of the response of the transmission channel of data transmitted according to a multi-carrier modulation, said estimation taking account of said single-carrier pilot signal.