Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2602—Signal structure
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/005—Control of transmission; Equalising
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/0202—Channel estimation
  • H04L25/0224—Channel estimation using sounding signals
  • H04L25/0228—Channel estimation using sounding signals with direct estimation from sounding signals
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
  • H04L27/24—Half-wave signalling systems
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2602—Signal structure
  • H04L27/261—Details of reference signals
  • H04L27/2613—Structure of the reference signals
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2626—Arrangements specific to the transmitter only
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2647—Arrangements specific to the receiver only

Definitions

• 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.
• 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.
• the total throughput offered to users of radiotelephony equipment is limited in particular by the width of the available frequency band.
• we have traditionally used 20 in particular, a densification of cells in a given territory.
• a drawback 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.
• the data rate although high, is not optimal.
• the more cells, and therefore the fixed stations the more complex the management.
• the transmitted signals are generally subject to echoes resulting in the presence of multiple paths with different amplitudes and delays. The combination of these paths can lead to fading in the receiver, which can seriously disturb reception.
• 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 countering 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).
• 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 Telecommunications System” or "Universal Mobile Telecommunications System”).
• the third generation systems under development are based, like the existing radiotelephony systems, on a symmetrical structure.
• 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).
• FDD from the English “Frequency Division Duplex” or “duplex par frequency distribution”
• TDD link from the English “Time Division Duplex” or “time division duplex”
• 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.
• HSDPA broadband downlink
• This link is based on packet data transmission using: - or a single carrier modulation (also called single carrier) of spread spectrum type (CDMA from English "Code Division Multiple Access” or “Multiple Access to Distribution by Code” in French); - either a modulation with multiple carriers (or sub-carriers)
• a CDMA channel for the "basic" symmetrical link
• an OFDM channel for an additional data transmission link
• 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 sub-bandwidths so that a channel subjected to multiple paths, and therefore frequency selective becomes not selective in each sub-band. The channel then becomes multiplicative on each sub-band, which facilitates equalization and effectively combats the selectivity of the propagation channel.
• Figure 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.
• the symbol 1641 comprises a first subcarrier 111 associated with the frequency FI, a second subcarrier associated with a frequency F2 and so on up to a 64 th subcarrier associated with an F64 frequency.
• Certain frequencies are reserved for transmitting a pilot while others are reserved for the transport of data (the corresponding subcarriers being represented in the form of empty ellipses) .
• the subcarriers 111, 112, l lp associated with the frequency FI allow data transport 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 loaded convert the received signal into a succession of samples which will be processed later.
• the OFDM signal 20 comprises a sum of several symbols each modulating a subcarrier over a duration corresponding to an OFDM symbol.
• the subcarriers being 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 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 multi-carrier modulation. 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.
• the transmission channel comprising L paths can be modeled in the form of the following transfer function h (t):
• - a) represents a coefficient of the channel along the f me path; ⁇ , an associated delay f me path; t time; and - ⁇ the distribution of Dirac.
• the invention according to its various aspects aims in particular to overcome these drawbacks of the prior art.
• an objective of the invention is to provide a method and devices for transmitting data through a radio channel (and therefore liable to be 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 available resources, and which is particularly suitable for transmitting 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.
• an objective of the invention is to allow the sharing of the high speed transmission resource.
• 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.
• the invention provides a method of transmitting radio data between a transmitter and a receiver, implementing at least one pilot signal with single carrier and at least one first signal for transmitting data transmitted according to a modulation with multiple carriers , 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 account of the single-carrier pilot signal, a part at less of the pilot signal coinciding in time with at least part of the first 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.
• At least part of said pilot signal coinciding temporally with at least part of the first signal means, here, that all or part of the pilot signal coincides temporally with all or part of the first signal According to a particular characteristic, the method is remarkable in that the part of the pilot signal, taken into account by the estimation coincides integrally with at least a part of the first signal.
• the method is remarkable in that the pilot signal and the first signal are asynchronous.
• the implementation of the method is simple, its constraints being less strong. According to a particular characteristic, the method is remarkable in that the pilot signal and the first signal are synchronous.
• the estimation of the response of the channel of the first signal is direct and there is no need for extrapolation of the rhythm of the first signal and of the pilot signal.
• the method is remarkable in that the frequency band used for the pilot signal on a transmission channel includes the frequency band used for the first transmission signal.
• 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.
• 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 corresponding band at the first multicarrier transmission signal, this extrapolation giving less reliable results than an estimate over the entire band.
• 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.
• 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.
• the method is remarkable in that the estimation takes into account at least one autocorrelation performed on the pilot signal.
• 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.
• the entire transmission channel can be finely estimated and an echo determination is not necessary.
• 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.
• 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 case mobile terminals).
• a selection of journeys based on the determination of echoes is moreover generally implemented in a mobile system with a single carrier. Thus, this step does not consume additional resources.
• the method is remarkable in that it comprises a step of determining a frequency response taking into account the autocorrelations.
• a channel estimation both time and frequency can be provided, which is particularly well suited to an equalization of data transmitted on a multi-carrier signal.
• 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.
• the method is remarkable in that the pilot signal is of the spread spectrum type.
• the invention allows compatibility with spread spectrum systems (in particular of the UMTS type), elements dedicated to the processing of spread spectrum signals which can advantageously be used for the equalization of data transmitted on a multi-carrier channel. .
• the method is remarkable in that the first data transmission signal transmitted according to a multi-carrier modulation does not include a pilot symbol.
• the method allows an economy of bandwidth and, in particular, an improvement in the overall transmission rate (or useful data rate).
• the method is remarkable in that the first transmission signal is of the OFDM type.
• 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 IOTA type is particularly advantageous since in this case, a so-called first ring processing aimed at eliminating pilot interference in the multi-carrier IOTA signal is not implemented. work here.
• 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.
• the modulation of the IOTA type 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 ⁇ 0 , the spacing v 0 between two neighboring sub-carriers being equal to half the inverse of the symbol time ⁇ 0 , and each subcarrier undergoing shaping filtering of its spectrum having a bandwidth strictly greater than twice the spacing between subcarriers v 0 , the filtering being chosen so that each symbol is strongly concentrated in the time domain and in the frequency domain.
• 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
• a single carrier channel can be used for the transmission of information and / or signaling data, the channel estimation from the single carrier pilot signal making it possible both to equalize the data transmitted on a signal.
• single-carrier 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 radio communication standards (in particular the UMTS standard and more generally mobile network standards based on the use of single carrier channels).
• the method is remarkable in that the transmitter and the receiver belong to a mobile communication network.
• 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.
• 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 carrier without pilot.
• 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 data transmission signal. using multi-carrier, high-speed modulation when necessary.
• 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.
• 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 low signaling and / or information data throughput on a single carrier channel, - the terminal transmitting signaling and / or information data to the base station on a single carrier channel.
• the method is remarkable in that it comprises a step of generating a reference clock associated with the first data transmission signal transmitted according to a multi-carrier modulation, the generation of a reference clock taking account of the single-carrier pilot signal, and the reference clock supplying the estimation of the response of the transmission channel of the first transmission signal of data transmitted according to a multi-carrier modulation.
• the method is remarkable in that it comprises an equalization of the data transmitted according to a multi-carrier modulation, the first data transmission signal transmitted according to a multi-carrier modulation comprising pilot symbols and the clock. reference feeding the equalization.
• the transmission channel when, in particular, the transmission channel is very noisy and / or disturbed, it is useless to reserve OFDM symbols containing only pilots.
• the useful bandwidth corresponding to the multi-carrier modulation is therefore optimized, the determination of a reference clock and / or the frequency control of the receiver on the transmitter being carried out taking into account the pilot signal with single carrier.
• the method is remarkable in that it implements at least two modes of transmission of data transmitted according to a multicarrier modulation, the first signal of transmission of data transmitted according to a multicarrier modulation comprising symbols pilots according to a first mode and not comprising a pilot symbol according to a second mode.
• the method is remarkable in that it comprises a step of switching from the first mode to the second mode and vice versa as a function of the quality of reception of the first data transmission signal transmitted according to a multicarrier modulation.
• an unmanned communication mode on the multi-carrier signal is preferred when the reception quality is sufficient; on the other hand, a mode of communication with pilot on the signal with single carrier and on the signal with multiple carriers is implemented if the quality of reception without pilot on the signal with multiple carriers is insufficient and the number of pilot is increased or reduced depending on the quality of reception.
• 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 for estimation of the transmission channel response of the data transmission signal transmitted according to a multi-carrier modulation, the estimation taking into account the single-carrier pilot signal, at least part of the pilot signal coinciding in time with at least part of the first 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 multi-carrier modulation, the estimation taking account of the single pilot signal carrier, at least part of the pilot signal coinciding in time with at least part of the first signal.
• the invention relates to a radio data transmission signal comprising at least one pilot single carrier channel and one communication channel.
• multi-carrier data transmission 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 into account the single carrier pilot signal, at least part of the pilot signal coinciding in time with at least part of the first 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 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, at least part of the pilot signal coinciding in time with at minus part of the first 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.
• FIG. 1 presents an example of an OFDM signal known per se
• FIG. 2 shows a 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
• FIG. 5 describes a transceiver module associated with a terminal implemented in the network of FIG. 3;
• Figure 8 shows a communication protocol in the mobile communication network of Figure 3.
• FIG. 9 illustrates equalization means implemented in the transmitter / receiver of Figure 5 according to an alternative embodiment of the invention.
• the technique known per se and illustrated with reference to FIG. 1 consisting in demodulating and separately equalizing a single-carrier channel and a multi-carrier 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.
• 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.
• 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).
• a single carrier pilot signal for example of the CPICH type as used in the context of UMTS
• OFDM type for example OFDM type
• the channel estimate provided by the pilot signal is used.
• the pilot signal undergoes an auto-correlation over a length corresponding to that of an OFDM symbol, 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.
• the pilot signal is processed in a simplified manner by considering only the most relevant delays.
• FIG. 3 a block diagram of a mobile radio network implementing the invention is presented.
• 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
• 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.
• the terminal 32 and the base station 31 are connected in communication by:
• a single carrier downlink 310 allowing the transport of signaling and / or control data communication with terminal 32 as well as the transmission of a pilot signal;
• 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.
• 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.
• 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” from English “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” in English)
• 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 “3 rd Generation Partnership Project” standard;
• FIG. 4 illustrates a transceiver module 40 belonging to the base station 31 implemented in the network 30.
• the module 40 notably comprises:
• 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 of the decoded data received by the antenna 43.
• This chain 41 the implementation of which is well known to those skilled in the art, 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 multi-carrier channel 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 a multi-carrier OFDM modulation; - a signal processing processor (or DSP from English
• the DSP 428 is associated with a hardware accelerator for the combination:
• - single carrier signals to be transmitted including the CPICH 4211 pilot channel and possibly signals carrying control, signaling data and / or useful information to be transmitted on a single carrier channel;
• the OFDM channel here carries only useful information data and does not include subcarriers associated with pilots.
• the pilot channel 4211 and the multi-carrier signals 4212 are combined synchronously (the symbols
• pilot channel 4211 and the multi-carrier signals 4212 are combined asynchronously.
• FIG. 5 illustrates a transmission-reception 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 includes in particular:
• 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 not described further.
• the reception chain 51 is adapted to receive:
• the reception chain 51 comprises: a low noise amplifier 510
• a bandpass filter 423 centered around the intermediate frequency and a bandwidth corresponding to the width used for the transmission of the signal; an I / Q 514 baseband converter controlled by a 515 synthesizer; 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 multi-carrier signals; and - Equalization means 519 adapted to demodulate and equalize the single-carrier and multi-carrier signals supplied by the DSP 518.
• DSP signal processing processor
• 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 (of OFDM type) and supplied by the DSP 518.
• the CPICH input notably includes a signal of CPICH type 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
• the means 60 accept as input a CPICH type signal in single carrier and comprises in particular: auto-correlation means 600; and - Fourrier transform means 602.
• the autocorrelation means 600 perform 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 ⁇ l a ⁇ n, ⁇ l corresponding to the direct path, ⁇ 2 to a second path and ⁇ n to the path the longer (each of the selected paths corresponding to a direct path or to a relevant echo), n autocorrelations are thus calculated.
• ⁇ k is equal to the product of a factor k by the chip period Te of the CPICH code (equal to 1/3840000 s or approximately 0.26 ⁇ s within the framework of the UMTS standard), k being preferably a integer or a multiple of 0.5.
• the OFDM symbols are transmitted synchronously with the CPICH symbols.
• the autocorrelation function is implemented on a window corresponding to a CPICH code symbol (or equivalently in the case of synchronization between the different signals, to an OFDM symbol).
• the OFDM symbols and the CPICH code symbols are transmitted asynchronously.
• several variants can be implemented: according to a first variant, one calculates autocorrelations of the CPICH symbol closest in time to the symbol
• 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.
• n is chosen to be greater than or equal to the number of subcarriers used in the OFDM channel.
• n is chosen to be greater than or equal to the number of subcarriers used in the OFDM channel.
• the means 602 implement a fast Fourrier transform (or FFT 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.
• the means 602 if the number of OFDM subcarriers is not a power of 2, the means 602 preferably implement a discrete Fourrier transform (or DFT from the English "Discrete Fourrier Transform") of suitable length.
• a discrete Fourrier transform or DFT from the English "Discrete Fourrier Transform" of suitable length.
• each sub-carrier of the OFDM channel has a bandwidth equal to 3.75 kHz, and if each OFDM symbol is modulated on 600 sub-carriers, a useful band of the order of 2 MHz is obtained and the means 602 implement a DFT of length 600 providing 600 coefficients. This gives an estimate of the frequency channel which can be used for OFDM equalization.
• 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.
• 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).
• the means 64 demodulate the input OFDM signal and supply demodulated OFDM symbols to the OFDM equalization unit 66.
• 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 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).
• OFDM symbols are divided by the channel.
• 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 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.
• the receiver implements an echo detection and an estimation of r delays ⁇ l a ⁇ r corresponding (for example from a primary synchronization channel (“Primary SCH” according to the UMTS standard)) .
• Primary SCH primary synchronization channel
• the equalization means 79 include:
• - estimation means 70 adapted to estimate a channel from a pilot signal with single carrier; - OFDM demodulation means 64; and
• the estimation means 70 accept as an input a signal of the CPICH type in single carrier, as well as a list of the r-delays ri to ⁇ r to be taken into account and notably includes:
• 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 ⁇ l to ⁇ r to be taken into account (according to a method or variants similar to those implemented in the means of auto-correlation
• the autocorrelation means 700 transmit to the Fourier transform means 602, on n outputs 601: the r results of autocorrelations performed corresponding to the delays ⁇ l ⁇ r; and
• the autocorrelation means 700 carry out an estimation of the channel in function of the CPICH signal and more precisely an autocorrelation of the CPICH signal for each of the delays ⁇ l to ⁇ m equal to or close to the delays ⁇ l to ⁇ r.
• a delay is close to a delay ⁇ i, if it differs by at most P chip periods Te from the delay xi considered, P preferably being equal to 2 (but being able to take other values, for example 1 or 3) .
• an autocorrelation will preferably be carried out by the means 700 for the delays ⁇ i-2Tc, ⁇ i-Tc, ⁇ i, ⁇ i + Tc and ⁇ i + 2Tc.
• the larger the value of P the finer the estimate.
• the smaller the value of P the simpler the implementation of the autocorrelation means 700.
• the delays taken into account and obtained, for example, by interpolation of the signal CPICH are non-integer multiples of the chip time Te.
• FIG. 8 illustrates a communication protocol between the base station 31 and the terminal 32 during a communication implementing the channels 310 to 312.
• This protocol comprises two phases: a phase 80 of communication establishment essentially comprising exchanges signaling data and a communication phase 81 implementing high speed data transmission using an OFDM channel and a CPICH channel for estimating the transmission channel.
• 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.
• the terminal 32 is synchronized on the SCH channel of the base station 31. It is noted that this SCH signal 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 synchronizes again on 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.
• the terminal 32 listens to the PCH channel indicated by the signal 802.
• 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.
• 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.
• 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 communication mode are compatible with the first two layers (physical and link) defined by the UMTS standard.
• the base station indicates where, when and how to listen to the OFDM.
• 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 805 CPICH is transmitted continuously by the base station 31.
• the mobile sends a request via the uplink PRACH 806 channel (physical channel corresponding to the RACH channel) while listening to the FACH 804 channel, to obtain 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 communication to listen to the associated OFDM channel for data transmission.
• 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 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 multi-carrier communication mode) without changing the physical characteristics of transmission of the RACH (channel up) and FACH (down channel).
• the FACH channel carries signaling information allowing the mobile to listen to the OFDM channel correctly.
• the FACH indicates when (i.e.
• 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.
• 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 preferably maintained.
• the base station 31 transmits data on the common OFDM channel via the successive signals 810, 811 and following, the pilot signal CPICH 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
• the terminal 32 and / or the base station 31 indicate via the FACH channel that the communication ends.
• FIG. 9 illustrates equalization means 90 implemented in the terminal 32 according to an alternative embodiment of the invention particularly well suited when the transmission channel is very noisy and / or disturbed (for example by a strong type effect Doppler or an environment with many echoes which cause signal fading, difficult to process when the OFDM signal does not have a pilot symbol according to certain embodiments of the invention).
• a person skilled in the art inserts into the OFDM signal not only symbols comprising for example 10% of subcarriers associated with pilots (as represented in FIG. 1) but also a learning sequence which includes only pilot type subcarriers. These latter symbols not containing data represent several percent (for example 10%) of the OFDM symbols and consequently reduce the bandwidth usable for the data.
• a transmitter transmits a CPICH signal continuously and data according to an OFDM modulation to a receiver implementing the equalization means 90.
• certain symbols OFDM include drivers for frequency estimation.
• the equalization means 90 carry out on the one hand a frequency estimation from the CPICH channel making it possible to calibrate the frequency of the reference clock (13 MHz clock also called VTCXO and in particular conforms to GSM and UMTS standards (in particular TS 25.101) defined by the 3GPP (or 3rd Generation Project Partnership) standardization committee of the receiver on the transmitter, because the reference clock of the receiver is different from that of the transmitter.
• the equalization means 90 demodulate the signal OFDM and equalize it taking into account the frequency estimation made from the CPICH channel.
• the equalization means 90 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 reference frequency.
• the equalization means 90 further comprise: frequency estimation means 91 adapted to estimate the frequency of the corresponding to the signals received from a pilot signal with single carrier; an oscillator 97; a frequency synthesizer 98;
• the means 91 accept as input a signal of the CPICH type in single carrier. They perform a non-coherent demodulation of the CPICH signal including in particular an autocorrelation of the CPICH signal (“descrambling” in English) providing a time estimate of the symbols of the CPICH from which the phase between two successive symbols of the CPICH signal is calculated (implementing in particular a rake receiver, a weighted sum and an integration with a first order filter to correct excessive fluctuations).
• the means 91 thus make it possible to supply a signal making it possible to control the servo of the oscillator 97 which generates a reference clock at 13 MHz associated with the signals received throughout the receiver.
• the frequency synthesizer 98 generates a digital clock 92 CLK derived from the reference clock and transmits this clock 92 to the different parts of the equalization means 90.
• a digital clock 92 CLK derived from the reference clock and transmits this clock 92 to the different parts of the equalization means 90.
• the symbols OFDM are transmitted synchronously with the CPICH symbols. Only the transmission frequencies of the OFDM and CPICH signals derive from the same reference clock (the RF carriers are not necessarily the same).
• a CLK 92 reference frequency or clock is thus obtained which is used for OFDM equalization and is supplied by the means 90 to the other parts of the transmitter / receiver, in particular the frequency estimation means 91, the means 96 of channel estimation, the OFDM demodulation means 93 and the OFDM equalization unit 95. We thus obtain a closed loop control.
• the means 93 demodulate the input OFDM signal using the reference clock 92 and supply demodulated OFDM symbols to the OFDM equalization unit 95.
• the channel estimation means 96 take into account symbols demodulated by the means 93 and the reference clock 92 to provide amplitude and phase corrections for the equalization means 95, determined from the OFDM signal.
• the equalization unit 95 receives in parallel the clock 92, a channel estimate and demodulated OFDM symbols 94, communicated respectively by the means 91, 96 and 93.
• the unit 95 equalizes the OFDM symbols from the reference clock 92 and as a function of a time estimate of the channel associated with the OFDM symbols then supplies the information data corresponding to the OFDM symbols processed on the output 55.
• the equalization means 90 are implemented in the transceiver module 50: either in place of the equalization means 519 illustrated previously for this relatively simple implementation which is particularly well suited to any type of channel (strongly or slightly noisy); or either combined with the means 519.
• a receiver combining the means 90 and the means 519 is particularly well suited to optimizing the useful bandwidth whatever the disturbances of the channel.
• Such a receiver and the corresponding transmitter preferentially implement dynamic switching management of OFDM signal processing with or without pilots: when the channel is very noisy, the OFDM signal includes pilots and the receiver uses the CPICH channel for an estimation of the reference frequency and the OFDM channel for a temporal estimation of the channel with setting work of means similar to means 90; on the other hand, when the channel is not very noisy, the transmitter transmits an unmanned OFDM signal and the receiver implementing means similar to the means 519 estimates the channel from the CPICH signal to equalize the OFDM signal.
• the transmitter and / or the receiver then comprise means for identifying good or bad reception when the OFDM signal does not have a pilot or more generally means for identifying the mode of transmission best suited to the channel, possibly taking into account a required quality of service (for example bandwidth requirements: the best bandwidth being offered when there is no driver, the unmanned mode will be favored when the bandwidth requirement is high).
• the transmitter and the receiver agree on the mode of transmission via, for example, the RACH and FACH channels in a similar manner to that described previously with reference to FIG. 8 and the transmitter and the receiver implement means for processing different modes of communication (without OFDM pilot or with more or less OFDM pilots).
• the base station preferentially uses modulation
• the base station switches to a second communication mode.
• certain OFDM symbols include pilots making it possible to estimate the frequency and the equalization means 90 carrying out on the one hand frequency estimating from the CPICH channel making it possible to set the frequency of the reference clock as indicated above with reference to FIG. 9.
• the reception quality improves (thanks in particular to a reduction in noise or an increase in the power of the received signal to reduce the signal to noise ratio)
• the base station switches to the first communication mode in order to optimize the useful bit rate.
• a base station transmitter
• several terminals receiveivers
• two cases can be envisaged: - according to a first case, the communications are time multiplexed (for example according to a TDMA protocol from English
• the communications are frequency multiplexed (for example according to an FDM A protocol from English
• Frequency Division Multiple Access and, possibly, time; several radio links can then be active simultaneously; at a given instant, OFDM pilots using the entire frequency band allocated according to the second mode, all OFDM communications use the same mode with (second mode) or without pilot (first mode); for each time interval allocated to one or more receivers, the base station determines the most appropriate communication mode according to any criterion (for example, the reception quality of at least n terminals is insufficient to allow them to demodulate and equalize the signal
• n is a threshold parameter, and is worth, for example, one or any other predetermined or dynamically updated value (depending on the number of terminals in particular)).
• the network according to the invention which, in particular, implements the first and the second modes (or one of the two) is adapted to coexist with a network which does not implement a channel of the CPICH type and in particular with a base station adapted to communicate in a third mode where the symbols OFDM contain more pilots (for example, according to the third communication mode, a known state of the art modulation is implemented where 90% of OFDM symbols include 10% of subcarriers associated with pilots and, in addition, a learning sequence not comprising pilot-type subcarriers).
• 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 type ( or Frequency Shift Keying), QAM (or “Quadrature Amplitude Modulation”))
• phase modulation type for example of the PSK (or “Phase Shift Keying”), GMSK (or “Gaussian Minimum Shift Keying”)
• amplitude in particular of the FSK type ( or Frequency Shift Keying), QAM (or “Quadrature Amplitude Modulation”)
• amplitude in particular of the FSK type ( or Frequency Shift Keying)
• QAM or “Quadrature Amplitude Modulation”
• a person skilled in the art can make any variant in the type of multi-carrier modulation used.
• the modulation may 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 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 even to two network infrastructure stations) especially when high spectral efficiency and / or bandwidth savings are desired.
• the possible supports of the invention are, for example, digital terrestrial broadcasting systems, be it images, sounds and / or data or digital communication systems towards high speed mobiles. (in mobile networks, local radio networks or for transmissions to or from satellites) or even for underwater 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
• the invention allows the use of the single-carrier channel to perform processing specific to the OFDM channel, in particular: initial synchronization and monitoring of synchronization in time or in frequency, measurement of the quality of the modulation channel, ...

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• Signal Processing (AREA)
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• Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

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  • 2004-02-13 WO PCT/FR2004/000344 patent/WO2004077774A1/fr active Application Filing
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