FR2933253A1 - DATA TRANSMISSION METHOD, RECEIVING METHOD, AND TRANSMISSION APPARATUS THEREOF - Google Patents

Abstract

The invention relates to a data transmission implemented in at least one transmitter (2, 111 to 113, 121, 122). In order to improve the utilization of the resources, the transmission comprises: - a construction (92) of OFDM symbols, from first data and second data, of the first and second sets of subcarriers (61) carrying representative information respectively first and second data; the construction comprising: coding of the first and second data by codes of the SISO or MIMO coded type, of different dimensions; an OFDM modulation of the first data coded by the first code and second data coded with the second code; and a transmission (93) of the OFDM symbols intended for a plurality of receivers.

Description

Method of data transmission, receiving method and corresponding transmission apparatus

1. Field of the invention

The invention relates to the field of telecommunications and more specifically to wireless data transmission.

2. State of the art According to the state of the art, the transmission of data or the broadcasting of services, for example television, is done through noisy channels and subjected to disturbances (for example, fading corresponding to multiple paths related to echoes). In order to improve the reception, the multi-sub-carrier modulations of the OFDM (or Orthogonal Frequency Division Multiplexing) type associated with SISO (Single Input Single Output) systems single input simple output) implementing a single transmitting antenna or MIMO (Multiple Input Multiple Output English or multiple input multiple output) using multiple antennas in transmission and reception are relatively effective. According to a technique known from the prior art called SFN (English single frequency network or French single frequency network), several transmitters of the SISO type synchronously transmit the same OFDM signal. In this way, a receiver receives a combination of the signals from several transmitters and decodes the combination thus obtained using the OFDM specific properties of intersymbol interference cancellation. This technique has the disadvantage of monopolizing a large part of the spectral resource in a large geographical area for the diffusion of a single service.

3. Summary of the invention. The invention aims to overcome these disadvantages of the prior art.

More particularly, the invention aims to enable data transmission, adapted to specific needs that do not require as many resources.

For this purpose, the invention proposes a method of data transmission, implemented in at least one transmitter. In order to improve the use of resources, the method includes steps of: OFDM symbol construction, from first data and second data, a first set of subcarriers carrying information representative of the first data in each OFDM symbol ; a second set of subcarriers carrying information representative of the second data in each OFDM symbol, the first and second sets of subcarriers being disjoint; the construct comprising: a first encoding of the first data by a first code of the SISO type or MIMO coded, the first code having a first dimension; a second coding of the second data by a second code of the MIMO type, the second code having a second dimension, the first dimension being strictly less than the second dimension; OFDM modulation of the first data encoded by the first code and second data encoded with the second code and 25 - of transmission (93) of the OFDM symbols for a plurality of receivers. Advantageously, the first coding is of dimension equal to 1. According to a particular characteristic, the first coding corresponds to an identity coding, the data not being modified by the coding (this may correspond to a simple link or a simple read of memory). Advantageously, the construct includes weighting the first data, generating a plurality of weighted symbols from an incoming symbol, and OFDM modulation of each weighted symbol. According to another characteristic, the first coding is of dimension strictly greater than 1 and comprises a generation of a plurality of symbols coded from an incoming symbol and in that said construct comprises an OFDM modulation of each symbol. code. Advantageously, the method comprises steps of: receiving first data from a first source; and receiving second data from a second source separate from said first source. According to a particular feature, the first data is associated with a first broadcast service and the second data is associated with a second broadcast service separate from the first service. The invention also relates to a data reception method implemented in at least one remarkable receiver in that it comprises the steps of: receiving (101) OFDM symbols representing first data and second data; decoding (102) the received OFDM symbols, a first set of subcarriers (61) carrying information representative of the first data in each OFDM symbol; a second set of subcarriers (72) carrying information representative of the second data in each OFDM symbol, said first and second sets of subcarriers being disjoint; said decoding comprising an OFDM demodulation of the received symbols and providing first decoded data and second decoded data: the first data being coded by a first code of the SISO type or MIMO coded, the first code having a first dimension; the second data being coded by a second code of the MIMO type, the second code having a second dimension, the first dimension being strictly less than the second dimension.

The invention also relates to a data transmission apparatus comprising OFDM symbol building means (92), based on first data and second data, a first set of subcarriers (61) carrying information representative of said first data in each OFDM symbol; a second set of subcarriers (72) carrying information representative of said second data in each OFDM symbol, said first and second sets of subcarriers being disjoint; the construct comprising: a first encoding of the first data by a first code of the SISO type or MIMO coded, the first code having a first dimension; a second coding of the second data by a second code of the MIMO type, the second code having a second dimension, said first dimension being strictly less than said second dimension; OFDM modulation of the first data encoded by the first code and second data encoded with the second code and transmission (93) of the OFDM symbols for a plurality of receivers. The invention also relates to a system comprising the transmission apparatus and apparatuses transmitting the first data synchronously. The invention also relates to a receiver corresponding to the reception method.

4. List of Figures. The invention will be better understood, and other features and advantages will appear on reading the description which follows, the description referring to the appended drawings in which: FIG. 1 illustrates a wireless communication system, implementing several transmitters and receivers, according to a particular embodiment of the invention; FIG. 2 presents a very schematic diagram of an emitter of the system of FIG. 1, according to the invention; FIG. 3 presents a very schematic diagram of transmitters of the system of FIG. 1; FIGS. 4 and 5 schematically illustrate respectively a transmitter and a receiver of the system of FIG. 1, according to the invention; FIG. 6 illustrates a broadcasting spectrum by an emitter of the system of FIG. 1; FIGS. 7 and 8 show the use of a scattering spectrum by different antennas of an emitter of the system of FIG. 1, according to the invention; FIG. 9 illustrates a method of data transmission according to a particular embodiment of the invention, implemented by transmitters of the system of FIG. 1; and FIG. 10 presents a method of receiving data according to a particular embodiment of the invention, implemented by receivers of the system of FIG. 1.

5. Detailed description of the invention.

The general principle of the invention is based on the use by a transmitter OFDM modulators for the transmission of two sets of data. A first set of data uses partial resources of an emitter: first signals are representative of the data of the first set and are of the SISO or MIMO encoded type associated with a first code of a first dimension. A second set of data makes full use of the OFDM modulation resources of one transmitter: second signals are representative of the data of the second set and are of the MIMO type associated with a second code of a second dimension. The first dimension is strictly smaller than the second dimension: if the second dimension is Ntx, the first dimension is for example 1 if the first data set is transmitted in SISO mode and greater than 1 and strictly less than Ntx if the first set of data is transmitted in MIMO mode. FIG. 1 illustrates a broadcasting system 1 implementing several transmitters 101 to 106, 111 to 113, 121 and 122, according to one particular embodiment of the invention. Transmitters 101 to 106 have a single transmitting antenna and are of the SISO type. Transmitters 111 to 113 and 121 and 122 are of the MIMO type and each has a MIMO encoder and several antennas transmitting a MIMO type signal. The system 1 also comprises receivers (not shown), some of the MIMO type able to receive and decode the signals emitted by the transmitters 111 to 113, 121 and / or 122 as well as the signals transmitted by the transmitters 101 to 106. The receivers are for example fixed receivers (television decoders in particular) or portable devices (or handheld device in English), for example adapted to receive and process broadcast services (eg recording and / or display of video data). The system 1 comprises a global server 100 connected to each of the transmitters 101 to 106, 111 to 113, 121 and 122 by links 106. The links 106 are, for example, wired links (for example, using a network of the IP type The global server 100 transmits data corresponding to a first service (in particular a video broadcast service) to all the transmitters to which it is connected via the Internet. The system 1 covers a geographical zone 10 which itself comprises different geographical areas 11 and 12. Thus, each of the transmitters 101 to 106, 111 to 113, 121 and 122 covering the zone 10 broadcasts the data corresponding to the first service towards all the receivers present in the zone 10. The emitters 101 to 106 are, for example, emitters of high power each covering a large area (for example several kilometers yon (eg 3, 10 or 50 km) included in zone 10.

The system 1 comprises a local server 110 connected to the transmitters 111 to 113 that are present in the zone 11. The local server 110 transmits data corresponding to a second service (including video broadcast service) to all the transmitters to which it is connected via any links (for example wired, wireless or satellite). The diffusion of emitters 111 to 113 covers this zone 11; in other words, the transmitters 111 to 113 broadcast the data corresponding to the second service to all the receivers present in the zone 11. The system 1 comprises a local server 120 connected to the transmitters 121 and 122 which are present in the zone 12. The local server 120 transmits data corresponding to a third service to all the transmitters to which it is connected via any links. The diffusion of the emitters 121 and 122 covers this zone 12; in other words, the transmitters 121 and 122 broadcast the data corresponding to the third service to all the receivers present in the zone 12. The servers 110 and 120 according to the embodiment described above are advantageously managed locally and separated. physically from the global server 100, which facilitates the implementation of networks specific to the areas 11 and 12 (including their installation to cover one-time or time-limited services). According to one variant, the servers 110 and 120 are integrated in the server 100. Advantageously, the server 100 sends the services to each of the transmitters according to their coverage area 10, 11 or 12. This variant has the advantage of a management centralized and limit the number of servers. According to the embodiment described, the zones 11 and 12 inside the largest zone 10 are disjoint. Thus, the reception of services is facilitated in each of the zones 11 and 12. According to one variant, the zones 11 and 12 inside the largest zone 10 are different and overlap in part. The reception of the second and third services is then disturbed in the overlapping part. On the other hand, the receivers present in zone 11 (respectively 12) and not present in zone 12 (respectively 11) correctly receive the first and second (respectively third) services. The invention is not necessarily implemented in a multi-zone system. Thus, according to one variant, the system 1 comprises only transmitters 111 to 113 of the MIMO type. In this case, synchronization is limited to these transmitters. The invention is also not limited to a data broadcast and also applies to the transmission of data in multipoint point to point (in English multicast) or point-to-point mode. In this case, the synchronization based on an external signal (for example sent by a server) is advantageously not implemented. FIG. 2 represents an architecture of a transmitter 2 adapted to transmit two sets of data (first and second sets) (associated or not with respectively two distinct services) according to the invention (broadcast, multipoint to point or point to point mode) to receivers. The emitters 111 to 113, 121 and 122 have, for example, the architecture of the emitter 2.

The transmitter 2 comprises: an encoder 20 receiving a set of first data 200 associated, for example, with a first service and a first broadcast area (for example the area 10); an encoder 21 receiving a set of second data 210 associated, for example, with a second service and a second broadcast area (for example the area 11), distinct from the first broadcast area; Ntx OFDM modulators 221 to 22Ntx emitting OFDM symbols on at least one antenna respectively 231 to 23Ntx; and a synchronization module 24 receiving a synchronization signal 240 (for a transmitter used in broadcast mode) and transmitting a signal 241 synchronizing the OFDM modulators 221 to 22Ntx. The synchronization signal 240 generates the signal 241 according to any method known to those skilled in the art. The signal 240 is for example a signal including a precise time stamp. The synchronization module 24 then generates the signal 241 by using complementary means (for example by using a GPS signal (Global Positioning System) .The synchronization module 24 can also generate the signal 241 to From a signal conveyed over an Internet network, OFDM modulators are advantageously synchronized with a precision of the order of 11.1 s and more generally with a precision which allows the guard intervals of the OFDM symbols to absorb receivers, the possible offsets between the transmitters and the delays of transmissions related to the paths traversed by the scattered signals According to a point-to-multipoint or point-to-point embodiment, the synchronization of the OFDM modulators is advantageously carried out locally without the use of a external signal 240. The encoder 20 (respectively 21) comprises: a channel encoder 201 (respectively 2 11) receiving the data 200 (respectively 210), protecting them with channel coding (eg convolutional code (or convolutional in English) or in block) against noisy transmission-related errors and formatting them to form blocks encoded data 202 (respectively 212), and a modulator 203 (respectively 213) (for example of the type QAM (English quadrature amplitude modulation) or PSK (English Phase Shift Keying or phase shift keying) receiving coded data 202 (respectively 212) and producing modulated symbols 204 (respectively 214).

The encoder 21 also comprises: a MIMO coder 215 coding the modulated symbols 214 to form Ntx MIMO data block streams 2161 to 216Ntx intended respectively for each OFDM 221 to 22Ntx. Here, the antennas 231 to 23Ntx comprise the radio part or RF (of the English Radio Frequency) and in particular frequency transpositions, amplifications and filtering. Modulator 203 generates groups of Q modulated symbols. Q is for example equal to 1600 and is equal to the number m of subcarriers associated with the encoder 20.

The modulator 213 generates groups of Q 'modulated symbols. Q 'is, for example, equal to 200 and is equal to the product of the code rate used by the MIMO coder 215 by the number Ntx of transmitting antennas 231 to 23Ntx and by the number n of sub-carriers associated with the coder 21. n is by example equal to 100 with a coder rate of 215 equal to 1 (with full-rank coder of the Blast type) and 2 antennas (Ntx = 2). n is for example equal to 200 with a rate of the encoder 215 equal to 0.5 (with Alamouti type encoder) and 2 antennas (Ntx = 2). Advantageously, the total number of subcarriers is smaller than the size of the FFT (Fast Fourier Transform or Fast Fourier Transform) used in OFDM modulators. The number of subcarriers used respectively by the first and second services may be equal or different. Advantageously, they are adapted to the necessary bit rate: if the first requires more bit rate than the second service, the number of subcarriers allocated to the first service will be greater than that corresponding to the second service. The encoder 215 (and optionally the encoder 20) encode the input modulated symbols with spatial multiplexing (for example based on a BLAST multiplexing of the Bell laboratories (as described, for example, in the document written by GJ Foschini, entitled Layered Space -Time Architecture for Wireless Communication in a Fading Environment When Using Multiple Antennas (or space-time architecture for these wireless communications in a fading environment using multiple antennas and published in Bell Labs Technical Journal, Vol 1, No. 2 , Fall 1996, pp 41-59) or STBC / SFBC code (Space Time Block Code / Space Frequency Block Code), for example the STBC / SFBC code. , an orthogonal code (for example) of Alamouti or Golden A Golden Code is described in the document "The Golden Code: A 2 x 2 Full-Rate Space-Time Code with Non-Vanishing Determinants," (or Golden's code: a 2x2 full-time space-time code with non-fading determinants) written by J.-C. Belfiore, G. Rekaya, and E. Viterbo (and published in IEEE Transactions on Information Theory, flight. 51, n. 4, pp. 1432-1436, April 2005.). Alternatively, the STBC code is described in "Space-Time block codes from orthogonal designs" written by V. Tarokh, H. Jafarkhani, and RA Calderbank (and published in IEEE Transactions on Information Theory, 45, pp. 1456-1467, July 1999). An Alamouti orthogonal code is described in the document A simple transmit diversity technique for wireless communications (or a simple transmission diversity technique for wireless communications published in IEEE Journal on Selected Area in Communications in October 1998). At its output, the encoder 215 (respectively 20), the data blocks MIMO 2161 to 216Ntx (respectively 2061 to 2060Ntx 'with Ntx' strictly less than Ntx if the encoder 20 implements a MIMO coding) are each assigned to a modulator OFDM. According to another variant, the encoder 20 is of the SISO type (the associated code is of dimension equal to 1) and also comprises a phase and amplitude weighting module using a weighting vector. The weighting module receives the symbols generated by the modulator 203. It produces for each received symbol, Ntx "weighted symbols in phase and in amplitude and supplies Nb (OFDM modulators 221 to Ntx" and Ntx "antennas 231 to 23Ntx", so Ntx "may take any value less than or equal to Ntx.According to various embodiments, the coverage area can thus be balanced (no direction being preferred), or on the contrary favor certain directions ( and / or to disadvantage other directions The weighting vector can be obtained by simulation, calculation and / or measurements in situ (disregarding the encoder 21) according to techniques known to those skilled in the art (for example, training of beam or beam forming in English) applied to a transmitter not using an encoder 21. According to another variant, the encoder 20 also comprises a MIMO coder encoding the modulated symbols 2 04 forming Ntx 'stream of data blocks respectively for each OFDM modulators 221 to 22Ntx'. Thus, the size of the encoder 20 is equal to Ntx 'and that of the encoder 21 is equal to Ntx, Ntx' being strictly less than Ntx. The MIMO encoders of the encoders 20 and 21 may be of the same type or of a different type (for example a full diversity scheme for the coder 20 (in particular orthogonal space / time coding (or OSTBC of orthogonal English STBC) for example Alamouti coding) and a full rank scheme (or full rate in English) for the encoder 21 (in particular BLAST coding type spatial multiplexing) In general, the system comprises or not transmitters comprising only similar coders. to the encoders 20, this variant makes it possible in particular to ensure a different quality of service and a different bit rate for the signals coming from the coders 20 and 21, and therefore an adaptation to the needs in a system 1 comprising transmitters 101 to 105 and transmitters 2 with MIMO encoder, this variant makes it possible to have a greater spectral efficiency for a first service associated with the encoder 20 and a larger bit rate for a second service associated with the encoder 21. FIG. 3 represents an architecture of a transmitter 3 adapted to broadcast data associated with a separate service to receivers. The transmitters 101 to 105 have, for example, the architecture of the transmitter 3. The transmitter 3 comprises the elements of the transmitter 2 allowing the transmission of first data associated or not with a first service. These elements are similar to the corresponding elements of the transmitter 2 and bear the same references. The transmitter 3 comprises: the encoder 20 receiving data 200 associated with the first service and the first broadcast zone (for example the zone 10); an OFDM modulator 221 transmitting OFDM symbols on a single antenna 231; and a synchronization module 24 receiving a synchronization signal 240 and emitting a signal 241 synchronizing the OFDM modulator 221. According to the embodiment described, the transmitter 3 comprises a single encoder associated with a transmission of a set of first data ( for example a first service) (encoder 20) which allows a dedicated implementation.

According to one variant, the transmitter 3 has a structure similar to the transmitter 2, the part associated with the transmission of other data sets (for example other services) (encoder 21) being: hard-disabled, this part being unable to be used but the manufacturing can be facilitated; or can be validated on demand; for example, following the start of the transmission of a second set of data or a second service, an activation signal validating the use of the encoder 21 and the corresponding subcarriers in the OFDM modulators or acting directly at the OFDM modulators for allowing or disallowing the use of the subcarriers associated with the second set of data. FIG. 6 illustrates a spectrum 61 used by the transmitters 101 to 105 at a given instant t. Spectrum 61 comprises m contiguous subcarriers F1 to Fm 610 at 61 m. The subcarriers F1 to Fm broadcast a signal carrying information representative of data associated with a first set of data (for example at the first service S1) in each OFDM symbol. FIG. 7 illustrates the combination of the spectrum 61 and a spectrum 72 used by the antenna or antennas (antenna 231 or antennas 231 to 23Ntx ') transmitting a signal coming from coders 20 and 21. The spectrum 72 comprises n contiguous sub-carriers F'1 to F'n 720 to 72n. The subcarriers F'1 to F'n transmitted by these antennas broadcast a signal carrying information representative of data associated with the second set of data (for example the second service S2) in each OFDM symbol. FIG. 8 illustrates the spectrum 72 used by the antenna or antennas (antenna 232 to 23Ntx if the encoder 20 uses only the antenna 231 or antennas 23 (Ntx '+ 1) at 23Ntx if the coder 20 uses the antennas 231 to 23Ntx' ) transmitting a signal from the encoder 21 and not transmitting a signal from the encoder 20. Thus, at a time t, when the invention is implemented in a broadcasting system, the transmitters 101 to 105, 111 to 113, 121 and 123 are synchronized with the signal 240 and broadcast synchronously on the same sub-carriers of the spectrum 61 information representative of data associated with the first set of data (or first service Si), these data being modulated and coded of the same way. At the same instant t, the transmitters 101 to 105 do not use the spectrum 72; the transmitters 111 to 113 broadcast on the subcarriers of the spectrum 72 information representative of data associated with the second set of data (for example second service S2), these data being modulated and coded in the same way; the transmitters 121 and 122 broadcast on the same subcarriers of the spectrum 72 information representative of data associated with a third set of data (for example third service S3), these data being modulated and coded in the same way. Thus, a receiver placed in the zone 10 receives the signal broadcast by at least one of the transmitters of the zone 10 and decodes the signal corresponding to the spectrum 61 to obtain the data associated with the first set of data. A receiver placed in the zone 11 (respectively 12) receives the signal diffused by at least one of the emitters of the zone 11 (respectively 12) and possibly a signal diffused by a transmitter of the zone 10 outside the zone 11 (respectively 12 ); it decodes the signal corresponding to the spectra 61 and 72 to obtain the data associated with the first and second (respectively third) set of data. The fact that the transmitters of the zone 11 (respectively 12) broadcast the data associated with the first and second (respectively third) sets, allows the receiver of the zone 11 (respectively 12) to have a better reception of the data associated with the first set of data, which is particularly advantageous when the reception of the signals emitted by the emitters outside the zone 11 (respectively 12) is difficult or impossible (for example, where the zone 10 is very wide (several kilometers in radius) and zone 11 (respectively 12) corresponds to an area inside buildings). In addition, the use of spectral resources is optimized in areas where not all frequency bands are used for the first service covering the widest area. This also allows the first service to use a smaller number of subcarriers than the number of available subcarriers. According to an advantageous embodiment of the invention, the first and / or second sets of subcarriers 61 and 72 are fixed.

This allows in particular to facilitate implementation. According to another advantageous embodiment of the invention, the first and / or second sets of subcarriers 61 and 72 are variable; they vary in time, for example, every 10 or 100 OFDM symbols allowing a compromise between a statistical gain related to frequency changes (the more frequent the changes are, the better the gain) and the reliability of the channel estimation ( the channel can be better estimated if the changes are less frequent). Thus, if one or more frequencies are noisy or poorly received, the corresponding subcarriers are affected. By varying the spectra 61 and 72, this allows a diversity of frequencies for the receivers and the effects of disturbances on a given service are more limited. According to this embodiment, the transmitters of the system 1 transmit OFDM symbols, all or part of the subcarriers used corresponding to the subset 61. Thus, the transmitters 101 to 105 implement a selection of subcarriers 61 in a set of subcarriers available. Advantageously, the subcarriers associated with at least one of the data sets (first, second or third) are contiguous, which allows the receivers to have a more accurate channel response estimate (for example by frequency interpolations). . Thus, according to FIGS. 6, 7 and 8, the spectra 61 and 72 use consecutive sub-carriers respectively F1 to Fm and F'1 to F'n in the available spectrum comprising n + m subcarriers ranging from F1 to F 'not. Other embodiments are possible with contiguous (or consecutive) subcarriers in a spectrum comprising frequencies F "1 to F" m + n (F "1 = F1; F" m = Fm; F "m + 1 = F'1 and F "m + n = F'n) for at least one of the data sets: for example, an embodiment where the spectrum associated with the first set of data S1 uses m subcarriers of F" i to F "i + m and where the spectrum associated with the second (S2) or third (S3) data sets uses n subcarriers F" 1 to F "i-1 and F" i + m + 1 to F "m + n. According to another embodiment, the spectrum associated with the first set of data S1 uses m subcarriers F "1 to F" i-1 and F "i + n + 1 to F" m + n and where the spectrum associated with the second (S2) and third (S3) dataset uses n subcarriers from F "i to F" i + n. According to another variant, the sub-carriers used by the services are not consecutive, which may in certain cases make it possible to obtain a greater diversity of frequencies and a better resistance to the disturbances of the channel. FIG. 4 schematically illustrates an example of a hardware embodiment of a transmitter 4 corresponding, for example, to the transmitter 2. The transmitter 4 comprises, interconnected by a bus 44 of addresses and data, also carrying a signal of clock: a microprocessor 41 (or CPU); a non-volatile ROM type memory (of the English Read Only Memory) 42; a random access memory (Random Access Memory) 43; an interface 45 adapted to receiving a first set of data (for example service); an interface 46 adapted to receiving a second set of data different from the first set; an interface 47 adapted to the transmission of data sets (for example broadcast of services or point or point-to-point multipoint transmission) and performing in particular the functions of coders 20 and 21, OFDM modulators 221 to 22Ntx and antennas 231 at 23Ntx; an interface 48 adapted to receive the synchronization signal 240 and to synchronize the interface 47; and / or - an interface MMI (or man machine interface of the English Man Machine Interface) 49 or to a specific application adapted to the display of information for a user and / or the entry of data or parameters ( for example the setting of sub-carriers and data sets to be transmitted). It will be observed that the word register used in the description of the memories 42 and 43 designates in each of the memories mentioned, as well a memory area of small capacity (a few binary data) that a memory area of large capacity (for storing a program whole or all or part of the representative data of data received and to be broadcast). The ROM 42 comprises in particular: a prog program 420; parameters 421 of physical layers; and parameters 422 associated with the subcarriers. The algorithms implementing the steps of the method specific to the invention and described below are stored in the ROM 42 associated with the transmitter 4 implementing these steps. On power up, the microprocessor 41 loads and executes the instructions of these algorithms. The RAM 43 comprises in particular: in a register 430, the operating program of the microprocessor 41 charged at powering on the transmitter 4; incoming data 431 corresponding to the first set of data S1; incoming data 432 corresponding to another set of data S2; coded data 433 for the transmission of data sets. FIG. 5 schematically illustrates an example of a hardware embodiment of a receiver 5 belonging to the system 1 and adapted to receive and decode the signals emitted by the emitters 2 (for example 11 to 113, 121 and 122). Advantageously, the receiver 5 is adapted to receive the signals emitted by the transmitters 101 to 105. Thus, the management of the system 1 is facilitated. The receiver 5 comprises, interconnected by a bus 54 of addresses and data, also carrying a clock signal: a microprocessor 51 (or CPU); a non-volatile ROM type memory (Read Only Memory) 52; a random access memory (Random Access Memory) 53; a radio interface 55; an MMI interface 56 adapted to the display of information for a user and / or the entry of data or parameters (for example the parameterization of the sub-carriers and data sets transmitted); and an interface 57 to a specific application adapted to process the data set data transmitted by the transmitters of the zone to which the receiver 5 belongs and received by the receiver 5. It is observed that the word register used in the description of the memories 52 and 53 designates in each of the memories mentioned, both a memory area of low capacity and a large memory area (for storing an entire program or all or part of the data representative of data sets received or decoded ). The ROM 52 comprises in particular: a prog program 520; parameters 521 of physical layers; and parameters 522 associated with the subcarriers of the received data sets. The algorithms implementing the steps of the method specific to the invention and described hereinafter are stored in the ROM memory 52 associated with the receiver 5 implementing these steps. On power up, the microprocessor 51 loads and executes the instructions of these algorithms. The random access memory 53 comprises in particular: in a register 530, the operating program of the microprocessor 51 charged at powering on the receiver 4; incoming data 531 corresponding to the data received and decoded by the receiver 55; decoded data 532 formatted to be transmitted to the interface to the application 57. Other structures of the transmitter 4 and / or receiver 5 than those described with reference to FIGS. 4 and 5 are compatible with FIG. the invention. In particular, according to variants, the transmitters and / or the receivers compatible with the invention are implemented in a purely hardware ("hardware") embodiment, for example in the form of a dedicated component (for example in an ASIC or FPGA or VLSI) (respectively Application Specific Integrated Circuit in English, meaning Integrated Circuit for a specific application, Field-Programmable Gate Array in English, meaning Programmable Gate Network ln-Situ, Very Large Scale Integration in English , meaning very large-scale integration)) or of several electronic components integrated in a device or in the form of a mixture of hardware elements and software elements (software in English). The radio interface 55 is adapted to reception of the signals emitted by the transmitters of the system 1. It notably comprises a decoder associated with the encoders 20 and 21 of the transmitters. Advantageously, it comprises Ntx 'OFDM demodulators if the corresponding transmitters comprise an encoder 20 implementing a size code Nt and / or Ntx OFDM demodulators corresponding to the encoder 21 of the transmitters. The demodulators used to decode the signals from the encoder 231 are reused for decoding the signals from the encoder 20 according to certain embodiments and are not used according to other embodiments. In particular, the receiver is adapted to receiving a broadcast signal that may comprise a part of the available subcarriers (for example, subcarriers F1 to Fm corresponding to the first set of data) or all available frequencies (for example sub-carriers). carriers F1 to Fm + n). Advantageously, the receiver 5 decodes each received OFDM symbol for each set of subcarriers. According to a particular embodiment, the receiver separately decodes the first and second signals sequentially in time by using common hardware resources or in parallel using resources dedicated to each service. The receivers corresponding to the transmitters of the system 1, which according to one variant also implement a selection of the subcarriers 61, also implement a selection of the set 61 to receive and decode the first associated data (for example by detection subcarriers 61 used in all available subcarriers or exchanges of information between a transmitter or management apparatus and the receiver). FIG. 9 shows a method of data transmission implemented in the transmitter 4 according to a particularly advantageous embodiment of the invention. During an initialization step 90, the various parameters of the transmitter 4 are updated. In particular, the parameters corresponding to the data sets to be transmitted and the corresponding sub-carriers are initialized in any manner (for example, following the reception of initialization messages sent by one or more servers or other element of the system 1 or by user commands). Then, during a step 91, the transmitter 4 generates or receives first data corresponding to a first set of data if to be transmitted and second data corresponding to the second set of data S2. According to some embodiments, the transmitter 4 is configured according to the zone to which it belongs. Advantageously, it then generates or receives the data associated with the data sets (for example services) that it broadcasts in its zone. According to a variant, the transmitter 4 carries out a step of filtering the data sets by processing for broadcast only the set data corresponding to the zone to which it belongs, the other data not being broadcast. Advantageously, step 90 comprises receiving data corresponding to a first data set of a first source and data sets corresponding to a second service of a second source distinct from the first source.

Thus, although the data come from different sources, they are advantageously issued with optimization of material and spectral resources. According to one variant, the data corresponding to the first and second sets of data come from the same source. Thus, subcarriers and coverage areas are associated with each set of data whether the sources of the first and second sets of data are the same or distinct. Then, during a step 92, the transmitter 4 carries out a step of constructing the OFDM symbols, each symbol bearing information representative of the first data and the second data. In particular, after coding (in particular channel coding), modulation (for example QAM or QPSK), possible MIMO coding, the transmitter 4 associates with the data associated with the first (respectively second) service, a first (second) set of subscribers. carriers F1 to Fn (respectively F'1 to F'm) bearing information representative of the first (respectively) data in each OFDM symbol as illustrated with reference to the previous figures. The first and second sets of subcarriers are disjoint.

Then, during a step 93, the transmitter 4 broadcasts the OFDM symbols corresponding to the services associated with the zone to which it belongs. Step 91 is then repeated. According to some embodiments, steps 91 to 93 are successive. According to other advantageous embodiments, steps 91 to 93 are carried out simultaneously and in parallel (data being received at the same time as OFDM symbols corresponding to other previously received data, are constructed and OFDM symbols are broadcast ). FIG. 10 shows a reception method implemented in the receiver 5 adapted to receive signals emitted by the transmitter 2 according to a particularly advantageous embodiment of the invention. If the receiver 5 receives signals emitted by the transmitters 101 to 105, it is also adapted to decode these signals. During an initialization step 100, the various parameters of the receiver 5 are updated. In particular, the parameters corresponding to the transmitted data and the corresponding sub-carriers are initialized in any way (for example, following the reception of initialization messages sent by one or more servers, transmitters or other element of the system 1, or again, by commands from a user). Then, during a reception step 101, the receiver 5 receives OFDM signals transmitted by the transmitter 2. The received signals comprise first signals of the SISO type or corresponding MIMO coded associated with a second code of a first dimension the first signals coming from the encoder 20; second MIMO coded signals associated with a second code of a second dimension, the second signals coming from the encoder 21. The first dimension Ntx 'is strictly smaller than the second dimension. A first set 61 of subcarriers carries the first signals as illustrated in FIG. 7. A second set of subcarriers 72 carries the second signals as illustrated in FIGS. 7 and 8, the first and second sets 61 and 72 of subcarriers. being disjointed. Then, during a reception step 102, the receiver 5 decodes the signals received during the step 101. Advantageously, the receiver 5 decodes each received OFDM symbol for each set of subcarriers 61 and 72. In a particular embodiment, the receiver separately decodes the first and second signals sequentially over time using common hardware resources or in parallel using resources dedicated to each service.

Of course, the invention is not limited to the embodiments described above. In particular, when the invention is applied to broadcasting, it is not limited to broadcasting two services but may be extended to more than two services (for example three, four ... ten or more). In a given geographical area, at each service, a transmitter belonging to this zone constructs OFDM symbols by associating with each service a set of dedicated subcarriers. According to one variant, several services associated with the same zone are grouped and associated with the same set of sub-carriers.

As mentioned above, the invention generally applies to the transmission of data sets and in particular to sets of two, three or more generally any number of data sets. Here, a set of data corresponds in particular to a service (for example audiovisual), to data coming from the same source, to data coming from, to the same application and / or different types of transmission (for example distribution of a first set of data and point-to-point or point-to-multipoint transmission of a second set of data). According to the invention, different types of transmission (for example point-to-point, point-to-multipoint or broadcast can advantageously be combined.) The spectrum of sets of sub-carriers allocated to data sets each associated with a specific zone is advantageously dissociated when specific areas intersect: for example if areas 11 and 12 overlap and if data from a first set of data covers both areas 11 and 12 and data from a second (respectively third) set of data covers the zone 11 (respectively 12) without covering the zone 12 (respectively 11), advantageously, the transmitters of the zone 11 (respectively 12) allocate a first set of sub-carriers for the first service and a second (respectively third) together subcarriers for the second (respectively third) service The first, second and third sets do not overlap, allowing avoid disturbances in overlapping geographic areas. The choice of subcarriers can for example be made according to a message sent by a transmitter, a receiver (via for example a return channel), a user or any other means. According to an alternative embodiment associated with different coverage areas, the local areas 11 and 12 are not totally covered by the zone 10 and only partially cut the zone 10 (receivers that can be in both the zones 10 and 11, or only in one of zones 10 and 11). 10

Claims (9)

REVENDICATIONS1. Method for transmitting data, implemented in at least one transmitter (2, 111 to 113, 121, 122), characterized in that it comprises five steps: OFDM symbol construction (92), from first data and second data, a first set of subcarriers (61) carrying information representative of said first data in each OFDM symbol; a second set of subcarriers (72) carrying information representative of said second data in each OFDM symbol, said first and second sets of subcarriers being disjoint; Said construct comprising: a first encoding of the first data by a first code of the SISO type or MIMO encoded, the first code having a first dimension; a second coding of the second data by a second code of the MIMO type, the second code having a second dimension, said first dimension being strictly less than said second dimension; OFDM modulation of the first data encoded by the first code and second data encoded with the second code and transmission (93) OFDM symbols for a plurality of receivers. 2. Method according to claim 1, characterized in that said first coding is of dimension equal to 1. 3. Method according to claim 2, characterized in that said first coding corresponds to an identity coding. 35 4. Method according to claim 3, characterized in that said construction comprises a weighting of the first data, generating a plurality of weighted symbols from an incoming symbol and an OFDM modulation of each weighted symbol. 5. Method according to claim 1, characterized in that said first coding is of dimension strictly greater than 1 and comprises a generation of a plurality of symbols coded from an incoming symbol and in that said construct comprises an OFDM modulation. of each coded symbol. 6. Method according to any one of claims 1 to 5, characterized in that it comprises steps of: receiving said first data from a first source; and receiving said second data from a second source separate from said first source. 7. Method according to any one of claims 1 to 6, characterized in that said first data are associated with a first broadcast service and in that said second data are associated with a second broadcast service distinct from said first service. 8. Method of receiving data, implemented in at least one receiver (5), characterized in that it comprises the steps of: receiving (101) OFDM symbols representative of first data and second data, of decoding (102) received OFDM symbols, a first set of subcarriers (61) carrying information representative of said first data in each OFDM symbol; A second set of subcarriers (72) carrying information representative of said second data in each OFDM symbol, said first and second sets of subcarriers being disjoint; said decoding comprising an OFDM demodulation of the received symbols and providing first decoded data and second decoded data: said first data being encoded by a first code of the SISO type or MIMO coded, the first code having a first dimension; said second data being coded by a second code of the MIMO type, the second code having a second dimension, said first dimension being strictly less than said second dimension; 9. Data transmission apparatus: characterized in that it comprises means (construction) (92) OFDM symbols, from first data and second data, a first set of subcarriers (61) carrying information representative of said first data in each OFDM symbol; a second set of subcarriers (72) carrying information representative of said second data in each OFDM symbol, said first and second sets of subcarriers being disjoint; said construct comprising: a first coding of the first data by a first code of the SISO type or MIMO coded, the first code having a first dimension; a second coding of the second data by a second code of the MIMO type, the second code having a second dimension, said first dimension being strictly less than said second dimension; OFDM modulation of the first data encoded by the first code and second data encoded with the second code and transmission (93) of the OFDM symbols for a plurality of receivers.