Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L5/00—Arrangements affording multiple use of the transmission path
  • H04L5/0001—Arrangements for dividing the transmission path
  • H04L5/0014—Three-dimensional division
  • H04L5/0016—Time-frequency-code
  • H04L5/0021—Time-frequency-code in which codes are applied as a frequency-domain sequences, e.g. MC-CDMA
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/69—Spread spectrum techniques
  • H04B1/707—Spread spectrum techniques using direct sequence modulation
• • 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
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/18—TPC being performed according to specific parameters
  • H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/18—TPC being performed according to specific parameters
  • H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
  • H04W52/241—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters taking into account channel quality metrics, e.g. SIR, SNR, CIR, Eb/lo
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/18—TPC being performed according to specific parameters
  • H04W52/26—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service]
  • H04W52/267—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service] taking into account the information rate
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J13/00—Code division multiplex systems
  • H04J13/0007—Code type
  • H04J13/004—Orthogonal
  • H04J13/0048—Walsh
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L5/00—Arrangements affording multiple use of the transmission path
  • H04L5/003—Arrangements for allocating sub-channels of the transmission path
  • H04L5/0058—Allocation criteria
  • H04L5/006—Quality of the received signal, e.g. BER, SNR, water filling
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L5/00—Arrangements affording multiple use of the transmission path
  • H04L5/003—Arrangements for allocating sub-channels of the transmission path
  • H04L5/0058—Allocation criteria
  • H04L5/0064—Rate requirement of the data, e.g. scalable bandwidth, data priority

Definitions

• the field of the invention is that of multi-carrier signals, and in particular signals combining multi-carrier and code division access modulation.
• the invention presents a technique for transmitting such a multicarrier signal (for example according to a modulation of OFDM type, in English “Orthogonal Frequency Division Multiplex”), and to spread spectrum (for example of type access code division multiple CDMA, in English "Code
• the invention relates to the allocation of source data for forming such multi-carrier and spread-spectrum signals such as MC-CDMA (Multi Carrier Code Division Multiple Access) signals.
• MC-CDMA Multi Carrier Code Division Multiple Access
• the invention finds particular applications in all fields implementing transmission and broadband communication techniques.
• the invention applies mainly, but not exclusively, to communications in cable networks, such as xDSL type networks (Digital Subscriber Line), powerline communications (home automation, electrical distribution network, ...), intra-vehicle connections, etc.
• cable networks such as xDSL type networks (Digital Subscriber Line), powerline communications (home automation, electrical distribution network, ...), intra-vehicle connections, etc.
• the invention also finds applications in wireless communications, such as radiocommunications inside buildings, communication beams, etc.
• a modulation is determined to be applied to each carrier of a multicarrier signal to distribute the source data, based on the quality of the link (quality of the propagation channel) and the desired link budget.
• the OFDM multiplex carriers have a low link budget (ie a signal-to-noise ratio which is too low to transmit data). bits of information) can not be exploited. We can not transmit information about these carriers.
• an object of the invention is to propose a transmission technique of a multicarrier and spread spectrum signal making it possible to optimize the distribution of the source data on the spreading codes.
• an object of the invention is to provide such a technique for attributing an optimum power and / or rate to each of the spreading codes.
• the invention also aims to implement such a technique to optimize a noise margin of the transmission system for a given spreading code length.
• This noise margin corresponds in particular to the maximum possible difference between the real performance of the transmission system, operating with a certain bit error rate, and the theoretical performance of the transmission system, defined by the Shannon limit.
• Yet another object of the invention is to provide such a transmission technique having better performance compared to the techniques of the prior art, and in particular a better resistance to electromagnetic jammers. 4. Presentation of the invention
• such a method comprises a step of assigning a power or an energy and / or a flow rate to each of the spreading codes, as a function of information representative of the noise and / or information representative of the quality of the link, said allocation step taking into account a target bit rate (overall bit rate).
• the invention is based on an entirely new and inventive approach to the distribution of source data, intended to form a signal, for example of the MC-CDMA type, on the carriers and the spreading codes associated with such a signal.
• the invention makes it possible to determine the number U of spreading codes required, the power or energy E 11 assigned to each of these codes (where the power corresponds to the energy E 11 per unit time), and / or the rate R 11 allocated to each of these codes, as a function of information representative of the noise, in particular of the signal-to-noise ratio, and / or information representative of the quality of the link, that is, that is, the estimation of the transmission channel, and a target bit rate R.
• the quality of the link is in particular a function of the estimation of the coefficients h t of the transmission channel, and the variance N 0 of the noise, supposed white Gaussian.
• the invention makes it possible to optimize the margin of noise ⁇ of the system, by optimizing the distribution of the energy E 11 and / or the flow rate R 11 assigned to each of the U spreading codes.
• This noise margin ⁇ corresponds in particular to the maximum difference between the real performance of the transmission system and the theoretical limit performance, as defined by the Shannon theorem.
• the bit error rate must remain lower than this quality, even in the presence of noise.
• the target rate R is determined in particular according to the desired application.
• the target bit rate R to be reached can be 512 bits per OFDM symbol.
• this target bit rate R corresponds to the sum of the bit rates R 11 allocated to each of the U spreading codes during the attribution step:
• the transmission technique according to the invention based on an optimal allocation of resources is implemented on the basis of an algorithm having a linear structure, unlike the noise margin maximization algorithms in the context of the invention.
• DMT which have an iterative structure.
• the allocation step can also take into account a desired QoS quality of service, determined from a bit error rate (BER) to be respected, the coding gain provided by the channel coding and the various impairments of the transmission and reception system that can be taken into account in the noise margin F, etc., hence the necessary optimization of resources to ensure the best possible service under the performance constraints required in reception.
• BER bit error rate
• the allocation step may further take into account an overall power spectral density.
• This overall power spectral density which can in particular be defined by a standardization organization, defines a power mask that the MC-CDMA signal must not exceed. From this spectral density of power and the bandwidth of a sub-carrier, it is possible to define a power or global energy E to be distributed between the different codes. It is recalled that a multi-carrier signal is formed of a temporal succession of symbols consisting of a set of data elements, each of the data elements modulating a carrier frequency of the signal, one of the carrier frequencies modulated at a given instant. by one of the data elements being called subcarrier.
• This global energy E corresponds to the sum of the energies E 11 assigned to each of the U spreading codes during the attribution step:
• the step of allocating a bit rate comprises, for each of the spreading codes, a step of selecting a modulation for at least some, and in particular all, subcarriers of the signal.
• the source data to be transmitted are modulated according to a quadrature amplitude modulation MAQ, such as MAQ4, MAQ16, MAQ64,
• the allocation step comprises the following sub-steps: verification of the feasibility of the target rate R; if the target rate is achievable: o determination of the rate to be assigned to each of the spreading codes:
• target bit rate R is strictly less than twice the length k of the spreading codes, assigning two bits on each of R / 2 codes;
• the target rate R is not feasible, that is to say if Theorem 2 presented in Appendix 2 is not respected, it is desirable to modify the desired QoS quality of service and / or the target rate R desired, in order to respect this theorem 2.
• the value of the target rate R must be compared with the length of the spreading codes. If this value is strictly less than twice the length of the spreading codes, the distribution is expressed by the relation R - - x 2, this
• the allocation step also comprises a substep of determining the energy E 11 representative of the power, or directly of the power (energy per unit of time), to be assigned to each of the spreading codes. , expressing itself in the form:
• R 11 the rate assigned to said spreading code u
• the invention also relates to a device for transmitting a signal implementing the transmission method described above.
• the invention also relates to a method for receiving a multi-carrier and spread spectrum signal MC-CDMA, comprising a step of demodulating a signal transmitted according to the transmission method described above, as well as a reception device corresponding.
• the invention finally relates to a multi-carrier and spread spectrum signal MC-CDMA, transmitted by a transmission device and / or received by a reception device as described.
• FIG. 1 presents an MC-CDMA transmission chain implementing the transmission technique based on the allocation of information according to the invention
• FIGS. 2A to 2D illustrate the noise margin ⁇ as a function of the length k of the codes, for two target rates R and two lengths L of the ADSL channel, in a transmission chain according to FIG. 1
• FIGS. 3A to 3D illustrate the optimal length k of the codes as a function of the length L of the ADSL channel for four target rates R
• Figures 4A to 4D show the performance of the invention compared to the performance of the techniques of the prior art.
• the general principle of the invention is based on the allocation of source data intended to form a MC-CDMA multi-carrier and spread spectrum signal, based on the determination of a number of spreading codes, a distribution of source data on codes, and a distribution of energies or powers
• the invention presents an information allocation algorithm applied to multi-carrier waveforms and using spread spectrum.
• spreading codes are allocated to groups of carriers, and the spreading code associated with each group of carriers is optimized to obtain a target bit rate R.
• a desired QoS quality of service eg a BER of 10 "7
• the bit error rate must remain below this quality, even in the presence of noise.
• MC-CDMA systems are well known, and are described in particular in documents 1 and 2 cited in Appendix 1.
• an MC-CDMA signal can be seen as the inverse Fourier transform of a CDMA signal.
• the length k of the spreading codes is equal to the number of subcarriers used.
• the spreading codes are orthogonal codes that can be extracted from Hadamard matrices of dimensions k x k.
• the number of codes used is U ⁇ k.
• FIG. 1 shows a simplified representation of an MC-CDMA transmission chain comprising a transmitter 11, a transmission channel 12, and a receiver 13, according to a preferred embodiment of the invention.
• a bit stream 111 composed of the source data to be formatted, enters a quadrature amplitude modulation block MAQ 112.
• the order of the modulation to be applied to each of the carriers carrying the source data is in particular determined. from a centralized allocation block 14, according to this preferred embodiment of the invention.
• the number U of spreading codes, as well as the energy E 11 allocated to each of these codes, are also determined from the centralized allocation block 14.
• the CDMA C • X signal thus obtained is then modulated according to a modulation OFDM in block 114, to form a MC-CDMA signal, and then converted to an analog signal in CNA block 115, according to this preferred embodiment.
• a static or quasi-static transmission channel 12 is considered, and the OFDM component of the MC-CDMA signal adapted to the transmission channel 12 is assumed.
• the channel 12 can then be modeled in the frequency domain with a coefficient by sub-carrier, as proposed in document 3 cited in appendix 1.
• the analog signal is converted into a digital signal in the CAN block 131, then undergoes an OFDM demodulation, using a Fourier transform and the suppression of the guard interval, in the block 132. then uses an equalizer ZF 133 (in English "zero forcing", in French
• the equalized signal is then despread in a CDMA despreading block 134, taking into account the number U of spreading codes, and the energy E 11 assigned to each of these codes, determined from the centralized allocation block 14 .
• the signal Y 11 received by each of the spreading codes is then subjected to a MAQ demodulation 135, taking into account the order of the modulation determined from the centralized allocation block 14.
• the allocation block 14 thus makes it possible to determine: the number U of spreading codes to be used;
• R 11 to be assigned to each of the spreading codes; and the energy E 11 to be assigned to each of the spreading codes, based on information representative of the noise and / or information representative of the quality of the link, and of the target rate R to be reached.
• the MC-CDMA system is thus sized according to this target bit rate, which makes it possible to optimize the noise margin. So we are not trying to maximize the bit rate, but to optimize the noise margin by reaching this target bit rate. More precisely, the information representative of the quality of the link depends on the quality of the estimation of the transmission channel, that is to say the parameters h t and N 0 .
• the information representative of the noise depends in particular on the link budget, that is to say the signal-to-noise ratio at the output of the transmission system.
• the centralized allocation block 14 takes into account a target bit rate R and a quality of service QoS (for example a BER of the order of 10) to be reached, defined depending on the intended application, and an overall power spectral density, represented by the overall energy E, not to be exceeded, defined by the standardization bodies. It is thus assumed, according to this preferred embodiment, the use of a power mask on transmission, limiting the overall power spectral density (DSP) of the transmitted signal. This constraint is important since it is within this framework that the allocation of information is carried out.
• the amplitude of the received signal then depends on the number of subcarriers k.
• the spread brings power, which is consistent with the constraint, not in total power transmitted, but in spectral power density.
• the invention makes it possible in particular to find the number of spreading codes, the distribution of the modulations on the codes, and the distribution of the energies attributed to these codes, under the constraint of a target bit rate and possibly under duress. a spectral density of power.
• the so-called "optimal" distribution is considered to maximize the noise margin of the transmission system for a given code length, ie to maximize the difference between the actual performance of the transmission system and the theoretical performance obtained. by the Shannon boundary.
• the maximum number of usable subcarriers is 220, and an example of target rate R is 512 bits per OFDM symbol. Considering Document 4 quoted in Appendix 1, the maximum order modulation is 32768 MAQ.
• R 11 the flow rate assigned to the spreading code u; k the length of the spreading code; h ⁇ the estimation of the coefficients of the transmission channel; ⁇ the noise margin of the transmission system; F the noise margin of the MAQ modulations, as described in Document 3 cited in Appendix 1;
• E 11 the energy assigned to the spreading code u.
• noise margin Y can also take into account the gain provided by the channel coding.
• equation (2) the unknowns are R 11 , E 11 , U, and it is sought to optimize the noise margin ⁇ of the transmission system.
• first u l summation
• second summation 2 ⁇ R 1 u 1 - ⁇
• DSP power spectral density
• R / 2 codes carrying 2 bits, which corresponds to quadrature amplitude modulation of order 4 (MAQ 4).
• the centralized allocation algorithm 14 has the following structure:
• the MC-CDMA system does not, in itself, make it possible to obtain a better noise margin than that obtained with the DMT systems of the prior art. But added to the noise margin, the spreading gain gives the system greater robustness.
• the invention makes it possible to further improve these results.
• FIGS. 2 to 4 show a few simulation results of an exemplary application of the invention in the ADSL context.
• FIGS. 2A to 2D illustrate in particular the noise margin ⁇ as a function of the length k of the codes, for two target rates R and two lengths L of the ADSL channel.
• FIG. 2A shows the evolution of the noise margin ⁇ as a function of the length k, for a rate R of 512 bits / symbols and a channel length L of 2000 meters
• FIG. 2B for a flow rate R of 512. bits / symbols and an L-channel length of 3000 meters
• Figure 2C for a R-bit rate of 1024 bits / symbols and an L-channel length of 2000 meters
• Figure 2D for a R-bit rate of 1024 bits / symbols and a L-channel length of 3000 meters.
• the optimum value of k is about 130; for the configuration of FIG. 2B, the optimum value of k is about 90; For the configuration of FIG. 2C, the optimum value of k is about 175; and for the configuration of FIG. 2D, the optimum value of k is about 125.
• FIGS. 3A to 3D illustrate the optimal length k of the codes as a function of the length L of the ADSL channel for four target rates R (304 bits / symbols - FIG. 3A, 512 bits / symbols - Figure 3B, 1024 bits / symbols - Figure 3C, and 2048 bits / symbols - Figure 3D).
• FIGS. 4A to 4D illustrate the performances of the invention in an MC-CDMA system implementing an allocation of a bit rate and / or a power to each of the spreading codes according to the invention, compared to the performance of the techniques of the prior art in a DMT type system.
• FIGS. 4A to 4D illustrate the margin of the systems in dB as a function of the length of the ADSL channel for four R target rates (304 bits / symbols - FIG. 4A, 512 bits / symbols - FIG. 4B, 1024 bits / symbols - FIG. 4C, and 2048 bits / symbols - FIG. 4D). So :
• curve 1 (+) presents the noise margin of a transmission system according to the DMT technique as a function of the length L of the channel
• curve 3 (V) presents the noise margin of a transmission system according to the MC-CDMA technique with an optimal code length k for each length of the channel, with the noise margin ⁇ in full lines, and the margin of noise combined with the spreading gain in broken lines.
• the invention makes it possible to optimize the noise margin ⁇ of the system, thanks to an optimal distribution of the energies E 11 and flow rates R 11 on the U spreading codes.
• the invention gives the communications greater robustness in environments disturbed by electromagnetic jammers.
• this transmission technique based on a debit assignment and / or energy to each of the spreading codes offers all its interest in systems multiplexing several elementary MC-CDMA modules in the frequency domain, as presented in document 8 cited in appendix 1.
• This transmission technique can also be implemented for different channels (ADSL, PLC), in a point-to-multipoint or multipoint-to-point context (multi-user communication). respectively broadcast or access), especially when the multiplexing is frequency.
• the overlay layer related to the multi-user context is not part of the present invention.
• the invention thus provides greater robustness to communications in environments disturbed by electromagnetic jammers, and in particular to wireline communications.
• radiocommunications inside buildings, as well as communication beams can be made through static channels, relative to the flow of communications.
• the invention may be envisaged for certain wireless communications.
• the invention can also be used in systems where the number of subcarriers is greater than the length of the codes.
• ADSL Digital Subscriber Line

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• 2006
  • 2006-09-14 CA CA002622774A patent/CA2622774A1/fr not_active Abandoned
  • 2006-09-14 US US12/066,959 patent/US20080260003A1/en not_active Abandoned
  • 2006-09-14 WO PCT/EP2006/066385 patent/WO2007031568A1/fr active Application Filing
  • 2006-09-14 EP EP06793536A patent/EP1925105A1/de not_active Withdrawn

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