WO2011051629A2

WO2011051629A2 - Reception method and receiver for encoded serial digital transmission over a non-stationary channel

Info

Publication number: WO2011051629A2
Application number: PCT/FR2010/052318
Authority: WO
Inventors: Caroline Amiot-Bazile; Jérôme Lacan; Wilfried Chauvet; Frédéric LACOSTE
Original assignee: Centre National D'etudes Spatiales (C.N.E.S.)
Priority date: 2009-10-30
Filing date: 2010-10-28
Publication date: 2011-05-05
Also published as: WO2011051629A3; FR2952254A1; FR2952254B1

Abstract

The invention relates to a method for receiving data over a noisy channel with non-stationary attenuation in which at least one value representing an error rate ER of the received bit stream is produced without decoding. A mutual information value I_k is produced (34) according to a predetermined transmission quality function Q_k, and the average mutual information <I_n > is produced (35) for every encoded word received; then at least one error rate ER value of the received bit stream is produced (38) according to each average mutual information <I_n > value using a predetermined standard function on a channel with added white Gaussian noise.

Description

RECEIVING METHOD AND RECEIVER FOR DIGITAL TRANSMISSION CODED SERIES ON NON-STATIONARY CHANNEL

The invention relates to a reception method and a receiver for coded and modulated serial digital transmission over a non-stationary attenuation noisy channel between:

an emitter comprising:

a coding device adapted to generate, from a stream of bits to be transmitted, called said transmitted bits stream, at least one stream of coded words, called transmitted streams of coded words, resulting from the coding, according to at least one method; predetermined coding, of said transmitted bit stream,

a modulation device adapted to generate at least one modulated symbol stream, said transmitted stream of modulated symbols, according to a predetermined modulation scheme (in particular PSK phase modulation and / or QAM quadrature amplitude modulation), on at least a carrier signal, each transmitted stream of modulated symbols being representative of at least a part of each transmitted stream of coded words,

a device for transmitting, on a non-stationary attenuation attenuated channel, each transmitted stream of modulated symbols,

- and a receiver comprising:

a reception device adapted to receive, for each transmitted stream of modulated symbols on said channel, a stream of modulated symbols, said received stream of modulated symbols,

a demodulation device adapted to generate at least one stream of coded words, said received stream of coded words, from each received stream of modulated symbols,

- A decoding device adapted to generate a bit stream, said bits received stream, by decoding, according to the coding method implemented by the transmitter, each received stream of codewords.

The coding of such a digital transmission makes it possible to enhance its reliability. In various applications, the transmission channel used, generally of wireless type (radio frequencies and / or microwaves ...) has a non-stationary attenuation, that is to say which varies substantially in time during the transmission. of each code word. This phenomenon is reinforced by the presence of a channel interleaver.

This is the case, for example, with mobile receiver terminals (for example of the GPRS or UMTS type, Satellite DVB-SH) and / or when the coding is of the "turbocode", LDPC or iterative type. Indeed, the channel conditions and its performance can be fluctuating depending on the position of the receiver. In addition, when an interleaver is provided, the function of such an interleaver has the effect of reducing variations in attenuation seen by code word.

Nevertheless, in general numerical data representative of variations over time of attenuation and noise of the channel are available. These digital data can come from the known characteristics of the interleaver, or from known statistical characteristics from the physical properties of a channel. The channel data is estimated from the received signal on either pilot symbols or modulated symbols. Successive signal-to-noise ratios by codeword are reconstructed from the channel interleaver.

In this general context, a problem that arises is the prediction of the performance of the transmission, that is to say the determination, without performing the decoding, of an error rate ER (error rate BER bit and / or PER word error rate) in the bit stream received as a function of attenuation variations of the channel during the reception of each coded word.

Such a performance prediction makes it possible in particular to implement appropriate protocols to ensure good transmission quality: automatic retransmission request (so-called ARQ technique) possibly hybrid (H-ARQ); incremental redundancy (IR); combination of Chase; adaptation of the characteristics of the transmitter and / or the transmission link: choice of the coding method, signal strength, modulation scheme ...

A first known method of predicting performance to take into account the attenuation variations of a channel consists in determining an average value of SNR signal-to-noise ratio on each received codeword. In particular, the same processing is applied for two different coded words having the same average value of the signal-to-noise ratio but different attenuation variations. This method provides in practice overly optimistic performance predictions.

In a second known method, a bit error rate BER is determined for each elementary bit of each coded word received from an average value of the average signal-to-noise ratio Ej N _t for this elementary bit, itself calculated from an average value of the signal-to-noise ratio EN _t of each received modulated symbol divided by the number of bits per symbol, the value of BER being obtained from a known function (in the form of a curve or a a table) giving the BER value as a function of the signal-to-noise ratio on an additive Gaussian white noise channel. An average of the bit error rate is then calculated for the received code word and is used as a performance criterion. This method is more accurate (that is, provides more realistic results) than the previous one but provides predictions that in practice turn out to be too pessimistic.

EP 1564924 discloses a method in which each received coded signal is divided into a plurality of predetermined fixed length segments, and the average value over the signal to noise ratio per symbol frame (EN _t ) p is obtained by calculation for each segment of a parameter C _m using a numerical convex function obtained empirically according to the modulation (BPSK or QPSK) applied to the average value

of each segment, then calculating an average value C of this parameter on the frame, then inverse computation with the inverse function. Ic 1. Then, the average value on the average signal / noise ratio frame (E] y / N _t ) p for each elementary bit is obtained from a table, and the error rate per FER frame is obtained. based on a given reference curve on an additive Gaussian noise channel.

This method is based on a numerical approximation of the function f. It is limited to the modulation schemes for which this digital function is given in this document, namely BPSK and QPSK. It is therefore not applicable to other modulation schemes. Moreover, it does not take into account channel attenuation variations at the symbol level, but with a granularity at segments of determined length. Its accuracy depends in fact on the good adaptation of the fixed size of each segment to the dynamics of the attenuation variations, adaptation that can not be adjusted beforehand according to each application.

In this context, the invention aims to overcome all these drawbacks by proposing a method and a receiver in which a performance prediction is obtained without performing the decoding, both by taking into account the true variations of attenuation of the channel, and with good accuracy of results, high reliability and fast and light computing treatments.

The invention also aims at providing such a method and such a receiver that can be applicable to any modulation scheme, including other than BPSK or QPSK, in particular 2 "-PSK n> 3 or QAM.

To this end, the invention relates to a method for receiving digital data transmitted over a coded and modulated serial digital transmission over a non-stationary attenuation attenuated channel, in which:

a stream of modulated symbols, said received stream of modulated symbols, corresponding to an emitted stream of modulated symbols on said channel, is received by a reception device,

at least one stream of coded words, said received stream of coded words, is generated by demodulation from each received stream of modulated symbols,

a stream of bits, called bits received stream, is generated by decoding each received stream of coded words, according to a decoding method corresponding to a coding method implemented on transmission on the channel of the transmitted stream of symbols modulated,

method in which at least one value representative of an error rate ER of the received bit stream is generated without performing the decoding, from stored digital data representative of variations over time of the attenuation, and / or the noise from the channel, and / or interference,

characterized in that

digital data are memorized making it possible to determine:

at least one value, called transmission quality Q, of formula c & E, where c & represents each attenuation value of the channel over time, where k is a time index, E _s represents an average energy per emitted symbol and No represents a spectral density of Gaussian white noise on the channel,

- and changes over time of said transmission quality (¾ F ^or each received symbol of the received stream of modulated symbols,

and in that :

in a first step, for each value of said transmission quality Q.sub.i, a mutual information value I.sub.i is produced according to a predetermined function of said transmission quality Q.sub.i,

in a second step, for each codeword of the received stream of code words, a mean of mutual information is developed by averaging the different mutual information values 1 i determined in the first step for the different values taken by said transmission quality (¾ on the said coded word,

in a third step, for each coded word of the received stream of coded words, at least one value of the error rate ER of the received stream of bits is elaborated from each value of the mutual information mean determined in the second step, and using stored data representative of variations of an equivalent error rate according to at least one function, called standard function, of the signal-to-noise ratio, each standard function being predetermined for the coding devices and decoding on an additive Gaussian white noise channel.

In a first possible and advantageous embodiment of the invention, each mutual information value 1 is determined according to the function defined by the following formula (I):

mlm

-I ^E S

M being the cardinal of the alphabet ^ ^- {^ o '' * * * '^ Μ-ί} modulated symbols. Advantageously and according to the invention, this analytical formula can be discretized for its evaluation by digital treatment, for example according to the function defined by the following formula (II):

threshold threshold

- AuAv Σ / (# Aw, rAv) log ₂ (/ (4Aw, rAv))

q = - threshold r = - threshold threshold =

. . . threshold

and Au = Av = 2- β

In a second possible and advantageous embodiment of the invention, each mutual information value 1 ^ is

determined according to the function of the mutual information computed between the j th bit (^ ^{≤ J≤ p ~} ) of the emitted symbol and the received symbol that function being defined by the following formula (III):

u = -∞ v = - °°

+ {g _j (u, v) log ₂ (g _j (u, v)) dudv

v = -

and

M being the cardinal of the alphabet A-

modulated symbols

L m ^{) Q} <m≤2 ^p -1 £ _as the set of standardized symbols ^m of p bits 0 ^{≤ ≤} P ^_ 1 whose bit numbered m is equal to 0,

L m io≤m≤2 ^p £ -1 _as the set of bits p of standardized symbols ¹⁷¹ ^ ⁰ ^"1

whose bit numbered m is 1.

Advantageously and according to the invention, this analytical formula can be discretized for its evaluation by digital processing, by

example according to the function defined by the following formula (IV):

threshold

Σf (qAu, rAv) log ₂ (f (qAu, rAv))

r = - threshold

threshold threshold

Σ g. (qAu, rAv) log ₂ (g _j (qAu, rAv))

threshold threshold threshold

. . _ threshold

and Au = Δν = 2

β

Moreover, advantageously and according to the invention, the The attenuation values of the channel over time are measured values - in particular by the receiver - as and when the coded words are received.

In addition, advantageously and according to the invention, a channel attenuation value Ck and / or a value of the transmission quality (¾ is (are) elaborated for each symbol of the received stream of modulated symbols.

Advantageously and according to the invention, in said third step:

an equivalent signal-to-noise ratio value SNR _eq on the received code word is determined from said mutual information mean by the inverse function 1 ^ ¹ ,

then each ER error rate value is obtained from said equivalent signal-to-noise ratio value SNR _eq and said stored data representative of variations of an equivalent error rate according to a predetermined standard function for the coding devices and decoding on an additive Gaussian white noise channel. Other embodiments are possible.

Furthermore, advantageously and according to the invention, the mutual information values 1 and / or the mutual information mean and / or each error rate ER of the received bit stream is (are ) developed by the receiver.

Furthermore, advantageously a method according to the invention is also characterized in that a deinterleaving is performed after demodulation of the symbols of the received stream of modulated symbols so as to form each coded word of the received stream of coded words, and in that each mutual information value 1 ^ and / or the mutual information mean and / or the error rate ER of the received stream of bits is elaborated for each coded word obtained at the end of such a deinterlacing.

In addition, advantageously and according to the invention, for each coded word of the received stream of coded words, a control signal of the decoding device is elaborated as a function of each value of the error rate ER of the received stream of bits.

Advantageously and according to the invention, for each coded word of the received stream of coded words, a single value of the error rate ER of the received stream of bits is developed from a single standard function, and the control signal is adapted. to activate the decoding device if said value of the error rate ER of the bit stream received is less than a predetermined threshold value.

As a variant, advantageously and according to the invention, for each coded word of the received stream of coded words, a plurality of series of values of the error rate ER of the received stream of bits are elaborated from a plurality of standard functions, each standard function corresponding to a decoding method chosen from a plurality of predetermined decoding methods, and said control signal is designed to activate the decoding device according to the decoding method for which said value of the ER error rate of the received stream of bits is the closest to a predetermined threshold value while being lower than this threshold value.

Advantageously and according to the invention, the decoding methods of the same plurality of decoding methods differ from each other only by a number of decoding iterations.

The invention also extends to a receiver for encoded and modulated serial digital transmission over a non-stationary attenuation attenuated channel, comprising:

a receiving device adapted to receive modulated symbol streams, called received streams of modulated symbols, corresponding to transmitted streams of modulated symbols on said channel,

a demodulation device adapted to generate at least one stream of coded words, said received stream of coded words, from each stream received modulated symbols,

a decoding device adapted to generate a bitstream, said received bit stream, by decoding each received stream of coded words, according to a decoding method corresponding to a coding method implemented at the emission of the transmitted stream; symbols modulated on said channel,

said receiver comprising a channel performance prediction module adapted to develop without performing the decoding, from stored digital data representative of time variations of attenuation and / or noise of the channel and / or interference, to the minus a value representative of an error rate ER of the received stream of bits,

characterized in that, digital data being stored for determining:

at least one value, called transmission quality Q ^, of formula E / No, where each channel attenuation value is represented over time, where k is a time index, E _s represents an average energy per emitted symbol, and No represents a spectral density of Gaussian white noise on the channel,

- and changes over time of said T ^o transmission of each symbol received quality of the received stream of modulated symbols,

said channel performance prediction module is adapted to:

in a first step, elaborating for each value of said transmission quality Q 1, a mutual information value 1 according to a predetermined function of said Q transmission quality,

in a second step, for each coded word of the received stream of coded words, elaborating an average of mutual information, by averaging the different values of mutual information 1 ^ determined in the first step for the different values taken by said transmission quality on said coded word,

in a third step, for each coded word of the received stream of coded words, elaborating at least one value of the error rate ER of the stream received from bits of each value of the mutual information average determined in the second step, and using stored data representative of variations of an equivalent error rate according to at least one function, called standard function, of the signal-to-noise ratio, each standard function being predetermined for the coding and decoding on an additive Gaussian white noise channel.

A receiver according to the invention is also advantageously characterized in that it is suitable for the implementation of a method according to the invention.

Thus, in a first possible and advantageous embodiment of the invention, said channel performance prediction module is adapted to elaborate each mutual information value 1 ^ according to the function defined by the formula (I).

Advantageously and according to the invention, said channel performance prediction module is adapted to discretize this analytical formula for its evaluation by digital processing, that is to say to elaborate each mutual information value 1 ^ according to the formula ( II).

In a second possible and advantageous embodiment of the invention, said channel performance prediction module is adapted to develop each mutual information value 1 ^ according to the function defined by the formula (III).

Advantageously and according to the invention, said channel performance prediction module is adapted to discretize this analytical formula for its evaluation by digital processing, that is to say for develop each value of mutual information

mutual information calculated between the j th bit (- iP ^~ ^) of the symbol

transmitted and the received symbol being defined by the formula (IV).

A receiver according to the invention is also advantageously adapted to measure the attenuation values of the channel over time as and when the coded words are received. Advantageously and according to the invention it is adapted to develop a Q value, attenuation of the channel and / or a value of the transmission quality P ^or each symbol of the received stream of modulated symbols.

Moreover, advantageously and according to the invention, said channel performance prediction module is adapted for, in said third step:

developing a value of the equivalent signal-to-noise ratio SNR _eq on the coded word received from the said mutual information average

by the inverse function 1 ^ ¹ ,

and then elaborating the value of the ER error rate from said equivalent signal-to-noise ratio value SNR _eq and said stored data representative of variations of an equivalent error rate according to a function of the signal-to-noise ratio, this function being predetermined for the coding and decoding devices on an additive Gaussian white noise channel.

Advantageously and according to the invention, said performance prediction module is adapted to elaborate the mutual information values 1 and / or the mutual information mean and / or each error rate ER of the received stream of bits for each coded word from a de-interleaver module of the demodulation device.

In a first embodiment of a receiver according to the invention, said channel performance prediction module is adapted to elaborate, for each coded word of the received stream of codewords, a control signal of the decoding device according to each value of the error rate ER of the stream received bits. Advantageously and according to the invention, said channel performance prediction module is adapted to elaborate, for each coded word of the received stream of coded words:

a unique value of the error rate ER of the received stream of bits from a single standard function,

and said control signal for activating the decoding device if said value of the error rate ER of the received stream of bits is less than a predetermined threshold value.

In a second variant embodiment of a receiver according to the invention, said channel performance prediction module is adapted to elaborate, for each coded word of the received stream of code words:

a plurality of series of error rate values

ER of the received bit stream from a plurality of standard functions, each standard function corresponding to a decoding method selected from a plurality of predetermined decoding methods,

and said control signal so as to activate the decoding device according to the decoding method for which said value of the error rate ER of the received stream of bits is the closest to a predetermined threshold value while being lower than this threshold value.

The invention extends to a coded and modulated serial digital transmission device on a nonstationary attenuation attenuated channel between:

an emitter comprising:

a coding device adapted to generate, from a stream of bits to be transmitted, called said transmitted bits stream, at least one coded word stream, said coded word transmitted stream, resulting from the coding, according to at least one predetermined coding method, said transmitted bit stream,

a modulation device adapted to generate at least one stream of modulated symbols, said transmitted stream of modulated symbols, according to a predetermined modulation scheme, on at least one carrier signal, each transmitted stream of modulated symbols being representative of at least one part of each transmitted stream of codewords,

- and a receiver comprising:

at least one decoding device adapted to generate a bitstream, said received bit stream, by decoding each received stream of codewords, according to a decoding method corresponding to a coding method implemented by the transmitter,

said receiver comprising a channel performance prediction module adapted to develop without performing the decoding, from stored digital data representative of variations over time of attenuation and noise of the channel, at least one representative value of a error rate ER of the received stream of bits,

characterized in that the receiver is in accordance with the invention and implements a method according to the invention.

The inventors have found that the invention makes it possible in practice to obtain a fast and accurate performance prediction, and in particular considerably more precise than in all methods. previous known, while remaining as fast. This result is surprising, especially since there is no direct relationship between the mutual information on the coded bits and the performance of the decoder.

However, it is not so, and on the contrary, the calculation of this mutual information and its average on each coded word makes it possible in practice to take into account the temporal variations of attenuation with a great precision. It appears that two coded words having the same average mutual information have the same performance at the output of the decoder.

The value of the mutual information can even be elaborated from an analytical formula, the implementation of which is therefore simple and precise by numerical calculation, including for the calculation of the inverse function.

Moreover, these advantages provided by the invention make it possible to envisage its use in real time at a receiver to optimize its operation, and in particular to determine whether or not a received coded word must be decoded and, where appropriate , the minimum number of iterations to be used by the decoding module, in the case where the latter is of the iterative type (LDPC, turbocode, ...).

Thus, the invention makes it possible to envisage the production of a receiver whose performances are auto-adaptive and minimized according to the quality of transmission. Such a receiver has in particular the advantage of having a minimum energy consumption which is a considerable advantage for receivers embedded on mobile systems, in particular on space systems. Indeed, the reduction of energy consumption makes it possible on the one hand to save money in use, and on the other hand to minimize the performance requirements of the energy sources, and therefore their costs, their weight and their size. , or improve their operating life when it comes to a storage battery.

The invention extends to a non-stationary coded serial digital transmission method incorporating a reception method according to the invention, as well as to a non-stationary channel coded serial digital transmission device comprising a receiver according to the invention.

The invention also relates to a reception method, a receiver, a transmission method and a transmission device characterized in combination by all or some of the characteristics mentioned above or below.

Other objects, features and advantages of the invention will appear on reading the following description which refers to the appended figures representing, by way of non-limiting examples, embodiments of the invention and in which:

FIG. 1 is a block diagram showing a transmission device according to the invention incorporating a receiver according to the invention,

FIG. 2 is a schematic flow chart showing an embodiment of a reception method according to the invention,

FIG. 3 is a schematic diagram of examples of reference curves that can be used, according to different modulation schemes, for a predetermined function for determining a mutual information value on a Gaussian white noise additive-dependent channel; the signal-to-noise ratio of this channel,

FIG. 4 is a schematic diagram showing the use of a reference curve similar to FIG. 3 for performing a first step of a method according to the invention,

FIG. 5 is a schematic diagram showing the use of a reference curve similar to FIG. 3 for performing a first part of a third step of a method according to the invention,

- Figure 6 is a schematic diagram showing the use of a representative curve of a standard function for the execution of a second part of a third step of a method according to the invention. FIG. 1 generally represents a coded and modulated serial digital transmission device on a non-stationary attenuation attenuated channel. This device comprises a transmitter 11, a receiver 12 and a physical link 13 wireless forming the transmission channel. The physical link 13 may for example be a radio frequency link, such as for example linking mobile terminals such as cellular telephones, personal digital assistants, laptops, wireless cards, land vehicles, ships, aircraft, satellites, space probes or other space systems ... at a base station, itself fixed (terrestrial) or mobile (vehicle, satellite, ...) accessing a data transmission network such as the Internet network or any other private network. In general, the transmission can be bidirectional, that is to say that each mobile terminal is sometimes issuer, sometimes receiver.

The transmitter 11 comprises a first module 14 delivering data in the form of a bit stream (baseband signal) to be transmitted, said transmitted bit stream. This transmitted bit stream is supplied to a coding module which executes a predetermined coding method to form, from the bits, a stream of coded words, the so-called coded word stream. Such a coding method makes it possible in particular to increase the reliability of the transmitted data by increasing the redundancies while ensuring the correction of errors, that is to say the restitution of the initial data despite the disturbances that can undergo the channel 13 of transmission.

The invention applies to any coding method, and regardless of the exact nature of the coding method used. It may be in particular an encoding method chosen from the so-called LDPC (hollow matrix parity code) type processes, the turbocode type methods and the other iterative decoding coding methods. In most modern coding methods that achieve performance near the Shannon limit, the coding module comprises a plurality of coders-notably two coders-. Thus, the coding module 15 delivers coded words, which are then modulated, according to a predetermined modulation scheme, by a modulator circuit 18 which supplies a modulated symbol stream, called the transmitted stream of modulated symbols, to an interleaver circuit 17. the latter providing modulated and interleaved symbols to a radiofrequency transmitter circuit 19 capable of transmitting corresponding signals on the physical link 13.

The receiver 12 comprises a radiofrequency reception circuit 20 able to receive the signals transmitted via the physical link 13, and to deliver a stream of modulated and interleaved symbols, said received stream of modulated and interleaved symbols, to a de-interleaver circuit 22 which performs the inverse processing of the interleaver 17 of the transmitter 11, that is to say the progressive reconstitution of a de-interlaced modulated symbol stream, from the digital data stream from the reception circuit 20. The de-interleaver circuit 22 provides the de-interlaced modulated symbols to a demodulator circuit 21 adapted to apply a demodulation, the symbols received, according to the scheme and the modulation map used on transmission. The demodulator circuit 21 allows the progressive reconstitution of a stream of coded words, said stream of received codewords, from the stream of deinterleaved modulated symbols. These received coded words are then supplied to a buffer memory 23 and then progressively processed by a decoding module 25, comprising one or more decoders (in particular two decoders), and making it possible to deliver a stream 27 of received bits included in the decoder. signal conveyed by the physical link 13 and corresponding to the stream of bits emitted by the generator circuit 14.

The receiver 12 also comprises a channel estimation and equalization module 24, and a performance prediction module 28.

The channel estimation and equalization module 24 receives the flow of the de-interleaved modulated symbols from the de-interleaver circuit 22 and makes it possible to associate, with each received symbol, a plurality of quality values of transmission, each transmission quality value being representative of the quality of the transmission on the physical link 13 for a received symbol, that is to say for a part of the received coded word, this part corresponding to the received modulated symbols for which the attenuation of the channel remains the same. Thus, the channel estimation and equalization module 24 calculates the value of the transmission quality for each modulated symbol received.

To do this, the estimation module 24 performs the quality estimation as close as possible to the channel from the de-interlaced modulated symbols provided by the de-interleaver circuit 22 and / or from the modulated symbols supplied by the reception circuit 20 (before the deinterleaver circuit 22). It then reconstructs the attenuation of the symbols or groups of symbols of each code word as a function of the deinterleaver 22 used.

The modulated symbols transmitted at the output of the modulator block 18 (which carries out the mapping of the modulation, often referred to as the "mapping") belong to a constellation of complex symbols of cardinal M which is a power of 2 (M = 2 ^P ). They can only take M complex values. These symbols are then transmitted on channel 13. The effect of the channel on these symbols is twofold:

the channel 13 attenuates each symbol and is called the attenuation undergone by a symbol X

channel 13 assigns the attenuated symbol Xkj a Gaussian complex white noise additive of power N (2 on the imaginary and real channels, and thus represents a spectral density of a Gaussian white noise on the channel. thermal noise and possibly interference.

The symbol received at the input of the demodulator 21 is then called correspondant, thus corresponding to the symbol Χ transmitted attenuated and noisy. The attenuation values are provided by the estimation module 24 and equalization of the channel. If E _s represents an average energy per emitted symbol,

E / No represents the signal-to-noise ratio at transmission. The quality Q _k of transmission can thus be represented for each received symbol x¾j) by the formula

Q _k = c _k ² .EN ₀

If E _b denotes the average energy per transmitted coded bit and E _{s is} the average energy per emitted symbol, these two quantities are linked by the relation:

E _s = ¾ x log ₂ ()

The value of E _s is calculated from the different symbols of the constellation

by the relation:

The channel estimation and equalization module 24 realizes the equalization of the channel by defining new standardized symbols.

The performance prediction module 28 makes it possible to determine an error rate, before the decoding (and therefore without requiring the latter to be performed), for each symbol received, taking into account the attenuation variations of the channel on the symbols received. , that is to say on the different parts of the corresponding received coded words.

FIG. 2 thus represents a flowchart of an exemplary reception method according to the invention implemented in a receiver 12 according to the invention. In the first step 31, a modulated signal (modulated and interleaved received symbols yk) is received by the reception circuit 20. In the subsequent step 32, the received stream of codewords is deinterleaved by the deinterleaver 22. It is then demodulated by the demodulator 21 in the subsequent step 40, then stored in the buffer memory 23 in step 41.

In step 33, the different values of the attenuation Q, and / or the signal-to-noise ratio E / No and / or the transmission quality Q _k are measured and / or calculated by the module 24 for estimating channel from the received stream of de-interleaved codewords from step 32, and for each received symbol, and for each received corresponding coded word stored in the memory 23, the received stream of codewords.

From these different values Q _k , a mutual information value 1 ^ is developed by the performance prediction module 28, in the subsequent step 34, according to a predetermined function.

Two variants of the invention are possible with regard to the choice of the predetermined function for the calculation of said mutual information value 1 ^.

If we consider a received symbol y ^, this symbol corresponds to the emitted symbol attenuated by c & and noisy by additive Gaussian white noise. Due to the chosen modulation of cardinal M = 2 ^P , this symbol received

b ^k ₂ .. b ^k _p .

A first embodiment of the invention consists in considering the mutual information

equal to the mutual information 1 ^ between the emitted symbol and the received symbol y ^. This variant has the advantage of proposing a unique theoretical formula for calculating a reference curve of the mutual information which depends solely on the nature of the modulation considered. This approach does not take into account the implementation the modulation ("mapping") and the fact that the constituent p bits of the symbol are not all protected in the same way against the noise of the channel.

In this first variant, each mutual information value 1 ^ is determined according to the function defined by the aforementioned formula (I).

The expression of f (u, v) is in analytical form and can therefore be evaluated for all the values of u and v. For the integral, it is enough to discretize this integral by any numerical method. For example using a method of rectangles, we obtain each mutual information value 1 ^ according to the function defined by the following formula (II):

β threshold threshold

- AuAv Σ Σf (qAu, rAv) \ og ₂ (f (qAu, rAv))

q = - threshold r = - threshold

threshold

and Au

β

As can be seen, for a given modulation, a channel attenuation and a known noise spectral density, the mutual information between the transmitted and received symbols depends only on the transmission quality Q _k . However, each value of the transmission quality Q _k corresponds to the signal-to-noise ratio (SNR) on reception. The mutual information 1 ^ therefore depends only on this SNR signal-to-noise ratio.

A reference curve for each modulation scheme can therefore be obtained by numerical evaluation of the previous expression. For example, the reference curves represented on the Figure 3, respectively for the following modulation schemes: QPSK, BPSK, 16QAM, 64QAM.

A second variant consists of taking into account the actual implementation ("mapping") of the modulation and considering each bit. For each of the p bits the mutual information is calculated

ue bit and received symbol

The reference curve used to obtain the mutual information is then the sum of these p curves.

Thus, in this second variant, each mutual information value I _k is determined according to the function I ^^ _b yt) of the mutual information computed between the j th bit (^ ^{~ J ~ p} ^) of the transmitted symbol Xk and the received symbol y ^, this function being defined by the above-mentioned formula (III).

This general formula (III) is valid in the case where geometrically these two sets of standardized symbols have the same geometric distribution in the complex plane, that is to say when these two sets are equal to a rotation or translation of the plane by . Otherwise, an analytic formula can also be written but it is more complex. The above hypothesis includes PSK modulations in geometric distribution called "Gray mapping".

The expressions of f (u, v) and g (u, v) are in analytical form and can therefore be evaluated for all the values of u and v. For the integral, it is enough to discretize this integral by any numerical method. For example, using a method of rectangles, each mutual information value 1 ^ is obtained according to the function I ^ bk, yk) of the mutual information computed between the j th bit (^ ^{≤ J≤ p ~} ) of the transmitted symbol. and the received symbol yk, this function I ^ b being defined by the following formula (IV)

threshold threshold

(bl, y _k ) = AuAv Σ Σ f (qAu, rAv) log ₂ (f (qAu, rAv))

q = threshold r = threshold

threshold threshold

⁺ Σ Σ g _j iqAu, rAv) log ₂ (g _j (qAu, rAv))

q = threshold r = threshold

With, if we want to evaluate the different Gaussians of f (u, v) and gu, v) up to at least their probability a on a number of points β in the mesh, the following values of threshold and ( ^Δ "' ^Δν ):

threshold

and Au = Δν = 2- β

^is between 0 and 1. The reference curve to be used on each symbol is the sum of the curves for each of the p bits.

Whatever the variant used, a reference curve is thus obtained representing a predetermined function providing a mutual information value 1 ^ as a function of a signal-to-noise ratio SNR.

It should be noted that each reference curve referred to throughout the text is in practice materialized by a table of digital values stored in mass memory. The performance prediction module 28 uses such a table to determine the appropriate numerical values allowing the use of such a curve.

In step 34 of calculating mutual information 1, as shown in FIG. 4, the performance prediction module 28 considers the reference curve mentioned above, that is to say the recorded digital values, and each value of the transmission quality Q _k as the value of the signal-to-noise ratio to be plotted on the abscissa to determine each value of 1 ^. In the subsequent step 35, for each codeword of the received stream of code words, a mutual information average is constructed by averaging the different mutual information values 1 i determined in step 33. for the different values taken by said transmission quality Q _k on said code word.

In the subsequent step 36, the performance prediction module 28 reuses the same reference curve (i.e., the same table of numerical values) to determine an equivalent signal-to-noise ratio SNR _eq on the coded word received from said mutual information mean . In other words, the performance prediction module 28 uses the inverse function I ^ ¹ .

In the subsequent step 37, the performance prediction module 28 calculates each ER error rate value from said SNR _eq equivalent signal-to-noise ratio value and stored data representative of changes in a rate of error. equivalent errors according to a predetermined standard function for the coding and decoding modules used on an additive Gaussian white noise channel.

Indeed, for a predetermined coding module 15 and a decoding module 25, there exists a standard function, obtained in a manner known per se by simulation on the stationary Gaussian channel, expressing the error rate per PER coded word or the rate errors per BER bit as a function of the signal-to-noise ratio. FIG. 6 represents an example of curves representative of such standard functions, the different curves being obtained for the same decoding coding modules and varying from one another as a function of the number of iterations used for the decoding.

For each value of the equivalent signal-to-noise ratio SNR _eq , the performance prediction module 28 calculates, from these curves, that is to say, tables of digital values recorded. corresponding, a set of error rates ER that is to say an error rate value for each number of iterations that can be used decoding. The error rate values Ε¾ are decreasing with the number of iterations. This set of values Ε¾ therefore constitutes an error rate vector (ER), determined for each coded word received.

In the example of FIG. 6, four standard function curves are represented: a first curve CS1 corresponding, for example, to a single iteration, a second curve CS2 corresponding, for example, to four iterations, a third curve CS3 corresponding, for example, to eight iterations, and a fourth curve CS4 corresponding for example to sixteen iterations. Thus, from the value of the equivalent signal-to-noise ratio SNR _eq , an error rate vector having four components is obtained: (ER) = (ER1, ER2, ER3, ER4).

It should be noted that the two steps 36, 37 can be combined in one and the same step 38, if the standard functions are combined with the inverse function I ^ ¹ into a single function directly providing, for each number of iterations, curves of variation of the error rate ER as a function of the mean of mutual information .

The received stream of de-interleaved codewords stored in the buffer memory 23 is decoded in step 42 by the decoding module 25 from, in particular, a control signal developed in step 39 from each value of error rate calculated by the performance prediction module 28.

In a first variant in which the decoding method has a fixed number of iterations that can not be modified by control, the control module of the performance prediction module 28 generates a control signal chosen from among an authorization signal from the decoding and a signal prohibiting decoding. In this case, the performance prediction module 28 calculates a single error rate value ER (PER or BER). In In practice, a decoding authorization signal will be developed when the value of the calculated error rate is lower than a predetermined and recorded set error rate, and a decoding prohibition signal will be developed when the value of the decoding rate is determined. The calculated error is greater than this setpoint error rate value. This variant is particularly interesting especially when the coded block is received on several disjointed time ranges that can spread over a very long period (several seconds in the case of the time dispersal of DVB-SH). It makes it possible to trigger a single decoding by codeword without attempting decoding upon receipt of each new piece of the coded word.

According to a second variant, the performance prediction module 28 also advantageously incorporates a control module making it possible, during step 39, to produce a control signal for the decoding module 25 so that the latter implementing, for each coded word received to be decoded, a number of iterations calculated as a function of the error rates Ε¾. For example, the control module determines in the set of error rates Ε¾, the ER _opt value, of the error rate which is the largest and less than a predetermined and recorded set error rate, and controls the decoding module 25 as a function of the number of iterations corresponding to this value ER _opt .

The invention can be the subject of many alternative embodiments and applications other than those mentioned above.

Claims

1 / - A method of receiving digital data transmitted over a coded and modulated serial digital transmission over a non-stationary attenuation channel, in which:

a stream of modulated symbols, said received stream of modulated symbols, corresponding to an emitted stream of symbols modulated on said channel, is received by a reception device,

characterized in that

digital data are memorized making it possible to determine:

at least one value, called transmission quality Q ^, of formula c & .E NQ, where C & represents each attenuation value of the channel over time, k being a temporal index, E _S representing an average energy per emitted symbol and No represents a spectral density of Gaussian white noise on the channel,

- and changes over time of said T ^o transmission quality of each received symbol stream received from modulated symbols, and in that:

in a first step (34), for each value of said transmission quality Q.sub.1, a mutual information value I.sub.i is elaborated according to a predetermined function of said transmission quality (¾ _>

in a second step (35), for each coded word of the received stream of coded words, a mean of mutual information is produced by averaging the different mutual information values I _k determined in the first step for the different values taken by said transmission quality on said coded word,

in a third step (38), for each coded word of the received stream of coded words, at least one value of the error rate ER of the received stream of bits is elaborated from each value of the mutual information average determined in the second step, and using stored data representative of variations of an equivalent error rate according to at least one function, called standard function, of the signal / noise ratio, each standard function being predetermined for the devices. coding and decoding on an additive Gaussian white noise channel.

21 - Process according to claim 1, characterized in that each mutual information value 1 ^ is determined according to the function defined by the following formula (I):

f (u, v)

M being the cardinal of alphabet A

modulated symbols.

3 / - Method according to claim 1, characterized in that each mutual information value 1 ^ is determined according to the function defined by the following formula (II):

β threshold threshold

- AuAv Σ / (# Aw, rAv) log ₂ (/ (4Aw, rAv))

q = - threshold r = - threshold

with, to evaluate the different Gaussians of f (u, v) up to at least their probability a on a number of points β in the mesh, the following values of threshold and ^(Δ "' ^Δν) :

threshold

and Au = Av = 2-

M being the cardinal of alphabet A

modulated symbols.

4 / - Method according to claim 1, characterized in that each mutual information value 1 ^ is determined according to the function Ik hyk) of the mutual information computed between the j th bit ( ^{0≤ j≤ p 1} ) of the transmitted symbol Xk and the received symbol that function being defined by the following formula (III): (K> y _k ) = - \ \ f {u, v) \ og ₂ {f {u, v)) dudv

u = -∞ v = - °°

1

m i-- m

S

M being the cardinal of the alphabet A ^-

modulated symbols, gJ, oj 'lm ^{) where} <m≤2 ^p -1 is the set of normalized symbols ^m of p bits - j - whose bit numbered m is equal to 0,

\ _Β ϊΛ _p _ _x $

m i0≤m≤2 ^p -1 being the set of standardized symbols ^m of p bits -iP ^~ ^ whose bit numbered m is 1. 5 / - Method according to claim 1, characterized in that each mutual information value 1 ^ is determined according to the function defined by the following formula (IV):

threshold

Σf (qAu, rAv) log ₂ (f (qAu, rAv))

r = - threshold

threshold threshold

⁺ Σ Σg _j (qAu, rAv) \ og ₂ (g _j (qAu, rAv))

q-- threshold r - threshold with, to evaluate the different Gaussian def (u, v) and gu, v) up to at least their probability on a number of points β in the mesh, the following values of threshold and of ( ^Δ "' ^Δν ); threshold = - ¾ -¾n (a) + Max _Q≤k≤M _ _l (real (cl ^ -S _k ) g (c _k ² ^ -S _k ))

N _Q N _Q N _Q N _Q

threshold

and Au = Av = 2- β

M is the cardinal of the alphabet ^- {Ό ^ '^' ^••• ^ -li modulated symbols.

6 / - Method according to one of claims 1 to 5, characterized in that the attenuation values of the channel over time are measured values - in particular by the receiver - as and when the receipt of the coded words .

11 - Method according to one of claims 1 to 6, characterized in that an attenuation value of the channel and / or a value of the transmission quality (¾ is (are) developed (s) for each flow symbol received from modulated symbols. 8 / - Method according to one of claims 1 to 7, characterized in that in said third step (38):

an equivalent signal-to-noise ratio value SNR _eq on the received code word is determined (36) from said mutual information mean by the inverse function 1 ^ ¹ ,

- then each value of the ER error rate is obtained

(37) from said equivalent signal-to-noise ratio value SNR _eq and said stored data representative of variations of an equivalent error rate according to a predetermined standard function for coding and decoding devices on a white-noise channel Gaussian additive.

91 - Method according to one of claims 1 to 8, characterized in that the mutual information values 1 ^ and / or the mutual information mean and / or each ER error rate of the Bit stream received is (are) elaborated by the receiver.

10 / - Method according to one of claims 1 to 9, characterized in that deinterleaving is performed after demodulation of the symbols of the received stream of modulated symbols so as to form each coded word of the received stream of codewords, and in that each mutual information value and / or the mutual information mean and / or the error rate ER of the received bitstream is elaborated for each coded word obtained at the end of such deinterlacing.

11 / - Method according to one of claims 1 to 10, characterized in that for each codeword of the received stream of codewords, a control signal of the decoding device is developed according to each value of the error rate ER the bit stream received.

12 / - Method according to claim 11, characterized in that, for each coded word of the received stream of code words, a single value of the error rate ER of the bit stream is generated from a standard function unique, and in that the control signal is adapted to activate the decoding device if said value of the error rate ER of the received stream of bits is less than a predetermined threshold value.

13 / - Method according to claim 11, characterized in that, for each coded word of the received stream of codewords, a plurality of series of values of the error rate ER of the received stream of bits are developed from a plurality of of standard functions, each standard function corresponding to a decoding method chosen from among a plurality of predetermined decoding methods, and in that said control signal is developed so as to activate the decoding device according to the decoding method for which said value the error rate ER of the received stream of bits is the closest to a predetermined threshold value while being lower than this threshold value.

14 / - Method according to claim 13, characterized in that the methods of decoding the same plurality of decoding methods differ from each other only by a number of decoding iterations.

15 / - Receiver for digital serial transmission coded and modulated on a noise channel with non-stationary attenuation, comprising:

a receiving device (20) adapted to receive modulated symbol streams, called received streams of modulated symbols, corresponding to transmitted streams of modulated symbols on said channel,

a demodulation device (21) adapted to generate at least one stream of coded words, said received stream of coded words, from each received stream of modulated symbols,

a decoding device (25) adapted to generate a bitstream, said received bitstream, by decoding each received stream of codewords, according to a decoding method corresponding to a coding method implemented on transmission the emitted stream of modulated symbols on said channel,

said receiver comprising a channel performance prediction module (28) adapted to develop without performing decoding, from data stored digital signals representative of variations over time of attenuation and / or noise of the channel and / or interference, at least one representative value of an error rate ER of the bit stream received,

characterized in that, digital data being stored for determining:

and the variations over time of said transmission quality for each symbol received from the received stream of modulated symbols,

said channel performance prediction module is adapted to:

in a first step (34), elaborating for each value of said transmission quality Q ^, a mutual information value 1 ^ according to a predetermined function of said transmission quality Q ^,

in a second step (35), for each coded word of the received stream of coded words, elaborating an average of mutual information, by averaging the different mutual information values determined in the first step. for the different values taken by said transmission quality on said coded word,

in a third step (36), elaborating for each coded word of the received stream of coded words, at least one value of the error rate ER of the received stream of bits from each value of the mutual information mean determined in the second step, and using stored data representative of variations of an equivalent error rate according to minus a function, called standard function, of the signal-to-noise ratio, each standard function being predetermined for the coding and decoding devices on an additive Gaussian white noise channel.

16 / - Receiver according to claim 15, characterized in that it is adapted for the implementation of a method according to one of claims 1 to 14.

17 / - Code-coded and modulated digital transmission device on a nonstationary attenuation noisy channel between:

an emitter (11) comprising:

and a receiver (12) comprising:

at least one decoding device adapted to generate a bitstream, said bitstream, by decoding each received stream of words coded according to a decoding method corresponding to a coding method implemented by the transmitter,

characterized in that the receiver is according to one of claims 15 or 16.