Method, apparatus, and program for adaptive modulation and demodulation of data frames

Abstract

The invention relates to a method for demodulating a frame comprising N information words, wherein a word at position # in the frame is modulated by a symbol in a dictionary of K symbols. The method is characterized in that it comprises the steps of obtaining (300) a priori knowledge about the distribution of symbols at a plurality of positions in the frame, determining (301) a differential representation of the a priori knowledge, determining (303) a differential representation of the received frame, correlating (304) the determined differential representations to obtain a consolidated estimate of the difference between symbols in the received frame, and demodulating (305) the received information words in accordance with the obtained consolidated estimate. The invention also relates to a corresponding modulation method as well as to devices and programs for implementing the methods.

Description

Technical Field

[0001] This invention generally belongs to the field of telecommunications, and more specifically relates to a modulation technique for improving the demodulation performance of data frames, particularly in communication systems that rely on the relative representation of information to transmit and / or process information. Background Technology

[0002] Communication systems that transmit and / or process information based on the relative representation of information are known. A common example is the use of differential modulation.

[0003] For example, consider a symbol with 5 symbols The frame, each symbol encoded Each information bit is used to obtain the information. The frame has several values. One possible differential representation of this frame could be... In this example, what is encoded is therefore the difference between values, and a single absolute reference is sufficient to decode the entire frame. Of course, in this configuration, within the finite domain considered (in this case, ), (i.e., with) Subtraction or any other operation can be performed using the modulo operator.

[0004] This representation can be used for signal processing or transmission purposes within a communication chain. For example, it may be particularly effective for transmitting differences between samples when the variation between consecutive samples is small.

[0005] This differential representation of frames can also prove useful in some receivers, for example when receiving signals modulated by cyclic rotation of a complex symbol root sequence (such as CCSK (Cyclic Code Shift Keying) modulation).

[0006] CCSK modulation proposes modulating the data to be transmitted by cyclically rotating / shifting a sequence of complex symbols called the root sequence. The root sequence is such that its shifted versions are orthogonal to each other, i.e., it has a good autocorrelation function. Therefore, a specific cyclic shift of the same root sequence is associated with each binary word to be transmitted.

[0007] For example, by selecting a root sequence consisting of four complex symbols [a; b; c; d], CCSK modulation allows two information bits to be modulated orthogonally via rotation of this sequence. The binary word '00' can correspond to the transmission of the sequence [a; b; c; d]; the binary word '01' can correspond to the transmission of the sequence [d; a; b; c]; the binary word '10' can correspond to the transmission of the sequence [c; d; a; b], and so on.

[0008] CCSK sequences can be advantageously transmitted in CP - OFDM (Cyclic Prefix Orthogonal Frequency Division Multiplexing) frames, for example, in time - frequency frames, where each of the N time steps contains a complete CCSK sequence of size K distributed over a set of frequency sub - carriers, as Figure 2 shown.

[0009] The receiver knowing the absolute shift of a particular sequence of the frame allows demodulation of the entire frame. For example, when the shift of the first sequence is known, e.g., by convention when a particular sequence is present at the beginning of the frame, the receiver can demodulate the frame by estimating the shift of other sequences relative to the known sequence.

[0010] Therefore, it is necessary to fully understand the differences between sequences of the same frame in order to correctly demodulate the data. However, sometimes the effects of interference on symbols transmitted in the same frame are not the same, which may cause problems during their demodulation.

[0011] Therefore, a method for improving demodulation performance is needed, especially when the communication is based on the relative representation of information. Summary of the Invention

[0012] For this purpose, a method for demodulating a received data frame is proposed, the frame comprising N information words , where the word at position in the frame is modulated by symbols from a dictionary having symbols, and the method comprises the steps of: - Obtaining prior knowledge about the symbol distribution at multiple positions in the frame,

[0013] - Determining a differential representation of the prior knowledge, which represents the probability that the difference between two symbols has a particular value,

[0014] - Determining a differential representation of the received frame, which represents the probability that the difference between two symbols in the frame has a particular value,

[0015] - Associating the determined differential representations to obtain a combined estimate of the differences between symbols in the received frame,

[0016] - Demodulating the received information words based on the obtained combined estimate.

[0017] - Demodulating the received information words based on the obtained combined estimate.

[0018] Assume a sequence of discrete random variables . The definition of prior knowledge refers to the distribution law of these variables The choice and / or knowledge of the distributions of these random variables constitutes very useful knowledge for estimating the values ​​of these variables, especially when these variables are affected by interference phenomena such as noise, which may modify the distribution of the transmitted symbols in an uncontrollable way.

[0019] Therefore, a priori knowledge of the symbol distribution in a frame is proposed to be represented in differential form. This priori knowledge is obtained, for example, by convention or by means of previous message exchanges. Combining this differential representation of the priori knowledge with a differential representation determined based on the actually received symbols by product allows for a better estimation of the probability of differences between symbols. Thus, this method improves demodulation performance.

[0020] Understanding the prior distribution of the transmitted symbols improves the estimation of the received symbols, especially when the transmission channel is affected by interference (noise, attenuation, etc.), which modifies the distribution of the transmitted symbols in an uncontrollable way.

[0021] Therefore, in the context of demodulation algorithms that utilize the differential representation of data frames (i.e., focusing on the difference between symbols rather than the representation of the symbols themselves), this method leverages prior knowledge of the symbol distribution at the time of frame generation to improve demodulation performance.

[0022] Therefore, the step of determining the differential representation of the prior knowledge utilizes prior knowledge of the distribution law of each symbol according to its position in the frame to determine the probability that the difference between two symbols at a particular position has a specific value. These are prior differences, independent of the transmission channel.

[0023] The step of determining the differential representation of a received frame is performed based on the actual received symbols by estimating the probability that the difference between two symbols in the received frame has a specific value for multiple symbols in the frame.

[0024] Of course, when the value of the demodulated symbol cannot be determined, each received symbol can conventionally be considered to follow a certain distribution law. discrete random variables Then, the probability that the difference between two symbols has a specific value takes into account this uncertainty and can be represented by a difference random variable. In other words, for a position in the frame... Each symbol at the location And for dictionaries Each symbol Determine the probability vector ,in, It is a location The symbol at the location is a symbol. The probability of each symbol in the frame. This distribution is determined, for example, by conventionally performing a cross-correlation operation between the symbol at position i and various symbols in the dictionary. Therefore, each symbol in the frame... From random variable X i This indicates that the two symbols in the frame... and The difference between them, within the meaning of this invention, is a difference random variable. The distribution of this difference random variable (called the relative distribution) is expressed as: .

[0025] For example, consider symbol frames as having a distribution law. Sequence of discrete random variables It is possible to construct a set containing differenced random variables. The matrix such that And the corresponding distribution can be constructed. The matrix such that ,in, It is a cross-correlation operator. Given the similarity between the concepts of summation and difference in the context of modular arithmetic operations in a finite field, it is also possible to define a set of random variables. The matrix such that And the corresponding distribution can be defined. The matrix such that ,in, This time it's the convolution operator. In this document, "relative distribution" "Indicates two random variables" and The distribution of a random variable is obtained by the difference (or sum) of the two variables.

[0026] This differential representation of the received frame will be distinguished from a frame that is differentially modulated during transmission according to a conventional differential modulation technique, in which information is modulated by a transition between two consecutively transmitted symbols.

[0027] In one particular embodiment, the demodulation method enables the dictionary to contain the... Each of the symbols is associated with a symbol of size . finite group Different index values ​​are associated, and such that:

[0028] - Obtaining prior knowledge includes: for each symbol in this frame. Obtain a vector containing K probabilities. This vector is called the prior distribution, where the rank is The element is the symbol. As index symbols of the dictionary The probability,

[0029] - Determining the differential representation of the prior knowledge includes: for each pair of prior distributions Determine a vector containing K probabilities. This vector is called the relative prior distribution, where the rank is The elements are obtained by distributing these elements. and Determined by association, with these symbols and The difference between related indexes equals The probability,

[0030] - Determining the differential representation of the received frame includes: for each symbol pair in the received frame ( ; ), determine by using these symbols and A vector containing K probabilities, determined by association. This vector is called the relative distribution, where the rank is The elements are related to these symbols and The difference between related indexes equals The probability, and

[0031] -Associating these determined difference representations includes: these distributions With these distributions Perform element-wise multiplication.

[0032] This arrangement allows for the determination of: a first matrix comprising a "relative" probability distribution obtained from symbol pairs in the frame—that is, a matrix determined based on the received symbols—which, for each symbol pair in the frame, includes the probability that the difference between these symbols has a certain value; and a second matrix comprising a "prior" relative distribution determined based on prior knowledge of the symbol distribution, which, for each symbol pair in the frame, includes the probability that the difference between these symbols has a certain value. The product of these matrices produces a merged matrix in which each element is a symbol. and Combined distribution of the probability that the difference between them takes a certain value Of course, considering the probabilistic nature of the distributions obtained through multiplication, it may be necessary to prove that normalization of these distributions is required.

[0033] It should be noted here that a group is a set that is associative internally and allows the existence of a unit element. Such a group is called "finite" when it consists of a finite number of elements.

[0034] By associating different index values ​​with each element of the dictionary, the difference between symbols can be represented as the difference between the indices associated with those symbols. For this purpose, the K symbols of the dictionary are related to a finite group of order K. K distinct symbols are associated, and the associative law of this K-order finite group is addition (and therefore with the value 0 as the identity element). This arrangement allows operations (especially summation and difference) to be performed on indices modulo K of the symbol dictionary, provided that the indices are in the form {0, 1, ..., K-1}, such that any difference (or sum) between elements in the set, modulo K, also belongs to the set.

[0035] According to one particular embodiment, an information word is modulated by a sequence of K complex values, which is obtained by performing a specific cyclic shift on the root sequence.

[0036] Therefore, the information words are modulated by CCSK sequences, which are particularly well-suited for obtaining a differential representation of frames. The index associated with a symbol is, for example, the shift value of the sequence transmitted within the symbol relative to the root sequence. This modulation method is particularly well-suited for the differential representation of frames, as the shift can be represented as an absolute term relative to the root sequence, or as a relative term between the sequence pairs that constitute the frame.

[0037] According to a particular embodiment, the received frame is a time-frequency frame, wherein each of the N time steps contains a complete symbol of size K distributed over a set of K frequency subcarriers.

[0038] Therefore, the CCSK sequence is integrated within the CP-OFDM frame to obtain the time-frequency frame in its simplest form, where each of the N time steps contains a complete CCSK sequence of size K distributed across the set of frequency subcarriers. This allows the method to determine a representation of the OFDM frame in the form of a probability distribution matrix of relative shifts between symbols in the frame. This matrix is ​​combined with a matrix containing the probability distributions of prior relative shifts between symbols in the frame, which are determined based on pre-obtained knowledge related to the shift distribution of each word in the frame.

[0039] This arrangement allows for the use of various CCSK symbols contained in the CP-OFDM frame as multiple estimates of the transmission channel, thus enabling better estimation of the transmission channel and / or pilotless transmission schemes. Therefore, CCSK-CP-OFDM modulation is particularly well-suited for small packet transmission in IoT with high energy efficiency.

[0040] According to one particular embodiment, the method enables prior knowledge to be received in advance in the message.

[0041] This instruction is obtained, for example, in a configuration message sent by the transmitter or by the control equipment of the communication system. This arrangement enables, for example, dynamic adaptation of prior knowledge of the symbol distribution based on the context of the communication.

[0042] According to this demodulation method, a method for modulating a data frame to be transmitted is also proposed, and the frame includes N information words , wherein the word at position in the frame is modulated by symbols in a dictionary having symbols, and the method enables at least one information word to be modulated by symbols obtained from a subset of the symbol dictionary, and the subset is selected according to the position of the word in the frame and / or the target reliability level for transmitting the word.

[0043] Therefore, it is proposed to modulate at least one information word in the frame by symbols obtained from a specific subset of the symbol dictionary . The symbol subset for modulating the word is selected according to the position of the word in the frame and / or according to the desired reliability level for transmitting the word. For example, when high reliability is desired for transmitting the symbol, the method allows for the selection of a subset that includes few symbols.

[0044] In this way, the amount of information that can be transmitted for a word at a specific position in the frame is reduced, while the reliability of transmitting the word is increased. In fact, by reducing the number of its possible values, the symbol carries less information, but provides stronger prior knowledge to the receiver, thus improving the transmission reliability.

[0045] The term "position" in the frame corresponds to the position of a word relative to other words. This term does not refer to the position in the bit stream, so the position of a word in the frame is independent of the size of the information word.

[0046] Therefore, the efficiency of the frame can be finely adapted in the following ways: making the transmission of some symbols more robust so that different symbols are more reliable in an adaptive manner according to their importance levels; or by strengthening the prior knowledge of some symbols to incorporate information with strong prior knowledge throughout the frame.

[0047] According to a specific embodiment, the modulation method associates each of the K symbols in the symbol dictionary with a different index value from a K - order finite group H, and the symbol subset selected for a specific position consists of symbols associated with index values belonging to a subset of the finite group H.

[0048] It should be noted here that a group (in the mathematical sense of the term) is a set with an associated single internal associative law and having an identity element. A finite group is a group that includes a finite number of elements.

[0049] A subgroup G of a finite group H is a subset of H that includes the identity element of H, and such that, according to the laws of H, the composition of any two elements in G always belongs to G, and the inverse of any element of G itself (according to the associative law of H) belongs to G.

[0050] By associating distinct index values ​​with each element of the dictionary, the difference between symbols can be represented as the difference between the indices associated with those symbols. For this purpose, the K symbols of the dictionary are associated with the K distinct symbols of a K-order finite group, whose associative law is addition (and therefore has the value 0 as the identity element). This arrangement allows operations (specifically summation and subtraction) to be performed on the indices modulo K of the dictionary of symbols, provided that the indices are in the form {0, 1, ..., K-1}, such that any difference (or sum) between elements in the set, modulo K, also belongs to the set.

[0051] According to a particular embodiment, this modulation method enables finite groups It is a group ,in, .

[0052] about The group law is Definition, making It is a commutative group that allows the existence of identity element zero. For example, for a dictionary with K = 4 symbols, the index set is {0, 1, 2, 3}.

[0053] Therefore, the group Depend on The index set consists of multiples of the given numbers. With K = 4 symbols and m = 2, the index set is {0, 2, 4, 6}.

[0054] Summation and difference operations in this group are based on... The modulo operation is executed.

[0055] In one particular embodiment, the modulation method causes a subset of symbols selected for a specific location to consist of symbols associated with index values ​​of a subgroup belonging to the finite group, the subgroup including only multiples of the value M, such that K is an integer multiple of M greater than 1.

[0056] In this way, a subset of symbols can be defined whose cardinality depends on the value of M. By changing M, the efficiency of the frame (i.e., the number of useful bits that a symbol can carry) changes. Therefore, the value M = K has zero efficiency but provides good transmission reliability. Conversely, when M = 1, efficiency is maximized, but transmission reliability decreases.

[0057] In other words, if If it is fixed, then The higher the value of , the lower the transmission efficiency. By reducing the number of possible values, each symbol carries less information (in this case, each symbol carries

[0058] one bit), but provides stronger prior knowledge to the receiver, thus improving the transmission reliability. Therefore, the value of

[0059] indicates the possible symbols at a specific position, and thus allows the probability distribution to be limited to certain symbols, and thus allows the determination of the symbol probability distribution at a given position.

[0060] According to a specific embodiment, the modulation method further includes the step of transmitting a message to the receiver, the message including information representing at least one symbol probability distribution at a specific position in the frame.

[0061] The receiver is, for example, a communication control entity or a terminal targeted by the modulated frame. This arrangement enables the receiver to obtain prior knowledge of the values of the transmitted symbols. , where the word at position in the frame is modulated by symbols from a dictionary having symbols, and the device includes a processor (502) coupled to a memory (501) containing program instructions (503) configured to perform the following steps: - Obtain prior knowledge of the symbol distribution at multiple positions in the frame,

[0062] - Determine a differential representation of the prior knowledge, which represents the probability that the difference between two symbols has a specific value,

[0063] - Determine a differential representation of the received frame, which represents the probability that the difference between two symbols in the frame has a specific value,

[0064] - Correlate the determined differential representations to obtain a combined estimate of the differences between the symbols in the received frame,

[0065] - Demodulate the received information words based on the obtained combined estimate.

[0066] In a manner corresponding to the demodulation device, the present invention also relates to a device for modulating a data frame to be transmitted, the frame including N information words

[0067] , where the word at position in the frame Through having Symbols in a dictionary The device includes a processor (602) coupled to a memory (601) containing program instructions (603) configured to perform the following steps:

[0068] - For each word in this frame , :

[0069] -According to the word Position in this frame And / or according to the transmitted word The target reliability level is determined by selecting a specific subset of symbols from the K symbols in the dictionary.

[0070] - Using symbols obtained from the selected subset to describe the word Modulation,

[0071] - Transmit modulated frames.

[0072] The present invention also relates to a terminal including the demodulation device and / or modulation device as described above, and to a communication system including such device and / or terminal.

[0073] In one particular embodiment, the different steps of the modulation and demodulation methods are determined by computer program instructions.

[0074] Therefore, the present invention also relates to a computer program comprising instructions adapted to implement the modulation and / or demodulation methods described above when the program is executed by a processor.

[0075] The program can use any programming language and can take the form of source code, object code, or intermediate code between source code and object code, such as partially compiled code or any other desired form of code.

[0076] The present invention also relates to a computer-readable information medium having a computer program recorded thereon, the computer program including instructions for performing steps of the modulation method and / or demodulation method as described above.

[0077] The information medium can be any entity or device capable of storing programs. For example, the medium can include storage devices such as ROM (e.g., CD-ROM or microelectronic circuit ROM), flash memory, or even magnetic recording devices (e.g., hard disk).

[0078] On the other hand, the information medium can be a transmissible medium, such as an electrical or optical signal, which can be routed via cable or fiber optic cable, radio, or other means. The program according to the invention can be downloaded, in particular, via the Internet.

[0079] Alternatively, the information medium may be an integrated circuit in which the program is incorporated, the circuit being adapted to perform or be used to perform the method in question.

[0080] The above-described embodiments or features can be added individually or in combination to the steps of the modulation and demodulation methods.

[0081] These devices, terminals, systems, programs, and information media offer advantages similar to those provided by the methods they correspond to. Attached Figure Description

[0082] Other features and advantages will become apparent when reading the preferred embodiments described with reference to the accompanying drawings, in which:

[0083] - Figure 1 A communication system suitable for performing modulation and demodulation methods according to a particular embodiment is shown.

[0084] - Figure 2 The diagram illustrates a time-frequency frame, where each of the N time steps contains a set of CCSK symbols of size K distributed across a set of frequency subcarriers.

[0085] - Figure 3 This is a flowchart illustrating the main steps of a demodulation method according to a particular embodiment.

[0086] - Figure 4 This is a flowchart illustrating the main steps of a modulation method according to a specific embodiment.

[0087] - Figure 5 This is a diagram illustrating the architecture of a device suitable for performing a demodulation method in a particular embodiment, and

[0088] - Figure 6 This is a diagram illustrating the architecture of a device suitable for performing a modulation method according to a particular embodiment. Detailed Implementation

[0089] In the following description, embodiments are depicted based on non-limiting examples that allow for the interpretation of the concepts upon which this invention is based. In particular, while the examples and terminology used may refer to certain well-known techniques or standards, these references are non-limiting, and other techniques may also be suitable for implementing the concepts of this invention. For example, the CCSK modulation technique mentioned may be replaced by other modulation techniques (such as QPSK (Quadrature Phase Shift Keying) or QAM (Quadrature Amplitude Modulation)) without modifying the invention.

[0090] Figure 1 An environment suitable for performing modulation and demodulation methods according to a particular embodiment is shown.

[0091] The environment includes a communication system 100, which includes a transmitting device 101 and a receiving device 102. The transmitting device 101 is, for example, a communication terminal, a user equipment (UE), a base station, a connection object, etc. The receiving device 101 is, for example, a user equipment, a terminal, a connection object, or any other device suitable for receiving data.

[0092] Devices 101 and 102 include radio frequency communication means, such as transceivers, adapted to enable devices 101 and 102 to communicate by exchanging time-frequency data frames (e.g., CP-OFDM frames). In one particular embodiment, such a frame includes a plurality of information words, for example, of size [missing information]. The binary word is represented by the CCSK symbol (i.e., by a value of a size with a good autocorrelation function). The specific complex value sequence obtained by cyclically shifting the root sequence is modulated. Such a sequence is, for example, the Zadoff-Chu sequence.

[0093] Therefore, the communication system 100 implements CCSK-CP-OFDM modulation. The CCSK-CP-OFDM method combines CP-OFDM technology with CCSK modulation to achieve small packet communication for IoT with high energy efficiency. However, it should be noted that other modulation techniques are conceivable without modifying the invention. For example, BPSK, QPSK, or QAM modulation can be used.

[0094] Figure 2 An example of a CCSK-CP-OFDM frame is shown, where each of the N time steps contains a set of K frequency subcarriers of size K = 2. p A complete CCSK sequence, such that each symbol corresponds to a word of maximum size p bits.

[0095] The set of K CCSK symbols constitutes a symbol dictionary with cardinality K.

[0096] Each symbol in the dictionary is associated with a different index, such that the K symbols of the dictionary are each associated with a K index value. In the case of CCSK modulation, each CCSK sequence in the dictionary is therefore associated with a single numerical value (e.g., a value representing the shift of the sequence relative to the root sequence).

[0097] According to one particular embodiment, K index values ​​associated with symbols in a dictionary form a finite group H of size K, such that each symbol in the dictionary is associated with a distinct value belonging to the finite group H.

[0098] Therefore, operations on the indexes (especially summation and difference) are performed in a finite group of size K, i.e., modulo the cardinality K of the symbolic dictionary, provided that the indexes are in the form {0, 1, ..., K-1}, such that any difference (or sum) between elements in the set, modulo K, also belongs to the set.

[0099] In a particular embodiment, a finite group The index value is determined by the group Define, and thus consider Perform modular arithmetic on the remainder of the divisor, where is... Strictly positive integers, It is a set of relative integers.

[0100] For example, with m = 2 and K = 4, we obtain the index set [0, 2, 4, 6] such that any difference (or sum) between elements in this set is equal to 0. The modulo operation also belongs to the set of values. Therefore, in this example, we can actually observe 0 – 2 = -2 [8] = 6, 0 – 4 = -4 [8] = 4, 2 – 4 = -2 [8] = 6, etc.

[0101] In one particular embodiment, the position within the frame Information word P at the location i By using from what can be used for this location A subset of symbols used to encode characters at a given location The obtained symbols are modulated, and this subset is based on the position of the word to be encoded. The subset is selected based on the target reliability level of the transmitted information words. This subset consists of symbols associated with indices whose values ​​belong to a specific subset of a finite group H.

[0102] Therefore, according to a particular embodiment, each information word in a frame is associated with a specific symbol dictionary based on its position in the frame and / or the desired level of reliability for transmitting the word to that specific position. More generally, some words in the same frame may be encoded using symbols obtained from a dictionary containing K values, while other words may be encoded using symbols obtained from a first subset of that dictionary, and still others may be encoded using symbols obtained from a second subset of that dictionary. The first and second subsets may have different cardinalities depending on the desired level of reliability for transmitting the information words associated with these subsets respectively. In practice, the fewer symbols that can be used to encode a word at a specific position in the frame, the more reliable the transmission.

[0103] In other words, by reducing the number of possible values ​​for a symbol, the symbol carries less information but provides the receiver with stronger prior knowledge, thus improving transmission reliability.

[0104] Of course, the receiver knows the symbol dictionary used by the transmitter in order to perform demodulation. Furthermore, according to the general principles of the invention, the receiver understands the probability distribution of the symbols in the received frames. This understanding is obtained, for example, by convention (reference standard) or by means of configuration messages.

[0105] This arrangement allows for improved demodulation performance by using receiving devices adapted to utilize the differences between symbols in a frame (and not just the absolute values ​​of these symbols, nor just the differences between a symbol and a reference symbol). For example, in the case of CCSK modulation, demodulation can be performed based on the differences between symbols in a frame. In this case, prior knowledge of the symbol distribution at each location in the frame allows for the establishment of prior knowledge of the relative distribution, i.e., prior knowledge of the probability distribution of the differences between symbol pairs in the frame.

[0106] This performance improvement is achieved through a demodulator adapted to correlate a differential representation of the prior knowledge of the probability distribution of the prior symbols with the differential representation of the received frames, thereby enabling better estimation of the differences between symbols. In the case of differential modulation, performance is improved when the value associated with one symbol can be represented as the difference between the value associated with another symbol.

[0107] Accordingly, a modulator suitable for modulating information words in a data frame from a symbol dictionary is proposed, wherein at least one information word is modulated by symbols whose values ​​are selected from a subset of the symbol dictionary, the subset being selected based on the position of the word in the frame and / or the target reliability level of transmitting the word or based on a symbol probability distribution associated with the position of the word.

[0108] The calculation of differences between symbols mentioned in this document can vary depending on the modulation technique used without modifying the invention. In the case of CCSK modulation, such differences correspond, for example, to the cyclic shift value of the considered sequence relative to another sequence, and in the case of QPSK modulation, to phase shift or angular shift, etc. Differences between symbols can also correspond to the differences between the index values ​​associated with symbols in the symbol dictionary (which, according to the indexing system, are equal to the set {0, 1, ..., K-1} in an isomorphic sense) and their corresponding probabilities. Therefore, the differences are estimated in a finite group of size K, i.e., modulo the cardinality of the symbol dictionary, provided that the index is in the form {0, 1, ..., K-1}.

[0109] In one particular embodiment, a specific location in the frame The prior knowledge of the symbol distribution at a given location consists of a vector of size K, the number of elements of which is equal to the cardinality K of the symbol dictionary, where the index elements... Including position in the frame The value associated with the symbol at the location is the same as the value. The probabilities of associated dictionary symbols. In this document, this vector is referred to by the term "prior distribution".

[0110] For example, when all symbols in the dictionary are likely to be used for a word at a specific position in the modulated frame, the prior distribution associated with that position is uniform. According to another example, when only symbols associated with even-numbered index values ​​in the dictionary are likely to be used at a specific position in the frame, the probability of that distribution at odd-numbered indices is zero.

[0111] Prior knowledge of the symbol distribution within this frame is used to determine the "prior relative distribution." For a pair of positions... The prior relative distribution is determined based on the prior distributions associated with these two locations. For each pair of positions in the frame This prior relative distribution includes position within the frame. The probability that the difference between the signs at a given point has a certain value. For example, the prior relative distribution. It is a vector of K elements corresponding to the K elements of the symbol dictionary, where the elements are... Position in frame and The difference between the sign values ​​at each point has a value The probability of.

[0112] Therefore, for each pair of positions in the frame We obtain the prior relative distribution such that we can construct a matrix in which the elements at coordinates (i, j) are the prior relative distribution. .

[0113] In one particular embodiment, this matrix of prior distributions is combined with a second matrix comprising relative distributions, which represent differences between symbols or differences between values ​​associated with symbols actually received in the frame. These relative distributions are generated for all symbol pairs in the frame by means of cross-correlation or convolution operations. ( It is certain. More precisely, the symbol. With symbols The difference between them is determined by associating these symbols through cross-correlation or convolution. For example, this difference could correspond to a shift value between two CCSK sequences. Therefore, for each symbol pair... Determine the vector The size of this vector is equal to the cardinality K of the symbol dictionary, and each element in this vector... Including symbols and The difference between them has a value The probability of these relative distributions. These relative distributions provide a relative distribution matrix, in which the elements at coordinates (i, j) are the relative distributions. .

[0114] These two matrices are combined by multiplication such that the probability of the difference between the values ​​associated with the actual received symbols is weighted by probabilities determined based on prior knowledge of the values ​​of these symbols. Of course, given the probabilistic nature of the distributions obtained through the product, it may be necessary to normalize these distributions.

[0115] Therefore, the matrix generated by this combination includes distributions known as “merged relative distributions”, which are better estimated because they take into account prior knowledge of the sign distribution.

[0116] For example, consider a frame containing 5 CCSK symbols of size 4 (each symbol encodes 2 bits of information) and their relative distribution: (Representing the probability of shift between the symbols at indices 3 and 5), it can be inferred that the most likely relative shift of symbol 3 relative to symbol 5 is... In other words, the values ​​of these two symbols are determined through... They are connected.

[0117] For example, if the distribution and Prior knowledge follows even indexes (e.g.) and A subset of ) can determine the following prior relative distribution obtained after cross-correlation and normalization: .

[0118] Prior distribution With distribution The product of these products, after normalization, yields the following merged distribution: .

[0119] It can be seen that this merger produces This differs from the initial estimate. Therefore, the initial estimate is improved due to prior knowledge.

[0120] In the case of CCSK modulation, the information word is modulated by cyclic shifts of a specific sequence called the root sequence, for example, by cyclic shifts of the Zadoff-Chu sequence (which has good autocorrelation properties and is particularly suitable for this purpose). Therefore, the difference between two symbols can be represented by a shift between them.

[0121] Similarly, the difference between two BPSK symbols can be expressed as the difference between the corresponding angles associated with those symbols.

[0122] More generally, the difference between index values ​​associated with symbols in a dictionary of symbols can be represented, as described above. For this purpose, according to a particular embodiment, K symbols in the dictionary are associated with K distinct index values ​​derived from a finite group of order K. This set of indexes provides a modular arithmetic operation suitable for representing the difference between all symbols in the dictionary.

[0123] This improved estimation of the relationship between the symbols of the received frames can be advantageously used during frame demodulation.

[0124] For example, when a frame includes at least one symbol (such as a pilot symbol) with a known value at a known location, it is proposed to use a combined relative distribution to demodulate other information words. This can be done using a single row of a combined relative distribution matrix, which includes information indicating the shift probabilities between all symbols in the frame. However, data from different rows of this matrix can be combined to further improve the estimation. In fact, through transitivity, the relative distribution... By using relative distribution and This can be represented by correlation. This type of correlation can be achieved through cross-correlation or convolution. Symbol estimation relative to pilot symbols can be improved by selecting combinations of distributions in the matrix that are associated with the highest probabilities.

[0125] According to another example, when no sign is known in the absolute terms, the determined merged relative distribution allows for shift demodulation. Shift demodulation involves demodulating the frame by using an arbitrary sign value as a reference, and performing an integrity check on the resulting information words. If the integrity check fails to validate the frame, a new demodulation is performed using another sign value as a reference, and a new integrity check is performed. These steps are repeated until the frame is validated through the integrity check.

[0126] Figure 3 The main steps of a demodulation method according to a specific embodiment are illustrated. This method, for example, is... Figure 2 The equipment 102 is implemented.

[0127] During the first step 300, the method includes obtaining information related to the symbol distribution in one or more frames. As shown, this knowledge may be contained in a message received by device 102, for example, in a communication configuration message. This knowledge may take the form of a probability distribution associated with one or more locations in the frame, or it may consist of transmission values ​​from which such distribution can be determined. This knowledge may also be determined conventionally (e.g., by referring to a communication standard).

[0128] The method includes step 301, during which device 102 determines a prior relative distribution based on the knowledge obtained in step 300.

[0129] These relative prior distributions are obtained as described above by applying cross-correlation or convolution to prior distributions determined based on the obtained prior knowledge, and according to a particular embodiment, these relative prior distributions are arranged as a matrix, wherein the elements (i, j) include relative prior distributions representing the probabilities of the differences between values ​​associated with symbols at positions i and j in the data frame.

[0130] In one particular embodiment, steps 300 and 301 are combined to make the prior relative distribution available directly in the configuration message or through a reference standard.

[0131] In step 302, device 102 determines the probability distribution of each symbol in the received frame. For example, the device determines that the size is... vector In this vector, each element It is a symbol It is an index symbol in a dictionary. The probability of [element]. In the case of CCSK modulation, [element]. Includes, for example, sequences The shift value between the reference sequence and the value The probability. For this purpose, device 102, for example, performs a cross-correlation (or convolution) operation on each sequence. The result is compared with the root sequence to determine the probability of the shift value relative to the root sequence for each symbol.

[0132] In step 303, for multiple symbol pairs in the received frame Device 102 estimates the symbols in the received frame. and The relative distribution of the differences between them, where, .

[0133] As mentioned above, when K symbols of a dictionary are associated with K distinct index values ​​belonging to a finite group of order K, the difference is estimated in the finite group K, i.e., modulo the cardinality of the symbol dictionary, provided that the index is in the form {0, 1, ..., K-1}; or when the symbols belong to a finite group When indexing by value, use Perform modulus extraction, where, It is a strictly positive integer.

[0134] In one particular embodiment, this processing produces a representation of the frame in the form of a matrix (or a relative distribution within the sense of this invention) of the probability distribution of relative shifts between CCSK symbols in the frame:

[0135]

[0136] In this matrix, each index Therefore, it contains a size of The vector, where the vector Each element contains the symbols in the frame. and The difference between them has a value The probability of.

[0137] Of course, it is conceivable to determine only a subset of these posterior relative distributions without modifying the present invention.

[0138] In step 304, the prior relative distribution determined in step 301 is combined with the corresponding relative distribution determined in step 303 to obtain a merged relative distribution. In a particular embodiment, for this purpose, device 102 generates a product of matrices in which prior and posterior relative distributions are respectively arranged.

[0139] The method concludes with a demodulation step 305, during which at least a portion of the merged relative distribution is used to estimate the value of another symbol based on the symbol used as a reference. As described above, demodulation can be performed based on the merging probability of the difference between a symbol (e.g., a pilot symbol) with a known value and position in the frame and other symbols in the frame. According to another example, device 102 performs shift demodulation based on the merged relative distribution.

[0140] Although this method is described here with reference to the discrete law, this proposition can also be applied, for example, by approximating the continuous law with the discrete law, or by using its parameters (e.g., the mean as a parameter of the normal law). and variance We can model the distribution to generalize to the continuity law. Therefore, it is appropriate to represent the relationship between the parameters of the relative distribution.

[0141] Figure 4 The main steps of a modulation method according to a particular embodiment are shown.

[0142] This modulation method is, for example, derived from... Figure 2 The equipment 101 is implemented.

[0143] The method includes a first step 400 of obtaining a data frame to be transmitted, the data frame comprising N information words. The information word is, for example, a maximum size of A binary word of 12 bits.

[0144] During step 401, device 101 determines a symbol dictionary to be used for the binary words in the modulation frame. This symbol dictionary includes at least [symbols related to...]. Associated with different index values A symbol. K index values ​​constitute a... A finite group of order, having an identity element and an addition law, such that summation or difference operations between index values ​​are performed in modular arithmetic, i.e., with the cardinality of the symbolic dictionary. Modulo operation is performed when the index is in the form {0, 1, ..., K-1}, such that any difference (or sum) between elements in the set is equal to the sum of its components. The value after taking the modulo also belongs to this set.

[0145] In one particular embodiment, the index value is determined by the group. Define, and thus consider Modular arithmetic is performed on the remainder of the divisor, where, It is a strictly positive integer. It is a set of relative integers.

[0146] According to one particular embodiment, the method includes step 402, in which device 101 selects a specific subset of symbols. Position in the frame ( ) specific information words Related. This subset of symbols forms a finite group. The dictionary symbols associated with the index values ​​of a specific subset are constituted. For example, such a subset may consist only of dictionary symbols associated with even numbers, or only of dictionary symbols associated with odd numbers.

[0147] In one particular embodiment, this subset consists only of values ​​that are strictly positive. The multiple and The divisor is composed of dictionary symbols associated with the value. It is determined based on the position of the information word in the frame and / or based on the target reliability level of transmitting that information word. Therefore, if If it is fixed, then The higher the value, the lower the transmission efficiency. By reducing the number of possible values, the symbol carries less information (in this case, each symbol carries...). (individual digits), but provides the receiver with stronger prior knowledge, thereby improving transmission reliability.

[0148] Of course, it is conceivable to associate multiple different subsets with different information words in the frame, so that the reliability and efficiency of transmission can be finely adapted.

[0149] For example, consider a size of There are 1 symbol, and each symbol is 1 unit in size. CCSK-CP-OFDM frames, and those composed of finite groups A dictionary of symbols with distinct value indices. This frame can be constructed as follows:

[0150] - Symbols selected from a subset of the symbol dictionary (For example, pilot symbols), this subset consists of values. The symbol associated with the index value of a multiple of the number is composed of a multiple of the index value. This symbol has... Useful data rate per bit / symbol

[0151] - Symbols selected from a subset of the symbol dictionary This subset is composed of values. The symbol associated with the index value of a multiple of the number is composed of a multiple of the index value. This symbol has... Useful data rate per bit / symbol

[0152] - Symbols selected from a subset of the symbol dictionary This subset is composed of values. The symbol associated with the index value of a multiple of the number is composed of a multiple of the index value. This symbol has... Useful data rate per bit / symbol, and

[0153] - Two non-key symbols and Its value is selected from a subset of the symbol dictionary, which is composed of the values ​​of and . The symbol associated with the index value of a multiple of the number is composed of a multiple of the index value. This symbol has... Useful data rate per bit / symbol.

[0154] The properties of the subsets of symbols associated with different symbols in a frame make it possible to determine the prior distribution of these symbols.

[0155] In one particular embodiment, device 101 determines a specific subset of symbols that can be used to modulate information words at specific locations in a frame by applying a communication standard also known to receiver 102.

[0156] In one particular embodiment, device 101 determines a specific subset of symbols that can be used to modulate information words at specific locations in a frame based on the content of a configuration message transmitted by receiver 102, a communication control entity, or a radio access point (such as a base station or a WiFi® router).

[0157] In one particular embodiment, device 101 determines a specific subset of symbols that can be used to modulate information words at a specific location in a frame, based on data characteristics of a transmission channel, for example, transmitted by receiver 102.

[0158] In one particular embodiment, the method includes step 403 of transmitting a message to device 101 or a communication control entity, the message including at least one symbol distribution associated with one or more information words and / or specific locations in a frame. It should be understood that the symbol distribution can therefore be transmitted to receiver 101 at any time (e.g., before the transmission of multiple frames). Of course, such a message may include prior distributions associated with multiple frames, a particular type of frame, or a communication session.

[0159] The method includes step 404, during which information words are modulated based on a symbol dictionary and / or based on a determined subset of symbols to encode specific words. To this end, for each word to be encoded at a specific position in the frame, the device can look up a table in which the position in the frame is... with symbol subset The identifier is associated with the word and is to be used to... A subset to be modulated It is determined based on the target reliability level of symbol transmission. The device uses the position of the information word within the frame... Related subsets The selected symbol is used to modulate the message word.

[0160] The method concludes with step 405, which involves transmitting the modulated frame to device 102. In one particular embodiment, the frame is transmitted using OFDM modulation, according to which each of the N time steps contains a complete CCSK coded sequence of information word size K distributed across a set of frequency subcarriers.

[0161] Figure 5 A simplified architecture of a device 500 suitable for performing a demodulation method according to a particular embodiment is shown.

[0162] Device 500 includes a data processing module comprising storage space 501 (e.g., memory (MEM)) and processing unit 502 equipped with, for example, a microprocessor (PROC) and driven by a computer program (PGR) 503 whose instructions are configured to execute as referenced above. Figure 3 The demodulation method described.

[0163] During initialization, before the code instructions of computer program 503 are executed by the processor of processing unit 502, these code instructions are loaded into, for example, memory 501. The microprocessor of processing unit 502 executes the instructions of computer program 503 as described above. Figure 3 The steps of the demodulation method are described.

[0164] For this purpose, in addition to memory 501 and processor 502, the device also includes communication device 504, such as an OFDM transducer designed to receive signals on multiple orthogonal carriers. Communication device 504 is configured, for example, by computer program instructions to receive at least one time-frequency frame (where each of N time steps contains a complete symbol of size K (e.g., a CCSK sequence) distributed across a set of frequency subcarriers) and demodulate the received N OFDM symbols.

[0165] The device 500 also includes a module 505 for determining one or more prior distributions of symbol probabilities in a received frame. Module 505 is implemented, for example, by program instructions configured to associate a vector of size K with at least one information word in a frame received by the communication module 504, wherein each index element... The value of the symbol at the position associated with the vector is an index symbol in a symbol dictionary of size K. The probability of the distribution. These program instructions are further configured to construct such a priori distribution by reference to a standard, by receiving a message from a control entity or from the transmitter of a frame, the message including at least one indication identifying a particular symbol distribution at one or more specific locations.

[0166] Device 500 includes module 506 for determining a set of prior relative distributions based on a prior distribution determined by module 505. Module 506 is implemented by program instructions configured to determine a vector having K elements corresponding to K elements in a symbol dictionary, wherein the index element... Position in frame and The difference between the sign values ​​at each point has a value The probability. According to a particular embodiment, the program instructions are further configured to construct a matrix based on a determined prior relative distribution, wherein the element at coordinate (i, j) includes the prior relative distribution of the difference between the values ​​of the symbols at positions i and j in the frame received by the communication module.

[0167] Device 500 also includes a set of probability distributions for determining the probability distribution set. Module 507 (e.g., a matrix, referred to as a relative distribution), where each element of the matrix... It is a plurality of symbol pairs (representing the symbols formed by the symbols of the frames received by the communication device 504) ; The symbols in ) and A vector of K probabilities of at least one difference between associated index values, where, and The difference is calculated based on modular arithmetic operations. Module 507 is implemented, for example, by computer program instructions configured to calculate the difference between index values ​​associated with two symbols in a frame through cross-correlation and / or convolution operations, and to combine a pair of sequences ( ; The result of the difference between the elements in the matrix is ​​stored as the coordinates in the matrix. Place.

[0168] The device includes a merging module 508 adapted to combine a prior relative distribution determined by module 506 with a relative distribution determined by module 507. This module is implemented, for example, by program instructions configured to produce a product of matrices constructed by modules 506 and 507, and thus obtain a matrix including the merged relative distributions.

[0169] The device 500 finally includes a demodulation module 509 adapted to demodulate symbols transmitted in a received frame based on a relative distribution merged by module 508. For example, module 509 is implemented by program instructions adapted to perform shift demodulation of data frames based on merged relative shifts between sequences of frames (e.g., based on shifts updated in one or more specific rows of a merge matrix). In another example, these instructions are configured to demodulate the symbols based on the difference between the symbols in the frame and a reference symbol (whose position and value are known).

[0170] In one particular embodiment, device 500 is integrated into a communication terminal, a connected object, a vehicle, a gateway, an access point, or a base station.

[0171] Figure 6 A simplified architecture of a device 600 suitable for performing a modulation method according to a particular embodiment is shown.

[0172] Device 600 includes a data processing module comprising a storage space 601 (e.g., memory (MEM)) and a processing unit 602 equipped with, for example, a microprocessor (PROC) and driven by a computer program (PGR) 603 whose instructions are configured to execute as referenced above. Figure 4 The modulation method described.

[0173] During initialization, before the code instructions of computer program 603 are executed by the processor of processing unit 602, these code instructions are loaded into, for example, memory 601. The microprocessor of processing unit 602 executes the instructions of computer program 603 as described above. Figure 4 The steps of the modulation method are described.

[0174] For this purpose, in addition to a memory 601 and a processor 602, device 600 includes a means for obtaining N information words (e.g., a maximum size of N). Module 604 is a frame of N bits (a binary word). For example, module 602 can be implemented by instructions suitable for forming frames by segmenting application data streams and adding values ​​to them to check their integrity.

[0175] The device also includes a module 605 for selecting at least one subset of symbols obtained from a symbol dictionary to modulate at least one information word at a specific location. For this purpose, module 605 is implemented, for example, by program instructions suitable for selecting a subset of symbols based on the position of the word to be modulated in the frame and / or the desired level of reliability for transmitting the information word.

[0176] The device 600 includes a module 606 for modulating information words based on a subset of symbols determined by module 605 for each information word.

[0177] The device includes a communication device 607, such as an OFDM transducer designed to transmit signals via multiple orthogonal carriers. The communication device 607 corresponds to, for example, a 3G, 4G, 5G, or WiFi® network interface, which is configured by computer program instructions to enable the transmission of at least one time-frequency frame, wherein each of N time steps contains a complete symbol (e.g., a CCSK sequence) of size K distributed across a set of frequency subcarriers. According to a particular embodiment, the communication device is configured by instructions to transmit to a receiving device at least one information element characterizing the probability distribution of symbols at one or more locations within one or more frames.

[0178] In one particular embodiment, device 600 is integrated into a communication terminal, a connected object, a vehicle, a gateway, an access point, or a base station.

[0179] According to one particular embodiment, the modulation device and the demodulation device are contained in the same device.

Claims

1. A method for demodulating a received data frame, the frame comprising N information words. ,in, The character at the position in this frame is modulated by a symbol from a dictionary having symbols, and the method makes the method include the following steps: ​ - Obtain (300) prior knowledge about the symbol distribution at multiple locations in the received frame, - Determine the difference representation of the prior knowledge (301), which represents the difference representation for multiple position pairs. ,in, The probability that the difference between two symbols at these positions in a frame has a specific value. - Determine (303) the differential representation of the received frame, which represents the probability that the difference between two received symbols in the frame has a specific value. - The determined differential representations are correlated (304) to obtain a combined estimate of the differences between symbols in the received frame. - Demodulate the received information words based on the obtained merging estimate (305).

2. The method as described in claim 1, wherein, The dictionary Each of the symbols is associated with a symbol of size . finite group Different index values ​​are associated, and among them: - Obtaining prior knowledge includes: for each symbol in this frame. , obtain A vector of probabilities This vector is called the prior distribution, where the rank is The element is the symbol. For the index symbols of this dictionary The probability, - Determining the differential representation of the prior knowledge includes: for each pair of prior distributions Determine a vector containing K probabilities. This vector is called the relative prior distribution, where the rank is The elements are obtained by distributing these elements. and Determined by association, with these symbols and The difference between related indexes equals The probability, - Determining the differential representation of the received frame includes: for each symbol pair in the received frame ( ; ), determine by using these symbols and Determined by association, containing A vector of probabilities This vector is called the relative distribution, where the rank is The elements are related to these symbols and The difference between related indexes equals The probability, and -Associating these determined difference representations includes: these distributions With these distributions Perform element-wise multiplication.

3. The method as described in any of the preceding claims, wherein, A message word The sequence of complex values ​​is modulated by modulating a sequence of size . It is obtained by performing a specific cyclic shift on the root sequence.

4. The method as described in any of the preceding claims, wherein, The received frame is a time-frequency frame, in which, Each of the time steps contains distributions in The size of the set of frequency subcarriers is The complete symbol.

5. The method as described in any one of the preceding claims, wherein, This prior knowledge is received in advance in the message.

6. A method for modulating a data frame to be transmitted, the frame comprising... Information words ,in, The character at position in this frame is modulated by symbols from a dictionary having symbols, such that at least one information character <{0000067}>is modulated by symbols obtained from a subset of the symbol dictionary, the subset being selected according to the position of the character in the frame and / or the target reliability level for transmitting the character.

7. The method of claim 6, wherein, The dictionary Each of the symbols is associated with a symbol of size . finite group Different index values ​​are associated, and among them, for a specific location Selected subset of symbols By and belonging to the finite group The index values ​​of a subset are associated with symbols.

8. The method of claim 7, wherein, This finite group It is a group , Strictly speaking, it is correct.

9. The method according to any one of claims 6 to 8, wherein, The subset of symbols selected for a specific location is determined by the finite group. The subgroup consists of symbols associated with the index values ​​of the subgroup, which includes only the symbols associated with the subgroup. The multiple value of , making yes A multiple of 1.

10. The method of any one of claims 6 to 9, further comprising the step of transmitting a message to a receiver, the message including information representing the probability distribution of at least one symbol at a specific location in the frame.

11. An apparatus for demodulating a data frame, the frame comprising Information words ,in, The character at the position in this frame is modulated by symbols from a dictionary having symbols. The device includes a processor (502) coupled to a memory (501) that contains program instructions (503) configured to perform the following steps: - Obtain prior knowledge about the symbol distribution at multiple locations within the frame. - Determine a difference representation of the prior knowledge, which represents the difference for multiple position pairs. ,in, The probability that the difference between two symbols at these positions in a frame has a specific value. - Determine the differential representation of the received frame, which represents the probability that the difference between two received symbols in the frame has a specific value. - The determined differential representations are correlated to obtain a combined estimate of the differences between symbols in the received frame. - Demodulate the received information words based on the obtained merging estimate.

12. An apparatus for modulating a data frame to be transmitted, the frame comprising... Information words ,in, The character at the position in this frame is modulated by symbols in a dictionary having symbols, and the device includes a processor (602) coupled to a memory (601) containing program instructions (603) configured to perform the following steps,​​ - For each word in this frame , : -According to the word Position in this frame And / or according to the transmitted word The target reliability level is derived from the dictionary. Select a specific subset of symbols from a set of symbols. - Using symbols obtained from the selected subset to describe the word Modulation, - Transmit modulated frames.

13. A communication terminal, comprising the demodulation device as described in claim 11 and / or the modulation device as described in claim 12.

14. A computer program comprising instructions adapted to implement the demodulation method as claimed in any one of claims 1 to 5 and / or the modulation method as claimed in any one of claims 6 to 10 when the program is executed by a processor.

15. A computer-readable information medium having a computer program thereon containing instructions for performing the steps of the demodulation method as claimed in any one of claims 1 to 5 and / or the steps of the modulation method as claimed in any one of claims 6 to 10.

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