JP6327138B2 - Receiving machine - Google Patents

Description

  The present invention relates to a receiver of a communication system that uses an error correction code and bi-orthogonal modulation concatenated together.

  An orthogonal modulation method that performs transmission by assigning a bit sequence to be transmitted to an orthogonal sequence is a communication system that can suppress bit errors in a white Gaussian noise transmission line when the dimension of the orthogonal sequence to be used is large and that requires high power efficiency. This is a particularly useful method. Orthogonal sequences used in the orthogonal modulation scheme can be configured as long as the sequences can be orthogonal to each other, and an orthogonal sequence of the orthogonal modulation scheme is defined using an orthogonal matrix.

  In addition, as an extension of the orthogonal modulation method, there is a non-orthogonal modulation method (Non-Patent Document 1) that defines an orthogonal sequence using an orthogonal matrix and a matrix generated by inverting each element of the orthogonal matrix, for example. .陪 According to the orthogonal modulation method, the number of orthogonal sequences to which the bit string to be transmitted can be doubled compared to the orthogonal modulation method, so that the number of bits that can be transmitted with one modulation signal can be doubled. It is possible to improve the utilization efficiency.

  On the other hand, in a communication system, an error correction code such as a convolutional code is generally applied to reduce bit errors caused by noise or the like mixed in a transmission path. Such an error correction code can be applied to an orthogonal modulation system. In Patent Document 1, in a communication system that uses a convolutional code and a Walsh orthogonal code (orthogonal modulation) concatenated together, a correct orthogonal code cannot be estimated by correlation detection, which exceeds the correction capability of soft decision error correction decoding. In such a situation, a receiving apparatus is disclosed that improves the error correction performance and reduces bit errors by estimating and demodulating the maximum likelihood path of a trellis diagram combining a convolutional code and a Walsh orthogonal code. .

JP-A-6-252879 (FIG. 5)

Myong C. KIM, and Steven A. TRETTER, “Performance of sequential decoding with biorthogonal modulation and Q-level Quantization,” IEEE Transaction on Communication Technology, pp.88-92, February 1971.

However, the conventional decoding method based on the trellis diagram disclosed in Patent Document 1 is a decoding method of a signal obtained by orthogonally encoding data error-corrected with a convolutional code with a Walsh orthogonal code. It cannot be used in a communication system using a method. For this reason, in a communication system using a quadrature modulation method, when error correction code and bi-quadrature modulation are concatenated and used together, it is not possible to improve the error correction performance and realize good communication with reduced bit errors. There was a problem.
The present invention has been made in order to solve the above-described problems. In a communication system using both an error correction code and bi-orthogonal modulation, an error rate of information transmitted with improved error correction performance is improved. The object is to obtain a receiver that can be reduced.

A receiver according to the present invention includes a symbol including a symbol generated by assigning a sequence of encoded information in which information to be transmitted is encoded with an error correction code to any one of a plurality of orthogonal sequences used in quadrature modulation Based on the correlation processing unit for obtaining the correlation between the input signal obtained from the received signal and each of the plurality of orthogonal sequences for each received symbol unit, and the received symbol unit correlation obtained by the correlation processing unit, A soft decision unit that performs a soft decision on a received symbol for each of a plurality of encoded information sequences assigned to any of a plurality of orthogonal sequences, and an error correction code and an error code using a soft decision result by the soft decision unit and a decoder for restoring the information to be transmitted by performing the decoding based on the trellis diagram which is determined in advance in accordance with the orthogonal modulation, a plurality of orthogonal sequences are orthogonal matrices and the quadrature The matrix is defined by a matrix whose phase is rotated, and the correlation processing unit obtains a correlation for a set of orthogonal sequences having different matrix elements in the orthogonal matrix that is the source of phase rotation from among a plurality of orthogonal sequences, and performs a soft decision. The unit obtains a soft decision value, which is a result of the soft decision for each of a plurality of encoded information sequences, based on the real axis component and the imaginary axis component of the correlation for the set of orthogonal sequences obtained by the correlation processing unit. , That is.

  According to the present invention, an input signal obtained from a signal received from a transmitter that generates and transmits transmission symbols by performing error correction coding and 陪 orthogonal modulation, and an orthogonal sequence of 陪 orthogonal modulation for each received symbol. By obtaining a correlation, performing soft decision for each received symbol based on the obtained correlation, and obtaining a soft decision value for a sequence of encoded information corresponding to each orthogonal sequence of quadrature modulation. Using the decision value, it is possible to restore the information transmitted by the transmitter based on the trellis diagram determined in advance according to the error correction coding and bi-orthogonal modulation performed by the transmitter, improving the error correction performance Thus, the error rate of information transmitted can be reduced.

It is a block diagram which shows an example of a function structure of the receiver which concerns on Embodiment 1 of this invention. It is a block diagram which shows an example of the encoder which carries out an error correction encoding of the information bit which the transmitter facing the receiver of Embodiment 1 of this invention transmits. It is a table | surface which shows an example of allocation of the transmission bit sequence with respect to the orthogonal sequence in the transmitter facing the receiver of Embodiment 1 of this invention. It is a schematic diagram which shows an example of arrangement | positioning on the complex plane of the reference | standard complex correlation value and the complex correlation value of a received symbol in the receiver of Embodiment 1 of this invention. It is a table | surface which shows an example of the soft decision value which the soft decision part of the receiver of Embodiment 1 of this invention calculated | required. It is a trellis figure which the decoding part of the receiver of Embodiment 1 of this invention uses. It is a table | surface which shows the modification of allocation of the transmission bit sequence to the orthogonal sequence of the receiver of Embodiment 1 of this invention. It is a table | surface which shows an example of allocation of the transmission bit sequence to the orthogonal sequence of the receiver which concerns on Embodiment 2 of this invention. It is a schematic diagram explaining the soft decision process of the receiver of Embodiment 2 of this invention. It is a schematic diagram explaining the soft decision process of the receiver of Embodiment 2 of this invention. It is a table | surface which shows an example of the soft decision value which the soft decision part of the receiver of Embodiment 2 of this invention calculated | required. It is a schematic diagram explaining the modification of the soft decision process of the receiver of Embodiment 2 of this invention. It is a table | surface which shows an example of the soft decision value which the soft decision part of the modification of the receiver of Embodiment 2 of this invention calculated | required.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In the drawings referred to in the following description, the same or corresponding parts are denoted by the same reference numerals.

Embodiment 1 FIG.
1 is a block diagram showing an example of a functional configuration of a receiver according to Embodiment 1 of the present invention. The receiver of this embodiment includes a receiving antenna 10, an analog processing unit 20, an analog / digital conversion (A / D conversion) unit 30, a synchronization estimation unit 40, a synchronization correction unit 50, a correlation processing unit 60, a soft decision unit 70, A decoding unit 80 is provided.

  The receiving antenna 10 receives a radio signal transmitted by an opposite transmitter by performing error correction coding and bi-orthogonal modulation on information to be transmitted. The analog processing unit 20 performs analog signal processing on the signal received by the receiving antenna 10 and outputs the result. The A / D conversion unit 30 converts the signal processed by the analog processing unit 20 into a digital signal and outputs it.

  The synchronization estimation unit 40 performs synchronization estimation using the signal output from the A / D conversion unit 30 and the pilot signal held in advance in the synchronization estimation unit 40, and outputs a synchronization estimation result. The synchronization correction unit 50 performs a synchronization correction process on the signal output from the A / D conversion unit 30 based on the synchronization estimation result output from the synchronization estimation unit 40, and outputs a signal after synchronization correction.

  The correlation processing unit 60 receives the signal subjected to the synchronization correction by the synchronization correction unit 50, and obtains the correlation between the input signal and the orthogonal sequence used in the orthogonal modulation performed by the transmitter. The soft decision unit 70 performs a soft decision based on the correlation obtained by the correlation processing unit 60. The decoding unit 80 performs error correction decoding using the soft decision result of the soft decision unit 70 and restores the information transmitted by the transmitter.

  The analog processing unit 20, the A / D conversion unit 30, the synchronization estimation unit 40, the synchronization correction unit 50, the correlation processing unit 60, the soft decision unit 70, and the decoding unit 80 are hardware such as an ASIC (Application Specific Integrated Circuit). It can also be realized by using a processor including peripheral circuits such as a memory and a program executed on the processor. Further, by combining hardware such as ASIC, a processor, and a program, it is possible to realize some functions with hardware such as ASIC and implement some functions with software.

  Next, the operation of the receiver of this embodiment will be described. First, a signal received from a transmitter facing the receiver will be described. Hereinafter, the information transmitted by the transmitter will be described as information represented by bits, and information to be transmitted is referred to as information bits.

  The transmitter performs predetermined error correction coding on the information bits to be transmitted to generate encoded bits (encoded information), and the encoded bit sequence (transmitted bit sequence) includes a plurality of orthogonal sequences used in orthogonal modulation. Any one of them is assigned, and a symbol (transmission symbol) to be transmitted is generated based on the assigned orthogonal sequence. The generated transmission symbols are arranged in a predetermined format together with the same pilot signal used for synchronization estimation in the synchronization estimation unit 40 of the receiver, and a transmission frame is generated. The generated transmission frame is converted from a digital signal to an analog signal, and further up-converted to a signal in a high frequency band to generate a transmission signal. The generated transmission signal is transmitted wirelessly from the transmission antenna of the transmitter.

  FIG. 2 is a block diagram illustrating an example of an encoder that performs error correction coding. FIG. 2 shows the configuration of a convolutional encoder with a constraint length of 3 and an encoding rate of 1/2. According to this encoder, since the encoding rate is ½, 1 information bit is encoded into 2 encoded bits. In this embodiment, it is assumed that the information bits are error correction encoded by the encoder of FIG.

  陪 Orthogonal modulation method is an extended orthogonal modulation method by defining an orthogonal sequence using an orthogonal matrix and a matrix in which the sign of each element of the orthogonal matrix is inverted. The part defined by the matrix with the element sign inverted is regarded as a signal having an opposite phase to the orthogonal sequence signal defined by the original orthogonal matrix, that is, a signal whose phase is rotated by π. Can do. Furthermore, since there is no need to limit the phase rotation amount to π, the quadrature modulation method is a new orthogonal matrix in which the original one orthogonal matrix and its orthogonal matrix are phase rotated by a predetermined phase rotation amount. It can be generalized as a method of transmitting transmission information using an orthogonal sequence defined by

It is also possible to define multiple orthogonal sequences by creating multiple orthogonal matrices with different phase rotations for one orthogonal matrix, and in this case, the phase that rotates the phase of the orthogonal matrix The number of orthogonal sequences to which transmission information can be assigned increases according to the number (type) of rotation amount. As described above, the quadrature modulation method is a modulation method in which the number of orthogonal sequences can be expanded according to the dimension of the original orthogonal matrix and the number (type) of phase rotation amounts for phase rotation of the orthogonal sequences.
Hereinafter, in this embodiment, it will be described that bi-orthogonal modulation is performed using orthogonal sequences defined by four different orthogonal phase states (four types of phase rotation amounts) based on a four-dimensional Hadamard matrix. .

  FIG. 3 is a table showing an example of correspondence between orthogonal sequences of orthogonal modulation and transmission bit sequences performed in this embodiment. Note that the association between the orthogonal sequence and the transmission bit sequence shown in FIG. 3 is an example, and is not necessarily limited to this, and may be another association. In the orthogonal sequence shown in FIG. 3, the orthogonal sequences with numbers 1 to 4 indicate orthogonal sequences defined by a four-dimensional Hadamard matrix. The numbers 5 to 8 indicate orthogonal sequences defined by a matrix obtained by rotating a four-dimensional Hadamard matrix by a phase rotation amount π. Similarly, the range of numbers 9 to 12 is a phase rotation amount π / 2, and the range of numbers 13 to 16 is a phase rotation amount −π / 2 and is defined by a matrix obtained by phase rotation of a four-dimensional Hadamard matrix. Each series is shown. In FIG. 3, j is an imaginary unit.

  As shown in FIG. 3, in this example, 16 orthogonal sequences can be defined, and thus it is possible to transmit 4 bits with one transmission symbol generated based on one orthogonal matrix. is there. That is, the transmission bit sequence is a 4-bit sequence.

  Receiving antenna 10 receives the transmission signal including the symbol generated as described above and transmitted wirelessly from the opposite transmitter, and outputs the received signal to analog processing unit 20. The analog processing unit 20 performs predetermined analog signal processing on the reception signal output from the reception antenna 10. Here, the predetermined analog signal processing includes known processing according to the radio system of the communication system to which the receiver of this embodiment is applied, such as down-conversion processing for converting a high frequency band signal into a low frequency band signal. Just do it. The A / D conversion unit 30 converts the signal processed by the analog processing unit 20 from an analog signal to a digital signal, and generates a complex baseband signal of the digital signal. Here, the complex baseband signal is a signal having a real axis component and an imaginary axis component. The analog / digital conversion processing performed by the A / D conversion unit may be performed by a known method.

  The synchronization estimation unit 40 performs a predetermined synchronization estimation process using the complex baseband signal generated by the A / D conversion unit 30 and the pilot signal held in advance by the synchronization estimation unit 40, and the synchronization estimation result is converted into a synchronization correction unit. Output to 50. Here, the synchronization estimation process is a process for estimating the synchronization timing of the complex baseband signal generated by the A / D conversion unit 30 such as frequency synchronization, symbol timing synchronization, and carrier phase synchronization. Band signal frequency, clock timing, carrier phase, and the like. The synchronization estimation process performed by the synchronization estimation unit 40 may be a known process according to a communication system to which the receiver according to this embodiment is applied.

  The synchronization correction unit 50 performs a complex baseband signal synchronization correction process based on the synchronization estimation result input from the synchronization estimation unit 40, and outputs the complex baseband signal after the synchronization correction. Here, the synchronization correction processing is processing for correcting frequency, clock timing, carrier phase, and the like. The synchronization correction process performed by the synchronization correction unit 50 may be performed by a known method according to a communication system to which the receiver of this embodiment is applied.

  The correlation processing unit 60 uses the complex baseband signal subjected to synchronization correction by the synchronization correction unit 50 as an input signal, and receives each orthogonal sequence for each symbol (received symbol) received for the input complex baseband signal after synchronization correction. Correlation processing for obtaining the correlation (complex correlation value) is performed. Here, the complex correlation value is a correlation value composed of a real axis component and an imaginary axis component. In addition, the correlation process should just perform the well-known correlation process according to the used quadrature modulation. Note that the correlation processing may be performed on the orthogonal base sequence (the orthogonal base numbers 1 to 4 shown in FIG. 3) defined by the complex baseband signal subjected to synchronization correction and the orthogonal matrix with the phase rotation amount zero. This is because the complex correlation value obtained by the correlation process with the orthogonal sequence defined by the orthogonal matrix with the phase rotation amount of zero is different from the other orthogonal sequences shown in FIG. By expressing the correlation. Note that it is not necessary to limit the target of correlation processing to an orthogonal sequence defined by an orthogonal matrix with a phase rotation amount of zero. For example, correlation processing is performed by selecting a set of orthogonal sequences having different matrix elements in the orthogonal matrix that is the source of phase rotation, such as making the orthogonal sequence number 7 instead of the orthogonal sequence number 4 the target of correlation processing. May be performed.

  FIG. 4 is a schematic diagram for explaining the complex correlation value obtained by the correlation processing unit 60 of this embodiment. 4A shows a complex plane representing a complex correlation value obtained by correlation processing with the orthogonal sequence {1, 1, 1, 1} of number 1 in FIG. 3, and similarly, FIG. The sequence {1, -1,1, -1}, (c) is the number 3 orthogonal sequence {1,1, -1, -1}, and (d) is the number 4 orthogonal sequence {1, -1 , -1, 1}, complex planes representing complex correlation values obtained by correlation processing are shown. The white circles (◯) shown on the real axis and the imaginary axis in FIG. 4 are obtained when the orthogonal series symbols corresponding to the transmission bit series 0000 to 1111 are received under the condition where there is no noise or signal distortion. Represents an expected complex correlation value (reference value of the complex correlation value). Hereinafter, an ideal complex correlation value is referred to as a reference complex correlation value.

  In addition, black circles (●) in FIG. 4 show examples of complex correlation values actually obtained when correlation processing is performed on an input signal (complex baseband signal after synchronization correction) affected by noise or the like. FIG. 4 shows an example of a complex correlation value when a symbol of an orthogonal sequence {1, 1, 1, 1} (number 1 in FIG. 3) is transmitted and the symbol is received by a receiver. And At this time, if the received signal is not deteriorated due to the influence of noise or the like, the obtained complex correlation value should match the white circle corresponding to the transmission bit sequence 0000 in the complex plane of FIG. It shows a state where the complex correlation value is observed at a position shifted due to noise or the like.

  If there is no influence of noise or the like, the complex correlation values in the complex planes of FIGS. 4B, 4C, and 4D are zero and should not be observed in these complex planes. This shows that complex correlation values can be obtained in each complex plane. The complex correlation value (correlation value in each complex plane in FIG. 4) obtained by the correlation processing unit 60 for each orthogonal sequence to be correlated with the input signal is output to the soft decision unit 70.

  When soft decision section 70 receives the complex correlation value from correlation processing section 60, soft decision section 70 performs soft decision on the input signal for each transmission bit sequence based on each complex correlation value in units of received symbols, and makes a soft decision result (soft decision result) Value) to the decoding unit 80. Here, the soft decision processing performed by the soft decision unit 70 will be specifically described by taking as an example the case where the complex correlation value illustrated in FIG. 4 is input. The complex correlation values indicated by black circles in FIGS. 4A to 4D are x0, x1, x2, and x3, respectively, and the real axis component of each complex correlation value is Re [•] (for example, Re [x0]). The imaginary axis component is expressed as Im [•] (for example, Im [x0]).

  The soft decision unit 70 holds a reference complex correlation value corresponding to each transmission bit sequence shown in FIG. 4 in advance. The soft decision unit 70 determines whether or not the sign of the real axis component or the imaginary axis component matches between the complex correlation value input from the correlation processing unit 60 and the reference complex correlation value corresponding to each transmission bit sequence. To do. For example, when obtaining a soft decision value with the transmission bit sequence 0000, does the code of the real axis component Re [x0] of x0 match the code of the real axis component of the reference complex correlation value corresponding to the transmission bit sequence 0000? Determine whether or not. As another example, when a soft decision value with the transmission bit sequence 1001 is obtained, the code of the imaginary axis component Im [x1] of x1 and the code of the imaginary axis component of the reference complex correlation value corresponding to the transmission bit sequence 1001 Is matched.

  When the codes match, the real axis component or the imaginary axis component of the complex correlation value for which the code is determined is output as it is as a soft decision value for the transmission bit sequence, and when the codes do not match, the complex correlation value A value obtained by inverting the sign of the real axis component or the imaginary axis component is output as a soft decision value. In the case of the complex plane in FIG. 4A, the complex correlation value x0 is positive for both the real axis component and the imaginary axis component, so the soft decision value for the transmission bit sequence corresponding to the complex plane in FIG. As shown in (a) of the table of FIG. Similarly, in the complex planes of FIGS. 4B, 4C, and 4D, the soft decision values for the respective transmission bit sequences are shown in FIGS. 5B, 5C, and 5D in the table of FIG. It is determined as follows.

  As described above, the soft decision unit 70 performs the soft decision for each transmission bit sequence associated with the orthogonal sequence used in the quadrature modulation based on the complex correlation value obtained from the complex baseband signal after synchronization correction. To obtain a soft decision value. In the case of this embodiment, since there are 16 transmission bit sequences, a total of 16 soft decisions are made.

  The decoding unit 80 performs error correction decoding using the soft decision value obtained by the soft decision unit 70, and restores information bits corresponding to a sequence of encoded bits (transmission bit sequence) transmitted by the opposite transmitter. To do. In this embodiment, a transmission composed of encoded bits obtained by performing error correction encoding using a convolutional code having a constraint length of 3 and an encoding rate of 1/2 shown in FIG. Since the bit sequence is transmitted, the decoding unit 80 performs error correction decoding by Viterbi decoding corresponding thereto. Specifically, Viterbi decoding based on a trellis diagram in which state transitions for two consecutive convolutional codes are combined into one is performed, and 2 information bits corresponding to a 4-bit transmission bit sequence are decoded.

  FIG. 6 shows a part of a trellis diagram of error correction decoding performed by the decoding unit 80 of this embodiment. FIG. 6 shows one state transition (two internal state transitions of the convolutional code encoder) extracted from the trellis diagram of this embodiment. Note that the 2-bit and 4-bit bit values delimited by the slash “/” attached to each branch are respectively an information bit input to the encoder and an encoded bit (transmission bit sequence) output from the encoder. ). As can be seen from the trellis diagram of FIG. 6, the number of branches per state transition is 16, and each branch has a one-to-one correspondence with the transmission bit sequence transmitted in one symbol.

  The decoding unit 80 assigns the soft decision value obtained by the soft decision unit 70 to each branch of the trellis diagram of FIG. 6, and selects the most likely path using the Viterbi algorithm. The process of selecting the most probable path by the Viterbi algorithm based on the soft decision value of the received symbol and the trellis diagram may be performed using a known technique. Then, the decoding unit 80 restores the information bits based on the most probable path finally selected.

  As described above, according to the receiver of this embodiment, the information to be transmitted is generated by allocating a sequence of encoded information obtained by performing error correction encoding to any one of a plurality of orthogonal sequences used in bi-orthogonal modulation. A correlation processing unit that obtains a correlation with each orthogonal sequence for each received symbol unit with respect to an input signal obtained from a signal that has received a signal from an opposing transmitter including Based on the correlation, a soft decision unit that performs soft decision on the received symbol for each encoded information sequence assigned to the orthogonal sequence, and a result of the soft decision on each encoded information sequence in the soft decision unit A decoding unit that restores information to be transmitted transmitted by the transmitter based on an error correction code used in the transmitter and a trellis diagram determined in advance according to quadrature modulation , It was to prepare for the.

  As a result, even when error correction coding and bi-orthogonal modulation are performed, it is possible to obtain a soft decision value of the received symbol for each encoded information sequence associated with the orthogonal sequence used in bi-orthogonal modulation. Thus, decoding based on a trellis diagram can be performed in units of symbols of 陪 orthogonal modulation. Thereby, the error correction performance in the receiver can be improved in a communication system in which error correction code and bi-orthogonal modulation are used together.

  In addition, the correlation processing performed by the correlation processing unit is a set of orthogonal sequences having different matrix elements in the orthogonal matrix that is the source of phase rotation among the orthogonal sequences used in orthogonal modulation (in the above example, the amount of phase rotation). Is a zero and is defined as an orthogonal sequence defined from the original Hadamard matrix itself), the complex correlation value of each orthogonal sequence and the received symbol is obtained, and the soft decision unit obtains each complex correlation obtained by the correlation processing unit. The correlation processing amount is reduced by obtaining the soft decision value of the received symbol for the encoded information sequence corresponding to each orthogonal sequence used in the orthogonal orthogonal modulation from the real axis value and the imaginary axis value. It is possible.

  In Embodiment 1 described above, the orthogonal sequence used in bi-orthogonal modulation is configured based on the Hadamard matrix, but the present invention is not limited to this. For example, you may comprise based on the discrete Fourier-transform matrix which is a kind of orthogonal matrix. In this case, each row of the discrete Fourier transform matrix has complex sine waves orthogonal to each other, so that the correlation processing unit of the receiver can obtain the complex correlation value by performing the discrete Fourier transform.

  In the first embodiment, the orthogonal sequence used in the quadrature modulation is configured based on the four-dimensional orthogonal matrix. However, the orthogonal sequence is configured based on the arbitrary-dimensional orthogonal matrix according to the requirements for the communication system. You may make it do. For example, FIG. 7 shows an example of correspondence between an orthogonal sequence composed of an 8-dimensional Hadamard matrix and four different phase states and a transmission bit sequence.

  In the orthogonal sequence shown in FIG. 7, numbers 1 to 8 are orthogonal sequences defined by an 8-dimensional Hadamard matrix, and numbers 9 to 16 are defined by a matrix obtained by phase-rotating an 8-dimensional Hadamard matrix by a phase rotation amount π. Orthogonal sequences, numbers 17 to 24 are orthogonal sequences defined by a matrix obtained by phase-rotating an 8-dimensional Hadamard matrix with a phase rotation amount π / 2, and numbers 25 to 32 are 8-dimensional Hadamard matrices having a phase rotation amount −π. Each orthogonal sequence defined by a matrix rotated in phase by / 2 is shown. In this example, 32 orthogonal sequences can be defined by combining four phase states using an 8-dimensional orthogonal matrix, and 5 bits can be transmitted with one transmission symbol. .

  Even in such a case, the correlation processing unit calculates eight complex correlation values using an 8-dimensional Hadamard matrix, and the soft decision unit performs comparison with the reference complex correlation value to perform soft decision processing for each received symbol. be able to. Then, the decoding unit may perform Viterbi decoding using a trellis diagram in which a plurality of consecutive state transitions are combined at one time so that 5 consecutive encoded bits can be assigned to one branch. Note that with a coding rate 1/2 convolutional code, 2 encoded bits are generated in one state transition, and therefore, to assign 5 encoded bits to one branch, 5 consecutive bits are required. What is necessary is just to combine the state transitions of one time into 10 times so that 10 encoded bits are represented by one state transition. Thus, by assigning soft decisions for two consecutive symbols as a unit to a branch of a trellis diagram, an error correction decoding process using a Viterbi algorithm can be realized.

  In this embodiment, the case where the orthogonal sequence used in the quadrature modulation is configured by the orthogonal matrix and the four types of phase rotation amounts has been described. However, if the orthogonal sequence can be configured, the phase rotation amounts can be changed by four types. It is not limited to. For example, when two types of phase rotation amounts are used and an orthogonal sequence is defined by the original four-dimensional Hadamard matrix and a matrix given the phase rotation amount π, the soft decision unit performs the realization of the complex plane. A soft decision on the reference complex correlation value on the axis may be performed. In addition, since 3 encoded bits can be transmitted per symbol, the decoding unit may perform decoding based on a trellis diagram corresponding to the encoded bit.

  In this embodiment, transmission symbols generated in the transmitter are multiplexed with pilot signals to form a transmission frame. For example, an interleaver that changes the order of transmission symbols in a predetermined pattern is used. Later, it may be multiplexed with a pilot signal to form a transmission frame. In this case, the receiver replaces the received symbols in the reverse order of the order change performed on the transmitter side, and then performs decoding. As a result, it is possible to enjoy the effect that communication quality deterioration can be suppressed when the communication environment continuously deteriorates due to fading or the like.

  In the present embodiment, the soft decision unit compares the complex correlation value obtained by the correlation processing unit with the reference complex correlation value on the real axis or the imaginary axis, and if the codes match, the soft bit for the transmission bit sequence is soft. The decision value is the real or imaginary axis value of the complex correlation value, and if the signs do not match, the soft decision value for the transmission bit sequence is reversed with respect to the real or imaginary axis value of the complex correlation value However, the present invention is not limited to this. For example, when the complex correlation value and the reference complex correlation value are compared on both the real axis and the imaginary axis, if the signs do not match, the soft decision value for the transmission bit sequence may be zero (invalid value). In this case, the error correction performance of the decoding unit deteriorates, but the decoding process can be simplified.

Embodiment 2. FIG.
In the first embodiment, the form in which the orthogonal sequence used in the quadrature modulation is configured using four types of phase rotation amounts has been described. In the second embodiment, the orthogonal sequence is configured with eight types of phase rotation amounts. explain. The configuration of the receiver of this embodiment is the same as that of the receiver of the first embodiment shown in FIG.

  Next, the operation will be described. The receiver according to the first embodiment has received the transmission symbol generated by assigning the transmission bit sequence to the orthogonal sequence of the quadrature modulation scheme shown in FIG. 3 at the opposite transmitter. The receiver according to this embodiment Receives a transmission symbol generated by assigning a transmission bit sequence to the orthogonal sequence shown in FIG. The association between the orthogonal sequence and the transmission bit sequence shown in FIG. 8 is an example, and the present invention is not limited to this, and other associations may be used.

  In FIG. 8, the orthogonal sequences with numbers 1 to 2 indicate orthogonal sequences defined by a two-dimensional Hadamard matrix, and the orthogonal sequences with numbers 3 to 4 are obtained by rotating the two-dimensional Hadamard matrix by a phase rotation amount π / 4. An orthogonal sequence defined by a matrix is shown. Similarly, the orthogonal sequences numbered 5-6 are phase rotation amount π / 2, the orthogonal sequences numbered 7-8 are phase rotation amount 3π / 4, the orthogonal sequences numbered 9-10 are phase rotation amount π, and numbers 11-12. Is a two-dimensional Hadamard matrix with phase rotation amount −3π / 4, orthogonal sequences numbered 13 to 14 with phase rotation amount −π / 2, and orthogonal sequences numbered 15 to 16 with phase rotation amount −π / 4. Are orthogonal sequences defined by a matrix whose phase is rotated.

  As shown in FIG. 8, in this example, 16 orthogonal sequences can be defined. Therefore, it is possible to transmit 4 bits with one transmission symbol generated based on one orthogonal matrix. is there. That is, the transmission bit sequence is a 4-bit sequence.

  The operation of the receiver of this embodiment is the same as that of the first embodiment with respect to the receiving antenna 10, analog processing unit 20, A / D conversion unit 30, synchronization estimation unit 40, synchronization correction unit 50, and correlation processing unit 60. It is. In this embodiment, since there are two orthogonal sequences with zero phase rotation, two complex correlation values are obtained.

  Soft decision section 70 of this embodiment performs soft decision of received symbols for transmission bit sequences respectively assigned to orthogonal sequences corresponding to eight different phase rotation amounts. The soft decision unit 70 of this embodiment holds a reference complex correlation value as shown in FIG. FIG. 9A shows a complex plane representing a reference complex correlation value corresponding to the orthogonal sequence {1, 1}, and FIG. 9B represents a reference complex correlation value corresponding to the orthogonal sequence {1, -1}. Indicates a complex plane. As in FIG. 4, white circles (◯) indicate reference complex correlation values corresponding to orthogonal sequences of the transmission bit sequences.

  Also, in FIG. 9, similarly to FIG. 4, an example of the complex correlation value obtained by the correlation processing unit 60 is indicated by a black circle (●). Here, it is assumed that the transmission symbol is a symbol corresponding to transmission bit sequence 0000, and FIG. 9A shows a complex correlation at a position close to the reference congestion correlation value corresponding to transmission bit sequence 0000. In FIG. 9B, a complex correlation value exists at a position close to zero. 9 (a) and 9 (b), the reference complex correlation value is an orthogonal sequence symbol located on the real axis or the imaginary axis, that is, transmission bit sequences 0000, 0100, 1000, 1100, 0001, 0101, 1001, and 1101. The soft decision of the corresponding symbol can be performed by a process equivalent to the process of the soft decision unit 70 of the first embodiment.

  On the other hand, for soft decision of symbols whose reference complex correlation values are not located on the real axis or the imaginary axis, that is, symbols corresponding to the transmission bit sequences 0010, 0110, 1010, 1110, 0011, 0111, 1011, 1111, The determination unit 70 performs −π / 4 phase rotation on the complex correlation value obtained by the correlation processing unit 60 and the reference complex correlation value, and performs a soft decision on the complex correlation value and the reference complex correlation value after the phase rotation. Do. In addition, about the reference | standard complex correlation value, it is also possible for the soft decision part 70 to hold | maintain the value after phase rotation. FIGS. 10A and 10B are the reference complex correlation value illustrated in FIGS. 9A and 9B and the reference complex after phase rotation obtained by performing phase rotation of −π / 4 with respect to the complex correlation value, respectively. It is a figure which shows a correlation value.

  As can be seen by comparing FIG. 9 and FIG. 10, in FIG. 10, the reference correlation value that was not on the real or imaginary axis before the phase rotation of −π / 4 is on the real or imaginary axis after the phase rotation. Will be located. Therefore, by using the reference complex correlation value and the complex correlation value after the phase rotation, it is possible to perform the soft decision by the same processing as in the first embodiment. The complex correlation values shown in FIGS. 9A and 9B are y0 and y1, respectively, and the complex correlation values after phase rotation of −π / 4 shown in FIGS. 10A and 10B are z0 and y0, respectively. When z1 is set, the received symbol soft decision result for each transmission bit sequence is as shown in FIG.

  Thereafter, the decoding unit 80 performs the same decoding process as in the first embodiment based on the soft decision value obtained by the soft decision unit 70 to restore the information bits transmitted by the transmitter.

  In the description of the above-described second embodiment, the phase rotation amount of the phase rotation in the soft decision unit 70 is set to −π / 4, but this corresponds to the phase rotation amount at the time of determining the orthogonal sequence of the quadrature modulation method. It is determined. For example, when there are 16 phase rotation amounts at intervals of π / 8 on the unit circle, the phase rotation amount of the phase rotation performed by the soft decision unit 70 is −π / 8, −π / 4, −3π / 8. What is necessary is just to carry out in three ways.

  In the description of the second embodiment, the phase rotation amount of the phase rotation in the soft decision unit 70 is defined in the minus direction as −π / 4. However, this is not always necessary, and for example, π / 4. It is good. FIGS. 12A and 12B show the complex plane when the reference complex correlation value and the complex correlation value shown in FIGS. 9A and 9B are rotated by π / 4 phase. At this time, if the values obtained by rotating the complex correlation values y0 and y1 by π / 4 phase are set to w0 and w1, the orthogonal sequence corresponding to the reference complex correlation value that does not exist on the real axis or the imaginary axis before the phase rotation is received. The soft decision values of the symbols are as shown in FIG.

  As described above, according to the receiver of this embodiment, the input obtained from the signal received from the opposite transmitter including the transmission symbol generated by performing the orthogonal correction with the error correction code. For a signal, a correlation processing unit that obtains a correlation with each orthogonal sequence for each received symbol, a correlation value obtained by the correlation processing unit, and a soft decision for each symbol based on the correlation value obtained by phase-rotating the correlation value And a soft decision unit that obtains a soft decision value for each orthogonal sequence of orthogonal modulation, and an error correction code used in the transmitter and an error code based on the soft decision value for each orthogonal sequence obtained by the soft decision unit A decoding unit that restores information transmitted by the transmitter by obtaining a maximum likelihood path of a trellis diagram determined in advance according to orthogonal modulation. As a result, even when the granularity of the phase rotation amount when defining the orthogonal sequence of the bi-orthogonal modulation scheme is smaller than π / 2, the error correction performance in the receiver is improved as in the receiver of the first embodiment. be able to.

  10 reception antennas, 20 analog processing units, 30 analog-digital conversion units, 40 synchronization estimation units, 50 synchronization correction units, 60 correlation processing units, 70 soft decision units, 80 decoding units.

Claims (4)

Obtained from a signal that has received a transmission signal including a symbol generated by assigning a sequence of encoded information in which information to be transmitted is encoded with an error correction code to any of a plurality of orthogonal sequences used in quadrature modulation A correlation processing unit for obtaining a correlation between an input signal and each of the plurality of orthogonal sequences for each received symbol;
Based on the correlation of the received symbol units obtained by the correlation processing unit, the received symbol soft decision is performed for each of the plurality of encoded information sequences allocated to any of the plurality of orthogonal sequences. A soft decision part;
Using the results of soft-decision by the soft decision unit, and the error correction code and the Bi-orthogonal modulation according to performed decoding based on the trellis diagram predetermined to restore the transmitted information on object decryption unit Prepared,
The plurality of orthogonal sequences are defined from an orthogonal matrix and a matrix obtained by phase rotation of the orthogonal matrix,
The correlation processing unit obtains the correlation for a set of orthogonal sequences having different matrix elements from each other in the orthogonal matrix that is a source of phase rotation among the plurality of orthogonal sequences,
The soft decision unit, based on the real axis component and the imaginary axis component of the correlation for the set of orthogonal sequences obtained by the correlation processing unit, performs the soft decision for each of the plurality of encoded information sequences. Find the soft decision value that is the result,
A receiver characterized by that. The soft decision unit holds a correlation reference value corresponding to each of the plurality of encoded information sequences;
When the reference value corresponding to the encoded information sequence to be subjected to the soft decision is a real axis value, if the reference value and the real axis component of the correlation obtained by the correlation processing unit match, If the sign of the real axis component does not match, the value obtained by inverting the sign of the real axis component is set as the soft decision value for the encoded information series corresponding to the target reference value.
When the reference value corresponding to the encoded information series to be subjected to the soft decision is a real axis value, if the reference value and the imaginary axis component of the correlation obtained by the correlation processing unit match, If the sign of the imaginary axis component does not match, the value obtained by inverting the sign of the imaginary axis component is set as the soft decision value for the encoded information sequence corresponding to the reference value of interest.
The receiver according to claim 1 . The soft decision unit, when the positive or negative of the real axis component or the imaginary axis component of the correlation obtained by the reference processing unit and the correlation processing unit do not match, the coding information sequence corresponding to the reference value The receiver according to claim 2 , wherein the soft decision value is an invalid value. The correlation processing unit phase-rotates the correlation obtained for the set of orthogonal sequences by a predetermined amount of phase rotation, and implements the obtained correlation on a complex plane represented on a real axis or an imaginary axis. the correlation for the orthogonal sequence represented in a position other than on either axis of the shaft or the imaginary axis, either one of claims 1 to 3, characterized in that determined on the basis of the correlation the phase rotation The receiver according to one item.

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