JP2022076112A - Log-likelihood ratio calculation circuit and wireless receiver - Google Patents

Abstract

To improve the calculation accuracy of a log-likelihood ratio and improve the error correction capability of low-density parity check.SOLUTION: For bits that are distinguished whether they are 0 or 1 depending on a phase angle φi of an ideal symbol point, a log-likelihood ratio LLRφm is calculated using the phase angle xφ of received signal based on probability density distribution that becomes 0 and probability density distribution that becomes 1 depending on the phase angle. For bits that can be divided into an amplitude distinction symbol point that is distinguished to become 0 or 1 depending on amplitude and a phase distinction symbol point that is distinguished to become 0 or 1 depending on the phase angle, regarding the amplitude distinction symbol point, the log-likelihood ratio LLRφm is calculated using amplitude xR of a received signal based on probability density distribution that becomes 0 and probability density distribution that becomes 1 depending on the amplitude, and regarding the phase distinction symbol point, the log-likelihood ratio LLRφm is calculated using the phase angle xφ of the received signal based on probability density distribution that becomes 0 and probability density distribution that becomes 1 depending on the phase angle.SELECTED DRAWING: Figure 1

Description

The present invention relates to a log-likelihood ratio calculation circuit and a wireless receiving device, and more particularly to a circuit for calculating a log-likelihood ratio used in error correction in low-density parity check decoding and a wireless receiving device including the circuit.

Conventionally, in low density parity check (LDPC: short for Low Density Parity Check) decoding, an error is made using the log-likelihood ratio (LLR: short for Log-Likelihood Ratio) calculated based on the distribution of thermal noise of the received signal. A method for making corrections is known (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2013-201582

By the way, in the high multi-value modulation method, there is a problem that the influence other than the thermal noise such as the phase noise and fading of the received signal is large, and the error correction ability of the low density parity check is reduced. Specifically, the conventional method for calculating the log-likelihood ratio is based on the premise that the amplitude of the received signal fluctuates based on the normal distribution / Gaussian distribution around the ideal symbol point due to the thermal noise of the received signal. However, in this method, it is not possible to consider the fluctuation when the phase of the symbol is rotated due to the phase noise of the received signal, fading, or the like. For this reason, the accuracy of calculating the log-likelihood ratio deteriorates, especially in an environment where phase noise is present, and the error correction capability of the low-density parity check is reduced.

Therefore, the present invention includes a log-likelihood ratio calculation circuit and a radio reception including the log-likelihood ratio calculation circuit, which can improve the calculation accuracy of the log-likelihood ratio and improve the error correction capability of low-density parity check. The purpose is to provide the device.

In order to solve the above problem, the invention according to claim 1 corresponds to the phase angle of the ideal symbol point among the 4-bit received signals modulated by the orthogonal phase amplitude modulation method having a multi-value number of 16 on the transmitting side. For the bit that is distinguished whether it becomes 0 or 1, the phase angle of the received signal is used, and the probability density distribution that becomes 0 and the probability density distribution that becomes 1 according to the phase angle are used. The logarithmic likelihood ratio is calculated, and it is set to 0 or 1 depending on the phase angle and the ideal symbol point (called "amplitude distinction symbol point") that distinguishes between 0 and 1 according to the amplitude. For a bit divided into an ideal symbol point (referred to as a "phase distinction symbol point") in which it is distinguished, which of the amplitude distinction symbol point and the phase distinction symbol point is received. After making a judgment based on the amplitude of the signal, for the amplitude distinction symbol point, using the amplitude of the received signal, the logarithmic probability is based on the probability density distribution that becomes 0 and the probability density distribution that becomes 1 according to the amplitude. The degree ratio is calculated, and for the phase distinction symbol point, the logarithmic likelihood ratio is calculated based on the probability density distribution that becomes 0 and the probability density distribution that becomes 1 according to the phase angle, using the phase angle of the received signal. It is a log-amplitude ratio calculation circuit characterized by calculating.

The invention according to claim 2 is characterized in that the log-likelihood ratio calculation circuit according to claim 1 calculates the log-likelihood ratio of each bit according to a predetermined mathematical formula.

The invention according to claim 3 is a wireless receiving device comprising the log-likelihood ratio calculation circuit according to claim 1 or 2.

According to the inventions of claim 1 and claim 2, the log-likelihood also considers the probability distribution when the phase of the symbol rotates / fluctuates based on the normal distribution / Gaussian distribution due to the phase noise or fading of the received signal. Since the degree ratio is calculated, it is possible to improve the calculation accuracy of the log-likelihood ratio even in an environment where the phase noise of the received signal is dominant, and by extension, the error correction of the low-density parity inspection is possible. It becomes possible to improve the ability.

According to the third aspect of the present invention, it is possible to exert the above-mentioned effects in a wireless receiving device that performs error correction in low density parity check decoding using a log-likelihood ratio.

It is a functional block diagram which shows the schematic structure of the radio reception device in embodiment which includes the LLR calculation part as the log-likelihood ratio calculation circuit which concerns on embodiment of this invention. It is a figure which shows the arrangement of the ideal symbol point of a 16QAM system, and the bit string assigned to each ideal symbol point. It is a figure explaining the setting of the variable related to the calculation of the log-likelihood ratio. It is a figure explaining the concept of the calculation formula of the log-likelihood ratio of the 1st bit, and in particular, it is a figure explaining the region where the 1st bit is 0 and the region where the 1st bit is 1. It is a figure explaining the concept of the calculation formula of the log-likelihood ratio of the 1st bit. It is a figure explaining the concept of the calculation formula of the log-likelihood ratio of the 2nd bit, and in particular, it is a figure explaining a symbol which puts bit information on an amplitude, and a symbol which puts bit information on a phase. It is a figure explaining the concept of the calculation formula of the log-likelihood ratio of the 2nd bit. It is a figure explaining the problem of the conventional method of calculating the log-likelihood ratio, and the measures by the log-likelihood ratio calculation circuit which concerns on this invention. It is a functional block diagram which shows the schematic structure of the evaluation system used in the verification example of the effectiveness of the log-likelihood ratio calculation circuit which concerns on this invention.

Hereinafter, the present invention will be described based on the illustrated embodiment. In the following, the characteristic configuration of the present invention will be described, and the description of the conventional mechanism for performing wireless communication will be omitted. Further, in each figure, the signal line and the imaginary part (Q signal; in other words, the orthogonal component and the Q signal component) that transmit the real part (I signal; in other words, the in-phase component and the I signal component) constituting the complex signal are transmitted. ) Is displayed as one signal line together with the signal line to be transmitted. Further, "greater than or equal to" and "greater than or equal to" in the following description may be replaced with each other, and further, "less than or equal to" and "less than or equal to" may be replaced with each other.

FIG. 1 is a functional block diagram showing a schematic configuration of a wireless receiver 1 according to an embodiment, including an LLR calculation unit 20 as a log-likelihood ratio calculation circuit according to an embodiment of the present invention.

The antenna 10 receives a signal wave transmitted from a radio transmission device (not shown) and transfers the signal wave as a reception signal to the channel filter 11.

Here, the wireless transmission device applies low-density parity inspection coding to the wireless frame to be transmitted and uses a quadrature amplitude modulation method (that is, 16QAM method; QAM is an abbreviation for Quadrature Amplitude Modulation) having a multi-value number of 16. It is modulated and then transmitted from the antenna. That is, the wireless receiving device 1 receives a multi-value modulation signal that has been subjected to low-density parity check coding and is modulated by a quadrature-amplitude modulation method (16QAM method) having a multi-value number of 16.

The channel filter 11 is a filter for limiting the reception band, and may be specifically configured by, for example, a bandpass filter. The channel filter 11 receives the input of the received signal transferred from the antenna 10, performs band limiting processing on the received signal, extracts the received signal in a desired frequency band from the received signal, and outputs the received signal.

The mixer 13 receives the input of the received signal output from the channel filter 11 and receives the input of the local signal output from the local oscillator 12, and multiplies the received signal by the local signal to obtain the frequency of the received signal. Convert (specifically, down-convert) and output.

The automatic gain control unit 14 receives the input of the received signal output from the mixer 13 and performs a gain adjusting process on the received signal so that the level of the received signal becomes constant at a predetermined level to adjust the gain. The received signal (which is an analog signal) after processing (in other words, after level correction) is output.

The A / D converter 15 (Analog-to-Digital converter) receives the input of the received signal output from the automatic gain control unit 14, performs analog-digital conversion processing on the received signal, and converts the received signal from the analog signal. Convert to a digital signal. That is, the A / D converter 15 outputs a digital received signal.

The digital orthogonal detection unit 16 receives an input of a digital reception signal output from the A / D converter 15 and converts the received signal into a baseband signal by orthogonal detection. Specifically, the digital orthogonal detection unit 16 has a multiplier in which a cos wave is input from a numerically controlled oscillator and synchronously detects in-phase components of the received signal, and a sine wave is input from the numerically controlled oscillator to detect the received signal. It is equipped with a multiplier that synchronously detects orthogonal components. The digital orthogonal detection unit 16 performs orthogonal detection of multi-value modulation by digital signal processing, and is expressed by IQ orthogonal coordinates of the real number component (I signal) constituting the real part and the imaginary number component (Q signal) constituting the imaginary part. Complex signals (in other words, detection signals of in-phase components and orthogonal components) are generated and output.

The numerically controlled oscillator of the digital orthogonal detection unit 16 is an oscillator that oscillates at a frequency corresponding to a set value, and generates cos waves and sine waves whose phases differ from each other by 90 ° to each of the two multipliers. Supply.

The roll-off filter 17 receives the input of the baseband signal (in other words, the detection signal of the in-phase component and the orthogonal component) output from the digital orthogonal detection unit 16, and the in-phase component and the orthogonal component of the baseband signal are respectively. The baseband signal is subjected to a process for removing the inter-code interference, and the spectrum waveform of the baseband signal is shaped and output so as to have a desired roll-off.

The equalizer 18 receives the input of the baseband signal output from the roll-off filter 17, and removes intersymbol interference due to frequency selective fading for each of the in-phase component and the orthogonal component of the baseband signal. The baseband signal (received signal) after the adaptive equalization process is output.

The decoding unit 19 receives the input of the log-likelihood ratio (LLR: an abbreviation of Log-Likelihood Ratio) output from the LLR calculation unit 20, and uses the log-likelihood ratio to reduce the density according to, for example, the sum-product decoding method. Perform parity check / decryption processing.

The LLR calculation unit 20 is a circuit for calculating the log-likelihood ratio used in error correction in low-density parity check decoding, and is incorporated in the wireless receiver 1.

The LLR calculation unit 20 according to the embodiment becomes 0 according to the phase angle φ _i of the ideal symbol point among the 4-bit received signals modulated by the orthogonal phase amplitude modulation method having a multi-value number of 16 on the transmitting side. For the bit that distinguishes between 1 and 1, using the phase angle xφ of the received signal, the log-amplitude ratio is based on the probability density distribution that becomes 0 and the probability density distribution that becomes 1 according to the phase angle. LLR φ _m is calculated, and the ideal symbol point (called “amplitude distinction symbol point”) that distinguishes whether it becomes 0 or 1 according to the amplitude and whether it becomes 0 or 1 depending on the phase angle For a bit that is divided into an ideal symbol point (referred to as a "phase-distinguishing symbol point") in which is distinguished, which of the amplitude-distinguishing symbol point and the phase-distinguishing symbol point is the amplitude x _R of the received signal. After making a _judgment based on Calculate _m , and for the phase distinction symbol point, use the phase angle xφ of the received signal to obtain the logarithmic likelihood ratio LLRφ _m based on the probability density distribution that becomes 0 and the probability density distribution that becomes 1 according to the phase angle. I am trying to calculate.

First, FIG. 2 shows the arrangement of ideal symbol points in the 16QAM system and the bit sequence assigned to each ideal symbol point (in other words, the signal space diagram of 16QAM). In FIG. 2, A _i is a homeomorphic component of the ideal symbol point arrangement, and B _i is an orthogonal component of the ideal symbol point arrangement (however, i = 1, 2, 3, 4). Further, FIG. 3 shows the setting of the variables used in the following formulas 1 to 7, which are defined for the arrangement of the ideal symbol points shown in FIG.

The LLR calculation unit 20 calculates the log-likelihood ratio LLR φ _m of the m bit based on the following mathematical formulas 1A and 1B.

The meanings of the symbols and variables in the above formulas 1A and 1B are as follows. The "φ" of the phase angle of the ideal symbol point among the following is displayed as "Φ" in the drawing.
m: Bit number (however, m = 1, 2, 3, 4)
xφ: Phase angle of received signal x _R : Amplitude of received signal φ _i : Phase angle of ideal symbol point (however, the subscript i of φ i = 0, 1, 2, ..., 11)
R _i : Amplitude of ideal symbol point (however, subscript i of R = 0, 1, 2)
σ ² : Noise dispersion R _i (m) = 1: Amplitude of the ideal symbol point (amplitude distinction symbol point) where the mth bit is 1 R _i (m) = 0: Ideal symbol where the mth bit is 0 Amplitude of point (amplitude distinction symbol point) φ _i (m) = 1: Phase of ideal symbol point (phase distinction symbol point) where mth bit is 1 φ _i (m) = 0: mth bit is 0 The phase of the ideal symbol point (phase distinction symbol point) that is

For R _i (m) and φ _i (m), in the mapping method shown in FIG. 3 and specifically, when m = 2, R _i (m) = 1 is R ₀ , and R _i (m). ) = 0 is R ₂ , φ _i (m) = 1 is φ ₂ , φ ₃ , φ ₈ and φ ₉ , and φ _i (m) = 0 is φ ₀ , φ ₅ and φ ₆ , And _φ11 .

The above formula 1A is used when the amplitude x _R of the received signal satisfies the following formula 2 and a plurality of corresponding ideal symbol points exist in the same phase, and the above formula 1B is used in cases other than the above. Be done. In the case of the 16QAM method, in the case of the example shown in FIG. 3 (in other words, the setting), the subscript i of R in the following formula 2 is 1.

The case where a plurality of corresponding ideal symbol points exist in the same phase is a case where a plurality of ideal symbol points exist for a phase angle φ _i (Φ _i in the drawing) of a certain ideal symbol point, and FIG. Specifically, in the mapping method shown in, for example, the phase angle Φ ₁ of the ideal symbol point in which the bit columns “0000” and “0101” exist, and the ideal symbol point in which the bit columns “1000” and “1101” exist. This is the case such as when the phase angle is _Φ4 .

When the above formula 1 is expanded for each of the bit numbers m = 1, 2, 3, 4 in the case of the 16QAM method, it becomes the following formulas 3 to 6. The meanings of the symbols / variables in Formulas 3 to 6 are as follows. The "φ" of the phase angle of the ideal symbol point among the following is displayed as "Φ" in the drawing.
xφ: Phase angle of received signal x _R : Amplitude of received signal φ _i : Phase angle of ideal symbol point (however, the subscript i of φ i = 0, 1, 2, ..., 11)
R _i : Amplitude of ideal symbol point (however, subscript i of R = 0, 1, 2)
σ ² : Noise variance R _thre1 : First amplitude threshold R _thre2 : Second amplitude threshold

The log-likelihood ratio LLR φ ₁ of the first bit is calculated according to the following formula 3.

In the second bit log likelihood ratio LLR φ ₂ , the amplitude x _R of the received signal is equal to or greater than the first amplitude threshold R _thre1 or equal to or less than the second amplitude threshold R _thre2 (that is, x _R ≧ R _thre1 or x _R ≦ R _thre2 ). When the amplitude x _R of the received signal is less than the first amplitude threshold value R _thre1 and larger than the second amplitude threshold value R _thre2 (that is, R _thre2 <x _R <R _thre1 ). Is calculated according to the following formula 4B.

The log-likelihood ratio LLR φ ₃ of the third bit is calculated according to the following formula 5.

In the 4th bit log likelihood ratio LLRφ ₄ , the amplitude x _R of the received signal is equal to or greater than the first amplitude threshold R _thre1 or equal to or less than the second amplitude threshold R _thre2 (that is, x _R ≧ R _thre1 or x _R ≦ R _thre2 ). When the amplitude x _R of the received signal is less than the first amplitude threshold value R _thre1 and larger than the second amplitude threshold value R _thre2 (that is, R _thre2 <x _R <R _thre1 ). Is calculated according to the following formula 6B.

The above formulas 3 to 6 are based on the following ideas (see FIGS. 4 to 7).

In the first bit, the phase angle is from −90 ° to + 90 ° (in other words, from 270 ° to 360 ° / 0 ° to 90 °; that is, in FIG. 4, the phase angles Φ ₉ to Φ ₁₁ and Φ ₀ of the ideal symbol point are set. It becomes ₀ in the 4th and 1st quadrants of the IQ orthogonal coordinate system including up to Φ2, and the phase angle is from + 90 ° to -90 ° (in other words, from 90 ° to 180 ° to 270 °; that is. , In FIG. 4, it becomes 1 in the second and third quadrants of the IQ orthogonal coordinate system including the phase angles Φ ₃ to Φ ₅ and Φ ₆ of the ideal symbol point to Φ ₈ . Therefore, assuming that the phase of the received signal fluctuates based on the normal distribution / Gaussian distribution, the probability density that the 1st bit becomes 0 is shown as shown in FIG. 5A, and the probability density that the 1st bit becomes 1 is shown in FIG. 5B. Is shown. Based on this, by considering these probability density distributions as each term, the above equation 3 for calculating the log-likelihood ratio LLR φ1 of the _first bit is derived (see FIG. 5C).

The 3rd bit is based on the same idea as the 1st bit, that is, the 3rd bit has a phase angle of 0 ° to + 90 ° and then + 180 ° (that is, the phase angle of the ideal symbol point in FIG. 4 is Φ ₀ to Φ ₂ , It becomes 0 in the first and second quadrants of the IQ orthogonal coordinate system including Φ ₃ and up to Φ ₅ , and the phase angle is 0 ° from + 180 ° to + 270 ° (that is, the ideal symbol point in FIG. 4). It becomes ₁ when the phase angle of Φ ₆ to Φ ₈ and Φ ₉ is included in the IQ orthogonal coordinate system (third quadrant and fourth quadrant). Based on this, the above equation 5 for calculating the log-likelihood ratio LLR φ ₃ of the 3rd bit by considering the probability density distribution in which the 3rd bit becomes 0 and the probability density distribution in which the 3rd bit becomes 1 as each term. Is derived.

Further, since the same idea can be applied to all the quadrants of the IQ orthogonal coordinate system for the second bit, the first quadrant of the IQ orthogonal coordinate system will be described as an example. As shown in FIG. 6, the second bit is an ideal symbol point in which whether it becomes 0 or 1 is distinguished by the amplitude (“symbol with bit information on the amplitude” in the figure; the amplitude distinction. (It is a symbol point) and an ideal symbol point where 0 or 1 is distinguished by the phase (“symbol with bit information on the phase” in the figure; it is a phase distinction symbol point. ) And. Therefore, by comparing the amplitude x _R of the received signal with the first amplitude threshold R _thre1 and the second amplitude threshold R _thre2 , the received signal / symbol puts the bit information on either the amplitude or the phase. The method of calculating the logarithmic likelihood ratio is changed for each of them. The probability density distribution in which the second bit becomes 0 and the probability density distribution in which the second bit becomes 1 are shown as shown in FIG. 7A for the symbol on which the bit information is placed on the amplitude. The probability density distribution in which the second bit becomes 0 and the probability density distribution in which the second bit becomes 1 are shown as shown in FIG. 7B, respectively. Based on this, by considering these probability density distributions as each term, the above equation 4 for calculating the log-likelihood ratio LLR φ ₂ of the second bit is derived (see FIG. 7C).

The 4th bit is also based on the same idea as the 2nd bit. For the symbol which puts the bit information on the amplitude, it is the same as the 2nd bit, and for the symbol which puts the bit information on the phase, the 4th bit becomes 0. The phase angles of the ideal symbol points are Φ ₂ , Φ ₃ , Φ ₈ , and Φ ₉ , and the phase angles of the ideal symbol points are Φ ₀ , Φ ₅ , Φ ₆ , and Φ ₁₁ . Based on the fact, the probability density distribution that the 4th bit becomes 0 for the symbol that puts the bit information on the amplitude, the probability density distribution that the 4th bit becomes 1, and the 4th bit is 0 for the symbol that puts the bit information on the phase. By considering the probability density distribution in which the 4th bit becomes 1 and the probability density distribution in which the 4th bit becomes 1 as each term, the above equation 6 for calculating the logarithmic likelihood ratio LLRφ ₄ of the 4th bit is derived.

The first amplitude threshold R _thre1 and the second amplitude threshold R _thre2 are not limited to specific values. For example, the first amplitude threshold R _thre1 is between the amplitudes _R1 and _R2 of the ideal symbol point. The second amplitude threshold R _thre2 is set between the amplitudes R ₀ and R ₁ of the ideal symbol point, and then the bit information is put on the amplitude and the bit information is put on the phase. It is appropriately set to an appropriate value after considering that it can be satisfactorily distinguished from a symbol (in other words, a case where a plurality of corresponding ideal symbol points exist in the same phase can be appropriately extracted). Specifically, for example, it is conceivable that the first amplitude threshold value R _thre1 is set as in the following formula 7A, and the second amplitude threshold value R _thre2 is set as in the following formula 7B.
(Number 7A) R _thre1 = R ₁ + (R ₂ -R ₁ ) / 2
(Number 7B) R _thre2 = _Ro + (R ₁ -R ₀ ) / 2

The LLR calculation unit 20 receives the input of the baseband signal (received signal) output from the equalizer 18, acquires the phase angle _xφ of the received signal and the amplitude xR of the received signal from the baseband signal, and receives the received signal. Taking into consideration the magnitude relationship between the signal amplitude x _R and the first amplitude threshold R _thre1 and the second amplitude threshold R _thre2 , the log-like likelihood ratio LLRφ _m of the m-bit th is determined according to the above equations 3 to 6. Calculate and output.

Then, the decoding unit 19 receives the input of the log-likelihood ratio LLR φ _m output from the LLR calculation unit 20, and uses the log-likelihood ratio LLR φ _m to perform low-density parity check decoding processing according to, for example, the sum-product decoding method. I do.

According to the LLR calculation unit 20 as the log-likelihood ratio calculation circuit according to the embodiment, the probability distribution when the phase of the symbol rotates / fluctuates based on the normal distribution / Gaussian distribution due to the phase noise or fading of the received signal. Since the log-likelihood ratio is calculated in consideration of the above, it is possible to improve the calculation accuracy of the log-likelihood ratio even in an environment where the phase noise of the received signal is dominant, and the log-likelihood ratio is low. It is possible to improve the error correction capability of the density parity check.

Specifically, as shown in FIG. 8, in the conventional method for calculating the log-likelihood ratio, the amplitude of the received signal fluctuates based on the normal distribution / Gaussian distribution around the ideal symbol point due to the thermal noise of the received signal. (Refer to the broken line circle Cf in the figure). Therefore, if there is a fluctuation when the phase of the symbol is rotated due to the phase noise of the received signal (see the arc arrow Fp in the figure), the signal Sf judged to have a high reception probability is the actual transmission signal Ss. It will be different. On the other hand, in the LLR calculation unit 20 as the log-likelihood ratio calculation circuit according to the embodiment, the distribution of fluctuations due to the phase noise of the received signal is taken into consideration, that is, due to the phase noise of the received signal. Since the log-likelihood ratio is calculated in consideration of the situation where the symbol fluctuates on the envelope E, the fluctuation when the phase of the symbol is rotated by the phase noise of the received signal (arc arrow Fp in the figure). Even if there is (see), it is possible to improve the error correction ability of the low density parity inspection by matching the signal determined to have a high reception probability with the actual transmission signal Ss.

An example of verifying the effectiveness of the log-likelihood ratio calculation circuit according to the present invention will be described below.

The purpose of this verification example is to compare the calculation accuracy of the log-likelihood ratio between the conventional method for calculating the log-likelihood ratio and the log-likelihood ratio calculation circuit according to the present invention in an environment where phase noise is present. The evaluation system shown in FIG. 9 was used. In the evaluation system of this verification example, a predetermined sample signal is modulated by the 16QAM method (reference numeral 31 in the figure) and phase noise is added (reference numeral 32), and then a logarithm is obtained based on the distribution of thermal noise of the received signal. The log-likelihood of each of the conventional method for calculating the likelihood ratio (reference numeral 33) and the log-likelihood ratio calculation circuit (reference numeral 20) according to the present invention for calculating the log-likelihood ratio in consideration of the phase noise of the received signal. It was configured as a system to compare the calculation accuracy of the degree ratio.

Here, the log-likelihood ratio takes a positive value when the probability that the transmission bit is 0 is high, and takes a negative value when the probability that the transmission bit is 1 is high. Taking advantage of this, the actual transmission bit is compared with the code of the logarithmic likelihood ratio calculated by the conventional method (reference numeral 33 in FIG. 9) to count the number of times the code is incorrect (reference numeral 34). The actual transmission bit was compared with the code of the logarithmic likelihood ratio calculated by the logarithmic likelihood ratio calculation circuit (reference numeral 20) according to the present invention, and the number of times the code was incorrect was counted (reference numeral 35).

As a result of the evaluation system shown in FIG. 9, the code error rate in the case of the conventional log-likelihood ratio calculation method is 0.829%, and the code error rate in the case of the log-likelihood ratio calculation circuit according to the present invention. Was 0.307%. From this result, it was confirmed that according to the log-likelihood ratio calculation circuit according to the present invention, the bit error rate of the code is reduced to about one-third as compared with the conventional method for calculating the log-likelihood ratio.

Although the embodiment of the present invention has been described above, the specific configuration is not limited to the above-described embodiment, and even if there is a design change or the like within a range that does not deviate from the gist of the present invention. Included in the invention.

Specifically, in the above-described embodiment, the log-likelihood ratio calculation circuit according to the present invention is incorporated as the LLR calculation unit 20 in the wireless receiver 1 whose schematic configuration is shown in FIG. The configuration of the wireless device into which the log-likelihood ratio calculation circuit can be incorporated is not limited to the wireless receiver 1 whose schematic configuration is shown in FIG. 1, and the log-likelihood ratio calculation circuit according to the present invention has another configuration. It may be incorporated into a wireless device.

1 Wireless receiver 10 Antenna 11 Channel filter 12 Local oscillator 13 Mixer 14 Automatic gain control unit 15 A / D converter 16 Digital orthogonal detector 17 Roll-off filter 18 Equalizer 19 Decoding unit 20 LLR calculation unit

Claims (3)

Of the 4-bit received signals modulated by the quadrature amplitude modulation method with a multi-valued number of 16 on the transmitting side
For bits that are distinguished whether they are 0 or 1 depending on the phase angle of the ideal symbol point,
Using the phase angle of the received signal, the log-likelihood ratio is calculated based on the probability density distribution that becomes 0 and the probability density distribution that becomes 1 according to the phase angle.
An ideal symbol point that distinguishes between 0 and 1 depending on the amplitude (called an "amplitude distinction symbol point") and an ideal that distinguishes between 0 and 1 depending on the phase angle. For bits that can be divided into symbol points (called "phase-distinguishing symbol points")
After determining which of the amplitude-distinguishing symbol point and the phase-distinguishing symbol point is based on the amplitude of the received signal,
For the amplitude distinction symbol point, the log-likelihood ratio is calculated based on the probability density distribution that becomes 0 and the probability density distribution that becomes 1 according to the amplitude, using the amplitude of the received signal.
For the phase distinction symbol point, the log-likelihood ratio is calculated based on the probability density distribution that becomes 0 and the probability density distribution that becomes 1 according to the phase angle, using the phase angle of the received signal.
A log-likelihood ratio calculation circuit characterized by this. The log-likelihood ratio is calculated according to the following formula 1 for the 1st bit, which is a bit that is distinguished whether it becomes 0 or 1 depending on the phase angle of the ideal symbol point, and according to the following formula 3 for the 3rd bit. Calculate the log-likelihood ratio and
The logarithmic likelihood ratio is calculated according to the following mathematical formula 2 for the second bit, which is the bit divided into the amplitude-distinguishing symbol point and the phase-distinguishing symbol point, and the logarithmic likelihood ratio is calculated according to the following mathematical formula 4 for the fourth bit. However, when x _R ≧ R _thre1 or x _R ≦ R _thre2 , the formulas 2A and 4A are used, and when R _thre2 <x _R <R _thre1 , the formulas 2B and 4B are used).

Here,
xφ: Phase angle of received signal x _R : Amplitude of received signal φ _i : Phase angle of ideal symbol point (however, the subscript i of φ i = 0, 1, 2, ..., 11)
R _i : Amplitude of ideal symbol point (however, subscript i of R = 0, 1, 2)
σ ² : Noise dispersion R _thre1 : First amplitude threshold value R _thre2 : Second amplitude threshold value The log-likelihood ratio calculation circuit according to claim 1. The log-likelihood ratio calculation circuit according to claim 1 or 2.
A wireless receiver characterized by that.

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