Log likelihood ratio calculation circuit and wireless receiving device

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

[Technical field]

[0001] The present invention relates to a log-likelihood ratio calculation circuit and a radio 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 radio receiving device including said circuit. [Background technology]

[0002] Conventionally, in low density parity check (LDPC) decoding, a method for performing error correction using a log-likelihood ratio (LLR) calculated based on the distribution of thermal noise in a received signal has been known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-201582 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the high multilevel modulation method, the influence of factors other than thermal noise, such as phase noise and fading of the received signal, is large, and there is a problem that the error correction ability of the low density parity check is reduced. Specifically, in the conventional method of calculating the log likelihood ratio, it is assumed that the amplitude of the received signal fluctuates based on a normal distribution / Gaussian distribution centered on an ideal symbol point due to thermal noise of the received signal. However, this method cannot take into account the fluctuation when the phase of the symbol rotates due to phase noise and fading of the received signal. Therefore, the calculation accuracy of the log likelihood ratio deteriorates, especially in an environment where phase noise exists, and the error correction ability of the low density parity check is reduced.

[0005] Therefore, an object of the present invention is to provide a log-likelihood ratio calculation circuit and a wireless receiving device including the log-likelihood ratio calculation circuit, which can improve the calculation accuracy of the log-likelihood ratio and thereby improve the error correction capability of the low-density parity check. [Means for solving the problem]

[0006] In order to solve the above problem, the present invention provides a method for modulating a signal on a transmitting side using a quadrature amplitude modulation method with a multi-level number of 16. 、 4bit Modulated with data from and for a bit that is divided into an ideal symbol point (referred to as an "amplitude-distinguishing symbol point") that is distinguished as being 0 or 1 depending on the amplitude and an ideal symbol point (referred to as a "phase-distinguishing symbol point") that is distinguished as being 0 or 1 depending on the phase angle, a log-likelihood ratio is calculated based on the probability density distribution that becomes 0 and the probability density distribution that becomes 1 depending on the phase angle, using the phase angle of the received signal. For a bit that is divided into an ideal symbol point (referred to as an "amplitude-distinguishing symbol point") that is distinguished as being 0 or 1 depending on the amplitude and an ideal symbol point (referred to as a "phase-distinguishing symbol point") that is distinguished as being 0 or 1 depending on the phase angle, a determination is made based on the amplitude of the received signal as to whether the bit is the amplitude-distinguishing symbol point or the phase-distinguishing symbol point. Then, for the amplitude-distinguishing symbol point, a log-likelihood ratio is calculated based on the probability density distribution that becomes 0 and the probability density distribution that becomes 1 depending on the amplitude, using the amplitude of the received signal. And for the phase-distinguishing symbol point, a log-likelihood ratio is calculated based on the probability density distribution that becomes 0 and the probability density distribution that becomes 1 depending on the phase angle, using the phase angle of the received signal.

[0007] The invention recited in claim 2 is characterized in that in the log-likelihood ratio calculation circuit recited in claim 1, the log-likelihood ratio of each bit is calculated according to a predetermined formula.

[0008] The invention as set forth in claim 3 is a radio receiving device comprising the log-likelihood ratio calculation circuit as set forth in claim 1 or 2. Effect of the Invention

[0009] According to the inventions described in claims 1 and 2, the log-likelihood ratio is calculated taking into account the probability distribution when the phase of the symbol rotates or fluctuates based on a normal distribution / Gaussian distribution due to phase noise or fading of the received signal, etc., so that it is possible to improve the calculation accuracy of the log-likelihood ratio even in an environment where phase noise of the received signal is dominant, and ultimately to improve the error correction capability of the low-density parity check.

[0010] According to the invention as recited in claim 3, it is possible to achieve the above-mentioned advantageous effects in a wireless receiving device that performs error correction in low-density parity check decoding using a log-likelihood ratio. [Brief description of the drawings]

[0011] [Figure 1] 1 is a functional block diagram showing a schematic configuration of a wireless receiving device according to an embodiment of the present invention, including an LLR calculation unit as a log-likelihood ratio calculation circuit. [Diagram 2] FIG. 2 is a diagram showing an arrangement of ideal symbol points in the 16QAM system and bit strings assigned to each ideal symbol point. [Diagram 3] FIG. 13 is a diagram for explaining the setting of variables related to the calculation of a log-likelihood ratio. [Figure 4] FIG. 13 is a diagram for explaining the concept of a calculation formula for a log-likelihood ratio of the first bit, and in particular, a diagram for explaining a region where the first bit is 0 and a region where the first bit is 1. [Diagram 5] 11 is a diagram for explaining the concept of a calculation formula for a log-likelihood ratio of the 1st bit. FIG. [Figure 6] FIG. 13 is a diagram for explaining the concept of a calculation formula for a log-likelihood ratio of the second bit, and in particular, a diagram for explaining a symbol having bit information in amplitude and a symbol having bit information in phase. [Figure 7] FIG. 13 is a diagram for explaining the concept of a calculation formula for a log-likelihood ratio for the second bit. [Figure 8] 1 is a diagram for explaining problems with a conventional method for calculating a log-likelihood ratio and a countermeasure by a log-likelihood ratio calculation circuit according to the present invention; [Figure 9]FIG. 1 is a functional block diagram showing a schematic configuration of an evaluation system used in a verification example of the effectiveness of a log-likelihood ratio calculation circuit according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will be described below based on the illustrated embodiment. Note that the following describes the characteristic configuration of the present invention, and the description of the conventional mechanism for wireless communication will be omitted. In addition, in each drawing, a signal line transmitting a real part (I signal; in other words, an in-phase component, an I signal component) constituting a complex signal and a signal line transmitting an imaginary part (Q signal; in other words, a quadrature component, a Q signal component) are shown together as a single signal line. In addition, in the following description, "greater than or equal to" and "greater than" may be interchangeable, and further, "less than or equal to" and "less than" may be interchangeable.

[0013] FIG. 1 is a functional block diagram showing a schematic configuration of a wireless receiving device 1 according to an embodiment of the present invention, including an LLR calculation section 20 as a log-likelihood ratio calculation circuit according to the embodiment of the present invention.

[0014] The antenna 10 receives a signal wave sent from a radio transmitting device (not shown) and transfers the signal wave to a channel filter 11 as a received signal.

[0015] Here, the wireless transmitting device performs low-density parity check coding on the wireless frame to be transmitted, modulates it using a quadrature amplitude modulation method with a multi-level number of 16 (i.e., 16QAM method; QAM is an abbreviation for Quadrature Amplitude Modulation), and transmits it from an antenna. In other words, the wireless receiving device 1 receives a multi-level modulated signal that has been subjected to low-density parity check coding and modulated using a quadrature amplitude modulation method with a multi-level number of 16 (16QAM method).

[0016] The channel filter 11 is a filter for limiting the reception band, and specifically may be configured by, for example, a bandpass filter. The channel filter 11 receives the reception signal transferred from the antenna 10, performs band limiting processing on the reception signal, and extracts and outputs a reception signal of a desired frequency band from the reception signal.

[0017] The mixer 13 receives an input of the received signal output from the channel filter 11 and also receives an input of a local signal output from the local oscillator 12, multiplies the received signal by the local signal, and converts (specifically, down-converts) the frequency of the received signal and outputs it.

[0018] The automatic gain control unit 14 receives the received signal output from the mixer 13, performs gain adjustment processing on the received signal so that the level of the received signal becomes constant at a predetermined level, and outputs the received signal (which is an analog signal) after gain adjustment processing (in other words, after level correction).

[0019] A / D converter 15 (Analog-to-Digital converter) receives the received signal output from automatic gain control unit 14, and performs analog-to-digital conversion processing on the received signal to convert the analog signal into a digital signal. That is, A / D converter 15 outputs a digital received signal.

[0020] The digital quadrature detection unit 16 receives the digital received signal output from the A / D converter 15 and converts the received signal into a baseband signal by quadrature detection. Specifically, the digital quadrature detection unit 16 includes a multiplier that receives a cosine wave from a numerically controlled oscillator and synchronously detects an in-phase component of the received signal, and a multiplier that receives a sine wave from the numerically controlled oscillator and synchronously detects an orthogonal component of the received signal. The digital quadrature detection unit 16 performs quadrature detection of multi-level modulation by digital signal processing, and generates and outputs a complex signal (in other words, a detection signal of the in-phase component and the orthogonal component) expressed in IQ orthogonal coordinates with a real component (I signal) constituting a real part and an imaginary component (Q signal) constituting an imaginary part.

[0021] The numerically controlled oscillator of the digital quadrature detection unit 16 is an oscillator that oscillates at a frequency according to a set value, and generates a cosine wave and a sine wave whose phases differ from each other by 90°, and supplies them to each of the two multipliers.

[0022] The roll-off filter 17 receives the baseband signal (in other words, the detection signal of the in-phase component and the quadrature component) output from the digital quadrature detection unit 16, processes the in-phase component and the quadrature component of the baseband signal to remove inter-symbol interference, and shapes the spectrum waveform of the baseband signal to have a desired roll-off, and outputs the result.

[0023] The equalizer 18 receives the baseband signal output from the roll-off filter 17, performs adaptive equalization processing on each of the in-phase component and quadrature component of the baseband signal in order to remove inter-symbol interference due to frequency selective fading, and outputs a baseband signal after adaptive equalization processing (received signal).

[0024] The decoding unit 19 receives the log-likelihood ratio (LLR: abbreviation of Log-Likelihood Ratio) output from the LLR calculation unit 20, and performs low-density parity check decoding processing using the log-likelihood ratio according to, for example, a sum-product decoding method.

[0025] The LLR calculation unit 20 is a circuit that calculates a log-likelihood ratio used in error correction in low-density parity check decoding, and is incorporated in the wireless receiving device 1.

[0026] The LLR calculation unit 20 according to the embodiment calculates a quadrature amplitude modulation scheme with a multi-level number of 16 on the transmitting side. 、 4bit Modulated with data from The phase angle φ of the ideal symbol point of the received signal i For bits that are distinguished as 0 or 1 depending on the phase angle, the log-likelihood ratio LLRφ is calculated based on the probability density distribution that becomes 0 or 1 depending on the phase angle using the phase angle xφ of the received signal. m For bits that are divided into ideal symbol points that are distinguished as 0 or 1 depending on the amplitude (called "amplitude-distinguishing symbol points") and ideal symbol points that are distinguished as 0 or 1 depending on the phase angle (called "phase-distinguishing symbol points"), the amplitude x R Then, for the amplitude-distinguishing symbol point, the amplitude x of the received signal is R Based on the probability density distribution that becomes 0 and the probability density distribution that becomes 1 according to the amplitude, the log-likelihood ratio LLRφ m For the phase-distinguishing symbol point, the log-likelihood ratio LLRφ 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 xφ of the received signal. m The calculation is performed as follows.

[0027] First, the arrangement of ideal symbol points in the 16QAM system and the bit strings assigned to each ideal symbol point (in other words, the signal space diagram of 16QAM) are shown in Figure 2. i is the in-phase component of the ideal symbol constellation, and B i are orthogonal components of the ideal symbol point constellation (where i=1, 2, 3, 4). FIG. 3 shows the settings of variables used in the following formulas 1 to 7, which are defined for the ideal symbol point constellation shown in FIG.

[0028] The LLR calculation unit 20 calculates the log-likelihood ratio LLRφ for the m-th bit based on the following formulas 1A and 1B. m Calculate.

number

[0029] The meanings of the symbols and variables in the above formulas 1A and 1B are as follows: Note that the phase angle "φ" of the ideal symbol point in the following formulas is shown as "Φ" in the drawings. m: bit number (where m = 1, 2, 3, 4) xφ: Phase angle of the received signal x R : Received signal amplitude φ i : Phase angle of ideal symbol point (where φ subscript i = 0, 1, 2, . . . , 11) R i : Amplitude of ideal symbol point (where the subscript i of R = 0, 1, 2) σ 2 :Noise variance R i (m) = 1: Amplitude of the ideal symbol point (amplitude-distinguishing symbol point) where the mth bit is 1 R i (m) = 0: Amplitude of the ideal symbol point (amplitude-distinguishing symbol point) where the mth bit is 0 φ i (m) = 1: Phase of the ideal symbol point (phase-distinguishing symbol point) where the mth bit is 1 φ i (m) = 0: Phase of the ideal symbol point (phase-distinguishable symbol point) where the mth bit is 0

[0030] R i (m) and φ i Regarding (m), in the case of the mapping method shown in FIG. 3 and m=2, specifically, R i (m)=1 is R0, R i (m)=0 is R2 and φ i (m)=1 is φ2, φ3, φ8, and φ9, and φ i(m)=0 is φ0, φ5, φ6, and φ 11 It is.

[0031] The above formula 1A expresses the amplitude of the received signal x R satisfies the following formula 2 and is used when a plurality of corresponding ideal symbol points exist in the same phase, and the above formula 1B is used in other cases. In the case of the example (in other words, setting) shown in FIG. 3 in the case of the 16QAM system, the subscript i of R in the following formula 2 is 1.

number

[0032] When a plurality of corresponding ideal symbol points exist in the same phase, that is, when the phase angle φ of a certain ideal symbol point exists, i (In the drawing, i ), and in the mapping method shown in Figure 3, this refers to cases such as the phase angle Φ1 of the ideal symbol point where the bit sequences "0000" and "0101" exist, and the phase angle Φ4 of the ideal symbol point where the bit sequences "1000" and "1101" exist.

[0033] When the above formula 1 is expanded for each of bit numbers m=1, 2, 3, 4 in the case of the 16QAM system, it becomes formulas 3 to 6 below. The meanings of the symbols and variables in formulas 3 to 6 are as follows. Note that the phase angle "φ" of the ideal symbol point in the following formulas is shown as "Φ" in the drawings. xφ: Phase angle of the received signal x R : Received signal amplitude φ i : Phase angle of ideal symbol point (where φ subscript i = 0, 1, 2, . . . , 11) R i : Amplitude of ideal symbol point (where the subscript i of R = 0, 1, 2) σ 2 :Noise variance R thre1 : First amplitude threshold Rthre2 : Second amplitude threshold

[0034] The log-likelihood ratio LLRφ1 of the 1st bit is calculated according to the following Equation 3.

number

[0035] The log-likelihood ratio (LLRφ2) of the second bit is the amplitude of the received signal x R is the first amplitude threshold R thre1 Above or equal to the second amplitude threshold R thre2 Below (i.e., x R ≧R thre1 or x R ≦R thre2 ) is calculated according to the following Equation 4A, and the amplitude of the received signal x R is the first amplitude threshold R thre1 Less than a second amplitude threshold R thre2 Greater than (i.e., R thre2 <x R <R thre1 ) is calculated according to the following Equation 4B.

number

[0036] The log-likelihood ratio LLRφ3 of the 3rd bit is calculated according to Equation 5 below.

number

[0037] The log-likelihood ratio (LLRφ4) of the 4th bit is the amplitude of the received signal x R is the first amplitude threshold R thre1 Above or equal to the second amplitude threshold R thre2 Below (i.e., x R ≧R thre1 or x R ≦R thre2 ) is calculated according to the following Equation 6A, and the amplitude of the received signal x R is the first amplitude threshold R thre1 Less than a second amplitude threshold Rthre2 Greater than (i.e., R thre2 <x R <R thre1 ) is calculated according to the following Equation 6B.

number

[0038] The above formulas 3 to 6 are based on the following idea (see FIGS. 4 to 7).

[0039] The first bit is the phase angle from -90° to +90° (in other words, from 270° to 360° / 0° to 90°; that is, the phase angle of the ideal symbol point in Figure 4 is from Φ 11 , Φ0 to Φ2) and becomes 1 when the phase angle is +90° to -90° (in other words, 90° to 270° through 180°; that is, the second and third quadrants of the IQ orthogonal coordinate system including the phase angle of the ideal symbol point Φ3 to Φ8 through Φ5, Φ6 in FIG. 4). Therefore, if it is considered that the phase of the received signal fluctuates based on a normal distribution / Gaussian distribution, the probability density of the first bit being 0 is shown as in FIG. 5A, and the probability density of the first bit being 1 is shown as in FIG. 5B. Based on this, by considering these probability density distributions as each term, the above-mentioned Equation 3 for calculating the log-likelihood ratio LLRφ1 of the first bit is derived (see FIG. 5C).

[0040] The third bit is based on the same idea as the first bit; that is, the third bit is 0 when the phase angle goes from 0° to +90° to +180° (i.e., the first and second quadrants of the IQ orthogonal coordinate system including the phase angles of the ideal symbol points Φ0 to Φ5 through Φ2 and Φ3 in Fig. 4), and is 0 when the phase angle goes from +180° to +270° to 0° (i.e., the phase angles of the ideal symbol points Φ6 to Φ8 and Φ9 in Fig. 4). 11Based on this, the above formula 5 for calculating the log-likelihood ratio LLRφ3 of the 3rd bit is derived by considering the probability density distribution where the 3rd bit is 0 and the probability density distribution where the 3rd bit is 1 as each term.

[0041] As for the second bit, the same concept can be applied to all quadrants of the IQ orthogonal coordinate system, so the first quadrant of the IQ orthogonal coordinate system will be used as an example for the explanation. As shown in Fig. 6, the second bit is divided into ideal symbol points where the amplitude determines whether it is 0 or 1 (the "symbols that carry bit information in the amplitude" in the figure; these are amplitude-distinguishing symbol points), and ideal symbol points where the phase determines whether it is 0 or 1 (the "symbols that carry bit information in the phase" in the figure; these are phase-distinguishing symbol points). For this reason, when the amplitude x of the received signal is R The first amplitude threshold R thre1 and a second amplitude threshold R thre2 By comparing with, it is determined whether the received signal / symbol carries bit information in amplitude or phase, and the method of calculating the log-likelihood ratio is changed accordingly. The probability density distributions of the second bit being 0 and the probability density distributions of the second bit being 1 for symbols carrying bit information in amplitude are shown in Fig. 7A, and the probability density distributions of the second bit being 0 and the probability density distributions of the second bit being 1 for symbols carrying bit information in phase are shown in Fig. 7B. Based on this, by considering these probability density distributions as each term, the above formula 4 for calculating the log-likelihood ratio LLRφ2 for the second bit is derived (see Fig. 7C).

[0042] The fourth bit is based on the same idea as the second bit. For symbols that carry bit information in amplitude, the same applies as the second bit. For symbols that carry bit information in phase, the fourth bit is 0 when the phase angle of the ideal symbol point is Φ2, Φ3, Φ8, and Φ9, and 1 when the phase angle of the ideal symbol point is Φ0, Φ5, Φ6, and Φ 11Based on this, by considering as individual terms the probability density distribution in which the fourth bit is 0 and the probability density distribution in which the fourth bit is 1 for symbols carrying bit information in the amplitude, and the probability density distribution in which the fourth bit is 0 and the probability density distribution in which the fourth bit is 1 for symbols carrying bit information in the phase, the above-mentioned Equation 6 for calculating the log-likelihood ratio LLRφ4 for the fourth bit can be derived.

[0043] First amplitude threshold R thre1 and the second amplitude threshold R thre2 is not limited to a specific value, and may be, for example, the first amplitude threshold R thre1 is set between the amplitudes R1 and R2 of the ideal symbol points and a second amplitude threshold R thre2 is set between the amplitudes R0 and R1 of the ideal symbol points, and is appropriately set to an appropriate value while taking into consideration that a symbol having bit information in its amplitude and a symbol having bit information in its phase can be appropriately distinguished (in other words, a case in which a plurality of corresponding ideal symbol points exist in the same phase can be appropriately extracted). Specifically, for example, the first amplitude threshold value R thre1 is set as shown in Equation 7A below, and the second amplitude threshold R thre2 It is considered that the value is set as shown in the following formula 7B. (Number 7A) R thre1 = R1+(R2-R1) / 2 (Number 7B) R thre2 = R o +(R1-R0) / 2

[0044] The LLR calculation unit 20 receives the baseband signal (received signal) output from the equalizer 18, and derives from the baseband signal the phase angle xφ of the received signal and the amplitude x of the received signal. R and obtaining the amplitude x of the received signal. R and the first amplitude threshold R thre1 and the second amplitude threshold R thre2 The log-likelihood ratio LLRφ of the mth bit is calculated according to the above Equations 3 to 6, taking into account the magnitude relationship between m Calculate and output.

[0045] Then, the decoding unit 19 calculates the log-likelihood ratio LLRφ output from the LLR calculation unit 20. m The log-likelihood ratio LLRφ m is used to perform low density parity check decoding processing, for example, according to the sum-product decoding method.

[0046] According to the LLR calculation unit 20 serving as a log-likelihood ratio calculation circuit of the embodiment, the log-likelihood ratio is calculated taking into consideration the probability distribution when the phase of the symbol rotates or fluctuates based on a normal distribution / Gaussian distribution due to phase noise or fading of the received signal. This makes it possible to improve the calculation accuracy of the log-likelihood ratio even in an environment dominated by phase noise of the received signal, and ultimately makes it possible to improve the error correction capability of the low-density parity check.

[0047] Specifically, as shown in Fig. 8, the conventional method of calculating the log likelihood ratio is premised on the assumption that the amplitude of the received signal fluctuates based on a normal distribution / Gaussian distribution centered on an ideal symbol point due to thermal noise of the received signal (see dashed circle Cf in the figure). Therefore, if there is a fluctuation (see circular arc arrow Fp in the figure) when the phase of the symbol rotates due to the phase noise of the received signal, the signal Sf determined to have a high probability of being received will differ from the actual transmission signal Ss. In contrast, the LLR calculation unit 20 as the log likelihood ratio calculation circuit according to the embodiment is designed to take into account the distribution of fluctuations due to the phase noise of the received signal, that is, to calculate the log likelihood ratio while also considering the situation in which the symbol fluctuates on the envelope E due to the phase noise of the received signal. Therefore, even if there is a fluctuation (see circular arc arrow Fp in the figure) when the phase of the symbol rotates due to the phase noise of the received signal, the signal determined to have a high probability of being received will match the actual transmission signal Ss, making it possible to improve the error correction ability of the low density parity check.

[0048] An example of verifying the effectiveness of the log-likelihood ratio calculation circuit according to the present invention will be described below.

[0049] In this verification example, an evaluation system shown in Fig. 9 was used for the purpose of comparing the calculation accuracy of the log likelihood ratio between a conventional method for calculating a 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 in this verification example was configured as a system for comparing the calculation accuracy of the log likelihood ratio between a conventional method (reference number 33) that calculates a log likelihood ratio based on the distribution of thermal noise of a received signal after modulating a predetermined sample signal by the 16QAM method (reference number 31 in the figure) and adding phase noise (reference number 32), and the log likelihood ratio calculation circuit according to the present invention (reference number 20) that calculates a log likelihood ratio while also taking into account the phase noise of the received signal.

[0050] Here, the log-likelihood ratio takes a positive value when the probability that the transmitted bit is 0 is high, and takes a negative value when the probability that the transmitted bit is 1 is high. Using this, the actual transmitted bit is compared with the sign of the log-likelihood ratio calculated by the conventional method (reference number 33 in FIG. 9) to count the number of times the sign is incorrect (reference number 34), and the actual transmitted bit is compared with the sign of the log-likelihood ratio calculated by the log-likelihood ratio calculation circuit (reference number 20) according to the present invention to count the number of times the sign is incorrect (reference number 35).

[0051] 9, the code error rate in the case of the conventional log-likelihood ratio calculation method was 0.829%, while the code error rate in the case of the log-likelihood ratio calculation circuit according to the present invention was 0.307%. This result confirmed that the code error rate in the case of the log-likelihood ratio calculation circuit according to the present invention was reduced to approximately one-third compared to the conventional log-likelihood ratio calculation method.

[0052] Although the embodiment of the present invention has been described above, the specific configuration is not limited to the above embodiment, and even if there are design changes and the like within the scope of the gist of the present invention, they are included in the present invention.

[0053] Specifically, in the above embodiment, the log-likelihood ratio calculation circuit according to the present invention is incorporated as an LLR calculation unit 20 in the wireless receiving device 1 whose schematic configuration is shown in FIG. 1. However, the configuration of the wireless device in which the log-likelihood ratio calculation circuit according to the present invention can be incorporated is not limited to the wireless receiving device 1 whose schematic configuration is shown in FIG. 1. The log-likelihood ratio calculation circuit according to the present invention may be incorporated in a wireless device having another configuration. [Explanation of symbols]

[0054] 1 Radio receiving device 10 Antennas 11 Channel Filters 12 Local Oscillator 13 Mixer 14 Automatic Gain Control 15 A / D Converter 16 Digital quadrature detection section 17 Roll-off Filter 18 Equalizer 19 Decoding section 20 LLR calculation unit

Claims

1. On the transmitting side, the signal is modulated by a quadrature amplitude modulation method with a multi-value of 16, and the received signal is modulated with 4-bit data. For bits that are differentiated as 0 or 1 depending on the phase angle of the ideal symbol point, calculating a log-likelihood ratio based on a probability density distribution that becomes 0 and a probability density distribution that becomes 1 according to the phase angle of the received signal; Regarding bits that can be divided into ideal symbol points that are distinguished as being 0 or 1 depending on the amplitude (called "amplitude-distinguishing symbol points") and ideal symbol points that are distinguished as being 0 or 1 depending on the phase angle (called "phase-distinguishing symbol points"), determining whether the symbol point is the amplitude-distinguishing symbol point or the phase-distinguishing symbol point based on the amplitude of the received signal; calculating a log-likelihood ratio for the amplitude-distinguishing symbol point based on a probability density distribution that becomes 0 and a probability density distribution that becomes 1 according to the amplitude using the amplitude of the received signal; calculating a log-likelihood ratio for the phase-distinguished symbol point based on a probability density distribution that becomes 0 and a probability density distribution that becomes 1 according to the phase angle by using a phase angle of the received signal; A log-likelihood ratio calculation circuit comprising:

2. A log likelihood ratio is calculated for a first bit, which is a bit that is distinguished as being 0 or 1 depending on a phase angle of the ideal symbol point, according to the following Equation 1, and a log likelihood ratio is calculated for a third bit according to the following Equation 3, A log likelihood ratio is calculated for the second bit, which is a bit that is divided into the amplitude distinguishing symbol point and the phase distinguishing symbol point, according to the following formula 2A or 2B, and a log likelihood ratio is calculated for the fourth bit according to the following formula 4A or 4B (where R thre2 <R thre1 , x R ≧R thre1 or x R ≦R thre2 Formula 2A and Formula 4A are used when R thre2 <x R <R thre1 Formula 2B and Formula 4B are used when [0010] 【Number 2A】 【Number 2B】 [0030] [Number 4A] [Number 4B] Here, xφ: Phase angle of the received signal x R : Amplitude of the received signal φ i : Phase angle of ideal symbol point (where φ subscript i = 0, 1, 2, ..., 11) R i : Amplitude of ideal symbol point (where the subscript i of R = 0, 1, 2) σ 2 : noise variance R thre1 : first amplitude threshold R thre2 : second amplitude threshold 2. The log-likelihood ratio calculation circuit according to claim 1 .

3. A log-likelihood ratio calculation circuit according to claim 1 or 2, A radio receiving device comprising:

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