JP2018133740A - Radio communication device, phase noise correction method, and radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent deterioration in communication quality due to phase noise.SOLUTION: A radio communication device 10 for performing multicarrier transmission is provided. The radio communication device 10 includes: a measuring unit 11 that measures a power spectrum of phase noise on the basis of a reception signal y; and a computation unit 12 that identifies a sample point used for estimating the phase noise on the basis of an autocorrelation value of the phase noise calculated on the basis of the measured power spectrum, interpolates first phase noise estimated about the identified sample point to calculate an estimation value of second phase noise estimated about all sample points, and corrects the phase noise of the reception signal y on the basis of the calculated estimation value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wireless communication device, a phase noise correction method, and a wireless communication system.

  In recent years, there is a method of using a broadband signal as a method of improving the wireless transmission speed. A bandwidth allowed for wireless communication in a band based on a certain frequency is determined based on that frequency. Also, the higher the frequency, the wider the allowable bandwidth, and high-speed transmission using a wide bandwidth can be realized. For example, international standards such as IEEE802.11ad and IEEE802.11ay stipulate the use of a high frequency band (60 GHz band) in order to realize high-speed transmission.

  When the high frequency band as described above is used, phase noise due to frequency fluctuation of the local oscillator becomes large. For example, in a wireless communication system that employs an Orthogonal Frequency Division Multiplexing (OFDM) scheme, the orthogonality between subcarriers is disturbed due to the influence of phase noise as described above, resulting in ICI (Inter Carrier Interference) in which subcarriers interfere with each other. sell. When ICI occurs, communication quality deteriorates. Therefore, a method for correcting the above phase noise has been studied.

  As a method for correcting phase noise, for example, a phase noise correction coefficient is estimated using a pilot signal and a replica signal included in an OFDM symbol, and adjacent three channel equalized received subcarrier signals are combined, A method for correcting oscillator phase noise has been proposed. Also, a method has been proposed in which phase noise is suppressed by detecting phase fluctuations from a complex baseband signal before performing FFT (Fast Fourier Transform). In addition, phase error information is generated using the phase error information and amplitude distortion information of each subcarrier, the channel distortion correction coefficient is corrected based on the phase error information, and the phase noise is calculated using the channel distortion correction coefficient. A method for correcting the above has been proposed.

  Also, a method has been proposed in which a received signal replica is generated from a signal converted into the frequency domain by FFT, and a phase noise component is estimated and corrected so that the mean square error between the received signal and the received signal replica is minimized. Yes. In addition, a method for estimating and correcting a phase noise component using a convergence algorithm (LMS (Least Mean Square), RLS (Recursive Least Square), etc.) using a received signal and a received signal replica in a time domain has been proposed.

JP 2016-092454 JP Japanese Patent Laid-Open No. 11-220451 JP 2000-286819

Songping Wu and Yeheskel Bar-Ness, "Computationally Efficient Phase Noise Cancellation Technique in OFDM Systems with Phase Noise", ISSSTA2004, Sydney, Australia, 30 Aug.-2 Sep. 2004. Satoshi Suyama, Hiroshi Suzuki, Kazuhiko Fukawa and Jungo Izumi, "Iterative Receiver Employing Phase Noise Compensation and Channel Estimation for Millimeter-Wave OFDM Systems", IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 27, NO. 8, OCTOBER 2009.

  In the proposed method, estimation and correction of the phase noise component are performed using the power values sampled from all the sample points of the received signal. However, the sample points may include sample points at which the phase noise estimation accuracy is low. If the phase noise is corrected using the estimation result of the phase noise component at such a sample point, the phase noise is not sufficiently corrected, and there is a risk that the effect of suppressing deterioration in communication quality is reduced.

  According to one aspect, an object of the present invention is to provide a wireless communication device, a phase noise correction method, and a wireless communication system that can effectively suppress deterioration in communication quality due to phase noise.

  According to one aspect, in a wireless communication apparatus that performs multicarrier transmission, a measurement unit that measures a power spectrum of phase noise based on a received signal, and an autocorrelation value of phase noise that is calculated based on the measured power spectrum The second phase noise estimation value estimated for all the sample points is obtained by identifying the sample points used for the estimation of the phase noise based on and interpolating the first phase noise estimated for the specified sample points And a calculation unit that corrects the phase noise of the received signal based on the calculated estimated value.

  It is possible to effectively suppress deterioration of communication quality due to phase noise.

It is the figure which showed an example of the radio | wireless communications system which concerns on 1st Embodiment. It is the figure which showed an example of the radio | wireless communications system which concerns on 2nd Embodiment. It is the figure which showed an example of the hardware which the radio | wireless communication apparatus which concerns on 2nd Embodiment has. It is the block which showed an example of the function which the radio | wireless communication apparatus which concerns on 2nd Embodiment has. It is the flowchart which showed the flow of the process of the phase noise correction | amendment by the radio | wireless communication apparatus which concerns on 2nd Embodiment. It is the block which showed an example of the function which the radio | wireless communication apparatus which concerns on the modification of 2nd Embodiment has. It is the flowchart which showed the flow of the process of the threshold value calculation which concerns on the modification of 2nd Embodiment. It is the figure which showed an example of phase noise PSD. It is the figure which showed an example of the autocorrelation value of phase noise. It is the figure which showed the comparison result of the average BLER characteristic. It is the figure which showed the comparison result (effect of a repetition process) of an average BLER characteristic.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. In addition, about the element which has the substantially same function in this specification and drawing, duplication description may be abbreviate | omitted by attaching | subjecting the same code | symbol.

<1. First Embodiment>
The first embodiment will be described with reference to FIG. 1st Embodiment is related with the radio | wireless communications system which implements multicarrier transmission using a high frequency band. FIG. 1 is a diagram illustrating an example of a wireless communication system according to the first embodiment. The wireless communication system 5 illustrated in FIG. 1 is an example of a wireless communication system according to the first embodiment.

  As shown in FIG. 1, the wireless communication system 5 includes wireless communication devices 10 and 20. Hereinafter, for convenience of description, the description will be given by taking as an example a case where an OFDM signal (see FIG. 1A) is transmitted from the wireless communication device 20 to the wireless communication device 10.

  The wireless communication device 10 includes a measurement unit 11 and a calculation unit 12. The wireless communication device 10 may be equipped with a memory (not shown) such as a RAM (Random Access Memory), a HDD (Hard Disk Drive), or a flash memory.

  The measuring unit 11 measures the power spectrum of the phase noise based on the signal (received signal y) received via the antenna. In the example of FIG. 1, the measurement unit 11 measures phase noise PSD (Power Spectral Density) using a known preamble signal included in the received signal y (see FIG. 1B). The function of the measurement unit 11 can be realized by, for example, a PLL (Phase Locked Loop) (frequency) synthesizer.

  The arithmetic unit 12 is a processor such as a central processing unit (CPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), or a field programmable gate array (FPGA). The calculation unit 12 may operate according to a program stored in the memory.

  The calculation unit 12 calculates an autocorrelation value of the phase noise based on the power spectrum of the phase noise measured by the measurement unit 11. And the calculating part 12 specifies the sample point used for estimation of a phase noise based on the autocorrelation value of a phase noise.

  For example, the arithmetic unit 12 obtains a time change of the autocorrelation value (see FIG. 1C) by performing IFFT (Inverse FFT) on the phase noise PSD. Further, the calculation unit 12 specifies a time T when the autocorrelation value is equal to or greater than a predetermined value (0.9 in the example of FIG. 1) from the time change of the autocorrelation value, and based on the specified time T, the power threshold value Th is calculated.

For example, the arithmetic unit 12 generates a replica signal (received signal replica) y ₀ (t) of the received signal y, and changes the power threshold Th to change the power value | y of the replica signal y ₀ (t) within the time T. ₀ (t) | The probability of appearance of a sample point (see FIG. 1D) at which | is greater than or equal to the power threshold Th is calculated. Moreover, the calculating part 12 specifies electric power threshold value Th from which the calculated appearance probability becomes more than predetermined probability (for example, 99%). In addition, the calculation unit 12 specifies a sample point at which the power value | y ₀ (t) | of the replica signal y ₀ (t) is equal to or greater than the power threshold Th.

  The computing unit 12 estimates phase noise (first phase noise) for the specified sample point. In addition, the calculation unit 12 interpolates the estimated first phase noise to calculate an estimated value of the second phase noise estimated for all the sample points. Moreover, the calculating part 12 correct | amends the phase noise of the received signal y based on the calculated estimated value.

There sample point estimate of the phase noise at (time t sample points _s) of can be calculated based on the received signal y (t _s) and the replica signal y ₀ (t _s). The time t received signal sample points before and after the _{s {y (t s -L)} , ..., y (t s + L)} and the replica signal _{{y 0 (t s -L)} , ..., y 0 (t _s + L)} may be used for estimation. In this case, it is possible to improve the estimation accuracy of the phase noise at time t _s. However, L is set in advance.

  For each sample point specified by using the power threshold Th, an estimated value of phase noise (first estimated value of phase noise) is obtained by the above method. For the remaining sample points, for example, the calculation unit 12 performs linear interpolation using the estimated value of the phase noise (the estimated value of the first phase noise) obtained by the above-described method, thereby reducing the phase noise. Get an estimate. Then, the calculation unit 12 corrects the phase noise included in the received signal y using the estimated value for the specified sample point and the estimated value for the remaining sample points.

  By applying the above method, it becomes possible to estimate the phase noise using a sample point whose power value is sufficiently larger than the noise power, and the estimation accuracy of the phase noise is improved. Moreover, the phase noise is effectively corrected by increasing the estimation accuracy of the phase noise, which contributes to the improvement of communication quality.

  Unlike the method of the first embodiment described above, in the case of the method of estimating the phase noise in the frequency domain using all the sample points (Comparative Example # 1), the inverse matrix operation of the FFT size is performed. The amount of computation increases. Further, even if a device for reducing the amount of calculation is applied, in the case of the comparative example # 1, there is a risk that a sample point having a power value smaller than the noise power is used for the estimation of the phase noise. Communication quality may be inferior to the method.

  Further, in the case of the method of estimating the phase noise in the time domain using the convergence algorithm (Comparative Example # 2), it takes time to calculate the convergence algorithm, unlike the method of the first embodiment described above. Further, like the comparative example # 1, there is a risk that a sample point whose power value is smaller than the noise power is used for the estimation of the phase noise, and the communication quality is inferior to the method of the first embodiment described above. There is. That is, by applying the method of the first embodiment described above, it is possible to expect a reduction in calculation amount and an improvement in communication quality.

The first embodiment has been described above.
<2. Second Embodiment>
Next, a second embodiment will be described. 2nd Embodiment is related with the radio | wireless communications system which implements multicarrier transmission using a high frequency band (millimeter wave band).

(system)
The wireless communication system 50 will be described with reference to FIG. FIG. 2 is a diagram illustrating an example of a wireless communication system according to the second embodiment. Note that the wireless communication system 50 illustrated in FIG. 2 is an example of a wireless communication system according to the second embodiment.

  As illustrated in FIG. 2, the wireless communication system 50 includes wireless communication devices 100 and 200. The wireless communication devices 100 and 200 are, for example, user terminals such as mobile phones, smartphones, and PCs (Personal Computers), or communication devices such as relay stations and base stations.

  In the following, for convenience of explanation, it is assumed that the wireless communication device 200 is a communication device and the wireless communication device 100 is a user terminal, and a situation where an OFDM signal is transmitted from the wireless communication device 200 to the wireless communication device 100 is taken as an example. To explain. However, the technique of the second embodiment to be described later also when the wireless communication device 200 is a user terminal and the wireless communication device 100 is a communication device, or when both the wireless communication devices 100 and 200 are user terminals and communication devices. Is applicable.

  The wireless communication device 200 transmits an OFDM signal using a millimeter wave band (for example, a 60 GHz band). The wireless communication device 100 receives the OFDM signal transmitted from the wireless communication device 200. Hereinafter, an OFDM signal received by the wireless communication apparatus 200 may be referred to as a received signal y (t), and a subcarrier component included in the OFDM signal may be referred to as a subcarrier signal. As will be described later, the wireless communication device 100 has a function of accurately estimating phase noise due to frequency fluctuations of a continuous wave (CW) and correcting the estimated phase noise.

(hardware)
The wireless communication device 100 has hardware as shown in FIG. FIG. 3 is a diagram illustrating an example of hardware included in the wireless communication apparatus according to the second embodiment. Note that the wireless communication apparatus 200 also has the same hardware as the wireless communication apparatus 100 illustrated in FIG. 3, and thus description of the hardware of the wireless communication apparatus 200 is omitted.

  As illustrated in FIG. 3, the wireless communication device 100 includes an antenna 101, amplifiers 102 and 110, multipliers 103 and 109, and an oscillator 104. The wireless communication apparatus 100 includes an A / D (Analog to Digital) converter 105, a processor 106, a memory 107, and a D / A (Digital to Analog) converter 108.

  The antenna 101 is a transmission / reception antenna that transmits an RF (Radio Frequency) signal as a radio wave toward the surroundings and receives the RF signal as a radio wave. The amplifier 102 is an amplifier that amplifies an RF signal received via the antenna 101. The oscillator 104 is a local oscillator that transmits a continuous wave (AC signal). The continuous wave output from the oscillator 104 and the amplified RF signal output from the amplifier 102 are input to the multiplier 103 and converted into a BB (Base-Band) signal by the multiplier 103.

  The A / D converter 105 converts the analog domain BB signal (analog BB signal) output from the multiplier 103 into a digital domain BB signal (digital BB signal). The processor 106 performs processing on the digital BB signal. Further, the processor 106 controls the operation of the wireless communication device 100. The processor 106 is, for example, a CPU, DSP, ASIC, FPGA, or the like.

  The memory 107 is a storage device for temporarily or permanently storing data used when the processor 106 executes processing. The memory 107 is, for example, a RAM, a ROM (Read Only Memory), an HDD, an SSD (Solid State Drive), a flash memory, or the like. The D / A converter 108 converts the digital BB signal output from the processor 106 into an analog BB signal.

  The analog BB signal output from the D / A converter 108 and the continuous wave output from the oscillator 104 are input to the multiplier 109 and converted into an RF signal by the multiplier 109. The amplifier 110 is an amplifier that amplifies the RF signal output from the multiplier 109. An RF signal output from the amplifier 110 is transmitted via the antenna 101.

  Note that the hardware illustrated in FIG. 3 is an example, and the number and shape of the antennas 101, the number of processors 106, and the like can be changed. Further, when the wireless communication apparatus 100 is used as a receiving apparatus, the D / A converter 108, the multiplier 109, and the amplifier 110 can be omitted. Such a modification naturally belongs to the technical scope of the second embodiment.

(Function block)
The function of the wireless communication device 100 will be described with reference to FIG. FIG. 4 is a block diagram illustrating an example of functions of the wireless communication apparatus according to the second embodiment.

  As illustrated in FIG. 4, the wireless communication device 100 includes an RF unit 131 connected to the antenna 101, an A / D converter 105 (ADC: Analog to Digital Converter) connected to the RF unit 131, and A / D conversion. And a synchronization unit 132 connected to the device 105.

  In addition, the wireless communication apparatus 100 includes a CP (Cyclic Prefix) removal unit 133, an FFT unit 134, a channel estimation unit 135, and a channel equalization unit 136. In addition, the wireless communication apparatus 100 includes a CPE (Common Phase Error) estimation unit 137, a CPE correction unit 138, a demodulation unit 139, a decoding unit 140, and a CRC (Cyclic Redundancy Check) unit 141. Furthermore, the wireless communication apparatus 100 includes a replica generation unit 142, a sample determination unit 143, a phase noise estimation unit 144, an interpolation unit 145, and a phase noise correction unit 146.

  Note that the function of the RF unit 131 can be realized by the above-described amplifier 102, multiplier 103, and oscillator 104, for example. The functions of the CP removal unit 133, the FFT unit 134, the channel estimation unit 135, the channel equalization unit 136, the CPE estimation unit 137, the CPE correction unit 138, the demodulation unit 139, the decoding unit 140, and the CRC unit 141 are the processor 106 and the memory 107. Can be realized. The functions of the replica generation unit 142, the sample determination unit 143, the phase noise estimation unit 144, the interpolation unit 145, and the phase noise correction unit 146 can be realized by the processor 106 and the memory 107.

  An OFDM signal (RF signal) received by the antenna 101 is input to the RF unit 131. The RF unit 131 converts the OFDM signal input from the antenna 101 into an analog BB signal. The A / D converter 105 converts the analog BB signal output from the RF unit 131 into a digital BB signal. The synchronization unit 132 synchronizes the digital BB signal output from the A / D converter 105. The CP removal unit 133 removes the CP from the digital BB signal output from the synchronization unit 132.

  The FFT unit 134 converts the time-domain digital BB signal (time-domain received signal y (t)) output from the CP removing unit 133 by the FFT into the frequency-domain digital BB signal (frequency-domain received signal Y (k)). ).

The time domain received signal y (t) is given by the following equation (1). In the following formula (1), s (t) represents an OFDM signal transmitted from the wireless communication apparatus 200. h _l represents the impulse response of the channel in the l-th path. τ _l represents the delay time in the l-th path. n (t) represents a noise component at time t. θ _t represents the phase noise component at time t.

  The OFDM signal s (t) transmitted from the wireless communication apparatus 200 is given by the following equation (2). In the following equation (2), S (k) represents the k-th subcarrier signal. N represents the number of FFT points (the number of sample points used for FFT). j is an imaginary unit.

  The frequency domain received signal Y (k) is given by the following formula (3) by the FFT of the time domain received signal y (t) given by the above formula (1). When the expression is expanded using the above expressions (1) and (2), Y (k) is expressed in the form shown in the lowermost stage on the right side of the following expression (3).

In the above formula (3), H (k) is given by the following formula (4). Π (k) is given by the following equation (5). Ψ (k−k ₀ ) is given by the following formula (6). Θ _t representing the phase noise component at time t is included in Ψ (k−k ₀ ) given by the following equation (6). Ψ (k−k ₀ ) (k ≠ k ₀ ) represents interference between subcarrier signals caused by the phase noise component θ _t .

Referring to Equation (3) above, since the second term in the lowest stage on the right side includes Ψ (k−k ₀ ) (k ≠ k ₀ ), it can be seen that there is interference due to phase noise. By performing correction so as to suppress this phase noise, ICI can be reduced and communication quality can be improved.

  Channel estimation section 135 performs channel estimation (calculation of attenuation amount and phase rotation amount) of the transmission channel between the antennas of radio communication apparatuses 100 and 200 using a known signal (preamble) included in the digital BB signal. . The channel equalization unit 136 uses the channel estimation value output from the channel estimation unit 135 to perform channel equalization processing (processing for correcting transmission path distortion).

The received signal Y ₀ (k) after channel equalization is given by the following equation (7). In the following equation (7), H ₀ (k) represents the channel estimation value of the k-th subcarrier signal.

  The CPE estimation unit 137 estimates the CPE of each symbol using the pilot signal inserted in each symbol of the digital BB signal. CPE is a phase change that occurs in a carrier due to phase noise, and is a phase error that occurs in common with each subcarrier signal. The CPE correction unit 138 corrects the CPE of each symbol using the CPE estimation value output from the CPE estimation unit 137.

The reception signal Y ₁ (k) after CPE correction is given by the following equation (8). Ψ (0) represents a phase rotation that is commonly multiplied to all subcarrier signals due to the influence of phase noise, and is given by the following equation (9). Ψ ₀ (0) included in the following expression (8) represents an estimated value of Ψ (0), and is given by the following expression (10).

The estimation of Ψ ₀ (0) is performed based on the following equation (10) using known signals transmitted and received by a plurality of subcarriers. In the following equation (10), K _p represents a set of subcarrier numbers used for transmission of known signals. S _p (k) represents a known signal transmitted on the kth subcarrier. N _p represents the number of subcarriers used for transmission of a known signal.

Demodulation section 139 performs demodulation processing of each subcarrier signal (In-phase / Quadrature-phase component extraction processing) based on CPE-corrected received signal Y ₁ (k) output from CPE correction section 138. . The decoding unit 140 performs decoding processing (data bit determination and error correction processing) using the output of the demodulation unit 139. The CRC unit 141 performs error detection on the data bits output from the decoding unit 140 using a CRC code. If there is no error, the CRC unit 141 outputs the data bit as a reception result of the transmission data.

  When there is an error, the replica generation unit 142 performs the same encoding process and modulation process as the transmission side on the data bits output from the decoding unit 140 to generate a replica signal (transmission signal replica). Further, replica generation section 142 generates a frequency domain received signal Y (k) replica signal (frequency domain received signal replica) from the transmission signal replica using the channel estimation value output from channel estimation section 135.

Further, the replica generation unit 142 generates a replica signal of the time domain received signal y (t) (time domain received signal replica y ₀ (t)) from the frequency domain received signal replica by IFFT. The received signal replica y ₀ (t) in the time domain is given by the following equation (11). In the following equation (11), S ₀ (k) represents a transmission signal replica.

The sample determination unit 143 compares the power value P of the sample points sampled at a predetermined interval from the reception signal replica y ₀ (t) output from the replica generation unit 142 with a preset power threshold Th _P To do. For example, the power value P (t _s ) at the sample point at time t _s is given by | y ₀ (t _s ) | ² . Then, the sample determination unit 143 selects a sample point at which the power value P is equal to or greater than the threshold value Th _P. The power threshold Th _P is set so that a sample point whose power value is sufficiently larger than the noise power is selected.

The phase noise estimation unit 144 calculates the estimated value of the phase noise using the sample points output from the sample determination unit 143. The estimated value θ _ts ⁽ⁿ⁾ of the phase noise at the time t _s of the selected sample point is given by the following equation (12). The phase noise estimation unit 144 uses the received signal y (t _s ) and the received signal replica y ₀ (t _s ) at the selected sample point to calculate an estimated value θ _ts ^{(n )} .

  The interpolation unit 145 uses the estimated phase noise value at the selected sample point to calculate an estimated value of phase noise at sample points other than the selected sample point by interpolation processing (for example, linear interpolation). The phase noise correction unit 146 calculates the phase noise included in the received signal y (t) based on the estimated phase noise value output from the phase noise estimation unit 144 and the estimated phase noise value output from the interpolation unit 145. to correct. That is, the phase noise correction unit 146 performs the phase noise correction process using the phase noise estimation values at all the sample points so that the phase noise included in the received signal y (t) is suppressed.

  As described above, the phase noise is estimated by selecting a sample point whose power value is sufficiently larger than the noise power, and the phase noise at all the sample points is estimated by interpolation processing based on the estimation result. Noise estimation accuracy is improved. As a result, the phase noise can be corrected more correctly, which contributes to improvement of communication quality. Note that the above processing may be repeatedly executed. For example, the above processing is repeatedly executed until there is no data bit error.

(Processing flow)
Next, the flow of processing for phase noise correction performed by the wireless communication apparatus 100 will be described with reference to FIG. FIG. 5 is a flowchart showing a flow of phase noise correction processing by the wireless communication apparatus according to the second embodiment. In the figure, the transmission signal replica and the reception signal replica may be simply referred to as a replica signal.

  (S101) The OFDM signal received by the antenna 101 is down-converted and converted into an analog BB signal, converted into a digital BB signal by A / D conversion, and processing such as CP removal, FFT, CPE correction, and demodulation is executed. And input to the decoding unit 140. The decoding unit 140 determines a data bit from the input complex symbol, performs error correction on the data bit, and inputs the data bit to the CRC unit 141. If the CRC unit 141 determines that there is no error in the data bits, the series of processes shown in FIG. 5 ends, and if there is an error, the process proceeds to S102.

(S102) The replica generation unit 142 performs the same encoding processing and modulation processing as the transmission side on the data bits output from the decoding unit 140 to generate a transmission signal replica. In addition, replica generation section 142 generates a frequency domain received signal replica from the transmission signal replica using the channel estimation value output from channel estimation section 135. Further, the replica generation unit 142 generates a time-domain received signal replica y ₀ (t) from the frequency-domain received signal replica by IFFT (see the above equation (11)).

(S103) The sample determination unit 143 uses the power value P of the sample points sampled at a predetermined interval from the received signal replica y ₀ (t) output from the replica generation unit 142, and a preset power threshold Th _P. And compare. Then, the sample determining unit 143 selects a sample point (selected sample point) at which the power value P is equal to or greater than the threshold value Th _P. The power threshold Th _P is set so that a sample point whose power value is sufficiently larger than the noise power is selected.

(S104) The phase noise estimation unit 144 calculates an estimated value of the phase noise using the selected sample point output from the sample determination unit 143 (see the above equation (12)).
(S105) The interpolation unit 145 calculates an estimated value of phase noise at sample points other than the selected sample point by interpolation processing (for example, linear interpolation) using the estimated value of phase noise at the selected sample point.

  (S106) The phase noise correction unit 146 is included in the received signal y (t) based on the phase noise estimation value output from the phase noise estimation unit 144 and the phase noise estimation value output from the interpolation unit 145. Correct phase noise. That is, the phase noise correction unit 146 performs the phase noise correction process using the phase noise estimation values at all the sample points so that the phase noise included in the received signal y (t) is suppressed.

  (S107) Similar to the processing for the digital BB signal output from the synchronization section 132, the received signal whose phase noise has been corrected by the phase noise correction section 146 is subjected to processing such as demodulation and decoding, and data from complex symbols Bits are restored.

  (S108) The CRC unit 141 performs error detection of the restored data bits and determines whether or not to end the phase noise correction. If an error is detected, the phase noise correction process is not terminated, and the process proceeds to S102. On the other hand, when no error is detected, the series of processes shown in FIG. 5 ends.

(Modification: Function block)
Here, a modification of the second embodiment will be described with reference to FIG. FIG. 6 is a block diagram illustrating an example of a function of a wireless communication apparatus according to a modification of the second embodiment.

In the above description, the power threshold Th _P is set in advance. However, in the modification described below, the power threshold Th _P is determined based on the autocorrelation value of the phase noise. In the above description, the phase noise is estimated based on the level values of the received signal y (t _s ) and the received signal replica y ₀ (t _s ) at each sample point. On the other hand, in this modified example, when phase noise at a certain sample point is estimated, sample points before and after that sample point are used.

  In order to add the above modifications, a phase noise PSD measurement unit 201, an autocorrelation calculation unit 202, and a power threshold value calculation unit 203 are added to the wireless communication apparatus 100 as shown in FIG. In addition, the functions of the sample determination unit 143 and the phase noise estimation unit 144 are partially modified. On the other hand, CP removal unit 133, FFT unit 134, channel estimation unit 135, channel equalization unit 136, CPE estimation unit 137, CPE correction unit 138, demodulation unit 139, decoding unit 140, CRC unit 141, replica generation unit 142, interpolation Since the functions of the unit 145 and the phase noise correction unit 146 are not modified, detailed description of these elements is omitted.

  The phase noise PSD measurement unit 201 extracts a known signal (such as a preamble) from the received signal, and calculates the power spectrum density (PSD; see FIG. 8) of the phase noise included in the received signal. The function of the phase noise PSD measurement unit 201 can be realized using, for example, a PLL synthesizer (or PLL frequency synthesizer) that outputs the PSD of the input signal. The autocorrelation calculation unit 202 calculates an autocorrelation value (see FIG. 9) of the phase noise by performing IFFT on the phase noise PSD output from the phase noise PSD measurement unit 201.

The power threshold calculation unit 203 refers to the autocorrelation value data output from the autocorrelation calculation unit 202 and calculates a time T when the autocorrelation value is equal to or greater than a predetermined correlation threshold (for example, 0.9). In addition, the power threshold calculation unit 203 uses the statistical properties of the OFDM signal to generate power at which a sample point that is equal to or higher than the power threshold Th _P within the time T appears with a probability equal to or higher than a predetermined probability threshold (for example, 99%). A threshold Th _P is specified.

For example, the power threshold calculation unit 203 calculates the above probability for a set of sample points acquired from a known signal with a width of time T while changing a parameter that is a candidate for the power threshold Th _P , and the probability is Identify parameters that are above the threshold. Then, the power threshold calculation unit 203 outputs the specified parameter as the power threshold Th _P. A plurality of parameters that are candidates for the power threshold Th _P may be set in advance.

The sample determination unit 143 uses the power threshold Th _P output from the power threshold calculation unit 203 and the power value of the sample points sampled at a predetermined interval from the received signal replica y ₀ (t) output from the replica generation unit 142. Compare P. Then, the sample determining unit 143 selects a sample point (selected sample point) at which the power value P is equal to or greater than the threshold value Th _P.

  The sample determination unit 143 selects L sample points (neighboring sample points) before and after the selected sample point. The number L of sample points selected as the neighboring sample points is set in advance to a value at which, for example, BLER (Block Error Rate) characteristics are good.

The phase noise estimation unit 144 calculates an estimated value of the phase noise based on the selected sample points output from the sample determination unit 143 and neighboring sample points corresponding to each selected sample point. For example, the estimated value of the phase noise at the selected sample point time t _s theta _ts ⁽ⁿ⁾ is given by the following equation (13) and (14).

In the following equation (13), v (t _s ) is the time t _s of the selected sample point and the time {t _s −L,..., T _s − of the selected sample point, as shown in the following equation (14). 1, t _s +1,..., T _s + L} is a vector whose element is the level value of the received signal y (t). Further, v ₀ (t _s), the time of the time t _s and near the sample point selection sample points _{{t s -L, ..., t} s -1, t s + 1, ..., t s + L} received signal replica of This is a vector whose elements are level values of y ₀ (t). In the following formula (14), the superscript T represents transposition.

  As described above, by determining the time T based on the autocorrelation value of the phase noise and selecting the sample point based on the time T, it is possible to select sample points in a range where the change in phase noise is small. Therefore, it is possible to reduce the risk that the estimation accuracy deteriorates by estimating the phase noise at sample points other than the selected sample point by linear interpolation. Further, the estimation accuracy of the phase noise can be improved by using neighboring sample points before and after the selected sample point.

(Modification: Processing flow)
The flow of processing for calculating the power threshold Th _P will be described with reference to FIG. FIG. 7 is a flowchart showing the flow of threshold value calculation processing according to a modification of the second embodiment. 8 and 9 may be referred to in the description. FIG. 8 is a diagram illustrating an example of the phase noise PSD. FIG. 9 is a diagram illustrating an example of an autocorrelation value of phase noise.

(S111) The phase noise PSD measurement unit 201 extracts a known signal (such as a preamble) from the received signal.
(S112) The phase noise PSD measurement unit 201 calculates the phase noise PSD (see FIG. 8) based on the known signal. The function of the phase noise PSD measurement unit 201 can be realized using, for example, a PLL synthesizer (or PLL frequency synthesizer) that outputs the PSD of the input signal.

  (S113) The autocorrelation calculation unit 202 calculates an autocorrelation value of phase noise (see FIG. 9) by performing IFFT on the phase noise PSD output from the phase noise PSD measurement unit 201.

  (S114) The power threshold calculation unit 203 refers to the autocorrelation value data output from the autocorrelation calculation unit 202, and detects the time T when the autocorrelation value is equal to or greater than a predetermined correlation threshold (for example, 0.9). To do.

(S115) The power threshold value calculation unit 203 calculates the appearance probability of sample points that are equal to or higher than the power threshold value Th _P within time T, and such sample points appear with a probability equal to or higher than a predetermined probability threshold value (for example, 99%). The power threshold Th _P to be specified is specified. When the process of S115 is completed, the series of processes shown in FIG.

(simulation result)
Here, referring to FIG. 10 and FIG. 11, a simulation result showing an effect when the phase noise correction according to the second embodiment described above is applied will be described. FIG. 10 is a diagram showing a comparison result of average BLER characteristics. FIG. 11 is a diagram illustrating a comparison result of average BLER characteristics (effect of repeated processing).

  The simulation was performed under the conditions where the carrier frequency was 60 GHz, the sampling rate was 600 MHz, the FFT / IFFT size (N) was 1024, the synchronization was ideal, and the Carrier Frequency Offset (CFO) was 0. In addition, a convolutional encoder with a constraint length of 7 and a coding rate of ½, which has been used in IEEE 802.11, is used, and a condition for setting the coding rate to 3/4 by puncturing is considered.

  Further, phase noise having PSD characteristics shown in FIG. 8 is added to the received signal. Further, transmission information bits per block are set to 2266 bits when the modulation scheme is 16QAM (Quadrature Amplitude Modulation), and 3392 bits when the modulation scheme is 64QAM, and set to be 1 block in one OFDM symbol. The example of FIG. 10 shows an average BLER characteristic when the modulation method is set to 16QAM. The example of FIG. 11 shows an average BLER characteristic when the modulation method is set to 64QAM.

  A chain line (white circle) in FIG. 10 indicates a simulation result (worst condition) under a condition where phase noise correction is not performed. A one-dot chain line (black circle) indicates a simulation result under a condition (best condition) in which phase noise is not added.

In addition, a thick solid line (white square) in FIG. 10 indicates a simulation result under the condition (example) in which the phase noise correction of the second embodiment described above is performed. A thin solid line (black triangle) indicates a simulation result under a condition (comparative example) in which the phase noise correction is performed using all the sample points without performing the determination based on the power threshold Th _P.

The simulation result of the example shows an average BLER characteristic that is close to the simulation result of the best condition with no phase noise as compared with the simulation result of the comparative example in the entire range of the average SNR. From this, it can be seen that improvement in communication quality can be expected by selecting a sample point based on the power threshold Th _P and correcting the phase noise using the estimated value of the phase noise at the selected sample point. .

  The simulation result of FIG. 11 shows the relationship between the number of repetitions of the above-described phase noise correction and the improvement of the average BLER characteristic. A chain line (white circle) in FIG. 11 indicates a simulation result (worst condition) under a condition where phase noise correction is not performed. A one-dot chain line (black circle) indicates a simulation result under a condition (best condition) in which phase noise is not added. The results of (A), (B), and (C) are all simulation results when the phase noise correction of the second embodiment described above is performed.

  (A) shows the result when the phase noise correction is performed once (without repetition). (B) shows the result when the phase noise correction is performed twice (one repetition). (C) shows the result when the phase noise correction is performed four times (repeated three times). Comparing the results of (A), (B), and (C), it can be seen that as the number of iterations increases, the simulation results approach the condition without phase noise. That is, it can be seen that the communication quality is improved by the above-described repetitive processing of the phase noise correction.

As described above, the communication quality can be improved by selecting the sampling point from the comparison between the power threshold Th _P and the level value of the received signal replica. In addition, it is expected that the influence of errors due to linear interpolation can be suppressed and communication quality can be improved by determining the power threshold Th _P in consideration of the autocorrelation of phase noise. Further, the estimation accuracy can be further improved by estimating the phase noise in consideration of the sample points before and after the selected sample point. Further, it is possible to expect further improvement in communication characteristics by repeatedly performing phase noise correction.

The second embodiment has been described above.
<3. Addendum>
The following additional notes are disclosed with respect to the embodiment described above.

(Supplementary Note 1) In a wireless communication apparatus that performs multicarrier transmission,
A measurement unit that measures the power spectrum of the phase noise based on the received signal;
A sample point used for estimation of the phase noise is identified based on an autocorrelation value of the phase noise calculated based on the measured power spectrum, and a first phase noise estimated for the identified sample point And calculating a second phase noise estimated value estimated for all the sample points, and correcting the phase noise of the received signal based on the calculated estimated value. Communication device.

(Appendix 2) The calculation unit
A time at which the autocorrelation value is equal to or greater than a first threshold is calculated, and based on an appearance probability of a sample point at which the power of the received signal is equal to or greater than a second threshold within the calculated time, The wireless communication apparatus according to attachment 1, wherein the second threshold value used for identification is determined.

(Supplementary note 3)
The wireless communication device according to claim 2, wherein a first replica signal is generated from the received signal, and a sample point at which power of the first replica signal is equal to or higher than the second threshold is specified as a sample point used for the estimation. .

(Supplementary note 4)
A process of generating a second replica signal from the corrected received signal and repeatedly specifying a sample point at which the power of the second replica signal is equal to or higher than the second threshold as a sample point used for the estimation The wireless communication device according to attachment 3.

(Supplementary Note 5) A wireless communication device performing multicarrier transmission is
Measure the power spectrum of phase noise based on the received signal,
Identifying a sample point used for estimation of the phase noise based on an autocorrelation value of the phase noise calculated based on the measured power spectrum;
Interpolating a first phase noise estimated for the identified sample points to calculate a second phase noise estimate estimated for all sample points;
A phase noise correction method for correcting phase noise of the received signal based on the calculated estimated value.

(Supplementary Note 6) In a wireless communication system that performs multicarrier transmission,
A first wireless device for transmitting a signal;
Measuring the power spectrum of the phase noise based on the received signal from the first wireless device;
Identifying a sample point used for estimation of the phase noise based on an autocorrelation value of the phase noise calculated based on the measured power spectrum;
Interpolating a first phase noise estimated for the identified sample points to calculate a second phase noise estimate estimated for all sample points;
A second wireless device for correcting phase noise of the received signal based on the calculated estimated value;
A wireless communication system.

(Supplementary Note 7) In a wireless communication apparatus that performs multicarrier transmission,
A receiver for receiving the signal;
A replica signal is generated from the signal, a sample point at which the power of the replica signal is equal to or higher than a predetermined power threshold is specified, and phase noise included in the signal based on the signal at the sample point and the power of the replica signal And a calculation unit that calculates the phase noise based on the estimated value.

(Supplementary note 8)
8. The phase noise autocorrelation value is calculated based on the phase noise power spectrum measured based on the known signal included in the signal, and the power threshold is determined based on the autocorrelation value. Wireless communication device.

(Supplementary note 9)
Identify the time when the autocorrelation value is greater than or equal to a predetermined correlation threshold;
While calculating a parameter that is a candidate for the power threshold, calculate the appearance probability of a sample point where the power of the signal is greater than or equal to the parameter within the time,
The wireless communication apparatus according to claim 8, wherein the parameter at which the appearance probability of the sample point is equal to or higher than a predetermined probability threshold is set as the power threshold.

(Additional remark 10) The said calculating part is
By performing an interpolation process using the estimated value of the phase noise at the specified sample point, the estimated value of the phase noise of the signal at a sample point other than the specified sample point is calculated, and the estimation at all the sample points is performed. The wireless communication apparatus according to appendix 7, wherein the phase noise correction process is executed based on a value.

(Supplementary Note 11) A wireless communication apparatus that performs multi-carrier transmission is
A replica signal is generated from the received signal, a sample point at which the power of the replica signal is equal to or higher than a predetermined power threshold is specified, and included in the signal based on the signal at the sample point and the power of the replica signal A phase noise correction method of calculating an estimated value of phase noise and executing the correction process of the phase noise based on the estimated value.

(Supplementary Note 12) In a wireless communication system that performs multicarrier transmission,
A first wireless device for transmitting a transmission signal;
A replica signal is generated from a signal received from the first radio apparatus, a sample point at which the power of the replica signal is equal to or higher than a predetermined power threshold is specified, and based on the power of the signal at the sample point and the power of the replica signal A second wireless device that calculates an estimated value of the phase noise included in the signal and executes the correction process of the phase noise based on the estimated value;
A wireless communication system.

(Supplementary note 13) The first wireless device is a wireless terminal,
The wireless communication system according to claim 12, wherein the second wireless device is a base station.

(Supplementary Note 14) The first wireless device is a base station,
The wireless communication system according to claim 12, wherein the second wireless device is a wireless terminal.

DESCRIPTION OF SYMBOLS 5 Wireless communication system 10, 20 Wireless communication apparatus 11 Measurement part 12 Calculation part y Reception signal Th Power threshold value

Claims (6)

In a wireless communication device that performs multi-carrier transmission,
A measurement unit that measures the power spectrum of the phase noise based on the received signal;
A sample point used for estimation of the phase noise is identified based on an autocorrelation value of the phase noise calculated based on the measured power spectrum, and a first phase noise estimated for the identified sample point And calculating a second phase noise estimated value estimated for all the sample points, and correcting the phase noise of the received signal based on the calculated estimated value. Communication device. The computing unit is
A time at which the autocorrelation value is equal to or greater than a first threshold is calculated, and based on an appearance probability of a sample point at which the power of the received signal is equal to or greater than a second threshold within the calculated time, The wireless communication apparatus according to claim 1, wherein the second threshold value used for identification is determined. The computing unit is
The wireless communication according to claim 2, wherein a first replica signal is generated from the received signal, and a sample point at which power of the first replica signal is equal to or higher than the second threshold is specified as a sample point used for the estimation. apparatus. The computing unit is
A process of generating a second replica signal from the corrected received signal and repeatedly specifying a sample point at which the power of the second replica signal is equal to or higher than the second threshold as a sample point used for the estimation The wireless communication device according to claim 3. A wireless communication device that performs multi-carrier transmission
Measure the power spectrum of phase noise based on the received signal,
Identifying a sample point used for estimation of the phase noise based on an autocorrelation value of the phase noise calculated based on the measured power spectrum;
Interpolating a first phase noise estimated for the identified sample points to calculate a second phase noise estimate estimated for all sample points;
A phase noise correction method for correcting phase noise of the received signal based on the calculated estimated value. In a wireless communication system that performs multi-carrier transmission,
A first wireless device for transmitting a signal;
Measuring the power spectrum of the phase noise based on the received signal from the first wireless device;
Identifying a sample point used for estimation of the phase noise based on an autocorrelation value of the phase noise calculated based on the measured power spectrum;
Interpolating a first phase noise estimated for the identified sample points to calculate a second phase noise estimate estimated for all sample points;
A second wireless device for correcting phase noise of the received signal based on the calculated estimated value;
A wireless communication system.

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