JP2009111576A - Telecommunication apparatus and method for compensating in-phase quadrature mismatching - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a telecommunication method for detecting in-phase quadrature mismatching without reducing the number of applicable sub-carriers. <P>SOLUTION: The telecommunication apparatus in the transmitting side transmits a quadrature modulated signal generated by the quadrature modulation and the signal generated on the basis of the signal including the reference signal of the predetermined amplitude. The telecommunication apparatus in the receiving side quadrature-demodulates the signal including the quadrature-modulated signal and the reference signal with the quadrature modulation method and outputs the first signal and the second signal to detect the in-phase quadrature mismatching based on the reference signal element included in the first signal and the reference signal element included in the second signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wired or wireless communication system using quadrature modulation / demodulation, and more specifically, in a receiving-side communication apparatus, a signal caused by asymmetry in a circuit that separates and processes an in-phase signal and a quadrature signal from a received signal. The present invention relates to a technique for compensating for deterioration.

  As a communication method that uses orthogonal modulation / demodulation processing, for example, there is a communication method based on orthogonal frequency division multiplexing (OFDM) modulation / demodulation. The OFDM modulation / demodulation technique is a method of transmitting transmission data in parallel using a plurality of subcarriers. Since the symbol rate of each subcarrier is relatively low, it is resistant to intersymbol interference, and can be used for digital terrestrial broadcasting, wireless LAN ( (Local Area Network) system has already been used, and application to an optical communication system is also being studied (for example, see Non-Patent Document 1).

  In an OFDM communication system, a transmission-side communication apparatus usually obtains a complex sample value on a time axis from data transmitted by each subcarrier by inverse fast Fourier transform (IFFT) processing, and from its real part, A quadrature baseband signal is generated from the imaginary part of the in-phase baseband signal. The in-phase baseband signal and the quadrature baseband signal are combined into one OFDM signal by a quadrature modulation process also called IQ multiplexing. Here, I means in-phase, and Q means quadrature. Specifically, the in-phase and quadrature baseband signals are multiplied by a sine wave signal having a predetermined frequency that is different from each other by π / 2, frequency-converted, and the frequency-converted signals are added to obtain an OFDM signal.

  For example, the OFDM signal generated by IQ multiplexing is further frequency-converted to a radio frequency (RF) signal and transmitted as a radio signal, or modulated with continuous light using an optical modulator. As a result, it is transmitted as an optical signal.

  The receiving-side communication apparatus receives a radio signal or an optical signal, converts the received signal into an OFDM signal in an intermediate frequency band, and performs orthogonal demodulation processing also called IQ separation. Specifically, the in-phase and quadrature baseband signals are output by multiplying the OFDM signal by a sine wave signal having a predetermined frequency that is different from each other by π / 2. Note that the phase of the sine wave signal is controlled according to the phase of the OFDM signal.

  Thereafter, the in-phase and quadrature baseband signals are sampled, and a fast Fourier transform (FFT) process is performed with the sample value obtained from the in-phase baseband signal as a real part and the sample value obtained from the quadrature baseband signal as an imaginary part. The data value represented by each subcarrier is determined.

  As described above, in a communication system using quadrature modulation / demodulation, a path for processing an in-phase signal and a quadrature signal is necessary, but when the phase difference of a sine wave signal multiplied in IQ multiplexing and / or IQ separation is π / 2, If there is no match, or if the amplitudes do not match, or if the gain, attenuation, etc. of the amplifiers in the paths that process the in-phase signal and the quadrature signal do not match, then the in-phase quadrature mismatch ( The received signal quality deteriorates due to an IQ mismatch effect.

  For this reason, Non-Patent Document 2 proposes a configuration in which in-phase quadrature mismatch is compensated in the receiving-side communication device. According to Non-Patent Document 2, in the IFFT calculation, the transmission side communication apparatus inputs a predetermined value to one of a pair of subcarriers having different signs and the same frequency, that is, a mirror subcarrier of a subcarrier that inputs a predetermined value. The value “0” is entered for. That is, a known data value is transmitted on one subcarrier, and the mirror subcarrier is not used. If the influence of noise is ignored, the signal appearing on the mirror subcarrier is due to in-phase quadrature mismatch, so the receiving side communication device monitors the mirror subcarrier and compensates based on the signal appearing at the position of the mirror subcarrier. An amplitude amount and a phase amount to be obtained are obtained, and in-phase and / or quadrature signal compensation is performed.

Arthur James Lowry, et al. , “Orthogonal-frequency-division multiplexing for dispersal compensation of long-haul optical systems”, 2006 Optical Society of America ETS E No. 14 6, March 2006 H. Shafiee et al. "Calibration of IQ Imbalance in OFDM Transceivers", 2003 IEEE, 0-7803-7802-4 / 03, pp. 2081-2085

  The configuration described in Non-Patent Document 2 uses a set of subcarriers having the same frequency and different codes, and the number of subcarriers that can be used for information transmission is reduced. In addition, the information transmission signal that is variously optimized is used, which may affect the detection of the in-phase / quadrature mismatch amount.

  Therefore, an object of the present invention is to provide a communication method and a communication apparatus for the method that detect the amount of in-phase quadrature mismatch without reducing the number of subcarriers that can be used. It is another object of the present invention to provide a communication method and a communication apparatus for the method that detect an in-phase / orthogonal mismatch amount without being affected by optimization of signals used for information transmission.

According to the communication device of the present invention,
Means for orthogonally demodulating a signal including a signal generated by quadrature modulation and a reference signal having a predetermined amplitude and outputting a first signal and a second signal; a reference signal component included in the first signal; And a means for detecting an in-phase quadrature mismatch amount based on the reference signal component included in the second signal.

According to another embodiment of the communication device of the present invention,
The in-phase quadrature mismatch amount is a phase amount and an amplitude amount that suppress fluctuations in amplitude of a complex signal in which the reference signal component included in the first signal is a real part and the reference signal component included in the second signal is an imaginary part. It is also preferable that there is.

According to another embodiment of the communication device of the present invention,
Quadrature modulation uses in-phase signal and quadrature signal as input, and compensates for in-phase quadrature mismatch from the first signal and the second signal based on the detected in-phase quadrature mismatch amount. It is also preferable to further include means for outputting a signal.

According to the communication method of the present invention,
Transmitting a signal generated based on a signal including a quadrature modulation signal generated by quadrature modulation and a reference signal having a predetermined amplitude in the transmission side communication device; and in the reception side communication device, the quadrature modulation signal and the reference signal And a step of outputting a first signal and a second signal, a reference signal component included in the first signal, and a reference signal included in the second signal And a step of detecting an in-phase quadrature mismatch amount based on the components.

According to another embodiment of the communication method of the present invention,
A complex signal having a reference signal component included in the first signal as a real part and a reference signal component included in the second signal as an imaginary part is converted by each estimated phase amount and estimated amplitude amount, and within a predetermined period, An average value obtained by dividing the absolute value of the converted complex signal by the maximum absolute value within the predetermined period is obtained, and an estimated phase amount and an estimated amplitude amount that maximize the obtained average value are obtained as in-phase orthogonal non-intensities. It is also preferable to set the matching amount.

According to another embodiment of the communication method of the present invention,
The generation of the signal including the quadrature modulation signal and the reference signal in the transmission side communication device is performed by adding a predetermined DC offset to the in-phase signal and / or the quadrature signal, and orthogonalizing the in-phase signal and the quadrature signal to which the DC offset is added. Preferably including a step of modulating.

  As described above, the in-phase quadrature mismatch is compensated by adding the reference signal having a predetermined amplitude to the quadrature-modulated signal. Since the present invention does not use a quadrature-modulated signal having information and various optimizations for detecting the in-phase quadrature irregularity, it is possible to perform compensation with higher reliability than the prior art. Further, there is no limitation on the modulation method of the orthogonally modulated signal, and even if the orthogonally modulated signal is OFDM, there is an advantage that the number of subcarriers that can be used is not reduced compared to the prior art.

  BEST MODE FOR CARRYING OUT THE INVENTION The best embodiment for carrying out the present invention, here, an embodiment using an OFDM modulation / demodulation technique will be described in detail below with reference to the drawings.

  FIG. 1 is a block diagram of a transmission side of a communication apparatus according to the present invention. As shown in FIG. 1, the communication apparatus includes an IQ multiplexing unit 11, a reference signal generation unit 12, and an addition unit 13. The IQ multiplexing unit 11 receives the in-phase signal I generated by the IFFT operation and the quadrature signal Q. Here, the in-phase signal I is a signal generated based on the real part of the complex sample value obtained by the IFFT calculation, and the quadrature signal Q is a signal generated based on the imaginary part. The IQ multiplexing unit 11 performs quadrature modulation on the in-phase signal I and the quadrature signal Q, that is, performs frequency conversion by multiplying each of the sine wave signals having predetermined frequencies different from each other by π / 2, and performs frequency conversion. The phase signal I and the quadrature signal Q are added. Hereinafter, the IQ multiplexed signal is referred to as the OFDM signal 30 regardless of the center frequency.

  The reference signal generator 12 generates a reference signal 50 that is a sine wave signal having a constant amplitude, and the adder 13 adds the OFDM signal 30 and the reference signal 50. The frequency of the reference signal 50 can be distinguished from that of the OFDM signal 30 on the frequency axis, and a signal that does not interfere, for example, a signal that is out of band is used. Note that the reference signal 50 does not need to be synchronized with the OFDM signal 30 and can be generated independently of the OFDM signal 30. FIG. 3A is a schematic spectrum of the electric signal output from the adding unit 13.

  It is also possible not to use one of the subcarriers in the OFDM signal 30 and to assign the position of this subcarrier to the reference signal 50. For example, it is possible to add the reference signal 50 by using a fixed value for the input corresponding to the subcarrier assigned to the reference signal 50 in the IFFT calculation. In this case, the adding unit 13 is not necessary. Preferably, the position of the direct current component of the OFDM baseband signal is used as the reference signal 50. In this case, the reference signal 50 can be added to the OFDM signal 30 by adding a DC offset to the in-phase and / or quadrature baseband signal obtained by analog conversion of the IFFT output. 13 can be omitted. FIG. 3B is a frequency spectrum when the position of the direct current component of the OFDM baseband signal is used as the reference signal 50.

  Note that the method of adding the reference signal 50 such as adding the reference signal 50 to the OFDM signal 30 in the RF band is not limited to the above-described form. In addition, if a signal of constant power exists in a form that can be distinguished and separated from the OFDM signal 30 on the frequency axis at a certain frequency position as seen on the frequency axis, the signal can be used as the reference signal 50. . That is, as long as a certain frequency has a frequency component of constant power, a signal obtained by phase-modulating a sine wave at a fixed symbol rate or a rectangular wave can be used as the reference signal 50.

  The signal including the OFDM signal 30 and the reference signal 50 is then converted into a radio signal or an optical signal by processing according to the transmission medium and output to the transmission medium.

  FIG. 2 is a block diagram of the receiving side of the communication apparatus according to the present invention. As shown in FIG. 2, the communication apparatus includes an IQ separation unit 21, a reference signal extraction unit 22, a detection unit 23, and a compensation unit 24. The IQ separation unit 21 receives a signal including the OFDM signal 30 converted from the signal transmitted to the transmission medium and the reference signal 50.

  In order to perform quadrature demodulation, the IQ separation unit 21 multiplies the input signal by a sine wave signal having a predetermined frequency that is different in phase by π / 2, and a first signal including the signal I ′ and the reference signal component X, A second signal including the signal Q ′ and the reference signal component Y is output. For example, the sine wave signal for outputting the first signal is generated by controlling the phase based on the carrier wave of the input signal, for example, and the sine wave signal for outputting the second signal is the first signal. Is generated by shifting the phase of the sine wave signal for outputting the above signal by π / 2.

  The reference signal extraction unit 22 extracts, from each signal output from the IQ separation unit 21, a reference signal component, more precisely, a signal component corresponding to a frequency portion having a fixed power of the reference signal 50 inserted on the transmission side. . The detection unit 23 detects the in-phase quadrature mismatch amount based on the extracted reference signal component, that is, the phase and gain for compensating for the signal degradation caused by the path for processing the in-phase signal and the path for processing the quadrature signal. The compensation unit 24 compensates for the signal output from the IQ separation unit 21 based on the detected in-phase / quadrature mismatch amount.

  FIG. 4 is a diagram for explaining the operating principle of the present invention. Since the reference signal 50 is a sine wave signal having a constant amplitude, it is represented by a certain point on the complex plane. Therefore, the signal Z = X + jY having the reference signal component X output by the IQ separation unit 21 together with the signal I ′ as the real part and the reference signal component Y output together with the signal Q ′ as the imaginary part is represented by a certain point on the complex plane. Signal. However, in general, a process for converting a received signal into an OFDM signal 30, for example, a frequency conversion process when a radio signal is received, a heterodyne detection process for an optical signal, and the like are received from the local communication signal of the receiving communication device. When the signal Z is observed in the receiving side communication apparatus due to the offset of the frequency difference from the signal or its fluctuation, the phase rotates. As shown in FIG. 4B, Z has a predetermined radius on the complex plane. The signal moves on a circle.

  Here, if there is further in-phase and quadrature mismatch, the signal Z is not a signal that moves in a circular shape with a predetermined radius due to the gain difference and the phase difference. For example, as shown in FIG. It becomes a moving signal. The detection unit 23 determines an amplitude compensation amount and a phase compensation amount for the reference signal component X and / or the reference signal component Y in order to convert the signal Z into a circle from the trajectory of the signal Z. The compensation unit 24 Based on the determination of the detection unit 23, the signal I ′ and / or the signal Q ′ is compensated, and the in-phase signal I and the quadrature signal Q are output.

  That is, the detection unit 23 obtains an in-phase quadrature mismatch amount that suppresses the amplitude fluctuation of the signal Z after conversion as much as possible. For example, the detection unit 23 sets the signal Z after conversion based on the estimated amplitude compensation amount and the estimated phase compensation amount to Z ′, and within a predetermined period, sets the absolute value of each Z ′ within the period of the absolute value of Z ′. Find the average of the values divided by the maximum value at. This value is obtained for each estimated amplitude compensation amount and estimated phase compensation amount, and the estimated amplitude compensation amount and estimated phase compensation amount that maximize this value are used for the signal compensation processing in the compensation unit 24. Amount.

  As described above, according to the present invention, in-phase quadrature mismatch is compensated by adding the reference signal 50 outside the band of the OFDM signal 30, and the number of subcarriers of the OFDM signal 30 used for information transmission is not reduced. In addition, compensation for in-phase and quadrature mismatch is performed by the reference signal 50 that is inserted irrelevantly instead of the OFDM signal 30 that carries information and is susceptible to nonlinear effects of the transmission path, etc., so that compensation more reliable than the prior art It can be performed. Further, even in the form in which the position of the subcarrier of the OFDM signal 30 is used as the reference signal 50, there is an advantage that the number of subcarriers used for information transmission is not reduced as compared with the prior art.

  Further, although the embodiments using the OFDM modulation / demodulation technology have been described, as will be apparent to those skilled in the art, the present invention can be applied to all communication systems that perform orthogonal modulation and demodulation. That is, the in-phase signal I and the quadrature signal Q input to the IQ multiplexing unit 11 are not limited to signals generated by the OFDM modulation technique.

It is a block diagram of the transmission side of the communication apparatus by this invention. It is a block diagram of the receiving side of the communication apparatus by this invention. It is a rough frequency spectrum of the electric signal which an addition part outputs. It is a figure explaining the principle of operation of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 IQ multiplexing part 12 Reference signal production | generation part 13 Addition part 21 IQ separation part 22 Reference signal extraction part 23 Detection part 24 Compensation part 30 OFDM signal 50 Reference signal

Claims (6)

Means for orthogonally demodulating a signal including a signal generated by quadrature modulation and a reference signal having a predetermined amplitude, and outputting a first signal and a second signal;
Means for detecting an in-phase quadrature mismatch amount based on a reference signal component included in the first signal and a reference signal component included in the second signal;
A communication device comprising:   The in-phase quadrature mismatch amount is a phase amount and an amplitude amount that suppress fluctuations in amplitude of a complex signal in which the reference signal component included in the first signal is a real part and the reference signal component included in the second signal is an imaginary part. The communication device according to claim 1. Quadrature modulation is an in-phase signal and quadrature signal input.
3. The apparatus according to claim 1, further comprising means for compensating for the in-phase quadrature mismatch from the first signal and the second signal based on the detected amount of the in-phase quadrature mismatch and outputting the in-phase signal and the quadrature signal. Communication device. In the transmission side communication device, transmitting a signal generated based on a signal including a quadrature modulation signal generated by quadrature modulation and a reference signal having a predetermined amplitude;
In the receiving-side communication device, a step of orthogonally demodulating a signal including the orthogonal modulation signal and the reference signal, and outputting a first signal and a second signal;
In the receiving communication device, detecting the in-phase quadrature mismatch amount based on the reference signal component included in the first signal and the reference signal component included in the second signal;
A communication method comprising: A complex signal having a reference signal component included in the first signal as a real part and a reference signal component included in the second signal as an imaginary part is converted by each estimated phase amount and estimated amplitude amount, and within a predetermined period, An average value obtained by dividing the absolute value of the converted complex signal by the maximum absolute value within the predetermined period is obtained, and an estimated phase amount and an estimated amplitude amount that maximize the obtained average value are obtained as in-phase orthogonal non-intensities. Alignment amount,
The communication method according to claim 4. Generation of a signal including a quadrature modulation signal and a reference signal in the transmission side communication device
Adding a predetermined DC offset to the in-phase signal and / or quadrature signal;
Quadrature modulating the in-phase signal and the quadrature signal to which a DC offset has been added;
The communication method according to claim 4 or 5, comprising:

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