JP4116591B2 - Digital receiver and receiving method - Google Patents

Description

  The present invention relates to a digital receiver and a receiving method, and more particularly, to a digital receiver and a receiving method in wireless communication for correcting imbalance between I and Q signals after quadrature demodulation.

  Orthogonal demodulation, such as OFDM (Orthogonal Frequency Division Multiplexing), which is one of the digital modulation methods used in wireless communications, etc., first converts the received signal to an intermediate frequency (Intermediate Frequency) signal. Is done. Further, the intermediate frequency signal is mixed with the local signal from the reference oscillator and outputs an I signal that is an in-phase component. At the same time, the intermediate frequency signal is realized by being mixed with a local signal whose phase is shifted by 90 degrees from the reference oscillator through a 90 degree phase shifter, and outputting a Q signal which is a quadrature component. After quadrature demodulation, the downstream circuit receives the I signal (in-phase component) and the Q signal (quadrature component) and converts them into, for example, video data baseband signals or wireless LAN baseband signals. Perform baseband signal processing. The baseband filters, A / D converters, etc. that exist in two circuits corresponding to each of the I signal and the Q signal included in the subsequent stage circuit may be composed of analog circuits, Relative error (IQ imbalance) occurs due to factors such as temperature change. For example, amplitude error and phase error. Such an error has an adverse effect on the reception characteristics in the end, and must be corrected.

  Conventionally, as this correction method, a difference from a reference value of a transfer characteristic of each signal path through which an I signal and a Q signal pass, for example, an amplitude error and a phase error are calculated, and based on this, each difference is calculated according to a predetermined algorithm. It has been proposed to calculate a correction value for a signal and correct the IQ signal based on the correction value (see, for example, Patent Document 1).

Alternatively, in order to measure the amplitude error and the phase error between both the I signal and the Q signal and calculate the correction value so as to reduce them, the attenuation of the variable attenuator and variable delay device provided for each signal system A method for adjusting a value or the like has also been proposed (see, for example, Patent Document 2).
JP 2001-86177 A JP 2001-333120 A

  In the conventional IQ imbalance correction method described above, a circuit for independently correcting the amplitude error and the phase error between both the I signal and the Q signal is provided, increasing the calculation cost and increasing the hardware scale. There was a problem of becoming.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a digital receiver and a receiving method capable of realizing IQ imbalance correction with a simple configuration.

According to one aspect of the present invention, means for distributing a received modulated digital signal into an I signal (in-phase component) and a Q signal (quadrature component), and signal processing for I signal for performing predetermined signal processing on the I signal Means, Q signal signal processing means for performing predetermined signal processing on the Q signal, means for detecting frequency characteristics of the I signal signal processing means,
Means for detecting the frequency characteristic of the signal processing means for Q signal, means for adding the detected frequency characteristic of the signal processing means for I signal to the signal path of the Q signal, and signal for the detected Q signal Means for adding a frequency characteristic of the processing means to the signal path of the I signal is provided.

According to one aspect of the present invention, the step of distributing the modulated digital signal into an I signal (in-phase component) and a Q signal (quadrature component), and signal processing for I signal for performing predetermined signal processing on the I signal A signal processing step for Q signal for performing predetermined signal processing on the Q signal, a step for detecting a frequency characteristic of the signal processing means for the I signal, and a frequency characteristic of the signal processing means for the Q signal are detected. And adding the detected frequency characteristic of the signal processing means for I signal to the signal path of the Q signal, and adding the detected frequency characteristic of the signal processing means for Q signal to the signal path of the I signal The receiving method is characterized by comprising the step of adding to the above.

  According to the present invention, a complicated algorithm for calculating the correction value is not required, and the calculation cost and the calculation cost can be reduced without measuring the difference in transfer characteristics such as the amplitude error and the phase error between the I signal and the Q signal. IQ imbalance can be corrected at hardware cost.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same portions are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a digital receiver according to the first embodiment of the present invention. As shown in FIG. 1, the digital receiver according to the first embodiment of the present invention includes an antenna 10, a frequency converter 11 using, for example, IG-BT switching, and a reference transmission employing, for example, a high-precision crystal module. 12, a mixer 15 that mixes a plurality of input signals, a 90-degree phase shifter 13 that changes the phase of a signal transmitted through the transmission path by 90 degrees, a step waveform input unit 14, and a baseband frequency BB (baseband) filters 21 and 22, A / D converters 31 and 32 that perform sampling, numerical calculation circuits 41 and 42 that generate a pulse-like signal by inverting amplification from a rectangular wave input signal, and a corrector 51, 52.

  Here, the high frequency received signal received by the antenna 10 is dropped to an intermediate frequency by the frequency converter 11 and then mixed with the local signal from the reference transmitter 12 to output an I signal (in-phase component), At the same time, the signal is mixed with a local signal whose phase is shifted by 90 degrees from the reference oscillator 12 via the 90-degree phase shifter 13, and a Q signal (quadrature component) is output.

  At the time of communication, the I signal and the Q signal thereafter pass through the BB filters 21 and 22, A / D converters 31 and 32, etc. for the purpose of removing interference waves, respectively, and the subsequent digital demodulation circuit (FIG. The process proceeds to (not shown).

  In general, in digital communication, there is a non-communication time, that is, before the start of communication, or a period during which communication is not performed. For example, in the IEEE 802.11 MAC layer (Media Access Control) specification, which is one of the standards for wireless LAN terminals, a time interval between frames is defined. That is, in a wireless LAN, communication is performed by exchanging two frames, that is, a data frame and an ACK frame. The data frame includes data that is actually exchanged (such as TCP / IP packets). The ACK frame is for informing the other party that the data has been correctly received. At the time of data transfer, the transmitting side sends a data frame, and the receiving side returns an ACK frame to complete. This frame exchange is not done without interruption. The transmission side receives the ACK frame and transmits a data frame after a certain time called DIFS (Distributed Coordination Function Interframe Space). The receiving side also transmits an ACK frame after receiving a data frame after a certain time called SIFS (Short Interframe Space). In this way, during a time interval that leaves a certain time, transmission / reception of data (frames) between a predetermined access point and a terminal is stopped (non-communication).

  In the embodiment of the present invention, a unit stepped step waveform signal is input to both the I signal and Q signal systems from the step waveform input unit 14 during non-communication as described above. In this embodiment, an example in which a step waveform is input by the step waveform input unit 14 will be described. However, the waveform is not limited to the step waveform as long as it is a waveform for measuring the IQ balance. Further, as the step waveform input unit 14, for example, if a transmission D / A conversion circuit is used, the hardware cost is not so high. The input step waveform signals are respectively input to the numerical calculation circuits 41 and 42 via the BB filters 21 and 22, the A / D converters 31 and 32, and the numerical calculation circuits 41 and 42 perform numerical differentiation and the like. Processing is executed. Thereby, an impulse response from the BB filter 21 to the A / D converter 31 through which the I signal passes is obtained by the numerical calculation circuit 41.

  In the above example, since a step waveform is input by the step waveform input unit 14 as a waveform for measuring the IQ balance, the numerical response circuits 41 and 42 obtain an impulse response by performing numerical differentiation. However, instead of this, when an impulse signal is input by the step waveform input unit 14 as a waveform for measuring the IQ balance, the numerical calculation circuits 41 and 42 obtain an impulse response from the A / D converters 31 and 32, respectively. It is done. Therefore, the numerical calculation circuits 41 and 42 need only pass through the signal without performing any particular calculation.

  When another waveform is used as a waveform for measuring the IQ balance, the numerical calculation circuits 41 and 42 may perform numerical calculation according to the other waveform to obtain an impulse response.

  Although the numerical calculation circuits 41 and 42 shown in FIG. 1 are divided into two, they may be configured by the same hardware, and perform calculations such as numerically differentiating the obtained output series, for example. Anything is acceptable.

  In the embodiment of the present invention, the impulse response from the BB filter 21 through the I signal, which is obtained by the numerical calculation circuits 41 and 42 to the A / D converter 31, respectively, is obtained by the corrector 52 through which the Q signal passes. The impulse response from the BB filter 22 through which the Q signal passes to the A / D converter 32 is used as the tap coefficient of the corrector 51 through which the I signal passes.

  Therefore, even when IQ imbalance occurs in the I signal and Q signal, the frequency characteristics from the BB filter 21 to the corrector 51 and from the BB filter 22 to the corrector 52 are substantially equal, and the IQ imbalance is reduced. It is corrected. In this case, the frequency characteristics from the BB filters 21 and 22 to the correctors 51 and 52 are substantially equal to the square characteristics of the frequency characteristics from the BB filters 21 and 22 to the A / D converters 31 and 32, but the BB filter 21 , 22 to A / D converters 31 and 32 originally have interference wave elimination characteristics, so that reception characteristics are not deteriorated. Needless to say, the square characteristic is set so as to have the optimum interference wave removal characteristic.

  As described above, if the above correction is executed during non-communication, it is possible to correct a fixed IQ imbalance caused by a manufacturing error, and it is possible to prevent deterioration of reception characteristics.

  Furthermore, if the above correction is appropriately executed during non-communication, it is possible to correct the IQ imbalance that changes over time due to temperature changes or the like as needed, and it is possible to prevent deterioration of reception characteristics.

  As described above, according to the present invention, a target value for correction is not calculated according to a specific algorithm, and a circuit for correcting amplitude error and phase error independently for each of I and Q is provided. In addition, the IQ imbalance can be corrected at any time with a small calculation cost and hardware cost.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a block diagram showing a configuration of a digital receiver according to the second embodiment of the present invention. As shown in FIG. 2, the digital receiver according to the second embodiment of the present invention includes an antenna 10, a frequency converter 11, a reference oscillator 12, and a mixer 15 that mixes a plurality of input signals. , 90-degree phase shifter 13, step waveform input unit 14, BB (baseband) filters 21 and 22, A / D converters 31 and 32, numerical calculation circuits 43 and 44 for performing numerical differentiation, and digital filters 61, 62.

  Here, the high frequency received signal received by the antenna 10 is dropped to an intermediate frequency by the frequency converter 11 and then mixed with the local signal from the reference transmitter 12 to output an I signal that is an in-phase component, At the same time, the signal is mixed from the reference oscillator 12 via the 90-degree phase shifter 13 with a local signal whose phase is shifted by 90 degrees, and a Q signal that is a quadrature component is output.

  At the time of communication, the I signal and the Q signal are then passed through the BB filters 21 and 22, A / D converters 31 and 32, and digital filters 61 and 62 for the purpose of removing interference waves, respectively. Processing proceeds to a digital demodulation circuit (not shown). The digital filters 61 and 62 are digital filters for performing a convolution operation (convolution), and here function to remove interference waves.

In the present embodiment, a step waveform signal having a unit step shape is input to both the I signal and Q signal systems from the step waveform input device 14 during non-communication. As the step waveform input device, as described in the first embodiment, if a transmission D / A conversion circuit is used, the hardware cost is not so high. The input step waveform signals are respectively input to the numerical calculation circuits 43 and 44 via the BB filters 21 and 22, the A / D converters 31 and 32, and the numerical differentiation is executed. Thus, impulse responses from the BB filters 21 and 22 to the A / D converters 31 and 32 are obtained by the numerical calculation circuits 43 and 44.

Although the numerical calculation circuits 43 and 44 shown in FIG. 2 are divided into two, they may be composed of the same hardware as long as the obtained output series is numerically differentiated.

In the present embodiment, the impulse response from the BB filter 21 through which the I signal passes to the A / D converter 31 obtained by the numerical calculation circuits 43 and 44, respectively, is the tap coefficient of the digital filter 62 through which the Q signal passes. The impulse response from the BB filter 22 through which the Q signal passes to the A / D converter 32 is used as the tap coefficient of the digital filter 61 through which the I signal passes.

As in the first embodiment, the Q signal additionally passes through the frequency characteristic from the BB filter 21 of the I signal to the A / D converter 31, and the A / D converter is converted from the BB filter 22 of the Q signal. The I signal is additionally subjected to frequency characteristics up to 32. In the second embodiment, the correction is performed by changing the initial tap coefficients of the digital filters 61 and 62. Realize with. Specifically, the above-described impulse response corresponding to the I signal is a0, a1, a2,..., An−1, and the above-described impulse response corresponding to the Q signal is b0, b1, b2,. The tap coefficients originally required for the digital filter to realize interference wave suppression are c0, c1, c2,. If the digital filters 61 and 62 have redundant taps,
The convolution of b0, b1, b2,..., bn-1 and c0, c1, c2,..., cm-1 is expressed as x (j) (where j is the sample number). Then, yi (j) is an input signal to the corrector 51 for I signal, and yq (j) is an input signal to the corrector 52 for Q signal.

as well as

It becomes. For example, if x (j) is an impulse response, tap coefficients zi (j) and zq (j) that can correct IQ imbalance can be set by convolving them with the characteristics of the original digital filter.

  As a result, when an IQ imbalance occurs when a difference due to a manufacturing error or a temperature change occurs in the frequency characteristics from the BB filter to the A / D converter of each of the I signal and the Q signal, the BB filter IQ imbalance can be corrected by making the frequency characteristics from 21 and 22 to the digital filters 61 and 62 substantially equal. In this case, the frequency characteristics of the BB filter to the digital filter are approximately equal to the original digital filter characteristic multiplied by the square characteristic of the frequency characteristic from the BB filter to the A / D converter. Since the frequency characteristics up to the D converter originally had interference wave elimination characteristics, the reception characteristics are not deteriorated. It is even better if it is designed from the beginning so that the square characteristic has the optimum interference wave elimination characteristic. As the digital filters 61 and 62, known FIR (Finite Impulse Response) filters can be used.

  As described above, if the above correction is performed at the time of non-communication, it is possible to correct a fixed IQ imbalance caused by a manufacturing error, and it is possible to prevent deterioration of reception characteristics.

  Furthermore, if the above correction is appropriately executed during non-communication, it is possible to correct the IQ imbalance that changes over time due to temperature changes or the like as needed, and it is possible to prevent deterioration of reception characteristics.

  As described above, according to the present invention, a target value for correction is not calculated according to a specific algorithm, and a circuit for correcting amplitude error and phase error independently for each of I and Q is provided. In addition, the IQ imbalance can be corrected at any time with a small calculation cost and hardware cost.

In the above embodiment, in determining impulse responses from the BB filters 21 and 22 to the A / D converters 31 and 32, step waveform signals are input to the BB filters 21 and 22, and the A / D converter A method of numerically differentiating the outputs of 31 and 32 was taken. However, when a signal close to the unit impulse waveform can be easily generated by using a transmission D / A conversion circuit, the unit impulse waveform obtained thereby is input to the BB filters 21 and 22, and the BB filter If the impulse responses from 21 and 22 to the A / D converters 31 and 32 are determined, the numerical differentiation functions of the numerical calculation circuits 41 and 42 and the numerical calculation circuits 43 and 44 become unnecessary.

  Further, the correctors 51 and 52 or the digital filters 61 and 62 may be provided after the A / D converters 31 and 32, and between the A / D converters 31 and 32 and the correctors 51 and 52 or the A / D. There is no problem even if other digital filters or other linear digital circuits exist between the converters 31 and 32 and the digital filters 61 and 62, and the installation position can be freely set as long as the gist of the present invention is satisfied. .

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a block diagram showing a configuration of a digital receiver according to a first embodiment of the present invention. The block diagram which showed the structure of the digital receiver which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Antenna, 11 ... Frequency converter, 12 ... Reference transmitter, 13 ... 90 degree phase shifter, 14 ... Step waveform input device, 21, 22 ... BB (baseband) filter, 31, 32 ... A / D conversion 41, 42... Numerical calculation circuit, 43, 44... Numerical calculation circuit, 51, 52.

Claims (6)

Means for distributing the received modulated digital signal into an I signal (in-phase component) and a Q signal (quadrature component);
I signal processing means for performing predetermined signal processing on the I signal;
Q signal signal processing means for performing predetermined signal processing on the Q signal;
Means for detecting frequency characteristics of the signal processing means for I signal;
Means for detecting frequency characteristics of the signal processing means for Q signal;
Means for adding the detected frequency characteristic of the signal processing means for I signal to the signal path of the Q signal;
Means for adding a frequency characteristic of the detected signal processing means for Q signal to the signal path of the I signal;
A digital receiver comprising: The means for adding the frequency characteristic of the signal processing means for I signal to the signal path of the Q signal is a digital filter, and the filter coefficient of the digital filter is an impulse response of the signal processing means for I signal,
The means for adding the frequency characteristic of the signal processing means for Q signal to the signal path of the I signal is a digital filter, and the filter coefficient of the digital filter is an impulse response of the signal processing means for Q signal. The digital receiver according to claim 1.   The digital receiver according to claim 2, wherein the digital filter is an FIR filter.   4. The digital signal according to claim 2, wherein the impulse response is determined by inputting a step waveform to each of the I signal and Q signal after quadrature demodulation and numerically differentiating the signal waveform after A / D conversion. Receiving machine.   The digital receiver according to any one of claims 2 to 4, wherein the determination of the impulse response is executed before the start of communication or when communication is not being performed. Distributing the modulated digital signal into an I signal (in-phase component) and a Q signal (quadrature component);
I signal processing step for performing predetermined signal processing on the I signal;
A Q signal signal processing step for performing predetermined signal processing on the Q signal;
Detecting a frequency characteristic of the signal processing means for I signal;
Detecting a frequency characteristic of the signal processing means for Q signal;
Adding the detected frequency characteristic of the signal processing means for I signal to the signal path of the Q signal;
A receiving method comprising the step of adding the detected frequency characteristic of the signal processing means for Q signal to the signal path of the I signal .

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