WO2006103922A1

WO2006103922A1 - Radio receiver

Info

Publication number: WO2006103922A1
Application number: PCT/JP2006/305032
Authority: WO
Inventors: Yuji Yamamoto
Original assignee: Pioneer Corporation
Priority date: 2005-03-25
Filing date: 2006-03-14
Publication date: 2006-10-05
Also published as: JP4523968B2; JPWO2006103922A1

Abstract

A radio receiver having an adaptive filter capable of stably suppressing multipath fading and flat fading. There are included an adaptive filter (9) that adaptively filters a digital IF signal (X) as A/D converted; and a determining part (12) that measures the field strength from the digital IF signal (X) and determines, based on a measurement result of the field strength, the influence of either multipath fading or flat fading. When the determining part (12) determines the influence of multipath fading, the adaptive filter (9) uses an IIR filter to adaptively filter the digital IF signal (X). An output signal (SIIR) from the adaptive filter (9) is then supplied to a detector (11) via a switching part (10). When the determining part (12) determines the influence of flat fading, the adaptive filter (9) uses an FIR filter to adaptively filter the digital IF signal (X). An output signal (SFIR) from the adaptive filter (9) is then supplied to the detector (11) via the switching part (10).

Description

Specification

Wireless receiver

Technical field

[0001] The present invention relates to a radio receiver including an adaptive filter that suppresses the effects of multipath fading and flat fading.

Background art

[0002] When a VHF band radio wave used for FM broadcasting is reflected by a building or the like, a direct wave and a reflected wave are added to the receiver to form a so-called multipath. When this multipath occurs, multipath fading (multipath distortion) due to interference between the direct wave and the reflected wave occurs in the FM wave, which degrades the reception quality. In particular, mobile radio receivers such as in-vehicle radio receivers and portable radio receivers installed in automobiles are used in environments that are susceptible to multipath, so the effects of multipath distortion are suppressed. Therefore, it is extremely important to prevent degradation of reception quality.

[0003] Therefore, conventionally, a radio receiver including an adaptive filter for suppressing multipath fading as shown in FIG. 1 (a) has been proposed.

[0004] The conventional radio receiver shown in Fig. 1 (a) performs A / D conversion after band-limiting and amplifying the intermediate frequency signal (IF signal) frequency-converted by the front end 1 by the IF amplifier 2. The digital IF signal X is converted to a digital IF signal X by the detector 3, and the adaptive processing is applied to the digital IF signal X by the adaptive filter 4 to generate a digital IF signal Y that suppresses multipath fading. I started to detect it.

Here, as shown in FIG. 1 (b), the adaptive filter 4 includes an IIR type digital filter that performs filtering on the digital IF signal X, and an IIR type digital filter that suppresses multipath fading. It has a coefficient update unit OPRT that variably adjusts the tap coefficient (filter coefficient) of the filter.

[0006] That is, the IIR type digital filter has a multiplier a0 that amplifies the digital IF signal X, an adder SUM1 that adds the output of the multiplier aO and a feedback signal FB described later, and one sample delay each. It has multiple delay elements (z ^{_ 1} ) and inputs the output of adder SUM1. Shift register SRG, and multipliers bO to bn that multiply the output of each delay element (z ^{_ 1} ) by the filter coefficient, and the outputs of multipliers bO to bn are added to obtain feedback signal FB. And an adder SUM2 to be generated.

[0007] The coefficient updating unit OPRT calculates the square root ε of the digital IF signals Y (t) and Y (tl) output from the adder SUM1 and shifted by one sample delay, and further calculates the square root of the square. The filter coefficients of the multipliers b0 to bn are variably adjusted so that the convergence error Err (t) between ε and the predetermined convergence value Vth converges to zero. In other words, the square root ε of the square and the convergence error Err (t) are calculated by performing the calculation represented by the following equations (1) and (2), and the multipliers b0 to bn are calculated based on the convergence error Err (t). Each filter coefficient is variably adjusted. Here, the convergence value Vth is a fixed value for effectively removing multipath fading, and is determined by experiments.

[0008] [Equation 1]

[0009] According to such a configuration, the adaptive filter 4 outputs the digital IF signal Y in which the multipath fading is suppressed from the adder SUM1, and the detector 5 detects the waveform distortion and the like so that the detection signal ( Baseband signal) Sout is output.

Disclosure of the invention

Problems to be solved by the invention

[0010] Since the adaptive filter 4 is formed of an IIR digital filter, the conventional radio receiver has a convenient configuration for suppressing multipath fading. In other words, multipath fading, which is frequency selective fading, is due to the fact that the AM component due to interference between the direct wave and the reflected wave is generated in the FM wave, so the ratio of the direct wave and the reflected wave is 1: 1. In this case, the impulse response of the IIR digital filter continues indefinitely. Therefore, the IIR type digital filter is effective, and the multipath fading converges to the convergence value Vth, so that the amplitude of the digital IF signal Y (the amplitude when an analog IF signal is used) is kept constant. Remove multipath feeding You can.

[0011] However, since fading also causes flat fading due to the attenuation of the direct wave itself, which is not only due to multipath, trying to remove this flat fading with an IIR digital filter with infinite length impulse characteristics. , Coefficient updating unit ○ Each filter coefficient of multipliers b0 to bn updated by PRT may diverge, causing a problem that the operation becomes unstable.

[0012] The present invention has been made in view of such a conventional problem, and is provided with a radio reception provided with an adaptive filter that can stably suppress multipath fading and flat fading. The purpose is to provide a machine.

Means for solving the problem

[0013] The invention of claim 1 is a wireless receiver that suppresses fading included in an intermediate frequency signal of an FM wave, the electric field strength is measured from the intermediate frequency signal, and the electric field strength is a predetermined threshold value. The IIR filter according to the determination means for generating a switching control signal indicating the first determination result when the electric field strength is smaller than the threshold and the switching control signal indicating the first determination result when the electric field strength is smaller than the threshold The intermediate frequency signal is adaptively filtered, and the FIR filter adaptively performs the filtering process on the intermediate frequency signal according to the switching control signal indicating the second determination result. According to the switching control signal indicating the second determination result and outputting the output signal of the IIR filter according to the adaptive filter means and the switching control signal indicating the first determination result It characterized by having a a switching means for outputting an output signal of the FI R filter.

[0014] In the invention according to claim 2, in the radio receiver according to claim 1, the adaptive filter means adaptively performs filtering on the intermediate frequency signal by the IIR filter. When the filter coefficient of the IIR filter is automatically adjusted to suppress fluctuations in the output of the IIR filter and the intermediate frequency signal is adaptively filtered by the FIR filter, the FIR filter It is characterized by having coefficient updating means for automatically adjusting the filter coefficient of the FIR filter so as to suppress fluctuations in the output of the filter.

[0015] The invention according to claim 3 is the radio receiver according to claim 1 or 2, wherein the IIR The output signal of the type filter is output from the position of the intermediate tap of the IIR type filter.

Brief Description of Drawings

FIG. 1 is a block diagram for explaining a configuration of a conventional radio receiver.

FIG. 2 is a block diagram showing a configuration of a wireless receiver according to the embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a wireless receiver according to an embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

A radio receiver according to an embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing the configuration of the wireless receiver of this embodiment.

In FIG. 2, this wireless receiver extracts an FM broadcast band RF signal from various broadcast waves received by the receiving antenna, and mixes the local oscillation signal and the RF signal of the local oscillation frequency. Output the intermediate frequency IF signal, the IF signal is output from the IF amplifier 7 and the IF amplifier 7 that outputs the IF signal as the desired wave by amplifying the IF signal by band limiting. An AZD converter 8 that converts the IF signal to be converted into a digital IF signal X from analog to digital, an adaptive filter 9, a switching unit 10, a detector 11, and a determination unit 12 are configured.

The determination unit 12 calculates an electric field strength (S meter) from the digital IF signal X, and compares the calculated electric field strength with a predetermined threshold value THD. When the electric field strength is larger than the threshold THD, the switching control signal SEL indicating the first determination result is sent to the adaptive filter 9 and the switching unit 10 when the electric field strength is smaller than the threshold THD. Supply.

[0020] When the switching control signal SEL indicating the first determination result is supplied from the determination unit 12, the switching unit 10 converts the output signal SIIR filtered by the adaptive filter 9 into a digital IF signal Y and detects the detector 11 When the switching control signal SEL indicating the second determination result is supplied, the output signal SFIR filtered by the adaptive filter 9 is transferred to the detector 11 as the digital IF signal Y.

The adaptive filter 9 includes an IIR type digital filter, an FIR type digital filter, and a coefficient updating unit that adjusts filter coefficients of these digital filters. When the switching control signal SEL indicating the first determination result is supplied from the determination unit 12, the adaptive filter 9 performs a filtering process using an IIR digital filter on the digital IF signal X, and outputs the filtered output. The signal SIIR is supplied to the detector 11 as a digital IF signal Y through the switching unit 10. On the other hand, when the switching control signal SEL indicating the second determination result is supplied from the determination unit 12, the digital IF signal X is filtered by the FIR digital filter, and the filtered output signal SFIR is switched. The digital IF signal Y is supplied to the detector 11 through the control unit 10.

Furthermore, the amplitude fluctuation of the digital IF signal Y that is the output of the above-described coefficient update unit force switching unit 10 provided in the adaptive filter 9 (the amplitude fluctuation when the digital IF signal Y is an analog signal) is calculated. Detect and adjust the filter coefficient of the IIR digital filter and the filter coefficient of the FIR digital filter variably so that the amplitude fluctuation converges to zero.

That is, when the output signal SIIR filtered by the IIR digital filter is output as the digital IF signal Y from the switching unit 10 according to the switching control signal SEL indicating the first determination result, the coefficient update described above is performed. This section detects the amplitude fluctuation of the digital IF signal Y and automatically adjusts the filter coefficient of the IIR digital filter so that the amplitude fluctuation converges to 0, thereby reducing the output signal SIIR. Is output from the IIR digital filter.

On the other hand, when the output signal SFIR filtered by the FIR type digital filter is output from the switching unit 10 as the digital IF signal Y according to the switching control signal SEL indicating the second determination result, the coefficient updating unit Detects the amplitude fluctuation of the digital IF signal Y, and automatically adjusts the filter coefficient of the FIR type digital filter so that the amplitude fluctuation converges to 0, thereby reducing the output signal SFIR with reduced fading. Output from FIR digital filter.

[0025] As described above, the radio receiver according to the present embodiment, when the electric field strength is larger than the predetermined threshold value THD, performs digital processing by the processing of the IIR digital filter in the adaptive filter 9 and the coefficient updating unit. Output signal SIIR with digital filtering applied to IF signal X to suppress the effects of forging as digital IF signal Y Detector 1 When the electric field strength is smaller than the predetermined threshold value THD, the digital IF signal X is digitally filtered by the FIR digital filter in the adaptive filter 9 and the coefficient updating unit, and then fed. The output signal S FIR that suppresses the influence of is supplied to the detector 11 as the digital IF signal Y.

[0026] This force provides the following effects. That is, when multipath feeding occurs, the electric field strength increases, so that the digital filtering process for the digital IF signal X is performed by the IIR digital filter in the adaptive filter 9. For this reason, even when the impulse response is infinite when multipath fading occurs in which the direct wave and reflected wave have a proportional force S1 to 1, the force S to converge the multipath fading can be obtained. Since the amplitude of the digital IF signal Y (the amplitude when an analog IF signal is used) can be kept constant, when the detector 11 detects the digital IF signal Y with FM, the detection signal (base Band) Sdet can be generated.

[0027] On the other hand, when flat fading occurs, the electric field strength decreases, and the digital filtering process for the FIR digital filter power digital IF signal X in the adaptive filter 9 is performed based on the comparison result with the threshold value THD. Do. For this reason, the flat fading can be converged by the FIR digital filter that operates more stably than the IIR digital, and the amplitude of the digital IF signal Y (amplitude in the case of an analog IF signal) is kept constant. Therefore, when the detector 11 performs FM detection on the digital IF signal Y, a detection signal Sdet with suppressed waveform distortion and the like can be generated.

[0028] Thus, according to the wireless receiver of the present embodiment, it is possible to stably suppress multipath fading and flat fading, and to improve reception quality. It can be done.

Example

Next, a more specific example will be described with reference to FIG. FIG. 3 (a) is a block diagram showing the configuration of the wireless receiver of this embodiment, and the same or corresponding parts as those in FIG. 2 are denoted by the same reference numerals. Fig. 3 (b) is a block diagram showing the configuration of the adaptive filter.

[0030] In Fig. 3 (a), this radio receiver amplifies the IF signal output from the front end 6 having the channel selection circuit 6a and the frequency converter 6b with the IF amplification unit 7 performing band limitation, A / D The converter 8 converts the digital IF signal X from analog to digital and outputs it.

[0031] The determination unit 12 includes an electric field strength measurement unit 12a that calculates an electric field strength (S meter) from the digital IF signal X, an electric field strength value Smtr calculated by the electric field strength measurement unit 12a, and a predetermined threshold value TH D And a comparison circuit 12b that outputs a switching control signal SEL. In other words, the threshold THD is determined to be a value between the electric field strength when multipath fading occurs and the electric field strength when flat feeding occurs by experiments. When the field strength value Smtr is larger than the threshold value THD, the comparison circuit 12b outputs a switching control signal SEL that is a logic “H” indicating the first determination result, and the field strength value Smt r is smaller than the threshold value THD. In some cases, the switching control signal SEL that is logic “L” indicating the second determination result is output.

[0032] The switching circuit 10 is formed of an analog switch or the like that performs switching operation according to the switching control signal SEL. When the switching control signal SEL indicating the first determination result is supplied, the output output from the adaptive filter 9 When the signal SIIR is transferred to the detector 11 as the digital IF signal Y and the switching control signal SEL indicating the second determination result is supplied, the output signal SFIR output from the adaptive filter 9 is used as the digital IF signal Y as the detector 11 Forward to.

The adaptive filter 9 has the configuration shown in FIG. 3 (b), and the digital IF signal X input under the control of the determination unit 12 having the electric field strength measurement circuit 12a and the comparison circuit 12b. A digital filtering process is performed on the signal, and the output signal SIIR or SFIR with the fading suppressed is supplied to the detector 11 via the switching circuit 10.

That is, the adaptive filter 9 includes an adder SUM1 that adds a digital IF signal X and a feedback signal FB supplied via a switch circuit SW described later, and a plurality of delay elements each having one sample delay ( z− ¹ ) and shifts the output of adder SUM1 by shifting the multistage shift register SRG, and multiple multiplications that multiply the output of adder SUM1 and each delay element (z— ¹ ) by the filter coefficient And an adder SUM2 that generates an output signal SFIR by adding the outputs of the multipliers b0 to b2n, and a coefficient updating unit OPRT.

[0035] Here, when the number of delay elements (z- ¹ ) is 2n (even), the number of multipliers b0 to b2n is set to a relationship of 2n + 1 (odd). For example, delay element (z ^_1 ) The number is 28, and the number of multipliers b0 to b2n is 29.

[0036] Then, an output signal SIIR is output from a middle point nTs that is a connection point between the nth delay element (z- ¹ ) and the (n + ¹ ) th delay element (z- ¹ ).

[0037] The switch circuit SW performs conduction (on) or cutoff (off) operation according to the switching control signal SEL, and the switching circuit 10 is switched and connected to the contact P1 side, and the output signal SIIR is output as the digital IF signal Y. When the output signal SFIR of the adder SUM2 is supplied as the feedback signal FB to the power calculator SUM1, the feedback signal FB and the digital IF signal are added to the adder SUM1. Add X and output the addition result to the shift register DRG side.

[0038] On the other hand, when the switching circuit 10 is switched and connected to the contact P2 side and the output signal SFIR is output as the digital IF signal Y, the switch circuit SW is cut off and the feedback signal FB is added. Operates so as not to supply to SUM1. As a result, the adder SUM1 outputs the input digital IF signal X as it is to the shift register DRG side.

[0039] When the switch circuit SW becomes conductive, the transfer function of the output signal SIIR with respect to the digital IF signal X is expressed in z conversion notation, and is expressed by the following equation (3), and the IIR digital filter is Realized. When an IIR digital filter is realized, the filter coefficient of the multiplier b0 is set to 0 by the coefficient updating unit OPRT.

[0040] [Equation 2]

H (z)--(3)

丄 "~ u Z

[0041] When the switch circuit SW is cut off, the transfer function of the output signal SFIR with respect to the digital IF signal X can be expressed in z-conversion notation, and the FIR digital filter can be realized by the following equation (4). Is done.

[0042] [Equation 3]

2n

H (z) = biz ' ^1- ''(4) [0043] The coefficient update unit OPRT includes the switching control signal SEL, the digital IF signal Y that is the output of the switching circuit 10, the output X0 of the adder SUM1, and each delay element of the shift register SRG (the outputs Xl to Enter X2n.

[0044] Then, when the switching control signal SEL indicating the first determination result is supplied, the output signal SIIR output from the midpoint nTs of the IIR type digital filter is supplied as the digital IF signal Y. Based on the digital IF signals Y (t), Y (tl), and the predetermined convergence value Vth, the square root of the square ε and convergence error Err (t) expressed by the following equations (5) and (6) Furthermore, based on the convergence error Err (t) and each delay element (outputs Xl to X2n of z-), each multiplier bl Calculate and adjust the filter coefficient of ~ b2n.

[0045] However, the filter coefficient of each multiplier b0 is set to 0. Coefficient H is a coefficient for converging the feeding, and the convergence speed can be adjusted by adjusting the value of the coefficient H.

[0046] [Equation 4] ε = IY (t) HY (tl) ² · '· (5)

E _rr (j = _ε _vtn

[0047] [Equation 5] bi (tl) = bi (t) -a 'Err (t)-{Xi (t) ■ Y (t) + Xi (t-1) · Y (tl)}…) ( Where bi (t-1) and bi (t) are the tap coefficients of each multiplier b0 to b2n)

[0048] As described above, when the coefficient updating unit OPRT automatically adjusts the filter coefficients of the multipliers b0 and bl to b2n, the multipath fading generated in the digital IF signal X is suppressed by the IIR digital filter. The output signal SIIR is supplied to the detector 11 as the digital IF signal Y through the switching circuit 10, and the detection signal Sdet with reduced waveform distortion and the like is generated.

[0049] Further, when the switching control signal SEL indicating the second determination result is supplied, the coefficient updating unit OPRT outputs the output signal SFIR output from the adder SUM2 of the FIR digital filter. Based on the digital IF signals Y (t) and Y (t_ 1) shifted by one sump delay and the predetermined convergence value Vth, The square root ε of the square and the convergence error Err (t) are calculated. Further, based on the convergence error Err (t), the output X0 of the adder SUM1, and each delay element (the outputs Xl to X2n of z—) By performing the calculation process represented by (7), the filter coefficients of the multipliers b0 to b2n are calculated and adjusted.

[0050] In this way, when the coefficient updating unit OPRT automatically adjusts the filter coefficients of the multipliers b0 to b2n, the flat fading that has occurred in the digital IF signal X is suppressed by the FIR type digital filter. The output signal SFIR is supplied to the detector 11 as the digital IF signal Y through the switching circuit 10, and the detection signal Sdet with reduced waveform distortion and the like is generated.

[0051] As described above, when the electric field strength is larger than the predetermined threshold value THD, the radio receiver according to the present embodiment includes the IIR type digital filter formed in the adaptive filter 9 and the coefficient updating unit OPRT. The digital IF signal X is subjected to digital filtering processing, and the output signal SIIR with the effect of fading suppressed is supplied to the detector 11 as the digital IF signal Y. When the electric field strength is smaller than the predetermined threshold THD, The digital IF signal X is digitally filtered by the FIR digital filter formed in the adaptive filter 9 and the coefficient updater OPRT. Supply signal SFIR as digital IF signal Y to detector 11

[0052] This force provides the following effects. That is, when multipath fading occurs, the electric field strength increases, and thus the digital filtering process for the digital IF signal X is performed by the IIR digital filter in the adaptive filter 9. For this reason, even when the impulse response is infinite when multipath fading occurs in which the direct wave and reflected wave have a proportional force S1 to 1, the force S to converge the multipath fading can be obtained. Since the amplitude of the digital IF signal Y (the amplitude when an analog IF signal is used) can be kept constant, when the detector 11 detects the digital IF signal Y with FM, the detection signal (base Band) Sdet can be generated.

[0053] On the other hand, when flat feeding occurs, the electric field strength decreases and the threshold THD On the basis of the comparison result, the digital filter processing is performed on the FIR type digital filter force digital IF signal X in the adaptive filter 9. For this reason, the flat fading can be converged by the FIR digital filter that operates more stably than the IIR digital, and the amplitude of the digital IF signal Y (amplitude in the case of an analog IF signal) is kept constant. Therefore, when the detector 11 performs FM detection on the digital IF signal Y, a detection signal Sdet with suppressed waveform distortion and the like can be generated.

As described above, according to the wireless receiver of the present embodiment, it is possible to stably suppress multipath fading and flat fading, and to improve reception quality. It can be done.

[0055] Furthermore, the output signal SIIR filtered by the IIR digital filter is output from the midpoint nTs of the shift register SRQ, and the output signal SFIR filtered by the FIR digital filter is output from the adder SUM2. Therefore, the phase of the impulse response of the output signal SIIR and the impulse response of the output signal SFIR coincide. For this reason, even if the switching circuit 10 performs switching operation according to the switching control signal SEL, each output signal is not changed when the output signal SIIR is switched to the output signal SFIR and when the output signal SFIR is switched to the output signal SIIR. A digital IF signal Y that is continuously switched and without distortion can be supplied to the detector 11.

Claims

The scope of the claims

[1] A radio receiver that suppresses fading included in an intermediate frequency signal of an FM wave, and measures the intermediate frequency signal force electric field strength and makes a first determination when the electric field strength is larger than a predetermined threshold value. As a result, when the electric field strength is smaller than the threshold value, a determination unit that generates a switching control signal indicating the second determination result;

According to the switching control signal indicating the first determination result, the intermediate frequency signal is adaptively filtered by the IIR filter, and according to the switching control signal indicating the second determination result, the FIR filter Adaptive filter means for adaptively filtering the intermediate frequency signal;

Switching means for outputting an output signal of the IIR filter according to a switching control signal indicating the first determination result, and outputting an output signal of the FIR filter according to a switching control signal indicating the second determination result;

A wireless receiver comprising:

[2] When the adaptive filter means appropriately performs filtering on the intermediate frequency signal by the IIR filter, the filter of the IIR filter is used to suppress fluctuations in the output of the IIR filter. The coefficient is automatically adjusted, and when the FIR filter adaptively filters the intermediate frequency signal, the filter coefficient of the FIR filter is automatically adjusted to suppress fluctuations in the output of the FIR filter. 2. The radio receiver according to claim 1, further comprising coefficient updating means for performing the following.

[3] The radio receiver according to claim 1 or 2, wherein the output signal of the IIR filter is output from a position of an intermediate tap of the IIR filter.