JP2019149629A - Radio equipment - Google Patents

Abstract

To provide radio equipment capable of restraining deterioration of reception quality.SOLUTION: The radio equipment includes: a nonlinear circuit input with a signal from an antenna; a variable attenuator for attenuating the signal input into the nonlinear circuit; and a measuring section which measures an offset frequency which is a difference between a level of tertiary intermodulation distortion output from the nonlinear circuit and a frequency of a disturbing wave input into the nonlinear circuit relative to a predetermined frequency of an input wave to be measured. The variable attenuator changes the magnitude of attenuation according to a measurement result of the measuring section.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a wireless device.

  2. Description of the Related Art Conventionally, in a wireless communication system used as a business infrastructure within a company office, social infrastructure for fire fighting or disaster prevention, it is common to allocate many channels within a narrow frequency band. In addition, a wireless device used in such a wireless communication system is not used in an ideal environment, and therefore receives an unnecessary interference wave in addition to a desired wave for performing wireless communication. Inevitable. However, since reception of such interference waves causes deterioration in reception quality of desired waves, many techniques for reducing the influence of interference waves in wireless devices have been proposed.

  For example, when a desired wave and an interference wave having a frequency close to the frequency of the desired wave are input to a nonlinear circuit (for example, a frequency conversion circuit) provided in the wireless device, the nonlinear circuit The desired wave and the interference wave may interfere (intermodulate) to generate an intermodulation wave. Among such intermodulation waves, a third-order intermodulation distortion (IM3) can be cited as an intermodulation wave that is the main cause of deterioration of reception quality of a desired wave in a wireless device. . Since the third-order intermodulation distortion (IM3) occurs in the same band as the desired wave, it is difficult to remove by a filter or the like, which affects the reception of the desired wave in the wireless device, and the reception quality of the desired wave is reduced. It will cause deterioration. In order to reduce the influence of IM3, it is effective to reduce the level of IM3 by attenuating the signal level of the interference wave input to the nonlinear circuit in the wireless device. For example, the gain of the amplifier in the wireless device and the attenuation amount of the attenuator are adjusted using a technique for detecting or estimating the signal level of the interference wave or IM3, or the detection or estimation result of the signal level of the interference wave or IM3 And as a technique which reduces the influence of IM3 with respect to reception quality, the technique disclosed by the following patent documents 1-4 can be mentioned.

JP 2000-68870 A JP 2012-209627 A JP 2000-174650 A Japanese Patent Laid-Open No. 10-327091

  The level of IM3 generated in the nonlinear circuit includes the signal level of two signals (for example, a desired wave and an interference wave) input to the nonlinear circuit and a third-order input intercept point (one of the circuit characteristics of the nonlinear circuit). Third Order Input Intercept Point (IIP3). In practice, however, the level of IM3 generated in the nonlinear circuit also depends on the offset frequency, which is the difference between the frequencies of the two signals input to the nonlinear circuit. For example, even when two signals are input to the same nonlinear circuit at the same signal level, the level of IM3 to be output is different if the offset frequency is different. Therefore, it is assumed that when two signals having such a small offset frequency that are not assumed in the design stage of the wireless device are actually input to the nonlinear circuit, the wireless device cannot accept them. IM3 having a higher level may occur, and reception quality may be deteriorated. In particular, in a wireless communication system in which many channels are allocated in a narrow frequency band, the signal of an adjacent channel becomes an interference wave with respect to a desired wave, and the above IM3 is likely to occur due to the influence of the signal. . Further, since signals of channels adjacent to each other have a small offset frequency, which is a frequency difference, IM3 having a level higher than a value assumed in the design stage of the wireless device is generated. Therefore, it can be said that the reception quality of the IM3 is likely to deteriorate in the wireless communication system as described above.

  However, in the techniques disclosed in Patent Documents 1 to 4, the signal level of the interference wave input to the nonlinear circuit in the wireless device is not attenuated in consideration of the offset frequency as described above. It is hard to say that the degradation of the reception quality due to is effectively reduced.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a new and improved radio apparatus capable of reducing deterioration of reception quality. There is.

  In order to solve the above problems, according to an aspect of the present invention, a nonlinear circuit to which a signal from an antenna is input, a variable attenuator for attenuating the signal to be input to the nonlinear circuit, and the nonlinear circuit A measurement unit that measures an output third-order intermodulation distortion level and an offset frequency that is a difference between a frequency of a disturbing wave input to the nonlinear circuit and a frequency of a desired input wave input to the nonlinear circuit; , And the variable attenuator changes the attenuation amount according to the measurement result of the measurement unit.

  The wireless device passes a signal in a predetermined frequency band including one of the two third-order intermodulation distortions output from the nonlinear circuit provided between the nonlinear circuit and the measurement unit. A filter may be further provided.

  The measurement unit may perform measurement using Fourier transform on a signal output from the nonlinear circuit.

  The wireless device may further include a control unit that controls the attenuation amount of the variable attenuator according to the measurement result.

  The control unit may determine whether to control the attenuation amount of the variable attenuator according to the level of the third-order intermodulation distortion.

  The control unit may control the attenuation amount of the variable attenuator according to the offset frequency.

  As described above, according to the present invention, it is possible to reduce degradation of reception quality.

It is explanatory drawing (the 1) for demonstrating generation | occurrence | production of IM3. It is explanatory drawing (the 2) for demonstrating generation | occurrence | production of IM3. It is an example of the block diagram of the radio | wireless apparatus 1 which concerns on embodiment of this invention. It is explanatory drawing (the 1) for demonstrating operation | movement of the radio | wireless apparatus 1 which concerns on embodiment of this invention. It is explanatory drawing (the 2) for demonstrating operation | movement of the radio | wireless apparatus 1 which concerns on embodiment of this invention. It is a flowchart of the control method of the control part 216 which concerns on embodiment of this invention. It is explanatory drawing for demonstrating operation | movement of the measurement part 214 which concerns on embodiment of this invention.

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

  Furthermore, in the following description, unless otherwise specified, “connection” means that a plurality of elements are electrically connected and a signal (a high-frequency analog signal or a digital signal) can be conveyed. Means. Furthermore, “connection” in the following description includes not only a case where a plurality of elements are directly connected but also a case where they are indirectly connected via other elements.

<< Background to the Embodiment of the Present Invention >>
First, prior to the detailed description of the embodiment of the present invention, the background of the inventor's achievement of the embodiment of the present invention will be described with reference to FIG. 1 and FIG. 1 and 2 are explanatory diagrams for explaining generation of IM3 in the above-described nonlinear circuit. Specifically, FIG. 1 is an example of a diagram in which a part of the output signal from the nonlinear circuit is converted into a state (frequency domain) indicating the relationship of the signal level to the frequency, for example, an output from the nonlinear circuit. The display is the same as that obtained when the signal is measured with a spectrum analyzer. FIG. 2 shows the output basic signal and the output signal level (P _out ) of IM3 with respect to the input signal level (P _in ) of the input basic signal when two basic signals are input to the nonlinear circuit. It is the graph which showed the change.

  As explained above, in wireless communication systems used as social infrastructure for business communication within a company office, fire fighting and disaster prevention, it is common to allocate many channels within a narrow frequency band. Is. In addition, a wireless device used in such a wireless communication system is not used in an ideal environment, and therefore receives an unnecessary interference wave in addition to a desired wave for performing wireless communication. Inevitable.

  For example, when a desired wave and an interference wave having a frequency close to the frequency of the desired wave are input to a nonlinear circuit (for example, an amplifier circuit or a frequency conversion circuit) in the wireless device, the nonlinear circuit In this case, the desired wave and the interference wave may interfere (intermodulate) to generate an intermodulation wave. Among such intermodulation waves, a third-order intermodulation distortion (IM3) can be cited as an intermodulation wave that is the main cause of deterioration of reception quality of a desired wave in a wireless device. .

Here, the third-order intermodulation distortion (IM3) will be described with a specific example. When a basic signal having two adjacent frequencies f ₁ and f ₂ is input to a nonlinear circuit (for example, an amplifier circuit), IM3 may occur due to the nonlinearity of the nonlinear circuit. Specifically, in the above-described case, as shown in FIG. 1, the nonlinear circuit separates the two basic signals having the frequencies f ₁ and f ₂ from the non-linear circuit, the frequency 2f ₁ -f ₂ and the frequency 2f ₂ − Two signals with f ₁ are output. Two signals having such frequency 2f ₁ -f ₂ and frequency 2f ₂ -f ₁ are third-order intermodulation distortion (IM3). As can be seen from FIG. 1, IM3 is generated in the same band as the desired wave, so that it is difficult to remove with a filter or the like, and removal is not easy. Therefore, it becomes noise or the like in the desired wave, which affects the reception of the desired wave in the wireless device, and degrades the reception quality of the desired wave. Therefore, in order to avoid such degradation of reception quality due to IM3, the wireless device attenuates the signal level of the interference wave input to the nonlinear circuit in the wireless device, and the IM3 generated in the non-linear circuit. It is effective to reduce the level.

A basic signal having two adjacent frequencies f ₁ and f ₂ is input to the nonlinear circuit, and an output basic signal (frequency f ₁ , f ₂ ) with respect to the input signal level (P _in ) of the input basic signal. a signal) having, when showing the change of the output signal level _{(P out)} of the two IM3 with a frequency _2f 1 -f ₂ and the frequency _2f 2 -f _1, for example, a graph as shown in FIG. 2 Can be obtained. As can be seen from FIG. 2, _{in the} region where the input signal level (P _in ) is low, the output signal level of the basic signal is very high compared to the level of IM3. However, in the region where the change in the basic signal and the output signal level of IM3 is linear, every time the output signal level of the basic signal increases by 1 dB, the level of IM3 increases by 3 dB. It can be seen that in the region where P _in ) is high, the output signal level of the basic signal approaches the level of IM3, and the influence of IM3 on the basic signal is large.

  In addition, a straight line indicating a change in the output signal level of the basic signal in a region where the change in the output signal level of the basic signal and IM3 has linearity intersects a straight line indicating a change in the output signal level of the IM3 in the region. The input signal level at this point is referred to as a third order input intercept point (IIP3). The IIP3 indicates device characteristics (linearity) of the nonlinear circuit, and also varies depending on various parameters such as the frequency of the input signal, the power supply voltage applied to the nonlinear circuit, and the ambient temperature during operation.

The level (dBm) of IM3 described above is expressed by the following equation (1): input signal levels (P _in ) (dBm) of two signals input to the nonlinear circuit, IIP3 (dBm) It is said that it depends on.

  However, in practice, the level of IM3 generated in the nonlinear circuit also depends on the offset frequency that is not included in the above equation (1) and is the difference between the frequencies of the two signals input to the nonlinear circuit. ing. For example, even when two signals are input to the same non-linear circuit at the same signal level, the output IM3 level differs depending on whether the offset frequency is 1 MHz or 10 kHz. There is.

  Therefore, it is assumed that when two signals having such a small offset frequency that are not assumed in the design stage of the wireless device are actually input to the nonlinear circuit, the wireless device cannot accept them. IM3 having a higher level may occur, and reception quality may be deteriorated. For example, in a commercial wireless communication system using a 400 MHz band, a large number of channels having a bandwidth of about several kHz are allocated in a narrow frequency band. In such a radio communication system in which many channels are allocated, the signal of the adjacent channel becomes an interference wave with respect to the desired wave, and the above IM3 is likely to occur due to the influence of the signal. Furthermore, since signals in channels adjacent to each other have a small offset frequency, which is a frequency difference, IM3 at a level higher than a value assumed in the design stage of the radio apparatus often occurs. Therefore, it can be said that the reception quality of the IM3 is likely to deteriorate in the wireless communication system as described above.

  However, in the conventional radio apparatus, although the signal level of the interference wave input to the nonlinear circuit in the radio apparatus is attenuated according to the level of IM3 generated to avoid deterioration of the reception quality, as described above It is not attenuated in consideration of the offset frequency of the interference wave. Therefore, it cannot be said that the conventional radio apparatus can effectively reduce the degradation of reception quality due to IM3.

  Specifically, in Patent Document 1, Patent Document 2, and Patent Document 4, the gain or attenuator of the amplifier in the radio apparatus is obtained using the detection or estimation result of the interference wave or the signal level of IM3. Or a switch that guides a signal to a path that bypasses the amplifier is attenuated to attenuate a signal level of an interference wave input to a non-linear circuit in the wireless device, thereby reducing degradation of reception quality.

  In view of the above situation, the present inventor considers the offset frequency of the jamming wave and attenuates the signal level of the jamming wave input to the nonlinear circuit in the wireless device, thereby reducing the reception quality. An embodiment of the present invention that can be reduced has been created. Hereinafter, details of such embodiments of the present invention will be sequentially described.

  The embodiment of the present invention described below can be applied to a wireless device such as a base station or a portable terminal of a business transceiver used in a specific area (for example, in an office), for example. More specifically, the wireless device according to the present embodiment includes, for example, an interface (base station or terminal) for short-range wireless communication such as Bluetooth (registered trademark) or ZigBee (registered trademark), or a wireless LAN ( Communication interfaces (base stations or terminals) such as Local Area Network), Wi-Fi (registered trademark), mobile communication networks (LTE, 3G), or in-vehicle terminals such as car navigation devices, ETC (Electronic Toll Collection) systems, It can be a wireless device for communicating with the in-vehicle terminal. Therefore, in this embodiment, the frequency of the signal received by the wireless device is not particularly limited. For example, the wireless device can receive a signal in the 400 MHz band or the like.

<< Embodiment >>
<Detailed Configuration of Wireless Device 1>
First, a detailed configuration of the wireless device 1 according to the embodiment of the present invention will be described with reference to FIG. FIG. 3 is an example of a block diagram of the wireless device 1 according to the embodiment of the present invention. Note that the wireless device 1 according to the present embodiment can be a base station or a mobile terminal in a wireless communication system, as described above.

  As shown in FIG. 3, the wireless device 1 according to the present embodiment has two main components: a radio frequency (RF) unit 10 composed of high frequency analog circuit elements and a digital processing unit 20 that processes a digital signal. Can be divided into blocks. Specifically, the wireless device 1 according to the present embodiment includes an antenna 100 that receives a signal, an RF unit 10 that processes a signal input to the antenna 100, a digital process that further processes the signal processed by the RF unit 10, and the like. And a digital processing unit 20. Further, as shown in FIG. 3, the RF unit 10 includes a bandpass filter (BPF) 102, a low noise amplifier (LNA) 104, and a variable attenuator (VATT) (variable attenuation). Instrument) 106, a frequency conversion circuit (MIXer) (non-linear circuit) 108, and an oscillator 110. The digital processing unit 20 mainly includes a BPF 202, a BPF (filter) 212, a demodulation unit 204, a measurement unit 214, and a control unit 216. Below, the detail of each block contained in the radio | wireless apparatus 1 which concerns on this embodiment is demonstrated.

(Antenna 100)
The antenna 100 receives electromagnetic waves (signals) propagating in the space, and inputs the received signals to the LNA 104 via the BPF 102 described later.

(BPF102)
The BPF 102 includes elements such as a resistor, a capacitor, and an inductor, and is connected to the antenna 100 described above. The BPF 102 selectively selects a signal having a frequency in a predetermined frequency band (for example, 400 MHz band) including a frequency of a signal (desired wave) to be processed by the wireless device 1 from signals received by the antenna 100. And a signal having a frequency other than the predetermined frequency band (for example, a signal having a wavelength of 1/2 or 1/4 of the desired wave) is attenuated. The signal that has passed through the BPF 102 is input to the LNA 104 described later.

(LNA104)
The LNA 104 is made of a semiconductor element such as a transistor, for example, and is connected to the BPF 102 described above, and can amplify a signal that has passed through the BPF 102. The LNA 104 is preferably an amplifier having a characteristic that a weak signal is amplified without being buried in noise, and a signal having a high signal level is amplified without causing distortion. Specifically, since the LNA 104, which is a nonlinear circuit, amplifies a weak desired wave, the interference wave input together with the desired wave is amplified to generate the above-described IM3. Therefore, in the present embodiment, it is preferable to suppress the occurrence of IM3 in the LNA 104 by using the LNA 104 having a high linearity, that is, the above-described LIP having a high IIP3. Then, the signal amplified by the LNA 104 is input to the VATT 106 described later.

(VATT106)
The VATT 106 uses an IC or the like that can adjust the amount of attenuation with an external signal. It is provided between the BPF 102 and the MIX 108 described above, and a signal (particularly an interference wave) input to the MIX 108 that is a nonlinear circuit can be attenuated. The attenuation amount in the VATT 106 is changed by the control by the control unit 216 described later according to the measurement result of the measurement unit 214 described later. That is, the amount of attenuation at the VATT 106 is not fixed, but can be made variable so that it is not attenuated when there is no need for attenuation (that is, when the amount of attenuation at the VATT 106 is 0 dB). , Deterioration of noise figure (NF) can be suppressed. Therefore, even when it is not expected that a large gain can be obtained in the LNA 104, it is possible to appropriately process the desired wave in the wireless device 1 by using the VATT 106 that can change the attenuation. Then, the signal attenuated by the VATT 106 is input to the MIX 108 described later.

(MIX108)
The MIX 108 is composed of, for example, semiconductor elements such as a plurality of transistors, and is connected to the VATT 106 described above. A signal input from the VATT 106 is a signal having a low frequency of about several MHz such as an intermediate frequency (IF). The frequency can be converted to More specifically, the MIX 108 multiplies the input signal by a local oscillation signal from an oscillator 110 described later, whereby a frequency corresponding to the sum and difference between the frequency of the input signal and the frequency of the local oscillation signal. A signal with can be obtained. The signal frequency-converted by the MIX 108 is input to the demodulation unit 204 via the BPF 202 described later, and further input to the measurement unit 214 via the BPF 212. The MIX 108 is a non-linear circuit and generates IM3 as described above.

(Oscillator 110)
The oscillator 110 is, for example, a PLL (Phase Locked Loop) having a crystal oscillator (not shown), a phase comparator (not shown), a frequency divider (not shown), a charge pump (not shown), and a loop filter (not shown). ) Synthesizer and connected to the MIX 108 described above. The oscillator 110 generates a local oscillation signal having a desired frequency with high accuracy and stability, and outputs the generated local oscillation signal to the MIX 108 described above. That is, the oscillator 110 can oscillate a signal serving as a reference for frequency conversion in the MIX 108.

(BPF202)
The BPF 202 includes elements such as a resistor, a capacitor, and an inductor, and is connected to the MIX 108 described above. The BPF 202 selectively passes a signal having a frequency in a predetermined frequency band including a frequency of a signal (a signal caused by a desired wave) to be processed by the demodulator 204 described later, from the signals from the MIX 108 described above. And a signal having a frequency other than the predetermined frequency band is attenuated. Then, the signal that has passed through the BPF 202 is input to the demodulation unit 204. The details of the signal input to the BPF 202 and the passband of the BPF 202 will be described later.

  Further, an amplifier (not shown) such as an IF amplifier may be provided at the subsequent stage of the BPF 202. That is, a signal that has passed through the BPF 202 may be amplified by the amplifier and then input to the demodulation unit 204. .

(Demodulator 204)
The demodulation unit 204 is configured by a DSP (Digital Signal Processor), an FPGA (Field-Programmable Gate Array), and the like, and is connected to the BPF 202. The demodulator 204 processes the signal that has passed through the BPF 202 using various methods (specifically, detects changes in various parameters (amplitude, phase shift, etc.) of the signal) and demodulates information included in the signal. be able to.

(BPF212)
The BPF 212 includes elements such as a resistor, a capacitor, and an inductor, and is provided between the MIX 108 described above and a measurement unit 214 described later. The BPF 212 selectively passes a signal having a frequency in a predetermined frequency band including a frequency of a signal to be measured by the measurement unit 214 described later, from among the signals from the MIX 108 described above, and other than the predetermined frequency band. Attenuate a signal with a frequency of. Specifically, the BPF 212 selectively passes a signal having a frequency in a predetermined frequency band including, for example, one of the two IM3s output from the MIX 108. The signal that has passed through the BPF 212 is input to the measurement unit 214. Details of the signal input to the BPF 212 and the passband of the BPF 212 will be described later.

(Measurement unit 214)
The measurement unit 214 is configured by a DSP, FPGA, or the like, and is connected to the BPF 212. The measurement unit 214 processes the signal that has passed through the BPF 212 and measures the level of IM3 and the offset frequency that is the difference between the frequency of the desired wave and the interference wave. The attenuation amount in the VATT 106 described above changes according to the control by the control unit 216 described later in accordance with the measurement result of the measurement unit 214. The measurement unit 214 may measure the level of IM3 and the offset frequency by performing a fast Fourier transform on the signal output from the MIX 108. Details of the measurement by the measurement unit 214 will be described later.

(Control unit 216)
The control unit 216 is configured by a DSP, FPGA, or the like, and is provided between the measurement unit 214 and the VATT 106. As described above, the control unit 216 changes the attenuation in the VATT 106 according to the measurement result of the measurement unit 214 described above. Details of control of the VATT 106 by the control unit 216 will be described later.

  Note that the wireless device 1 according to the present embodiment is not limited to the configuration shown in FIG. In the wireless device 1 according to the present embodiment, for example, an analog / digital converter (A / D converter) (not shown) may be provided between the MIX 108 and the measurement unit 214. Furthermore, in the wireless device 1 according to the present embodiment, for example, a memory device (not shown) such as a ROM (Read Only Memory) or a RAM (Random Access Memory) may be provided. In this case, various data and programs for the control unit 216 to execute control are stored in the memory device.

<Operation>
The detailed configuration of the wireless device 1 according to the present embodiment has been described above. Next, the operation of the wireless device 1 according to the present embodiment will be described with reference to FIG. 3, FIG. 4, and FIG. 4 and 5 are explanatory diagrams for explaining the operation of the wireless device 1 according to the present embodiment. Specifically, FIG. 4 is an example of a diagram in which an input signal input to the wireless device 1 is converted into a state (frequency domain) indicating a relationship of signal level with respect to frequency, and FIG. 5 is an input to the BPF 202. It is an example of the figure which converted and displayed the input signal made into the state (frequency domain) which shows the relationship of the signal level with respect to a frequency. That is, FIGS. 4 and 5 are the same as the display obtained when the input signal is measured with a spectrum analyzer.

First, an electromagnetic wave (desired wave, desired input wave) propagating in space is received by the antenna 100 of the wireless device 1 and input to the BPF 102. In the following description, a portion of the signal the antenna 100 receives, as shown in FIG. 4, a desired wave having a frequency f _r, the frequency f _i1 and the frequency f _i2 close to the frequency with the the desired wave Assume that there are two interference waves. In such a case, the two interference waves having the frequency f _i1 and the frequency f _i2 pass through the nonlinear element as described above, thereby generating the above-described IM3. As described above, the two interfering waves have a frequency f _i1 and a frequency f _i2 that are located in the vicinity of the desired wave, and thus are difficult to remove with a filter such as the BPF 202. As a result, IM3 is generated in a nonlinear circuit (for example, MIX 108) in the wireless device 1, and the generated IM3 becomes noise or the like in the desired wave, which affects reception of the desired wave in the wireless device 1, The reception quality of the desired wave is deteriorated.

In the example shown in FIG. 4, the frequency difference between the desired wave having the frequency f _r and the disturbing wave having the frequency f _i1 is the offset frequency Δf ₁ , and the desired wave having the frequency f _r and the frequency f _i2 are difference frequency of an interference wave with is offset frequency Delta] f _2. Further, in FIG. 4, for reference, is used in MIX108, a local oscillation signal having a frequency _{f L,} it is is also shown passing frequency band of the BPF 202.

Of the signals received by the antenna 100, signals having a frequency within a predetermined frequency band (e.g., 400MHz band) including frequency _{f r} of the desired wave that would be processed by the demodulating unit 204, selects the BPF102 Therefore, signals other than the predetermined frequency band are removed by the BPF 102. As described above, two interference waves having the frequencies f _i1 and f _i2 close to the frequency f _{r of the} desired wave are input to the LNA 104 without being removed by the BPF 102.

  A signal (desired wave and interference wave) that has passed through the BPF 102 is input to the LNA 104. The signals (desired wave and interference wave) input to the LNA 104 are amplified by a predetermined amplification degree by the LNA 104 and output to the VATT 106.

  Next, the signals (desired wave and interference wave) amplified by the LNA 104 are attenuated by the VATT 106 and input to the MIX 108. Due to the attenuation by the VATT 106, the interference wave to be input to the MIX 108 is attenuated, and IM3 that is caused by the MIX 108 that is a non-linear circuit and causes degradation of reception quality can be reduced. Note that the attenuation amount in the VATT 106 is changed by the control by the control unit 216 in accordance with the measurement result of the measurement unit 214. Details of the control by the control unit 216 will be described later.

Further, the signal (desired wave and interference wave) from the VATT 106 is frequency-converted into a signal having a low frequency by the MIX 108. Specifically, the desired wave from VATT106, using a local oscillation signal having a frequency _{f L,} the MIX108, is converted into a signal having a frequency _f L -f _r. Also, the two interference waves from the VATT 106 are converted into two signals having the frequency f _L -f _i1 and the frequency f _L -f _i2 by the MIX 108, respectively. Furthermore, the MIX 108, which is a non-linear circuit, outputs two IM3s. Each of these two IM3s has a frequency f _L − (2f _i2 −f _i1 ) and a frequency f _L − (2f _i1 −f _i2 ), and one of these two IM3s has a desired wave frequency converted. This coincides with the frequency f _L −f _{r of} the signal caused by the desired wave obtained.

Specifically, the signals output from the MIX 108 are a plurality of signals as shown in FIG. As can be seen from FIG. 5, one of the two IM3s having the frequency f _L- (2f _i2 -f _i1 ) and the frequency f _L- (2f _i1 -f _i2 ) is obtained by frequency-converting the desired wave. Since the frequency f _L −f _r of the signal caused by the desired wave coincides with the frequency f _L − (2f _i2 −f in FIG. 5, the signal caused by the desired wave having the frequency f _L −f _{r i1)} IM3 and are shown superimposed with) signal resulting from the desired wave, it is difficult to avoid the influence from one IM3 of the two IM3. In other words, it is difficult to separate the signal caused by the desired wave from one of the two IM3s. As a result, in the wireless device 1, the IM 3 adversely affects the reception of the desired wave in the wireless device 1, and the reception quality of the desired wave is deteriorated. Therefore, in this embodiment, in order to avoid such deterioration, the interference wave to be input to the MIX 108 is preferably attenuated by the VATT 106, and the level of IM3 generated in the MIX 108 is reduced.

The signal frequency-converted by the MIX 108 is input to the BPF 202. In the BPF 202, a signal having a frequency within a predetermined frequency band including the frequency of a signal (specifically, a signal caused by a desired wave) to be processed by the demodulation unit 204 is selectively passed. Therefore, for example, as shown in FIG. 5, a signal resulting from a desired wave having a frequency f _L −f _r and an IM 3 having a frequency f _L − (2f _i2 −f _i1 ) pass through the BPF 202. , Input to the demodulator 204. Then, the signal included in the signal can be demodulated by processing the signal input to the demodulator 204 (specifically, the signal resulting from the desired wave) by the demodulator 204.

  Further, the signal frequency-converted by the MIX 108 is input to the measurement unit 214 via the BPF 212. Details of the signal input to the BPF 212 and the passband of the BPF 212 will be described later.

  The measurement unit 214 measures the level of IM3 and the offset frequency using the signal that has passed through the BPF 212. The measurement result by the measurement unit 214 is output to the control unit 216, and the control unit 216 changes the attenuation amount in the VATT 106 according to the measurement result. Details of control of the VATT 106 by the control unit 216 and details of measurement by the measurement unit 214 will be described later.

<Control Method of Control Unit 216>
The operation of the wireless device 1 according to this embodiment has been described above. Next, a control method of the control unit 216 according to the present embodiment will be described with reference to FIG. FIG. 6 is a flowchart of a control method of the control unit 216 according to the present embodiment.

  As shown in FIG. 6, the control method of the control unit 216 according to this embodiment includes a plurality of steps from step S101 to step S111. Below, the detail of each step of the control method which concerns on this embodiment is demonstrated. The control method described below is an example of the control method according to the embodiment of the present invention, and the control method according to the present embodiment is not limited to the following control method. Details of the measurement by the measurement unit 214 will be described later.

(Step S101)
First, the control unit 216 acquires the measurement result of the IM3 level from the measurement unit 214, and determines whether the acquired IM3 level is equal to or higher than a predetermined threshold value. When the level of IM3 is equal to or higher than a predetermined threshold value, the control unit 216 proceeds to step S103 described later, and when the level of IM3 is not equal to or higher than a predetermined threshold value, step S111 described later is performed. Proceed to That is, it can be said that the step S101 is a step of determining whether or not to control the attenuation amount of the VATT 106 according to the level of IM3.

  The above-described threshold is determined in advance based on actual measurement values obtained when measurement is performed under various conditions using the wireless device 1 according to the present embodiment and the specifications of the wireless communication system. Specifically, even if the threshold value is affected by IM3 in the wireless device 1, the threshold value satisfies a predetermined carrier-to-noise ratio (CNR) defined as a specification. It is predetermined so that it can be done.

(Step S103)
The control unit 216 acquires the measurement result of the offset frequency from the measurement unit 214.

(Step S105)
The control unit 216 selects a table for setting the attenuation amount of the VATT 106 according to the measurement result of the offset frequency acquired in step S103. The table is stored in a memory device (not shown) provided in the wireless device 1 described above, and the control unit 216 selects the table according to the offset frequency.

  As described above, the level of IM3 generated in the non-linear circuit (here, MIX 108) also depends on the offset frequency and is different from the theoretical value obtained based on the above formula (1). Therefore, in the present embodiment, measurement is performed by inputting interference waves having various offset frequencies to the wireless device 1 according to the present embodiment, and the difference between the measured value and the theoretical value is recorded for each offset frequency. A table is created in advance and stored in the memory device (not shown). Then, the control unit 216 selects a table corresponding to the acquired offset frequency from the table stored in the memory device.

(Step S107)
The control unit 216 sets the attenuation amount of the VATT 106 according to the table selected in step S105 described above. Specifically, the control unit 216 considers the difference from the theoretical value of the IM3 level due to the offset frequency by adding the above-described difference determined in the selected table to the IM3 level acquired from the measurement unit 214. The attenuation amount of the VATT 106 can be set. In this way, the control unit 216 according to the present embodiment can control the attenuation amount of the VATT 106 according to the offset frequency.

(Step S109)
The control unit 216 controls the VATT 106 according to the attenuation set in step S107 described above. Then, the control unit 216 returns to step S101 described above. That is, in the control method according to the present embodiment, steps S101 to S109 are repeatedly performed until the IM3 level acquired from the measurement unit 214 is not greater than or equal to a predetermined threshold value set in advance.

(Step S111)
The control unit 216 controls the VATT 106 according to the currently set attenuation amount. And the control part 216 complete | finishes the process by the said control method.

  As described above, according to the control method according to the present embodiment, the attenuation amount of the VATT 106 can be controlled in consideration of not only the IM3 level but also the offset frequency. Can be effectively reduced.

<Measurement of measurement unit 214>
The control method of the control unit 216 according to the present embodiment has been described above. Next, measurement by the measurement unit 214 according to the present embodiment will be described with reference to FIG. FIG. 7 is an explanatory diagram for explaining the operation of the measurement unit 214 according to the present embodiment. Specifically, FIG. 7 is an example of a diagram in which the input signal input to the BPF 212 is converted into a state (frequency domain) indicating the relationship of the signal level to the frequency, and the input signal is measured with a spectrum analyzer. It is the same as the display obtained in the case. Note that the measurement method described below is an example of the measurement method according to the embodiment of the present invention, and the measurement method according to the present embodiment is not limited to the following measurement method.

As shown in FIG. 7, the signal output from the MIX108, as shown in FIG. 7, the signal having a frequency _f L -f _r due to the desired wave, and the frequency _{f L} due to two jammer - There are two signals with f _i1 and frequency f _L −f _i2 . As described above, since the MIX 108 is a non-linear circuit, the MIX 108 has two IM3s each having a frequency f _L − (2f _i2 −f _i1 ) and a frequency f _L − (2f _i2 −f _i1 ). Is output. Furthermore, as the signal output from the MIX108, desired wave having a frequency _{f r} which is input to the MIX108, 2 two interfering waves having a frequency _{f i1} and the frequency _{f i2,} and, also the local oscillation signal having a frequency _{f L} Can be mentioned.

Therefore, when IM3 is to be measured, two IM3s having a frequency f _L − (2f _i2 −f _i1 ) and a frequency f _L − (2f _i1 −f _i2 ) output from the MIX 108 are measured. As can be seen from FIG. 7, one IM3 of the two IM3s having the frequency f _L − (2f _i2 −f _i1 ) and the frequency f _L − (2f _i1 −f _i2 ) is in (Figure 7 because it matches the frequency f _L -f _r of signal due to the desired signal obtained by the desired wave is frequency conversion, the signal resulting from the desired wave having the frequency f _L -f _r And IM3 having a frequency f _L − (2f _i2 −f _i1 ) are superimposed on each other), and the other IM3 (in FIG. 7, a signal having a frequency f _L − (2f _i1 −f _i2 )) ) Level And thus to be constant.

Therefore, in the present embodiment, the pass frequency band of the BPF 212 is adjusted by control by digital processing, and one IM3 of the two IM3s (in FIG. 7, the frequency f _L − (2f _i1 −f _i2 )). A signal with The BPF 212 has a wider pass frequency bandwidth than the BPF 202 that selectively passes a signal input to the demodulation unit 204. That is, by setting the pass frequency band of the BPF 212 to a range as shown in FIG. 7 and selectively passing one IM3 of the two IM3s, a desired wave or an interference wave, these signals are measured. Input to the unit 214. Therefore, the measurement unit 214 can measure the level of one IM3 and the offset frequencies Δf ₁ and Δf ₂ that are the differences between the frequencies of the desired wave and the interference wave.

In the present embodiment, other methods may be used instead of adjusting the pass frequency band of the BPF 212 as described above. For example, in this embodiment, an A / D converter that converts a signal output from the MIX 108 into a digital signal from an analog signal having a frequency in a frequency band corresponding to several channels in the vicinity of the desired wave is used. , Convert to digital signal. The converted digital signal may be subjected to fast Fourier transform (FFT) to measure the level of IM3 and the offset frequencies Δf ₁ and Δf ₂ that are the difference between the frequency of the desired wave and the interference wave. .

<Summary>
As described above, according to the embodiment of the present invention, it is possible to control the attenuation amount of the VATT 106 in consideration of not only the IM3 level but also the offset frequency of the interference wave. Degradation can be effectively reduced. Specifically, when an interference wave having an offset frequency that generates IM3 of a level lower than the IM3 level assumed in the design stage of the wireless device 1 is input to the wireless device 1, the generated IM3 level is wireless. Since there is a margin with respect to the level allowed by the device 1, the amount of attenuation in the VATT 106 can be reduced. Therefore, since the attenuation amount in the VATT 106 can be reduced, deterioration of NF or the like in the wireless device 1 can be suppressed. On the other hand, when an interference wave having an offset frequency that generates an IM3 level higher than the IM3 level assumed in the design stage of the wireless device 1 is input to the wireless device 1, the offset frequency is taken into consideration in the VATT 106. Since control can be performed so as to increase the amount of attenuation, it is possible to effectively reduce deterioration of reception quality in the wireless device 1. In other words, according to the present embodiment, even if an interference wave having a signal level that is not assumed at the design stage of the wireless device 1 is input to the wireless device 1, it is not assumed at the design stage. Even if an interference wave having such an offset frequency is input to the wireless device 1, it can be expected that the reception quality in the wireless device 1 is maintained well.

  In the above description, it has been described that the attenuation amount of the interference wave input to the MIX 108 in the wireless device 1 is controlled. However, the embodiment of the present invention is not limited to this, and the wireless device 1 is not limited thereto. You may control the attenuation amount of the jamming wave input into the other nonlinear circuit (for example, amplifier). Furthermore, in the above description, it has been described that the attenuation amount of the interference wave input to the MIX 108 is controlled by the VATT 106 in the wireless device 1, but the embodiment of the present invention is not limited to this, and the VATT 106 is not limited thereto. Instead of this, a variable amplifier capable of changing the gain may be used.

<< Supplementary >>
The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  Further, the operation (control method) according to the embodiment of the present invention described above may not necessarily be operated or processed in the order described. For example, the steps of the above operation may be processed by changing the order as appropriate. Each step may be processed in parallel or individually instead of being processed in time series. Furthermore, the operation method or processing method of each step does not necessarily have to be operated or processed in accordance with the described method. For example, it may be operated or processed by another function unit in another method.

DESCRIPTION OF SYMBOLS 1 Radio | wireless apparatus 10 RF part 20 Digital processing part 100 Antenna 102, 202, 212 BPF
104 LNA
106 VATT
108 MIX
110 Oscillator 204 Demodulator 214 Measuring Unit 216 Control Unit

Claims (6)

A nonlinear circuit to which a signal from an antenna is input;
A variable attenuator for attenuating the signal input to the nonlinear circuit;
Measures the level of third-order intermodulation distortion output from the nonlinear circuit and an offset frequency that is the difference between the frequency of the desired input wave input to the nonlinear circuit and the frequency of the disturbing wave input to the nonlinear circuit. A measuring unit to perform,
With
The variable attenuator changes an attenuation amount according to a measurement result of the measurement unit.
Wireless device. A filter that is provided between the nonlinear circuit and the measurement unit and that passes a signal in a predetermined frequency band including one of the two third-order intermodulation distortions output from the nonlinear circuit;
The wireless device according to claim 1.   The wireless device according to claim 1, wherein the measurement unit performs measurement using Fourier transform on a signal output from the nonlinear circuit.   The radio apparatus according to claim 1, further comprising a control unit that controls the attenuation amount of the variable attenuator according to the measurement result.   The radio apparatus according to claim 4, wherein the control unit determines whether to control the attenuation amount of the variable attenuator according to a level of the third-order intermodulation distortion.   The radio apparatus according to claim 5, wherein the control unit controls the attenuation amount of the variable attenuator according to the offset frequency.

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