JP2008258840A - Line loss estimation device and wireless device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a line loss estimation device for obtaining loss in a cable for use in antenna connection without using measuring instruments of high precision, and to provide a wireless device. <P>SOLUTION: A measurement signal is supplied to a coaxial cable to which an antenna is connected, and amplitudes (detection values K1 to Kn) of a standing wave occurring on the coaxial cable are detected while gradually increasing a frequency of the measurement signal to frequencies f1 to fn, and these detection values are made to correspond to set values A1 to An for specifying the frequencies f1 to fn and stored (S110 to S150). A set value Aj made to correspond to the minimum detection value Kj out of the stored detection values K1 to Kn, and an index value j (corresponding to an amplification factor of a power amplifier) is specified from the se value Aj (corresponding to a cable length or cable loss) by using an amplification factor set table, and the amplification factor of the power amplifier for amplifying a transmission signal is set on the basis of the specific index value (S160 to S180). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a line loss estimation device built in a wireless device to which an antenna is connected via a cable and estimating a loss in the cable, and a wireless device incorporating the line loss estimation device.

  Conventionally, automobiles are equipped with wireless devices for realizing various services such as ETC. Since this type of wireless device is installed in the vehicle body so as not to be exposed to wind and rain, it is connected to an antenna installed at a position facing the outside of the vehicle via a cable (feed line).

  By the way, since the installation positions of the radio device and the antenna are variously different for each vehicle type, the cable line lengths are variously different (for example, about several tens of cm to 2 m). .

  Also, because the cable has a transmission loss, if the power sent from the radio (aerial power) is constant, the power radiated from the antenna (radiated power) differs depending on the cable line length. End up.

  However, since the antenna power and radiated power are normally defined by the standard (ARIB STD-T75 for ETC on-board equipment), each vehicle type (that is, the cable line to be used) conforms to the standard. It was necessary to adjust the radiated power (and antenna power) individually for each length.

On the other hand, by applying a DC voltage to the cable connected to the antenna, the voltage drop value at that cable is measured, and based on the measurement results, variations in characteristics occur depending on the line length, connection status, etc. An apparatus for correcting (impedance matching shift) has been proposed (see, for example, Patent Documents 1 and 2).
JP 2004-235707 A JP 2005-229203 A

  However, in the conventional device, when the line length of the cable is short, the detected voltage drop value is extremely small, so it is difficult to measure it with high accuracy both technically and on the equipment scale. There was a problem that it was difficult to apply to general consumer wireless devices.

  In order to solve the above problems, the present invention provides a line loss estimation apparatus and a radio device that can determine a loss in a cable used for connection to an antenna without using a high-precision measuring device. With the goal.

  In the line loss estimation apparatus of the present invention made to achieve the above object, the signal generation means capable of controlling the frequency generates a measurement signal to be applied to the connection end to which the cable is connected, and the amplitude detection means is connected. The amplitude of the standing wave that appears by combining the measurement signal from the end toward the antenna and the reflected signal reflected at the tip of the antenna and toward the connection end is output to the output end from which the signal generating means outputs the measurement signal. To detect.

  The frequency detection means gradually increases the frequency of the measurement signal generated by the signal generation means from a preset initial frequency, acquires the detection result by the amplitude detection means, and minimizes the detection result. The frequency of the measurement signal is detected, and the loss estimation unit estimates the loss in the cable based on the line length of the cable specified from the frequency detected by the frequency detection unit.

In addition, since the loss per unit length in a cable is known, if the line length of a cable is specified, it is easy to estimate the loss of the cable.
That is, in the line loss estimation apparatus of the present invention, the loss in the cable is not obtained by measuring the voltage drop value in the cable, but the loss in the cable is estimated from the line length of the cable. . Moreover, when measuring the line length of the cable, it is only necessary to detect the frequency of the measurement signal when the node of the standing wave coincides with the measurement point (the output end of the signal generation unit). Therefore, it is sufficient that the detection result (amplitude value) is compared in magnitude and the minimum value can be extracted, and it is not necessary to obtain the amplitude value with high accuracy.

Therefore, according to the line loss estimation apparatus of the present invention, the loss in the cable connecting the antenna and the wireless device can be obtained without using a highly accurate measuring device.
When the tip of the antenna is in an open state, the voltage waveform of the standing wave is a distance from the tip (open end) of the antenna, where λ is the wavelength of the measurement signal, as shown in FIG. It becomes a node (amplitude is minimum) at a position separated by (2m + 1) λ / 4 (where m = 0, 1, 2,...).

Therefore, it is desirable that the initial frequency is set to a frequency at which the in-line wavelength of the cable is greater than 4L, where L is the maximum length of the cable that may be connected to the connection end.
In this case, if the wavelength of the frequency at which the detection result by the amplitude means is the minimum first is λp, λp / 4 is the line length of the cable.

  When the tip of the antenna is short-circuited, the voltage waveform of the standing wave is a distance from the tip (short-circuited end) of the antenna, where λ is the wavelength of the measurement signal, as shown in FIG. A node (amplitude is minimum) is formed at a position separated by mλ / 2 (where m = 0, 1, 2,...).

Therefore, it is desirable that the initial frequency is set to a frequency at which the in-line wavelength of the cable is greater than 2L, where L is the maximum length of the cable that may be connected to the connection end.
In this case, if the wavelength of the frequency at which the detection result by the amplitude means is the minimum first is λp, λp / 2 is the line length of the cable.

  Further, the signal generating means may be specifically configured using a voltage controlled oscillator, or may generate a measurement signal by dividing or multiplying a system clock used in the radio device. It may be configured.

  In the former case, since the frequency of the measurement signal can be set finely, it is possible to measure the cable path length with high accuracy. In the latter case, a new signal is used to measure the cable path length. Since it is not necessary to provide an additional oscillator, the apparatus configuration can be simplified and the apparatus can be configured at low cost.

  Next, in the radio device of the second invention, the loss compensation means estimates the loss in the cable by operating the line loss estimation device, and amplifies the transmission signal supplied to the antenna when performing radio transmission Is set so that the estimated loss is compensated.

  According to the wireless device of the present invention configured as described above, the loss in the cable can be obtained without using a high-precision measuring device, and the amplification of the amplifier circuit is performed so that the obtained loss is compensated. Since the rate is set, the radiated power from the antenna can always be kept constant regardless of the length of the cable used for connection with the antenna.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a wireless device 1 used by being mounted on a vehicle.
<Overall configuration>
As shown in FIG. 1, the wireless device 1 transmits via the antenna 3 and the connector 10 to which the coaxial cable 5 for supplying power to the antenna 3 installed facing the outside of the vehicle is connected. The transmission unit 12 that generates a transmission signal, the measurement unit 14 that is used when estimating the loss in the coaxial cable 5 connected to the connector 10, and the transmission unit 12 and the measurement unit 14 according to a switching signal (not shown). One of these is provided with a changeover switch 16 that connects to the connector 10, and a transmission unit 12, a measurement unit 14, and a control unit 18 that controls the changeover switch 16.

In the present embodiment, the antenna 3 is installed such that its tip is an open end.
<Configuration of measurement unit>
Among them, the measurement unit 14 is configured to be able to control the oscillation frequency, and a voltage-controlled oscillator (VCO) 43 that generates a measurement signal by oscillating at a frequency corresponding to a signal level of a modulation signal described later, and a control unit Based on the set value Ai (i = 1, 2,..., N) supplied from 18, D / generates a modulation signal having a signal level such that the VCO 43 oscillates at a frequency associated with the set value Ai. The A converter 41 and the VCO 43 are connected to an output terminal that outputs a measurement signal, and a standing wave generated by a signal appearing at the output terminal, that is, a measurement signal and a reflected signal reflected from the tip of the antenna 3. Is detected through a capacitor 45, and an A / D converter 49 that converts the output of the detector 47, that is, the amplitude of the standing wave into a digital value and imports it into the control unit 18, is provided. .

FIG. 2A is a table showing the correspondence between the set value Ai and the oscillation frequency fi of the VCO 43, and the oscillation frequencies f1 to fn have the relationship shown in the equation (1).
f1 <f2 <... <fn (1)
However, f1 is set to a frequency where the maximum length of the coaxial cable 5 that can be connected to the connector 10 is Lmax, and the in-line wavelength in the coaxial cable 5 is larger than 4Lmax, and fn is connected to the connector 10 Lmin is the minimum length of the coaxial cable 5 that is likely to occur, and the line wavelength in the coaxial cable 5 is set to a frequency that is smaller than 4 Lmin. Further, the frequencies f1 to fn are set so that the frequencies change at regular intervals on the log scale.

  In the measurement unit 14 configured as described above, the D / A converter 41 to which the setting value Ai is supplied from the control unit 18 generates a modulation signal having a signal level corresponding to the setting value Ai, and the modulation signal The VCO 43 receiving the signal oscillates at the frequency fi. As a result, the VCO 43 outputs a measurement signal having the frequency fi.

  This measurement signal propagates through the coaxial cable 5 from the connector 10 toward the antenna 3 when the changeover switch 16 is set to connect the measurement unit 16 side to the connector 10, and at the tip of the antenna 3. The reflected signal propagates through the coaxial cable 5 from the antenna 3 toward the connector 10. As a result, a standing wave obtained by synthesizing the measurement signal (traveling wave) and the reflected signal (reflected wave) appears on the coaxial cable 5.

  In the present embodiment, since the tip of the antenna 3 is an open end, the voltage waveform of the standing wave has a phase of 0 at the tip of the antenna 3 as shown in FIG. , Mπ (m = 0, 1, 2,...) Is an antinode, and (2m + 1) π / 2 is a node.

  That is, as shown in FIG. 3B, when the in-line wavelength of the measurement signal is λ and the line length of the coaxial cable 5 is equal to (2m + 1) λ / 4, detection for detecting a standing wave is performed. The output of the device 47 is minimized. The output of the detector 47 that detects this standing wave is, as shown in FIG. 3B, the phase of the standing wave at the input end of the detector 47 (that is, the output end of the VCO 43). The length varies depending on the line length of the cable 5.

  However, here, the path length from the input end of the detector 47 (output end of the VCO 43) to the connector 10 is negligibly small compared to the line length of the coaxial cable 5, and the positions of both are the same. It can be considered.

  That is, the line length is detected by sweeping the frequency fi of the measurement signal and finding the frequency fi at which the first node of the standing wave is located at the input end of the detector 47 when viewed from the tip of the antenna 3. Such a frequency fi can be specified from the set value Ai when the output of the detector 47 is minimized.

<Configuration of transmitter>
Returning to FIG. 1, the transmission unit 12 is configured to generate a transmission signal by modulating a carrier wave by transmission data (not shown) supplied from the outside, and to control the amplification factor. A power amplifier 23 that amplifies the transmission signal generated by the signal 21 with an amplification factor Gi corresponding to a signal level of an amplification factor setting signal, which will be described later, and a setting value Bi for setting the amplification factor of the power amplifier 23 are stored. The memory 25 and the setting value Bj (j = 1, 2,..., N) supplied from the memory 25 are converted into an amplification factor setting signal having a signal level corresponding to the setting value Bi and supplied to the power amplifier 23. The D / A converter 27 is provided.

  Here, FIG. 2A shows a frequency setting table in which a portion surrounded by a solid line indicates a correspondence relationship between a setting value Bj stored in the memory 25 and an index value (address) j used when reading the Bi. In addition, a portion surrounded by a dotted line indicates the amplification factor Gj of the power amplifier 23 corresponding to the set value Bj. The amplification factors G1 to Gn have the relationship shown in the equation (2).

G1>G2>...> Gn (2)
<Control unit>
Next, the control part 18 consists of a known microcomputer mainly comprised CPU, ROM, and RAM. And CPU calculates | requires the line length of the coaxial cable 5 connected to the connector 10 using the measurement part 14, and sets the gain of the power amplifier 23 according to the cable loss estimated from the line length to memory 25, D. The adjustment process set via the / A converter 27 is executed.

  In the ROM, together with the adjustment processing program executed by the CPU, an index value used when the setting value Ai supplied to the D / A converter 41 and the setting value Bi supplied to the D / A converter 27 are designated. An amplification factor setting table that associates i is stored.

  Here, in FIG. 2C, the part surrounded by the solid line shows the amplification factor setting table, and the part surrounded by the dotted line shows the various parameters having a correspondence relationship with the set value Ai and the index value i. is there.

  That is, since the set value Ai is associated with the oscillation frequency fi of the VCO 43 (see FIG. 2B), the wavelength of the oscillation signal (that is, the measurement signal) of the VCO 43 (however, the in-line wavelength of the coaxial cable 5). ) Λi also has the correspondence shown in equation (3). However, c is the speed of light, and β is the wavelength shortening rate in the coaxial cable 5.

λi = c / fi × β (3)
Further, assuming that the node of the standing wave generated when the frequency of the measurement signal is fi is at the position of the connector 10 and there is no other node on the coaxial cable 5, the line of the coaxial cable 5 The length Li has a correspondence relationship shown in the equation (4) with the wavelength λi of the measurement signal.

Li = λi / 4 (4)
Furthermore, if the loss per unit length of the coaxial cable 5 is ΔLoss, the line length Li and the cable loss Lossi have the correspondence shown in (5).

Lossi = Li × ΔLoss (5)
That is, the gain setting table shown in FIG. 2B, that is, the setting of the D / A converter 27 that is the stored value of the memory 25 is obtained so that the gain Gi that compensates for the cable loss Lossi is obtained. Values B1 to Bn are set.

  2 and (3) to (4), the frequency fi is specified by specifying the in-line wavelength λi and the line length Li of the coaxial cable 5 connected to the connector 10. Further, this corresponds to estimating the cable loss Lossi of the coaxial cable 5.

<Adjustment process>
Next, adjustment processing executed by the CPU of the control unit 18 will be described with reference to the flowchart shown in FIG. This process is started every time the wireless device 1 is powered on.

When this process is started, first, in S100, a switching signal is output to the changeover switch 16, the connection of the changeover switch 16 is switched to the measurement unit 14 side, and the process proceeds to S110.
In S110, the parameter i used for specifying the set value Ai is initially set to 1. In the subsequent S120, the set value Ai is supplied to the D / A converter 41, thereby setting the oscillation frequency of the VCO 43 to fi, Proceed to S130.

  As a result, a measurement signal having the frequency fi is directed from the connector 10 to the antenna 3, and a reflected signal reflected from the tip of the antenna 3 is propagated toward the connector 10, whereby a standing wave is generated. When the wave is input to the detector 47 via the capacitor 45, a detection signal corresponding to the amplitude of the standing wave is supplied to the A / D converter 49.

  In S130, the signal level (detection value) Ki of the detection signal is acquired via the A / D converter 49, and this is stored in association with the set value Ai. In subsequent S140, whether the parameter i is n or not. Determine whether.

  If it is determined in S140 that the parameter i is not n (i ≠ n), the process proceeds to S150 and the parameter i is incremented (i ← i + 1) to increase the frequency of the VCO 43 by one step. Then, the process returns to S120, and the processes of S120 to S140 are repeated. As a result, the frequency fi of the measurement signal gradually increases, and the detected value Ki is collected corresponding to each frequency fi.

  On the other hand, if it is determined in S140 that the parameter i is n (i = n), the process proceeds to S160, and the detection value that becomes the minimum value from the detection values K1 to Kn stored in S130. The value Kj is extracted and the process proceeds to S170.

  In S170, the index value j corresponding to the set value Aj is specified by searching the amplification factor setting table (see FIG. 2C) stored in the ROM based on the set value Aj corresponding to the detected value Kj. In subsequent S180, by supplying the specified index value j to the memory 25, the amplification factor of the power amplifier 23 is set, and the process proceeds to S190.

  That is, the setting value Bj is read from the memory 25 that has been supplied with the index value j, and the D / A converter 27 generates an amplification factor setting signal based on the setting value Bj. By being supplied to the power amplifier 23, the amplification factor of the power amplifier 23 is set to Gj, that is, a magnitude that compensates for the cable loss Lossj specified from the index value j.

  In S190, the operation of the measurement unit 14 is ended, and a changeover signal is output to the changeover switch 16, whereby the connection of the changeover switch 16 is switched to the transmission unit 12 side, and this process is ended.

  Thereafter, in the transmission unit 12, the transmission signal generated by the transmission circuit 21 is amplified by the power amplifier 23 with an amplification factor that compensates for the loss in the coaxial cable 5, and then passed through the connector 10. Then, it is supplied to the coaxial cable 5 and thus the antenna 3, and is radiated as a radio wave from the antenna 3.

  In this embodiment, the VCO 43 is a signal generating means, the detector 47, the A / D converter 49 is an amplitude detecting means, S100 to S160 are frequency detecting means, S170 is a loss estimating means, S180 and the memory 25, D / A The converter 27 corresponds to loss compensation means.

<Effect>
As described above, in the wireless device 1, the cable loss Lossj in the coaxial cable 5 connected to the connector 10 is not obtained by measuring the voltage drop value in the cable, but the line length Lj of the coaxial cable 5. The frequency fj of the measurement signal corresponding to is detected, and the cable loss Lossj is estimated from the frequency fj.

  When the frequency fj is detected, the amplitude of the standing wave (detected values K1 to Kn) generated on the coaxial cable 5 by the measurement signal is measured while gradually increasing the frequency of the measurement signal. . However, the measurement accuracy may be such that the minimum value can be extracted by comparing the magnitudes of the measurement results, and it is not necessary to obtain the amplitude value with high accuracy.

Therefore, according to the wireless device 1, the loss in the coaxial cable 5 connected for feeding to the antenna 3 can be obtained without using a highly accurate measuring device.
In the wireless device 1, the amplification factor Gj of the power amplifier 23 that amplifies the transmission signal is set so that the estimated cable loss Lossj is compensated.

  Therefore, according to the radio device 1, the coaxial cable 5 is always connected to the coaxial cable 5 so that the power (radiated power) radiated from the antenna 3 is constant regardless of the line length of the coaxial cable 5 connected to the connector 10. And appropriate antenna power can be supplied.

In addition, since the wireless device 1 performs an adjustment process every time the wireless device 1 is turned on, the coaxial cable connected to the connector 10 by replacing the wireless device 1 with another vehicle or the like. Even when the line length of 5 has changed, the radiated power of the antenna 3 can be reliably adjusted so as to have a desired magnitude.
[Other Embodiments]
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, In the range which does not deviate from the summary of this invention, it is possible to implement in various aspects.

  For example, in the above-described embodiment, the setting value Aj and the index value j are associated with each other using the amplification factor setting table, but the cable loss Lossj is calculated from the detected frequency fj based on the above equations (3) to (5). A setting value Bj that can be calculated each time to obtain an amplification factor Gj that compensates for the cable loss may be directly supplied to the D / A converter 27 without using the memory 25.

Moreover, although the said embodiment demonstrated what the front-end | tip of the antenna 3 was made into the open state, the front-end | tip of the antenna 3 may be made into the short circuit state.
In this case, as shown in FIG. 5A, the voltage waveform of the standing wave that appears on the antenna 3 by the measurement signal has a phase at the tip of the antenna 3 of 0, and mπ (m = 0, 1, 2, ...) is a node, and the position (2m + 1) π / 2 is an antinode. That is, as shown in FIG. 5B, when the in-line wavelength of the measurement signal is λ and the line length of the coaxial cable 5 is equal to mλ / 2, the detector 47 that detects a standing wave is used. Output is minimal.

Therefore, it can be realized simply by rewriting the amplification factor setting table using equation (6) instead of equation (4).
Li = λi / 2 (6)
In the above embodiment, the measurement signal is generated by the VCO 43. However, the measurement signal is generated by dividing or multiplying the system clock used to operate the CPU of the control unit 18. May be.

  In this case, since it is not necessary to prepare an expensive oscillating element only for generating the measurement signal, the apparatus configuration can be simplified and the apparatus can be configured at low cost.

The block diagram which shows the structure of a radio | wireless machine. Explanatory drawing which shows the content of the frequency setting table used by adjustment processing, the content of an amplification factor setting table, and the correspondence of each parameter. The graph which shows the voltage waveform of a standing wave in case the front-end | tip of an antenna is open | released, and the relationship between the line length of the coaxial cable connected to the output of a detector, and a connector. The flowchart which shows the content of the adjustment process. The graph which shows the voltage waveform of a standing wave in case the front-end | tip of an antenna is short-circuited, and the relationship between the line length of the coaxial cable connected to the output of a detector, and a connector.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Radio equipment 3 ... Antenna 5 ... Coaxial cable 10 ... Connector 12 ... Transmission part 14 ... Measurement part 16 ... Changeover switch 18 ... Control part 21 ... Transmission circuit 23 ... Power amplifier 25 ... Memory 27, 41 ... D / A converter 43 ... Voltage controlled oscillator (VCO) 5 ... Capacitor 47 ... Detector 49 ... A / D converter

Claims (6)

A line loss estimation device built in a radio device to which an antenna is connected via a cable, and estimating a loss in the cable,
A signal generating means for generating a measurement signal to be applied to a connection end to which the cable is connected, and capable of controlling a frequency of the measurement signal;
The signal generation means measures the amplitude of a standing wave that appears by combining the measurement signal from the connection end toward the antenna and the reflected signal reflected from the antenna end and toward the connection end. Amplitude detecting means for detecting at the output end for outputting the signal for use;
The frequency of the measurement signal generated by the signal generation unit is gradually increased from a preset initial frequency, and the detection result of the amplitude detection unit is acquired, and the measurement signal that minimizes the detection result is obtained. A frequency detection means for detecting the frequency;
Based on the line length of the cable specified from the frequency detected by the frequency detection means, loss estimation means for estimating the loss in the cable;
A line loss estimation apparatus comprising: The tip of the antenna is open,
The initial frequency is set to a frequency at which an in-line wavelength of the cable is greater than 4L, where L is a maximum length of a cable that may be connected to the connection end. The line loss estimation apparatus according to 1. The tip of the antenna is short-circuited,
The initial frequency is set to a frequency at which an in-line wavelength of the cable is greater than 2L, where L is a maximum length of a cable that may be connected to the connection end. The line loss estimation apparatus according to 1.   The line loss estimation apparatus according to any one of claims 1 to 3, wherein the signal generation means comprises a voltage controlled oscillator.   4. The line loss according to claim 1, wherein the signal generation unit generates the measurement signal by dividing or multiplying a system clock used in the radio device. 5. Estimating device. The line loss estimation apparatus according to any one of claims 1 to 5,
An amplifier circuit that amplifies a transmission signal supplied to the antenna when performing wireless transmission;
Loss compensation means that estimates the loss in the cable by operating the line length detection device, and sets the amplification factor of the amplifier circuit so that the estimated loss is compensated,
A wireless device comprising:

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