JP2803348B2 - Mobile communication device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication device, and more particularly to a mobile communication device capable of preventing a demodulated signal from being lost when using homodyne detection.

[Prior art] In recent years, it has been attempted to attach an ID card to a moving object such as a container, a car, and a human body to perform distribution management, fee collection, gate management, and the like. A small and lightweight transceiver (responder) that responds to an identification code as read data in response to an interrogation signal from a central transceiver (interrogator) has attracted attention. .

In such a mobile communication device, since the transponder needs to be reduced as much as possible, a method for receiving, modulating and retransmitting a non-modulated carrier wave generated by an interrogator without providing an oscillator for generating a carrier wave is usually provided. Is adopted. In this case, detection by the interrogator is generally homodyne detection in which a modulated carrier and the unmodulated carrier are mixed by a mixer.

The device configuration in this case will be described with reference to FIG.
In, an unmodulated carrier is output from an oscillator 11 and transmitted from an antenna 13 via a circulator 12. The transmitted unmodulated carrier is received by the antenna 21 of the transponder 2 and is modulated by the modulator 27 by the modulation signal output from the modulation signal generation circuit 28. The modulation signal is generated according to read data stored in advance.

The modulated carrier is received by the antenna 13 of the interrogator 1 and is input to the homodyne detector 14 via the circulator 12. A part of the unmodulated carrier wave leaks into the detector 14 via the circulator 12, and the unmodulated carrier wave and the modulated carrier wave are mixed and homodyne detected. The detection signal is input to the signal processing circuit 15, and the read data is recognized.

Such homodyne detection has a feature of high sensitivity, but when it is used for communication with a moving transponder, it is mixed every time the relative distance between the interrogator and the transponder becomes 1/4 wavelength times the carrier. The detection output becomes zero, and communication becomes impossible.

In order to solve this, for example, JP-A-63-52082 discloses that modulated carrier waves received by an interrogator have mutually different phases.
A device has been proposed which distributes two received waves differing by 90 degrees, performs mixed detection with an unmodulated carrier wave, and performs envelope detection of this detected output to select and demodulate a received wave having a larger envelope output. I have.

FIG. 5 shows the structure of the interrogator in this device. The unmodulated carrier output from the oscillator 11 is transmitted from the antenna 13 via the directional coupler 16 and the circulator 12.
In the directional coupler 16, a part of the unmodulated carrier is extracted at a predetermined ratio, and is equally distributed with a phase difference of 90 degrees from each other by the distributor 17, and is homodyne detectors 14A and 14B as local oscillation signals, respectively. To enter.

After the modulated carrier from the transponder is received by the antenna 13, it is equally distributed by the distributor 18 via the circulator 12, and is input to the detectors 14A and 14B to be homodyne-detected.
Since these detection signals are obtained by mixing with the local oscillation signals having a phase difference of 90 degrees from each other, they do not become zero at the same time even if the transponder moves, and are input to the signal processing circuit 15. Read data is obtained.

[Problems to be Solved by the Invention] By the way, in the device described in the above publication, a part of the unmodulated carrier wave leaks into each of the detectors 14A and 14B via the circulator 12, and the local oscillation signal power is reduced to eliminate the influence. It is necessary to set the degree of coupling of the directional coupler 16 so that the power becomes sufficiently large with respect to the leaked carrier power. However, according to this, when the output of the transmitter is increased for long-distance communication, the power of the local oscillation signal is also increased, and the sensitivity of the detectors 14A and 14B is significantly reduced.

Further, in the above-described device, there is a problem that the configuration of the interrogator is considerably complicated.

Therefore, the present invention is to solve such a problem, and a mobile communication device capable of successfully performing mobile communication with a simple configuration as a whole without lowering the sensitivity of the detector of the interrogator and complicating the configuration. The purpose is to provide.

[Means for Solving the Problems] The configuration of the present invention will be described with reference to FIG. 1. In a mobile communication device that performs communication between an interrogator provided on a fixed side and a transponder provided on a mobile, The interrogator has a carrier generating means for continuously generating an unmodulated carrier, a transmitting means for transmitting the carrier, a receiving means for receiving the carrier modulated and returned by a transponder, and a receiving wave. Mixing means for mixing and detecting with the unmodulated carrier, and detecting means for detecting the mixed output by envelope detection to obtain read data, while the transponder includes read data generating means for generating read data And a modulation signal generating means for outputting a pulse-like first modulation signal and a second modulation signal which become "1" levels at different timings while the read data maintains the "1"level; modulation First modulation means for modulating the reflected wave by switching reflection and passage of the carrier with the first modulation signal, and phase means for changing the phase of the unmodulated carrier wave passing through the first modulation means by 45 degrees; The second method modulates the reflected wave by switching between reflection and absorption of the unmodulated carrier wave changed by 45 degrees with the second modulation signal.
Modulation means.

[Operation] In the device having the above configuration, the modulated carrier wave returned from the interrogator after the unmodulated carrier wave is reflected by the first modulator means, and the unmodulated carrier wave from the interrogator communicates with the first modulator means and the phase means. The phase of the modulated carrier wave that passes through, is reflected by the second modulating means, passes through the phase means and the first modulation main stage, and returns again is different from that of the modulated carrier by 90 degrees as the latter reciprocates through the phase means. . Therefore, even if the transponder moves and the distance to the interrogator changes, the signal obtained by mixing and detecting these modulated carriers with the unmodulated carrier has the first level corresponding to the read data of "1" level. One of the modulation signal and the second modulation signal is always included,
Moreover, since the modulated signal is a non-modulated carrier that has passed through the first modulating means and the phase means, the carrier modulated by the second modulating signal is inferior to the conventional modulated signal obtained by mixed detection. Not over a certain level. By performing envelope detection on such a mixed detection signal, read data can be obtained.

According to such a configuration, the configuration of the interrogator can be greatly simplified, and since it is not necessary to take out a part of the unmodulated carrier with the directional coupler, there is also a problem that the sensitivity of the detector decreases with an increase in the transmission output. Does not occur.

[Embodiment] In FIG. 2, an interrogator 1 is provided on a fixed side, and has an oscillator 11 for generating an unmodulated carrier wave in a microwave region, a circulator 12, an antenna 13 for both transmission and reception, homodyne detection. And a signal processing circuit 15. The signal processing circuit 15 includes an AC coupling capacitor 15
1, an amplifier 152, an envelope detector 153, and a comparator that compares the envelope detection outputs at a predetermined level and outputs a rectangular demodulated wave
154.

The unmodulated carrier is transmitted from the antenna 13 via the circulator 12, is modulated by a transponder described later, and is received by the antenna 13 again. The received modulated carrier is input to the homodyne detector 14 via the circulator 12, where it is mixed with the unmodulated carrier leaking through the circulator 12 to be homodyne detected and input to the signal processing circuit 15.

The transponder 2 is attached to a moving container or the like, and includes a transmitting / receiving antenna 21, a read data generating circuit 22, a modulation signal generating circuit 23, a first return circuit 24, a phase shifter 25, and a second return circuit 26. I have.

The read data generation circuit 22 has predetermined read data stored in the ROM in advance, and repeatedly generates and outputs read / read data at a constant cycle. The modulation signal generation circuit 23 includes a pair of pulse generation circuits 231A and 231B, AND gates 232A and 232B, and an output resistor 2
The pulse generation circuits 231A and 231B output pulses of a frequency sufficiently higher than the clock frequency of the read data. Thus, only while the read data indicates the "1" level (FIG. 3 (1)), the AND gates 232A and 232B are opened and the pulses of the pulse generation circuits 231A and 231B are changed to the first modulation signal 23a and the second modulation signal. Signals 23b are input to the first and second reply circuits 24 and 26, respectively (FIGS. 3 (2) and (3)). As is clear from the figure, the pulses of the first and second modulation signals 23a and 23b become "1" levels at different timings and do not overlap.

The first return circuit 24 is composed of a choke coil 241 connected in series with the resistor 233A to block the passage of radio frequency, a PIN diode 242, and an AC coupling capacitor 243. The PIN diode 242 is a "1" level first modulation. When a forward current is supplied through the choke coil 241 by the signal 23a, the resistance becomes low, and the received carrier is totally reflected and returned from the antenna 21 to the interrogator 1. Modulated signal 23
When a is at the “0” level, no current flows through the PIN diode 242 and the resistance becomes high, so that the received carrier passes through the phase shifter 25 without being reflected.

The phase shifter 25 is composed of a microstrip 251 and delays a received carrier passing therethrough by 1/8 wavelength (electrical angle 45 degrees).

The second return circuit 26 includes the same choke coil 261, PIN diode 262, and AC coupling capacitor 2 as those of the first return circuit 24.
A termination resistor 264 having a characteristic impedance of the line is connected to the AC coupling capacitor 263. Therefore, when the second modulation signal 23b is at the "1" level, the PIN diode 262 has a low resistance, and the received carrier wave that has passed through the phase shifter 25 is totally reflected, passes through the phase shifter 25 again, and returns to the antenna. Reply to interrogator 1 from 21. In this case, since the received carrier wave reciprocates through the phase shifter 25, its phase is delayed by 90 degrees from that returned from the first return circuit 24.

When the second modulation signal 23b is at the “0” level, the PIN diode 262 has a high resistance, and the received carrier wave has a terminating resistance 264.
Is absorbed.

In this way, the unmodulated carrier transmitted from the interrogator 1 is received by the transponder 2, and when the read data is at the “0” level, it is returned to the interrogator 1 without any modulation,
In the case of "1" level, the first and second modulated signals 23a, 23a
The data is modulated by 3b and returned to the interrogator 1. In this case, the phase of the carrier modulated by the second modulation signal 23b is delayed by 90 degrees. Here, the pulses of the first and second modulation signals 23a and 23b become “1” levels at different timings as described above and do not overlap, so that the carrier wave from the interrogator 1 has the first and second modulation signals. signal
The data is modulated by 23a and 23b and efficiently returned to the interrogator 1.

The carrier received by the antenna 13 of the interrogator 1 is mixed by the homodyne detector 14 with the unmodulated carrier in the process described above. When the read data is "0" level and the carrier is returned from the transponder without modulation, the level of the mixed detection signal becomes zero, and when the read data is "1", the carrier is modulated by the transponder 2. In the case where the response is sent in response, the signal level increases in a pulse manner at the timing of the modulation signals 23a and 23b appearing in a sufficiently short cycle as compared with the read data.

Thus, when the mixed detection signal is amplified by the amplifier 152 and detected by the envelope detector 153, while a pulse-like level change corresponding to the modulation signal appears in the mixed detection signal,
The level of the envelope detection signal is kept high accordingly,
As a result, the rectangular demodulated wave obtained from the comparator 154 is “1”.
The level read data is reproduced.

By the way, the signal level of the mixed detection signal periodically becomes zero when the relative distance between the interrogator and the transponder changes, but the phase of the modulated carrier wave modulated by each of the modulation signals 23a and 23b differs by 90 degrees from each other. Therefore, no matter how the relative distance changes, the signal level of the mixed detection signal corresponding to each of the modulation signals 23a and 23b does not become zero. In addition, the signal level of the transponder 2 efficiently returns the received carrier to the interrogator 1 as described above, so that the signal level is comparable to the signal level obtained by the conventional mixed detection. This is shown in FIG. 3 (4), where (i), (iv)
Indicates the case where the signal level corresponding to one of the modulation signals becomes zero, and (ii) and (iii) indicate the case where the signal levels (absolute values) corresponding to both the modulation signals have the same magnitude. .

Thus, the mixed detection signal always includes a pulse of a certain level or more when the read data indicates the “1” level. Therefore, by performing envelope detection and shaping this, a change in the distance between the interrogator and the transponder is obtained. Regardless, read data can be reliably obtained.

[Effects of the Invention] As described above, according to the mobile communication device of the present invention, data is read from a moving transponder without complicating the structure of the interrogator and without lowering the detection sensitivity. Is always good.

[Brief description of the drawings]

FIG. 1 is a claim correspondence diagram, FIG. 2 is a block diagram showing a device configuration, FIG. 3 is a time chart of each signal, FIG. 4 is a block diagram showing a configuration of a conventional device, and FIG. It is a block diagram of a structure of the interrogator in the example of FIG. 1 Interrogator 11 Oscillator 12 Circulator 13 Antenna 14 Homodyne detector 15 Signal processing circuit 153 Envelope detector 2 Transponder 21 Antenna 22 Read data Generation circuit 23 Modulation signal generation circuit 24 First return circuit 25 Phase shift circuit 26 Second return circuit

Continuation of the front page (56) References JP-A-63-279621 (JP, A) JP-A-2-263178 (JP, A) JP-A-1-199185 (JP, A) JP-A-2-38984 (JP) , A) JP-A-63-75584 (JP, A) JP-A-55-87066 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01S 7/00-7/42 G01S 13/00-13/95 H04B 1/59

Claims (1)

(57) [Claims] 1. A mobile communication device for performing communication between an interrogator provided on a fixed side and a transponder provided on a mobile body, wherein the interrogator includes a carrier wave which continuously generates an unmodulated carrier wave. Generating means, transmitting means for transmitting the carrier wave, receiving means for receiving the carrier wave modulated and returned by the transponder, mixing means for mixing and detecting the received wave with the unmodulated carrier wave, and mixing output Detection means for obtaining read data by envelope detection of the
A read data generating means for generating read data; and a modulation for outputting a pulse-like first modulation signal and a second modulation signal having a "1" level at different timings while the read data maintains the "1" level. Signal generating means, first modulating means for modulating the reflected wave by switching the reflection and passage of the received unmodulated carrier wave with the first modulated signal, and the unmodulated carrier wave having passed through the first modulating means Phase means for changing the phase by 45 degrees, and second modulation means for modulating the reflected wave by switching reflection and absorption of the unmodulated carrier wave changed by 45 degrees with the second modulation signal. Characteristic mobile communication device.