JPS63121773A - Moving body identifier - Google Patents

Abstract

PURPOSE:To obtain a moving body identifier with high performance by applying a level difference between upper and lower side bands of a receiving signal by a filter in an interrogator, mixing the signal with a output from an oscillator and modulating the mixed signal. CONSTITUTION:A non-modulated wave from the interrogator 1 is modulated by a responder 2 with an identification signal and returns the modulated signal. The interrogator 1 receives the modulated signal, applies a level difference between the upper and lower side bands by a filter 105 through a circulator 102 and converts the signal into a residual side band signal or a single side band signal to prevent the disappearance of a demodulation signal which may be generated when the upper and lower side bands are almost equal amplitude. Then, an oscillator 104 is switched to a local oscillation source, homodyne detection is executed by a mixer 106 and the detected signal is processed by a signal processor 197 to demodulate the identification signal from the responder 2. Even if a relative distance between the interrogator 1 and the responder 2 is changed in said constitution, the identification signal can be correctly demodulated.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a demodulation method for a receiver, and in particular, a method for demodulating a receiver between a transmitting/receiving device serving as an interrogator and a transponder mainly attached to a mobile object. This is used in a receiving section of an interrogator of a mobile object identification device that transmits and receives data over a relatively short distance.

<Background> In recent years, small-sized devices have been mainly attached to moving objects.

A simple mobile object identification device that transmits and receives data between a transponder, which is a lightweight and simple wireless terminal, and an interrogator, which has a transmitting and receiving function, has been in the spotlight.

Possible uses for these include product management within a factory, gate management by having people carry transponders, and room entry/exit management.

Among these, for example, when used for production management in a factory, part code numbers and processing procedures on the production line.

A transponder, in which individual data such as the transport route is input into a storage unit in advance, is attached to each part, while interrogators are installed at major points on the production line.

The interrogator emits radio waves to the transponder installed on each part flowing on the production line, reads its internal data as described above, outputs a control signal to control the flow of the line, and controls the production line on each part. control accordingly. By using such a mobile object identification device, it is possible to form a highly flexible production line, and its range of applications spans a wide range of fields.

<Conventional technology> FIG. 6 shows an example of a conventional mobile object identification device.

2 shows the configuration of the interrogator and 2 the responder.

The interrogator 1 includes an oscillator 1042, a distributor 103. Circulator 102. Transmitting/receiving antenna 101. It is composed of a mixer 106 and a signal processing circuit 107 that demodulates the identification signal. - The force transponder 2 has a transmitting/receiving antenna 201. Modulator 202
．． It is composed of a signal processing circuit 203 that stores identification signals.

The unmodulated wave of frequency fQ generated by the oscillator 104 inside the interrogator 1 is transmitted to the distributor 103. It passes through the circulator 102 and is radiated toward the transponder 2 from the transmitting/receiving antenna +01. On the transponder 2 side, this unmodulated wave is received by a transmitting/receiving antenna 201, modulated by an identification signal by a modulator 202, and then re-radiated from the transmitting/receiving antenna 201. On the interrogator 1 side, the re-radiated radio wave from the transponder 2 is received by the transmitting/receiving antenna 101, and the received signal is guided to the mixer 106 through the circulator 102, and is output from the fQ oscillator 104 taken out through the distributor 103. Homodyne detection is performed using the local oscillation signal that is part of the output. Further, the detected signal is demodulated in the signal processing circuit 07, and the transponder 2 is identified.

However, in such a device, the interrogator 1 and the transponder 2
When the distance from the interrogator I changes, the phase of the received signal of the interrogator I changes, and a shift occurs between the phase of the received signal and the phase of the fQ oscillator 104 used as the local oscillation signal.

As a result, the amplitude of the output of the homodyne detection also changes periodically in response to the phase shift, and the amplitude eventually reaches zero at a certain distance, resulting in a phenomenon in which the identification signal cannot be demodulated correctly.

To prevent this phenomenon, it is possible to automatically control the phase of the local oscillation signal, or to use a synchronous detection method that performs carrier regeneration in synchronization with the received wave, but this would complicate the circuit and increase the size. The disadvantages are that it becomes larger and the cost becomes higher.

<Objective> It is an object of the present invention to improve these problems and to make it possible to always demodulate an identification signal with a small and simple circuit configuration.

<Embodiment> Fig. 1 shows a configuration diagram of an embodiment of the present invention. 01 is an interrogator;
2 is a transponder. The interrogator 1 has a transmitting/receiving antenna 101.
Circulator l021 Distributor 1032 Oscillator 104.
Filter 105. Mixer 106 and signal processing circuit 10
It consists of 7. On the other hand, the transponder 2 has a transmitting/receiving antenna 2
01° modulator 202. It consists of a signal processing circuit 203 that stores identification signals.

Now, the unmodulated wave of fO generated by the oscillator +04 is divided into two by the distributor 103, and one is divided by the circulator +02.
is radiated from the transmitting/receiving antenna 101 to the transponder 2,
The other is a mixer 106 as a local oscillation source for homodyne detection.
sent to work. In the transponder 2, the identification signal written in the internal storage element is digitally frequency-modulated (FSK) in the signal processing circuit 203, and the unmodulated wave from the interrogator received by the transmitting/receiving antenna 201 is shot by this signal. The signal is modulated by a modulator 202 composed of a key barrier diode, etc., and re-radiated from the transmitting/receiving antenna 201 to the interrogator 1.

The signal received by the transmitting/receiving antenna 101 of the interrogator 1 passes through the circulator 102, and after creating a level difference between the upper and lower sidebands depending on the frequency characteristics of the filter +05, the signal is sent to the mixer 106 using the oscillator 104 as a local oscillation source. The signal is subjected to homodyne detection, and the signal processing circuit 107 demodulates the identification signal.

By the way, generally when performing homodyne detection like this,
If the received signal is a double sideband (DSB) signal in which the upper and lower sidebands have approximately equal amplitude as shown in Fig. 2, the interrogator 1 and the transponder 2
The phase difference Δφ− between the phase φi of the input signal to the mixer 106 and the phase φt of the local oscillation signal due to changes in the relative distance from
1φ1−φt1, the mixer output, that is, the amplitude of the demodulated signal fluctuates with a period of Δφ, and especially when the relative distance between the interrogator 1 and the transponder 2 satisfies the relationship Δφ−0, the demodulation The signal disappears and it's over.

However, in this embodiment, the received signal is filtered through the filter 10.
5 to create a level difference between the upper and lower sidebands and convert them into vestigial sideband (vsB) signals, single sideband (SSB) signals, etc. as shown in Figures 3 and 4 = button tt. This prevents the demodulated signal from disappearing. That is, the general formula of the demodulated signal in the case of homodyne detection is expressed by the following formula, (A: amplitude of carrier wave, B: amplitude of upper sideband, amplitude of C8 lower sideband, ωS: angular frequency of modulated signal) In the case of a DSB signal, B=C, so the formula (■) becomes, and as mentioned above, when the formula 0 is satisfied, 13cosωst・cos(φ1−φt)=
0, and the demodulated signal disappears. However, VSB
Alternatively, in the case of a signal such as SSB, since B)C, the demodulated signal will not disappear in equation (2) even if the value of Δφ changes.

The same is true for filter outputs such as those shown as other signals in FIG.

Therefore, as shown in the present invention, if the filter 105 converts the received signal into a signal with a level difference between the upper and lower sidebands and performs homodyne detection, the relative distance between the interrogator ■ and the transponder 2 will vary. The identification signal can be correctly demodulated.

<Effects of the Invention> As explained above, by using the filter shown in the present invention, an effect equivalent to that of a synchronous detection circuit can be obtained with a simple circuit configuration, and a small and high-performance mobile object identification device can be realized at a low cost. It can also be constructed at low cost, and its benefits are great.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing an embodiment of the present invention, Figure 2 is a DS
Figure 3 shows the spectrum of the B signal, Figure 3 shows the spectrum of the VSB signal, Figure 4 shows the spectrum of the SSB signal, Figure 5 shows the spectrum of other signals, and Figure 6 shows the spectrum of the conventional signal. FIG. 2 is a configuration diagram showing a mobile object identification device of FIG.

Claims (1)

[Claims] 1. In a mobile object identification device configured such that an unmodulated wave emitted from an oscillator inside an interrogator is received by a transponder, modulated by an identification signal inside the transponder, and sent back to the interrogator. , a signal in which a level difference is created between the upper and lower sidebands of the received signal by a filter inside the interrogator is mixed with the output of the oscillator, and the mixed output is demodulated by a demodulation circuit. mobile object identification device.