JPH02208587A - Identifying apparatus - Google Patents

Abstract

PURPOSE:To make it possible to exclude radiowave interference between interrogators by setting frequencies so that the difference between the transmitting frequencies of the interrogators is smaller than the value which is obtained by subtracting one half of the bandwidth of a BPF from the data-signal carrier frequency of a responder. CONSTITUTION:When a transmitting frequency F1 is transmitted from an interrogator Q1, a responder A1 modulates the signal with a data frequency fm and transmits the signal. The interrogator Q1 synchronously detects the modulated reflected wave and a source signal from a signal generator 1 in a mixer 5. Then, the detected signal of the frequency fm is made to pass through a BPF 6 having the characteristics of a central frequency fm and a bandwidth 2Bm and taken out of a demodulated signal output terminal 7. At this time, a signal frequency F2 from a neighboring interrogator Q2 is readily mixed into the interrogator Q1, and the frequencies F1 and F2 are mixed in the mixer 5. Thus an interference wave ¦F1 - F2¦ is generated by the beat. In order to remove the wave, the frequencies are set so that ¦F1 - F2¦ < fm - Bm is obtained. This is possible by decreasing the difference between F1 and F2 or by making the data frequency fm higher.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention uses multiple pairs of interrogators and transponders at the same time to improve the frequency and demodulation of identification systems that are effectively used in factory automation, security systems, etc. This is related to setting the signal bandwidth.

<Prior Art> Recently, a mobile object identification system has been approved as one type of in-premises wireless equipment and is being used inside the home.

This system basically consists of an interrogator and a transponder, and the signal (radio wave) sent from the interrogator is received by the transponder.
The signal is modulated using the data (identification number, etc.) in the transponder and sent out. The interrogator receives this modulated signal,
Usually, the modulated signal is demodulated by synchronous detection and data from the transponder is extracted.

Since this system has a mobile object identification function, it is expected to be used in a wide range of applications such as factory automation, security systems, and personal identification systems.

FIG. 4 is a basic configuration diagram of a commonly used mobile object identification device. Q is an interrogator, 1 is a signal generator with an instantaneous frequency F+ (including temperature drift, etc.), 2 is a coupler, 3
4 is a circulator, 4 is an antenna, 5 is a mixer (demodulator), 6 is a bandpass filter for signal detection, and 7 is an output terminal for a demodulated signal. Although omitted in the figure, the synchronous detector has two
System may be used.

On the other hand, A is a transponder, 8 is an antenna, 9 is a duplexer, 10
1 is a modulator, 11 is a demodulator, and 12 is a signal processing unit including a CPU and memory.

Next, this operation will be explained.

A signal of interrogator Q and frequency F1 is generated by a generator 1, passes through a circulator 3, and is sent out from an antenna 4 (solid line). The signal reaches transponder A, and the signal received by antenna 8 in transponder A passes through demultiplexer 9 and enters modulator 10.

On the other hand, from the signal processing unit 12, data stored in a memory (instantaneous frequency fm) acts on the modulator 10, and in the modulator 10, the input signal (frequency F+) is applied to the modulator 10.
is modulated, and the modulated signal (indicated by a broken line) passes through the duplexer 9 again and is sent out to the antenna 8. Modulator 1
0, an AM or PM modulator is generally used.

In the interrogator Q, the received modulated wave and the source signal from the signal generator 1 are mixed by a mixer 5, and as a result, data (frequency fm) is detected. The demodulated signal passes through a bandpass filter (center frequency fm, bandwidth 2Bm) 6 and is extracted from a demodulated signal output terminal 7.

For example, the frequency tolerance range of the signal generator 1 is extremely loosely regulated in systems that utilize microwaves [e.g., 2434.25 MHz to 2465.75 MHz].
] Therefore, the signal generator 1 is normally formed very simply, with only stabilization using a dielectric resonator.

By the way, this system did not cause any problems when there was only one interrogator Q or when the interrogators were installed at a sufficient distance from each other so that interference between the interrogators was not a problem at all.

<Problems to be Solved by the Invention> In the mobile object identification system described above, when a plurality of interrogators are used, a very serious problem often arises due to radio wave interference between the interrogators.

Let me explain this problem.

FIG. 1 shows a state in which a plurality of interrogators Q are used. It is assumed that the interrogator Ql of interest now faces the transponder A1 and data transmission is being performed.

A signal frequency Fl is transmitted from the interrogator Q1, and the transponder A1 modulates the signal at a data frequency fm and sends it out. CF and fm are instantaneous frequency values including temperature drift, etc.] In the interrogator Q1, the signal (reflected wave) modulated by the transponder A1 is synchronized with the source signal from the signal generator 1 by the mixer 5. Detected. Reference numeral 6 denotes a bandpass filter for extracting the detected signal, and as shown in FIG. 2, it has the characteristics of a center frequency fm and a bandwidth of 2Bm.

As a result, the detector signal of frequency fm from the mixer 5 passes through the filter flea and is extracted from the demodulated signal output terminal 7.

FIG. 3 shows the spectrum of the data signal obtained from terminal 7. That is, the demodulated data (solid line) is accompanied by sideband signals on both sides of the center frequency fm (solid line).

Since the demodulated data is band-limited with a bandwidth of 2 Bm, only the passing signal is extracted and other signal components are removed. This bandwidth is determined by the modulation speed of the data (carrier frequency fm). By the way, the signal level sent from the antenna of the interrogator Q1 is usually several mW to 300 mW (0 to +24 dBm).
It will be about.

On the other hand, the signal level at which the signal is modulated and reflected by the transponder Al and input to the interrogator Q1 is several tens of dBm (
For example, it is extremely small, about -30 to -90 dBm). Such a small modulated signal is demodulated by synchronous detection.

By the way, let us consider a case where a plurality of interrogators other than interrogator Q1 are used at the same time.

In FIG. 1, the adjacent interrogator is Q2 and its transmission signal frequency is F2.

Generally, when this type of device is used indoors, radio waves are subject to complex reflections from indoor obstacles and exhibit unpredictable radio wave propagation characteristics.

That is, the signal from the adjacent interrogator Q2 is easily transmitted to the interrogator Q2.
mix into l. When the signal from the interrogator Q2 is mixed into the interrogator Q+, the mixer 5 in the interrogator Ql mixes the signal components of frequencies F1 and F2, and the mixer 5 generates the beat.

Now, the difference between the transmission frequencies of interrogators Q1 and Q2 ΔF=IFI−
If F21 falls into fm-Bm<ΔF<fm+Bm,
The signal obtained from the demodulated signal ratio cuff of interrogator Q1 is
As shown in the figure, in addition to the regular data demodulated signal (solid line), Fl
An interference wave F+ -F2 (dashed line) is generated due to the beat of F2. This interference wave component often reaches a sufficiently high level as compared to the demodulated data signal, and the interrogator Q cannot operate normally.

This type of phenomenon is a problem peculiar to this system, in which there is a large signal level difference between the transmitting output and receiving input of the interrogator, and there are many cases in which a plurality of interrogators are used indoors at the same time. Particularly when these systems are used as factory automation equipment on a production line and multiple interrogators are installed close to each other in a room, serious problems arise.

Means for Solving the Problem> The difference ΔF between the oscillation frequencies F of the signal generator built into each interrogator, the bandwidth 2Bm of the bandpass filter, and the modulation data frequency fm of the transponder is ΔF<fm −Bm. Make sure that the relationship holds true.

In order to establish the above relationship, it is preferable to use, for example, a highly stable phase-locked oscillator in the signal generator built into each interrogator.

If the bandwidth is below the lower limit of the bandpass filter, the beat is cut by the bandpass filter and no beat is output from the demodulated signal output terminal.

<Example> The basic configuration of the present invention is the same as that shown in FIG. 4, but the transmission frequency of the interrogator, the bandwidth of the bandpass filter for data signal detection, and the data signal carrier frequency of the transponder to realize the present invention are as follows. The following describes the constraint conditions and means of constructing a transmission source (signal source) that satisfies them.

Now, in the system examples shown in FIGS. 4 and 1, the transmission frequency of the interrogator Q is Fl, the bandwidth of the bandpass filter 6 is 2Bm, and the data sent from the signal processing unit 12 of the transponder A is set as above. Let the carrier wave of the signal be fm (the data rate given to the carrier wave is 2Bm).

As an example, Fl is 2,450MHz, 2Bm is 20
KH2, fm is selected to be about 100KH2. The difference in the transmission signal frequency between this and the quantizer, that is, the beat component 1F+-Fil, can be taken outside the demodulation signal bandwidth 2Bm in FIG. A better measure would be to implement FIF21.
m-Bm. To achieve this, either reduce the difference between Fl and F2 on the interrogator side, or, if the data signal speed is constant on the transponder side, change the carrier frequency of the data signal. This can be achieved by increasing fm.

Of course, the optimum value for these should be selected by considering cost, simplicity of hardware, etc., and balancing either or both of them.

Increasing fm extremely high in the transponder A poses problems in terms of the operation of the CPU and memory of the signal processing section 12 and the response speed of the modulator 10, and rather increases the frequency of the signal generator 1 of the interrogator. It is better to increase stability.

As the frequency-stabilized oscillator 1, it is most appropriate to employ a phase periodic oscillator that is controlled using a crystal oscillator as a reference.

An example of a phase-locked oscillator configuration is shown in FIG. In Figure 5,
13, the frequency stability may be limited to within 90 KHz, including the stability due to the transistor serving as the oscillation source, etc.

16 is a phase comparator, 17 is a crystal oscillator serving as a reference for the oscillation frequency, and 18 is a signal output terminal.

This oscillation operation is well known; the frequency of the oscillator 13 is divided by the prescaler 14, and the output signal is phase-compared with the signal of the reference crystal oscillator 17 by the phase comparator 16. The output of the phase comparator 16 passes through the loop filter 15 and is fed back to the oscillator 13. In this operation, the stability of the oscillation frequency of the oscillator 13 is approximately equal to the stability of the reference crystal oscillator 17. Oscillation frequency is 2,450MHz
This type of oscillator is inexpensive to construct and practical.

The frequency stability of the oscillator 13, which depends on the crystal oscillator, is limited to <lF+-Fil<rm-Bm as described above.

<Effects of the Invention> As explained above, according to the present invention, since the problem of interference caused by the oscillation (transmission) frequency of the interrogator is eliminated, it becomes possible to use a plurality of interrogators at the same time, especially indoors. The range of applications of the system is expanded widely.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the identification system according to the present invention, Fig. 2 is a diagram showing the characteristics of a bandpass filter used for mixer output, and Fig. 3 explains the problems of the conventional example and the present invention. FIG. 4 is a diagram showing the basic configuration of the identification system, and FIG. 5 is a diagram showing an example of a phase synchronized oscillator. In the figure, 1: signal generator, 5: mixer (demodulation means), 7: output terminal, 10: modulator. 4: Antenna, 6: Bandpass filter 8: Antenna, Agent Patent attorney Takeshi Sugiyama (and 1 other person) Figure 2 Collection 3

Claims (1)

[Claims] 1. Consisting of a plurality of pairs of interrogators and transponders, the interrogator transmits a signal with a frequency F, the transponder receives the signal, and reflects the modulated signal modulated with the modulation signal fm. The identification system transmits a modulated signal, receives the modulated signal by an interrogator, demodulates it by a built-in demodulating means, and extracts the data from the transponder. Difference ΔF between transmission frequencies Fa and Fb = |Fa
-Fb|(a, b are integers of 1, 2, ..., n, and a≠b) The transmission frequency F of each interrogator is set so that ΔF<fm-Bm An identification system featuring: