JPH0541673A - Full duplex transmission reception modulation system for digital communication - Google Patents

Abstract

PURPOSE:To improve the system modulating a data signal with the frequency lower than voice band frequency during the communication through speech of digital telephone set or the like. CONSTITUTION:To reduce the creeping of the modulation carrier output frequency of the transmitter to the receiver, the reference frequency is applied to a first station origination frequency synthesizer 20 of the receiver from a single reference oscillator 10, and the output frequency from a second station origination frequency synthesizer 30 of the receiver modulated by a DATA signal is applied to the second station origination and a transmission frequency synthesizer 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulation system for control signals and data signals for individual identification in mobile communications such as car telephones.

[0002]

2. Description of the Related Art Generally, in an automobile telephone system, F
By the data demodulation method adopting the SK method, a low frequency (a low frequency of the voice frequency of 300 hertz to 3.4 kilohertz band or lower) can be set before the call with the other party.
Data such as an ID signal is used to control the radio and identify the caller. Then, even when a voice communication is being performed, it is required as a requirement that the data can be transmitted and received, and for that purpose, the voice frequency band is often used.

By the way, as shown in FIG.
Oscillates a highly accurate reference frequency from the phase detector 7,
The transmission carrier frequency f _TX is synthesized via the low pass filter 6, the adder 8 and the voltage controlled oscillator 9, and the output frequency is fed back to the phase detector to form a PLL system, and DATA for control or individual identification is formed. Is added to the adder above,
Since the composite frequency that is phase-synchronized is modulated,
The data signal is regarded as a kind of disturbance signal for the PLL system and operates in a direction of canceling the data signal. When this is applied to the radio of a car telephone, it is not possible to apply FSK modulation of 100 to 200 bps, for example, based on the action of a loop that cancels a data signal having a frequency component below the voice frequency band in relation to the channel switching speed. It's very difficult.

Therefore, as a countermeasure, the circuit configuration as shown in FIG. 3 is adopted, and DA is applied to the reference frequency of the reference oscillator 10 itself.
This is a method of modulating with a TA signal, but normally this reference frequency serves as the reference of the transmission carrier and is also used for the local oscillation frequency of the receiver, so this transmission data is received by modulating the reference frequency with the data to be transmitted. Since it goes around to the machine side, it cannot be adopted in this full-duplex system, and in order to eliminate this obstacle, it is possible to cancel the above transmission data after demodulation of the receiver, but this method is a circuit Due to variations in the parts that make up the equipment, careful adjustment is required for each machine in the production and inspection processes, which adversely affects performance and production efficiency, and inevitably increases the size of the entire apparatus.

As a measure for preventing the transmission carrier modulated by the data signal to the receiver from sneaking into the receiver, the data input to the second local oscillator 50 which heterodyne the receiver as shown in FIG. There is also a system in which after adjusting by the adjuster 60, the frequency of the second local oscillation is additionally oscillated, and a modulation sufficient to cancel the wraparound is applied, but this also avoids the occurrence of variations in the modulation sensitivity of the second local oscillation. The amount of delay generated by the first station also varies, and despite the adjustment by the phase / gain adjuster, the number of adjustment points in each part still does not decrease, and the reference oscillator is divided and arranged separately. In that case, there is a disadvantage in that it causes a disadvantage in space and cost, and eventually goes against the reduction in size and weight of the wireless device and the improvement in performance.

[0006]

SUMMARY OF THE INVENTION The present invention seeks to significantly reduce the modulation carrier from the transmitter to the extent that it does not interfere with the receiver.

[0007]

Thus, the present invention provides a frequency synthesizer for each of the first and second local oscillators of the receiver from the reference frequency of a single reference oscillator, and modulates the second local oscillator frequency with a data signal. And is used as a frequency source for generating the second local oscillator frequency and the transmission carrier frequency.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below with reference to FIG. 1, and the same portions are denoted by the same reference numerals throughout the drawings. The modulated wave captured by the antenna 1 is transmitted from the RFAMP 21 in the high frequency stage of the receiver to the first mixer M ₁ ,
Bandpass filter 4, IFAMP 22, second mixer M
_2. After passing through the bandpass filter 5, it is guided to the detection circuit DET for demodulation. Next, the transmitter is composed of a transmission frequency synthesizer 40 whose reference is the output frequency of the second station-use frequency synthesizer 30.

With the above construction, the output frequency of each frequency synthesizer is proportional to the reference frequency of the reference oscillator.
In the conventional system of FIG. 2, the frequency synthesizer operates by responding by considering the modulated signal of the low frequency due to the data communication as the disturbance, so if the response speed of the modulated signal is slowed against the disturbance, the frequency synthesizer becomes Modulation can be applied, but if the response is delayed, it takes time to switch the frequency when switching the channel, which is inconvenient.

Therefore, in the present invention, since it is possible to leave the switching of the frequency to the first local oscillator and the transmitting frequency synthesizer of the receiver, it is not necessary to switch the output frequency of the second local oscillator. Even if the response speed is slow, there is no problem, so that it is possible to apply modulation at a low frequency.

Next, comparing the present invention with the prior art, the above-mentioned embodiment will be explained with concrete numerical values. The reception frequency is 860M.
Hz, transmission carrier frequency 915 MHz, first station frequency 8
When 05MHz, the first intermediate frequency 55MHz, the second local oscillator frequency 54.55MHz, the second intermediate frequency 450KHz, and the transmission data frequency deviation ± 700Hz, the transmission data frequency deviation value ± 700HZ for the transmission carrier frequency 915MHz is ± 7 as a credit frequency synthesizer
00Hz / 915 = ± 0.77ppm, and 54.55MHz × 0.77ppm = for the frequency of the second station.
It becomes ± 42 Hz. This means that 42H is required as a received signal to obtain a transmission output frequency with a frequency deviation of ± 700Hz.
This means that the signal of z wraps around. In the conventional method of FIG.
The frequency of Hz = 616 Hz wraps around to the receiver side. Therefore, according to the present invention, the sneak frequency of the transmission output frequency to the receiver side is 616 Hz / 42 MHz = 1.
4.7 In other words, it is reduced to about 1/15, and even if the second local oscillator and transmission frequency synthesizer are modulated by the low-frequency data signal, the wraparound to the receiver side is small, It can be seen that there is almost no obstacle that ignores the incoming signal of the data signal or is disturbed by the incoming signal during the call by the voice frequency.

[0012]

According to the present invention, a stable modulated wave of low-frequency data can be obtained without delaying the frequency switching time of the synthesizer that applies the modulation as described above. Also, the difficulty of applying FSK modulation because the low-frequency data signal related to the channel switching speed is canceled by the PLL is eliminated, and the labor of adjusting the variation of the circuit parts like the method of canceling the transmission data after demodulation is eliminated. Can be completely eliminated, and space and cost requirements can be fully met.

[Brief description of drawings]

FIG. 1 is a circuit block configuration diagram for explaining a full-duplex transmission / reception modulation system of digital communication according to the present invention.

FIG. 2 is a block diagram of a PLL circuit modulated by a data signal.

FIG. 3 is a block diagram of a PLL system block circuit in which a reference oscillation frequency is modulated with a modulation signal based on a data signal.

FIG. 4 is a circuit block configuration diagram for explaining a conventional full-duplex transmission / reception modulation system.

[Explanation of symbols]

M ₁ , M ₂ mixer 4, 5 band pass filter 10 reference oscillator 20, 30, 40 frequency synthesizer 50 second station 60 phase / gain adjuster DATA data signal

Claims (1)

[Claims] 1. A method for preventing a modulated wave from wrapping around in a full-duplex radio transceiver using a digital modulation method in which frequency synthesis is performed by a frequency synthesizer, wherein a reference frequency of a single reference oscillator is used as a frequency synthesizer for a first station at a receiving stage. , A second station-originated frequency synthesizer in which the reference frequency is modulated by a low-frequency data signal below the audio frequency band, and added to the second station-originated frequency synthesizer. A full-duplex transmission / reception modulation system for digital communications, characterized in that the output frequency is used to reduce the sneak of the transmission carrier frequency to the receiver.