JPS63139450A - Pcm radio transmission system - Google Patents

Abstract

PURPOSE:To simplify the whole circuit and to decrease coding error rate by adding a part of the output of a local oscillator for modulation to a PCM transmission signal on the transmission side, and detecting said part of the output for use as a reference signal on the reception side. CONSTITUTION:Digital signals in channels P, Q are inputted to a modulator from its input terminal 10 and supplied to ring modulators 1, 3. From an oscillator 4, a reference carrier signal is supplied to the ring modulators 1, 3. Modulated wave signals from the modulators 1, 3 are synthesized with each other by a synthesis circuit 5, and the result passes through a band elimination filter 6. The reference carrier wave from the oscillator 4 is subjected to an attenuator 7 and a delay(time) adjuster 8, and is synthesized with the output modulated wave from the filter 6, and outputted via a transmitter 8 from an output terminal 11. In a demodulator on the reception side, a high frequency wave signal inputted from a reception terminal 20 is converted to an intermediate frequency wave signal by a receiver 21, which is supplied to a band-pass filter 22 and a demodulator 26. The carrier in this input signal is picked up by the band-pass filter, and is made a reference signal for the reception local oscillator 24 in order to determine a leading-in phase.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a PCM wireless transmission system, and particularly to a PCM wireless transmission system that uses an absolute phase encoding system without using a differential encoding system.

[Conventional technology]

In the conventional PCM wireless transmission system, it is difficult to establish the same absolute phase on the receiving side as on the transmitting side, so a differential conversion method is used to reproduce the signal while detecting the phase difference.
The phase error signal extracts the phase information of the carrier wave and feeds it back to the receiving local oscillator.
This is a method in which carrier waves are regenerated using PLL (PLL).

[Problem that the invention seeks to solve]

The above-mentioned conventional differential encoding system has a drawback, compared to the absolute phase system, that a 1-bit error □ is received as a 2-bit error. In addition, along with the differential modulation circuit on the transmitting side, the receiving side uses a differential demodulating circuit and a stable carrier wave from the input signal that fluctuates from moment to moment.
The problem is that a complicated carrier regeneration circuit is required to generate .

SUMMARY OF THE INVENTION An object of the present invention is to provide a PCM wireless transmission system that solves these problems, simplifies the overall circuit, and improves the code error rate.

[Means for solving problems]

The configuration of the PCM wireless transmission system of the present invention is that on the transmitting side, a PC
A part of the output of the local oscillator for modulation is added to the M transmission signal and transmitted, and on the receiving side, the output of the local oscillator for modulation is detected from the output of the received signal through a narrowband bandpass-wave transducer, and this detection output is It is characterized by being used as a reference signal for a local oscillator for demodulation.

Embodiment] Next, an embodiment of the present invention will be described with reference to the drawings.

FIGS. 1(a) and 1(b) are block diagrams of a modulation device and a demodulation device showing an absolute phase method according to an embodiment of the present invention.

In FIG. 1 (a), first, digital signals of channels P and Q are input to the input terminal 10, and these channels P,
The Q digital signals are input to ring modulators 1 and 3, respectively.Next, a reference carrier signal is supplied from the oscillator 4 to the ring modulator 1 on the channel P side and the ring modulator 3 on the channel Q side. , the signal on the channel Q side passes through the π/2 phase shift circuit 2 and is input to the ring modulator 3 as a carrier signal whose phase is delayed by π/2. The modulated wave signals from these ring modulators 1 and 3 are combined by a combining circuit 5 and passed through a narrow band band limiting filter (BEF) 6.

On the other hand, the reference carrier wave from the oscillator 4 passes through the attenuator 7,
After passing through the delay (time) adjuster 8, the band-limiting filter 6
It is combined with the output modulated wave of the transmitter 9 and outputted from the transmitter 9 via the output terminal 11.

Next, in the demodulator of FIG. 1(b), the receiving end 20
The high frequency signal input from the receiver 21 becomes an intermediate frequency signal, and the modulated wave is passed through a bandpass filter (BPF).
22 and demodulator 26 . Bandpass uraha device 2
The carrier wave inserted on the transmitting side that has passed through the phase comparator 23
The received local oscillator 24 performs synchronous detection. Therefore, in the detection output, the carrier wave component inserted on the transmitting side appears as a DC component proportional to this, but since this DC component has a constant value determined by the carrier wave insertion level, the detection signal of the demodulator can be easily removed from the After the synchronous detection output, the delay time adjuster 25
The signal is input to the demodulator 26 through the . In other words, the carrier in the input signal is picked up by the bandpass wave generator 22 and used as a reference signal for the reception local oscillator 24 to determine the phase of the input signal.

In this embodiment, the reference carrier used in the modulation device on the transmitting side is transmitted as is to the receiving side, and the receiving side carrier is obtained based on this.

A BEF 6 with a very narrow bandwidth is placed on the output side of this modulation device, and a part of the output of the reference oscillator 4 used as a carrier in the modulation device is mixed into the IF (intermediate frequency) output and output.

Therefore, the carrier in the input signal can be picked up by the receiving side BPF 22 and used as a reference signal for the receiving local oscillator 24.

Many digital wireless transmission systems currently in use use a modulated wave signal in which the carrier suppression amplitude is modulated with a base frequency signal having a symmetrical waveform on the positive and negative sides of the zero level, or a signal created by combining these. transmission is being carried out. Furthermore, since the base frequency band signal is a signal created from a scrambled digital signal, it contains almost no DC component. Therefore, a line that satisfies this condition does not require B'E F 6 on the output side of the modulator, but a line that does not satisfy this condition requires BEF, and BEF 6 is used as necessary.

In this case, the optimal value for selecting the BEF bandwidth is determined by both the difficulty in manufacturing the BEF and the transmission characteristics required by the line. It is also possible to have an effect.

Note that in this description, the carrier is an IF, but the carrier does not have to be limited to an IF.

〔Effect of the invention〕

As explained above, the present invention uses an absolute phase method instead of a differential conversion method, which simplifies the circuit configuration, and also allows a 1-bit error caused by differential conversion to become a 2-bit error. Since it is never received, it has the effect of reducing the error rate by half compared to the conventional method.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are block diagrams of a modulating section and a demodulating section for explaining a PCM wireless transmission system according to an embodiment of the present invention. 1.3...Ring modulator, 2... π/2 transfer circuit,
4... Oscillator, 5... Synthesis circuit, 6... Band-limiting ura wave device, 7... Attenuator, 8.25... Delay time adjuster, 9... Transmitter, 10. ...Input terminal, 11...
Output end, 20... Reception input end, 21... Receiver, 2
2... Bandpass filter, 23... Phase comparator, 24
. . . Reception local oscillator, 26 . . . Demodulator, 27.
28...Output terminal.

Claims (1)

[Claims] On the transmitting side, a part of the output of the modulation local oscillator is added to the PCM transmission signal and transmitted, and on the receiving side, the output of the modulation local oscillator is detected from the output of the received signal through a narrow band pass filter. A PCM wireless transmission system characterized in that the output is used as a reference signal for a local oscillator for demodulation.