JPS6069929A - Reception system for eliminating adjacent interference in digital communication system - Google Patents

Abstract

PURPOSE:To utilize a frequency effectively by allowing a receiver to generate an adjacent interference wave by estimation and subtracting the interference wave from a reception signal so as to eliminate the wave thereby attaining the frequency assignment with superimposed spectrum. CONSTITUTION:The adjacent interference wave is extracted by a BPF9 from the reception signal through an antenna 1, a pre-BPF2 and a pre-stage AGC circuit 3, the carrier of the signal is generated by a carrier regenerating circuit 10, and an orthogonal carrier obtained through a pi/2 phase shifter 11 and an in-phase carrier are inputted respectively to interference wave generating circuits 12-1 and 12-2. The circuits 12-1 and 12-2 multiply (19) the adjacent interference wave and the carrier so as to generate a base band signal, and after the signal is formed into a rectangular wave at a limiter 20, the wave is converted into a modulation signal by an LPF21 and multiplied (22) with the carrier, a wave to be modulated is generated again, and the amplitude of the AGC circuit 23 is decided by the control from an AGC control signal generator 24 measuring the average power of an output signal of the multiplier 19. A signal adding (13) the outputs of the circuits 12-1 and 12-2 is given to a BPF14 so as to generate an estimated interference wave, and the adjacent interference wave is eliminated by subtracting the wave from the reception signal subjected to delay 15 at a subtractor 16.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes phase soft steering (Phase SI+ift key) among modulation methods for digital communication systems.
iIlg ;Hereinafter referred to as [PSKJ. This invention relates to an improvement in a reception method that eliminates adjacent interference waves in two-phase and four-phase 1'S' K of 2-phase and 4-phase 1'S' K, contributing to effective frequency utilization.

Figure 1 is a diagram showing the principle of frequency allocation that has been adopted in this system, showing the spectrum of each signal and the transmission frequency (Fl,
F2. F3. ...is shown. Δlim is the frequency interval. ). As shown in the figure, the principle of frequency allocation is to allocate frequencies at intervals of ΔF so that the spectra of adjacent signals do not overlap with each other. As shown in Figure 2, the receiver structure in such a case extracts only the signal sent to its own station using a pre-filter (hereinafter referred to as "BPFp") (2), and the receiver performs saturation operation. To prevent this, the level is controlled by the pre-AGC circuit (hereinafter referred to as AGCpj) (3), and then the carrier wave is regenerated by the carrier wave regeneration circuit (5), or the received wave is delayed by 1 bit, and the signal is Use the detection/judgment circuit (
It would have been better to determine whether a mark or a space was sent in step 4) and output it as data (6).

However, although this type of frequency allocation allows the receiver to have a simple structure, it has the disadvantage that the number of allocated frequencies is small.

The present invention is characterized by estimating and generating adjacent interference waves in a receiver in frequency allocation where spectra are superimposed, and removing the interference waves by subtraction from the received signal. The structure and operation of the present invention, which is to realize frequency allocation that enables efficient frequency allocation and achieves frequency allocation that aims at effective frequency utilization, will be explained.

FIG. 3 shows how frequencies are assigned in a state where spectra are superimposed on each other. Adjacent waves in the spectrum partially overlap each other. The allocated carrier frequency is t f'+ f2
+f3+...and the frequency interval is indicated by Δf. The occupied frequency bandwidth of the 1st sign is the same as in Figure 1, and Δ
If f-ΔF/n, the number of frequencies can be increased by a factor of 0 by the allocation method shown in FIG. 3 than by the frequency allocation method shown in FIG. However, the problem is that when the spectrum of adjacent interference waves becomes stronger due to spectrum superposition, the communication line will be destroyed. This situation is shown by the dotted line in Figure 3. A signal with a carrier frequency of f+ (hereinafter referred to as "fl signal")
That's what it means. ) with a bandpass filter.
Even if 11 times the frequency is extracted, the signal whose carrier frequency is f2 (hereinafter referred to as “
f22 times." ) falls within the band, and the receiver is occupied by f22 times the interference component, making it impossible to receive the f+ times signal.

FIG. 4 shows a receiver that avoids this situation. The received signal is antenna (1), BPI;'p (2) and AGC
The path through p (3) is the same as in the conventional receiver structure.

After this, a bandpass filter (hereinafter [B
It's called PFuJ.

) (9) removes the f11 times component and extracts the f22 times component of the interference wave, and the carrier wave regeneration circuit (10) regenerates the carrier wave of the interference wave. The interference wave generation circuit (12) is composed of BPFu (9
) and an in-phase carrier wave obtained from a carrier regeneration circuit (10) or an orthogonal carrier wave obtained by passing it through a π/2 phase shifter (11), and predictably generates an interference wave. . The structure of this device is shown in FIG. A carrier wave is input to the terminal (17), and an interference wave is input to the terminal (18). A multiplier (19) synchronously detects the interference wave and generates a baseband signal. Since this signal is distorted, a limiter (
20) into a rectangular pulse, and after shaping the spectrum with a low-pass filter (2J) with exactly the same characteristics as the transmitting side, the terminal (
The carrier wave input from 17) is multiplied by the multiplier (22) to generate a modulated wave again. On the other hand, the average power of the signal output from the multiplier (19) is converted to the AGC control signal generator (24).
) to obtain the coherence) AGC control signal, and
The circuit (23) is operated to control the amplitude of the interference wave and output the predicted interference wave from the terminal (25). In the case of a two-phase PSK, only the interference signal generating circuit (12) (1) is required. In the case of 4-phase I) S K, (12) ■ and (1
2) ■ is required. These output signals are sent to an adder (13
), the distortion generated in DPI"p (2) is generated again in the bandpass filter (14). After adjusting the time delay involved in these signal processings in the delay circuit (15), the subtracter In (16), the predicted interference wave is subtracted from the received wave to remove the interference wave.The subsequent receiver structure is the same as the conventional receiver, including the detection/judgment circuit (4) and the carrier regeneration circuit (5).
) etc. are UN <. The operation of this receiver is that as the power of the interference wave increases, the estimation becomes more accurate and the interference wave removal effect increases, while as the interference wave becomes smaller, the AG
The present invention, which works by reducing the amplitude of interference waves and suppressing the generation of interference waves by the C circuit (23), can eliminate adjacent interference waves in digital communication systems.
It becomes possible to allocate frequencies in a state where spectra are superimposed, and it is possible to use frequencies effectively. Furthermore, this method aims to be applied to l) S■ (
In principle, it can also be applied to other digital modulation methods.

[Brief explanation of drawings]

Fig. 1 is a diagram showing conventional frequency allocation, Fig. 2 is a receiver block diagram in general digital communication, Fig. 3 is a diagram showing frequency allocation in spectrum superimposition, and Fig. 4 is a receiver block diagram in the present invention. FIG. 5 is a block diagram of the interference wave generation circuit. 1...Antenna, 2,9.14...Band filter,
3.23...AGC circuit, 4...Detection/judgment circuit,
5, 10... Carrier wave regeneration circuit, 11... π/2 phase shifter, 12... Interference wave generation circuit, 13... Adder,
15...Delay circuit, 16...Subtractor, 17, 18.
25...terminal, 19.22...multiplier, 20...
Limiter, 21...Low pass filter, 24...AGC control signal generator. Patent Applicant: Director, Radio Research Institute, Ministry of Posts and Telecommunications Part 2, Figure 3, Figure 4 (!1 7, Figure 5)

Claims (1)

[Claims] In a communication system in which the modulation method and adjacent frequency interval are determined, adjacent interference waves are extracted by a bandpass filter (9), the carrier wave of the signal is generated by a carrier wave regeneration circuit (10), and the in-phase carrier wave and orthogonal carrier wave are respectively generated. The interference wave generating circuit (12) multiplies the output signal of the bandpass filter (9) and the input carrier wave by a multiplier (19) to generate a baseband signal. is generated, converted into a rectangular pulse by a limiter (20), converted into a modulation signal by a low-pass filter (21), and then sent to a multiplier (
The multiplier is multiplied by the carrier wave input in 22) to generate a modulated wave again, and operates under the control of the AGC control signal generator (24), which measures the average power of the signal after output from the multiplier (19). The amplitude is determined by the AGC circuit (23), and an interference wave in phase with the carrier wave and an interference wave orthogonal to the carrier wave are output from different interference wave generation circuits (12), and they are combined by a p adder (18). An adjacent interference wave removal reception method in a digital communication system, characterized in that adjacent interference waves are removed by subtracting them from a received signal using a subtractor (16).