JPH0558307B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a repeater for digital transmission in the microwave band.

(Prior art and its problems) The conventional microwave band relay system employs a two-frequency system in which one round-trip system is configured with two carrier waves. Figure 2 shows the situation. 100,
101 and 102 indicate repeaters, and ₁ and ₂ indicate two carrier frequencies. In this example, if we take the repeater 101 as an example, it transmits at the same frequency ₁ in two directions, left and right,
The same frequency ₂ is being received from two opposite directions, left and right. The details of this method are described in the document "Digital Microwave Communication" (Kikaku Center) supervised by Moriji Kuwahara.

As described later, the two-frequency method uses different frequencies for transmission and reception, so it has the advantage of being able to reduce interference between transmitter and receiver, but compared to the single-frequency method described below, the two-frequency method uses different frequencies for transmission and reception. There is a problem that a frequency band is required.

FIG. 3 is a diagram for explaining the single frequency system, in which separate antennas are usually prepared for transmission and reception, and are operated side by side to minimize interference between them.

FIG. 4 is a diagram illustrating interference between transmitter and receiver in a single frequency system, and is drawn using the repeater 101 in FIG. 3 as an example. Signal 203 is 2 from left to right as an uplink.
00 and is relayed as a signal 20 as a downlink.
1 is relayed from right to left as 202.
Now, when considering the interference between the transmitter and the receiver for the received signal 201, there are an interference signal 203 from the uplink transmission signal 200 and an interference signal 204 from the downlink transmission signal 200. 180,1 in the figure
Reference numerals 81 indicate regenerative repeaters for uplink and downlink, respectively.

FIG. 5 shows an equivalent baseband model of the repeater shown in FIG. 4 with interference between transmitting and receiving. In the figure, 180' and 181' are signal identifiers (identifying transmission codes) corresponding to the regenerative repeater, delay circuits 134,
135, 136, and 137 correspond to the propagation time from the transmitting antenna to the receiving antenna,
It is always attached to interference signals between transmitter and receiver. Multipliers 130, 131, 132, and 133 represent the phase rotation of the interference wave signal caused by a slight difference in each carrier frequency, and the rotational angular velocity Δω _i is generally Δω _i <<symbol rate. Adders 140 and 141 indicate that a transmitter-receiver interference signal is added to the received signal. Terminals 1001 and 1003 are transmitting antennas, terminal 100
4,1005 is connected to a receiving antenna.

(Objective of the Invention) An object of the present invention is to eliminate such interference between transmitter and receiver by adaptive control technology, and to realize a single frequency system with excellent frequency utilization efficiency.

(Structure of the Invention) The present invention transmits a first digitally modulated wave from a transmitting port, and transmits a second digitally modulated wave of the first digitally modulated wave from a receiving port provided in the same direction as the transmitting port. In the receiving single-frequency repeater, (a) a frequency shifter that extracts a part of the first digital modulated wave, shifts the frequency by the difference between the transmission and reception frequencies of the first and second digital modulated waves, and outputs the frequency shifter (b) (c) a multiplier that multiplies the output of the frequency shifter by a coefficient proportional to the amount of interference between the transmission port and the reception port; a subtractor (c) that subtracts the output of the multiplier from the second digital modulated wave obtained from the reception port; d) Detecting a phase difference between the multiplier output and a code identification error (demodulated signal - identification value of the demodulated signal) of the signal demodulated from the receiving port, and adjusting the frequency shifter according to the polarity of the phase difference. The single frequency repeater includes a phase difference detector that controls a frequency shift amount, and eliminates interference between transmissions from the transmitting port to the receiving port.

(Detailed explanation of the configuration) In the interference model in Fig. 5, terminal 1200→12
01 interference, that is, side-to-side interference of the antenna, is the largest interference, so only this will be considered. Furthermore, if we simplify by assuming that the propagation time from the transmitting antenna to the receiving antenna represented by the delay circuit 134 is negligible with respect to the transmission rate, the maximum interference path is simply the multiplier 1.
It can be replaced with a frequency shift circuit based on the frequency difference Δω between transmitting and receiving, represented by 30. Figure 6 shows ω _IF [rad/s] applied to the input terminal 1200.
This figure shows a frequency shifter that frequency-shifts the input signal p(t) in the intermediate frequency band by Δω and outputs q(t)=p(t)exp(jΔωt). 11, 12 in the figure
13 is a multiplier, 13 is a π/2 phase shifter, 15 and 16 are low-frequency wave generators 14, and an oscillator that outputs ω _IF [rad/s] constitutes a block 90, which functions as a synchronous detector. Now, if the output frequency of the oscillator 14 is Δω _V , the two output terminals of the block 90 are considered as complex output terminals, and the previous input signal p(t) is expressed as p(t)=B _R (t)cosω _IF t+B _I ( t) sinω _IF t (B(t)=B _R (t)+jB _I (t)), then γ(t)=B(t)・exp{j(ω _IF −ω _V )t} The following output is obtained. The block 91 is a normal quadrature modulator consisting of a multiplier 17, an 18π/2 phase shifter 19, an oscillator 20 whose oscillation frequency is ω _IF , and an adder 21, and Re{r(t)} cosω _IF t+I _n
{r(t)}sinω _IF t is output. As a result, the output terminal 1201 has q for the input signal p(t).
(t)=p(t)·exp{j(ω _IF −ω _V )t} is obtained. If ω _IF −ω _V is chosen equal to the frequency difference Δω between the transmitted and received signals, this frequency shifter 1 will perfectly simulate the multiplier 130 of FIG. 5.

FIG. 7 shows a transmitter-receiver interference removing device. In the figure, 4 is a transmitter, and 5 is a receiver, which are operated by single-frequency relay using antennas 8 and 9, respectively. 1 is the frequency shifter, 2 is the amount of interference between transmitter and receiver α
(α is a complex coefficient), a multiplier that multiplies the output of the frequency shifter by -α in order to remove interference, 3 is a multiplier that multiplies the output of the frequency shifter by -α in order to remove interference corresponding to (t) sum r(t)=α・p(t)exp(j△
Multiplier output α・p(t) after ωt)+R(t)
This is a subtracter for subtracting exp(jΔωt) and leaving only the normal signal R(t). As a result, the signal input to the receiver 5 becomes R(t), with interference between transmitter and receiver completely removed.

Although FIG. 7 shows an example of removing antenna side-to-side interference, by doing the same as shown in FIG. 8, front-to-back interference can also be removed. Each element in the diagram is the seventh
is equivalent to the element with the same reference number in the figure, but
6 is a delay circuit, which is the delay 135 of the interference model in Figure 5.
It corresponds to this, and is inserted because it is normal that this cannot be ignored in the case of replay relay.

The above explanation is for the case where Δω hardly changes, and the coefficient (complex number) α of the multiplier 2 absorbs the phase rotation of the interference component caused by a slight change in Δω. (A control circuit for α is not shown in this embodiment.) However, in reality, Δω cannot be considered as a constant due to the stability of a microwave band oscillator. Therefore, a method is required to accurately observe the change in Δω and control the frequency shift amount of the frequency shifter based on this. Assuming that the transmission code is S, this appears as interference on the receiving side as α·S·exp(j△ω _i t). Therefore, the received signal r(t) is expressed as r(t)=R(t)+αSexp(j
△ωt) On the other hand, since the interference cancellation signal is added through the subtracter 3 (Fig. 7), the baseband signal after demodulation is α′・S・exp from r(t).
The value of (j△ω ₂ t) is subtracted. Therefore, the code identification error (difference between the input and output of the code discriminator) e(t) on the receiver side is as follows: e(t) = R(t) + α・Sexp(j△ω ₁ t) −α′・Sexp( j△ω ₂ t)−R(t) =S{α・exp(j△ω ₁ t)−α′・exp(j
By multiplying △ω ₂ t)}e(t) by the complex conjugate S〓 of the transmission code S, e(t)・S〓 represents the error vector between the interference component and the interference cancellation signal, and its value is e(t)・(output of multiplier 2) = |P(t)| ²・[α・α′〓・exp{j△w ₁ t−
△w ₂ t)}−|α′| ² ] Here, α=a・exp(jθ _I ) Complex coefficient representing the interference of the interference signal α′=a′・exp(jθ _c ) Initial phase of the interference canceled signal,
Expressed as amplitude, the imaginary part of the above equation is θ _e (t) = |p(t) | ² aa′・Sin(θ _I +△ω ₁ t
−[θ _c
+△ω ₂ t]) θe obtained from the above equation indicates the phase shift from the optimal value at which the (interference signal) removal signal created from the interference component and the transmission signal cancels each other out in opposite phases. Therefore, it is necessary to rotate the phase of the removal signal by this deviation angle θe. This is the oscillator 2 in the frequency shifter 1 whose configuration is shown in FIG.
0 is a voltage controlled oscillator, and this frequency is momentarily t
If you change the phase by △ for a second, the signal phase that comes out to the output 1201 will be shifted by 2π (△t (rad). Specifically, this control is very simple and θe
(for example, output as a voltage) can be added as is as a control signal to the voltage-controlled oscillator.
If there is overcontrol, the polarity of θe will be reversed and control will be applied in the opposite direction.

(Embodiment) FIG. 1 is a diagram showing an embodiment of the present invention, in which numerals 1, 2, 3, 4, and 5 are the same as those in FIGS. 7 and 8. 7 is a phase difference detector for determining the above θe(t), which includes a code discriminator 70 and a subtracter 7.
The code discrimination error ε(t) is found from )
will be output directly.

Note that since there is normally a time difference between the transmitter-receiver interference signal and the source signal, it is necessary to insert a delay circuit as shown in FIG. 8 after the multiplier 2 in order to absorb this time difference.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an embodiment of the present invention, Figure 2 is a diagram explaining a conventional two-frequency relay system, Figure 3 is a diagram explaining a single-frequency relay system, and Figure 4 is a diagram explaining a single-frequency relay system. FIG. 5 is a diagram showing the baseband equivalent circuit of FIG. 4,
Fig. 6 shows an embodiment of a frequency shifter, which is one of the components of the present invention, Fig. 7 shows a block diagram of a basic transmitter/receiver interference removal circuit, and Fig. 8 shows a front back FIG. 3 is a diagram showing a block diagram of a transmitter-receiver interference cancellation circuit. In the figure, 1...frequency shifter, 2...multiplier, 3...subtractor, 4...transmitter, 5...receiver, 6...delay circuit, 8, 9...antenna, respectively.

Claims (1)

[Claims] 1. A first digital modulated wave is transmitted from a transmission port, and a second digital modulated wave having the same frequency as the first digital modulated wave is transmitted from a reception port provided in the same direction as the transmission port. (a) a frequency shifter that extracts a part of the first digital modulated wave, shifts the frequency by a difference between the transmission and reception frequencies of the first and second digital modulated waves, and outputs the same; b) a multiplier for multiplying the frequency shifter output by a coefficient proportional to the amount of interference between the transmitting port and the receiving port; (c) a subtractor for subtracting the multiplier output from the second digitally modulated wave obtained from the receiving port; (d) Detecting the phase difference between the multiplier output and the code identification error (demodulated signal - identification value of the demodulated signal) of the signal demodulated at the receiving port, and adjusting the frequency according to the polarity of the phase difference. A single frequency repeater, comprising: a phase difference detector that controls a frequency shift amount of a shifter; and removes interference between transmission and reception from the transmission port to the reception port.