JPS585616B2 - Heterodyne relay method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-relay heterodyne relay system in which two or more relay devices are connected in cascade, and particularly to a relay system that reduces nonlinear distortion noise generated in the transmission power amplifier of each relay device.

As shown in FIG. 1, a relay device used in a heterodyne relay system conventionally used in wireless communication systems converts a signal received by a receiving antenna 11 into a carrier band signal from a carrier signal source 13 in a down converter 12. The frequency is converted to an intermediate frequency band by After being amplified by the intermediate frequency band amplifier 14, the signal source 13 is again transferred to the up converter 15.
The signal is frequency-converted into a carrier wave band, amplified to a high power level by a transmission power amplifier 16 such as a traveling wave tube amplifier, and transmitted to the next relay device via a transmission antenna 17.

In the conventional heterodyne relay system, each relay device has the same configuration.

Therefore, the distortion noise generated in the transmission power amplifier 16 of each relay device has almost the same amplitude and the same phase, and the distortion noise of the entire relay system is the voltage addition of the distortion noise generated in the transmission power amplifier 16 of each relay device. .

Therefore, if the number of relay devices is N, then at the receiving terminal station, the distortion noise power generated by one relay device is 20logn[d
There was a drawback that distortion noise increased by B] was received.

In order to solve this drawback, the present invention uses at least one relay device that takes the upper side band of the output of the up converter and one that takes the lower side band as the relay device constituting the relay transmission system. For example, by creating a configuration in which these are used alternately, it is possible to reduce the addition of distortion noise in the repeater, and at the same time. A nonlinear distortion compensator is added to a relay device such as a receiving terminal station in order to suppress compensation residual distortion in the entire relay system.

FIG. 2 shows an example of a heterodyne relay system according to the present invention, in which parts corresponding to those in FIG. The frequency is converted to the carrier wave band of the upper side band in the transmission power amplifier 22.
The signal is amplified and sent to the receiving antenna 11 of the relay device via the transmitting antenna 23.

The upconverter 15 of the repeater uses the lower side band to convert the frequency to the carrier band.

Further, in this example, an intermediate frequency band nonlinear distortion compensator 24 is inserted in series between the intermediate frequency amplifier 14 and the up converter 15.

First, the intermediate frequency band nonlinear distortion compensator 24 is not used. The description will be made assuming that the output of intermediate frequency amplifier 14 is directly supplied to upconverter 15.

Now, each input voltage of the transmission power amplifiers 16 and 22 is expressed as x(t
), and the output voltage is y(t), the input/output characteristics of the transmitting power amplifier can be expressed as y(t) = a1x(t) - a3x3(t) (1), focusing on the output signal related to the fundamental frequency. Can be approximated.

Here, t is a variable representing time, a1 is a real constant, and a3 is a complex constant.

In this case, input/output amplitude nonlinearity and phase nonlinearity (AM-P
M transformation) can be expressed simultaneously.

The upconverter 21 at the transmitting end uses the upper sideband. If the angular frequency of the intermediate frequency signal from the terminal 18 is ωo, and the carrier angular frequency of the carrier signal source 19 is ωc, then the input signal x1(t) of the transmission power amplifier 22 is x1(t)=acos
(ωc+ωo)t(2).

Here a is a constant. The output voltage y1(t) of the transmission power amplifier 22 is expressed by equation (1) and (
From equation 2), ψ”=arg(a3).

In equation (3), the second term on the right side is the third-order distortion component.

This output signal is sent to the next relay device, and the output voltage y11(t) of the receiving down converter 12 becomes.

A is a constant representing propagation loss and the like. After y11(t) is amplified by the intermediate frequency band amplifier 14 to the same level as the power level at the transmitting terminal station, it is frequency-converted again to the carrier band by the up-converter 15, but the sideband wave used in this frequency conversion is Therefore, the output signals x2(t) of the up-converter 15 have different phase terms of third-order distortion as follows.

In other words, in the case of the upper sideband, and in the case of the lower sideband, becomes.

(5) The presence of a1 in the denominator in the second term on the right side of equation (6) means that the amplitude of the signal component in the first term is the transmission signal x1(t
This is because the gain was adjusted by the amplifier 14 to the amplitude of ).

When these x2u(t) and x2L(t) are amplified by the transmission power amplifier 16, third-order distortion noise is newly added. The output signals y2u(t) and y2L(t) in each case are (
5) Substitute equation (6) into equation (1) and ignore the term a9 since a<<1, and since we are focusing only on the fundamental frequency component, the angular frequencies 3(ωc+ωo) and 3( ωc
-ωo), equations (7) and (8) are obtained.

Here, as mentioned above, the distortion component generated by the input of the distortion component in the amplifier 16 is omitted as the minimum term in consideration of the condition that a<<1.

Equation (8) will be explained below using the vector diagram shown in FIG.

A vector 25 in the figure is a main signal (undistorted signal) at the output of the transmission power amplifier 16, and a vector 26 is a third-order distortion component generated in the transmission power amplifier 16 along with the main signal output of the vector 25.

First, it will be explained that the output of a microwave band amplifier such as a traveling wave tube amplifier can be expressed by a vector diagram as shown in FIG.

As is well known, microwave band amplifiers exhibit not only input/output saturation characteristics but also phase nonlinearity called AM-PM conversion in which the phase between input and output signals changes depending on the input level.

It is known that the input/output characteristics of an amplifier exhibiting such vibration and phase nonlinearity can be approximated by a power series of complex coefficients as shown in equation (1).

Now single frequency input signal x(t) = acosωc1
Considering this, the output y(t) focusing on the fundamental frequency is (3)
As we obtained the formula, it is given by the following formula.

This formula shows that the output signal of the amplifier is the output a which is linearly proportional to the input.
1 acos(ωc+ωo)t, which means that it can be decomposed into third-order distortion components having a specific phase difference of 180°-ψ, regardless of the input magnitude a.

If this state is expressed in principle, a vector diagram as shown in FIG. 7 can be obtained.

In Figure 7, (H) shows the phase delay, and F(y) is the output y
(t) shows the trajectory.

40 is the linear output component. 41 is the cubic distortion output component, and 42 is the output y(t
) is shown.

In the figure, the output y(t) gradually lags in phase from the linear output 40 as the input level a increases, and the amplitude also changes non-linearly, as shown in the figure, taking as an example the case where the input signal amplitude a is doubled. begins to

In other words, this nonlinear phase change is AM-PM conversion. The amplitude change corresponds to the amplitude nonlinearity of the amplifier, which is represented by saturation characteristics.

However, in the case of FIG. 7, only the third-order term is taken into consideration, so the amplitude saturation characteristics are not clearly expressed.

In this way, the input/output characteristics of an amplifier that is nonlinear in two aspects, amplitude and phase, can be intuitively expressed using a vector diagram as shown in FIG.

Therefore, returning to FIG. 3, the relationship between the output vectors of each amplifier will be explained.

For the distortion vector 26 generated in the transmission power amplification by the transmission power amplifier 16, the transmission power amplifier 22
As mentioned above, the third-order distortion component generated by
] is shown in the second term.

Therefore, the third-order distortion component generated by the transmission power amplifier 22 is represented by a vector 27 in FIG.

In this way, in FIG. 3, the third-order distortion component generated by the transmission power amplifier 22 is vectorially added to the distortion vector 26 caused by the transmission power amplifier 16. The vector sum becomes vector 28.

The obtained vector 28 is clearly expressed by the final induction equation (8).

In other words, if the passing sidebands in the frequency converters 21 and 15 are the same, the 3
The next distortion has the same amplitude. Transmission power amplifier 1 to be in the same phase
The third-order distortion at the output of the amplifier 6 is equivalent to twice the vector 26, as expressed by equation (7), that is, the distortions of the two amplifiers 22 and 16 are added in voltage.

On the other hand, when the passing sidebands in the frequency converters 21 and 15 are different, the third-order distortion at the output of the power amplifier 16 becomes a vector 28 which is the sum of the mutually conjugate vectors 26 and 27.

It is represented by the third-order distortion component vector 28 in equation (8).

In other words, by adopting such a configuration, the distortion components generated from one amplifier can be reduced to cosψ without any additional circuitry.
It can be seen that it can be reduced by a factor of two.

In a transmitting power amplifier with large phase nonlinearity such as a traveling wave tube, ψ takes a value of 80° to 85°, so the third-order distortion component is suppressed by 15 to 20 dB.

Next, in FIG. 2, the intermediate frequency band nonlinear distortion compensator 24
The effect of this will be explained.

This intermediate frequency band nonlinear distortion compensator 24 has a function of generating a distortion component that cancels out the compensation residual distortion component (vector 28), and as a result, the transmission power amplifier 16
The third-order distortion component in the output signal of is further reduced.

The distortion component to be inserted is generated using a nonlinear element. It is sufficient to insert the signal at a level that cancels out the distortion while monitoring it with a spectrum analyzer.

Figure 9 shows a specific example of such a nonlinear distortion compensation circuit. In FIG. 9, 51 is an input terminal, and 52 is an output terminal. 53 is a x3 element composed of an anti-parallel circuit of diodes, etc. 54 is a variable resistor, and 55 is a variable transfer device.

Using such a circuit, the distortion component generated by the x3 element 53 is added to the signal to cancel out the distortion component remaining after compensation.

The nonlinear distortion compensator 24 is used to cancel the residual distortion component of third-order distortion compensation that utilizes the difference in sideband waves used in the frequency converter of each repeater, and the location where it is added is shown in Figure 2. The present invention is not limited to only intermediate frequency bands such as the above.

That is, the method of using the nonlinear distortion compensator 24 is as shown in FIG. As shown in FIG. 5, a nonlinear distortion compensator is provided in the receiving end station device 32 so as to cancel out the total residual distortion component at the last receiving end station. Transmitting terminal device 33
and when the relay device 34 is not provided with a nonlinear distortion compensator. Alternatively, as shown in Fig. 6, a nonlinear distortion compensation device is used in any repeater in the repeater system so that distortion in all repeaters is reduced. Various examples can be considered.

One that uses the upper sideband as an up-converter for adjacent repeaters in multi-stage repeaters. This is not only the case when the relay devices are installed alternately with those that use the lower side band, but also the case where almost half of the relay devices are up converters that use the upper side band and the remaining half are those that use the lower side band, without specifying a particular order. good.

In addition, at least one of all relay devices is an up converter that uses the upper sideband. Even if at least one of the remaining upconverters is an upconverter that utilizes the lower sideband, it is still effective in reducing distortion to some extent.

As explained above, by using this invention, it is possible to reduce the distortion noise of the transmitting power amplifier in the heterodyne relay system. Moreover, since it has the effect of alleviating the addition of distortion noise generated in each repeater, there is an advantage that a low-distortion multi-relay communication system can be constructed.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an example of the configuration of a conventional heterodyne repeater. Fig. 2 is a block diagram showing an example of the configuration of a relay system according to the present invention, and Fig. 3 is a vector diagram showing the difference in sidebands passed by frequency converters and the principle of distortion compensation. 4 to 7 are block diagrams showing configuration examples of relay systems according to the present invention, and FIG. 7 is a vector diagram showing nonlinear characteristics.
FIG. 8 is a diagram showing the circuit configuration of the nonlinear distortion compensator. 11... Receiving antenna, 12... Frequency converter (down converter), 13... Carrier wave signal source. 14... intermediate frequency band amplifier, 15,
21... Frequency converter (up converter),
16, 22... Transmission power amplifier, 17...
...Transmission antenna, 24...Nonlinear distortion compensator. 18...Transmission input end, 31...Relay device equipped with a nonlinear distortion compensation device, 34...
A relay device that does not include a nonlinear distortion compensation device.

Claims (1)

[Claims] 1. In a heterodyne multi-relay transmission system in which two or more repeaters are connected in series, at least one of the repeaters is equipped with a frequency converter that uses an upper sideband. At least one of the other relay devices is equipped with the same number of frequency converters that use lower sideband waves as the frequency converters that use upper sideband waves. and generates a signal that cancels residual third-order distortion waves present in the output signal of a frequency converter that uses the upper side band wave and the lower side band wave only in at least one repeater or receiving terminal station, and A heterodyne relay system comprising a nonlinear distortion compensator that adds a signal to the residual third-order distorted wave.