JPS6161299B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In microwave communication, power amplifiers are used in transmitters and repeaters, and distortion of nonlinear signal waveforms caused by the power amplifiers becomes a major transmission obstacle. The present invention provides an automatic waveform shaping device that realizes accurate waveform transmission by automatically converting the transmission signal waveform so that it is least susceptible to the above-mentioned nonlinear distortion.

The signal transmitted from the transmitter must have its power limited to avoid nonlinear distortion due to the power amplifier. On the other hand, there is a desire to increase the power of the transmitted signal as much as possible in order to improve the signal-to-noise power ratio on the receiving side. Therefore, conventionally, the transmission signal power has been increased to the limit where the influence of nonlinear distortion becomes a problem. Nonlinear distortion caused by a power amplifier generally depends on the envelope of the signal to be amplified. Therefore, if the envelope always has a constant value, the nonlinear distortion that the signal receives will also always have a constant value, which is equivalent to a case where the signal is not subject to any distortion at all. The automatic waveform shaping device of the present invention is a device that automatically transforms the transmitted pulse waveform so that the transmitted signal has an envelope of a constant value as much as possible. It has the characteristic that distortion can be avoided.

The present invention is directed to an orthogonal amplitude modulation method (hereinafter simply referred to as "orthogonal amplitude modulation method") in which data points expressed on a complex plane are arranged equidistant from the origin. An offset orthogonal amplitude modulation digital information transmission system in which the effects of the automatic waveform shaping apparatus of the present invention are most exhibited will be explained, and then the principle of the automatic waveform shaping apparatus of the present invention will be explained.

The offset quadrature amplitude modulated signal can be expressed as follows.

where fc is the carrier frequency, P(t) is the in-phase signal, Q(t) is the quadrature signal, a _k is the in-phase data, b _k is the quadrature data, and m(t) is the transmitted pulse. , and T is the transmission period of the transmission data. Also, the envelope is √() ² +() ²
and the random data a _k and b _k are +1
Or when it is a binary value of -1, the transmission pulse m
(t) can be appropriately selected so that the envelope has a substantially constant value.

The principle of this invention will be explained below with reference to FIG. In-phase data is input to line 1, and quadrature data is input to line 2 with a delay of T/2 seconds from the in-phase data. These data are input to low pass filters 3 and 4, respectively, and the output signals x(t) and y(t) are input to transversal filters 5 and 6 with variable attenuators. In the transversal filter 5 with variable attenuator, variable attenuation C _o (n=0, 1, ..., N-1) and x
(t) is performed, and the in-phase signal P
(t) is output. In the transversal filter 6 with a variable attenuator, the variable attenuation amount C _o and y
(t), and the orthogonal signal Q
(t) is output. Then, the in-phase signal P(t)
is multiplied by cos2πf _c t, and the orthogonal signal Q(t)
is multiplied by sin2πf _c t, and the multiplication results are added together to produce a signal [P(t) cos2πf _c t+Q
(t) sin2πf _c t] is sent out from the line 7 as a transmission signal.

Here, the two transversal filters with variable attenuators perform the control described below, so that the transmission signal [P(t)cos2πf _c t+Q(t)
sin2πf _c t] is operated so that the envelope curve becomes a constant value. Assuming that the outputs of the two transversal filters with variable attenuators are P(t) and Q(t), P(t) and Q(t) are expressed as shown below. However, τ≦T.

The envelope is √() ² + () ² , but
N variable attenuation amounts _Co are adjusted so that this envelope maintains a constant value over time. This adjustment method can be performed automatically as follows. First, P(t) and Q(t) are sampled at a period shorter than T/2 seconds. The above sampling period is assumed to be Δ seconds. Appropriately, Δ is approximately T/8 seconds, for example. Control of the variable attenuation amount (tap coefficient) is performed as follows. In the present invention, the distance that the square of the envelope {P(kΔ) ² +Q(kΔ) ² } at a certain time kΔ is away from a constant value p, that is, {P(kΔ)
The variable attenuation amount C _o is controlled by the LMS method so as to minimize the root mean square value of Δ) ² +Q(kΔ) ² −p}.

First, set the objective function as follows.

= {() ² + () ² −} ² Then, the following control equation is obtained by the LMS method.

C ^k+1 _o = C ^k _o −α′∂/∂C _o {P(kΔ) ² +
Q(kΔ) ² −p} ² By performing this partial differentiation and setting 4α′=α, the control equation for _Co shown below can be obtained.

C ^k+1 _o =C ^k _o −α{x(kΔ−nτ)+y(kΔ
−
nτ)} × {P(kΔ)+Q(kΔ)}{P(kΔ) ² +Q(kΔ) ² −p} (n=0, 1, 2,...N-1) This formula is applied every Δ seconds Therefore, by adjusting the variable attenuation C _o , the envelope can be adjusted to the desired size √
It is possible to successively converge to a variable attenuation amount while keeping the value constant.

In the above equation, α is a correction coefficient, and the smaller the value, the longer the convergence time, but it is possible to reduce the fluctuation of the solution after convergence.

An embodiment of the present invention will be described below with reference to FIG. Although the embodiment shown in FIG. 2 is for N=3, in general N may be any value.

Signals x(t) and y(t) are input from lines 11 and 12, respectively. 13 and 14 are delay lines, and three variable attenuators 15, 16, 17, 18, 19, and 20 are attached to each delay line. 21, 22, and 23 are storage devices for storing the attenuation amount of each variable attenuator. The three outputs of the variable attenuators 15, 16, 17 are added by an adder 24, and the outputs of the variable attenuators 18, 1
The three outputs 9 and 20 are added by an adder 25. The output of adder 24 corresponds to P(t), and the output of adder 25 corresponds to Q(t). Adder 26 calculates the sum x(t) + y(t) of x(t) and y(t), and similarly adders 27 and 28 calculate the sum x(t-τ) + y(t-τ), respectively. Sum x(t-
2τ)+y(t-2τ) is obtained. Adder 2
9, the sum of P(t) and Q(t) is P(t)+Q
(t) is obtained, and this result is sent to the multipliers 30 and 3.
1, 32, x(t)+y(t), x(t-τ)+y(t-τ) and x(t-2τ)+y, respectively
(t-2τ). 33 and 34 are squarers for calculating the squares of P(t) and Q(t), respectively; the squarer 33 outputs P(t) ² , and the squarer 34 outputs Q(t) ^2. Output. The above P(t) ² and Q(t) ² are added in an adder 35, and further added to the line 3 in a subtracter 36.
The incoming constant value ρ is subtracted from 7. 38,3
9, 40 are multipliers, and multipliers 38, 39, 4
0 to (x(t)+y(t))(P(t)+
Q(t))(P(t) ² +Q(t) ² -p) and (x
(t-τ)+(y(t-τ))(P(t)+Q(t))
(P(t)+Q(t)-ρ) and (x(t-2τ)+y
(t-2τ))(P(t)+Q(t))(P(t) ² +
Q(t) ² −ρ) is output. The above three multiplication results are obtained by sampling circuits 41, 42, and 4, respectively.
3, and these sample values are input into the corresponding memory devices 23, 22 and 21 to modify the attenuation stored therein.

In the explanation of the principles and examples of the present invention, digital information transmission using offset orthogonal amplitude modulation was targeted, but a modulation method that can be applied to the present invention is such that the transmission signal is P(t)cos2πf _c t+Q
(t) sin2πf _c Includes all cases that can be expressed as t.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining the principle of the invention, and FIG. 2 is a block diagram showing an embodiment of the invention. In FIG. 2, there is a portion consisting of a delay line 13, variable attenuators 15, 16, 17, and an adder 24, and a portion consisting of a delay line 14 and variable attenuators 18, 19, 20.
The portions consisting of the
0, 31, 32, 38, 39, 40 and squarer 3
3, 34, subtracter 36, and sampling circuit 41,
42, 43 and storage devices 21, 22, 23 are circuits that realize the variable attenuation correction method of the present invention.

Claims (1)

[Claims] 1 An automatic waveform shaping device that is supplied with a quadrature amplitude modulation method in which all data points expressed on a complex plane are equidistant from the origin, which receives an in-phase signal and whose delay time interval is shorter than the baud interval. a first transversal filter of n-tap, a second transversal filter of n-tap which has a tap coefficient common to the first transversal filter, receives a quadrature signal as input, and has a delay time interval shorter than the baud interval; a first arithmetic circuit that calculates the sum of the output of the transversal filter and the output of the second transversal filter; and the sum of the square of the output of the first transversal filter and the square of the output of the second transversal filter. A second arithmetic circuit that calculates , a third arithmetic circuit that subtracts a certain value from the output of the second arithmetic circuit, and a third arithmetic circuit that multiplies the output of the first arithmetic circuit and the output of the third arithmetic circuit. a fourth arithmetic circuit; a fifth arithmetic circuit that calculates the sum of the n-th stage output of the first transversal filter and the n-th stage output of the second transversal filter for each n; a sixth arithmetic circuit that calculates the correlation between each output of the arithmetic circuit and the output of the fourth arithmetic circuit; and a seventh arithmetic operation that multiplies each output of the sixth arithmetic circuit by a positive value. and a tap coefficient changing circuit that subtracts each of the tap coefficients common to the first transversal filter and the second transversal filter by the value of each output of the seventh arithmetic circuit. Automatic waveform shaping device.