JPS58105658A - Adaptive type modulating equipment - Google Patents

Abstract

PURPOSE:To obtain a proper amplitude and phase with an output, by distorting the input of the nonlinear amplifier in advance. CONSTITUTION:Transmitting data series are inputted in parallel from an input terminal 100 and become addresses of an RAM 10 and an ROM 20. An original signal point arrangement is stored in the ROM 20 as a complex number value, and a value which is distorted so that the output of a nonlinear amplifier becomes a proper signal point is stored in the RAM 10 as a complex number value. The output of the ROM 20 is DC-AC converted after it is converted into an analog signal by a DA converter 30, and outputted to the nonlinear amplifier through a terminal 101. To adaptively change the content of the RAM 10, the output of the nonlinear amplifier is inputted through a terminal 102 and demodulated by a demodulating circuit 60. The signal is subtracted 80 by a signal read out from the ROM 20 and multiplied by a fixed coefficient at a correcting amount generating circuit 90, and then, added to the output of the RAM10.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applicable to multilevel modulation, especially multilevel modulation that uses the amplitude and phase of a carrier wave as information, such as quadrature amplitude modulation, to compensate for the nonlinearity of an amplifier. The present invention relates to a modulation device that transforms a transmission pattern in advance and sends it out.

Conventionally, in multilevel modulators, the output of the amplifier is operated at a level lower than the maximum output in order to avoid deterioration due to nonlinearity in the saturation region of the amplifier. However, it had the disadvantage that a large output could not be obtained despite the large power consumption, and the power utilization efficiency of the amplifier was poor.

An object of the present invention is to provide an adaptive modulation device that can obtain an output power of .

According to the present invention, in multilevel digital communication.

A rewritable Ill memory that outputs a transmission signal in response to an input signal series, a @20 memory with fixed content that outputs a transmission signal in response to an input signal series, and the first
a modulation tR circuit that modulates a carrier wave with the output of the memory and outputs it to the nonlinear amplifier, a demodulation circuit that demodulates the output of the nonlinear amplifier, and subtracts the output of the demodulation path from the output of the '2nd memory. a correction amount generation circuit that generates a correction amount from the output of the subtraction circuit, and an addition circuit that adds the output of the correction amount generation circuit to the memory output of the @l, The circuit output is
Adaptively change the contents of the first memory by writing to the memory of Il! ¥! It is possible to obtain a unidirectional lid modulator with a characteristic characteristic.

Next, the present invention will be explained in detail with reference to the drawings.

Figure 1 is a diagram showing the input/output characteristics of a normal amplifier.The nonlinear characteristics of a normal amplifier are the saturation characteristic of the output amplitude called AM-AM conversion, and the input amplitude of the output phase called AM-PM conversion. There are changes due to

At a point where the input amplitude is sufficiently small from the saturation point, the amplitude characteristic is linear and there is no change in phase.However, as the input amplitude approaches the saturation point, the output amplitude becomes saturated and the output phase begins to rotate. Therefore, in multilevel transmission, the operating point should be set at a value far below the saturation level to avoid this nonlinearity of the amplifier.

Figure 2 shows the model numbers for nonlinear amplifier signals. It is assumed that the modulation is 16[QAM]. @2 Figure 1
Figure 1) shows the distribution of signal points in the phase plane of the amplifier output when the operating point is lowered, and Figure 2 (27) shows the distribution of signal points in the phase plane of the amplifier output when the operating point is lowered to near the saturation level. shows.

The signal point in FIG. 2 (2) is distorted compared to the signal point +1). The receiver judges that the signal point in Figure 2 (1) is sent as 9, so if the signal point in Figure 1!2 (21) is sent, it will cause an error due to small noise. The modulator of the present invention distorts the input of the nonlinear amplifier in advance, and the nonlinearity of the amplifier is distorted in such a way that a correct amplitude and phase is obtained at the output. effect).

FIG. 3 shows an embodiment of the present invention.

Transmission data sequences are input in parallel from the input terminal 100. In the case of 16-value QAMO, it is 4 bits.

@3 The diagonal lines above the connections in the diagram indicate multiple connections.
Memory to (RAM(Random 1ccess
MImry)) and the second memory
Only Memory 20 (ROM (Read 0nl)
y Memoryl 〕7)' V
The original signal point arrangement as shown in Fig. 2 (1) is stored in the ROM 20 as a complex number value, and the contents of the RAM 10 are values distorted so that the output of the non-bell-shaped amplifier becomes a single signal point. is also stored as a complex value *RAM1o
The output of oscillator 51 is converted into an analog signal by digital-to-analog converter f+30, and output from oscillator 51 by postmortem modulation circuit 40.
In order to orthogonally modulate and adaptively change the contents of *RAMto output from terminal 101 to the nonlinear amplifier, the output of the nonlinear amplifier is input from terminal 102 and demodulated by demodulation circuit 60 using oscillator 51. The same oscillator 51 can be used for the modulation circuit 40 and the demodulation circuit 60KJ'fjH, so the demodulation circuit 601C does not require a carrier extraction circuit.If a good signal is demodulated by the demodulation circuit 60, This demodulated complex digital signal, which is converted into a complex digital signal by the analog-to-digital conversion 1i) 70, is subtracted from the original signal read from the ROM 20 by a subtraction circuit sO, and the result is subtracted by the correction amount generation circuit 9.
[Multiply by 1 by a constant coefficient (generally a sufficiently smaller value than ktil), and add it to the output read from RAM10 in adder circuit 91. If the demodulated value is larger than the original value from the ROM 20, the content of the 8mm MIO is controlled to be smaller, and the demodulated value is transferred to the ROM 20.
If the original value from 1 is also small, control is performed to increase the contents of the MIO. By using this mechanism, the modulation device of the present invention is such that even if the input/output characteristics of the nonlinear amplifier change, the output of the nonlinear amplifier, that is, the input signal from the terminal 102 will always be at * in Fig. 2 (1). The contents of KRAMIO can be controlled to ensure the correct signal point arrangement. Suppose that the input/output characteristics of a nonlinear amplifier are as shown in Fig. 2 (11)
If we input a signal like this and get an output like that shown in Figure 2 (2), the contents of lLANl0 in that case will have a signal point arrangement as shown in Fig. 411. When the RAM 100 signal points are passed through a nonlinear amplifier, the result shown in Fig. 2 (
1) Owt signal point is obtained.

In this embodiment, the correction amount generation circuit was described as one that multiplies by a constant coefficient, but one circuit is used to generate the correction amount so that only the sign of the output of the subtraction circuit 80 is retained and the magnitude is a constant small value. Even when used as a circuit, the l113-like O effect can be obtained. In this embodiment, 16-level QAM modulation has been described, but it is clear that deterioration due to nonlinear amplifiers can be prevented using a similar method for any other QAM modulation method.

As described above, the modulation device of the present invention can automatically adjust the output of the nonlinear amplifier to the correct signal point in accordance with the characteristics of the nonlinear amplifier, and adjustment is extremely easy. (9) It is possible to follow changes in amplifier characteristics due to temperature.

Furthermore, in the embodiment shown in FIG. 3, if the delay time from the digital-to-analog converter 30 to the analog-to-digital converter 570 is longer than the symbol period, this can be dealt with by inserting a delay circuit into the output of the ROM 20. In this case, it is necessary to similarly delay the write address of the RAM and switch it to the read address.

[Brief explanation of drawings]

Figure 1 is a diagram showing the input/output characteristics of a nonlinear amplifier, and the 2nd tH
A diagram showing distortion caused by a nonlinear amplifier of a 16-level QAM signal,
FIG. 3 is a diagram showing one embodiment of the present invention, with reference numerals IQ,
20, 40, 50, 60, 80, 90, 91 respectively indicate a first memory, a second memory modulation circuit, a nonlinear amplifier, a demodulation circuit, a subtraction circuit, a correction amount generation circuit, and an addition circuit. It is a figure which shows the signal point memorize|stored in RAM10. Figure 1: Input swab hair, Figure 3, Quasi-4-Figure

Claims (1)

[Claims] In multilevel digital communication, a rewritable first memory outputs a transmission signal in response to an input signal series; a second memory with fixed content outputs a transmission signal in response to the input signal series; A modulation circuit that modulates a carrier wave with the output of the first memory and outputs it to the non-bell amplifier; a demodulation circuit that demodulates the output of the non-tsy # amplifier; A subtraction circuit that subtracts from the output, a correction amount generation path that generates a correction amount from the output of the key subtraction circuit, and an addition path that adds the output of the correction amount generation circuit to the first memory output. an adaptive modulation side L configured to adaptively change the content of the first memory by writing the output of the adder circuit to the first memory;