JP3153086B2 - Mobile satellite communication terminal transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmitter for amplifying a phase-modulated signal by a high-frequency power amplifier and transmitting the amplified signal in a microwave band, and more particularly to an AM / PM conversion distortion of the transmission power of a mobile satellite communication terminal. The present invention relates to a transmitter that reduces the transmission.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing a configuration of a conventional transmitter.

[0003] In the figure, the input data of the transmitter is:
These are orthogonal binary baseband signals, that is, two series of transmission data signals D _I and D _{Q including an} in-phase channel (I channel) and an orthogonal channel (Q channel).

[0004] These data both use NRZ signals.

A Nyquist filter 11 for removing high frequency components in a base band and a Nyquist filter 1
1 as an input and outputs a 4-phase modulated signal, and a modulation signal (Q
(PSK signal) into a high frequency band signal in a microwave band, and a high frequency power amplifier for transmitting a high output signal in the microwave band. Such a configuration is described in, for example, Japanese Patent Application Laid-Open No. Hei 3-171953.

[0006]

In general, in a QPSK signal which is not band-limited, the envelope of the modulated signal is a constant envelope, so that the influence of the nonlinearity of the transmission path (for example, AM-AM conversion, AM-PM conversion, AM is not amplitude modulated and PM is phase modulated).

However, the band-limited QPSK signal is
The envelope is no longer constant, and the spectrum is broadened due to the non-linear amplification characteristics of the power amplifier and affected by AM-PM conversion and the like, and the bit error rate characteristics are degraded. Therefore, in order to avoid the influence of non-linear amplification such as a power amplifier, a constant envelope modulation characteristic is required as much as possible. For the above operation, refer to “TDMA communication”
(Shuzo Kato et al., IEICE) is described in detail. The effect of such non-linearity of the power amplifier will be described with reference to FIG.

In FIG. 7, a four-phase phase modulator 13
In the output of (3), the band is limited using a three-band filter in order to suppress unnecessary spurious components in the wireless section and prevent interference with adjacent signals.

The modulated signal whose band has been limited is input to a high-frequency power amplifier 14. Since the power amplifier 14 used in the transmitter of the mobile satellite communication terminal needs to be particularly small in size and low in power consumption, it is desirable to use the input / output characteristics in the nonlinear amplification region as much as possible. However, when used in the non-linear region of the input / output characteristics, the amplitude of the output signal of the four-phase modulator 13 changes in accordance with the amplitude at each phase.
M-PM conversion distortion occurs, and the phase error of the transmission signal increases.

A transmission signal having this phase error is transmitted to another earth station via a satellite. If a demodulator on the receiving side demodulates the above-described modulated signal into two orthogonal I and Q channel data signals, a demodulation error of the quadrature detector directly occurs, which causes deterioration of the code error rate.

For example, when the power amplifier 14 uses a class B or class C high frequency FET amplifier and operates near the saturation point, the AM-PM conversion characteristic is 8 to 12 deg / dB.
Value.

As a result, the AM-P generated at the transmitter output
The M conversion distortion generates a phase error at the output of the demodulator on the receiver side, and when compared with the case of no distortion in theory, the value of Eb / No is about 0. 3dB
It will deteriorate.

Here, Eb / No is the ratio of the power per bit at the receiver input (1 W) to the noise power density at the receiver input (W / Hz).

[0014] This deterioration of Eb / No requires operation of the lowest possible Eb / No like satellite communication and transmission of a large amount of information. Therefore, it is necessary to review the line design and change the antenna dimensions. Was a major problem.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a mobile satellite communication terminal capable of transmitting data without being affected by AM-PM conversion distortion even when a power amplifier in a nonlinear region is used. To provide a transmitter.

[0016]

SUMMARY OF THE INVENTION Accordingly, the present invention provides
At the front stage of the four-phase phase modulator, there is provided an envelope equalizer that receives two series of Nyquist filter outputs and keeps the envelope on the orthogonal axis of the Nyquist filter outputs constant.

Since the amplitude of the output of the phase modulator can be made constant by inputting the output of the envelope equalizer to the four-phase phase modulator, the influence of the AM-PM conversion distortion by the large power amplifier is removed. Thus, the phase error can be reduced.
Note that this envelope equalizer uses a Nyquist filter
The entire waveform is unchanged without changing the shaped waveform itself.
Deterioration of intersymbol interference due to increase / decrease in width level
Of intersymbol interference by non-linear amplifier without noise
it can.

[0018]

FIG. 1 is a functional block diagram of a transmitter of a mobile satellite communication terminal used in the present invention. In the figure, the Nyquist filter 11, the four-phase modulator 13 and the power amplifier 14 are the same as those shown in FIG.

In this figure, the Nyquist filter 11
7 in that an envelope equalizer 12 is provided between the phase equalizer 13 and the four-phase modulator 13. In the figure, two series of transmission data signals D _I and D _Q are input to a Nyquist filter 11, and are equalized in waveform. Next, after the output of the Nyquist filter 11 is input to the envelope equalizer 12, the amplitude of each transmission data is fixed, and then the power amplifier 14
Is input to

Next, the function of the envelope equalizer 12 will be described in detail below.

That is, the envelope equalizer 12 converts the two-sequence data signal D _I 'whose waveform has been equalized by the Nyquist filter 11
D _Q enter ', has a function of converting the amplitude of each of the phase data signals D _I of two series of constant ", D _Q" on.

FIG. 2 is a diagram showing the phase points of the quadrature phase modulator 13 of the two-series data I and Q orthogonal to each other on a phase plane. The envelope equalizer 12 equalizes the trajectory (envelope) of each phase point with respect to the phase change so as to draw a circular trajectory in which the distance from the origin is always constant (the value of a shown in the figure). It has the function to do.

Next, FIG. 3 shows a specific example of the configuration of the envelope equalizer 12. In the figure, an input terminal A, the of B, orthogonal data D _I 'and D _Q' and are input.
X in FIG. 3 shows the phase points in one quadrant in this case. In this case, the point is different from the circular locus. In this equalizer, absolute values | D _I ′ | and | D _Q ′ | of the orthogonal data D _I ′ and D _Q ′ are obtained by the absolute value circuit 20. Each value is input to a divider 21 where a division operation of | D _I '| / | D _Q ' | is performed.

Therefore, D = | D _I ′ | / | D _Q ′ | (1) is obtained from the output of the divider 21.

Next, the output of the divider 21 is input to the arctangent calculator 22, based on the quotient D obtained by the divider 21, the phase angle of 'the data D _Q' data D _I and θ is calculated by the following relational expression.

Θ = tan ⁻¹ D = tan ⁻¹ (| D _I ′ | / | D _Q ′ |) (2) The output of the arc tangent calculator 22 is sent to a cosine calculator 23 and a sine calculator 24, respectively. Is entered.

Since the distance a from the origin is known in FIG. 3, the cosine calculator 23 performs the following calculation so as to draw a constant locus using the phase angle θ, and outputs the output data DI
″ Get.

D _I ″ = a × cos θ (3) Similarly, the sine calculator 24 performs the following calculation to draw a constant trajectory.

D _Q ″ = a × sin θ (4) As a result, the output of the envelope equalizer 12 is converted into data of the phase point Y in FIG.

As a result, the data Y is a distance a from the origin.
Can draw a constant circular locus.

Here, the cosine calculator 23 and the sine calculator 24 multiply the distance a from the origin by the formulas (3) and (4), but this multiplication processing is unnecessary by normalizing in advance. You can also.

Next, a specific configuration of the envelope equalizer 12 is shown in FIG.

In this figure, two orthogonal data D _I ′ and D _Q ′ input to input terminals 34 and 35 are input. In this drawing, for example, each data signal is a parallel 8-bit data signal.

These data signals are divided into 1-bit sign bits 36 and 37 and 7-bit information bits 38 and 39.

The seven information bits 38 and 39 are input to absolute value conversion circuits 42 and 43, respectively, and the absolute value | D _I '
|, | D _Q ′ | are calculated.

The output signals of the absolute value conversion circuits 42 and 43 are
Each of them is combined to form a 14-bit signal in ROM
32.

The ROM 32 has absolute value conversion circuits 42 and 43
Using the absolute values | D _I ′ | and | D _Q ′ | determined by the above as addresses (14 bits), the following values giving a previously stored circular locus are output as data.

| Cos (tan ⁻¹ (| D _I ′ | / | D _Q ′ |) | (5) | sin (tan ⁻¹ (| D _I ′ | / | D _Q ′ |) | (6) Assuming that the output of the ROM 12 is 16-bit data, the data is 16 bits for an input address of 14 bits, so that the output can be realized with a capacity of about 256 kbits. Are separated into sign bits 36 and 3 respectively.
7 is multiplied by the multiplication circuits 31 and 33.

As a result, orthogonal data D _I ″ and D _Q ″ are obtained in which the distance from the origin of the envelope is always constant.

Next, another embodiment of the envelope equalizer 12 will be described with reference to FIG.

The two series of data outputs D _I ′ and D _Q ′ of the Nyquist filter 11 are input to an envelope calculator 53.

The envelope calculator 53 obtains the distance R from the origin according to the following calculation formula.

[0043]

The output R of the envelope calculator 53 is divided by the divider 5
1, 52. Since the dividers 51 and 52 also receive the two series of data DI 'and DQ', respectively,
The following division processing is performed to obtain DI ″ and DQ ″. Here, from the origin of the two series of data DI ", DQ"
Is normalized to be 1.

DI ″ = DI ′ / R (8) DQ ″ = DQ ′ / R (9) As a result, orthogonal data DI ″ and DQ ″ signals whose distance from the origin of the envelope is always constant can be obtained. it can.

In the embodiment described above, the configuration using the four-phase phase modulator has been described. However, it is obvious that the present invention is not limited to the four-phase phase modulation but can be similarly applied to other digital modulation systems.

For example, FIG. 6 shows a 16-phase phase modulation (16P
SK).

In the figure, reference numeral 61 denotes a 16-phase mapper for decomposing the input digital signals D _{1 to} D ₄ into two orthogonal components D _I and D _Q.

[0049] 62 and 63 are Nyquist filters 62 and 63 to eliminate high frequency components of D _I component or D _Q components decomposed by the 16 phase mapper.

The outputs of the Nyquist filters 62 and 63 are
After being input to the envelope equalizer 12 and equalizing the distance from the origin to be constant, data D _I ″ and D _Q ″ are obtained.
The signal is input to the PSK modulator 60 and amplified by the power amplifier 14 as a high-frequency signal to obtain a transmission wave.

[0051]

As described above, in the transmitter used in the mobile satellite communication terminal of the present invention, the amplitude of the output of the phase modulator is kept constant, so that the AM-PM conversion of the high-frequency power amplifier is performed. Even if the distortion is large, it is not affected, so that the phase error can be reduced.

By using the transmitter of the present invention, even in a class C high-frequency amplifier used in the non-linear region, the amplitude component of the output of the transmission filter is subjected to waveform equalization by a simple envelope equalizer, so that the code can be obtained. Since it is possible to operate in a region where the back-off is small without increasing the interference between the terminals, there is an effect of realizing the small size and low power consumption required for the mobile satellite communication terminal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing waveforms on the orthogonal axis of each phase point of the configuration shown in FIG.

FIG. 3 is a block diagram showing a first embodiment of the envelope equalizer shown in FIG. 1;

FIG. 4 is a diagram illustrating a specific configuration of an envelope equalizer illustrated in FIG. 3;

FIG. 5 is a block diagram showing a second embodiment of the envelope equalizer shown in FIG. 1;

FIG. 6 is a block diagram of a second embodiment in which the phase modulator of the present invention is applied to a 16-phase phase modulator.

FIG. 7 is a block diagram illustrating a configuration of a transmitter of a conventional mobile satellite communication terminal.

[Explanation of symbols]

 Reference Signs List 11 Nyquist filter 12 Envelope equalizer 13 Four-phase modulator 14 Power amplifier 20 Absolute value circuit 21 Divider circuit 22 Arc tangent calculator 23 Cosine calculator 24 Sine calculator 31 Multiplier 32 ROM 33 Multiplier 34, 35 Data Input terminals 36, 37 Sign bit data 40, 41 Data output terminals 42, 43 Absolute value conversion circuits 51, 52 Divider 53 Envelope calculator 60 16-phase modulator 61 16-phase mapper 62, 63 Nyquist filter

Claims (4)

(57) [Claims] 1. A transmitter for use in a mobile satellite communication terminal, comprising: a Nyquist filter for inputting two series of orthogonal data and removing high frequency components; and a two-series orthogonal data output of the Nyquist filter.
An envelope equalizer that keeps the distance from the origin of the envelope constant when displaying an orthogonal axis based on the phase angle between data, and a phase modulation that inputs an output signal of the envelope equalizer and performs phase modulation. A transmitter for a mobile satellite communication terminal, comprising: a transmitter; and a high-power amplifier that receives an output signal of the phase modulator, converts the signal into a high-frequency signal, and transmits the signal with high power. 2. The envelope equalizer receives an input of the two series of filter outputs, and calculates an absolute value circuit for calculating an absolute value of each of the two series of filter outputs; a division circuit that divides an output of the absolute value circuit; An arc tangent calculator for calculating an arc tangent and calculating a phase angle of the data of the two series of filter outputs, a cosine calculator for calculating a cosine value of the phase angle, and a sine value of the phase angle And obtaining two orthogonal data signals each having a constant distance from the origin of the envelope based on the output data of the cosine calculator and the sine calculator. The transmitter for a mobile satellite communication terminal according to claim 1, wherein 3. The envelope equalizer receives two orthogonal data sequences of the Nyquist filter output, separates them into information data and code bits, and calculates an absolute value of the information data. A second absolute value conversion circuit; and a composite value of a phase angle of an output signal of the first and second absolute value conversion circuits, and a sine value for the phase angle stored in advance using the composite data as an address; 3. The moving device according to claim 2, further comprising: a ROM for reading cosine value data; and a multiplying circuit for separating output data from the ROM into two series of information data, and multiplying the information data by the sign bit. A communication device for a satellite communication terminal. 4. An envelope equalizer that receives two orthogonal data sequences of the Nyquist filter output and calculates a mean square of each of the data, and an output signal of the envelope calculator. the 2 and a divider for dividing each of the series of data, the divider output at the claim 2, wherein the outputting the data signal to be orthogonal envelope equalized two series of Communication equipment for mobile satellite communication terminals.