JPH066394A - Encoding and modulating device - Google Patents

Abstract

PURPOSE:To lower the amplitude variation and decrease the power consumption by converting an encoded signal into a modulated wave complex envelope, and suppressing the amplitude variation of a sample value and performing modulation. CONSTITUTION:A phase converter 11 converts the data series outputted by a convolutional encoder 82 into a signal phase phia. A phase difference detector 13 detects the phase difference between the signal phase phia at specific time ta and a signal phase at time tn-1 which is obtained one symbol before through a delay unit 12. A phase computing element 14 calculates the quantity Sa of signal phase variation by using the phase difference thetan and performs specific signal conversion corresponding to the calculated value to make the amplitude constant. Then the amplitude vairation is suppressed and an orthogonal modulator 84 performs modulation by using the continuous waveform of the complex envelope. Consequently. a nonlinear amplifier which has high power efficiency is usable, so the amplitude variation is reduced and the power consumption is reducible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coding / modulating apparatus which adopts a modulation system in which a convolutional coding system and a digital modulation system are combined in digital communication.

[0002]

2. Description of the Related Art A coded modulation system can realize excellent transmission characteristics because of its high coding gain. For example, Trellis-Coded 8-Phase Phase Modulation
8 PhaseShift Keying: TC8PSK) can theoretically obtain a coding gain of about 3 dB in the same band as QPSK (G. Ungerboeck, "Channel coding wit
hmultilevel / phase signals ", IEEE Trans.Inf. Theory,
vol.IT-28, No.1, pp55-67, Jan.1982).

FIG. 8 is a block diagram showing an example of the configuration of a conventional TC8PSK coding and modulating apparatus. In the figure, input data is a serial / parallel (S / P) converter 81.
_Are converted into two data sequences x _n (x _1n , x _2n ) and input to the convolutional encoder 82. An example of the convolutional encoder 82 is shown in the above document, and its circuit configuration is shown in FIG. Here, three delay circuits (T) 91
˜93 and two exclusive OR circuits 94 and 95, and the output data series y _n is (y _0n , y _1n , y _2n )
Then, the relationship between the input and output is y _0n = x _{1, n-1} (1a) y _1n = x _{1, n-2} * x _2n (1b) y _2n = x _1n * x _{2, n-} It becomes ₁ … (1c). However, * represents an exclusive OR.

The data sequence y _n output from the convolutional encoder 82 is input to the IQ converter 83 and converted into modulated wave complex envelope signals I (t) and Q (t). In the process, first, y _n is mapped onto the signal phase φ _n of 8-phase PSK shown in FIG. Here, the relationship between φ _n and y _n is φ _n = −22.5 ° + 45 ° a _n (2) However, a _n = 4y _2n + 2y _1n + y _0n (3)

When the amplitude is r, the modulated wave complex envelope signals I (t _n ) and Q (t _n ) at the time point of t = t _n are I (t _n ) = r cos (φ) from this signal phase φ _{n. n) ... (4a) Q (} t n) = rsin (φ n) can be obtained as ... (4a). Waveforms at times other than t = t _n are created from these values to generate continuous waveforms I (t) and Q (t). As a method of generating a continuous waveform, for example, from t = t _n to t = t _{n + 1,} I (t _n ) and Q (t _n ) are respectively generated.
It is made constant by using the value of.

The modulated wave complex envelope signals I (t) and Q (t) obtained by the IQ converter 83 are input to the quadrature modulator 84.
The quadrature modulator 84 generates a modulated wave by quadrature modulation using the local oscillation signal output from the oscillator 85. In order to limit the band of the modulated wave, the band of the modulated wave complex envelope signals I (t) and Q (t) may be roll-off limited. FIG. 11 shows a signal space locus of a conventional TC8PSK signal band-limited by the root roll-off (roll-off rate 0.5).

[0007]

By the way, in the coded modulation wave output from the conventional coded modulation device, the amplitude fluctuation is unavoidable as shown in FIG. When a modulated wave having such amplitude fluctuation is transmitted, in order to amplify the modulated wave without widening the band, a transmission power amplifier having high linearity is required. However, linear amplifiers are generally less power efficient than non-linear amplifiers such as class C amplifiers operating in the saturation region.

Therefore, it has been difficult to use the coded modulation method in the modulation device whose power consumption is limited. In other words, it is essential to sufficiently suppress the amplitude fluctuation of the coded modulation wave in order to enable the use of a non-linear amplifier with high power efficiency, and how to improve the power efficiency even when using a linear amplifier. Was a challenge.

An object of the present invention is to provide an encoding / modulating apparatus capable of suppressing the amplitude fluctuation of an encoded modulated wave and reducing the power consumption in the transmission power amplifier in the subsequent stage.

[0010]

According to the present invention, convolutional coding means for generating a convolutional coded signal from input data, and the convolutional coded signal is converted into a modulated wave complex envelope sample value, and the sampled value A signal conversion unit that generates a continuous waveform of a complex envelope after suppressing the amplitude variation,
And a modulation unit that performs modulation using a continuous waveform of the complex envelope.

[0011]

According to the present invention, the convolutionally coded signal is converted by the signal converting means into the modulated wave complex envelope sample value, and the amplitude variation of this sample value is suppressed. Then, the amplitude fluctuation of the coded modulated wave can be suppressed within a predetermined range by converting the modulated wave complex envelope signal into a continuous waveform and performing the modulation process.

[0012]

1 is a block diagram showing the configuration of a first embodiment of the present invention. In the figure, serial / parallel (S /
P) converter 81, convolutional encoder 82, quadrature modulator 84
The oscillator 85 is the same as the conventional one.

The feature of the present invention lies in that in this embodiment, a phase converter 11, a delay device (T) 12, a phase difference detector 13, and a phase calculator are used as signal converting means in place of the conventional IQ converter 83. 14, adder 15 and waveform converter 1
A constant-amplification TC8 that includes 6 and has a constant amplitude.
It is configured to output a PSK signal.

The phase converter 11 converts the data sequence y _n output from the convolutional encoder 82 into the 8-phase PSK signal phase φ _{n shown} in FIG. The relationship between φ _n and y _n is as shown in equations (2) and (3). Phase difference detector 13, a signal phase phi _n at time t _n, the phase difference between the time t _n-1 of the signal phase phi _n-1 corresponding to before one symbol obtained through the delay unit 12 theta _n ( However, | θ _n | ≦ 180 °) is detected.

The phase calculator 14 uses this phase difference θ _n to change the signal phase from φ _{n-1 at} time t _n-1 + t _m (0 <t _m ≤t _n -t _n-1 ). Calculate δ _m . For example,
When the value of a _n changes from 0 to 3, the conventional TC8
In the PSK signal, the signal changes as shown by the dotted line in FIG. 2, but constant amplitude is realized by changing the signal as shown by the solid line in accordance with the signal phase change amount δ _m calculated by the phase calculator 14. can do. As an example of a function for obtaining δ _m from φ _n-1 in the phase calculator 14, when the symbol rate is 1 / T _S and the roll-off rate is α,

[0016]

[Equation 1]

There is a raised cosine function according to When this function is used, the phase change becomes smooth and it becomes possible to narrow the spectrum band. Figure 3 shows how the phase changes according to Eq. (5). Note that the normal TC8PSK signal has a rectangular phase change, which corresponds to the case of α → 0 in the equation (5).

In the adder 15, this signal phase change amount δ _m
Is added to φ _n−1 to obtain the signal phase p _nm . Also, θ _n
= 180 °, the rotation direction of the signal is indefinite, but this rotation direction is the same as the rotation direction of the signal immediately before in this embodiment. For example, the value of a _n is 0 → 1 → 5
4 changes as shown in FIG. 4, the rotation direction of 1 → 5 is counterclockwise as in 0 → 1.

In the waveform converter 16, the modulated wave complex envelope signals I (t _n-1 + t _m ), Q (at the time t _n-1 + t _m such that the signal amplitude becomes r from the signal phase p _nm. t _n-1 + t _m )
Can be calculated as I (t _n-1 + t _m ) = r cos (p _nm ) ... (6a) Q (t _n-1 + t _m ) = rsin (p _nm ) ... (6a) where r is the amplitude. it can. From these values, continuous waveforms I (t) and Q (t) are generated. The continuous wave generation method is
For example, from t = t _n-1 + t _m to t = t _n-1 + t _{m + 1} , the values of I (t _n-1 + t _m ) and Q (t _n-1 + t _m ) are used as constant values. To do.

The quadrature modulator 84 quadrature-modulates the modulated wave complex envelope signals I (t) and Q (t) to generate a modulated wave. Therefore, the envelope of the modulated wave becomes constant, and a non-linear amplifier such as a class C amplifier having high power efficiency can be used as the power amplifier for transmission, and the power efficiency can be improved as compared with the conventional case.

FIG. 5 is a block diagram showing the configuration of the second embodiment of the present invention. In the figure, serial / parallel (S
/ P) converter 81, convolutional encoder 82, quadrature modulator 8
4 and oscillator 85 are similar to conventional ones.

In this embodiment, a T / 2 sample IQ value converter 51, an amplitude limit converter 52, and an interpolation waveform generator 53 are provided as signal converting means in place of the conventional IQ converter 83.

In the T / 2 sample IQ value converter 51, T
/ 2 band-limited modulated wave complex envelope signal I (t), Q
Find the sample value of (t). In the amplitude limiting converter 52,
The minimum value R _min of the allowable amplitude is set, and when the amplitude is smaller than R _min in the sample value output from the T / 2 sample IQ value converter 51, the sample value is corrected. In this embodiment, for the sampled values I ₁ and Q ₁ ,
The new sample values I ₂ and Q ₂ are set to I ₂ = I ₁ (R _min / r ₁ ) ... (7) Q ₂ = Q ₁ (R _min / r ₁ ) ... (8) However, r ₁ = (I ₁ ² + Q ₁ ² ) ^1/2 (9). For example, as shown in FIG. 6, when the signal point moves from 0 to 3, a new sample point S ₂ is set when the amplitude of the intermediate sample point S ₁ is smaller than the minimum value R _min .

The interpolated waveform generator 53 interpolates a value from the sample value corrected by the amplitude limiting converter 52 with a T / 2 sampling function to obtain a continuous waveform I.
Generate (t) and Q (t). The quadrature modulator 84 performs quadrature modulation using the modulated wave complex envelope signals I (t) and Q (t) to generate a modulated wave.

FIG. 7 shows the signal space locus of the TC8PSK signal of the second embodiment of the present invention band-limited by the root roll-off (roll-off rate 0.5) when R _min /r=0.25. It can be seen that the amplitude fluctuation is limited compared to the conventional signal space locus shown in FIG. Linear amplifiers are generally less power efficient when the input amplitude is small, so
In the case of amplifying the TC8PSK signal of this embodiment in which there is no signal point whose amplitude is close to 0, the power efficiency can be improved even in the linear amplifier as compared with the case of amplifying the conventional TC8PSK signal.

The amplitude limiting converter in the second embodiment
At 52, the amplitude is R_minCorrect for smaller ones
The amplitude fluctuation is limited by
Value R _maxIf it is larger, the value is corrected and the amplitude peak
Method to limit the amplitude fluctuation by suppressing the
Very good. Normally, in a linear amplifier such as a class A amplifier,
The power supplied to the amplifier needs to exceed the output peak power.
Therefore, in this case, the peak value of the amplitude is suppressed.
Power supply can be reduced, resulting in improved power efficiency
Can be planned.

Incidentally, the method of suppressing both the amplitude exceeding the upper limit and the amplitude lower than the lower limit with respect to the predetermined range can similarly improve the power efficiency in the linear amplifier.

[0028]

As described above, the coded modulation apparatus of the present invention can limit the amplitude fluctuation of the coded modulated wave and can use a non-linear amplifier having high power efficiency, or a linear amplifier. It is possible to improve the power efficiency in.

Therefore, it is possible to apply the coded modulation method even to a modulation device whose power consumption is limited. For example, even in the case of a mobile phone that uses a battery as a power source and the usable power is limited, such as a mobile phone in mobile communication, a coding modulation method with a high coding gain can be used, which can contribute to improvement of transmission characteristics. .

[Brief description of drawings]

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

FIG. 2 is a diagram illustrating a signal transition method according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an example of a phase transition function of the first embodiment of the present invention.

FIG. 4 is a diagram showing an example of signal transition according to the first embodiment of the present invention.

FIG. 5 is a block diagram showing the configuration of a second embodiment of the present invention.

FIG. 6 is a diagram illustrating a signal transition method according to the second embodiment of the present invention.

FIG. 7 is a diagram showing an example of a signal space locus of a TC8PSK signal according to the second embodiment of the present invention.

FIG. 8 is a block diagram showing a configuration example of a conventional TC8PSK coding and modulating apparatus.

FIG. 9 is a block diagram illustrating a configuration example of a convolutional encoder.

FIG. 10 is a diagram showing a phase arrangement of TC8PSK signals.

FIG. 11 is a diagram showing an example of a signal space locus of a conventional TC8PSK signal.

[Explanation of symbols]

 11 phase converter 12 delay device (T) 13 phase difference detector 14 phase calculator 15 adder 16 waveform converter 51 T / 2 sample IQ value converter 52 amplitude limit converter 53 interpolation waveform generator 81 serial / parallel ( S / P converter 82 Convolutional encoder 83 IQ converter 84 Quadrature modulator 85 Oscillator 91-93 Delay circuit (T) 94, 95 Exclusive OR circuit

Claims (1)

[Claims] 1. Convolutional coding means for generating a convolutional coded signal from input data; converting the convolutional coded signal into a modulated wave complex envelope sample value; and suppressing an amplitude variation of the sample value. An encoding / modulating apparatus comprising: a signal converting unit that generates a continuous waveform of a complex envelope and a modulating unit that performs modulation using the continuous waveform of the complex envelope.