Amplitude-modulated Eight-phase Phase-modulation System

Abstract

A multiple modulation system for obtaining an amplitude-modulated eight-phase phase-modulated wave employed for transmitting three channels of binary information, in which the amplitude of an eight-phase phase-modulated wave is deviated by substantially six decibels when the eight-phase phase-modulated wave assumes any of four phase-positions alternately predetermined from possible eight-phase positions.

Description

This invention relates generally to multiple modulation systems and, more particularly, to an amplitude-modulated phase-modulation system in which eight-phase phase-modulation and amplitude-modulation are combined.

In conventional phase-modulation systems, any one kind of two quantum phase positions, four quantum phase positions, eight quantum phase positions, - 2.sup.n quantum phase positions ("n" is the number of channels to be transmitted) is employed to meet with requirement for the signal-to-noise ratio and error rate. The quantity of transmitted information can be increased, in view of the requirement for a constant error rate, by increasing the number of quantum phase positions in accordance with an increase of the signal-to-noise ratio. In this case, extension from the two quantum phase-positions to four quantum phase-positions can be performed as described in detail below by improving the signal-to-noise ratio by three decibels for doubling the quantity of transmitted information, since there is no interference between channels transmitted by a four-phase phase-modulated wave due to an orthogonal relationship among the four quantum phase positions. However, since there are no plane vectors having orthogonal relationship in eight quantum phase positions, extension from four quantum phase positions to eight quantum phase positions can not be performed by improving the signal-to-noise ratio by three decibels due to mutual interference among the transmitted channels. Accordingly, the signal-to-noise ratio must be increased by 5.34 decibels to increase by 50 percent the quantity of transmitted information.

An object of this invention is to provide a multiple-modulation system for producing a phase-modulated telegraphic wave having the same quantity of transmitted information as an ordinary eight-phase phase-modulated wave and obtainable of the same error rate as an ordinary eight-phase phase-modulated wave in a signal-to-noise ratio lower than the ordinary eight-phase phase-modulated wave.

The principle, construction and operations of this invention will be understood from the following detailed discussion taken in conjunction with accompanying drawings, in which the same or equivalent parts are designated by the same reference numerals, characters and symbols, and in which:

FIGS. 1, 2 and 3 are vector diagrams respectively explanatory of necessary power for two-phase, four-phase and eight-phase phase modulation in conventional manner;

FIG. 4 is a vector diagram explanatory of the principle of this invention;

FIG. 5 is a vector diagram explanatory of the modified principle of this invention;

FIG. 6 is a vector diagram explanatory of assignment of codes to different phase-positions;

FIG. 7 is a block diagram illustrating an embodiment of this invention;

FIGS. 8 and 10 are block diagrams explanatory of examples of circuits used in the embodiment shown in FIG. 7;

FIG. 9 is a diagram of waveforms or time chart explanatory of operations of the example shown in FIG. 8;

FIG. 11A and 11B are block diagrams each illustrating another embodiments of this invention;

FIGS. 12 and 13 are vector diagrams explanatory of the principle for demodulating an amplitude-phase modulated wave produced in accordance with this invention;

FIG. 14 is a block diagram illustrating an example of a circuit for demodulating an amplitude-phase modulated wave produced in accordance with this invention; and

FIG. 15 is a block diagram illustrating another example of a circuit for demodulating an amplitude-phase modulated wave produced in accordance with this invention.

With reference to FIGS. 1, 2 and 3 showing vector diagrams for two-phase, four-phase and eight-phase phase-modulated waves respectively, the electric power of a carrier wave is increased for noise balls having the same diameter for maintaining a constant error rate. If it is assumed that the radius of the noise ball is equal to one, respective amplitudes for two-phase (2 .phi.), four-phase (4 .phi.) and eight-phase (8 .phi.) modulated waves become as follows: A.sub.2.sub..phi. = 1; A.sub. 4.sub..phi. = .sqroot.2 ; and A.sub.8.sub..phi. = 1/sin .pi. /4. The above amplitudes A.sub.2.sub..phi., A.sub.4.sub..phi. and A.sub.8.sub..phi. correspond respectively to 0 decibel, 3 decibels and 8.34 decibels in term of power. In other words, power-up of 5.34 decibels is necessary to increase by 50 percents (1.75 decibels in term of power) the quantity of transmitted information in a case of extension from four-phase phase modulation to eight-phase phase-modulation as mentioned above.

With reference to FIG. 4 showing a vector diagram of a phase-modulated wave produced in accordance with the basic principle of this invention, four vectors are further provided in addition to four quantum phase positions so that all noise balls are contacted with adjacent noise balls. In this case, each longer vector has a value (1 +.sqroot.3) while each shorter vector has a value .sqroot.2 . If it is assumed that any of all the vectors are successively selected at random in accordance with phase-modulation, an average power becomes 6.75 decibels which is lower by 1.59 decibels in comparison with conventional eight-phase phase-modulation. However, since reference carrier waves for detecting each one of the eight-quantum phase positions have not a simple relationship, such as orthogonal or parallel relationship, as shown in FIG. 4 by dotted lines, detection of this phase-modulated wave is not easy.

To improve overcoming of the above mentioned difficulty, four longer vectors are modified as shown in FIG. 5 so that phase-positions of reference carrier waves shown by dotted lines make an angle of 45.degree. or 90.degree. with respect to a vector of the phase-modulated wave. In this case, each longer vector has a value 2.sqroot.2, while each shorter vector has a value .sqroot.2. An average power of this phase-modulated wave is equal to 6.99 decibels, which is improved by 1.35 decibels in average power in comparison with a conventional eight-phase phase-modulated wave.

Eight binary codes formed by binary information "0" and "1" of channels A, B and C are assigned, as shown in FIG. 6, to eight vectors respectively. In each binary code, three bits of binary information are representative of channels A, B and C from left to right.

With reference to FIG. 7, an example of a multiple modulator of this invention comprises an oscillator 1, an eight-phase phase modulator comprising a frequency divider 2 and a selector 3, an attenuation circuit 4 employed as an amplitude-modulator, a low-pass filter 5 and an amplifier 6. The oscillator 1 generates a wave 100 having a frequency equal to eight-times a desired frequency of a carrier wave. The frequency divider 2 divides the frequency of the wave 100 to one-eighth, so that eight rectangular waves 113 having successive phase delay of 45.degree. between adjacent two thereof are obtained. The selector 3 selects one of the eight rectangular waves 113 in accordance with a combination of respective states ("0" or "1") of input channels A, B and C so as to meet with conditions shown in FIG. 6. The attenuation circuit 4 attenuates by 6 decibels the output 114 of the selector 3 only when the channel C assumes the state "0". Accordingly, the output 114 of the selector 3 passes through the attenuation circuit 4 without any attenuation when the channel C assumes the state "1". Since longer vectors and shorter vectors shown in FIG. 6 are sufficient to have relative levels to each other, an amplifier having a gain of 6 decibels can be replaced in place of the attenuation circuit 4. The low-pass filter 5 is employed to eliminate harmonic components higher than the third higher harmonic component. At the output of the low-pass filter 5, an amplitude-phase modulated sinusoidal wave 116 is obtained and applied to the amplifier 6 as an output wave 117.

With reference to FIG. 8, an example of the frequency divider 2 comprises a schmit trigger circuit 7, bistable circuits (e.g.; flip-flop circuits) 8a, 8b, 8c, 8d, 8e, 8f and 8g and a matrix circuit 9. With reference to FIG. 9, the output 100 of the oscillator 1 is reshaped as a rectangular wave 101 by the schmit trigger circuit 7. The rectangular wave 101 is frequency-demultiplied by a scale-of-8 counter comprising three bistable circuits 8a, 8b and 8c. Respective outputs 102, 103 and 104 are applied to the matrix 9, which generates eight pulse trains 105, 106, 107, 108, 109, 110, 111 and 112 having different timing. The eight outputs of the matrix 9 are reshaped by four bistable circuits 8d, 8e, 8f and 8g so as to produce eight rectangular waves 113 having successive phase differences of .pi./4.

With reference to FIG. 10, an example of the selector 3 comprises a matrix 10 and a gate circuit 11 including eight AND gates, while an example of the attenuation circuit 4 comprises a NAND gate 12, and AND gate 13 and an attenuator 14. The matrix 10 generates an output "1" at one of eight output lines in accordance with an instant combination of states of the channels A, B and C. One of the eight AND gates is opened in the gate circuit 11 so as to correspond to the output "1" of the matrix 10, so that an output 114 is obtained by passing one of the eight rectangular waves 113. Either the NAND gate 12 or the AND gate 13 is opened in accordance with the state of the channel C, so that the output 114 of the selector 3 is converted to the signal 115 by passing through the attenuator 14 in response to opening of the NAND gate 12 and by transmit without passing through the attenuator 14.

With reference to FIG. 11A, another example of the eight-phase phase modulator comprises three phase-shifters 16, 17 and 18 which have shift angles .pi., .pi./2 and .pi./4 respectively. While phase modulation is performed by use of digital technique in the example shown in FIG. 7, phase modulation is performed by use of an analogue technique in this example. A wave 120 generated from an oscillator 15 has a frequency equal to the frequency of A wave 120, a desired carrier wave, and the phase position of the wave 120 is shifted by a value n. .pi./4 (where n = 0, 1, - or 7) in accordance with an instant combination of respective states of the channels A, B and C. Operations in an attenuation circuit 19 and an amplifier 20 are performed similarly to the operations in the circuits 4 and 6 in FIG. 7. An attenuator provided in the attenuation circuit 19 may be replaced by an amplifier having a gain of 6 decibels.

With reference to FIG. 11B, another embodiment of this invention comprises an oscillator 15, a .pi./4 phase-shifter 40, an attenuation circuit 41, four-phase phase modulators 42-1 and 42-2, a selector 43, and amplifier 20. A carrier wave 120 generated from the oscillator 15 is phase-shifted by .pi./4 in the phase-shifter 40, and the output 160 of the phase shifter 40 is attenuated one-half in amplitude in the attenuation circuit 41. The output 170 of the attenuation circuit 41 is four-phase phase-modulated in the four-phase phase-modulator 42-1 in accordance with an instant combination of respective states of channels A and B, while the carrier wave 120 is four-phase phase-modulated in the four-phase phase-modulator 42-2 in accordance with an instant combination of respective states of channels A and B. Accordingly, a phase-modulated wave 180 obtained from the four-phase phase-modulator 42-1 has an amplitude equal to one half the amplitude of a phase-modulated wave 190 obtained from the four-phase phase-modulator 42-2. Possible four phase positions of the phase-modulated wave 180 have phase-difference of .pi./4 with respect to possible four phase positions of the phase-modulated wave 190. The selector 43 selects the phase-modulated wave 180 or 190 in accordance with the state "0" or "1" of the channel C so as to produce a wave 191. The wave 191 is amplified in the amplifier 20 for obtaining an output wave 192 whose vectors can be indicated as a vector diagram shown in FIG. 6. The attenuation circuit 41 may be replaced by an amplifier having a gain of 6 decibels. The phase shifter 40, the attenuation circuit 41 and the four-phase phase-modulator 42-1 may be arranged in another order among them.

Demodulation operation of an amplitude-phase modulated wave generated in accordance with this invention will be described below. A vector plane is divided into eight-zones (I), (II), (III), (IV), (V), (VI), (VII) and (VIII) as shown in FIG. 12 by threshold lines which correspond to dotted lines shown in FIG. 5. A demodulated code representative of respective states of output channels Aa, Ba and Ca is obtained by detecting one of the eight zones (I) to (VIII) in which the vector V of a transmitted amplitude-phase modulated wave is included. The transmitted amplitude-phase modulated wave is phase-detected by use of four reference waves Ra, Rb, rc and Rd as shown in FIG. 12 and then integrated for each signal element, so that four voltages x, y, a and b are obtained for the vector of the transmitted amplitude-phase modulated wave as shown in FIG. 13 with respect to four reference waves Ra Rb, Rc and Rd. In this case, if both of respective absolute values of the vectors x and y exceed a threshold voltage Vs, the vector V of the transmitted amplitude-phase modulated wave is included in any of four zones (V), (VI), (VII) and (VIII). Thereafter, one of the four zones (V), (VI), (VII) and (VIII) can be determined in accordance with possible four combinations (+,+), (+,-), (-,-) and (-,+) of polarities of the vectors x and y. If at least one of respective absolute values of the vectors x and y is smaller than the threshold voltage Vs, the vector V of the transmitted amplitude-phase modulated wave is included in any of other four zones (I), (II), (III) and (IV). Thereafter, one of the four zones (I), (II), (III) and (IV) can be determined in accordance possible four combinations of polarities of the vectors a and b. Accordingly, demodulation is performed so as to obtain output codes in accordance with conditions shown in FIG. 6.

With reference to FIG. 14, an example of a circuit for demodulating an amplitude-phase modulated wave produced in accordance with this invention comprises four phase detectors 21, four integrators 22, four polarity detectors 23, two full-wave rectifier 24, two voltage comparators 25, an AND circuit 26, a logic circuit 27, .pi./2 phase shifters 28a and 28b, and a .pi./4 phase shifter 29. A signal 131 corresponding to the reference wave Rx shown in FIG. 12 is shifted by the .pi./2 phase shifter 28a, by the .pi./4 phase shifter 29, and by the .pi./2 phase shifter 28b and the .pi./4 phase shifter 29, so that reference waves 132, 133 and 134 corresponding respectively to the reference waves Rv, Ra and Rb are obtained. A received wave 130 is phase-detected by the four detectors 21 by the use of the four reference waves 131, 132, 133 and 134 respectively, and respective detected outputs of the phase detectors 21 are integrated for each signal element in a start-stop manner. Respective outputs 135, 136, 137 and 138 of the integrator 22 correspond vectors x, y a and b respectively shown in FIG. 13. Respective polarities of the outputs 135, 136, 137 and 138 are detected by the polarity detectors 23, so that detected outputs X, Y, .alpha. and .beta. respectively indicated by reference numerals 142, 143, 144 and 145 and corresponding to binary codes "1" (plus polarity) or "0" (minus polarity) of the vectors x, y, a and b are obtained. Respective absolute values of the vectors x and y are obtained by rectifying the integrated outputs 135 and 136 by the full-wave rectifiers 24. Accordingly, rectified outputs 139 and 140 correspond respectively values .vertline.x.vertline. and .vertline.y.vertline.. The rectified outputs 139 and 140 are compared with a reference 150 corresponding the reference voltage Vs in voltage comparators 25, each of which generates an output "1" when the rectified output 139 or 140 exceeds the reference voltage Vs. The output 141 of the AND gate 26 assumes the state "1" if both outputs of the voltage comparators 25 and 26 assume the state "1" in conditions: .vertline.x.vertline. > vs and .vertline.y.vertline. > Vs . In the following description, the output 141 of the AND gate 26 is indicated by a reference Z. The logic circuit 27 determines states of output channels Aa, Ba and Ca in accordance with combinations of states of the rectified output 142 (X), 143(Y), 144 (.alpha.) and 145 (.beta.) and the output 141 (Z) of the AND gate 26 as shown in Table 1 of a truth table. Logic operations in this truth table are indicated as follows:

Aa = .beta. Z + Y Z

Ba = .alpha. Z + X Z

Ca = Z --------------------------------------------------------------------------- TABLE 1

Zone Aa Ba Ca X Y .alpha. .beta. Z __________________________________________________________________________ (I) 0 0 0 * * 1 1 0 (V) 0 0 1 1 1 * * 1 (II) 0 1 0 * * 0 1 0 (VI) 0 1 1 0 1 * * 1 (IV) 1 0 0 * * 1 0 0 (VIII) 1 0 1 1 0 * * 1 (III) 1 1 0 * * 0 0 0 (VII) 1 1 1 0 0 * * 1 __________________________________________________________________________

With reference to FIG. 15, another example of a circuit for demodulating an amplitude-phase modulated wave comprises circuits 21 to 28 similar to those shown in FIG. 14, and an adding & subtracting circuit 30. Components a and b of the vector V are not independent from components x and y but indicated as follows:

a = (y + x)/.sqroot. 2

b = (y - x)/.sqroot.2

Accordingly, values corresponding to integrated results 137 and 138 can be obtained by performing the above logic operations in the adding & subtracting circuit 30 from the integrated results 135 and 136. In this case, since components a and b are employed for polarity detection, the value .sqroot.2 of the denominator is not to be absolutely fixed. Accordingly, the above equation may be modified as follows:

a' = y + x

b' = y - x

Therefore, if a sum (y + x) and a difference (y - x) are produced as outputs 151 and 152 from the adding & subtracting circuit 30, succeeding operations can be performed in the same circuits 23 to 27 as the example shown in FIG. 14. Two phase detectors and two integrators can be eliminated in the example shown in FIG. 15 in comparison with the example shown in FIG. 14.

As mentioned above, an amplitude-phase modulated wave generated in accordance with this invention can be transmitted by use of smaller power in comparison with a conventional eight-phase phase-modulated wave and can be demodulated by relatively simple circuitry mentioned above.

Claims

What we claim is:

1. An amplitude-modulated phase-modulation system, comprising oscillation means for generating a carrier wave,

input terminal means for receiving and applying three binary input signals;

phase modulation means connected to the oscillation means and the input terminal means for eight-phase phase-modulating the carrier wave in accordance with combinations of respective states of the three binary signals;

amplitude modulation means connected to the phase modulation means; and

control means connected to the input terminal means and the amplitude modulation means for controlling the amplitude modulation to deviate, by substantially six decibels, the output of the phase modulation means when the output of the phase modulation means assumes any of four phase-positions alternately predetermined from possible eight-phase positions.

2. An amplitude-modulated phase-modulation system according to claim 1, in which the phase modulation means comprises means for generating from the carrier wave eight rectangular waves respectively having eight different phase positions, and selection means for selecting one of the eight rectangular waves in accordance with combinations of respective states of the three binary input signals.

3. An amplitude-modulated phase-modulation system, according to claim 2, in which the phase-modulation means comprises a Schmidt trigger circuit for converting the carrier wave to a rectangular wave, a scale-of-8 counter connected to the Schmidt trigger circuit for counting pulses of the rectangular wave, a matrix connected to three stages of the scale-of-8 counter, four bistable circuits connected respectively four pairs of outputs of the matrix to produce the eight rectangular waves.

4. An amplitude-modulated phase-modulation system according to claim 2, in which the selection means comprises a matrix connected to the input terminal means for generating eight control outputs respectively corresponding to eight possible combinations of the respective states of the three input signals, and eight gates respectively controlled by the eight control outputs of the matrix for gating a corresponding one of the eight rectangular waves.

5. An amplitude-modulated phase-modulation system according to claim 1, in which the phase-modulation means comprises three phase shifters having respectively phase shift angles .pi., .pi./2, and .pi./4 and connected in cascade, the three input signals being respectively controlled by the three input signals.

6. An amplitude-modulated phase-modulated system according to claim 1, in which the phase modulation means comprises means for phase-modulating the carrier wave, by two of the three input signals, to obtain two four-phase phase-modulated waves whose phase positions have each a phase difference of .pi./4 from adjacent ones of possible four phase positions of another one, and selection means for selecting one of the two four-phase phase-modulated waves in accordance with the state of the remainder of the three input signals, and in which the control means is combined with the phase modulation means.