QAM Modulator

Abstract: A digital communication system using a QAM signal and a honeycomb constellation multilevel signal. The digital communication system includes a modulator (100a) having a unit (101) transforming in-phase and quadrature-phase data (D(i), D(q)) arranged in a quadrature lattice constellation into two data arranged in a honeycomb constellation, and a unit (102) amplitude-modulating the transformed data, and a demodulator (200a) for demodulating a transmitted signal output from the modulator.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulator. More particular, the present invention relates to a modulator which is suitable to be used for multilevel amplitude modulation communication system including a transmitter having a modulator which modulates multilevel quadrature amplitude signals into honeycomb type multilevel amplitude signals. 2. Description of the Related Art In a digital communication system, particularly, in a digital radio communication system, to improve the frequency availability efficiency, a multileveling of a modulation has been found to be an effective measure, and a quadrature amplitude modulation (QAM) is a well known method of realizing such multileveling with a simple circuit configuration. In a QAM modulator, in-phase (I) and quadrature-phase (Q) data are independently converted from digital to analog, to obtain a modulation, and in a QAM demodulator, received signals are converted from analog to digital to obtain a demodulation. To further improve the frequency availability efficiency, a modulation level of the QAM has been increased to 16, 64, and 256. However, a high modulation level requires a large transmission power, and thus a bulky transmission power amplifier having a sufficient "back-off". In addition, this large transmission power has an adverse affect on other communication systems, as a noise source. This will be described in more detail with reference to a specific example. From EP-A-0 062 435 a quadrature carrier modulated communiction system is known which includes means for receiving in-phase data and quadrature-phase data arranged in a quadrature lattice constellation and for amplitude-modulating said data, and further includes means operatively connected to said modulating means for frequency-converting the modulated data from the modulating means. This system further comprises means for receiving a signal modulated two signal components having a honeycomb constellation in a quadrature amplitude modulation method, and synchronously detecting the received signal to provide quadrature detected signal components. SUMMARY OF THE INVENTION An object of the present invention is to provide a modulator by which an increase of the modulation level is obtained with a high transmission power consumption efficiency and a constant high transmission quality. This object is attained by providing a modulator according to claim 1. Further improvements according to the present invention are obtained by providing a modulator according to the sub-claims 2 to 11. More specifically, according to the present invention, there is provided a modulator including: a unit for receiving in-phase data and quadrature-phase data, arranged in a quadrature lattice constellation, and transforming a signal position of the received data into another coordinate arranged in a honeycomb constellation; a unit operatively connected to the signal position transformation unit, for amplitude-modulating the coordinate-transformed data; and a unit, operatively connected to the amplitude-modulating unit, for frequency-converting the modulated data from the modulating unit. The signal position transformation unit may include a position rearrangement unit for receiving the input in-phase data and the input quadrature-phase data and rearranging specific received data among the received data to form a predetermined quadrature lattice constellation, two digital to analog converters, operatively connected to the position rearrangement unit, provided in parallel to receive the rearranged in-phase data and quadrature-phase data and output digital converted data, and a coordinate transformation unit, operatively connected to the digital to analog converters, for receiving the two digital-converted data and transforming the received data having the quadrature lattice constellation into two data having the honeycomb constellation. The predetermined quadrature lattice constellation is defined by the number of the multilevels of the data input to the position rearrangement unit and can be adapted for transforming the coordination into the honeycomb constellation. The position rearrangement unit may include two read-only-memories, both receiving the in-phase data and the quadrature-phase data, one read-only-memory rearranging specific in-phase data among the input in-phase data to form the predetermined quadrature lattice constellation, and another read-only-memory rearranging specific quadrature-phase data among the input quadrature-phase data to form the predetermined quadrature lattice constellation. The coordinate transformation unit may include an analog subtractor, an analog first coefficient multiplier having a first coefficient of √3/2, and an analog second coefficient multiplier having a second coefficient of 1/2. The subtractor receives the in-phase rearranged data through one digital-to-analog converter at a positive input terminal and data, multiplied by the second coefficient to the rearranged quadrature-phase data at the second multiplier, at a negative input terminal, to provide one coordinate transformed data. The first multiplier multiplies the first coefficient and the input rearranged quadrature-phase data to provide another coordinate transformed data. The amplitude-modulating unit may include a first roll-off-filter receiving one coordinate-transformed data, a first multiplier connected to the roll-off-filter, an adder, a second roll-off-filter receiving another transformed data, a second multiplier connected to the second roll-off-filter, a carrier oscillator providing a carrier to the second multiplier, and a π/2-radian-phase shifter receiving the carrier from the carrier oscillator and supplying another carrier shifted by π/2 radian to the carrier to the first multiplier, the adder receiving outputs from the first and second multipliers and outputting the amplitude modulated data. The signal position transformation unit may include a unit for receiving the input in-phase data and the input quadrature-phase data, rearranging specific data among the received data to form a predetermined quadrature lattice constellation, and transforming the rearranged data into two data having the honeycomb constellation. The predetermined quadrature lattice constellation is defined by the number of the multilevels of the input data and can be adapted for transforming the coordination into the honeycomb constellation. The signal position transformation unit also includes two digital to analog converters, operatively connected to the rearranging and transforming unit and provided in parallel to receive two rearranged and coordinate-transformed data, outputting two digital data. The rearranging and transforming unit may include two read-only-memories, both receiving the in-phase data and the quadrature-phase data, one read-only-memory outputting one rearranged and transformed data, and another read-only-memory outputting another rearranged and transformed data. The signal position transformation unit may include a position rearrangement unit for receiving the input in-phase data and the input quadrature-phase data and rearranging specific received data among the received data to form a predetermined quadrature lattice constellation, and two digital to analog converters, operatively connected to the position rearrangement unit, provided in parallel to receive the rearranged in-phase data and quadrature-phase data and output digital converted data. The amplitude-modulating unit may include a first roll-off-filter receiving one coordinate-transformed data, a first multiplier connected to the roll-off-filter, an adder, a second roll-off-filter receiving another transformed data, a second multiplier connected to the second roll-off-filter, a carrier oscillator providing a carrier to the second multiplier, and a phase shifter receiving the carrier from the carrier oscillator and supplying another carrier shifted by 2π/3 radian or π/3 radian to the carrier to the first multiplier, the adder receiving outputs from the first and second multipliers and outputting the amplitude modulated data. The frequency-converting unit may include a multiplier and an oscillator, the multiplier multiplying the amplitude-modulated signal and a signal from the oscillator. The synchronous detecting unit may include a first multiplier, a first low-pass-filter connected to the first multiplier, a second multiplier, a second low-pass-filter connected to the second multiplier, an oscillator outputting a reproduction carrier and a π/2 radian phase shifter connected between the oscillator and the first multiplier. The first multiplier multiplies the received modulated signal and a π/2 radian phase-shifted reproduction carrier generated by the phase shifter to provide one quadrature-detected signal component through the first low-pass-filter. The second multiplier multiplies the received modulated signal and the reproduction carrier from the oscillator to provide another quadrature-detected signal component through the second low-pass-filter. The coordinate transforming unit may include a coordinate transformation circuit formed by an analog circuit, receiving two quadrature-detected signal components and transforming three analog signal components, and a discrimination circuit connected to and discriminating the three analog signal components to supply three discriminated signals. The coordinate transformation circuit may include a line, a first coefficient multiplier having a first coefficient of √3/2, an adder, a second coefficient multiplier having a second coefficient of 1/2, and a subtractor. The line receives one received quadrature-detected signal component and outputs the same as the first transformed signal. The first coefficient multiplier multiplies one received quadrature-detected signal component and the first coefficient and outputs the same to a positive input terminal of the adder and a positive input terminal of the subtractor. The second coefficient multiplier multiplies another received quadrature-detected signal component and the second coefficient and outputs the same to another positive input terminal of the adder and a negative input terminal of the subtractor. As a result, the second transformed signal is output from the adder and the third transformed signal is output from the subtractor. The discrimination circuit may include three parallel-connected analog-to-digital converters receiving three transformed signal components and outputting three digital-converted signals. The coordinate transforming unit may include a discrimination circuit receiving two quadrature-detected signal components and outputting two discriminated signals, and a coordinate transformation circuit connected to receive the two discriminated signals and transforming the two received discriminated signals into three digital signals. The discrimination circuit may include two parallel-connected analog-to-digital converters independently receiving two quadrature-detected signal components and outputting two digital-converted signals. The coordinate transformation circuit is formed by a digital circuit, and includes a line, a first coefficient multiplier having a first coefficient of √3/2, an adder, a second coefficient multiplier having a second coefficient of 1/2, and a subtractor. The line receives one received discriminated signal component and outputs the same as the first transformed signal. The first coefficient multiplier multiplies one received discriminated signal component and the first coefficient and outputs the same to a positive input terminal of the adder and a positive input terminal of the subtractor. The second coefficient multiplier multiplies another received discriminated signal component and the second coefficient and outputs the same to another positive input terminal of the adder and a negative input terminal of the subtractor. As a result, the second transformed signal is output from the adder and the third transformed signal is output from the subtractor. The judging unit may include a read-only-memory inputting three signal components as addresses and outputting a corresponding data among data previously determined as demodulated data, defined by the three addresses. A demodulator may further include a unit, operatively connected between the synchronous detecting unit and the coordinate transforming unit, for equalizing the detected signal components. According to the present invention, there is further provided a multilevel amplitude modulation and demodulation communication system including: a transmitter including any one of the modulators, a transmission line, and a receiver including any one of the demodulators. BRIEF DESCRIPTION OF THE DRAWINGS other objects and features of the present invention will be described below in detail with reference to the accompanying drawings, in which: Fig. 1 is a diagram of a prior art multilevel QAM modulator; Fig. 2 is a graph of a 64 QAM signal constellation; Fig. 3 is a graph representing an S/N increment; Fig. 4 is a graph representing an equivalent deterioration; Fig. 5 is a graph of a honeycomb constellation to which the present invention is applied; Fig. 6 is a diagram of an embodiment of a modulator in accordance with the present invention; Figs. 7 and 8 are graphs explaining the operation of the modulator of Fig. 6; Fig. 9 is a graph of the characteristics of a C/N of the modulator of Fig. 6; Figs. 10 and 11 are diagrams of other embodiments of a modulator in accordance with the present invention; Fig. 12 is a graph explaining the operation of the modulator of Fig. 11; and Fig. 13 is a block diagram of a digital communication system including a modulator according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the preferred embodiments of the present invention, an example of a prior art modulator is described with reference to Figs. 1 to 4. Figure 1 is a diagram of a prior art multilevel QAM type modulator. The modulator includes digital-to-analog converters (DACs) 11 and 12, a QAM circuit 2, a frequency converter consisting of a frequency multiplier 31, and a local oscillator 32, and a transmission power amplifier 3. The QAM circuit 2 includes roll-off filters 21 and 22, multipliers 23 and 24, an adder 25, a carrier oscillator 26, and a π/2 phase shifter 27. The modulator receives an in-phase input digital data D(i) and a quadrature-phase-shifted input digital data D(q), both being independent from one another. These input digital data D(i) and D(q) are independently converted to analog data at the DACs 11 and 12. The converted analog data are passed through the roll-off filters 21 and 22 and supplied to the multipliers 23 and 24. The in-phase analog data is modulated by a carrier f'c, supplied from the π/2 phase shifter 27 and phase-shifted by a π/2 radian to a carrier fc from the oscillator 26, at the multiplier 23. The quadrature-phase-shifted analog data is also modulated by the carrier fc from the oscillator 26 at the multiplier 24. Both modulated signals are added at the adder 25. The added signal from the QAM circuit 2 is frequency-converted at the frequency converter 31 by using a frequency signal from the local oscillator 32, and supplied to the transmission power amplifier 3. A transmitter (not shown) including the modulator transmits the QAM signal having a signal constellation as shown in Fig. 2. Figure 2 shows a 64 QAM signal constellation having a quadrature lattice constellation. In Fig. 2, an abscissa indicates an in-phase component I, and an ordinate indicates a quadrature-phase component Q. Figure 3 is a graph explaining a comparison of an increment of S/N between a QAM method and a phase-shift keying (PSK) method. In Fig. 3, an abscissa indicates a multilevel number n , and an ordinate indicates the S/N increment (dB). Compared with the PSK method, the QAM method provides a smaller S/N when an error rate is equal. However, when the multilevel number is increased, the QAM requires a large S/N, and accordingly, requires a large transmission power. Referring again to Fig. 2, four corner signals a(1) to a(4) define a maximum transmission power. A ratio of the maximum transmission power and an average transmission power is increased by increasing the multilevel number n . For the above reasons, when a same transmission power amplifier is used, the amplifier needs a large "back-off". Figure 4 shows this problem. In Fig. 4, the abscissa represents an output back-off, and the ordinate represents an equivalent C/N deterioration. As shown in Fig. 4, the output back-off of the 16-level QAM method, which gives a same equivalent C/N deterioration, is greater than that of a 4-phase PSK equivalent to 4-level QAM. As described above, in the transmitter using the multilevel modulator, when the multilevel number is increased to improve a frequency availability efficiency, the transmission power is greatly increased. In a 256-level QAM, the transmission power thereof is eighty times that of the 4-level modulation: 4-phase PSK. This requires a high power amplifier and a large power consumption. Also, a high power amplifier having a sufficient back-off is needed. Furthermore, the high transmission power may cause interference with other communication systems, resulting in communication problems. A honeycomb signal constellation, which enables a reduction of a ratio of the maximum transmission power and the average transmission power, and the back-off of the transmission amplifier even if the multilevel number is increased, is known. Figure 5 shows the honeycomb signal constellation having 64 levels. However, a transmission by using a pure honeycomb signal constellation modulation requires a very complex circuit construction, and economic and practical honeycomb signal constellation modulators are not known. Referring to Fig. 6, first, an embodiment of a modulator, provided in a transmitter, of the present invention will be described. The modulator modulates a 64-level signal. In Fig. 6, reference numerals 51 and 52 denote mapping read-only-memories (ROMs), 11 and 12 are digital-to-analog converters (DACs), 4 is a coordinate transformation circuit, 2 is a quadrature amplitude modulation (QAM) circuit, 31 is a frequency converter, 32 is a local oscillator, and 3 is a transmission power amplifier. The coordinate transformation circuit 4 consists of coefficient multipliers 41 and 42 and an adder 43. The QAM circuit 2 consists of roll-off filters 21 and 22, multipliers 23 and 24, an adder 25, a carrier oscillator 26, and a π/2 phase shifter 27. The ROMs 51 and 52 input an in-phase data D(i) and a quadrature-phase data D(q), which are arranged in the quadrature lattice constellation as shown in Fig. 2, and rearrange that constellation as shown in Fig. 7. Namely, the ROMs 51 and 52 move signal points in areas I and II to signal points of an area III. In Fig. 7, signal points of the 64 QAM signal constellation each indicated by a signal circle are arranged in the quadrature lattice constellation of a square of 8 x 8 signal points. The signal point constellation rearranged by the ROMs 51 and 52 is akin to an ellipse. Data x a and y a rearranged from the signal points at the ROMs 51 and 52 are converted to coordinate data Ia and Qa at the DACs 11 and 12. The coordinate transformation circuit 4 transforms the input data Ia and Qa into coordinate transformed signals I'a and Q'a in accordance with the following formulae: I'a = Ia - βa·Qa Q'a = αa·Qa where, a = √3 / 2 , and βa = 1 / 2 Figure 8 shows a signal point constellation of the coordinate transformed signals I'a and Q'a, i.e., a honeycomb type signal point constellation. In Fig. 8, signal points in areas I', II' and IV correspond to the signal points marked by the single circles including the signal points in the areas I and II. But, since the signal points in the areas I and II in Fig. 7 are actually rearranged to be the signal points in the area III, the signal points in the areas I' and II' shown in Fig. 8 do not exist. The signal points in the area III shown in Fig. 7 correspond to signal points marked by stars shown in Fig. 8. In Fig. 8, the area IV includes 64 signal points: a center signal point C₀ , a first inner hexagonal-ring consisting of six signal points C₁₁ to C₁₆, a second inner hexagonal-ring consisting of 12 signal points C₂₀₁ to C₂₁₂ , a third inner hexagonal-ring consisting of 18 signal points, a fourth inner hexagonal-ring consisting of 23 signal points, and four outer points. Adjacent signal points, for example C₀ , C₁₄ , and C₁₅ , form a triangle. A length of each side of the triangle is equal to a length of each side of the square of the adjacent four points in Fig. 7. Thus, a transmission error will not increase more than that of Fig. 7. An outer contour of the signal point constellation of the area IV is akin to a hexagon. Accordingly, a ratio of an average transmission power and a maximum transmission power, which is defined by a maximum distance among the signal points in the area IV, becomes smaller than that of Fig. 7, and thus the back-off of the transmission power amplifier can be reduced. Figure 8 shows a characteristic between the back-off and the C/N. A solid curve shows the characteristic of the honeycomb constellation having 256 levels, and a dotted curve shows the characteristic of the quadrature lattice constellation. Referring to Fig. 6, the QAM circuit 2 modulates the honeycomb constellation signals I'a and Q'a; the frequency multiplier 31 converts a frequency of the modulated signal with a frequency signal from the oscillator 32; the power amplifier 3 amplifies the frequency converted signal; and, the amplified signal is transmitted to a receiver (not shown) by the transmitter including the modulator shown in Fig. 6. By adding the ROMs 51 and 52, and the coordinate transformation circuit 4 to the modulator shown in Fig. 1, the modulator shown in Fig. 6 provides the honeycomb signal point constellation, resulting in a reduction of the maximum transmission power, and thus a reduction of the back-off of the power amplifier 3, without lowering the transmission quality. As described above, a multilevel amplitude modulation communication system, which includes the modulator shown in Fig. 6, can increase the multilevel number to improve the frequency availability efficiency, while maintaining the transmission power efficiency and further maintaining the back-off of the transmission power amplifier. The multi-level amplitude modulation communication system can be constructed economically and practically. Figure 10 shows another modulator of a second embodiment of the present invention. Compared with the modulator shown in Fig. 6, the modulator shown in Fig. 6 omits the coordinate transformation circuit 4 between the DACs 11 and 12 and the QAM circuit 2. The ROMs 61 and 62 function as the mapping ROMs 51 and 52 plus the coordinate transformation circuit 4. The ROMs 61 and 62 receive the in-phase data D(i) and the quadrature-phase data D(q) and directly output signals of the honeycomb constellation as shown in Fig. 8. The modulated transmission signal from the modulator of Fig. 10 is substantially equal to that of the modulator of Fig. 6. The modulator shown in Fig. 10 is simpler than the modulator shown in Fig. 6. Figure 11 shows still another modulator of a third embodiment of the present invention. Compared with the modulator shown in Fig. 6, the modulator shown in Fig. 11 omits the coordinate transformation circuit 4 and modifies the QAM circuit 2 to an amplitude modulation circuit 2a. Compared with the QAM circuit 2 shown in Fig. 6, the amplitude modulation circuit 2a is provided with a 2π/3 phase shifter 28 instead of the π/2 phase shifter 27. In Fig. 6, the coordinate transformation circuit 4 transforms the quadrature data Ia and Qa from the DACs 11 and 12 into the signals I'a and Q'a arranged in the honeycomb constellation as shown in Fig. 8, and the QAM 2 further modulates the signals I'a and Q'a by using the π/2 phase shifter 27. A combination of the coordinate transformation circuit 4 and the QAM circuit 2 on an angle in the signal constellation is a coordination transformation changing by a 2π/3 radian (120°) anticlockwise with respect to an I axis or by π/3 radian (60°) clockwise with respect to the I axis, as shown in Fig. 12. Accordingly, the amplitude modulation circuit 2a directly transforms the coordination of the signals in the honeycomb constellation and amplitude-modulates those signals. The modulator shown in Fig. 11 is very simple. The 2π/3 phase shifter 28 in the amplitude modulation circuit 2a can be replaced by a π/3 phase shifter. Figure 13 shows a conceptual construction of a multilevel amplitude moduJation and demodulation communication system including a modulator according to the present invention. The communication system includes a transmitter 100 having a modulator 100a, a transmission line 300, and a receiver 200 having a demodulator 200a. The modulator 100a includes a signal point transformation portion 101 receiving an in-phase data D(i) and a quadrature-phase data D(q), adaptive for a QAM method, and transforming that data on a coordination constellation to rearrange a honeycomb constellation, and an amplitude modulation portion 102 for outputting a QAM signal. The demodulator 200a includes a synchronous detection portion 201 receiving the transmitted QAM signal and synchronously detecting that signal to provide detected quadrature signals xb and yb, a coordinate transformation portion 202 transforming a coordination of the detected quadrature signals to provide three data x, u, and v on X-, U-, and V-axes, spaced at a π/3 radian, and a signal judgment circuit 203 outputting a demodulated signal. Optionally, an equalizing portion 204 can be provided.

Claims: A modulator comprising: means (101) for receiving an in-phase data (D(i)) and a quadrature-phase data (D(q)), arranged in a quadrature lattice constellation, and transforming a signal position of said received data into another coordinate arranged in a honeycomb constellation; means (102) operatively connected to said signal position transformation means for amplitude-modulating said coordinate-transformed data; and means (31 and 32), operatively connected to said amplitude-modulating means (102) for frequency-converting the modulated data from the modulating means; characterized in that said signal position transformation means (101) comprises a position rearrangement means (51, 52) for receiving the input in-phase data (D(i)) and the input quadrature-phase data (D(q)) and rearranging specific received data among the received data to form a predetermined quadrature lattice constellation, two digital-to-analog converters (11, 12), operatively connected to said position rearrangement means, provided in parallel to receive the rearranged in-phase data (x a ) and quadrature-phase data (y a ) and output digital converted data (Ia, Qa), and a coordinate transformation means (4), operatively connected to said digital to analog converters, for receiving the two digital-converted data and transforming said received data having the quadrature lattice constellation into two data having the honeycomb constellation, the predetermined quadrature lattice constellation being defined by the number of multilevels of the data input to said position rearrangement means and being adaptive for transforming the coordination into the honeycomb constellation. A modulator according to claim 1 wherein said position rearrangement means comprises two read-only-memories (51 and 52), both receiving the in-phase data (D(i)) and the quadrature-phase data (D(q)), one read-only-memory rearranging specific in-phase data among the input in-phase data to form said predetermined quadrature lattice constellation, and another read-only-memory rearranging specific quadrature-phase data among the input quadrature-phase data to form said predetermined quadrature lattice constellation. A modulator according to claim 2, wherein said coordinate transformation means (4) comprises an analog subtractor (43), an analog first coefficient multiplier (41) having a first coefficient (α a ), of √3/2, and an analog second coefficient multiplier (42) having a second coefficient (β a ) of 1/2, said subtractor receiving the in-phase rearranged data through one digital-to-analog converter (11) at a positive input terminal and a data, multiplied by the second coefficient to the rearranged quadrature-phase data at the second multiplier (42), at a negative input terminal, to provide one coordinate transformed data (I'a), and said first multiplier (41) multiplying the first coefficient and the input rearranged quadrature-phase data to provide another coordinate transformed data (Q'a). A modulator according to claim 1, wherein said coordinate transformation means (4) comprises an analog subtractor (43), an analog first coefficient multiplier (41) having a first coefficient (α a ) of √3/2, and an analog second coefficient multiplier (42) having a second coefficient (β a ) of 1/2, said subtractor receiving the in-phase rearranged data through one digital-to-analog converter (11) at a positive input terminal and a data, multiplied by the second coefficient to the rearranged quadrature-phase data at the second multiplier (42), at a negative input terminal, to provide one coordinate transformed data (I'a), and said first multiplier (41) multiplying the first coefficient and the input rearranged quadrature-phase data to provide another coordinate transformed data (Q'a). A modulator according to claim 1, wherein said amplitude-modulating means (102) comprises a first roll-off-filter (21) receiving one coordinate-transformed data, a first multiplier (23) connected to the roll-off-filter, an adder (25), a second roll-off-filter (22) receiving another transformed data, a second multiplier (24) connected to the second roll-off-filter, a carrier oscillator (26) providing a carrier to the second multiplier, and a π/2-radian-phase shifter (27) receiving the carrier from the carrier oscillator and supplying another carrier shifted by a π/2 radian to the carrier to the first multiplier, the adder (25) receiving outputs from the first and second multipliers and outputting the amplitude modulated data. A modulator according to claim 1, wherein said signal position transformation means (101) comprises means (61, 62) for receiving the input in-phase data (D(i)) and the input quadrature-phase data (D(q)), rearranging specific data among the received data to form a predetermined quadrature lattice constellation, and transforming the rearranged data into two date having the honeycomb constellation, the predetermined quadrature lattice constellation being defined by the number of multilevels of the input data and being adaptive for transforming the coordination into the honeycomb constellation, and two digital-to-analog converters (11, 12), operatively connected to the rearranging and transforming means and provided in parallel to receive two rearranged and coordinate-transformed data, outputting two digital data. A modulator according to claim 6, wherein said rearranging and transforming means comprises two read-only-memories (61, 62), both receiving the in-phase data and the quadrature-phase data, one read-only-memory outputting one rearranged and transformed data, and another read-only-memory outputting another rearranged and transformed data. A modulator according to claim 6, wherein said amplitude-modulating means (102) comprises a first roll-off-filter (21) receiving one coordinate-transformed data, a first multiplier (23) connected to the roll-off-filter, an adder (25), a second roll-off-filter (22) receiving another transformed data, a second multiplier (24) connected to the second roll-off-filter, a carrier oscillator (26) providing a carrier to the second multiplier, and a π/2-radian-phase shifter (27) receiving the carrier from the carrier oscillator and supplying another carrier shifted by a π/2 radian to the carrier to the first multiplier, the adder (25) receiving outputs from the first and second multipliers and outputting the amplitude modulated data. A modulator according to claim 1, wherein said signal position transformation means (101) comprises a position rearrangement means (51, 52) for receiving the input in-phase data (D(i)) and the input quadrature-phase data (D(q)) and rearranging specific received data among the received data to form a predetermined quadrature lattice constellation, and two digital-to-analog converters (11, 12), operatively connected to said position rearrangement means, provided in parallel to receive the rearranged in-phase data (Xa) and quadrature-phase data (Ya) and output digital converted data (Ia, Qa), and said amplitude-modulating means comprises (102) a first roll-off-filter (21) receiving one coordinate-transformed data, a first multiplier (23) connected to the roll-off-filter, an adder (25), a second roll-off-filter (22) receiving another transformed data, a second multiplier (24) connected to the second roll-off-filter, a carrier oscillator (26) providing a carrier to the second multiplier, and a phase shifter (27) receiving the carrier from the carrier oscillator and supplying another carrier shifted by a 2π/3 radian or π/3 radian to the carrier to the first multiplier, the adder (25) receiving outputs from the first and second multipliers and outputting the amplitude modulated data. A modulator according to claim 9 , wherein said position rearrangement means comprises two read-only-memories (51 and 52), both receiving the in-phase data (D(i)) and the quadrature-phase data (D(q)), one read-only-memory rearranging specific in-phase data among the input in-phase data to form said predetermined quadrature lattice constellation, and another read-only-memory rearranging specific quadrature-phase data among the input quadrature-phase data to form said predetermined quadrature lattice constellation, the predetermined quadrature lattice constellation being defined by the number of multilevels of the data input to said position rearrangement means and being adaptive for transforming the coordination into the honeycomb constellation. A modulator according to claim 1, wherein said frequency-converting means comprises a multiplier (31) and an oscillator (32), the multiplier multiplying the amplitude-modulated signal and a signal from the oscillator.

Inventors: AONO YOSHIHITO, DAIDO YOSHIMASA, IWAMATSU TAKANORI, MINOWA MORIHIKO, NAKAMURA HIROSHI, TAKENAKA SADAO, AONO, YOSHIHITO, DAIDO, YOSHIMASA, IWAMATSU, TAKANORI, MINOWA, MORIHIKO, NAKAMURA, HIROSHI, TAKENAKA, SADAO
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1988
Main classification: H04L27
IPC codes: H04L27