JP3397840B2 - π / 4 shift QPSK modulation method and circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a .pi. / 4 shift QPSK modulation method and circuit for directly generating a phase modulated wave by a digital circuit.

[0002]

2. Description of the Related Art Generally, in QPSK (Quadrature Phase Shift Keying), a modulation signal is composed of two orthogonal carriers, so a band-limited signal is created using two independent series of data to generate a modulation signal. Can be generated.

FIG. 5 is a table lookup type QPS.
1 illustrates an example of a configuration of a K signal modulation circuit, in which 11 is transmission data, 12a and 12b are I-channel and Q-channel registers having a capacity of a restricted symbol length for accumulating the transmission data 11, respectively, 13 is a register 12a, A switch circuit for selectively switching the output of 12b, 14 is a ROM that stores signal waveforms in a table, 15 is a frequency division counter that indicates the position of a slot, 16 is a baseband band-limited signal (band-limited baseband) read from ROM 14. Waveform data), 17 is a sign inversion circuit that inverts the sign of the baseband band limited signal 16,
Reference numeral 18 is a D / A converter that obtains a modulated signal by analogizing the baseband band limiting signal 16 whose sign is inverted by the sign inverting circuit 17, and 19 is a high-frequency removal filter configured by a low-pass filter to remove high-frequency components of the modulated signal. , 20 are the obtained modulated signals.

With the above-mentioned structure, the transmission data 11
Is input to the two registers 12a and 12b. Since the waveform of the output band-limited signal is generated from the data of several symbols before and after, the ROM that stores the waveform in a table
By inputting the data accumulated in the register 12a or 12b and the count value of the frequency dividing counter 15 as the address of 14, the digital value of the waveform at that time, that is, the I channel (Ich) and the Q channel (Qch) is input from the ROM 14. Alternating baseband band-limited signal
16 is read.

For the baseband band-limited signal 16 thus read out, the sign inversion circuit 17 outputs I channel and Q
The sign is inverted every two data for each channel.
The value of the baseband band limiting signal 16 output from the sign inverting circuit 17, which is appropriately sign-inverted, is converted into an analog signal by the D / A converter 18, and a high-frequency component is removed by the D / A converter 18 to obtain a modulated signal 20. It is what is done.

FIG. 6 exemplifies the modulation signal output from the D / A converter 18. In the figure, the hatching of the upward-sloping line indicates the signal A corresponding to the carrier phase 0-π, and the hatching of innumerable points indicates the carrier phase π.
The signal B corresponds to / 2-3π / 2. Since the signal A and the signal B are orthogonal to each other, a waveform is generated using the accumulated data composed of the transmission data,
It is possible to synthesize. Therefore, there is an advantage that the capacity of the ROM 14 for storing the waveform can be set small.

Here, for example, the constraint symbol length is 10 symbols, the number of stages of the frequency division counter 15 is 6, and the number of quantization bits is 8.
In this case, the storage capacity required for the ROM 14 is 8 ^{× 10 + 6} bits.

On the other hand, in π / 4 shift QPSK,
0-π, π / 4-5π / 4, π / 2-3π / 2, 3π /
It is equivalent to that formed from a signal having a carrier phase of 4-7π / 4. Therefore, the carriers are not orthogonal to each other, and it is impossible to generate and synthesize the waveform by using the accumulated data composed of the transmission data independently as in the above QPSK. Therefore, it is necessary to use all data to obtain the waveform.

FIG. 7 shows a π / 4 shift Q corresponding to FIG.
The configuration of the PSK signal modulation circuit is shown as an example, and since it is basically the same as that of the above-mentioned FIG. 5, the same portions are denoted by the same reference numerals and the description thereof is omitted.

However, both the I-channel and Q-channel transmission data 11 stored in the registers 12a and 12b are sent to the ROM 14 '. This ROM 14 'reads the baseband band limiting signal 16 of the digital value at that time by inputting the data accumulated in the registers 12a and 12b and the count value of the frequency dividing counter 15 as an address.

The baseband band limiting signal 16 read out from the ROM 14 'is appropriately sign-inverted by the sign inverting circuit 17, then analogized by the D / A converter 18, and directly output as the modulation signal 20.

As shown, ROM 14 'includes register 12
The baseband band limiting signal is read by using both a and 12b and the count value of the frequency dividing counter 15 as an address. Therefore, a memory having a larger capacity than the ROM 14 shown in FIG. 5 is required.

Here, when the restricted symbol length is 10 symbols, the number of stages of the frequency division counter 15 is 6 and the number of quantization bits is 8 as in the case illustrated in FIG. 5, the storage capacity required for the ROM 14 'is It becomes 8 ^{+ 20 + 6} bits.

[0014]

As described above, in the modulation circuit of π / 4 shift QPSK, the capacity required for the memory for storing the modulated signal waveform becomes enormous, so that the scale of the entire circuit becomes large. However, there was a problem that the cost was high.

The present invention has been made in view of the above circumstances, and an object thereof is a π / 4 shift QPS which can be realized by using a memory having a capacity as small as possible.
It is to provide a K modulation method and circuit.

[0016]

That is, the present invention provides π /
Paying attention to the fact that the 4-shift QPSK signal is a composite wave of two QPSK signals with the absolute phase of the carrier shifted by π / 4, the I channel and the Q channel of the QPSK signal, and the absolute phase of the QPSK signal and the carrier are π / 4. A register section for storing transmission data of each of the I channel and Q channel of the QPSK signal deviated by a certain amount, and a switch circuit as a synthesizing means for sequentially switching and selecting the transmission data stored in the register section and temporally synthesizing the transmission data. , Corresponding to each transmission data which is sequentially switched and selected by this switch circuit, Q
A ROM that stores band-limiting signals of all waveform patterns corresponding to PSK transmission data and selectively outputs the band-limiting signal based on the transmission data sequentially sent from the switch circuit; and a band output from the ROM. A sign inverting circuit for sequentially inverting the sign of the limit signal data at appropriate intervals and outputting the same, and a D for A / D converting the band limit signal data output from the sign inverting circuit to create a modulation signal of π / 4 shift QPSK. / A converter.

[0017]

With the above-described structure, a memory having a capacity approximately the same as that of the QPSK waveform storage memory is used as the memory used for the lookup table.
It becomes possible to generate a 4-shift QPSK modulated signal.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the basic circuit configuration thereof. The transmission data 21 of the π / 4 shift QPSK signal includes a first QPSK signal and a second QPSK signal in which the absolute phase of the carrier deviates by π / 4. QPSK signal is divided into two systems, and in each system, in-phase (hereinafter abbreviated as “I channel”) and quadrature phase (hereinafter “Q channel”).
Will be abbreviated), and register units 22a,
Input is held in each of 22b.

The register units 22a and 22b are provided with registers 23a and 23b or 23c and 23d having a capacity corresponding to the restricted symbol length of the transmission data, and the transmission data of each symbol are input and held. Switch circuit 24
Read to.

The switch circuit 24 includes register sections 22a and 22b.
The transmission data held in the registers 23a to 23d are sequentially switched and selected in an appropriate order to be described later, temporally combined, and the output is sent to the ROM 25.

The ROM 25 is a table lookup type memory in which QPSK baseband band-limited signals (band-limited baseband waveform data) corresponding to all patterns of transmission data are stored in a table form. The two QPs are used by using the transmission data sent as an address and the count value input from the frequency division counter 26 that performs the counting operation indicating the position in the symbol.
The SK baseband band-limited signal 27 is read.

The read baseband band limiting signal 27 has its sign inverted by a sign inverting circuit 28 at an appropriate cycle and is subsequently converted into an analog signal by a D / A converter 29 to be a modulated signal. By removing the high frequency component of the signal with the high frequency removal filter 30 formed of a low pass filter, a desired π / 4 shift QPSK modulated signal 31 can be obtained.

Next, the concept of the present invention and the operation of the above embodiment will be described. The π / 4 shift QPSK signal can be defined as a composite wave of two QPSK signals in which the absolute phase of the carrier is shifted by π / 4. Figure 2 shows two QPS
K signals (0, π / 2, π, 3π / 2 and π / 4, 3π /
4, 5π / 4, 7π / 4), and FIG. 3 shows a space diagram thereof. As can be seen from these figures, QP can be obtained from the data of the symbols separated by one.
By independently generating SK signals and synthesizing them, the π / 4 QPSK signal can be synthesized.

In the configuration shown in FIG. 1, however, the transmission data is divided into two QPSK signals whose carrier absolute phase is shifted by π / 4, which is further divided into an I channel and a Q channel, and the register section 22a is provided. , 22b register 23
Input is held in a to 23d. Here, the registers 23a-23
The transmission data stored in d is data of symbols separated by one as described above.

The transmission data held in the registers 23a to 23d are read out to the ROM 25 in an appropriate order via the switch circuit 24. The transmission data sent in the ROM 25 and the symbols in the symbols from the frequency division counter 26 are stored in the ROM 25. Two QPs stored in advance with the count value indicating the position as an address
The SK baseband band limiting signal 27 is read to the sign inverting circuit 28.

The sign inverting circuit 28 inverts the sign of the input baseband band-limited signal 27 every 4 samples to perform D / A.
The modulated signal which is sent to the converter 29 and which the D / A converter 29 converts into an analog signal and outputs is as shown in FIG.

That is, FIG. 4 illustrates the modulation signal output from the D / A converter 29. In the figure, the hatching of the upward-sloping line indicates the signal A corresponding to the carrier phase 0-π, the hatching of the vertical line indicates the signal B corresponding to the carrier phase π / 4-5π / 4, and the downward-sloping line. In the figure, the hatched line indicates the signal C corresponding to the carrier phase π / 2-3π / 2, and the hatched line indicates the signal D corresponding to the carrier phase 3π / 4-7π / 4.

The modulated signal analogized by the D / A converter 29 in this manner has its high-frequency component removed by the high-frequency removal filter 30 and is output as the desired π / 4-shift QPSK modulated signal 31.

As described above, since the π / 4 shift QPSK modulation circuit can be realized only by storing the QPSK baseband band limiting signal 27 for one series of transmission data in the ROM 25, the capacity required for the ROM 25 is increased. QP
It can be almost the same as the SK modulation circuit.

Now, considering the capacity required for the ROM 25 under the same conditions as those illustrated in FIGS. 5 and 7, the constraint symbol length is 10 symbols, and the number of stages of the frequency division counter 15 is 7 (the output is compared to QPSK). Therefore, if the number of quantization bits is 8, the storage capacity required for the ROM 25 is 8.2.
^{Since it is 10 + 7} bits, the required storage capacity can be halved compared to the ROM 14 'shown in FIG.

According to the present invention, however, the four orthogonal combined waveforms, that is, the two I-channel and Q-channel waveforms can be combined on the time axis as described above, so that the truncation symbol length is n. In such a case, since it is only necessary to generate four orthogonal waveforms, it is only necessary to create a band-limited waveform using n / 2-bit data, and the capacity required for the memory for storing the waveform is increased. It can be halved. Further, not only the capacity of the memory can be halved, but also complete digitalization is possible, so that a circuit that can be easily integrated into LSI and does not require adjustment can be realized.

[0032]

As described above in detail, according to the present invention, the memory used for the lookup table is QPSK.
It is possible to provide a π / 4 shift QPSK modulation method and a circuit that can be realized by using a memory having almost the same capacity as that of the memory used in.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration according to an embodiment of the present invention.

FIG. 2 is a diagram showing a principle concept according to the embodiment.

FIG. 3 is a diagram showing a principle concept according to the embodiment.

FIG. 4 is a diagram illustrating a waveform of a modulation signal generated by the D / A converter in FIG.

FIG. 5 is a block diagram showing a configuration of a conventional QPSK modulation circuit.

6 is a diagram showing an example of a waveform of a modulation signal generated by the D / A converter shown in FIG.

FIG. 7 is a block diagram showing a configuration of a conventional π / 4 shift QPSK modulation circuit.

[Explanation of symbols]

11, 21 ... Transmission data, 12a, 12b, 23a to 23d ... Register, 13, 24 ... Switch circuit, 14, 14 ', 25 ... ROM, 1
5, 26 ... Dividing counter, 16, 27 ... Baseband band limiting signal, 17, 28 ... Sign inversion circuit, 18, 29 ... D / A converter,
19,30 ... High frequency removal filter, 20,31 ... Modulation signal, 22
a, 22b ... Register section.

Front page continuation (72) Inventor Eiji Harasaka 44-2 Daichi-cho Goumae, Iwakura City, Aichi Prefecture (56) References JP-A-4-255140 (JP, A) JP-A-3-235553 (JP, A) ( 58) Fields investigated (Int.Cl. ⁷ , DB name) H04L 27/00

Claims (2)

(57) [Claims] 1. The waveform data of the QPSK signal to be output is stored in ROM in advance, and the absolute phase of the carrier is π.
I phase of each of the two QPSK signals shifted by / 4 and
The transmission data corresponding to the Q-phase is sequentially switched and selected to be temporally combined, and the RO is sequentially output based on the combined transmission data.
Sign inversion of waveform data read from M at appropriate intervals
While performing D / A conversion, a modulated wave corresponding to transmission data of π / 4 shift QPSK is generated.
/ 4 shift QPSK modulation method. 2. An I-phase, a Q-phase of the QPSK signal and the QP
QP in which the absolute phase of SK signal and carrier is shifted by π / 4
A register unit that stores the I-phase and Q-phase transmission data of the SK signal, a synthesizing unit that sequentially switches and selects each transmission data stored in the register unit, and a synthesizing unit that sequentially switches the SK signal transmission data. The band-limited signals of all the waveform patterns corresponding to the selected transmission data and corresponding to the QPSK transmission data are stored, and the band-limiting signal is selectively output based on the transmission data sequentially sent from the synthesizing means. ROM, a sign inverting means for sequentially inverting the sign of the band-limited signal data output from the ROM at appropriate intervals, and outputting the band-limited signal data, and D / A converting the band-limited signal data output from the sign inverting means to π / And a D / A conversion means for creating a 4-shift QPSK modulated signal.
4-shift QPSK modulation circuit.