JP3352729B2 - π / 4 shift QPSK modulation waveform shaping circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an auxiliary circuit of a .pi. / 4 shift QPSK modulation system which is a digital modulation system used for mobile communication or the like which requires an improvement in frequency utilization efficiency.

[0002]

2. Description of the Related Art GMSK, quaternary FM, PLL are used as digital modulation methods used for mobile communication such as automobile telephones.
Although there is -QPSK or the like, a π / 4 shift QPSK modulation scheme is adopted as a modulation scheme with higher frequency use efficiency. Then, in the burst transmission of the mobile communication adopting the TDMA system, for example, as shown in [A] of FIG. 5, control is performed so that transmission is performed only for one third of the time every 20 ms. Therefore, the spectrum of the transmission power is broadened at the time of the rising and falling of the burst transmission, and a problem occurs that the leakage power that interferes with the adjacent channel is generated as shown in FIG. 5B.

Therefore, in the conventional π / 4 shift QPSK modulation method, at the rise and fall of burst transmission, for example, a ramp function as shown in FIG. , And the rising and falling are gently shaped to prevent the spread of the transmission power spectrum.

FIG. 6 shows an example of such a circuit configuration.
6, reference numeral 101 denotes a π / 4 shift QPSK signal generation unit, 102 denotes a waveform shaping unit, 103 denotes a ramp function ROM, 104
Is a D / A converter for the I channel, 105 is a D / A converter for the Q channel, and 106 and 107 are roll-off filters. In the ramp function ROM 103, for example, [1 / 2-
1 / 2cosωt] is written as a ramp function.

Here, the initial data x1, y1 of the transmission data input in synchronization with the burst-in is a preamble, and the respective values are x1 = 0, y1 = 0. Then, the waveform shaping unit 102 multiplies the four internally generated ramp bits (all values are “0”) by the ramp function data in the ramp function ROM 103. When the ramp bit ends and becomes a data bit, the multiplication process by the waveform shaping unit 102 is invalidated, and the data is input to the D / A converters 104 and 105 without waveform shaping. In this way, the waveform is shaped by multiplying the baseband signals I and Q by the ramp function, and the waveform is shaped at the time of the rise of the transmission output.

Similarly, waveform shaping at the falling edge is performed on the ramp function ROM 103 with respect to four guard bits.
Is multiplied by the ramp function data. A delay circuit is provided to match the burst-in and burst-out timings with the rise and fall timings of the transmission data.

[0007]

In such a conventional circuit system, the rise and fall of the transmission output can be gently shaped, but the circuit scale is large since a ramp function ROM and a waveform shaping section are required. There is a problem that the size of the apparatus increases and the cost of the apparatus increases. In addition, since it is necessary to read the ramp function ROM with a high-speed clock and perform digital arithmetic processing in the waveform shaping unit, there is a problem that power consumption increases.

[0008] In view of the above problems, an object of the present invention is to realize a circuit capable of gently shaping the rise and fall of a transmission output with a simpler circuit configuration as in the related art.

[0009]

According to the present invention, a π / 4 shift QP that performs burst transmission by using two baseband signals represented as sine waves having phases different by 90 °.
In the SK modulation type waveform shaping circuit, the waveform of the baseband signal is compared with the center voltage, and at the time of burst-in, the first timing at which any of the baseband signals first matches the center voltage is detected. At the time of burst-out, a timing detection circuit for detecting a second timing at which any of the baseband signals first matches the center voltage, and a timing detection circuit for shifting the phase by 90 ° from the first timing. Means that only the baseband signal that matches the center voltage at the first timing is passed, the other baseband signal is blocked, and the phase is shifted by 90 ° from the second timing. Cuts off the baseband signal that coincides with the center voltage at the second timing and passes only the other baseband signal. And a gate circuit.

[0010]

According to the present invention, the transmission output P of a quadrature modulator such as a QPSK modulator using baseband signals Q and I having phases different from each other by 90 ° can be expressed by the following equation (1).

[0011]

(Equation 1)

However, when the voltage of the baseband signal Q is V
Q, let VI be the voltage of the baseband signal I. When the ramp bit and the guard bit are “0”, the phase of the π / 4 shifted QPSK baseband signal via the roll-off filter is shifted by π / 4 for both the baseband signals Q and I. The waveforms of the signals Q and I are sine waves that are 90 ° out of phase as shown in [C] and [D] in FIG. The present invention focuses on the fact that a ramp function can be generated using this sine wave.

Here, in the timing detection circuit,
At the time of burst-in, the timing at which any of the baseband signals first matches the center voltage is detected as the first timing. From the first timing T0 to a timing T1 at which the phase shifts by 90 ° (between two symbols), the baseband signal (baseband signal I in FIG. 2) which has become equal to the center voltage at the first timing is used. The gate circuit is turned on to pass through the gate circuit, and the other baseband signal (baseband signal Q in FIG. 2) is turned off and not passed through the gate circuit.

At this time, both baseband signals I and Q
Are represented by either [A] or [B] of Equation 2 below.

[0015]

(Equation 2)

Here, in both the case [A] and the case [B] in the above equation (2), when it is substituted into the above equation (1), the transmission output P1 during this period is represented by the following equation (3).

[0017]

(Equation 3)

Since the waveform of the transmission output P1 gradually rises from "0" as shown in the waveform (a) of FIG. 2E, the spectrum of the transmission power does not spread.
Similarly, in the timing detection circuit, at the time of burst out, the timing at which any of the baseband signals first matches the center voltage is detected as the second timing.

From this second timing T2, the phase is 90
Until the transition timing T3 (between two symbols), the baseband signal (baseband signal Q in FIG. 2) which has become equal to the center voltage at the timing T2 is turned off by the gate circuit and cut off by the gate circuit. Then, the other baseband signal (baseband signal I in FIG. 2) is turned off at timing T3 when it becomes equal to the center voltage with a delay of 90 °,
The voltages VI and VQ of both baseband signals I and Q are represented by either [A] or [B] in Equation 2 above.

Therefore, the waveform of the transmission output P1 during this period becomes a waveform that gradually falls toward "0" as shown in (c) of FIG. 2E, and the spectrum of the transmission power does not spread. In this way, the rise and fall of the baseband signal are made gentle.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A waveform shaping circuit of the π / 4 shift QPSK modulation system of the present invention will be described below in detail with reference to FIG. In FIG. 1, reference numeral 1 denotes an I-channel baseband signal ID and a Q-channel baseband signal Q.
Π / 4 shift QPSK signal generating section for generating D and 2,
3 is a D / A converter for converting the baseband signals ID and QD into analog signals, 4 and 5 are roll-off filters,
Reference numerals 6 and 7 denote gate circuits for controlling on / off of the passage of the baseband signals ID and QD, and reference numeral 8 denotes a center voltage generator for outputting a center voltage VC.

Reference numeral 9 denotes a timing detection circuit which counts a transmission clock TXCK and outputs a determination signal indicating a ramp bit and a guard bit. The data discriminator 11 compares the band signal ID and the Q-channel baseband signal QD with the center voltage VC and outputs an I-channel gate control signal GI and a Q-channel gate control signal GQ having a pulse width of 4 bits. A delay circuit 12 for delaying each of the gate control signals GI and GQ by the same time as the group delay time in the roll-off filters 4 and 5;
It is composed of 13 and.

In the data discriminating unit 11, when the discrimination signal indicates burst-in, when the baseband signal I first matches the center voltage VC,
A point in time when the coincidence is detected is detected as a first timing T0, and a point in time when the phase shifts by 90 ° and the other baseband signal Q coincides with the center voltage VC is defined as timing T1. Then, from the timing T0 to the timing T1, the I-channel gate control signal GI is turned on, and the Q-channel gate control signal GQ remains off.

Conversely, when the baseband signal Q matches the center voltage VC first, the time when the baseband signal Q matches is detected as the first timing T0, and the phase shifts by 90 ° from this time to change the other baseband signal. The time when the signal I coincides with the center voltage VC is defined as timing T1, and between the timing T0 and the timing T1, the I-channel gate control signal G
I remains off and the Q channel gate control signal G
Q turns on.

When the discrimination signal indicates burst-out, if the baseband signal Q first matches the center voltage VC, the time when the baseband signal Q matches is detected as the second timing T2. The point in time at which the phase shifts by 90 ° and the other baseband signal I matches the center voltage VC is defined as timing T3. And the timing T
From 2 to timing T3, the I-channel gate control signal GI remains on and the Q-channel gate control signal GQ is off.

Conversely, if the baseband signal I matches the center voltage VC first, the point of coincidence is detected as the second timing T2, and the phase shifts by 90 ° from this point, and the other baseband signal is shifted. The time when the signal Q matches the center voltage VC is defined as timing T3, and during the period from timing T2 to timing T3, the I-channel gate control signal G
I is turned off, and the Q channel gate control signal GQ remains on.

FIG. 4 showing a configuration example of the data discriminating unit 11.
, The determination signal includes a transmission enable signal longer than the transmission time and a data enable signal shorter than the transmission time, and the flip-flops F1, F2, F3, and F
4 and the OR gates G1 and G2 output an I channel gate control signal GI and a Q channel gate control signal GQ.

Reference numeral 14 denotes π / 4 based on the waveform-shaped baseband signals I and Q output from the gate circuits 6 and 7.
A modulation unit that performs shift QPSK modulation.

In the above configuration, at the time of burst-in,
As for the baseband signals ID and QD, the signal which is equal to the center voltage VC is first turned on during the period from the first timing T0 to the timing T1, that is, for four ramp bits, and the other signal is turned off. . For example, as shown in [A] and [B] of FIG. 2, when the baseband signal I matches the center voltage first at the first timing T0, the period from the first timing T0 to the timing T1 is changed. Since the I-channel gate control signal GI turns on and the G-channel gate control signal GQ turns off, the voltage VI of the baseband signal I output from the gate circuit 6
Is as shown in [C] of FIG. 2 and Expression 2, and the voltage VQ of the baseband signal Q output from the gate circuit 7
Is "0" as shown in [D] of FIG. Accordingly, the transmission output obtained in the modulation unit 14 is as shown in the waveform (a) in [E] of FIG.
It has a waveform equivalent to a state where the ramp function [1-Cosωt] is multiplied.

When the ramp bit ends at the timing T1, both the I-channel gate control signal GI and the G-channel gate control signal GQ output from the timing detection circuit 9 are turned on, and the baseband signals I and Q remain unchanged as they are. Output to The transmission output at this time is “1” according to Equation 1, and the waveform (b) of FIG.
It becomes as shown in.

At the time of burst-out, at the beginning of the guard bit, the baseband signal that has become equal to the center voltage VC first is turned off from the second timing T2 to timing T3, and the other baseband signal is turned on. . After timing T3, both baseband signals are turned off until the next burst-in.

For example, as shown in FIGS. 2A and 2B, during the period from the second timing T2 to the timing T3, I
Since the channel gate control signal GI remains on and the G channel gate control signal GQ turns off, the voltage VI of the baseband signal I output from the gate circuit 6 becomes
As shown in [C] of FIG. 2 and Expression 2, the voltage VQ of the baseband signal Q output from the gate circuit 7 becomes “0” as shown in [D] of FIG. Become. Therefore, the transmission output obtained in the modulation section 14 is as shown in the waveform (c) in FIG. 2E and the equation (3), and has a waveform equivalent to that obtained by multiplying the ramp function.

When the guard bit ends at timing T3, both the I-channel gate control signal GI and the Q-channel gate control signal GQ are turned off, and the modulation unit 14
Is "0" until the next burst-in.

As described above, when the baseband signals Q and I whose waveforms have been shaped by the waveform shaping circuit of the present invention are modulated in the modulation section 14, the rise and fall of the transmission output become gradual. The spread is reduced, and interference power to adjacent channels can be suppressed. When the spread of the spectrum in the above embodiment was measured, the waveform shaping in the present embodiment shown in FIG. 3B was performed as compared with the case where the waveform shaping shown in FIG. 3A was not performed. ± 60
The leakage power in the adjacent channel of 0 kHz is about 12d
B or more.

[0035]

As described above, according to the waveform shaping circuit of the π / 4 shift QPSK modulation system of the present invention, the spread of the frequency spectrum of the transmission output can be achieved without the need for a ramp function ROM or the like operated by a high-speed clock. Is obtained, and interference due to leakage power to an adjacent channel can be suppressed.

Therefore, since the frequency of the clock can be reduced, the effect of reducing power consumption can be obtained. In addition, since the waveform shaping circuit mainly includes timing detection and gate control, it can be easily realized by a digital circuit, the circuit can be easily integrated, and the entire π / 4 shift QPSK modulator can be downsized. In addition to the above, the effect that the cost can be reduced can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a π / 4 shift QPSK modulation type waveform shaping circuit according to the present invention.

FIG. 2 is a waveform chart for explaining a relationship between signals in the embodiment.

FIG. 3 is a distribution characteristic diagram of a frequency spectrum of a transmission output in the embodiment.

FIG. 4 is a detailed configuration diagram illustrating a configuration example of a data determination unit in the embodiment.

FIG. 5 is a waveform diagram illustrating a waveform in a conventional π / 4 shift QPSK modulation method.

FIG. 6 is a block diagram of an example provided with a conventional π / 4 shift QPSK modulation type waveform shaping circuit.

[Explanation of symbols]

 Reference Signs List 1 π / 4 shift QPSK signal generator 2, 3 D / A converter 4, 5 Roll-off filter 6, 7 Gate circuit (gate circuit) 9 Timing detection circuit 10 Counter 11 Data discrimination unit 12, 13 Delay circuit 14 Modulation unit

Claims (1)

(57) [Claims] 1. A π / 4 shift QPSK modulation type waveform shaping circuit that performs burst transmission using two baseband signals represented as sine waves having phases different from each other by 90 °. Voltage, and at the time of burst-in, the first timing at which any baseband signal matches the center voltage first is detected, and at the time of burst-out, any baseband signal is detected first. A timing detection circuit for detecting a second timing coinciding with the center voltage, and a baseband that coincides with the center voltage at the first timing until the phase shifts by 90 ° from the first timing. Only the signal is passed, the other baseband signal is cut off, and a 90 ° phase shift from the second timing is performed. Between the 2nd
Blocking the baseband signal of the direction which coincides with the center voltage in timing, [pi / 4, characterized in that a gate circuit for passing only the other of the baseband signal Shi
Waveform shaping circuit of shift QPSK modulation system.