JPH06125369A - Waveform shaping circuit for qpsk modulation system - Google Patents

Abstract

PURPOSE:To suppress the spread of a spectrum in the pi/4 shift QPSK modulation system. CONSTITUTION:When a base band signal I is coincident with a center voltage early in the base of burst-in a timing detection circuit 9, the point of time is set as a 1st timing T0 and only one gate circuit 6 or T is open from the 1st timing T0 till a timing T1 to pass only a base band signal I of the I channel thereby shaping a leading of a transmission output slowly as shown in Figure [E](a). Similarly in the case of burst-out, the one gate circuit 6 or 7 is open from a timing T2 till a timing T3 to pass only a base band signal I of the I channel thereby shaping a of a transmission output wave slowly as shown in figure [E] (c).

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 and the like in which frequency utilization efficiency is required to be improved.

[0002]

2. Description of the Related Art Digital modulation systems used for mobile communications such as car telephones include GMSK, 4-level FM, PLL.
Although there are -QPSK and the like, the π / 4 shift QPSK modulation method is adopted as a modulation method with higher frequency utilization efficiency. Then, in burst transmission of mobile communication adopting the TDMA method, for example, as shown in [A] of FIG. Therefore, the spectrum of the transmission power spreads at the rising time and the falling time of such burst transmission, and there arises a problem that leakage power that interferes with an adjacent channel is generated as shown in FIG. 5B.

Therefore, in the conventional π / 4 shift QPSK modulation system, a ramp function as shown in FIG. 5C, for example, is applied to the I and Q channel baseband signals at the rise and fall of burst transmission. It is configured to multiply both of the baseband signal Q of 1. and gently shape the rising and falling to prevent the spread of the spectrum of the transmission power.

FIG. 6 shows an example of such a circuit configuration.
In FIG. 6, 101 is a π / 4 shift QPSK signal generator, 102 is a waveform shaper, 103 is a ramp function ROM, and 104 is a ramp function ROM.
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-
The data table corresponding to the function 1 / 2cosωt] is written as a ramp function.

Here, the first data x1 and y1 of the transmission data input in synchronization with the burst-in are preambles, and their values are x1 = 0 and y1 = 0. Then, the ramp function data in the ramp function ROM 103 is multiplied in the waveform shaping section 102 by 4 bits of the internally generated ramp bits (values are all “0”). When such a 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 baseband signals I and Q are multiplied by the ramp function to shape the waveform, and the waveform is shaped at the rising edge of the transmission output.

Similarly, the waveform shaping at the falling edge is performed by the ramp function ROM 103 for 4 bits of the guard bit.
Multiply the ramp function data of. A delay circuit is provided to match the burst-in and burst-out timings with the rising and falling timings of the transmission data.

[0007]

In such a conventional circuit system, the rising and falling of the transmission output can be shaped gently, but the ramp function ROM and the waveform shaping section are required, so that the circuit scale is large. There is a problem that the device becomes large and the cost of the device increases. Further, since it is necessary to read out the ramp function ROM with a high-speed clock and perform digital calculation processing in the waveform shaping section, there is a problem that power consumption increases.

In view of the above problems, it is an object of the present invention to realize a circuit capable of gently shaping the rising and falling of the transmission output as in the conventional case with a simpler circuit configuration.

[0009]

SUMMARY OF THE INVENTION In the present invention, a π / 4 shift QP that also performs burst transmission by using two baseband signals represented as sine waves having 90 ° different phases.
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 one of the baseband signals first coincides with the center voltage is detected. However, at the time of burst-out, between the timing detection circuit that detects the second timing at which one of the baseband signals first coincides with the center voltage, and the 90 ° phase transition from the first timing. Means to pass only the baseband signal that matches the center voltage at the first timing, block the passage of the other baseband signal, and keep the phase shift of 90 ° from the second timing. Shuts off the baseband signal that matches the center voltage at the second timing and passes only the other baseband signal. And a gate circuit that makes it possible.

[0010]

The transmission output P of a quadrature modulator such as a QPSK modulator which uses baseband signals Q and I having different 90 ° phases as in the present invention can be expressed by the following formula 1.

[0011]

[Equation 1]

However, the voltage of the baseband signal Q is V
Let Q be the voltage of Q and the baseband signal I. When the ramp bit and the guard bit are “0”, the π / 4 shift QPSK baseband signal waveform through the roll-off filter has a phase shift of π / 4 for both the baseband signals Q and I. The waveforms of the signals Q and I are sine waves with a 90 ° phase shift, as shown in FIGS. 2C and 2D. 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 one of the baseband signals first matches the center voltage is detected as the first timing. From the first timing T0 to the timing T1 when the phase shifts by 90 ° (between two symbols), the baseband signal (baseband signal I in FIG. 2) that is equal to the center voltage at the first timing is used. , The gate circuit is turned on to pass through the gate circuit, while the other baseband signal (baseband signal Q in FIG. 2) is turned off and does not pass through the gate circuit.

At this time, both baseband signals I and Q are
The voltages VI and QI of are expressed by either [A] or [B] of the following mathematical expression 2.

[0015]

[Equation 2]

Here, in both cases of [A] and [B] of the above formula 2, when substituting into the above formula 1, the transmission output P1 during this period is expressed by the following formula 3.

[0017]

[Equation 3]

Since the waveform of the transmission output P1 has a waveform that gently rises from "0" as shown in the waveform (a) of FIG. 2E, the spectrum of the transmission power does not spread.
Similarly, the timing detection circuit detects, as the second timing, the timing at which one of the baseband signals first coincides with the center voltage at the time of burst-out.

From this second timing T2, the phase is 90
° Until the timing T3 when transition occurs (between two symbols), the baseband signal (baseband signal Q in FIG. 2) that becomes equal to the center voltage at timing T2 is turned off by the gate circuit and cut off by the gate circuit. However, the other baseband signal (baseband signal I in FIG. 2) is turned off at a 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 the formula [A] or the formula [B] of the above-mentioned formula 2, respectively.

Therefore, the waveform of the transmission output P1 during this period is a waveform that gently falls toward "0" as shown in (c) of [E] of FIG. 2, 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]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A QPSK modulation type waveform shaping circuit of the present invention will be described below in detail with reference to FIG. In FIG. 1, reference numeral 1 denotes a π / 4 shift QPSK signal generator that generates an I channel baseband signal ID and a Q channel baseband signal QD, and 2 and 3 convert the baseband signals ID and QD into analog signals. Do D
A / A converters, 4 and 5 are roll-off filters, 6 and 7 are gate circuits that control on / off of passage of the baseband signals ID and QD, and 8 is a center voltage generator that outputs a center voltage VC.

Reference numeral 9 denotes a timing detection circuit, which is a counter 10 which counts the transmission clock TXCK and outputs a discrimination signal indicating a ramp bit and a guard bit, and a base for the I channel in synchronization with the discrimination signal from the counter 10. A data discriminating unit 11 that 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. And a delay circuit 12, which delays each gate control signal GI, GQ by the same time as the group delay time in the roll-off filters 4, 5.
It is composed of 13 and.

In the data discriminating section 11, when the discrimination signal indicates burst-in, if the baseband signal I first coincides with the center voltage VC,
The time when they match is detected as the first timing T0, and the time when the 90 ° phase shifts from this time and the other baseband signal Q matches the center voltage VC is set as the 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.

On the contrary, when the baseband signal Q first coincides with the center voltage VC, the coincident time point is detected as the first timing T0, and the phase shifts by 90 ° from this time point and the other baseband signal is detected. Timing when the signal I coincides with the center voltage VC is timing T1, and the I channel gate control signal G is provided between timing T0 and timing T1.
I remains off, Q channel gate control signal G
Q turns on.

Further, when the discrimination signal indicates burst out, and when the baseband signal Q first coincides with the center voltage VC, the coincident time is detected as the second timing T2, and from this time point. Timing T3 is a time point when the 90 ° phase shift occurs and the other baseband signal I matches the center voltage VC. And 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.

On the contrary, when the baseband signal I first coincides with the center voltage VC, the coincident time point is detected as the second timing T2, and the phase shifts by 90 ° from this time point and the other baseband signal is detected. Timing when the signal Q coincides with the center voltage VC is timing T3, and the I channel gate control signal G is provided between timing T2 and timing T3.
I turns off and the Q channel gate control signal GQ remains on.

FIG. 4 showing an example of the configuration of the data discrimination unit 11
In the decision signal, 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, F
4 and 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.
It is a modulator that performs shift QPSK modulation.

In the above structure, at the time of burst-in,
The baseband signals ID and QD are turned on for the signal that is equal to the center voltage VC first from the first timing T0 to the timing T1, that is, for 4 bits of the ramp bit, and the other signal is turned off. . For example, as shown in [A] and [B] of FIG. 2, when the baseband signal I first coincides with the center voltage at the first timing T0, the first timing T0 to the timing T1 Since the I channel gate control signal GI is turned on and the G channel gate control signal GQ is turned off, the voltage VI of the baseband signal I output from the gate circuit 6
Is as shown in [C] of FIG. 2 and Equation 2, and is the voltage VQ of the baseband signal Q output from the gate circuit 7.
Becomes "0" as shown in [D] of FIG. Therefore, the transmission output obtained in the modulator 14 becomes as shown in the waveform (a) in [E] of FIG.
It has a waveform equivalent to the state in which it is multiplied by the ramp function [1-Cosωt].

When the ramp bit ends at 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 are unchanged as they are in the modulator 14. Is output to. The transmission output at this time is “1” according to Equation 1, and the waveform (b) of [E] in FIG.
As shown in.

At the burst-out time, the baseband signal that has become equal to the center voltage VC at the beginning of the guard bit is turned off from the second timing T2 to the 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 [A] and [B] of FIG. 2, between the second timing T2 and 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 is
As shown in [C] of FIG. 2 and Equation 2, the voltage VQ of the baseband signal Q output from the gate circuit 7 is “0” as shown in [D] and Equation 2 of FIG. Become. Therefore, the transmission output obtained in the modulator 14 is as shown in the waveform (c) in [E] of FIG. 2 and Equation 3, and has a waveform equivalent to the state in which the ramp function is multiplied.

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 modulator 14
The transmission output that is output from is "0" until the next burst-in.

As described above, when the modulating section 14 modulates the baseband signals Q and I whose waveforms have been shaped by the waveform shaping circuit of the present invention, the rising and falling edges of the transmission output become gentle. The spread is reduced, and the interference power to the adjacent channel can be suppressed. As a result of actually measuring the spread of the spectrum in the above-mentioned embodiment, 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. In case of ± 60
Leakage power in adjacent channel of 0 kHz is about 12d
It was reduced by B or more.

[0035]

As described above, according to the waveform shaping circuit of the QPSK modulation system of the present invention, the spread of the frequency spectrum of the transmission output can be prevented without the need for a ramp function ROM or the like which operates with a high speed clock, The effect that the interference due to the leakage power to the adjacent channel can be suppressed can be obtained.

Therefore, since the clock frequency can be lowered, the effect of reducing the power consumption can be obtained. Further, since this waveform shaping circuit has timing detection and gate control as main elements, it can be easily realized by a digital circuit and the circuit can be easily integrated, and the entire π / 4 shift QPSK modulator can be miniaturized. It is possible to obtain the effect that the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a waveform shaping circuit of the QPSK modulation system of the present invention.

FIG. 2 is a waveform diagram 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 showing a configuration example of a data discriminating unit in the embodiment.

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

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

[Explanation of symbols]

 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)

[Claims] 1. A waveform shaping circuit of a π / 4 shift QPSK modulation system which also uses two baseband signals represented as sine waves having 90 ° different phases to perform burst transmission, and a waveform and a center of the baseband signal. The voltage is compared, and at the time of burst-in, the first timing at which one of the baseband signals first matches the center voltage is detected, and at the time of burst-out, one of the baseband signals is detected first. A timing detection circuit that detects a second timing that coincides with the center voltage, and a baseband that coincides with the center voltage at the first timing between the first timing and a phase shift of 90 °. Only the signal is passed, the passage of the other baseband signal is blocked, and the 90 ° phase shift from the second timing is performed. Between the second
And a gate circuit that blocks the baseband signal that matches the center voltage at the timing of 1 and passes only the other baseband signal.
Modulation type waveform shaping circuit.