JP2883086B2 - Modulated wave carrier frequency measurement method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for accurately measuring a carrier frequency of a modulated wave.

[Conventional technology]

In the field of communication, an angle-modulated wave that modulates the phase or frequency of a carrier wave is often used.

This angle-modulated wave S (t) can be expressed as S (t) = I (t) cos (2πct) -Q (t) sin (2πct).

I (t) and Q (t) represent the amplitudes of the in-phase and quadrature components, respectively, and c is the carrier frequency.

The trajectory of the complex envelope E (t) = I (t) + jQ (t) is shown in FIG.

FIG. 5 (a) is a diagram showing a signal space diagram of a modulated wave having a constant amplitude, in which an angle θ of a point P on a circular locus having a constant amplitude r changes due to modulation.

FIG. 5 (b) is a diagram showing a signal space diagram of a modulated wave whose amplitude fluctuates, and shows a 4-phase PSK in which information corresponding to four phases of P ₀ , P ₁ , P ₂ and P ₃ is transmitted. ing.

On the receiving side, in order to demodulate a signal from such a modulated wave, it is necessary to extract a carrier wave. In order to measure the frequency c, usually, a frequency counter is used for a fixed period T. Is measured, and the value obtained by dividing N by T is used as the carrier frequency of the modulated wave.

[Problems to be solved by the invention]

In a method of measuring a carrier frequency using a frequency counter, when a modulation frequency of a modulation wave is large, a frequency largely fluctuates due to modulation, or when an amplitude becomes extremely small, a measurement error increases. There's a problem.

The reason why this error increases will be described with reference to FIG.

FIG. 6 (a) shows the case of constant amplitude modulation, which is a time waveform of the modulated wave S (t) shown in FIG. 5 (a). In this figure, at time point A, two modulated waves α and β having different modulation frequencies are connected in phase continuation.

The frequency measurement counter displays the time waveform S within a certain period.
The number of zero-cross points at the rise of (t), that is, the wave number is measured.

If the carrier frequency c is measured in a short time by such a method, the frequency fluctuates due to the influence of the modulation, so that the frequency cannot be measured accurately.

Also, FIG. 6 (b) shows the case of PSK, a time waveform in the case of changes from P ₁ of the modulated wave as shown in FIG. 5 (b) to P _3. In this figure, at time B, the modulation phase is 180
° Two different modulated waves α and β are connected. Therefore, the rising of the carrier wave exists twice in one cycle,
The modulation causes an error in the frequency measurement counter. A similar error occurs even if the phase changes in the area indicated by C in FIG. In such a modulated wave, further deterioration occurs due to the filtering process on the modulated wave.

FIG. 6 (c) shows the result of filtering the waveform of FIG. 6 (b). When the phase changes by 180 ° as shown in this figure, the amplitude of the filter output γ becomes extremely small. As a result, there have been drawbacks in that the frequency measurement counter malfunctions and is easily affected by noise.

The present invention has been made in view of the above problems, and has as its object to provide a highly accurate method for removing a frequency fluctuation due to modulation when measuring a carrier frequency of a modulated wave.

[Means for solving the problem]

According to the present invention, the above objects are achieved by a method as set forth in the appended claims.

That is, the present invention measures the wave number N of the modulated wave in a certain period T, estimates the amount of phase fluctuation due to the modulation during that period from the waveform obtained by detecting the modulated wave, and converts the amount of phase fluctuation into a wave number n Or a modulated wave carrier frequency measuring method characterized in that a value obtained by dividing a value N−n obtained by subtracting the converted value n from the wave number N by T is a carrier frequency of a modulated wave, or In a system that performs modulation and demodulation using the modulation wave, the modulation wave is transmitted for a certain period T while the modulation wave subjected to multi-level phase modulation using a code sequence in which the amplitude of the modulation wave is suppressed to a certain value or less and the phase transition is suppressed, On the double tone side, a modulation wave carrier frequency measuring method is characterized in that the wave number N of the modulation wave in the certain period is measured and a value obtained by dividing N by T is used as the carrier frequency of the modulation wave.

[Action]

The present invention estimates the amount of phase variation of a modulated wave from a signal detected during a frequency measurement period on the receiving side, converts it to a wave number, and counts the rise of the actual modulated wave to obtain a wave number. The frequency is obtained after the correction, or in the case of PSK modulation, during the period, a modulated wave with suppressed amplitude fluctuation is generated on the return side, thereby enabling accurate frequency measurement.

Furthermore, a greater effect can be achieved by a combination of both the transmission and reception methods.

〔Example〕

 A first embodiment of the present invention is shown in FIG. 1 and FIG.

FIG. 1 is a diagram showing the phase transition of a binary FSK modulated wave,
The change of the modulation phase φm (t) with respect to the time t in the binary FSK modulation wave having a constant amplitude is shown.

A thin line indicates a phase change that can be taken depending on a combination of transmission codes when φm (0) = 0.

The bold line is a specific example of the phase change, and indicates that the phase has changed in the order of D → E → G.

For example, in the case where the frequency is measured in a period T = 3τ from D to G in the same figure, from the detected waveform, the transmission code is 1 when D → E, 1 when E → F, 1 → F →
When G, it is determined to be -1. During this time, when ₀ , φ ₀ ,
If hotkey phi ₀ by a phase of over 1 degree of modulation to vary is set, it is estimated to vary the phase only phi ₀ between G from D. Expressing this as a wave number n,
n = φ ₀ / 2π.

On the other hand, if the rising of the modulated wave is N times during T, the estimated value of the carrier frequency c is c = (N
-N) / T.

FIG. 2 shows an example of a circuit for estimating the carrier frequency based on the above principle.

FIG. 2 shows a circuit block diagram of the demodulator, wherein 1 is a modulation wave input terminal, 2 is a limiter amplifier, 3 is a demodulator, 4 is a data output terminal, 5 is a frequency counter, 6 is a timing generation circuit, 7 Denotes a phase change estimating circuit, 8 denotes a frequency estimating circuit, and 9 denotes a frequency output terminal.

 The operation will be described below.

First, a digital modulation wave is input from the input terminal 1. This modulated wave is amplified by the limiter amplifier 2 to a specific amplitude. The amplified modulated wave is demodulated by the demodulator 3 to extract a data sequence. This data series is output from the data output terminal 4.

In order for the demodulator to operate, the carrier frequency of the modulated wave must be known. However, since the modulation is digital modulation, the data sequence can be accurately demodulated even if there is some frequency error.

On the other hand, the output of the limiter amplifier 2 is also input to the frequency counter 5 and measures the number of modulated waves. The measurement time of the wave number is controlled by the timing generation circuit 6,
The wave number N during the certain period T is counted. The phase change estimating circuit 7 is controlled by the same timing signal. Upon receiving the demodulated data sequence from the demodulator 3, the phase change estimating circuit 7 calculates the amount of phase change during a certain period T based on the configuration of the modulated wave. Further, the phase change amount (radian) is divided by 2π to output a wave number converted amount n.

The N and n obtained in this manner are used as the frequency estimation circuit 8
, The circuit calculates (N−n) / T, and the carrier frequency c is output from the frequency output terminal 9.

Since the amount of phase change is estimated from the detected signal and the measured wave number is corrected, the frequency can be accurately measured.

In addition, the carrier frequency of a modulated wave having a relatively high degree of modulation can be measured in a short time.

 A second embodiment of the present invention is shown in FIGS.

FIG. 3 is a diagram showing a phase transition of a four-phase PSK modulated wave,
This is an example of the four-phase PSK described with reference to FIG.

In the 4-phase PSK, the amount of transition of the modulation phase φm (t) for each τ, the modulation phase φm (t) −φm (t−τ) has four values,
That is, 0, ± π / 2, π, but the transition amount of π is prohibited during the measurement period to prevent the amplitude from becoming zero.

The phase fluctuation amounts that the thin line can take and the thick lines P ₀ , P ₁ , P ₂ , and P ₁ are specific examples of the transition. The measurement time is 3τ from time X to time Y. The phase transition during this period is τ / 4, and this value can be easily estimated from the detected data sequence. The carrier frequency c is given by c = (N
-N) / T.

In the second embodiment, since the code sequence is selected so that the amplitude does not become 0, the frequency accuracy is extremely improved.

For a specific circuit example of the second embodiment described above,
The receiving side may use the same one as in FIG.

In the case of selecting a code sequence whose amplitude does not become 0, the method of measuring the carrier frequency on the receiving side is to measure the wave number N of the modulated wave in a fixed period T, and to divide the value obtained by dividing N by T into the carrier. There is also a great effect on ordinary demodulators that use frequencies.

The characteristic feature of the second embodiment is that the phase transition π is prohibited, and various methods on the transmission side for realizing this are conceivable.

 FIG. 4 shows two embodiments.

FIG. 4 (a) is a block diagram of a PSK modulation circuit for inhibiting the phase transition π, 9 is a frequency output terminal, 10 is a data input terminal, 11 is a data conversion circuit, 12 is a data input enable signal terminal, Reference numeral 13 denotes a modulator, and 14 denotes a modulated wave output terminal.

In the case of this example, the input data system is controlled while the frequency is being measured.

Originally, although quaternary data can be transmitted, ternary transmission is performed while inhibiting the change of π, so the transmission rate must be reduced to 3/4 during the measurement time. For this purpose, in the case of FIG. 1, the signal input from the data input terminal 10 is converted by the data conversion circuit 11. This conversion is for converting into a sequence in which the phase shift of π does not occur in the modulator 13.

In this conversion process, the input signal is stored in the buffer memory, but when the data input is too fast and the buffer memory is full, the data input enable signal terminal 12
To “L” to suspend the data input operation. When there is room in the buffer again, the data input permission signal is set to "H" to perform input.

In this way, a modulated wave whose amplitude does not become 0 can be output from the modulated wave output terminal 14.

In such an embodiment, since the data transmission rate during this measurement period is reduced to 3/4, the receiving side needs to perform processing for it.

FIG. 4 (b) shows a block diagram of the QPSK / OQPSK modulator, where 15 is a data input terminal, 16 is a QPSK / OQPSK modulator, and 17 is a modulated wave output terminal.

The example of this figure is a method for transmitting the input from the data input terminal 15 without lowering the transmission rate.

In this method, the modulation uses a QPSK / OQPSK converter 16 that can switch between two modulations, QPSK and OQPSK. OQPSK is QPS
At the same transmission rate as K, the modulation wave timings of the in-phase component and the quadrature component are shifted by T / 2, and the phase change avoids the change of π as shown in FIG. 4 (c).

Therefore, during frequency measurement time, modulation is performed by OQPSK, and at other times, modulation is performed by QPSK. Accordingly, on the receiving side, a demodulator 3 shown in FIG. 4 that can demodulate both OQPSK and QPSK is used.

Generally, the demodulator operates more stably in QPSK than in OQPSK. Therefore, when frequency is not measured, QPSK transmission is performed.

〔The invention's effect〕

According to the present invention, it is possible to accurately measure a carrier frequency in a short time even in a modulated wave.

[Brief description of the drawings]

FIG. 1 is a diagram showing a phase transition of a binary FSK modulation wave, FIG. 2 is a circuit block diagram of a demodulator, FIG. 3 is a diagram showing a phase transition of a 4-phase PSK modulation wave, and FIG. Prohibit phase transition π
FIG. 4 (b) is a block diagram of the PSK modulation circuit, and FIG.
FIG. 4 (c) is a phase transition diagram of OQPSK, FIG. 5 (a) is a diagram showing a signal space diagram of a modulated wave having a constant amplitude, and FIG. 5 (b). ) Is a diagram showing a signal space diagram of a modulated wave whose amplitude varies, FIG. 6A is a time waveform of a modulated wave in the case of constant amplitude modulation, and FIG. 6B is a time of a modulated wave in the case of PSK. FIG. 6 (c) shows the filter output waveform. 1 ... modulated wave input terminal, 2 ... limiter amplifier, 3 ... demodulator, 4 ... data output terminal, 5 ... frequency counter,
6 timing generating circuit 7 phase change estimating circuit
8: Frequency estimation circuit, 9: Frequency output terminal, 10:
Data input terminal, 11 Data conversion circuit, 12 Data input enable signal terminal, 13 Modulator, 14 Modulated wave output terminal, 15 Data input terminal, 16 QPSK / OQPSK modulator,
17 …… Modulated wave output terminal

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-54-50261 (JP, A) JP-A-62-104251 (JP, A) JP-A-60-220650 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H04L 27/22 H04L 27/14

Claims (2)

(57) [Claims] 1. A method for measuring a wave number N of a modulated wave in a predetermined period T, estimating a phase fluctuation amount due to modulation in the period from a waveform obtained by detecting the modulated wave, and calculating a value n obtained by converting the phase fluctuation amount into a wave number. A modulated wave carrier frequency measuring method, wherein a calculated value is obtained by dividing a value N−n obtained by subtracting the converted value n from the wave number N by T as a carrier frequency of a modulated wave. 2. A system for performing modulation and demodulation using PSK, wherein a modulation side modulates a modulated wave subjected to multi-level phase modulation using a code sequence in which a phase transition in which the amplitude of the modulated wave becomes a certain value or less is suppressed for a fixed period. A modulated wave carrier frequency measuring method, wherein the modulated wave is transmitted during T and the double tone side measures the wave number N of the modulated wave in the fixed period, and a value obtained by dividing N by T is used as the carrier frequency of the modulated wave.