JPH0746787B2 - Transmission quality measuring device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission quality measuring apparatus which is added to a phase modulation type or QAAM type data modem receiver to measure the quality of a transmission line during data transmission.

SUMMARY OF THE INVENTION The present invention is added to a phase modulation type or QAAM type data modem receiver to normalize an error signal obtained by removing a frequency offset component, attenuation distortion, group delay distortion, etc. from a received demodulated signal, and to The noise and the phase jitter of the transmission line are calculated from the directional component and the quadrature component.

Even if the attenuation characteristic or group delay characteristic of the transmission line is poor,
There is an effect that the noise on the transmission line and the phase jitter can be accurately measured.

2. Description of the Related Art Conventionally, as a transmission quality measuring apparatus of this type, a power of a difference between an input signal and an output signal of a data determiner in a data modem receiver is measured and the measured power is compared with a predetermined value. Therefore, there is a method in which the quality of the transmission quality is determined. This method can judge the quality of the transmission line, but has the drawback that it cannot know the cause of the transmission quality defect and that the degree of the defect cannot be quantitatively analyzed and measured.

As a solution to this drawback, the spread of the received eye signal in the in-phase direction and the quadrature direction is measured.
There is a method of measuring the S / N ratio and the amount of phase jitter (see US Pat. No. 4,381,546). This method makes the measurement inaccurate when the attenuation characteristic or the group delay characteristic of the transmission line is bad. Also,
Since the received signal that has been subjected to the carrier phase reproduction is used as the received eye signal, there are drawbacks such as inaccurate measurement of phase jitter.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention solves the above-mentioned drawbacks of the related art, and accurately determines the S / N ratio and the amount of phase jitter in the transmission line even when the attenuation characteristic or group delay characteristic of the transmission line is poor. Provided is a transmission quality measuring device capable of performing high-speed measurement.

Means for Solving the Problems A transmission quality measuring apparatus of the present invention is a data modem receiver having a carrier phase control circuit for outputting a data signal by following a frequency offset, which is obtained during calculation of the carrier phase control circuit. Integrator which integrates the frequency offset amount and the output signal s of the integrator
A function generator that outputs e ^-js , a complex multiplier that performs a complex multiplication between the output of the function generator and the demodulated signal, and a complex automatic equalizer connected to the output of the complex multiplier, A subtracter that takes the difference between the output of the complex automatic equalizer and the decision data output of the data modem receiver and outputs it as an error signal, and the magnitudes of the in-phase direction and quadrature direction components of the error signal output by the subtractor. And a calculation means for measuring the height.

Embodiments of the Invention Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.
That is, the frequency offset amount 2 output from the data modem receiver 1 is integrated by the integrator 3 to output the output signal s of the integrator 3.
To output e ^-js , the demodulation output 5 output from the data modem receiver 1 is multiplied by the output of the function generator 4, and the output of the complex multiplier 6 An automatic equalizer 8 for automatic equalization, and a calculation unit for normalizing the difference between the output of the automatic equalizer 8 and the determination data output, and calculating the S / N ratio and the phase jitter from the in-phase component and the quadrature component. Composed of 10 and.

Now, if the transmission signal is Ak, the frequency offset is Δω, the phase jitter is φ (t), the stationary phase is θ, the impulse response of the transmission line is h (t), and the noise mixed in the transmission line is nk, Demodulator in data modem receiver 1 at t = KT
The demodulation output 5 output by 11 is Xk = h (t) * (Ake ^{j (Δωk + 4K + θ)} + nk).
It is expressed by (1). The data modem receiver 1 stores Δω in a built-in register in order to follow the frequency offset, and supplies the frequency offset amount 2 to the integrator 3. The output of the integrator 3 is input to the function generator 4. The function generator 4 is a function device that converts the input signal s into e ^-js and outputs it. As shown in FIG. 3, the function generator 4 uses a cosine function generator 28 and a sine function generator 29 to generate an in-phase component cos (S) and a quadrature component sin (s) with respect to an input signal s. )
Are output respectively. In-phase component cos (S) and quadrature component s
When in (s) is expressed on the complex plane, it becomes e ^-js .

The cosine function generator 28 and the sine function generator 29 are, for example,
This can be realized by the read only memories (ROM) 30 and 31 in which the cosine function value and the sine function value corresponding to the value of the address data are stored, as shown in FIG. That is, the input signal s is input as the addresses of the ROM30 and the ROM31 as shown in FIG. 5, and the output data of the ROM30 and the cos (S), sin
The value of (s) can be obtained.

Therefore, the output Pk of the function generator 4 becomes Pk = e- ^jΔωK (2).

When Pk is multiplied by the demodulation output Xk by the complex multiplier 6 to remove the frequency offset component, the output of the complex multiplier 6 is Qk = Xk Pk = h (t) * (Ak e ^{j (4K + θ )} + Nk e
_{^{-JΔωK) I t = KT ...... (}} 3) is obtained. The automatic equalizer 8 converges by referring to the judgment data output 7 output from the data modem receiver 1, and Ak (known)
Is used as a reference value, and the transmission path impulse response h (t) included in Qk is removed by the influence of the transmission path distortion and is output. Transmission line noise and phase jitter remain at the output of the automatic equalizer 8. That is, k = ^Ake-j4K + k (4) However, k = ^{nke-j (ΔωK + θ)} , | k | ² = | nk | ² . When φk is sufficiently small, the equation (4) is rewritten as follows.

k = Ak (1-jφk) + k (5) If the difference between this and the judgment data output 7 is taken, the error signal 9
Is obtained. That is, the error signal 9 is Becomes If this is normalized by Ak * Ak / | Ak | ² , To get Where k has only orthogonal components, Note that the term of has an orthogonal direction component and an in-phase direction component of the same magnitude.

Can be calculated as However, <> represents a time average calculation. The arithmetic unit 10 is configured to perform the above (7), (8),
This is a circuit for performing the calculation of equation (9).

FIG. 2 is a block diagram showing details of the above embodiment.
The data modem receiver 1 comprises a demodulator 11, a carrier phase control circuit 12 and a determiner 13. The subtracter 18 inputs the difference between the output of the automatic equalizer 8 and the judgment data output 7 (correct data) to the arithmetic unit 10 as an error signal k, and the coefficient of the automatic equalizer 8 is minimized so that the error signal is minimized. Converge. The arithmetic unit 10 multiplies the output of the subtractor 18 by the output of the normalization arithmetic unit 19 for normalization, extracts the in-phase directional component from the output of the complex multiplier 20 by the realization unit 21, and the realization unit 21 The output of is squared by a squarer 22, and an averager 23 takes a time average. The output of the averaging device 23 represents the S / N ratio. On the other hand, the imaginary number generator 24 extracts the orthogonal component, and the squarer 25 squares it. The subtracter 26 subtracts the output of the squarer 22 from the output of the squarer 25 and inputs it to the averaging device 27, and the averaging device 27 takes the time average and outputs it as a phase jitter measurement value.

The present embodiment has an effect that even if the attenuation characteristic or the phase characteristic of the transmission line is bad, the influence thereof can be removed by the automatic equalizer 8 and the noise and the phase jitter of the transmission line can be accurately measured. There is.

As described above, in the present invention, the error signal obtained by removing the frequency offset component, the attenuation distortion, the group delay distortion, and the like from the received demodulated signal is normalized, and the same direction component and quadrature component Since the configuration is such that noise and phase jitter are calculated, it is possible to accurately measure the noise and phase jitter of the transmission line even when the attenuation characteristic or group delay characteristic of the transmission line is poor. .

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing details of the above embodiment. FIG. 3 is a block diagram of the function generator 4, FIG. 4 is a diagram showing data stored in the ROM constituting the cosine function generator 28 and the sine function generator 29, and FIG. 5 is the ROM of FIG. It is a figure which shows an example of the function generator 4 comprised using. In the figure, in the figure, 1: data modem receiver, 2: frequency offset amount, 3: integrator, 4: function generator, 5: demodulation output, 6: complex multiplier, 7: decision data output, 8: complex Automatic equalizer, 9: error signal output, 10: arithmetic unit, 11: demodulator, 12: carrier phase control circuit, 13: decision unit, 18: subtractor, 19: normalization arithmetic unit, 20: complex multiplier , 21: Realizer, 22, 25: Squarer,
23, 27: Averager, 24: Imaginator, 26: Subtractor, 28: Cosine function generator, 29: Sine function generator, 30: ROM, 31: ROM

Claims (1)

[Claims] 1. A data modem receiver having a carrier phase control circuit for outputting a data signal following a frequency offset, comprising: an integrator for integrating a frequency offset amount obtained during calculation of the carrier phase control circuit; Output signal s of the integrator
A function generator that outputs e ^-js , a complex multiplier that performs a complex multiplication between the output of the function generator and the demodulated signal, and a complex automatic equalizer connected to the output of the complex multiplier, A subtractor that takes the difference between the output of the complex automatic equalizer and the decision data output of the data modem receiver and outputs as an error signal, and the magnitudes of the in-phase and quadrature component of the error signal output by the subtractor. A transmission quality measuring device, comprising: