JPS5834372A - Measurement system for c/n ratio - Google Patents

Abstract

PURPOSE:To narrow down the dynamic range of a detector and to eliminate the need for a divider, by exercising AGC over an amplifier for a received signal while using the detection output voltage of a carrier as a control signal. CONSTITUTION:A received burst signal is passed through an AGC amplifier 11 and divided into two; and a band-pass filter 3 extracts only a carrier from the burst signal, and a band-stopping filter 4 removes only the carrier from the burst signal. Outputs of the filters 3 and 4 are detected by detectors 5 and 6 and inputted to sample holding circuits 7 and 8, where they are sampled and held according to a nonmodulation forecasting signal. The output of the sample holding circuit is applied as an AGC control voltage to an AGC amplifier 11. Consequently, a carrier detection voltage has no relation with the input level of the received burst signal and a noise detection voltage substitutes for a scale of C/N ratios directly to be displayed on a display 10.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a C/J%' measurement method for measuring the ratio between the carrier level and the noise level in a received signal.

The C7X ratio is the ratio of carrier power (N) to noise power (N) in a received signal, and is widely used to evaluate the quality of the received signal.

For example, a PCM-TDMA signal in satellite communication arrives in a burst form, and has an unmodulated signal at the beginning for synchronizing a carrier recovery circuit in a receiving station. Therefore, in order to evaluate the quality of the PCM-TDMA received signal, a method of measuring the C7N ratio of this unmodulated signal portion is used.

FIG. 1 shows the configuration of a conventional C/N measurement method. In the figure, reference numeral 1 denotes an amplifier that amplifies a received burst signal with a constant gain. 2 is a hybrid (II) which divides the output of amplifier 1 into two and outputs the divided output. 3 is a band pass filter that extracts only the carrier wave from the burst signal input from the hybrid 2; A band rejection filter 4 removes only the carrier wave from the burst signal input from the hybrid 2. 5.6 are detectors, and carrier filters 3.6 and 5.6 are detectors, respectively. The output of the carrier removal filter 4 is detected and converted to DC. Reference numerals 7 and 8 are sampling and hold circuits (S/H), which detect detectors 5, 5, and 8, respectively, in accordance with the non-modulated wave prediction signal. Sample and hold the detection voltage of B. A divider (DIV) 9 divides the output voltage of the sampling and holding circuit 7 by the output voltage of the sampling and holding circuit 80, and generates an output of the division result. A display 10 displays the output of the division result of the divider 9 using a suitable visual display or the like.

In FIG. 1, the non-modulated part prediction signal is a signal that predicts the timing of the appearance of the next non-modulated part in the received signal, and is generated by extracting the repetition period of the burst signal in a synchronization part (not shown). . Therefore, the sampling and holding circuits 7 and 8 are
By performing sampling at , the detected voltage corresponding to the carrier level and noise level in the non-modulated portion at the beginning of the burst signal is maintained, so by calculating the ratio of both chamber pressures using the divider 9, c/
Since a signal corresponding to the A+ ratio is obtained, this is displayed on a suitable display.

However, the incoming signal level at the receiving device varies greatly based on changes in spatial conditions and the like. (3) Therefore, in order to accurately measure the C7N ratio, it is necessary to make the dynamic range of the detector with respect to the carrier wave and noise very wide, which is difficult to realize. Furthermore, the divider that calculates the ratio of both detection voltages is not only expensive but also has large errors due to temperature fluctuations.

The present invention aims to eliminate such drawbacks of the prior art, and its purpose is to narrow the dynamic range of a detector that detects carrier waves and noise,
Moreover, it is an object of the present invention to provide a system that can omit a divider that calculates the ratio of both detected voltages.

The φ measurement method of the present invention narrows the dynamic range required of the detector by applying AGC to the amplifier for the received signal using the detection output voltage of the carrier wave as a control signal, and also directly measures the C/N using the noise detection voltage. By displaying it, the divider is omitted.

Hereinafter, the present invention will be described in detail with reference to Examples.

FIG. 2 shows (4) one embodiment of the c/pr measurement method of the present invention.
) shows the configuration. In this figure, the same parts as in Figure 1 are indicated by the same numbers, and their operations are similar to those in Figure 1.
This is the same as the case shown in the figure. 11 is an AGC amplifier,
The output of the sample and hold circuit 7, which samples and holds the detected voltage of the carrier wave using the non-modulation part prediction signal, is
It is applied as a control voltage to perform AGC operation.

Now, set the detection voltage of the carrier wave to 6. , the noise detection voltage is , then the ψ ratio is expressed by the following equation.

'/x = ('c/a n) heat...
(11 In Fig. 2, when the AGC loop gain is sufficiently large, the carrier detection voltage #1 is constant regardless of the received burst signal input level.The carrier detection voltage at this time is If Ec, then the C7N ratio is the second
In the circuit shown in the figure, the equation is as follows.

C/N = (EC)”...
As is clear from equations (2) and (2), the ψ ratio is 2 of the noise detection voltage.
Therefore, the noise detection voltage can be directly replaced and displayed on the scale of the ψ ratio.

In the case of the φ measurement method of the present invention, the dynamic range of the detector can be narrowed compared to the conventional method. In other words, the input level of the detector for the carrier wave must always be almost constant, and the dynamic range of the detector for noise is equal to the C/N measurement range. It is possible to make it narrower.

In the C/N measurement method of the present invention, as a result of the carrier detection voltage being constant, the C/N measurement method is directly calculated by the noise detection voltage without using a divider as shown in equation (2).
It becomes possible to display the β ratio. Therefore, not only the circuit configuration becomes simple and the price can be reduced, but also the measurement accuracy can be improved because a divider which is susceptible to temperature fluctuations is not used.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the structure of a conventional c/N measurement method, and FIG. 2 is a block diagram showing the structure of an embodiment of the c/y measurement method of the present invention. 1...Amplifier, 2...Hybrid (H), 3...
-Band pass filter, 4...Band rejection filter, 5.
6... Detector, 7.8... Sampling hold circuit (s/II), 9... Divider (vrv), 10...
...Display, 11...AGC amplifier. Patent applicant Fujitsu Limited agent Patent attorney Gobe Tamamushi (3 others) (7)

Claims (1)

[Claims] a second filter that generates an output that blocks only a carrier wave from the output of the amplifier; and a first filter that detects the output of the first filter and feeds it back to the amplifier as an AGC control voltage.
and a second detector that detects and outputs the output of the second filter, and displays the C7N ratio of the received signal based on the detected output voltage of the second detector. C7N ratio measurement method.