JPS63175540A - Pilot signal detecting circuit - Google Patents

Abstract

PURPOSE:To attain the titled circuit low in cost and small in size by providing a 2nd hybrid branching a pilot signal to the transmission side and providing a correlation device taking correlation between the branched pilot signal and a received base band signal to the reception side, and devising the circuitry in a way capable of outputting a square of the amplitude of the correlated value. CONSTITUTION:The pilot signal outputted from a pilot signal oscillator 2 is branched by a hybrid 8, one is multiplexed onto a transmission base band signal and other pilot signal is inputted to a correlation device 3. The received base band signal is branched by a coupler 4 at the receiver side R and inputted to the correlation device 3, where the correlation with the pilot signal is taken. A detection circuit 5 applies square detection to both the real and imaginary parts of the correlation device 3, respectively, and outputs the square of the amplitude of the correlation value. The result is compared with a reference voltage of a bias circuit 7, by a comparator circuit 6. Thus, small in size and low in cost are attained to the titled circuit without using an expensive band pass filter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the detection of frequency division multiplexed pilot signals, and particularly to a pilot signal detection circuit that detects pilot signals without using a bandpass filter.

[Conventional technology]

Conventionally, in the FM communication field, a pilot signal (usually a single sine wave is used) is frequency-division multiplexed onto a baseband signal before FM modulation is applied on the transmitter side for the purpose of monitoring failures in lines and communication equipment in the radio section. However, on the receiving side, a narrowband bandpass filter was used to detect the pilot signal from the received baseband signal.

For example, as shown in FIG. 3, an example of a conventional circuit, on the transmitting side S, the hybrid 11 multiplexes the pilot signal output from the pilot signal oscillator 12 onto the transmission baseband and outputs it as a transmission baseband signal.

Also, on the receiving side R, the received baseband signal is sent to the coupler 1.
4, extracts only the pilot signal from the received baseband signal through a bandpass filter 13, detects this in a detection circuit 15, converts it into a DC voltage corresponding to the level of the pilot signal, and converts this voltage and Bias circuit 17
A comparison circuit 16 compares the voltage with the reference voltage set by the reference voltage.

Here, if the output voltage of the detection circuit 15 is higher than the reference voltage, the comparison circuit 16 determines that a pilot signal has been detected and outputs a biloft signal detection signal. Furthermore, if a drop in signal level occurs due to a failure in the communication line or communication device, the output voltage from the detection circuit 15 will drop, and if this drops below the reference voltage, the comparison circuit 16 will output a pilot signal detection signal. It disappears.

[Problem that the invention seeks to solve]

In the conventional pilot signal detection circuit described above, a bandpass filter is used as a means to extract the pilot signal from the baseband signal.In particular, in order to pass only the pilot signal, a bandpass filter with a narrow band and steep cutoff characteristic is used. A filter is required. However, such bandpass filters usually have a complex and large circuit configuration and take time to adjust.Furthermore, the center frequency of the filter band fluctuates due to temperature changes, so a temperature compensation circuit is required. The problem is that it is expensive and large.

SUMMARY OF THE INVENTION An object of the present invention is to provide a pilot signal detection circuit that does not require a bandpass filter and can therefore be constructed at low cost and in a small size.

[Means for solving problems]

The pilot signal detection circuit of the present invention is provided with a second noise lift on the transmitting side that branches the pilot signal, multiplexes one into the transmitting baseband, and outputs the other to the receiving side, and a detection circuit on the receiving side. A correlator for correlating the pyro node signal branched from the transmitting side with the received baseband signal is provided in the preceding stage, and the detection circuit performs square-law detection of the real part and imaginary part of the output value of the correlator, respectively. The configuration is such that the square number of the amplitude of the correlation value can be output.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which S indicates the transmitting side and R indicates the receiving side.

On the transmitting side S, 1 is a hybrid, and a hybrid 8 branches the pilot signal (f signals are single sine waves) output from the pilot signal oscillator 2 into two, and multiplexes one of them into a transmission baseband signal. The other branched pilot signal is input to the correlator 3.

On the receiving side R, the received baseband signal is split by a coupler 4 and input to the correlator 3, where it is correlated with the pilot signal on the transmitting side.

After a predetermined correlation is taken, the signal is detected by a detection circuit 5 and output as a DC voltage, which is compared with a reference voltage set in a bias circuit 7 in a comparator circuit 6, and a pilot signal is detected based on the comparison result. A signal will be output.

By the way, since a single sine wave is normally used for the pilot signal, this can be expressed as P t(t) = cI((dpt +c<)
(1). Here, W is the angular frequency of the pilot signal.

The received baseband signal has a frequency arrangement as shown in FIG. 2, where A is a frequency division multiplexed telephone signal and B is a pilot signal.

Here, the pilot signal B in the received baseband signal is P r (t) −r eI (up'◆β) (2)
Then, the correlator 3 outputs a correlation component between the pyro-node signal on the transmitting side and the pyro-node signal in the received baseband signal. In the above equation, T is the integrating circuit of the correlator (
is the time constant of the low-pass filter). Equation (1) and (2)
Substituting the formula into formula (3) yields.

Now, regarding the correlation between the pilot signal on the transmitting side and the multiplex telephone signal of the received baseband signal, the beat waves that make simple harmonic motion at the difference between the frequency of the pilot signal and each frequency of the multiplex telephone signal are superimposed countlessly. However, these can be blocked by increasing the time constant T of the integrating circuit (low-pass filter) of the correlator. Therefore, the correlator 3 outputs the correlation value between the pilot signal Pt(t) on the transmitting side and the pilot signal Pr(t) in the received baseband signal, which is expressed by equation (4), and This means that the pilot signal inside is extracted as a correlation value. The real part and imaginary part of the correlation value in equation (4) are WR, W
, then equation (4) becomes W=rcos(β-α)+j
r 5in(β−α)−WRj W +
...It can be expressed as (5).

For this reason, the detection circuit 5 performs square-law detection on the real and imaginary part outputs WR and W of the correlator 3, respectively, and then calculates the sum WR'→
-W1' is output.

Therefore, the detection circuit 5 outputs the square of the amplitude of the correlation value shown in equation (5), that is, the square of the amplitude r2 of the pilot signal in the received baseband signal.

This is connected to the reference voltage preset by the bias circuit of 7 and
If the output voltage of the detection circuit 5 is higher than the reference voltage, the pilot signal is received (determined to have been detected correctly from among the K baseband signals), and a pilot signal detection signal is output. Alternatively, in the case where a level drop occurs in the baseband signal system due to an abnormality in the radio equipment, etc., the amplitude r of the pilot signal Pr(t) decreases, so that the output voltage of the detection circuit 5 becomes lower than the reference voltage from the bias circuit 7. The comparator circuit 6 determines that no pilot signal is detected and does not output a pilot signal detection signal.

〔Effect of the invention〕

As explained above, the present invention provides a second hybrid on the transmitting side that branches the pilot signal, multiplexes one into the transmitting baseband, and outputs the other to the receiving side, and branches the pilot signal from the transmitting side before the detection circuit. A correlator for correlating the received baseband signal with the received baseband signal is provided on the receiving side, and a detection circuit is further installed to perform square detection of the real part and imaginary part of the output value of the correlator to calculate the amplitude of the correlation value by 2. Since it is configured to output a multiplier, it does not use an expensive band-pass filter, but instead uses a low-cost correlator that is miniaturized through integration. Temperature compensation is also not required, and the adjustment time can be significantly reduced. This has the effect of making the pilot signal detection circuit smaller and cheaper.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of a pilot signal detection circuit according to the present invention, FIG. 2 is a frequency allocation diagram of a received baseband signal, and FIG. 3 is a block diagram of a pilot signal detection circuit having a conventional configuration. DESCRIPTION OF SYMBOLS 1... Hybrid, 2... Pilot signal oscillator, 3... Correlator, 4... Coupler, 5... Detection circuit, 6... Comparison circuit, 7... Bias circuit, 8...・・・
Hybrid, 11... Hybrid, 12... Pilot signal oscillator, 13... Band pass filter, 1
4...Coupler, 15...Detection circuit, 16...Comparison circuit, 17...Bias circuit, S...Transmission side, R.
...Receiving side, A...multiplex telephone signal, B...pilot signal.

Claims (1)

[Claims] (1) A transmitting side that multiplexes a pilot signal into a transmitting baseband signal using a hybrid and outputting it, and a receiving baseband signal that passes through a coupler and then is detected by a detection circuit, and this detected output is used as a reference voltage for a bias circuit in a comparison circuit. and a receiving side that detects the pilot signal by comparison with the pilot signal, and the transmitting side has a second circuit that branches the pilot signal, multiplexes one part into the transmission baseband, and outputs the other part to the receiving side. A hybrid is provided, and a correlator that correlates the pilot signal branched from the transmitting side with the received baseband signal is provided at the front stage of the detection circuit on the receiving side, and the detection circuit detects the real part of the output value of the correlator. and the imaginary part, respectively, to output a square number of the amplitude of the correlation value.