JPH0454045A - Carrier recovery circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a carrier regeneration circuit used for synchronous detection of a signal obtained by angle modulating a data signal, typified by PSK, which tracks high-speed phase fluctuations due to Rician fading. death,
The present invention relates to a carrier regeneration circuit that also has a small phase slip ratio.

[Conventional technology]

In a line such as a satellite communication line where the reception level is low and thermal noise is dominant, for example, synchronous detection, which has better transmission quality than delay detection, is used as a demodulation method for PSK signals. The standard carrier required for synchronous detection is generally self-synchronized, in which the reference carrier is regenerated only from the received signal, and various carrier regeneration circuits have been used in the past.

FIG. 2 shows a configuration example of a conventional carrier regeneration circuit.

The PSK signal is input to the delay circuit 2 and is synchronously detected by the synchronous detector 1 using a reproduced carrier. The modulation phase of the detected signal is determined by the identification RN 3 to reproduce transmission data, and the received PSK signal, whose timing has been adjusted by the delay circuit 2, is inversely modulated by the inverse modulator 4 using the reproduced data to become an unmodulated carrier. . After the signal-to-noise ratio of this unmodulated carrier is increased by the filter 5, the amplitude is made constant by the limiter 6, and the unmodulated carrier is fed back to the synchronous detector 1 as a regenerated carrier.

[Problem to be solved by the invention]

In the conventional carrier regeneration circuit described above, under thermal noise, the input P
When the SK signal has a predetermined signal-to-noise ratio (S/N ratio), the iil overband width of the filter 5 is determined so that the phase slip rate of the reproduced carrier becomes a desired value. However, in Rician fading lines such as mobile satellite communications, the spectrum of the received signal is expanded by an amount equivalent to the fading frequency due to fading. The passband width of the filter makes it impossible to pass the spectrum corresponding to the carrier, and both the phase error and slip rate become large. Therefore, when using a conventional carrier regeneration circuit in a high-speed Rician fading line, it was necessary to select one of the following two methods.

One method is to reduce the phase error by making the passband width of the filter sufficiently larger than the fading frequency to pass the entire spectrum of the carrier.

The effect of the increase in slip rate, which is the price of increasing the passband width, is eliminated by using differential encoding.

The other method is to reduce the slip rate by making the passband width sufficiently smaller than the fading frequency. In this method, the phase of the output signal of the filter 5 becomes approximately the average value of the phase fluctuations of the carrier.

However, the former method has the disadvantage that the bit error rate increases due to differential encoding, and the latter method has the disadvantage that the
Since the phase of the output signal hardly follows the phase fluctuation of the carrier, there is a problem in that irreducible errors occur due to phase errors.

The present invention is intended to solve the above-mentioned problems, and it is an object of the present invention to provide a carrier regeneration circuit that can follow high-speed phase fluctuations due to Rician fading and has a small phase slip rate in a carrier regeneration circuit used for synchronous detection of PSK signals. purpose.

[Means to solve the problem]

The present invention detects the phase of a PSK-modulated input signal using a reference carrier, inversely modulates the detected signal with reproduced data to extract a carrier component for synchronous detection, limits the band of this carrier component, and returns it to a synchronous detector. In the regeneration circuit, the extracted carrier component is input to two types of filters having different passband widths, and a signal whose phase is an intermediate value between the output signal phases of these two filters is used as the reference carrier. .

〔Example〕

FIG. 1 is a block diagram showing a first embodiment of the present invention.

The detector 1, delay circuit 2, discriminator 3, and inverse modulator 4 are the same as the conventional one shown in FIG.

The input PSK signal is input to the delay circuit 2 and detected by the detector 1. After the modulation phase of this output is determined by the discriminator 3, the PSK signal whose timing has been adjusted by the delay circuit 2 is inversely modulated by the inverse modulator 4 to become an unmodulated carrier. This unmodulated carrier is input to filter 7 and filter 8. Here, the passband width of the filter 8 is sufficiently smaller than the fading frequency, and that of the filter 8 is sufficiently larger than the fading frequency. The outputs of both filters are made to have the same amplitude by limiters 9 and 10, respectively, and are combined by an adder 11. Since the two filter outputs are combined with equal amplitude, the phase of the adder output is equal to the average phase of each filter output. This output is fed back to the detector 1 as a regenerated carrier.

The above signal synthesis will be explained using FIG. FIG. 3 shows signal waveforms at various parts of the circuit when the input signal does not contain noise, with the horizontal axis representing time and the vertical axis representing phase. From this, since the filter 7 has a narrow band, the phase of its output signal is approximately equal to the average value of the phase fluctuation of the carrier, whereas since the filter 8 has a wide band, the phase of its output signal is approximately equal to the instantaneous value of the phase fluctuation of the carrier. It can be seen that they are almost equal.

Furthermore, since the output of the filter and the output of the filter 8 are combined as described above, it can be seen that the phase of the reproduced carrier takes an intermediate value between these phases. Here, since the output phase of the filter has hardly changed, the reproduced carrier phase changes around the output phase of the filter. Since the filter 7 has a small passband width and a low slip rate, the slip rate of the reproduced carrier is also small, and differential encoding is not necessary. In addition, the phase error of the reproduced carrier is
This is smaller than the conventional detection method using the average value of carrier phase fluctuations, so the irreducible error is also small.

FIG. 4 is a block diagram showing a second embodiment of the present invention. Here, a detector 1, a delay circuit 2, a discriminator 3, an inverse modulator 4,
The filters 7, 8, limiter 9, and IO1 adder 12 are the same as those shown in FIG.

The input PSK signal is input to the delay circuit 2 and 13, and is synchronously detected by the detector 1. After this output is determined by the discriminator 3 to determine the modulation phase and regenerate the transmission data, the delay circuit 2 performs the timing adjustment.
The signal is inversely modulated by an inverse modulator 4 to become an unmodulated carrier. This unmodulated carrier is filtered by filters 7, 8 and 12.
is input. Here, the passband width of the filter 8 is sufficiently smaller than the fading frequency, and that of the filter 8 is sufficiently larger than the fading frequency. Also filter 12
is on the same level as the fading frequency, and the amplitude and delay characteristics are almost flat within the passband.

The outputs of filters 7 and 8 are made to have the same amplitude by limiters 9 and 10, respectively, and are combined by an adder 11.

This output is fed back to the detector 1 as a first regenerated carrier. Further, the output of the filter 12 is set to a constant amplitude by a limiter 14, is inputted to a detector 15 as a second regenerated carrier, and a PSK signal whose timing is adjusted by a delay circuit 13 is detected. The modulation phase of the detector output is determined by a discriminator 16 to obtain received data. In this configuration, the filter 12 has a substantially flat amplitude within the passband.
Since it has a delay characteristic, the phase difference between the second reproduced carrier that is this output and the PSK signal whose timing has been adjusted by the delay circuit 13 is extremely small. Therefore, even better characteristics than the first example can be obtained.

〔Effect of the invention〕

According to the present invention, in a carrier regeneration circuit used for synchronous detection of PSK signals, it is possible to realize a carrier regeneration circuit that can follow high-speed phase fluctuations due to Rician fading and has a small phase slip rate.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention, FIG. 2 is a configuration of a conventional carrier regeneration circuit, FIG. 3 is an explanatory diagram of the operation of the first embodiment of the present invention, and FIG. This is the configuration of a second embodiment of the present invention. ■, 15... Detector, 2, 13... Delay circuit, 3.16... Discriminator, 4... Inverse modulator, 5.7, 8.12... Band pass filter, 6 , 9.10.14 ... Limiter, 11
... Adder. Figure 4

Claims (2)

[Claims] (1) Detection means for inputting and synchronously detecting a signal angle-modulated by a transmission data signal; identification means for identifying and reproducing the detected signal into a logical value of the transmission data; a delay means for delaying the delayed signal by the same amount of time, an inverse modulation means for modulating the delayed signal using the same modulation method as that on the transmitting side using the identified and regenerated signal, and a filter for inputting the inversely modulated signal, each of which has a different frequency band. Two band-pass filtering means with different widths, two amplitude limiting means for limiting the output amplitude of each band-pass filtering means to be the same, and synchronous detection by adding these two amplitude-limited signals. 1. A carrier regeneration circuit comprising an addition means for generating a reference carrier wave for use and supplying the generated reference carrier wave to the detection means. (2) The carrier regeneration circuit according to claim 1, further comprising: a second delay means for delaying the input angle modulated signal; and a second delay means for delaying the input angle modulated signal; a third bandpass filtering means for filtering the signal; a third amplitude limiting means for limiting the amplitude of the filter output signal; and synchronously detecting the output signal of the second delay means using the output as a reference carrier wave. A carrier regeneration circuit configured by adding a second detection means and a second identification means for identifying a detected signal and reproducing a logical value of transmission data.