JPS5839137A - Synchronous detection system - Google Patents

Abstract

PURPOSE:To apply the radio machine of a band diffusing communication system to a mobile radio, by taking out noise components of the output of a frequency discriminating circuit to detect synchronism and detecting the AGC level with the input of a tau dither detecting circuit. CONSTITUTION:When the synchronism between codes in the transmission side and the receiving side is established, the output of a frequency discriminating circuit 21 is almost noise components because the signal passing through amplifying circuits 12 and 20 has only noise components almost. Consequently, a signal obtained by amplifying the frequency band at the outside of the sound frequency band in a noise amplifying circuit 26 has a characteristic approximately equal to that for no signal, and the noise is detected in a noise detecting circuit 27 and is applied to a comparing circuit 28. A clock generating circuit 14 adds (or eliminates) clocks in accordance with the output of the comparing circuit 28 to change gradually the phase of the code in the receiving side. Thus, the range of the input voltage which can be controlled by an automatic gain adjusting circuit 25 corresponds to the gain of amplifying circuits 3, 4, 10, and 12, and a wide dynamic range is obtained in comparison with gain components before a mixing circuit for mixing a local oscillation band diffusing signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a synchronization detection method used in spread band communication radio equipment and the like.

A conventional synchronization detection method of this type will be explained.

Fig. 1 shows a spread band modulation receiver that uses an envelope detection method for synchronization detection.The spread band modulation signal input from the antenna 1 is band-limited by the band offshore circuit 2, and then is passed through the amplifier circuit. After being amplified by 3, it is mixed with the output of the local oscillation circuit 6 by a mixing circuit 4.

This signal is converted to a first intermediate frequency by an amplifier circuit 6 and a band Okinawa circuit 7. This first intermediate frequency signal is mixed with the output signal of the balanced modulation circuit 16 by the mixing circuit 9. The local oscillation balanced modulation signal is driven by the clock generation circuit 14 to the code generation circuit 16 to generate a specific pseudo-noise code string (hereinafter referred to as PN code), and this signal is sent to the local oscillation circuit 17. A balanced modulation circuit 16 is applied to the output signal of
The mixing circuit 9, which is generated by applying equilibrium modulation, has the function of a kind of correlator.

In other words, if the synchronization between the PN code on the transmitting side and the PN code on the receiving side is not established, the output signal that has passed through the band limiting circuit 11 and the amplifying circuit 12 of the amplifier circuit 10 is buried in noise and is therefore not enveloped. The line detection circuit 18 does not detect any signal, and the comparison circuit 19 outputs an asynchronous signal. As a result, the clock generation circuit 14 adds a clock (
or removal). In this way, if synchronization is not established, the phase of the PN code changes sequentially.

Next, when the PN code on the transmitting side and the PN code on the receiving side are synchronized, a detection signal appears at the output of the envelope detection circuit 18, drives the comparison circuit 19, and adds the clock to the clock generation circuit 14. (or removal) Generates a control signal to stop the operation. Once synchronization is established, tau dither clock tracking is performed, and an amplified modulation signal appears at the output of the amplifier circuit 12. This is detected by the tau dither detection circuit 13, which detects phase difference information between the transmitting and receiving clocks. The synchronized state is maintained by controlling the clock signal of the clock generation circuit 14.

When the synchronization state is entered in this way, the modulation signal of the second intermediate frequency always appears at the output of the amplifier circuit 12. Therefore, the amplitude of this signal is limited by the amplifier circuit 20, and the frequency discrimination circuit 21
After demodulating the signal, the signal is passed through the amplifier circuit 22 and a demodulated signal is output to the speaker 23.

Now, in order to maintain synchronization, the tau dither detection circuit 1
3, the amplitude modulation signal must always be detected, and based on the detection characteristics of the envelope detection circuit 18, the automatic gain adjustment circuit 8
It is necessary to insert the amplifier circuit immediately before the mixing circuit 9 and adjust the gains of the amplifier circuits 3 and 6.

Note that the output of the amplifier circuit 12 is taken and each amplifier circuit 3゜6.1
When AGC is applied to 0.12, the output of the envelope detection circuit 18 no longer shows a level difference between when the PN codes on the transmitting and receiving sides are synchronized and when they are not synchronized, so synchronization detection is not performed. .

Therefore, the input voltage range that can be controlled by the automatic gain adjustment circuit 8 is limited to the gain of the amplifier circuits 3 and 7, making it difficult to apply this circuit system to mobile radio where electric field fluctuations are severe.

However, if the gain of the amplifier circuit 3.6 is increased, there is a problem that it becomes difficult to use it in combination with other modulation methods, such as frequency modulation methods that do not apply band spreading, because of changes in characteristics due to gain distribution.

The present invention eliminates these drawbacks and makes it possible to apply the spread band modulation method to, for example, land mobile radio.

This will be explained below along with examples. FIG. 2 shows an embodiment of a spread band modulation radio device to which the present invention is applied. In this figure, parts corresponding to those in FIG. 1 are designated by the same reference numerals.

26 is an automatic gain adjustment circuit, and its output is the amplifier circuit 3.6
, 10.12 as a control signal. 26 is a noise amplification circuit that amplifies signals outside the audio frequency band; 27
28 is a noise detection circuit that detects the signal, and 28 is a comparison circuit that compares the detected output with a predetermined level, which controls the clock generation circuit.

Next, the operation of this embodiment will be explained. The parts having the same configuration as in FIG. 1 perform the same operation as the receiver.

Now, if synchronization of codes on the transmitting side and the receiving side is not established, the signals passing through the amplifier circuit 12 and the amplifier circuit 2o will have almost no noise components, and the output of the frequency discrimination circuit 21 will be It is a noise component. Therefore, the signal obtained by amplifying the frequency band outside the audio frequency band in the noise amplification circuit 26 has characteristics similar to those in the case of no signal, and the noise is detected by the noise detection circuit 27 and the signal obtained by the comparison circuit 28
added to. This comparison circuit 28 outputs an asynchronous signal and supplies it to the clock generation circuit 14. The clock generation circuit 14 adds (or removes) a clock according to the output of the comparison circuit 28, and gradually changes the phase of the code on the receiving side. In a state where the sending and receiving sides are synchronized,
Since the second intermediate frequency component appears in the amplifier circuit 12, the modulated audio signal is demodulated in the output signal of the frequency discrimination circuit 21, and the noise is suppressed at the same time. The noise detection output of the circuit 27 decreases. At this time, since the comparator circuit 28 outputs a synchronization detection signal, the clock addition (or removal) operation in the clock generation circuit 14 is stopped.

Note that the synchronization holding operation and demodulation output operation are the same as in the case of FIG.

According to this embodiment, the input voltage range that can be controlled by the automatic gain adjustment circuit is the gain of the amplifier circuit 3.4, 10°12, and the gain before the mixing circuit with the local oscillation band spread signal shown in FIG. A relatively large dynamic range can be obtained. In addition, this embodiment has the advantage that it has the same circuit configuration as the conventional frequency modulation method, and can be used in common by switching the modulation method with a simple switching circuit. It is also possible to use a frequency modulation method as the communication line.

Although the above embodiment describes a spread band radio device using a direct sequence method, it can be easily applied to other spread band methods such as frequency hopping and time hopping.

As is clear from the above explanation, according to the present invention, synchronization is detected by extracting the noise component of the output of the frequency discriminator circuit, so the AGC level detection of the receiver is performed by using the input of the tau/dither detection circuit. This has advantages such as expanding the dynamic range of the received input signal, making it possible to apply spread band communication type radio equipment to mobile radios.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional receiver, and FIG. 2 is a block diagram of a receiver to which a synchronization detection method according to the present invention is applied. 1... Antenna, 21... Frequency discrimination circuit, 26... Noise amplification circuit, 27...
Noise detection circuit.

Claims (1)

[Claims] This invention relates to a code synchronization detection method that receives a spread band modulation signal, performs noise detection on the output of a frequency circuit to which the received signal is applied, and detects that the amount of noise has decreased.