JPS62210761A - Carrier recovery system - Google Patents

Abstract

PURPOSE:To recover a carrier with a high SN, and to exactly demodulate a reception signal without making large an offset voltage, by inserting a carrier synchronizing signal in the data of a service channel SC system. CONSTITUTION:A transmission data processing part 1 multiplexes the data of the SC system on a main signal, or performs a framing. The analog output of a frequency divider 4 is converted to a digital signal by a coder 5, and is inserted to the data of the SC system as the one which represents a bit of carrier information. At a reception side, a reception data is branched with a hybrid circuit 20, then being transmitted to mixer 21 and 22. When the synchronization of a recovery carrier circuit is established, the data of the SC system is recovered at a reception data processing part 7. A change-over switch 9, in stead of a loop filter 8, outputs a signal from a loop filter 12 that is the data of the SC system synchronized with a transmission carrier. Thus, since the synchronization in the recovery carrier circuit is temporarily established by a PLL loop, and next, an accurate synchronizing signal is obtained from the data of the SC system obtained by a temporarily established synchronization, and a PLL loop is constituted, the synchronization with high accuracy can be established.

Description

[Detailed description of the invention] [Summary] A signal synchronized with a transmitting carrier is transmitted using a service channel system transmission path, and this signal is demodulated on the receiving side, and the voltage used for carrier recovery 4 is This signal is used as a control signal for a controlled oscillator to configure a carrier regeneration circuit with a high 8/N ratio.

[Industrial application field]

The present invention relates to a carrier regeneration method, and more particularly to a carrier regeneration method for a demodulator used in a digital wireless communication system.

In digital wireless communication systems, multi-value quadrature amplitude modulation (quadrature) such as 16-value, 32-value, 64-value, etc. is used to increase the amount of data transmitted within a limited number of stations and wave number bands and to improve frequency usage efficiency. AmplitudeMo
duration (hereinafter referred to as QAM) is used. In this QAM system, carrier waves of orthogonal phases are amplitude-modulated using transmission data, and the amplitude-modulated waves are combined and transmitted. This QAM method is divided into 16-value, 32-value, 6-value, and
This becomes a multi-value QAM signal such as 4-value or 128-value. (in Figure 4)
shows an example of the modulation points of the 64-value QAM system.

On the receiving side, the carrier wave is regenerated from the received multilevel QAM signal,
The received multilevel QAM signal is synchronously detected by forming carrier waves that are orthogonal to each other, and the amplitudes of the orthogonal components are identified to demodulate data. Therefore, on the receiving side, it is necessary to regenerate a carrier wave for synchronously detecting a multilevel QAM signal.

[Conventional technology]

By the way, due to requests for increased data transmission volume, etc.

A multilevel QAM system with a modulation point number of 32 or more is required, and for this reason, the applicant for this patent first filed a patent application in 1983-22.
No. 4441 (4I Patent Publication No. 117946/1986) for a carrier wave recovery circuit suitable for such a multilevel QAM system.

As shown in FIG. 4(a), this includes a serial-to-parallel converter 40. on the transmitting side. Multivalue converter 41. D/A converter 42.4
3. Low-pass filters 44, 45. Mixer 46, 47
．． Hybrid circuit 48. Pilot carrier insertion section 49. Carrier generation part 50°90 degree hybrid circuit 5
1, etc., to create a multilevel QAM signal, which is transmitted to a wireless transmitter (not shown) and transmitted. On the receiving side, after receiving this, the hybrid circuit 60. mixer 61+
62*Low pass filter 63, 64 . A/D converter 6
5.66, loop filter 67, voltage controlled oscillator 68.
Demodulated data is obtained by a demodulator including a 90 degree hybrid circuit 69 and the like.

That is, the transmission data Din is converted into parallel data by the serial/parallel converter 40 and transmitted to the multi-value converter 41. For example, in the case of 64-value QAM system.

The binary transmission data Din is converted into two series of parallel data of 3 bits each by the serial/parallel converter 4o, and these parallel data are converted into 8-value data by the D/A converters 65 and 66, respectively. The signal is transmitted to mixers 46 and 47. By the way, the offset voltage Vof of the DC voltage is added to the multi-value data DI of one channel from the multi-value converter 41 by the pilot carrier insertion section 49. The carrier wave signal CR output from the carrier generator 50 is directly sent to one mixer 46 via the 90-degree hybrid circuit 51.
It is applied to the other mixer 47 with a 90 degree phase shift. Therefore, the modulated output signals from the mixers 46 and 47 are obtained by amplitude modulating the quadrature phase carrier waves using multilevel data, and the modulated output signal from the mixer 45 has an offset voltage V.
OfK contains a carrier wave component due to giving an offset to the multilevel data Di. These modulated output signals are synthesized by a hybrid circuit 48 to form a multi-value Q
The AM signal is transmitted to the wireless transmitter.

(in Figure 4) is an example of a modulation point of a 64-value QAM signal)
, the horizontal axis is I and the vertical axis is Q. Offset voltage Vo
If f is not added to channel data DIK, the Q axis will exist at the position shown by the chain line, but by adding the offset voltage Vof it will be shifted to the position shown by the solid line. Therefore.

The probability of occurrence of a modulation point centered on the Q axis is smaller on the shift side, and due to the imbalance in the probability of occurrence of a modulation point, the carrier wave has a multi-level Q
It is transmitted by leaking into the AM signal.

FIG. 4(C) is an explanatory diagram of the transmission spectrum in the case of a multilevel QAM signal that does not include a 17° leakage carrier wave.

As shown by the dotted line, it has a relatively flat spectrum centered around the carrier frequency f.

By adding the offset voltage Vof, it becomes possible to extract the leaky carrier wave CR' that does not correspond to the spectrum shown by the solid line υ.

On the receiving side, a hybrid circuit 60 branches the received multilevel QAM signal transmitted from a wireless receiving section (not shown). 90 degree hybrid circuit 69 for mixers 61 and 62
The output signal from the voltage controlled oscillator 68 is applied with a phase of 90 degrees through the
The signal is synchronously detected.

By the way, since a signal with a level corresponding to the frequency difference and phase difference between the leakage carrier wave and the reproduced carrier wave is outputted to the multi-level data DQ of the Q channel of the output signal of the mixer 62, /I By configuring a phase synchronization circuit using a filter 67 or the like and controlling the phase of the output signal of the voltage controlled oscillator 68, that is, the phase of the recovered carrier wave, the phase of the recovered carrier wave can be synchronized with the phase of the leakage carrier wave. .

[Problem that the invention seeks to solve]

By the way, in order to make the reproduced data accurate, the 8N of the reproduced carrier wave is a problem, and in the circuit shown in Fig. 4, it is necessary to increase the offset voltage Vof in order to increase this SN. Become.

However, if this value is increased, high power is required, and furthermore, when a high-level signal is input to a high-power amplifier, it will be distorted, making it impossible to send out a high output.

The purpose of the present invention is not to increase the offset voltage (8
It is an object of the present invention to provide a carrier wave regeneration circuit capable of regenerating a high N carrier wave.

[Means for solving problems]

In order to achieve the above object, in the present invention, as shown in FIG. is modulated by the quadrature modulator 2 together with the main signal and sent out. At this time, in order to reduce the amount of carrier wave information, the frequency is divided by N by a frequency divider 4, and A/D conversion is performed by a coder 5 to obtain digital information. On the receiving side, the demodulator 6 uses the loop filter 8 to obtain a level corresponding to the frequency difference and phase difference between the leakage carrier wave and the recovered carrier wave, and the voltage controlled oscillator 10 is output from the loop filter 8. After controlling with the output and obtaining synchronization.

The carrier wave information included in the service channel obtained by the received data processing section 7 is used to control the stain pressure control oscillator 10. In addition, in FIG. 1, 9 is a changeover switch, and 11 is a phase comparator.

12 is a loop filter.

[For production]

In the present invention, after synchronization is first obtained by means similar to the conventional method, the stain pressure control oscillator 10 can be controlled by the changeover switch 9 based on the carrier wave information inserted into the service channel. Therefore, a reproduced carrier wave with an extremely high KSN ratio can be obtained without increasing the offset voltage.

〔Example〕

Before describing one embodiment of the present invention in detail with reference to FIG. 3, an overview of the service channel will be explained with reference to FIG.

The service channel (hereinafter referred to as SC) 2 is normally used as a signal for equipment maintenance and monitoring, and as a meeting line.In addition to the main signal, 8C system data is transmitted to the transmission data processing unit 1, and the orthogonal The main signal and SC data are multi-valued by the modulator 2, and sent as a multi-value QAM signal to the wireless transmitter (not shown), received by the receiver, demodulated by the demodulator 6, and converted into received data. The processing unit 7 separates the signal into a main signal and SC data. Since this SC uses several channels, it is possible to allocate one of them to the transmission of carrier wave information.

The present invention utilizes this to reproduce the carrier wave more accurately.

An embodiment of the present invention will be explained based on FIG. 3.0 In FIG. 3, the same reference numerals as those on the map indicate the same parts, 20 is a hybrid circuit, 21 and 22 are mixers, 23 is a 90 degree hybrid circuit, 24 is a decoder that converts digital signals to analog signals.

The transmission data processing unit 1 multiplexes and frames SC data on the main signal.This SC is prepared with several channels as described above, and its capacity is approximately 64 Kbps per channel. be.

The quadrature modulator 2 modulates the transmission data transmitted from the transmission data processing section 1, and for this purpose, a carrier wave is applied from the carrier wave output section 3. The carrier wave output from this carrier wave output section 3 is passed through a 9 frequency divider 4! The frequency is divided by 1/N. Then, the analog output of the branching unit 4 is converted into a digital signal by the coder 5, and inserted into the SC system data as indicating carrier wave information. This carrier wave information is used to create a signal synchronized with the transmission carrier, and the reason why the carrier original oscillation output is frequency-divided by N is to reduce the amount of data. In other words, the transmission capacity of the SC is, for example, 64 Kbp.
s (usually several 10 to several 100 Kbps), N
The divided frequency must be lower than this. 54K
If we look at bps in analog terms, it is about 3 KHz, and if the carrier wave output section 3 is 70 MHz, this is sent to the branching unit 4.
) When divided into 3KHffi, it becomes.

On the receiving side, the received data is branched into two by the hybrid circuit 20 and transmitted to mixers 21 and 22.

Mixers 21 and 22 are used to reproduce carrier waves.

Voltage controlled oscillator 1 via 90 degree hybrid circuit 23
The output signals from 0 are applied with a 90 degree phase. Here, the mixer 22 outputs a signal with a level corresponding to the frequency difference and phase difference between the leakage carrier wave and the regenerated carrier wave in the multilevel data DQ, as in FIG. 4(a). The signal is passed through the loop filter8. By forming a PLL path which is applied to the voltage controlled oscillator 10 via the changeover switch 9, synchronization of the regenerated carrier wave circuit is temporarily established.

Once this synchronization is established, the SC data will be played back.
The received data processing section 7 reproduces the SC data. By establishing this temporary synchronization, a switching control signal is applied to the changeover switch 9, and the changeover switch 9 outputs a signal from the loop filter 12, which is SC data synchronized with the transmission carrier, instead of the loop filter 8. I will do it. That is, when the SC data is regenerated by the received data processing unit 7, a signal synchronized with the transmission carrier among the SC data is transmitted to the decoder 24, and converted into an analog signal and transmitted to the phase comparator 11. be done.

The output of the voltage controlled oscillator 10 is applied to the phase comparator 11 after being frequency-divided by 1/N by the divider 24. The phase of the frequency-divided signal is compared, and the comparison signal is applied to the voltage controlled oscillator 10 via the loop filter 12 and changeover switch 9, and control is performed such that this phase difference becomes zero. That is, first, P using the same method as before.
Establish synchronization of the regenerated carrier circuit using LL loose.

Next, an accurate synchronization signal is obtained from the SC data obtained by establishing this temporary synchronization, and a PLL loop is constructed using this signal, so that synchronization with much higher precision can be established.

〔Effect of the invention〕

According to the present invention, a carrier synchronization signal is inserted into SC data and transmitted to the receiving side.

On the receiving side, first, synchronization of the regenerated carrier circuit is established using a normal PLL loop similar to the conventional one, but this
An accurate synchronization signal of the carrier wave can be obtained from the system data, so
Using this, it is possible to obtain a PLL loose signal with good LD+ quality and a frequency obtained by dividing the carrier wave by N. Therefore, a carrier wave with a high 8N ratio can be reproduced without increasing the offset voltage, and the received signal can be accurately demodulated.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of the present invention. FIG. 2 is a service channel instruction diagram. FIG. 3 is a configuration diagram of an embodiment of the present invention. FIG. 4 is an explanatory diagram of a conventional example. 1... Transmission data processing unit. 2... Quadrature modulator. 3...Carrier output section. 4... Branch unit. 5... Coda. 6... Demodulator. 7... Reception data processing unit. 8...Loop filter. 9... Selector switch. 10...Voltage controlled oscillator. 11... Phase comparator. 12...Loop filter.

Claims (1)

[Claims] A carrier wave regeneration method in which a modulated signal including a leaky carrier wave in the transmission spectrum is transmitted, and on the receiving side, the leaky carrier wave included in the modulated signal is extracted and a carrier wave for synchronously detecting the modulated signal is regenerated. A coder (5) is provided on the transmitting side for inserting a carrier signal into the service channel of the transmitted signal, and a filter (8) is provided on the receiving side for outputting a signal based on the leakage carrier component included in the synchronous detection output signal of the modulated signal.
), a voltage controlled oscillator (10), a switching means (9),
Decoder (2) that outputs the carrier signal of the service channel
4) and a comparison means (11), wherein the receiving side first controls the voltage controlled oscillator based on the leakage carrier wave component, and then controls the voltage controlled oscillator based on the carrier wave signal of the service channel. A carrier wave regeneration method characterized by the following configuration.