JPS63151123A - Narrow band signal communication system - Google Patents

Abstract

PURPOSE:To attain narrow band communication with high performance even in a transmission system of much phase noise by allowing a reception signal to pass tracking type band-pass filters and converting the frequency of a part of the output of a frequency synthesizer to an intermediate frequency IF frequency band as a local signal. CONSTITUTION:The reception signal is allowed to pass tracking type band pass filters 1 and 2 to select the signal of a channel to be received, and a reproduced pilot signal of the signal of the reception channel has the frequency converted to a low frequency band as the local signal. Further, a part of the output of a frequency synthesizer 5 has the frequency converted to the IF frequency band as the local signal to obtain a channel signal to be received in a certain frequency band independently of channels, and this signal is demodulated and reproduced. Thus, the phase noise generated in a transmission line part and a reception equipment is eliminated, and narrow band communication of stable and satisfactory characteristic is by attained the synchronous demodulation method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a communication system for transmitting narrowband signals between small earth stations via a communication satellite using small antennas and small-scale transmitting/receiving equipment.

[Conventional technology]

In recent years, improvements in the performance of communication satellites have made it possible to create small earth station communication systems that include small antennas and small-scale transmitting and receiving equipment. The capabilities of small earth stations are limited in terms of both transmission power and signal bandwidth.

There is no choice but to use narrowband communication. however.

In narrowband communication, phase noise caused by local frequency signal sources is added each time frequency conversion is performed several times in a transmission path. Due to this.

In some cases, this may cause a significant deterioration in communication quality.

Communication itself becomes impossible. These phase noises are low frequency noises that have an extremely large phase density in the very low frequency region.

Conventionally, in satellite communications, a synchronous detection method has been mainly used from the viewpoint of effective use of transmission power.

To improve the bandwidth of the carrier regeneration circuit,
It is normal to set it to about /100. However, in the case of narrowband communication, the follow-up characteristics of the carrier regeneration circuit deteriorate, causing large phase jitter and severe phase slag, which impedes normal communication.

FIG. 8 shows the local signal system of the satellite communication system.

In the figure, 50 is a modulator, 51 is a carrier oscillator, and 5
4 is an up converter, 55 is a local oscillator with an oscillation frequency fU, and 56 is a frequency conversion circuit.

57 is a local oscillator with an oscillation frequency fL, 58 is a down converter, 59 is a local oscillator with an oscillation frequency fD,
64 is a receiving IF system.

In the transmitting section, the carrier of 8 frequencies fc is modulated by the transmission data, and further frequency-converted to the broadcast link RF frequency fU by a local signal of frequency fU, and then sent out.

On the satellite, frequency conversion to downlink is performed using the local signal fL, and further, in the receiving section, frequency conversion is performed to a specified IF frequency band using one frequency fD, and demodulation is performed.

[Problem that the invention seeks to solve]

The received signal includes the phase noise of all local signal sources mentioned above. Especially when building a narrowband communication system between small earth stations using existing communication satellites.

The overwhelming majority of phase noise is generated by local oscillators onboard the satellite. Since the transmission signal of each earth station must be accurately transmitted on a 90% assigned frequency, an extremely highly stable frequency source is used. However, in the receiving section, the local oscillation frequency of the down converter cannot be expected to be so highly stable due to the scale of the device.

Therefore.

Most of the phase noise is generated in the transmission path and receiver.

For this reason, FSK modulation is conventionally used when communication is performed through a transmission path with large phase noise.

In FSX modulation, data O is transmitted at a frequency f(0), and data 1 is transmitted at a frequency f(1).

FIG. 9 shows an FSK signal receiving circuit. 70 is a down converter, 71 is a channel frequency synthesizer, 72 is a bandpass filter tuned to the frequency corresponding to data 0, 73
is a band p-wave generator tuned to the frequency corresponding to data 1, 7
4.75 is a square law detector.

76 is an amplitude comparator, and 77 is a clock recovery circuit.

78 is a data identifier.

The method using FSX modulation is an effective method in systems with large single phase noise, but because it is a square law detection method, the theoretical KBER characteristics are significantly worse than in the case of synchronous detection, and the FSX modulation Due to its characteristics, it has no choice but to have a wide band.

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned drawbacks and to realize a communication system that can perform high-performance narrowband communication even in a transmission system with large one-phase noise.

[Means for solving problems]

In the present invention, a predetermined pilot station sends out a neulot signal at a specified frequency, and at each earth station, the received signal is passed through a narrowband bandpass p-wave filter tuned to the neulot frequency. A frequency synthesizer that reproduces a noquilot signal and generates a channel frequency signal to be received, and a tracking bandpass filter that uses the frequency synthesizer as a local signal and has filtering characteristics tuned to the local signal. Then, by passing the received signal through the tracking type bandpass p-wave device, the signal of the channel to be received is selected, and the signal of the received channel is frequency-transmitted into a low frequency band using the regenerated pilot signal as a local signal. By converting a part of the output of the frequency synthesizer into the IF frequency band as a local signal, the channel signal to be received is obtained in a fixed frequency band regardless of the channel, and is demodulated and reproduced. It is a band communication method.

EMBODIMENT OF THE INVENTION A communication system to which the present invention is applied is shown in FIG. 2. 91
92 is a communication satellite, 92 is a pilot station, and 93 is a large number of small earth stations.

FIG. 3 shows the transmission signal spectrum according to the method of the present invention.

FIG. 1 shows a narrowband signal receiving circuit according to the present invention.

This is a part corresponding to the reception IF system 64 in FIG.

1 and 2 are frequency tracking band F wave generators, 3 is a mixer, 4 is a local oscillator for the /-' pilot signal, 5 is a channel frequency synthesizer, 6 is a low frequency F wave generator, 7 is a mixer, and 8 is a 10 is a demodulator.

FIG. 4 shows a frequency tracking type band ν wave device used in the present invention. 11.12 is a mixer, 13 is a π/2 phase shifter, 14.1
5 is a low-pass p-wave generator, 16.17 is a mixer, and 18 is an IF signal synthesizer.

The basic circuit of demodulator 10 is shown in FIG. 101 is a carrier recovery circuit, and 102 is a clock recovery circuit.

103 is a demodulator, and 104 is a data regenerator.

The communication principle of the communication system according to the present invention will be explained below. First, what is the received signal?

Pilot signal; τ, (t) = cas (ω.t+θ
j+θ. n) (1) Each channel signal; v, c(t
)=ctB(t+θj+θkn) (2). however.

ω. ;Pilot frequency θ. . ;Transmission line thermal noise ω5 added to the trouble lot signal;
Frequency of channel (k=1.2...N) θkn;
Thermal noise ψk(t) added to the channel signal: modulation phase (0 or π) θ,; phase noise generated in the transmission path.

The important fact here is that the phase noise θ is common to all channels.

Referring to FIG. 1, the local oscillator 4 is tuned to the pilot frequency, and the pilot signal of equation (1) is selectively extracted at the output of the bandpass filter 1. Similarly.

At the output of the band F wave generator 2, all signals (referred to as channels) to be received are selected from among the signals expressed by equation (2).

Result of multiplication in mixer 3.

v3ft)=ccs ((oh-ω.)t+face+θkn
-θon' (3) is obtained, and the two-phase noise θ is canceled out. Instead, 1-phase thermal noise θ. n is added, but this term can be changed by making the power of the main pilot signal thicker than other channels, or by making the bandwidth of the band P-wave device 1 narrower than that of the band-pass wave device 2. , θ. .

It is possible to suppress θkn to a very small amount, which is much smaller than θkn, and it is possible to make the S/N deterioration in the mixer 3 so small that it can be ignored.

Next, at mixer 7.

υ(t) ” cai ((”y−ωl−ω.) to 10+θkn−〇on)+1+ωto′−ω.
(4) is obtained. Here, 1' is the output frequency of the channel frequency synthesizer 5, and has a value extremely close to 1'. The band p wave filter 8 is tuned to ω and passes only the 10th term of equation (4), and the signal of the channel to be received is obtained in the frequency band ω regardless of the channel frequency. Band P
The output of the wave converter 8 is input to a demodulator 10 operating at the IF frequency ω to reproduce and output data and a clock.

In some cases, as shown in FIG. 1, the output of the band P-wave generator 8 may be frequency-converted to the baseband band (OHz band) using a part of the output of the local oscillator 4, and the signal may be converted into a signal using a synchronous or delay detection method. Can be played.

As described above, according to the present invention, it is possible to cancel phase noise generated in a transmission path and a receiving device.

Note that the phase noise generated in the transmitting section of each earth station may be made to be first-order. That is, it is sufficient if each earth station independently transmits the Nokilot signal. Figure 6 shows the transmission vector of each channel in this case.

The receiving device is shown in FIG. 52 is an IF signal synthesizer.

53 is a nogirot oscillator, 55' and 59' are channel frequency synthesizers, 60 is a band wave generator, 61 is a narrow band F wave generator, 62 is a mixer, 63 is a low frequency wave generator, and 10 is a demodulator. It is.

The operation of this system is basically the same as the system described above. Each station sends out a signal in addition to the modulation signal at a frequency position that differs by Cf −f ) from the carrier frequency of the high-speed signal within the assigned frequency band. In the receiving section, first, a channel frequency synthesizer 59' and a down converter 58. A band F wave generator 60 selectively outputs the received signal in a specified frequency band. Next, the narrow band F wave filter 61 extracts the pilot signal of that channel, and the mixer 62 uses it to extract the pilot signal of that channel.
By performing frequency conversion, the frequency band becomes Cf-f).

c. By obtaining a highly stable modulated signal from which phase noise generated in the transmitting section, transmission path section, and receiving device section has been removed, it is possible to perform signal reproduction using the normal synchronous demodulation method. Although this method causes some loss in terms of power efficiency and bandwidth efficiency, it is extremely effective when performing ultra-low-speed communication with a simple device through a transmission line with large two-phase noise. In other words, phase noise generated in all RF signal paths including the transmitter can be removed, making it possible to perform extremely low-speed communications using a very small station, and to enable mobile communications using a single communication satellite.

〔Effect of the invention〕

According to the present invention, the following effects can be achieved.

(1) First, the system and receiver of the present invention can remove phase noise generated in the transmission line and receiver, and the synchronous demodulation method enables stable and good narrowband communication.

(2) Therefore, it is possible to construct a system that performs narrowband communication between a large number of small stations using existing communication satellites.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a receiving device according to the present invention, and FIG.
The figure is a diagram for explaining a narrowband communication system to which the present invention is applied, Figure 3 is a diagram showing the transmission signal span of the present invention system, and Figure 4 is a diagram for explaining the frequency tracking type band transmission system used in the present invention. FIG. 5 is a block diagram showing the basic configuration of a synchronous demodulator used in the present invention, and FIG. 6 is a block diagram showing the transmission signal spectrum in another example of the present invention, that is, the signal superimposition method for each channel. FIG. 7 is a block diagram showing the communication system of the i4lot signal superimposition method for each channel, and FIG.
This shows a local signal system in a satellite communication system, and Figure 9 shows a conventional FSK modulated signal receiving circuit. A local oscillator, 5 a channel frequency synthesizer, 6 a low frequency F wave generator, 8 a band shifter, and 10 a demodulator. Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. In a system that performs narrowband communication between multiple small earth stations via communication satellites, a predetermined pilot station sends out a pilot signal at a specified frequency, and each earth station , a frequency synthesizer that regenerates the pilot signal by passing the received signal through a narrowband bandpass filter tuned to the pilot frequency and also generates a channel frequency signal to be received; and a frequency synthesizer that uses the frequency synthesizer as a local signal to generate the local signal. a tracking type bandpass filter having filtering characteristics tuned to the filter, and selecting the signal of the channel to be received by passing the received signal through the tracking type bandpass filter, and selecting the signal of the receiving channel. The regenerated pilot signal is frequency-converted as a local signal to a low frequency band, and a part of the output of the frequency synthesizer is further frequency-converted as a local signal to an IF frequency band, so that the signal is received in a constant frequency band regardless of the channel. A narrowband signal communication method that obtains, demodulates, and reproduces the desired channel signal.