JPH0119665B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Description of Technical Field] The present invention relates to a synchronization monitoring system in a master station of a TDMA (time division multiple access) satellite communication system in which a master station controls transmission of slave stations. especially,
The present invention relates to a device for monitoring the synchronization state of a slave station.

[Description of prior art]

In a TDMA satellite communication system that consists of at least one master station and multiple slave stations, and the master station collectively controls the transmission of each slave station, the slave stations are based on the standards that the master station periodically transmits. The burst is received and TDMA frame synchronization in reception is established using this as a time reference. Furthermore, the transmission control information contained in this reference burst is usually decoded and transmission is performed in accordance with this information.

Normally, this transmission control information is transmitted to each slave station in turn. When a predetermined master station sequentially transmits transmission control information to N slave stations under its control, the information returns to the first slave station and is repeatedly transmitted in sequence. One slave station transmits frames (hereinafter referred to as "control frames") for transmitting transmission control information to one slave station as N control frames (hereinafter referred to as "super control frames").
That's what it means. ) will be received periodically.

Generally, there are two types of transmission control information: transmission mode control commands and transmission timing control information. The transmission mode control commands are "stop transmission", "burst transmission for initial connection possible", "data burst transmission possible"
It instructs the slave station as to the type of burst to be transmitted and whether or not it can be transmitted. Further, the transmission timing control information indicates the time from the predefined reference position of the TDMA reception frame to the reference position of the transmission TDMA frame in this slave station. The slave station counts a given time value from the predefined reception reference position, presets the transmission TDMA frame counter to a position corresponding to the reference position, establishes transmission synchronization, and sets the transmission TDMA frame counter to the position corresponding to the reception reference position. Based on this, the transmission timing of the transmission burst is determined and the transmission is performed.

On the other hand, the master station opens an aperture of a predetermined width at the timing when it is expected to receive a burst from each slave station in a predetermined TDMA reception frame, and receives the data transmitted from the slave station into the aperture. monitors that incoming bursts are received. usually,
If the master station cannot continuously receive transmission bursts from the slave station over a predetermined L frame within the aperture, the master station determines that the slave station may be transmitting bursts at the wrong timing. , a "transmission stop" command is transmitted to this slave station as a transmission mode control command in the next control frame for this slave station.

The master station also measures the error between the timing at which it receives the burst from the slave station and the timing in the TDMA frame defined by the transmission timing control information sent to this slave station in the most recent control frame. , the transmission timing control information whose value has been corrected is transmitted to the next control frame for this slave station, similarly to the transmission mode control command described above. Normally, reception timing error measurement for one slave station is performed in order in the same way as when transmitting control information is sent out at the master station, and the period is the same as the control superframe.

Here, if a frame in which a reception timing error of one slave station is measured is called a measurement frame, reception timing error measurement is performed every N measurement frames (hereinafter referred to as "super measurement frames"). FIG. 1 shows the relationship between the control superframe and the measurement superframe. In Figure 1, A is a master station, B is a slave station, a is a control super frame,
a' indicates a control frame, b indicates a super-measurement frame, and b' indicates a measurement frame, respectively.

When the master station determines that transmission from this slave station can be performed normally to the slave station to which it has sent the "stop transmission" command, the master station sends the "initial connection Transmission control information including a transmission mode control command "Burst transmission enabled" and transmission timing control information is transmitted to this slave station in synchronization with the control frame. In this way, transmission by a slave station is controlled based on the monitoring result of the synchronization state with respect to the received TDMA frame of a burst transmitted from a slave station belonging to the same master station, and it is determined whether or not to stop the transmission.

FIG. 2 shows a block diagram of the main parts of a conventional example. In Figure 2, 1 is a unique word detector, 2 is an AND gate, 3 is a flip-flop, 4 is an inverter, 5 is a binary counter, 6 is an inverter, 7 is a comparator, and 8 is a transmission mode control command generation circuit. .

FIG. 3 is an operation time chart showing the signal waveforms at the points indicated by the x marks in FIG. 2.

Detection of a received burst is usually performed by detecting a unique word included in the received burst. Therefore, the received data sequence a is transmitted to the unique word detector 1.
guided by. When the unique word detector 1 detects a unique word included in the received data series a, it outputs a pulse of "1" as a detection output b. This detection output pulse b is gated with an AND gate 2 by an aperture signal c generated with a predetermined width at a timing in a predetermined TDMA frame, and is the result of burst detection from the slave station being monitored. A signal d is extracted.

Therefore, the detection result signal d becomes a "1" pulse only when detected. This signal d is led to the set terminal of flip-flop 3. The output e of the flip-flop 3 is led to an inverter 4 and a synchronous reset terminal of a binary counter 5. The output f of the inverter 4 is the binary counter 5
is led to the count enable terminal. The reset terminal of flip-flop 3 is connected to the receive TDMA
Received frame pulse g located at the beginning of the frame
is led, and the flip-flop 3 is reset at its trailing edge. The received frame pulse g is guided to an inverter 6, and a signal h having the opposite phase of the received frame pulse g is applied to the clock terminal of the binary counter 5. Since the flip-flop 3 is reset at the trailing edge of the received frame pulse g, its output e becomes a status signal at the end of the frame indicating the result of unique word detection in that frame.

That is, when the output e is "1", it is determined that the transmission burst from the slave station has been received;
The binary counter 5 is preset to a preset value "0" of a preset signal i prepared in advance. Conversely, when the output e is "0", it is determined that the transmission burst from the slave station has not been received, and the signal f led to the count enable terminal of the binary counter 5 becomes "1", and the reset is performed. The signal e input to the enable terminal becomes "0", and the binary counter 5 counts up at the beginning of the next frame.

The output j of the binary counter 5 is led to a comparator 7 and compared with a predetermined fixed value L. When the result is a match or the counter output j is larger than L, the output k is set to "1" as a judgment result signal, and when it is smaller, it is set to "0". Therefore,
The output k is "1" only when the transmission burst of the slave station cannot be received for consecutive L frames.
becomes. This judgment signal k is guided to the transmission mode control command generation circuit 8, and when the judgment signal k is "1", the next command directed to the slave station is "stop transmission".
A command l is generated. In this way, the master station monitors the synchronization state of the slave stations and controls the transmission of the slave stations.

By the way, it is known that the line quality of normal satellite lines deteriorates due to rain and the like. It is known that the received data sequence at the master station may contain erroneous data bits if the line quality is poor, and that the reliability of detecting a unique word included in a received burst depends on the line quality.

In the conventional system, if the master station does not detect a transmission burst from the slave station continuously over a predetermined L frame regardless of line quality, the slave station is forced to "stop transmitting". Sending out commands. For this reason, if the line quality is poor, the slave station may be instructed to "stop transmitting" even though it is transmitting at the correct timing; on the other hand, if the line quality is good, the slave station may Although it is certain that the transmission burst from the station cannot be detected and the transmission is performed at the wrong timing, there is a drawback that the command to "stop transmission" cannot be issued until L frames have been received.

In particular, in a communication system where the cycle of one control frame is significantly longer than the TDMA frame length, if an erroneous determination occurs in the frame immediately before the control frame for the slave station, it may seriously affect the entire communication system. . Furthermore, a slave station that is once erroneously determined to be out of synchronization and is forced to stop transmitting has the disadvantage that communication is interrupted for a considerable period of time until it rejoins the communication system.

[Explanation of purpose]

The present invention improves this point, and aims to provide a synchronization monitoring system that can perform reliable transmission control.

[Summary of the invention]

The present invention is characterized in that the line quality is periodically measured, the optimum value of L for the line quality at that time is determined, and this is used as a synchronization determination criterion.

That is, the present invention is provided with at least one master station and a plurality of slave stations, the master station is provided with means for sending a time division control signal addressed to the slave stations, and the slave stations are provided with means for transmitting a time division control signal addressed to the slave stations. means for receiving the timing signal and reproducing the frame timing; means for transmitting a signal to the master station for a time allotted to each slave station based on the timing signal; and means for transmitting a signal from each slave station at the master station. control means for configuring frames arranged in a line without overlapping on the time axis, and the master station monitors whether a signal from the slave station is received at a predetermined position on the time axis. and control means for stopping transmission from the slave station when the monitoring result is not received exceeding a determination reference value, the master station having a circuit for measuring line quality; and means for changing the judgment reference value given to the monitoring means to a more relaxed value when the line quality deteriorates in response to the output of the circuit.

[Explanation based on examples]

An embodiment of the present invention will be described based on the drawings.
FIG. 4 is a block diagram of the main parts of the first embodiment of the present invention. In comparison with the conventional device shown in FIG.
It is distinctive in that it leads to

Other points are similar to the conventional example shown in FIG. 2, and the same reference numerals indicate the same parts.

With this circuit configuration, the process of detecting the unique word included in the transmission burst from the slave station from the demodulated received data sequence a at the master station and obtaining the reception result signal j is the same as the conventional process shown in FIG. It is the same as the method. The reception result signal j is guided to a comparator 7.

Here, regarding the line quality measurement device 11 that directly measures the line quality from the received IF signal, (1) A Bit Error Rate Monitor for Digital
PSK Links JAMIN J.LEON et al. IEEE TRANSACTIONS ON
COMMUNICATIONS, VOL.COM−23, No.
5 MAY 1975 (2) Performance Monitor Techniques for
Digital Receivers Based on Extrapolation
of Error Rate DJGOODING, IEEE TRANSACTIONS ON
COMMUNICATION TECHNOLOGY,
It is described in detail in VOL COM−16 No.3, JUNE 1968. A signal m representing the line quality obtained by this line quality measuring device 11 is applied to a latch circuit 12. The line quality measuring device 11 constantly measures the line quality, and the signal m representing the line quality shows the latest measurement result. This signal m
is latched by the latch circuit 12 at the timing of the trailing edge of the received frame pulse g, and an output signal n is obtained. This output signal n is given as an address signal for the memory 13.

The corresponding content of the memory 13 specified by this address is written in advance in the memory 13 so that it becomes the corresponding optimal determination reference value L.
This judgment reference value L has a small value when the line quality is good, and a large value when the line quality is poor.

The judgment reference value L obtained in this way is given to a comparator 7, and compared with the above-mentioned reception result signal j to obtain a judgment signal k.

The determination signal k is applied to the transmission mode control command generation circuit 8, and the process of generating the transmission mode control command is similar to the conventional method shown in FIG.

FIG. 5 is a block diagram of main parts of a second embodiment of the present invention. The first embodiment described above is an embodiment realized by so-called hardware such as a gate element, a counter element, a comparator, etc., but in this second embodiment, these are realized by software (program) using a microprocessor. It is characterized by a simplified device/configuration and a reduction in the number of parts.

That is, the feature is that the binary counter 5, comparator 7, latch circuit 12 and memory 13 are omitted, and a microprocessor 15 is provided.

Other points are similar to the first embodiment shown in FIG. 4, and the same reference numerals indicate the same parts.

FIG. 6 is a flowchart showing the operation of FIG.

With this circuit configuration, the flip-flop 3 is activated by the detection result pulse b of the unique word detector 1.
The process until the output f is determined is the same as in the first embodiment.

A sufficiently narrow pulse h generated at the beginning of each received frame is applied to the microprocessor 15 as an interrupt signal. Upon receiving this interrupt signal h, the microprocessor 15 inputs the output m from the line quality measuring device 11 and temporarily stores it in a memory included in the microprocessor 15. Now, set the address of this memory to M01
shall be. Next, the state of the detection result signal f is input, and if the value is "1", it is assumed that the transmission burst from the slave station cannot be received, and the predetermined address of the memory included in the microprocessor 15 is input. Increase the contents of M02 by "1". If it is "0", it means that the address was received.
Set the contents of M02 to "0". Therefore, the content of this address M02 increases in value only when "1" is input as the detection result signal f over consecutive received frames, and becomes "0" if "0" is input even once. .

After performing this process, the optimum judgment reference value L stored in advance in the memory in the microprocessor 15 is read out corresponding to the line quality information temporarily stored at the address M01, and Compare with the value indicated by the contents of . If the value indicated by the contents of address M02 is greater than or equal to the judgment standard value L, it is assumed that the optimum judgment standard at that time is exceeded and the transmission burst from the flave station cannot be received, and the synchronization judgment result output k is set to "1". Output. On the other hand, if the value indicated by the contents of address M02 is less than the determination reference value L, "0" is output.
This signal k is guided to the transmission mode control command generating circuit 8, and the process of generating the transmission mode control command l is the same as in the first embodiment shown in FIG.

[Explanation of effects]

As explained above, according to the present invention, the transmission synchronization state of the slave station is determined by setting the optimum determination reference value according to the line quality at any time. Therefore, there is no risk of accidentally sending a "stop transmission" command to a slave station, and if the transmission synchronization state of the slave station is incorrect, the "stop transmission" command can be sent accurately in the shortest possible time. It becomes possible to eliminate obstacles to communication between other slave stations in the network.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the temporal relationship between a control superframe and a measurement superframe. FIG. 2 is a block diagram of the main parts of a conventional device. FIG. 3 is an operation time chart showing the signal waveforms at the points marked with x marks in FIG. 2. FIG. 4 is a block diagram of the main parts of the first embodiment of the present invention. FIG. 5 is a block diagram of a main part of a second embodiment of the present invention. 6th
The figure is a flowchart showing the operation of FIG. DESCRIPTION OF SYMBOLS 1... Unique word detector, 2... AND gate, 3... Flip-flop, 4, 6... Inverter, 5... Binary counter, 7... Comparator, 8... Transmission mode control command generation circuit, 11...
... Line quality measuring device, 12 ... Latch circuit, 15
...Microprocessor.

Claims (1)

[Claims] 1. At least one master station and a plurality of slave stations, the master station is equipped with means for sending a time-division control signal addressed to the slave stations, and the slave stations are equipped with a means for sending a time division control signal addressed to the slave stations. means for receiving the signal and reproducing the frame timing; means for transmitting the signal to the master station for a time allotted to each slave station based on the timing signal; and control means for configuring frames in which signals are arranged in a line without overlapping on the time axis, and the master station monitors whether the signal from the slave station is received at a predetermined position on the time axis. In the synchronous monitoring method, the master station is equipped with a circuit for measuring line quality. A synchronous monitoring method comprising: and means for changing the judgment reference value given to the monitoring means to a more relaxed value when the line quality deteriorates in response to the output of the circuit.