JPH0648805B2 - TDM frame synchronization establishment method - Google Patents

Description

The present invention relates to a frame synchronization establishment method for a TDM (Time Division Multiplex) data transmission system, and more particularly to a frame synchronization establishment method for a data modem with a TDM function that uses a voice band. Regarding

[Conventional technology]

Conventionally, TD has been used in data modems that use the voice band.
When transmitting M data, TDM frame synchronization and baud cycle were selected to be the same. For example, CCITT Recommendation V. With a 9600 bps modem compliant with 29, the baud rate is 240
At 0 Hz, the TDM frame period is (1/2400) seconds, and 4-bit TDM data is transmitted in one frame. Therefore, TDM
The serial data to be transmitted becomes 2400 bps or an integral multiple thereof, and if the sample timings of the transmission / reception system match, the TDM frame signal is naturally synchronized in the transmission / reception system.

[Problems to be solved by the invention]

By the way, in order to use the line more effectively,
Sometimes the baud rate must be other than 2400Hz. On the other hand, the transmission speed of a data terminal is generally 2400
Many are bps or an integer multiple of that. Therefore, since the baud cycle and the TDM frame cycle are different in such a modem, it is generally difficult to synchronize the phases even though the frequencies of the TDM frame signals can be matched in the transmission / reception system.

Therefore, an object of the present invention is to provide a TDM frame synchronization establishment method that eliminates the above-mentioned difficulties.

[Means for solving problems]

The TDM frame synchronization establishment method according to the present invention does not add a redundant bit for TDM frame synchronization, and in a data transmission system in which the frequencies of TDM frame signals are the same in both the transmitter and the receiver, the transmitter is Prior to data transmission, the receiver has means for transmitting a transmission frame signal instead of transmission data, and the receiver has a phase shifter that changes the phase of the reception frame signal according to a control signal and an output of this phase shifter. The phase comparator compares the phase with the phase of the transmission frame signal sent from the transmitter, and outputs the comparison result as a control signal to the phase shifter.

[Action]

Prior to the original data transmission, the transmitter transmits a transmission frame signal instead of the transmission data. In the receiver, the phase comparator adjusts the phase shift amount of the phase shifter so that the phase of the output of the phase shifter and the phase of the received data match.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, there is shown a block diagram of a TDM frame synchronization establishment system according to an embodiment of the present invention. The state in this figure shows the time when TDM frame synchronization is established.

In the transmitter, the master clock from the master clock generator 5 is frequency-divided by the frequency divider 4 and supplied as the baud clock of the modulator 6. On the other hand, the master clock from the master clock generator 5 is synchronously frequency-divided by the frequency divider 3 and supplied as a frame signal of the multiplexer 1 and also to one input terminal of the switcher 2. . The multiplexer 1 is connected to the other input terminal of the switch 2.
The output of is supplied. In the state shown in the figure, the switch 2 selects the output of the frequency divider 3, and the output of the switch 2 is the modulator 6
It is treated as transmission data to be input to. The output signal from the modulator 6 is sent as a modulated signal to the receiver via the transmission path.

In the receiver, the master clock from the master clock generator 8 is divided by N by the frequency divider 9 and supplied as the baud clock of the demodulator 7. At the same time, the master clock of the master clock generator 8 is divided by M in the frequency divider 10 and phase-shifted by the phase shifter 13, and then the demultiplexer 1
It is supplied as one frame signal. The phase shifter 13 has its phase shift amount adjusted by a control signal described later. The demodulator 7 demodulates the modulated signal sent from the transmitter into received data. This received data is input to the demultiplexer 11 and also to one input terminal of the phase comparator 12. The phase shifter 1 is connected to the other input terminal of the phase comparator 12.
The output of 3 is input. The output of the phase shift comparator 12 is input to the phase shifter 13 as a control signal.

When normal demodulation is performed, the frequencies of the master clock of the master clock generator 5 on the transmitter side and the master clock of the master clock generator 8 on the receiver side match and the demodulator 7 The output is the frame signal of the multiplexer 1 on the transmitter side.

However, the frame signal obtained as the output of the demodulator 7 generally has the same frequency as the frame signal supplied to the demultiplexer 11 on the receiver side, that is, the output of the phase shifter 13, but has a phase difference. Do not match.

In order to match the phases of the two frame signals described above, the phase comparator 12 detects the phase difference between them and outputs this phase difference as a control signal to the phase shifter 13 to determine the phase shift amount of the phase shifter. Adjust.

When the above operation is completed, the phase of the frame signal of the multiplexer 1 on the transmitter side and the phase of the frame signal of the demultiplexer 11 on the receiver side completely match.
Therefore, even if a line fluctuation or the like occurs thereafter, as long as the master clock of the transmitter-side master clock generator 5 and the master clock of the receiver-side master clock generator 8 remain in synchronization, the frame signals of the two match. Is kept. Therefore, the phase shift amount of the phase shifter 13 may be fixed.

〔The invention's effect〕

As described above, according to the present invention, in the TDM data transmission system, by notifying the receiver of the TDM frame signal on the transmitter side before data transmission, it is not necessary to match the TDM frame period with the baud period of the modulation / demodulation system. There is an effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a TDM frame synchronization establishing system according to an embodiment of the present invention. 1 ... Multiplexer, 2 ... Switcher, 3, 4 ... Divider, 5 ... Malta clock generator, 6 ... Modulator, 7 ...
… Demodulator, 8 …… Master clock generator, 9, 10 ……
Frequency divider, 11 ... Demultiplexer, 12 ... Ratio phase comparator, 13 ... Phase shifter.

Claims (1)

[Claims] 1. A data transmission system in which a redundant bit for TDM frame synchronization is not added and the frequencies of TDM frame signals are the same at both the transmitter and the receiver,
The transmitter has means for transmitting a transmission frame signal instead of transmission data prior to data transmission, and the receiver has a phase shifter for changing the phase of the reception frame signal according to a control signal, A phase comparator that compares the phase of the output of the phase shifter with the phase of the transmission frame signal sent from the transmitter and outputs the comparison result to the phase shifter as the control signal. A TDM frame synchronization establishment method characterized by.