JPS634376B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a time division multidirectional communication system that allows correct code reproduction in a master station of a time division multidirectional communication network.

In a time-division multidirectional communication network, a communication network is formed by a master station and a large number of scattered slave stations, and the master station emits multiplexed PCM signals in multiple directions on the time axis in a broadcast format. Each slave station operates in synchronization with the master station's clock included in the received signal, extracts and receives the portion assigned to it from the received signal, and transmits during the time slot assigned to it. The transmission time is adjusted so that the signals from each slave station are received by the master station in the order in which the slave stations transmit, arranged on the time axis. In this way, the transmission time between the master station and each slave station is communication can be carried out between them.

FIG. 1 is an explanatory diagram showing transmitted and received signals in a time division multidirectional communication system. In the figure, 1 indicates the master station transmission signal, and on the time axis t, the slave station,
,...N indicates that a PCM signal multiplexed with signals for N is emitted. In FIG. 1, . . . , N indicate signals for slave stations, and F is the frame length.

In FIG. 1, 2 indicates the received signal of the slave station,
It arrives with a delay of propagation delay time τ ₁ from the transmission from the master station. By extracting only the portion allocated to the slave station, the slave station can receive information regarding the slave station sent from the master station.

In Fig. 1, 3 indicates the transmission signal of the slave station,
After receiving the signal for the own station from the master station, the own station transmits the own signal to the master station with a delay of _Δ1 .

In FIG. 1, reference numeral 4 indicates a received signal of the master station, and the signal of the slave station reaches the master station with a delay of a propagation delay time τ ₁ ', which is approximately equal to τ ₁ . Other slave stations, ..., N perform reception and transmission in the same way, and as a result, at the master station, the received signals from each slave station do not overlap and are arranged in an orderly manner in the order of transmission from each slave station on the time axis. so that

However, the distances _{between the} master station and each child station _, .
Therefore _, after receiving the signals assigned to it from _the master station, _each slave station... By transmitting signals and adjusting the times Δ ₁ , Δ ₂ , ..., Δ _o at each slave station, the signals from each slave station are received at the master station in an orderly manner without overlapping. be able to.

FIG. 2 is a diagram showing the propagation delay time between the master station and each slave station and the transmission delay time at each slave station. In the same figure, P is the master station, ,...,N
each indicates a slave station. Each slave station has a propagation delay time τ ₁ , τ ₂ , ...τ _o between it and the master station, respectively,
They are shown to have transmission delay times Δ ₁ , Δ ₂ , . . . , Δ _o , respectively.

To do this, each slave station synchronizes with the frame bits included in the master station transmission signal and corrects the signal propagation delay time between itself and the master station using a delay equalizer or the like during the time slot assigned to the slave station. The above-mentioned objective can be achieved by simply transmitting the information.

On the other hand, the master station samples the signals from each slave station, performs identification, performs code regeneration, and removes distortion occurring in the transmission path. At this time, sampling is performed by the master station's clock, but if the phase position of the master station's sampling clock is not in the center of the data from each slave station, code errors will increase.

FIG. 3 is a diagram showing the phase relationship between the received signal and the sampling clock at the master station. In the figure, 1 indicates the received signals A, B, C,... from the slave stations, . . . in the form of an eye pattern, and 2 indicates the sampling clocks a, .
It shows a′. If the sampling clock is at the center of the received data, as shown in a, no code errors will occur, but if the sampling clock is shifted from the center of the received data, as shown in a', code errors will increase.

In this manner, when the phase of the sampling clock at the master station is taken into consideration, the timing of signal transmission from each slave station must be more strictly defined. For this reason, each slave station is equipped with a phase shifter for fine adjustment.
A method was used in which the transmission time was adjusted for each slave station.

FIG. 4 is a diagram showing signal transmission time adjustment means in each slave station. In this figure, the same parts as in Figure 2 are indicated by the same numbers, and are _1-1 , _1-2 ,...1.
- _o is a fine adjustment phase shifter provided in each slave station,...,N. In each slave station, by adjusting the fine adjustment phase shifters _1-1 , _1-2 ,..., 1- _o , the sampling clock in the master station is positioned at the center of the received data of each slave station. You can do it like this.

Conventionally, such adjustments are made by the master station monitoring the waveforms of the received signal and sampling clock and giving instructions to each slave station over the telephone, etc., and each slave station follows the instructions from the master station to This was done by adjusting a fine phase shifter. Therefore, when fine adjustment is required, not only is it time consuming, but it is not always possible to make a satisfactory adjustment.

The present invention aims to eliminate such drawbacks of the prior art, and its purpose is to eliminate the need for meetings and communications between the master station and each slave station to adjust the slave station signal transmission delay time. The object of the present invention is to provide a method that allows only the master station to determine the correct sampling clock phase position for each slave station received signal. To achieve this objective, in the time-division multi-directional communication system of the present invention, a master station and a large number of slave stations form a multi-directional communication network, and the master station transmits signals to each slave station in multiple directions in a time-division manner. A clock extraction method that extracts the clock from the received signal of a slave station at the master station of a time-division multidirectional communication network, in which each slave station transmits to the master station during its own assigned time period in synchronization with the master station clock. a first phase shifting means that operates with a long time constant to shift the phase of the master station clock signal to follow the slave station clock; and a first phase shift means that operates with a short time constant to phase shift the master station clock signal. A second phase shift means is configured to follow the slave station clock by holding the output of the first phase shift means for a certain period of time after switching the reception signal of each slave station, and then selects an output of the second phase shift means. , further comprising switching means for selecting the output of the first phase shifting means after a certain period of time or after the phase of the first phase shifting means has been established, and identifying the slave station signal by the output clock of the switching means. It is characterized by performing code reproduction.

The principle and embodiments of the present invention will be explained below.

In the time-division multidirectional communication system of the present invention, in order to optimally determine the phase of the sampling clock input to the discriminator with respect to the received signal from each slave station at the master station, the clock supplied to the discriminator is By providing a variable phase shifter in the signal path and controlling the variable phase shifter according to the phase difference between the clock signal extracted from the received signal and the master station clock signal,
The phase of the sampling clock in the discriminator is always made to match the phase of the clock in the received input signal.

However, when such a variable phase shifter is provided, it takes several bits or more to establish the phase at its output. Especially when the magnitude of each slave station burst signal at the master station is different, automatic gain control (AGC) installed in the master station receiver to prevent fading
The phase of the slave station burst signal is greatly disturbed at the beginning due to the limiter, and therefore the clock extracted from the slave station signal cannot be used for identification until the phase stabilizes.

FIG. 5 is a diagram showing phase fluctuations in the slave station burst signal and the master station received signal. In the same figure, a
indicates the burst signal of each slave station, and A data, B data, C data, ... are the slave stations, respectively.
It is a signal of... In this way, the signals from each slave station that reach the master station have different magnitudes.

In FIG. 5, b indicates a phase change in the burst signal B of a. In the figure, θ indicates a phase change in the burst signal B from the reference level. In this way, the phase of the initial portion of each slave station burst signal is greatly disturbed.

In such cases, a method is usually used in which a clock synchronization signal is inserted before the data signal to thereby establish the clock phase. However, in the case of time-division multidirectional communication, no synchronization signal is used. In addition, the clock phase shift of the signals from each slave station is usually not large. Therefore, in the time-division multidirectional communication system of the present invention, two variable phase shifters that operate with different time constants are provided, and their outputs are appropriately switched to adjust the phase of the sampling clock corresponding to each slave station received signal. We are trying to regulate the

FIG. 6 is a block diagram showing the configuration of an embodiment of the time division multidirectional communication system of the present invention. In the figure, 11 is a demodulator, 12 is a discriminator, 13 is a clock extractor, 14 is a phase detector, 15 is a clock oscillator, 16 and 17 are low frequency filters, 18 and 19 are variable phase shifters, and 20 2 is a switch SW, and 21 is a delay circuit.

In FIG. 6, the received signal from each slave station is applied as an intermediate frequency (IF) signal to a demodulator 11 for demodulation, and the demodulated signal is applied to an identifier 12 for identification by a sampling clock. code regeneration is performed to produce data output.

On the other hand, a clock extractor 13 extracts a clock from the demodulated signal, and the extracted clock is applied to one input of a phase detector 14. Clock oscillator 15 generates a reference clock at the master station. The reference clock is used as a transmit clock at the master station and is applied to the other input of phase detector 14. The phase detector 14 compares the phases of both inputs and generates an output signal according to the phase difference, and this output is applied to the variable phase shifter 18 via a low frequency filter 16 having a low cut-off frequency. The signal is applied to the variable phase shifter 19 via a low frequency filter 17 having a high cut-off frequency. As a result, the clock of the clock oscillator 15 is controlled by the variable phase shifter 1.
Following the phase shift determined by 8 and 19, respectively,
It is added to the switch 20. A burst signal corresponding to the signal of each slave station is applied to the switch 20 via a delay circuit 21. Therefore, the switch 20 applies the burst signal corresponding to the signal of each slave station to the delay circuit 2 from switching of the burst signal of each slave station.
The switching is delayed by the time τ determined by 1,
In this way, the clock phase shifted by either variable phase shifter 18 or 19 is arranged to be applied to the discriminator for sampling.

FIG. 7 is a time chart showing various signals in the time division multidirectional communication system of FIG. In the figure, a indicates input data from each slave station, and A data, B data, C data, . . . indicate input data of each slave station, . . . . b shows the phase difference Δθ between the clock phase and the reference phase in the received signal from each slave station, . . . , corresponding to each input data. In the method of the present invention, a case is considered in which the phase difference Δθ is not very large.

In FIG. 7, g indicates the state of phase establishment in the variable phase shifter 18, and g indicates the state of phase establishment in the variable phase shifter 19, corresponding to the input data of each slave station. In this way, the variable phase shifter 1
8 has a low frequency filter 16 with a low cutoff frequency, so its rise and fall are slow. On the other hand, since the variable phase shifter 19 includes the low frequency filter 17 with a high cutoff frequency, its rise and fall are quick.

In FIG. 7, c indicates the period during which the clock of the receiving slave station is used. In the figure, A clock, B clock, C clock, . . . indicate periods in which the clocks of the slave stations, . This time τ is set equal to the time τ ₀ at which the phase disturbance occurs as explained in FIG.

In FIG. 7, d indicates the output of the variable phase shifter input to the discriminator, and e indicates the corresponding switching operation of the switch 20. Here, φ ₁ indicates a period in which the variable phase shifter 18 is used, and φ ₂ indicates a period in which the variable phase shifter 19 is used. 7th
As is clear from FIG. d, even after the input data is switched, the clock for the previous slave station held by the variable phase shifter 18 is used for a time τ, and then the clock for the previous slave station held by the variable phase shifter 19 is used. The clock is switched to the clock for the slave station in the center, and after a certain period of time, the clock is switched to the output clock of the variable phase shifter 18.
In this way, in the time-division multidirectional communication system shown in Fig. 6, even after the slave station burst signal is switched, the time τ
During this time, the clock for the previous slave station is used as is. As mentioned above, the clocks of the previous slave stations have a slight phase difference, but this does not pose a problem in use. It is then switched to this only when the clock for the receiving slave station is established.

FIG. 8 is a circuit diagram showing an example of the configuration of a variable phase shifter. In the same figure, the output of gate circuit _G1 is a resistor
It is integrated by an integrating circuit consisting of a series circuit of R ₁ , capacitor C ₁ , varactor C _v and capacitor C ₂ ,
The gate circuit _G2 identifies the signal at a constant level and shapes the waveform to produce a delayed output. varactor
The amount of phase shift can be varied by changing the integration time constant by controlling the capacitance of C _v by the control voltage applied via resistors R ₃ and R ₂ .

FIG. 9 shows the second time-division multidirectional communication system of the present invention.
FIG. 7 is a block diagram showing the configuration of an embodiment of the present invention, in which the same parts as in FIG. 6 are designated by the same numbers.
31 and 32 are lock detectors.

In FIG. 9, lock detectors 31 and 32 detect the phase establishment for each child station burst in a loop including a low frequency filter 16 and a variable phase shifter 18, and a low frequency filter 17 and variable phase shifter 19, respectively. To detect. The switch 20 is controlled by the outputs of the lock detectors 31 and 32, and selects the output of the variable phase shifter 18 during the time τ after switching of each slave station burst, and then selects the output of the variable phase shifter 18. Select output 19.
Furthermore, after the phase of the variable phase shifter 18 is established, the output of the variable phase shifter 18 is selected. This allows selection of sampling clocks similar to the embodiment shown in FIG.

The method of the embodiment shown in FIG. 7 is suitable when the signal length of the input burst signal of each slave station is determined in advance, whereas the method of the embodiment shown in FIG. , is suitable when the time length of the input burst signal of each slave station is undefined.

FIG. 10 is a block diagram showing the configuration of a third embodiment of the time division multidirectional communication system of the present invention. In this figure, the same parts as in FIG. 6 are indicated by the same numbers, and 41 and 42 are phase detectors.

In FIG. 10, the outputs of variable phase shifters 18 and 19 are fed back to phase detectors 41 and 42, respectively, and compared with the slave station clock signal extracted by clock extractor 13. It is configured to control variable phase shifters 18 and 19 via bandpassers 16 and 17, respectively.
Therefore, in the embodiment shown in FIG.
differs from the embodiment shown in FIG. 6 in that each of them constitutes a phase-locked loop (PLL).
Selection of the sampling clock in the embodiment of FIG. 10 is also similar to that of the embodiment of FIG.
In the embodiment shown in FIG. 10, the switching of the switch 20 is not based on the burst signal input to the delay circuit 21, but as in the embodiment shown in FIG.
It goes without saying that the PLL may be provided with a lock detector and switched based on its output.

As explained above, according to the time division multi-directional communication system of the present invention, a clock signal having an optimal phase is generated for each signal from each slave station, and before the phase is established, the clock signal is generated with respect to the signal from the previous slave station. Since each slave station burst signal is sampled using the clock signal, each slave station received signal can always be identified with the correct phase, which is effective because code errors in waveform reproduction can be reduced. It is true.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing transmitted and received signals in the time division multi-directional communication system, Figure 2 is a diagram showing the propagation delay time between the master station and each slave station, and the transmission delay time at each slave station, Figure 3 is a diagram showing the phase relationship between the received signal at the master station and the sampling clock, Figure 4 is a diagram showing the signal transmission time adjustment means at each slave station, and Figure 5 is a diagram showing the phase relationship between the slave station burst signal and the master station received signal. FIG. 6 is a block diagram showing the configuration of an embodiment of the time division multidirectional communication system of the present invention, and FIG. 7 is a time diagram showing various signals in the time division multidirectional communication system of FIG. 6. 8 is a circuit diagram showing an example of the configuration of a variable phase shifter, and FIGS. 9 and 10 are block diagrams showing the configurations of other embodiments of the time-division multidirectional communication system of the present invention. . _1-1 , _1-2 , 1- _o ...Fine adjustment phase shifter, 11
... Demodulator, 12 ... Discriminator, 13 ... Clock extractor, 14 ... Phase detector, 15 ... Clock oscillator, 16, 17 ... Low frequency generator, 18, 19
...Variable phase shifter, 20...Switcher (SW), 21
... Delay circuit, 31, 32 ... Lock detector, 4
1,42...Phase detector, _G1 , _G2 ...Gate circuit, _C1 , _C2 ...Capacitor, _Cv ...Varactor,
R ₁ , R ₂ , R ₃ ...Resistance.

Claims (1)

[Claims] 1 A multidirectional communication network is formed by a master station and many slave stations, and the master station transmits signals to each slave station in multiple directions in a time-sharing manner, and each slave station assigns its own station in synchronization with the master station clock. A master station in a time-division multidirectional communication network that transmits data to a master station during a time period has a clock extraction circuit that extracts a clock from a received signal from a slave station, and a clock extraction circuit that operates with a long time constant to extract a clock signal from the master station. a first phase shifting means for shifting the phase of the master station clock to follow the slave station clock; a second phase shifting means operating with a short time constant for shifting the phase of the master station clock so that it follows the slave station clock; After the slave station reception signal is switched, the output of the first phase shifting means is held for a certain period of time, the output of the second phase shifting means is selected, and after a certain period of time or the first
and switching means for selecting the output of the first phase shifting means after the phase of the first phase shifting means is established, and the code of the slave station signal is reproduced by identification based on the output clock of the switching means. A time-division multidirectional communication system.