JPS6322654B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a time-division communication system, particularly to a system for avoiding unnecessary waves caused by switching.

A time division method is often used to communicate between a master station and multiple slave stations. FIG. 1 is a diagram explaining this, where 10 is a master station, 12a, 12b, 12c...
...are multiple slave stations. Transmission cycle (1 frame)
T is divided into multiple time slots (time slots) T ₁ , T ₂ , T ₃ . . . are slave stations 12a, 1.
2b, 12c, . . . , and each slave station communicates with the master station using the time slot assigned to itself. Since the transmission from the master station 10 is in a broadcast format and is simultaneously transmitted to each slave station, each slave station receives it in its own time zone. Although the broadcast frequency from the master station to the slave station and the transmission frequency from the slave station to the master station are different, the transmission frequency of each slave station is almost the same.
The master station identifies the source slave station of the signal based on the time zone of the signal that arrived.

In such time-division communication, each slave station stores transmission data in a register, for example, and transmits the data in a burst when its own time slot arrives. Figure 2 shows this part of the circuit, _S1 is the input signal, and fills in the data to be sent and the areas before and after it.
Consists of PN signals. 14 is a low pass filter (LPF), 16 is a modulator, and 18 is a switch.
The switch 18 is placed after the modulator 16, opens and closes in response to the burst on/off signal _S2 , and sends out the signal _S1 modulated by the modulator 16 during the time slot assigned to the own station. Fig. 3a shows the output of the switching device 18, and Fig. 3b shows the output of the switching device 18.
indicates the unnecessary waves generated at the rising and falling edges. When the switch 18 turns the signal on and off to produce a rectangular wave-like burst output as shown, the spectrum of the rectangular wave spreads on the frequency axis as shown by the solid curve in FIG. The envelope of this waveform is sinx/
x, and in terms of energy, it is its square. Broadening the spectrum is not desirable.
For example, in the time division system, multiple time division systems may coexist by using different frequencies, but if the spectrum spreads in such a case, there is a risk of interfering with other time division systems. However, if the envelope quickly attenuates by sinx/x or its square, there is no problem, but if the switching occurs rapidly and the width of the rising and falling parts of the signal in Figure 3a is infinitesimal, the instantaneous rise and fall A downward spectral distribution occurs, and this envelope becomes gentle (theoretically horizontal) as shown by the dotted line curve in FIG. 4, and in this case, interference with adjacent time division systems is large.

A simple way to limit this wide spread spectral distribution is the use of filters, an example of which is shown in FIG. 20 is the filter, whose passband is set to the fourth
Limit as shown in Figure B ₁ to remove unnecessary waves and prevent interference. However, with this method, of course
Unnecessary waves within the passband of BPF 20 cannot be removed.
As is known, it is difficult to construct a filter that provides an extremely narrow bandpass in the RF band. Therefore, even if bandpass is to be performed, it is conceivable to adopt a method of using an intermediate frequency and raising it to a high frequency (RF), and then limiting the band at the intermediate frequency, but this also has problems. That is, when the bit rate is high relative to the RF carrier frequency, unnecessary waves can be easily removed because the main rope is away from the carrier frequency, but when the bit rate is low, it is difficult to remove because the main rope is near the carrier frequency. Therefore, a method is being considered that limits the band on the LPF side, that is, the baseband, and then heterodynes it up to the RF. In the present invention as well, band limitation is performed at the baseband. In this baseband band limiting method, the following
There is no filter up to RF.

A simple measure against unnecessary waves accompanying switching is to dull the burst on/off signal _S2 , as shown in FIG. 6b. However, in this case, data may be lost, the level may drop, or interference between bursts may occur during the gentle rising and falling portions.

In order to eliminate such drawbacks, the present invention makes use of characteristics such as phase modulation and amplitude modulation in which an amplitude component is superimposed on a signal, and even if a simple switch is used, instantaneous unnecessary waves caused by switching are eliminated. This is to prevent this from occurring. That is, in the time-division communication system of the present invention, in which the carrier wave is phase-modulated with the transmitted data, the carrier wave is cut out by a switch that switches based on the burst on/off signal, and is transmitted during the allocated time slot of the own station, the modulated waves before and after the burst of transmitted data of the own station are 100%. Specific bits are added before and after the transmitted data so that the wave is subjected to % amplitude modulation, and the switching device is switched at the point where the amplitude of the modulated wave is zero, so that the data is transmitted during the time slot assigned to the own station. This is described in detail below using examples.

FIG. 7a shows the waveform (envelope) of the modulated wave used in the present invention. This is two-phase modulated and amplitude modulated. Furthermore, since the baseband signal is band-limited in advance by the LPF 14 (the transmission wave band is not band-limited in the IF or RF band), it has a narrow band. When such a modulated wave is input to the switch 18 and the switch ₁₈ is opened and closed using the on/off signal S2, if the signal _S2 has the phase shown in Figure 7b, the output after opening and closing will be as shown in Figure 7c. ,
The rise becomes steep and a transient phenomenon occurs. On the other hand, if the signal _S2 has a phase as shown in the figure d, there is no carrier at this point, so the output after opening and closing is e.
In this case, the occurrence of transient phenomena can be avoided.

However, when the modulator output is a continuous wave, the leading and trailing edges of the transmission burst of the own station are not necessarily as shown in FIG. 7e. For example, in the case of four-phase modulation, a wave with a certain phase and waves shifted by π/2, π, and 3/2π exist at the same time, so the waveform does not have a zero point as shown in Figure 7a, but as shown in Figure 7e. It is difficult to select the switching points to obtain such an output. Figure 8 shows the relationship before and after the switching point of each phase when switching four-phase modulated waves,
a is in the same phase before and after the switching point P, b is π, and c is shifted by ±π/2. The switching output of the modulated wave whose phase changes by π before and after the switching point is as shown in FIG. 7e, which is preferable. On the other hand, the switching output in FIG. 8a is as shown in FIG. 7c, and the switching output in FIG. 8c is intermediate between these. In order to do as shown in FIG. 8b, the signal should be set to 0 and π before and after the switching point.

FIG. 9 shows an embodiment of the invention. 22 is a memory, 24 is a π,0 pattern generator, and 25 and 26 are synthesizers. The signal S ₀ to be transmitted is temporarily stored in the memory 22 and sent out in bursts for use by the own station, with π,0 bits generated by the pattern generator 24 added before and after this. Furthermore, the synthesizer 26 inserts the PN signal _S1 in order to output a simulated signal even in bursts outside the allocated time of the own station and make the signal continuous. From then on, as described above, the LPF 14 limits the band, the modulator 16 performs two-phase modulation or four-phase modulation, etc., and the switch 18 switches between the inserted 0 and π bits to transmit the signal to the own station. The modulated output is transmitted in such a way that it enters the used time slot.

FIG. 10 is a diagram illustrating the addition of the π, 0 bits, switching, etc. in the case of two-phase modulation. a is data to be transmitted, and although not shown, the area before and after this is filled with a PN signal. b
indicates the π,0 bit to be added. Additional bits are inserted before and after the data as shown in c of the same figure.For example, as shown in d, the bits inserted before the data are 4 bits π, 0, π, 0, and the bits inserted after are 0. , π. Two bits each are sufficient if burst length is limited. Switching is performed between π and 0 and between those adjacent to data, as shown in g in the same figure. Therefore, the number of bits added to the data is one bit each at the front and rear. Since guard bits are usually provided before and after data to avoid failures caused by switching, the added 1 bit corresponds to this guard bit and does not increase the number of bits of the transmitted data. Even in the case of differential modulation, 0 and π do not change, and it is possible to switch between them.
Figures 10e and 10f show bit information in the case of two phases when communicating with this differential signal, e is an input bit, and when added, the signal after differential becomes f. Note that the method of the present invention is not limited to two phases, but can be similarly applied to four phases, eight phases, or more.

As explained above, according to the present invention, generation of unnecessary waves due to switching can be prevented by simply adding a small number of additional bits, and there is no need to devise the switching signal waveform, so it is possible to simply add a square wave on/off signal to the conventional pin diode. Modulation signals in the microwave band can be easily switched, providing great advantages in terms of cost and difficulty.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing an example of a time-division data communication system, Figs. 2 and 5 are block diagrams showing switching circuits for time-division transmission, Figs. 3, 4, and 6-6. FIG. 8 is a waveform diagram for explaining the operation, FIG. 9 is a block diagram showing an embodiment of the present invention, and FIG. 10 is a diagram for explaining the procedure for inserting π and 0 bits. In the drawing, Data indicates local transmission data, π and 0 indicate specific bits, and P indicates a switching point.

Claims (1)

[Claims] 1. In a time-division communication system in which a carrier wave is phase-modulated with transmission data, separated by a switch that switches based on a burst on/off signal, and transmitted during a time slot allocated to the own station, Modulation wave is 100
Specific bits are added before and after the transmitted data so that the wave is subjected to % amplitude modulation, and the switch is switched at the point where the amplitude of the modulated wave is zero, so that the data is transmitted during the time slot assigned to the own station. A time division communication method characterized by: