JPS6051294B2 - transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transmitter configured to establish frame synchronization between a transmitting side waveform generator and a receiving side waveform generator via a transmission path in which there is a large disturbance in phase, particularly in a satellite. Communication TD
The present invention relates to a transmitter that can quickly establish frame synchronization upon initial entry of an MA.

It is a well-known fact that in digital communications, synchronization with respect to frames, words, bits, etc. is essential, and for this purpose certain pulse patterns are sometimes transmitted as synchronization signals.

In a TDMA line, in order to set the own station's burst signal at a predetermined position within a frame, a specific pattern (hereinafter referred to as PN) that is formed at the same period of the frame is used.
Code. is transmitted to the satellite, first detects the PN signal from the satellite's output signal, performs PN synchronization with this, refers to the synchronization burst signal being received, and determines where in the frame the head of the transmitted PN code is located. There is also a method of detecting whether it is set. In such a case, the transmitted low-power PN code will be transmitted within the satellite to the working high-power T
The burst of DMA adds a disturbance to the amplitude. Moreover, since these bursts are arranged in an orderly manner within the frame, the PN code having the same period as this frame will be subjected to disturbances of the same waveform for a long time. Generally, for detection and synchronization of known signals, cross-correlation is performed between the received signal and a detection oscillator that outputs the known signal (mutual)
A correlator is used in the detector.

One problem in signal detection using a correlator is that if a known signal that is sent undergoes amplitude modulation with a waveform with the same period as the known signal, the input/output characteristics of the correlator cannot be accurately predicted. There is a point where it becomes difficult. When a PN code is used for a signal with a known fact, the correlator exhibits a maximum and unique cross-correlation amount only when the two signals are in phase. PN sent by
If the code undergoes amplitude modulation with a waveform of the same period as the above example, the received PN code no longer has properties different from the original PN code, so the detection waveform generator The amount of cross-correlation with the PN code of
In addition to the maximum value obtained when both PN codes are synchronized, many local maximum values occur in an asynchronous state. In this case, many pseudo stable points occur in a synchronizer using a correlator,
Convergence to the original stable point is no longer guaranteed. This difficult problem cannot be solved unless the receiving side applies inverse amplitude modulation to cancel this effect, as long as the transmitted PN code is subjected to amplitude modulation with a waveform having the same period as that of the transmitted PN code.

An object of the present invention is to reliably establish frame synchronization between a transmitting side waveform generator and a receiving side waveform generator through a transmission path that has disturbances that seriously affect the transmitted waveform. In particular, the aim is to quickly establish frame synchronization at the time of initial entry into a satellite communication system. Therefore, the output waveform period of the transmitting side waveform generator, which generates the same periodic waveform with almost the same period as that of the receiving side waveform generator, is set to be different from that of the receiving side by ΔT only at the time of pull-in.

Due to this difference in ΔT, the difference between the phase of the transmitted waveform and the output phase of the receiving side waveform generator increases with time, and finally increases to 2π and returns to the original phase difference. Assuming that the pull-in time is Ta (seconds) and the instantaneous force waveform period of the transmitter waveform generator is TO (this value changes, it is best to consider its approximate value or average value), then the two If we try to shift the phase of the waveform by 2π, then Δ
All you have to do is set T.

Therefore, even if the transmitted waveform is amplitude-modulated with a unique waveform within the transmission path, the influence of the unique waveform on the transmitted waveform changes from moment to moment.

Therefore, even when a PN code is used in the transmission waveform, the maximum value of the cross-correlation amount that occurs when the transmission PN code and the receiving side PN code are asynchronous does not continue for a long time. Therefore, only the maximum value of cross-correlation in the original synchronized state. This is the only correlation that continues stably. Based on this, if the PN code of the receiving side waveform generator is synchronized while the transmitting side PN code is undergoing a phase shift, it can be considered that both PN codes are definitely synchronized. The reason why the relative phase shift of the transmitted waveform is stopped after the pull-in is so that the transmitted waveform can fulfill its original function as a synchronization signal between the transmitter and the receiver.

According to the present invention, there is provided a transmitter for establishing frame synchronization between transmission and reception of a satellite communication line, the transmitter comprising:
A waveform generator that generates a frame synchronization pattern of an MA line, and a frame synchronization pattern transmission period of the waveform generator that is different from a normal value when the satellite communication TDMA line is initially entered, and at other times, the transmission period of the frame synchronization pattern is set to be It is possible to obtain a transmitter equipped with a means for adjusting the period to a normal value, and it is possible to separate the disturbance in the transmission path from the transmitted waveform without imposing a burden on a new device on the receiving side. The synchronization of is established correctly without getting stuck in many pseudo stable points.

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The system is waveform generator 1,
The transmitter includes a phase shifter 2 and a modulator 3, and a receiver includes a demodulator 4, a cross-correlator 5, and a receiving waveform generator 6. The phase shift speed of the waveform generator 1 on the transmitting side takes different values for a certain period of time during the pull-in period under the control of the phase shifter 2. After this fixed period, the speed is returned to its original value and synchronization between transmitting and receiving is established. The receiving side is a waveform phase synchronization device with a normal correlator as a phase difference detector. Each part of the embodiment will be explained in more detail.

Here, it is assumed that the transmission waveform is a PN code of a constant length. Therefore, a PN code generator is used as the waveform generator 6 on the receiving side, and a delay discriminator is used as the cross-correlator 5. There is no need to limit the transmitted waveform to a PN code, and the system configuration includes a waveform generator, phase shifter, and modulator on the transmitting side, and a demodulator and cross-correlator on the receiving side.

First, in the transmitting side PN code waveform generator 1, the clock is sent from the high speed clock generator 100 to the gates 101 and 102.
through the counter 103 from (a)00...00) to (
111...111).

The output of the counter 103 is read-only memory (ReadO
nlyMemOry=ROM) 104 as an address. The address/input of ROMIO4 is (a) 0
0...00) to (100...00), (111...
・As the PN code changes to 11), the PN code changes from the 1st bit to the Mth bit one after another in one period of M bits.
Outputs N code output. The output of the ROMIO4 is converted from the modulator 3 into a transmission PN code and transmitted. On the other hand, in the phase shifter 2, the high speed clock is transferred to the counter 201.
The state of the counter 201 is monitored by a comparator 202, and when a certain value is reached, the comparator 202 outputs an inhibit pulse and inhibits one clock of the PN code oscillator 1 using the gate 102. . Therefore, the phase will be delayed by this amount. The inhibit pulse also resets the counter 201. Therefore, the PN code oscillator 1
The clock is inhibited at regular intervals, and the phase is delayed each time. This inhibit pulse is also added to counter 203 and counted. When this number reaches a certain value, the comparator 204 detects this and applies an inhibit signal to the gate 200 through the delay shift register 205. As a result, the counter 201 is stopped, the gate 102 is held open, and the transmitted PN code is thereafter outputted in one cycle and at a constant time without causing a phase shift. Reset terminal 20
By applying a signal to 6, the counter 203 is reset and again the comparator 202 starts generating inhibit pulses until said counter 203 reaches a certain value, lengthening the period of the output waveform. In other words, by applying a signal to the reset terminal 206 at the pull-in start time, the relative phase shift that occurs due to the difference in the period of the transmitter-side waveform generator and the receiver-side waveform generator is corrected within a certain period of time from the start time. Occur. By establishing phase synchronization with the receiving side waveform generator during this relative phase transition, true phase synchronization can be achieved.

On the other hand, on the receiving side, a demodulator 4 detects the transmitted PN code, applies it to a delay discriminator 5, and detects a phase difference between it and the receiving side PN code waveform generator 6.

The delay discriminator 5 includes multipliers 500, 501 . It consists of an adder 502 and a low-frequency wave transducer 503, and its input/output characteristics are as shown in FIG. Here, Δ represents the bit length (seconds) of the PN code, and M represents the number of bits in one period of the PN code. The horizontal axis is the time of the page YN code (
Tε seconds), and the vertical axis represents the output of the delay discriminator 5. Based on this characteristic, by setting TE=0 as one stable point, the receiving side PN is determined by the output of the delay discriminator 5.
It can be seen that the phase of the waveform generator 6 on the code receiving side can be controlled. In other words, the phase difference between both PN codes (time lag TE
) becomes within ±2Δ in Figure 2, feedback control is applied and T
When IEl>0, the frequency (one cycle length) of the receiving side PN code receiving side waveform generator 6 is changed so that TE is moved in the negative direction, and when TO<0, the frequency (one period length) is moved, and the automatic Therefore, TE=0. Once the stable point of TE=0 is reached, in order to escape from this stable point, it is necessary to go over the large peak of the correlator characteristics shown in Figure 2, and this kind of thing does not occur with normal disturbances. It's getting difficult.

Reception W) The N-code waveform generator 6 has a shift register so that the phase of the shift register 601 for generating M-sequence PN codes can be controlled by changing the length of one cycle of the PN code. A voltage controlled variable frequency oscillator 600 is used as a high speed clock oscillator to drive.

In such a transmitting/receiving system, the phase of the transmitting side PN code changes, so the effect of any amplitude modulation received in the transmission path remains unique and constant at a certain point in one cycle of the CAL N code. I can't. Therefore, if the receiving side synchronizes to this while the code to the transmitter undergoes a phase shift, it will not reach a false stable point but will synchronize to the true stable point. In this embodiment, since a voltage-controlled variable frequency oscillator VCO whose frequency changes is used as the clock source for the shift register 601 that generates the PN code, the period of the PN code on the receiving side is controlled by the control input of the CO. Varies depending on Therefore, regardless of the period of the sending code, the receiving side PN code is synchronized with the sending side's PN code at the same period. However, at the time of pull-in, the PN code repetition frequencies on the transmitting and receiving sides are set to be different from each other to some extent, so both codes synchronize while repeating cycle slips. The cycle slip is overcome and the synchronization state is entered only when both the transmitting and receiving codes are near the true stable point and the delay discriminator 5 generates a large error output. The correlator output near the true stable point has a large output as shown in Figure 2, but the output similar to the characteristics shown in Figure 2 generated near the pseudo stable point is sufficiently large compared to the true one. Usually small. Therefore, due to the relative phase shift of both codes, the synchronization system passes through these pseudo-stable points before false lock occurs. However, near the true stable point, the correlator output is much larger than that near the pseudo stable point, so the PN period on the receiving side is strongly controlled, and the synchronization between it and that on the transmitting side is strong. Yes, and it is not weak like other pseudo-stable points. This is received a! by the present invention. This is the reason why 1PN code pseudo pull-in (false lock) is avoided. As explained above, according to the present invention, even when a transmission periodic waveform is subjected to amplitude modulation or phase modulation with a waveform having the same period as that period, or when a large disturbance is periodically added, By using a conventional synchronizer configured to synchronize the transmit waveform on the receiving side, synchronization between the transmitter and receiver is established precisely at the original stable point, rather than remaining at a pseudo stable point.

Therefore, there is no need for the receiving side to take any measures against disturbances within the transmission path, and the receiver can be simplified.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the present invention, in which 1 is a transmitting side waveform generator, 2 is a phase shifter, 3 is a modulator, 4 is a demodulator, 5 is a delay discriminator, and 6 is a receiving side waveform generator. It is a vessel.

Claims (1)

[Claims] 1 A transmitter that establishes frame synchronization between transmission and reception of a satellite communication TDMA line, which includes a waveform generator that generates a frame synchronization pattern of the satellite communication TDMA line, and a waveform generator that generates a frame synchronization pattern of the satellite communication TDMA line, and a waveform generator that generates a frame synchronization pattern of the satellite communication TDMA line at the time of initial entry of the satellite communication TDMA line A transmitter comprising: means for making a transmission cycle of a frame synchronization pattern of a generator different from a normal value, and otherwise making the transmission cycle the normal value.