JPS639700B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spread spectrum automatic synchronization establishment method with a simple configuration.

FIG. 1 shows the configuration of a general transmission method in direct spread communication and the state of signals in each part. FIG. 2 shows the configuration of a conventional receiving system.

In Fig. 1, 1 is a spread spectrum modulator, 2 is a PN code generator (PN signal generator) that generates a spread signal, 3 is a signal modulator, 4 is a signal input terminal, and 5
indicates the spread signal output terminal.

The input signal for transmission enters from 4 and is modulated by the signal modulator 3 into a normal FM or PM signal. The output a is modulated in the spreading modulator 1 by two PN signal generator outputs c controlled by the transmitting clock signal d and sent out as the output b.

Here, normally, a two-phase or four-phase PM modulator is used as the spreading modulator 1, and the modulation speed of the PN signal generator is several tens to several thousand times higher than the modulation speed of the signal modulator output a. Selected at twice the price. As a result, the bandwidth of the spread signal b from the signal output terminal 5 is
The bandwidth is much wider than the bandwidth of the modulation signal a. In the same figure, the sign of the signal c from the PN generator is
1, 0, 0, 1..., the spread modulator (two-phase PM
(assuming a modulator) shows that the phase of the output changes from ο, π, π, ο. Note that Δτ is
It represents 1 bit time length.

FIG. 2 shows a well-known reception method in the direct sequence communication system, in which 6 is a spreading demodulator (corresponding to the spreading modulator 1 in FIG. 1), 7 is a signal demodulator (FM or PM demodulator), 8 and 8' are spread demodulators for synchronization (equivalent to 1), 9 and 9' are envelope detectors with different polarities, 10 is a PN code generator for reception (PN signal generator), and 11 is a clock. The signal generator includes a delay line 12 giving a delay time Δτ/2, an input terminal 13 for a spread signal b, an output terminal 14 for a demodulated signal, and a control terminal 15 for a clock signal generator. 8,8′,
16 consisting of 9, 9', 10 and 11 is well known as a delay lock tracking loop.

Here, the PN signal generator 10 is equivalent to the PN signal generator 2 used in the transmission system of FIG. 1, and although the frequency of the clock generator 11 is variable, It is almost the same as the frequency of d.

In this receiving system, for the spread input signal b,
The despread signal of the spreading demodulator 6 (PN signal generator 10
If the outputs (outputs of
The output a of the spreading demodulator 6 is exactly the same as the modulated signal a of the transmission system in FIG.
Obtained from 4.

A delay lock tracking loop 16 maintains this frame and bit synchronization.

In a commonly used delay lock tracking loop, the output of the PN signal generator is 1 bit (or 2 bits).
The signals are applied to the spreading demodulators 8 and 8', respectively, with a delay time difference of 1 bit). At this time, the outputs e, f, and g of the envelope detectors 9 and 9', respectively, with respect to the phase difference between the input signal b and the output of the PN signal generator are shown in FIG.

e indicates the case where the polarity of the output of the envelope detector is positive, and f indicates the case where the polarity is negative, and the peak values of the respective outputs indicate the point where the signal b and the PN signal become in frame and bit common phase. The combined wave of outputs e and f forms a curve g similar to the discriminator of the FM demodulator, and this 0 point becomes the tracking point of the loop. That is, in this synchronization loop, the control signal g acts on the clock generator 11 to maintain synchronization at the tracking point.

Generally, when the receiving system starts receiving, the input signal b and the signal from the receiving PN signal generator 10 are completely asynchronous, and it is necessary to obtain the PN signal sequence and bit synchronization (frame and bit). In other words, upon establishment of synchronization, the delay lock loop is changed to the previous control output g.
tracking point.

This is usually done by manually adjusting the clock frequency of clock signal generator 11, or by manually adjusting the clock frequency of clock signal generator 11.
5, another sweep signal is applied, the clock frequency is changed, and the above-mentioned control point is searched.

By the way, synchronization is maintained in this delay lock tracking loop only when the input signal phase fluctuates by a few bits at most, and if the input signal phase fluctuates more rapidly than that, the tracking loop becomes uncontrollable. This condition often arises due to multipath effects particularly in mobile communication systems and has been cited as the most serious problem.

Therefore, it would be very effective if a simple system could quickly establish synchronization and maintain stable synchronization.

The present invention is intended to improve the above-mentioned problems of the conventional technology, and its purpose is to provide a method for automatically establishing and maintaining synchronization quickly. The feature of the present invention is to have a frame detector that constantly detects the input signal, generate an independent PN signal synchronized with the input signal at predetermined time intervals, and apply this to the PN signal generator in the delay lock loop. , at least one pair of spread signal demodulators 8, 8' which operate according to the output of the first PN signal generator 10 and receive a spread spectrum signal as input, and an envelope detector connected to the output of the demodulators. 9 and 9', and a first clock signal generator 11 whose frequency is controlled by a composite value of the outputs of each envelope detector and which controls the operation of the first PN signal generator. In a synchronization establishment method in spread spectrum communication, which has a delay lock tracking loop 16 and demodulates an input spread spectrum signal according to the output of the loop, a second clock frequency that generates a clock frequency different from the clock frequency of the input spread spectrum signal is used. a clock signal generator 21, a second PN signal generator 20 operated by the output of the clock signal generator, and a spread demodulator that despread demodulates the input spread spectrum signal in accordance with the output of the PN signal generator. 17, an envelope detector 18 connected to the output of the spreading demodulator, and a switch 19 that is turned on at a time controlled by the output of the detector. This is a spread spectrum communication synchronization establishment method in which synchronization is established by transferring the contents of each bit of the first PN signal generator to the corresponding bits of the first PN signal generator. Examples will be described below with reference to the drawings.

FIG. 4 shows an embodiment of the invention.

6, 7, 10, 16, 13, and 14 are the same spreading demodulator, signal demodulator, reception PN code generator, delay lock tracking loop, spread signal input terminal, and demodulated signal output terminal as shown in the conventional configuration example. 17 is another spreading demodulator similar to 6, 18 is an envelope detector similar to 9, 19 is a switching circuit, and 20 is 1
The same PN code (signal) generator as 0, 21 an independent clock signal generator that differs by α from the frequency of the transmitting clock signal d, 22 a frame synchronization detector composed of 17 and 18, and 23 as necessary. The measurement terminal is used accordingly.

The PN signal generators 10 and 20 are connected to each stage of the shift register through a switching circuit 19, and when the switch 19 is on, the signal state of each stage of the shift register in 20 is input to 10 as is. It will be in the same state as 20.

The spread input signal b enters the spread demodulator 17 and 20
The signal is spread demodulated by the PN signal from 18, and after being detected by 18, the output controls a switching circuit 19.

Now, the spread input signal entering the spread demodulator 17 from the input terminal 13 is controlled by a clock signal that differs from the transmitting clock signal frequency by α.
The output of the PN signal generator 20 is spread demodulated. The spread demodulated signal is detected by an envelope detector 18. Figure 5 shows time t on the horizontal axis.
The detection output characteristics are shown below. If one frame of the transmitted PN code sequence is N bits, the detection output from 18 is obtained at N/α time intervals. That is, the PN code sequence generated from the PN signal generator 20 every N/α time is synchronized (frame synchronized) with the spread PN code (transmission PN code) of the input signal b. Therefore, at this point, turn on the switch of the switching circuit 19 using the envelope detection output, and transfer the code state in the shift register of the PN code generator 20 as it is to the shift register of the receiving PN signal generator 10. For example, 10 PN code sequences are synchronized to input signal b.

The switching operation of the switching circuit 19 is as follows:
It is controlled by the output of the envelope detector 18.

On the other hand, the characteristic of the delay lock tracking loop is that, as explained in FIG. 3, the tracking control signal is generated near the synchronization point with the input spread signal.

Therefore, as explained above, the PN for frame detection
The receiving PN signal generator 10 to which the synchronization code state is transferred from the signal generator 20 is simultaneously subjected to the control effect of the delay lock loop, and synchronization is maintained. P.N.
The operation of transferring the shift register code from the signal generator 20 to the signal generator 10 may be performed at each synchronization timing obtained from the envelope detector 18 (signal obtained every N/α time), or may be performed several times. It may be performed once at the synchronization timing.

The control system including this frame detector effectively functions as a method for establishing and maintaining synchronization at the start of operation of the reception system or when synchronization is lost due to sudden fluctuations in the input signal phase.

As explained above, in the spread signal receiving system according to the present invention, in addition to the conventional delay lock tracking loop,
Other independent clock generators, PN signal generators,
It is equipped with a frame detection system consisting of a frame detector, etc., and constantly monitors the frame synchronization relationship between the received signal and this PM signal generator. Then, the code state of the PN signal generator obtained repeatedly is used for reception at the time of frame synchronization with the reception signal.
Transfer to PN signal generator. This allows for receiving
The PN signal generator is synchronized with the received spread signal and further synchronized by the action of a delay lock loop.
As a result, even when the receiving system starts operating or when the phase of the received signal changes rapidly, synchronization is automatically established and maintained quickly and stably.

The present invention includes an independent frame detection system, always continuously generates frame synchronization timing for received signals, and thereby controls the reception synchronization system. Therefore, the reception system maintains quick and stable automatic synchronization establishment and maintenance, and provides an effective spread spectrum synchronization establishment method especially in mobile communication systems where the reception input phase fluctuates rapidly.

[Brief explanation of the drawing]

Figure 1A is a configuration diagram of the transmission system of direct spread communication, Figure 1B is an explanatory diagram of the operation of Figure 1A, Figure 2 is a configuration diagram of the conventional reception system, and Figure 3 is the delay in Figure 2. FIG. 4 is a diagram showing a control signal of a lock tracking loop system, FIG. 4 is a block diagram of a receiving system employing the synchronization establishment method according to the present invention, and FIG. 5 is an example of operating waveforms in FIG. 4. 1; Spread spectrum modulator, 2; Transmission PN
Signal generator, 3; Signal modulator, 4; Signal input terminal, 5; Spread signal output terminal, 6, 8, 8', 1
7; Spreading demodulator, 7; Signal demodulator, 9, 9', 1
8; Envelope detector, 10; PN signal generator for reception, 20; PN signal generator for synchronization, 11; Clock signal generator, 12; Delay line, 13; Spread signal input terminal, 14; Demodulated signal output terminal , 15; external sweep signal input terminal, 16; delay lock tracking loop, 19; switching circuit, 21; clock signal generator, 22; frame synchronization detector, 23; measurement terminal.

Claims (1)

[Claims] 1 At least one pair of spread signal demodulators 8, 8' that operate according to the output of the first PN signal generator 10 and receive a spread spectrum signal as input, and an envelope detector connected to the output of the demodulators. 9 and 9', and a first clock signal generator 11 whose frequency is controlled by the composite value of the outputs of the respective envelope detectors and which controls the operation of the first PN signal generator. In a synchronization establishment method in spread spectrum communication, which has a delay lock tracking loop 16 and demodulates an input spread spectrum signal according to the output of the loop, a second clock frequency that generates a clock frequency different from the clock frequency of the input spread spectrum signal is used. a clock signal generator 21, a second PN signal generator 20 operated by the output of the clock signal generator, and a spread demodulator that despread demodulates the input spread spectrum signal in accordance with the output of the PN signal generator. 17, an envelope detector 18 connected to the output of the spreading demodulator, and a switch 19 that is turned on at a time controlled by the output of the detector,
A spread spectrum communication synchronization establishment method characterized in that the switch transfers the contents of each bit of the second PN signal generator to the corresponding bits of the first PN signal generator to establish synchronization.