JPS6411178B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiving device in a spread spectrum communication system, and when receiving and demodulating a signal modulated by a random code having particularly sharp autocorrelation characteristics, such as an M-sequence code, the present invention relates to a receiving device in a spread spectrum communication system. The present invention relates to a receiving apparatus that generates a code in a receiver, performs a convolution operation on both codes to quickly measure and correct the phase difference between the codes, and demodulates the received signal while keeping the phase difference in the same phase.

In any type of communication, if synchronization with the communication partner is not ensured, communication will be impossible. Synchronization includes "initial synchronization" for initial line connection, and "synchronization maintenance" for ensuring line synchronization in good condition after initial connection. Generally, the initial synchronization is done quickly and
A communication device needs to maintain synchronization as stably as possible.

Conventionally, one of the major problems with receiving devices in this type of spread spectrum communication system is that it takes a long time to establish initial synchronization. In this case, in order to achieve synchronization, the random code S of the received signal is
(t) and a random code R generated at the receiver
The phase (time) difference τ with (t) is investigated. To obtain this time difference τ, a correlation calculation is performed between both codes.
Letting the correlation output between the two be φ(τ), φ(τ)=∫S(t)R(t-τ)dt...(1) The baseband correlation output at this time is shown in Figure 1. It will be as follows. From the properties of the codes, it can be seen that the phase difference between the two codes disappears (synchronization is achieved) at point A in FIG. To do this, as shown in Figure 1, while changing the phase difference τ, it is necessary to repeat the sign 1.
It is necessary to integrate the period length. In other words, the initial synchronization operation is performed by changing the phase difference τ while φ
(t), and when the phase difference τ=0, φ(t)
Since this is equivalent to operating so that the maximum value is obtained, the time length determined by (length of one period of the code) x (number of integrations until finding point A) becomes the initial synchronization time.

In order to shorten the initial synchronization time, it is necessary to shorten the integration time and reduce the number of integrations. Further, in order to maintain stable synchronization after initial synchronization is established, conventional receiving apparatuses include a phase control circuit, such as a delay lock loop, to maintain the phase difference between both random codes in synchronization. These control circuits have a control capability of up to about 2 bits at most, and are susceptible to loss of synchronization due to some external noise, such as fading, interference signals, signal relay, etc.

The present invention has been made to solve the above-mentioned drawbacks of the prior art, namely, to provide a receiving device that can speed up the initial synchronization time and simultaneously provide stable synchronization maintenance capability.

Embodiments of the present invention will be described in detail below with reference to the drawings.

In the present invention, a convolver is used as a means for taking a correlation for synchronization acquisition. An example of a convolver is the paper (special issue) “SAW
Convoler: Surface Acoustic Wave
Convolver” P.579-P.807, May1976, Proc.
Familiar with IEEE.

The convolver has the structure shown in Fig. 2. When a signal S(t) is input from the A terminal and a signal R(t) is input from the B terminal, these two signals propagating in opposite directions at a propagation speed V are transmitted through the medium. is taken out at the central electrode output terminal C through the nonlinearity of . Its output signal H
(t) becomes H(t)=∫S(τ)R(2t−τ)dτ...(2), and is the convolution output of the signals S(t) and R(t). It's summery. In addition,
Note that the time element is twice t.

Here, it will be explained that when the above convolver is used, the initial synchronization time is shortened. Consider that a received signal S(t) is input to terminal A in FIG. 3, and a random code R(t) generated by a receiver is input to terminal B. The random code input from terminal B is time-reversed, so the convolver output is
From equation (2), H(t)=∫S(τ)R(τ−2t)dτ ...(3), and the base band component ∫S(τ)R(τ−2t)
Since dτ has the same form as equation (1), it becomes a correlation output. When a random code is input with the phase relationship shown in Fig. 3b, the length L convolver in Fig. 3a becomes
Since it propagates at speed V, it passes through time 1/2 L/V (Fig. 3 c), after L/V time (Fig. 3 d), and then 3/2 L/V (Fig. 3 e). After 2·L/V time (Fig. 3g), both patterns coincide. In other words,
As shown in Figure 3e, after L/V time, the random code patterns match perfectly and a correlation output with a sharp peak is obtained, and thereafter, a sharp peak appears every 1/2 L/V time. Take value. Furthermore, FIG. 4 shows the correlation output when a random code is input (FIG. 4b) with a phase relationship different from that in FIG.
After 11/12 L/V time, the random code patterns completely match (Fig. 4c), and then Fig. 4d
After the time 17/12・L/V of Figure 4 e, the time 23/12・L
The correlation output has a peak after /V has elapsed, but as shown in Figure 4e, the level of the correlation peak value after 11/12 L/V has elapsed is equal to the correlation peak value that occurs every subsequent L/2V. The level is 11/12.

From the above, by observing the correlation output, it is possible to measure the phase relationship between both codes, especially the relative phase relationship with the code R(t). This means that the correlation peak output of the convolver is detected and the time difference between it and the frame pulse generated at the receiver is measured. This shows that the relationship can be modified.

From the above explanation, it becomes clear that the initial synchronization by the convolver is completed within 2×L/V time, that is, within two random code frames. In this way, the convolver reduces the initial synchronization time because the convolver has a signal memory function and a matched filter function that determines the correlation output depending on the sign.The memory function reduces the number of integrations. This means that the mated filter function reduces the integration time.

Next, the advantages of maintaining synchronization when using a convolver will be explained. The synchronization maintenance operation must be performed simultaneously with the demodulation of the information. For example, in FIG. 3, 1 of the received random codes "1" to "6"
Considering that one data is represented by a frame, both random codes S(t) and R(t) completely match within the convolver of length L, including one data. That is, L/V time, 2×L/V,
3×L/V...The correlation output at a time point has information. On the other hand, in Figure 4, 11/1
2・L/V, 23/12・L/V, 35/12・L/V...The correlation output at the time point will have information, but both codes in the convolver contain one data. They do not match completely, and a deviation of about 1/2 bit occurs, and a correlation loss occurs according to the deviation. Therefore, Figure 3d
Maintaining the phase relationship is the synchronization maintenance operation of the convolver. However, due to some external noise, the third
Even if it becomes impossible to maintain the phase relationship in FIG. d and a phase shift occurs, it becomes possible to obtain information with a loss corresponding to the phase shift, making it easier to maintain synchronization.

Although the advantages of the present invention are understood from the above description, its specific configuration will be explained with reference to FIG. 5.
FIG. 5 shows the configuration blocks of the transmitting side and receiving side in the spread spectrum communication system.

First, in the transmitter 100, data input from the terminal 101 is sent to the flip-flop 103.
The latch is then engaged by a frame clock generated by a random code generator 104 driven by a clock generator 102. An exclusive OR circuit 105 scrambles the data from the flip-flop using a random code from a random code generator. A balanced modulator 106 generates a phase modulated signal from this scrambled data and a carrier wave generated by an oscillator 107. After being amplified by an amplifier 108, this signal is transmitted from a transmitting antenna 109.

In the receiver 200, the phase modulated signal received by the receiving antenna 201 is input to the SAW convolver 204 via the bandpass filter 202 and the amplifier 203. On the other hand, a random code obtained by time-reversing the random code of the transmitter random code generator 104 is generated from the memory 207 driven by the address generator 209. Local oscillator 205
generates a local oscillator signal of the same frequency as the carrier wave of the transmitter oscillator 107, and combines this local oscillator signal with the memory 2.
From the random code from 07 to the balanced modulator 20
6, a local phase modulation signal is generated and input to the SAW convolver 204. The SAW convolver 204 performs the above-mentioned convolution operation on both modulated signals, and the output is sent to the detector 210.
is input to the information demodulator 214. Detector 210
The envelope output is input to the threshold detector 211, and a preset threshold value is compared with the input envelope level. The threshold detector 211 outputs a stop signal for the counter 213 only if the envelope level is greater than the threshold.

The counter 213 is activated by a count start pulse generated through an input delay correction circuit 208 that corrects the frame pulse generated from the address generator 209 of the memory 207 to a time corresponding to the operation time of the SAW convolver 204. The counting is stopped by a counting stop pulse of the threshold value detector 211. The output value of the counter 213 is compared with the output value of the initial value setter 220 by a subtracter 215 . The subtracter output is input to a digital-to-analog converter 216 to create a control signal according to its polarity and absolute value, and the loop
Voltage controlled oscillator 217 via filter 218
control. Note that the counter 213 is counted by the clock output of the independent oscillator 212.

Here, the counter 213 measures the time from the input start point of the random code of one frame until the correlation peak detection is performed, and when complete synchronization is achieved, the time shown in FIG. The phase relationship of is realized. If the output value of the counter 213 at this time is N ₀ , if a phase advance occurs, then
The output value of the counter 213 will be less than N ₀ , and if a phase lag occurs, the output value of the counter 213 will be more than N ₀ . Therefore, N ₀ is set in the initial value setter 220, and the voltage controlled oscillator 217 is controlled so that the counter output value approaches N ₀ while constantly comparing it with the output value of the counter 213.

The correlation output of the SAW convolver 204 is shown in FIG.
And, as shown in Figure 4, 1/1 of the frame period
Since the digital-to-analog converter 215 takes a sharp peak value at an interval of 2, the digital-to-analog converter 215 outputs a control voltage within a range where |N ₀ −Nx| is within N ₀ /2, where the output value of the counter 213 is Nx. . Also, subtractor 2
When the absolute value |ΔN| of the output value ΔN of No. 15 exceeds a certain threshold value N _T that is larger than N ₀ /2, it is determined that synchronization has been lost, and the phase control circuit 221 changes the polarity of the subtracter output ΔN and its absolute value. The direct address generator 209 is configured by |ΔN|.

At the time of initial synchronization, the phase control circuit 221 mainly operates as coarse phase control, and when maintaining synchronization, the phase control circuit 221 operates as fine phase control. The phase control system is operated.

On the other hand, the correlation output sent to the demodulator 214 is subjected to PSK synchronous detection using a Costas loop, and demodulated data is obtained at a terminal 219.

The above description merely refers to one embodiment for convenience, and it is clear that the present invention has various other applicable scopes. For example, although FIG. 5, which shows an embodiment of the present invention, shows an example of a receiver using the PSK modulation method, it is of course applicable to the FSK modulation method as well.

According to the present invention, as detailed above, it is not only possible to speed up the initial synchronization time, but also to easily obtain a receiving device having a stable synchronization maintenance ability.

[Brief explanation of drawings]

Figure 1 is a baseband correlation output waveform diagram between two codes for synchronization acquisition, and Figure 2 is a SAW
Figures 3 and 4 showing the configuration of the convolver are
FIG. 5 is a block diagram showing an embodiment of the present invention. 100...Transmitter, 101...Data input terminal, 102...Clock generator, 103...Flip-flop, 104...Random code generator, 105...Exclusive OR circuit, 106...Balanced modulator , 107...Oscillator, 108...Amplifier, 109...Transmission antenna, 200...Receiver, 201...Reception antenna, 202...Band filter, 203...Amplifier, 204...SAW convolver, 205... ...local oscillator, 206...balanced modulator, 207...memory (random code generator), 208...input delay correction circuit, 209...
...Address generator, 210...Detector, 211...
...Threshold detector, 212...Clock generator,
213...Counter, 214...Demodulator, 215
...Subtractor, 216...Digital-to-analog converter, 217...Voltage controlled oscillator, 218...Loop filter, 219...Data output terminal, 2
20...Initial value setting value, 221...Phase control circuit.

Claims (1)

[Claims] 1. A random code generator that generates a random code that is time-reversed from a predetermined random code that modulates a received signal, and a reference signal generator that is driven by this random code and generates a predetermined reference signal. a convolver that performs a convolution operation of the reference signal and the received signal; a circuit that detects the peak value of the output of the convolver; 1. A receiving device comprising: a circuit for measuring a time difference up to the time when a hold is exceeded; and a phase control circuit for controlling an output phase of the random code generator based on this time difference. 2. A synchronization determination circuit in which the phase control circuit determines synchronization by monitoring a deviation between the time difference and a predetermined time, and a synchronization determination circuit that determines synchronization when the deviation is equal to or greater than a predetermined value, a circuit that controls the phase of the random code output by controlling a driving clock of the generator; and a circuit that drives the random code generator according to the deviation when the deviation is not zero and is equal to or less than the predetermined value. 2. The receiving device according to claim 1, further comprising a circuit that controls the oscillation frequency of a voltage controlled oscillator that controls the phase of a clock.