JP2000151466A - Pn code synchronization device, receiver and communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PN code synchronization device that can more quickly and surely acquire a synchronizing signal. SOLUTION: A transmission epoch denoting a head of a spread code at a transmission side of a modulation section 1 is synchronously with a timing of an inverse spread signal generated from an inverse signal generator 700 of a demodulation section 2 and the generator 700 outputs an inverse spread signal whose timing is coincident with the synchronized timing. A correlation value detector 400 outputs a shift control signal that shifts a phase of the inverse spread signal to detect a correlation between the received spread signal and the inverse spread signal whose phase is shifted by a spread phase shift circuit 800, and a synchronization discrimination device 500 discriminates the synchronization based on a level of the output correlation. Since a time of a radio wave returning to a ground station from a satellite is known in advance, the time is held and the initial phase of a PN code is captured before and after the known time to attain the capture in a short time in the unit of bits.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a spread spectrum communication system and a PN
It relates to a code synchronizer. More specifically, the present invention is applied to, for example, an SSA modulator / demodulator in a ground station equipment of a COMETS inter-satellite communication experiment system, and is a code of a spreading code included in a received signal and a despreading code generated in a receiver. The present invention relates to a PN code synchronizer that performs synchronization and a receiver using the same.

[0002]

2. Description of the Related Art In a spread spectrum communication system, in order to extract information from a received signal, a received spread code must be despread. In order to perform despreading, it is necessary to completely synchronize the spread code and change timing of the received signal with the local despread code and change timing of the demodulation unit. Conventionally, to perform such a synchronization process,
Both codes are synchronized using a code synchronization circuit as shown in FIG.

The code synchronization circuit of FIG. 3 is of the sliding type, and includes a correlation detector 10, a despread code phase shifter 20, a synchronization determiner 30, a despread code phase shift circuit 40, a code tracking loop, 50 and mixer 60
It is composed of

[0004] The spread signal, which is a received signal, is supplied to a correlation detector 1.
0, cross-correlate with the code from the despreading code phase generator 20, and output to the synchronization determiner 30. The synchronization determiner 30 determines whether or not the correlation value level is greater than a required threshold level. If the correlation value level is smaller, the phase of the despread code output from the despread code phase generator 20 is determined by the despread code phase shift circuit 40. Shift one phase. Until synchronization is obtained, a predetermined frequency clock is output from the code tracking loop 50. The above operation is repeated until the correlation value level exceeds a required threshold level. If the correlation value level exceeds the threshold level, the shift control of the despreading code phase shift circuit 40 is stopped at the current phase, and the code tracking loop 50 is operated.
Correct the phase shift.

Japanese Patent Application Laid-Open No. 6-276177 discloses a method in which the time at which the first bit of the next cycle of a received code sequence is input is predicted, and the received code sequence and the reference code sequence are forcibly synchronized. A code synchronization control method capable of performing synchronization in a short time is disclosed.

[0006]

However, in order to perform synchronization acquisition using the sliding synchronizer having the configuration shown in FIG. 3, it is necessary to slide the phase corresponding to the maximum code length and then make a synchronization determination. . Therefore, it takes time to acquire the synchronization. Further, in the method disclosed in Japanese Patent Application Laid-Open No. 6-276177, since the prediction is based on prediction only, there is a limit in shortening the synchronization time due to various factors such as disturbance.

An object of the present invention is to provide a PN code synchronizing apparatus which can more quickly and surely acquire synchronization.

[0008]

In order to achieve the above object, a PN code synchronizing apparatus according to the present invention comprises: A despread signal generator that outputs a despread signal that synchronizes with this timing, a spreading phase shift circuit that outputs a shift control signal that shifts the phase of the despread signal, A correlation value detector for detecting a correlation value with a despread signal whose phase is shifted by a phase shift circuit, and a synchronization determiner for determining synchronization from a level of an output correlation value of the correlation value detector. And

The above-mentioned correlation value detector holds in advance an internal delay amount for delaying a received spread signal inside the demodulation unit, detects a correlation value using the internal delay amount, and sends the detected correlation value to a spread phase shift circuit. It is preferable to output the shift control signal.

Further, the PN code synchronizer has a code tracking loop means for controlling ON / OFF operation of a synchronous operation of a synchronous circuit composed of a correlation value detector, a synchronous determinator and a spread phase shift circuit. Good to do.

The above-mentioned synchronizing operation forms a window based on the despread signal output from the despread signal generator and the amount of internal delay, and is executed by searching within the window. It is preferable that the number of bits of the spreading code constituted by the maximum amount and the internal delay amount of the demodulation unit be the maximum amount.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a PN code synchronizing apparatus, a receiving apparatus and a communication method according to the present invention.

FIG. 1 shows a configuration of a spread spectrum communication system according to a first embodiment of the present invention. This spread spectrum communication system includes a plurality of transmission / reception devices that perform mutual spread spectrum communication using an artificial satellite as a relay device.

Each transmission / reception device has a modulation unit (SSA (Spectrum Signature Analysis) modulation unit) 1 for transmitting a signal.
And a demodulation unit (SSA demodulation unit) 2 for demodulating a received signal
And

The modulator 1 multiplies a PCM signal sent from the baseband by a pseudo noise signal (PN code) and outputs a PSK-modulated spread spectrum IF (Intermediate Frequency) signal. And a spread code generator 100 and a reference clock generator 20
0 and a mixer 300.

The reference clock generator 200 generates a reference clock, and the spreading code generator 100 outputs a spreading code at the frequency of the reference clock according to the reference clock. Mixer 300 outputs a spread modulation signal by multiplying a PCM signal, which is transmission data transmitted from the baseband, by a spreading code. Also, the spreading code generator 100
Outputs a signal (epoch; transmission epoch signal) indicating the first bit of the spreading code.

The demodulation unit 2 has a spectrum-spread IF
It despreads the signal and outputs the PCM signal demodulated after carrier synchronization, bit synchronization, and bit synchronization to the baseband. The correlation value detector 400 and the synchronization determiner 500
, A code tracking loop 600, a despread signal generator 700, a spread phase shift circuit 800, a mixer 9
00.

The despread signal generator 700 generates a code equivalent to that of the spread code generator 100 on the transmitting side. Note that the despread signal generator 700 synchronizes the output timing of the despread code with the epoch signal and outputs the same at the same timing.

When the spectrum is spread by the demodulation unit 2,
PN code initial phase detection, that is, the starting point of each PN code string must be detected. In order to detect the PN code initial phase, it is necessary to generate the same PN code as the transmission PN code inside the demodulation unit 2, compare this with the reception PN code, and find a phase where both coincide.

The transmission code matches the local PN code of the demodulation unit 2 only for one phase of the PN code length.
Therefore, the initial phase detection time becomes longer or shorter depending on the length of the PN code length.

In this embodiment, the demodulation unit 2 uses a signal (epoch) indicating the first bit of the PN code on the transmitting side.
The PN code generator of the demodulation unit 2 is synchronized with the local PN code generator of
The code initial phase detection section shifts only a few phases before and after that to search for synchronization, and performs initial phase detection. In this scheme,
Since only several phases before and after need be searched, the initial phase detection time can be reduced. This relationship will be described in detail below.

FIG. 2 shows a timing chart of the code synchronization section using the epoch signal. FIG.
Each timing chart shown in (e) shows (a) output timing of spread code F, (b) spread code epoch,
(C) shows the output timing of the despread code, (d) shows the output timing of the despread code F 'after synchronization with the epoch signal, and (e) shows the timing of the actual received spread signal R.

1 and 2, the spreading code generator 100 of the modulator 1 outputs the spreading code F at the clock frequency from the reference clock generator 200 as shown in FIG. The mixer 300 multiplies the spread code F by the transmission data and outputs a modulated spread signal.

Also, the spreading code generator 100 has a
The spread code epoch shown in (b), that is, an epoch signal indicating the first bit of the spread code is output. This epoch signal is output in synchronization with the rise of the spread code length (or PN code length) as shown in FIGS. 2 (a) and 2 (b).

In the demodulation unit 2, the despread signal generator 7
2 outputs a code equivalent to the spread code (F) generated by the spread code generation unit 100 on the transmitting side at the same timing as the epoch signal, as shown in FIG. 2D.

The initial phase shift amount of the diffusion phase shift circuit 800 is set to "0" in advance. Originally, the spreading code F and the despreading code F 'synchronized with the epoch signal should be output at the same timing. However, actually, there is a delay on the line or an internal delay of the demodulation unit 2 until the input of the correlation value detector 400 of the demodulation unit 2 of the modulated spread signal output from the modulation unit 1, resulting in an n-bit delay. Thus, the spread signal R is input.

At this time, the phases of the spreading code F and the despreading code F 'are different, and the output correlation value level from the correlation value detector 400 is smaller than the determination threshold in the synchronization determiner 500. Therefore, the phase shift control signal is output from the synchronization determiner 500 to the spread phase shift circuit 800 without synchronization. Spreading phase shift circuit 800 receives this phase shift control signal, and outputs despreading code F ′ shifted by one from the previous output phase.

This operation is repeated, and it is assumed that the spread code and the despread code match when the operation is repeated N times. At this time,
Correlation value detector 400 detects the correlation peak value, and synchronization determiner 500 determines that a correlation value level equal to or higher than the threshold level has been input, and stops outputting the phase shift control signal to spreading phase shift circuit 800. Therefore, the spreading phase shift circuit 800 holds the phase of the despreading code F 'in that state.

Further, the synchronization determiner 500 outputs a loop control signal of loop control ON to the code tracking loop 600. Upon receiving this loop control signal, the code tracking loop 600 starts a loop operation and
The phase shift within the bit shift is corrected. As a result, code synchronization is completely performed, and accurate received signal information can be obtained from the mixer 900.

When the synchronization is lost, the synchronization determiner 500 outputs a reset signal to the spread phase shift circuit 800 to clear the previous phase shift amount and output a loop reset signal to the code tracking loop 600. And return to the initial state.

Here, it is necessary to determine the range of the phase shift inside the diffusion phase shift circuit 800.

The amount of delay from when the received spread signal is input to the correlation value detector 400 from the input terminal of the demodulation unit 2 is fixed. Therefore, this delay amount is measured in advance, and if there is an M-bit delay, a search is performed from the M phase shift. FIG. 2E shows this relationship together with the actual received spread signal R. As a specific range for the search, the maximum distance from the output of the modulation unit 1 to the demodulation unit by returning the artificial satellite is calculated, an expected delay amount is calculated from the value, and a range wider than the calculated value is set. Just do it.

As an example, it is assumed that the maximum amount of delay of the satellite return is 10 bits. If the internal delay amount M of the demodulation unit is M = 2 bits, the phase offset amount is “2” bits, and the search range may be in the range of “2” bits to “10 + 2” bits.

In the conventional example, the search for the code length is performed, but in the present embodiment, "several tens" bits or "several hundreds" bits is sufficient. For example, if the code length is "218-1" bits and the search range is "100" bits, the initial phase synchronization time is (218-1) / 1 compared to the conventional method.
00 = 2621 times faster.

The present invention is not limited to the above embodiment, but can be variously modified and applied.

[0036]

As described above, according to the present invention, the synchronization between the despreading code and the received spread signal can be acquired in a short time in bit units.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of a code synchronization control unit according to an embodiment of a PN code synchronization device of the present invention.

FIG. 2 is a timing chart of a code synchronization unit using an epoch signal.

FIG. 3 is a block diagram illustrating a configuration example of a code synchronization circuit based on a sliding method according to Conventional Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Correlation detector 20 Despread code phase 30 Synchronization determiner 40 Despread code phase shift circuit 50,600 Code tracking loop 100 Spread code generator 200 Reference clock generator 300,900 Mixer 400 Correlation value detector 500 Synchronization determiner 700 Despread signal generator 800 Spreading phase shift circuit

Claims (7)

[Claims] 1. A spread code is generated on a transmission side, a modulated spread signal is generated and transmitted using the generated spread code, and an epoch signal indicating the generation timing of the spread code is transmitted from the transmission side to the reception side. Receiving the modulated spread signal, receiving the transmitted epoch signal on the receiving side, outputting a despread signal substantially synchronized with the received epoch signal, shifting the phase of the despread signal, and receiving the spread signal A communication method comprising: generating a despread signal synchronized with the above, and demodulating a received spread signal by using the shifted despread signal. An epoch signal, which is supplied from a modulation section on the transmission side and indicates the beginning of a spread code generated for modulation on the transmission side, and a timing of a despread signal generated for demodulation in the demodulation section are synchronized. A despread signal generator that outputs the despread signal whose timings substantially coincide with each other; a spread phase shift circuit that outputs a shift control signal that shifts the phase of the despread signal; A correlation value detector for detecting a correlation value with a despread signal whose phase has been shifted by the spreading phase shift circuit; and determining whether or not both signals are synchronized from a level of an output correlation value of the correlation value detector. A PN code synchronizer, comprising: 3. The correlation value detector holds an internal delay amount for delaying the received spread signal in a demodulation section in advance, detects the correlation value using the internal delay amount, and detects the spread phase shift. The PN code synchronizer according to claim 2, wherein the PN code synchronizer outputs the shift control signal to a circuit. 4. The code tracking loop means for controlling the ON / OFF operation of a synchronous operation of a synchronous circuit comprising the correlation value detector, the synchronous decision unit and the spread phase shift circuit. The PN code synchronizer according to claim 2 or 3, wherein: 5. The synchronizing operation according to claim 1, wherein a window is formed based on the despread signal output from the despread signal generator and the internal delay amount, and the window is searched and executed. PN described in Item 4
Code synchronizer. 6. The window according to claim 5, wherein the window has a maximum number of bits of the spreading code constituted by a maximum amount of delay of the satellite loopback and an internal delay amount of the demodulation unit. PN code synchronizer. 7. A means for receiving a spread signal supplied from a modulator on the transmitting side via a satellite, and receiving an epoch signal supplied from the modulator on the transmitting side and indicating a generation timing of a spread code on the transmitting side. Means, a despread signal output means for outputting a despread signal substantially synchronized with the received epoch signal, and a shift for shifting the phase of the despread signal to generate a despread signal synchronized with the received spread signal Means for demodulating a received spread signal using the despread signal generated by the shift means.