JPH10260250A - Distance measurement signal generator using pn code - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance measurement signal generator using PN code executing in a short synchronous time the measurement of long distance such as to a planet surveyor. SOLUTION: Mutually synchronizing first PN code with period length N, second PN code with period length NXI, third PN code with period length NXIXJ and fourth PN code with period length NXIXJXK are input in selection circuits 11 and 12 in pair, the first and the third PN codes are selected by the selection circuit 11, the second and the fourth PN codes are selected by the selection circuit 12, which are supplied as I channel of a QPSK modulator 13 from the selection circuit 11 and as Q channel from the selection circuit 12, and the distance measurement signal is generated out of this modulator 13. Then, synchronism is taken in turn from the PN codes with longer period length so that the synchronism of the PN code with long period length measuring very long distance is surely taken in a short time and the measurement of long distance such as to a planet surveyor, for example, is conducted quickly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring signal generator using a PN code used for measuring a very long distance such as a distance to a planetary explorer.

[0002]

2. Description of the Related Art To measure a very long distance such as a distance to a planetary spacecraft, a ranging method using a PN code is used. In the ranging signal system using such a PN code, the code cycle length is 1 (N is a positive integer).
BPSK (Binary Phase Keying) modulation of two codes, or a PN code having a code cycle length of N and a PN code having a code cycle length of N × I (I is a positive integer).
One PN code is QPSK (Quadralure Phase Keying)
A method for performing modulation is known.

Here, assuming that the speed of light is c (m / s) and the clock frequency of the PN code is f (Hz), when the former PN code is BPSK modulated, (c / f) × N
/ 2 [m], and when the latter two PN codes are QPSK-modulated, only the distance up to (c / f) × N × I / 2 [m] can be measured. In order to further extend the limit length of the measurement distance, it is necessary to increase the code cycle length or I. However, the code cycle time required in the receiver is required when one PN code is subjected to BPSK modulation. Is N ×
T, when two PN codes are QPSK modulated, (N
+ I) × T (T is a proportional constant), and inevitably the cycle length N
Or, the synchronization time became longer in proportion to I.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been made in view of the above circumstances. To provide a ranging signal generating apparatus using a PN code which can reliably and quickly reduce the synchronization time in, for example, the distance to a planetary spacecraft. .

[0005]

According to the present invention, there is provided a ranging signal generator using a PN code according to the present invention, wherein the first PN code having a code period length of a positive integer and the first PN code having a code period length of N are provided. A second PN code that is a positive integer multiple, this second P
A first for generating a PN code of a third to n-th cycle length which is successively increased to a positive integer multiple of the cycle length of the N code.
Or one of the first to n-th PN codes generated by each of the first to n-th PN code generating means.
The PN code having the selected cycle length is output as a distance measurement signal.

For example, the PN code generating means comprises first to fourth PN code generating means, each having a cycle length N, N × I, N
A PN code of .times.I.times.J and N.times.I.times.J.times.K (N, I, J and K are positive integers) is generated, and the first and third PN codes are generated by a first selection circuit. One is selected, one of the second and fourth PN codes is selected by a second selection circuit, and the output PN codes from each of the first and second selection circuits are modulated by QPSK modulation means and measured. The distance signal is used.

In a ranging signal generator using a PN code configured as described above, a PN code having a short cycle length is selected from a plurality of PN codes, and synchronization with the selected code signal is performed. The PN code is sequentially switched to the PN code having the longer cycle length in the taken state, and the receiver can be quickly synchronized based on the PN code having the shortest cycle length, and particularly the long distance. In this case, the synchronization time at the time of measurement is effectively reduced.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a configuration of a device for generating a ranging signal by a PN code.
First PN of cycle length N from a code generator (not shown)
Code, second PN code of cycle length N × I, cycle length N ×
I × K third PN code and period length N × I × J ×
The fourth PN code of K is input.

Here, the second PN code having the cycle length N × I is synchronized with the first PN code having the cycle length N, and the cycle length N × I
The third PN code of × J is the fourth PN code of N × I × J × K.
It is assumed that it is synchronized with the code.

This distance measuring signal generating apparatus comprises first and second
The first selection circuit 11 receives first and third PN codes having a cycle length of N and N × I × J, and one of them is selectively output. The second selection circuit 12 receives second and fourth PN codes of N × I and N × I × J × K. Then, one of the PN codes is selectively output.

The first and second selection circuits 11 and
The PN codes selected in step 12 are input to a QPSK modulator 13 as an I channel and a Q channel, respectively, and the modulator 13 generates a QPSK-modulated ranging signal.

The procedure for synchronizing the ranging signals generated by the ranging signal generator having such a configuration will be described with reference to FIG.
First, first and second selection circuits 11 and 12 select a first PN code N and a second code N × I from the input PN codes, respectively, and as shown in step 101, the QPSK modulator 13 The first ranging signal 1 is output after QPSK modulation.

When the first QPSK modulated distance measuring signal 1 is generated in this way, in step 102, the signal obtained by reflecting the distance measuring signal 1 on the object to be measured is received by the receiver. In this receiver, a first PN code having a cycle length N is synchronized based on the first ranging signal 1. In step 103, it is determined whether or not the synchronization has been achieved. If it is determined that the synchronization has been achieved, the process proceeds to step 104.

Here, when the synchronization of the PN code of the cycle length N is completed, the first PN code of the cycle length N and the second PN of the cycle length N × I are maintained while maintaining the state of the synchronization. By using the synchronization relationship with the code to synchronize, the synchronization time is reduced.

Since the synchronization time of a PN code is generally proportional to the cycle length N, if the time required to synchronize a PN code with a cycle length N is N × T (T is a proportional constant), the synchronization relationship The time required for synchronizing the second PN code N × I that does not use is N × I × T. Therefore, when the synchronization relationship is used as described above, the time required for synchronizing the second PN code N × I is reduced to 1 / N, and I × T
It is said.

When the synchronization of the first PN code having the cycle length N is completed, the third PN code N × I × J is selected in the first selection circuit 11 in step 104, and the second selection is performed. The second PN having the cycle length N × I is continued as it is in the circuit 12.
You have selected a code. And the first and second
Output PN codes from the selection circuits 11 and 12 are QPS
The signal is supplied to the K modulator 13 and modulated to obtain a second distance measurement signal 2.

The second ranging signal is transmitted, and the receiver receives the ranging signal 2 returned from the object to be measured. However, the synchronization on the first PN code side having the cycle length N is lost. , The synchronization on the side of the second PN code having the cycle length N × I is maintained.

In such a state, in step 105, the third PN code having a cycle length of N × I × J is synchronized.
At this time, while maintaining the synchronization state of the second PN code of the cycle length N × I, the synchronization relationship between the PN code of the cycle length N × I and the third PN code of the cycle length P × I × J is used. Then, N × I × J when the synchronization time does not use the synchronization relationship
It is reduced from × T to J × T.

In this manner, the third P having the cycle length N × I × J
When the synchronization of the N codes is completed, the first selection circuit 11 continuously selects the third PN code having the cycle length N × I × J, and the second selection circuit 12 has the cycle length N × I × J × K 4th
PN code is supplied to the QPSK modulator 13 and QPSK modulated as in step 106 to generate and transmit a third ranging signal.

When a reflected signal from the object to be measured of the third ranging signal transmitted by the receiver is received, a period length N × I
Is out of synchronization on the side of the second PN code, but the period length N ×
Synchronization between the I × J third PN code and the cycle length N × I × K is maintained.

In this state, the fourth PN code having a cycle length of N × I × J × K is synchronized as in step 107. At this time, while maintaining the synchronization state of the third PN code having the cycle length of N × I × K, the synchronization relationship between the third PN code and the fourth PN code having the cycle length of N × I × J × K is maintained. Is used, when the synchronization time does not use the synchronization relationship, N
It is reduced from × I × J × K × T to K × T. Then, in step 108, the synchronization is confirmed.

In the next step 109, the cycle length N × I × J
And the fourth P of the cycle length N × I × J × K
The N code is QPSK-modulated and transmitted, and in step 110, the receiver synchronizes the fourth PN code with a cycle length of N × I × J × K. If it is confirmed in step 111 that synchronization has been achieved, distance measurement is started. The synchronization time obtained in the above process is (N + I + J + K) × T as a whole.

On the other hand, the distance measurable by the distance measurement signal obtained by the procedure of this embodiment is (c / f) × N × I × J × K / 2 [m]. To the single PN code B
If an attempt is made to achieve this by PSK modulation, synchronization of a PN code having a cycle length of N × I × J × K must be performed independently, so that synchronization of (N × I × J × K) × T is performed. Time is needed.

Here, if N, I, J, and K are set to integers equal to or more than "3", then (N + I + J + K) <(N + I + J + K), so that the procedure shown in this embodiment has a shorter synchronization time. Become.

In the embodiment shown in FIG.
Although an example using N codes has been shown, it is possible to synchronize PN codes with a longer cycle length in a short time by repeatedly performing the above procedure using five or more PN codes. It is.

[0026]

As described above, according to the ranging signal generating apparatus using the PN code according to the present invention, particularly when a very long distance is measured, such as a distance to a planetary explorer, the measurement is performed. Long period length PN required for
Code synchronization can be performed in a sufficiently short time, and the distance measurement operation can be performed quickly and smoothly.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an example according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating an operation procedure of the embodiment.

[Explanation of symbols]

11, 12: first and second selection circuits, 13: QPSK modulator.

Claims (4)

[Claims] 1. A first PN code generating means for generating an N first PN code having a code cycle length of a positive integer, and a second PN code generation means having a code cycle length of a positive integer multiple of N. A second to n-th PN code generating means for generating a PN code, and a PN code having a third to n-th cycle length which is successively increased to a positive integer with respect to the cycle length of the second PN code; Selecting means for selecting one of the first to n-th PN codes generated from each of the first to n-th PN code generating means, wherein the PN code having a cycle length selected by the selecting means is provided. A distance measurement signal generator using a PN code, which outputs a distance measurement signal as a distance measurement signal. 2. The first to n-th PN code generating means is composed of an even number of the first to n-th PN code generating means.
The N code signal is supplied to each of a plurality of selection circuits constituting the selection means as a pair, one of them is selected, and QPSK modulation is performed based on the last remaining pair of PN codes to be a distance measurement signal. A distance measuring signal generator using the PN code according to claim 1. 3. The PN code generating means includes first to fourth PN codes, each having a period length of N, N × I, N
PN codes of × I × J and N × I × J × K (N, I, J, and K are positive integers) are generated.
And the third PN code, one of which is selected by a first selection circuit, and the second and fourth PN codes, one of which is selected by a second selection circuit, and the first and second selection circuits, respectively. Output PN code is supplied to the QPSK modulating means as an I channel and a Q channel.
3. The distance measuring signal generator using a PN code according to claim 2, wherein the distance measuring signal is generated by the PSK modulation means. 4. A first transmitting means for QPSK-modulating and transmitting a PN code having a cycle length of N and a PN code having a cycle length of N × I, and a first means for synchronizing the PN code having a cycle length of N with a receiver. A second synchronizing means for synchronizing the N × I PN code with the receiver in a state where the synchronizing is performed by the first synchronizing means; and a synchronizing means for synchronizing with the second synchronizing means. The cycle length N ×
QP of I × J PN code and PN code of cycle length N × I
A second transmitting means for performing SK modulation and transmission, a third synchronizing means for synchronizing a PN code having a cycle length of N × I × J at a receiver, and a state in which the third synchronizing means is synchronized. And the cycle length N ×
Third transmission means for transmitting the I × J PN code and the PN code of the cycle length N × I × J × K by QPSK modulation, and synchronization of the PN code of the cycle length N × I × J × K at the receiver And a distance measuring unit based on the PN code of this cycle length N × I × J × K is started in a state synchronized with the fourth synchronizing means. A distance measuring signal generator using the PN code according to claim 3.