JPS62269433A - Correlation receiver - Google Patents

Abstract

PURPOSE:To obtain timing information accurately even when timing information is extracted from a filter output by outputting a data near the initial timing of a head frame and ANDing the said output and the initial timing in a pseudo noise code at the receiving side. CONSTITUTION:A pseudo random noise code generator 2 consists of two sets of shift register groups and exclusive OR circuits multiplying the outputs, and one frame is constituted by changing the combination of each bit started from the initial timing where all bits go to level '1'. A window controller 8 outputting a data near the initial timing of the head frame of the pseudo random noise code being an object among demodulated outputs based on the information signal in the demodulated output is provided, and the output of the controller 8 and the initial timing of the pseudo random noise code are ANDed. Thus, even when the timing information is extracted from the filter output, the timing information is obtained accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a correlation receiver used for detecting the position of a moving object in a global system (GPS system).

[Conventional technology]

Conventionally, 18 artificial satellites covered the entire earth,
A global orientation system has been proposed in which three-dimensional position information and time information can be obtained using radio waves from four of these satellites. Each satellite transmits two signals: an M-sequence pseudo-random noise code and time and other information signals.
It transmits all heavily modulated radio waves of about 1.5 gigahertz. Further, the information signal and the pseudorandom noise code are synchronized. The M sequence is the longest code sequence generated by a shift register or delay element of a certain length, and the details can be found in Jacchik Publishing's ``Spread Spectrum Communication System J'' (by RlC-Dixon, translated by Satoshi Tateno). Are listed.

The transmitted radio waves are correlated using a pseudo-random noise code of the same format as that used on the transmitting side, and only the necessary band of the correlation output is extracted via a filter. However, the signal outputted from the filter 1 and the filter tends to be delayed, and the delay time also varies depending on the environmental conditions.

However, since it is necessary to determine the time based on all the signals sent, it is not possible to accurately determine the time with such unstable signals. For this reason, conventionally, the time signal is extracted by a special detection circuit with multiple branches before the filter.

[Problem that the invention seeks to solve]

However, such conventional methods are susceptible to interference such as noise, and if the interference resistance is improved, the processing time becomes long and time accuracy cannot be ensured.

[Means for Solving the Problems] In order to solve the above problems, the present invention analyzes the first frame of the target pseudorandom noise code of the multiple image output based on the information signal being demodulated and output. A window control device is provided that outputs data near the initial timing, and the logical difference between the output of the window control device and the initial timing of the pseudo-random noise code on the receiving side is obtained.

[Effect]

The initial timing of the first frame can be identified from among the initial timings of each frame of the pseudorandom noise code.

〔Example〕

The first part is a block diagram showing an embodiment of the present invention.

In the figure, 1 is an input terminal, 2 is a pseudo-random noise code generator, 3 is a multiplier, 4 is a bandpass filter, and 5
is a Costas loop type PLL.

6a to 6c are output terminals, T is a phase shifter, 8 is a window control device, and 9 is an AND circuit. The pseudo-random noise code generator 2 consists of two sets of shift registers and an exclusive OR that multiplies their outputs, so that all pits are "1".
One frame is constructed by changing the combination state of each pit starting from the initial timing at which the level is reached, and a signal is generated to repeat this frame t-111N times.

As will be described later, the window control device 8 extracts a signal of a predetermined period including the initial timing of the first frame of the pseudorandom noise code from the demodulated output.

The operation of the device configured in this way is as follows.

On the transmitting side, spectrum spreading is performed using the pseudorandom noise code shown in Fig. 2(a), and the second
As shown in Figure (b), a certain frame PN01' is set as the first frame, and radio waves including that frame and fully modulated by an information signal representing positional information are transmitted as one frame group, flJt, 2o frames e. At this time, the pseudorandom noise code used on the transmitting side has the same format as that used on the receiving side, but the initial timing of the information signal, that is, the initial timing of the first frame of the pseudorandom noise code, is the time information. The trigger timing is to obtain the .

By correlating the radio wave modulated with such a signal and the pseudorandom noise code on the receiving side, an initial timing signal representing the initial timing of each frame as shown in FIG. 2(d) can be obtained. Since the satellite is located at an altitude of 30,000 meters above the ground, the propagation time of radio waves is approximately 100 m8. On the other hand, in this embodiment, one frame group is 120 m long, so if the real time is written as is in FIG. 2, the portion in FIG. 2 @) will protrude from this figure. Therefore, from FIG. 2(d) onwards, the values are shown as values obtained by subtracting 20xn (n is an integer) from the propagation time. Therefore, it is assumed that the output is obtained at tl, which is delayed by Tt from timing 1o on the transmitting side. The time information sent from the transmitting side can be known from the initial timing signal obtained from the first frame of this initial timing number 6.

If the time on the transmitting side is known, the position tt at the measurement point can be accurately determined from the time difference between the transmitting side and the receiving side and data representing the demodulated position. At this time, the time on the receiving side must have the same accuracy as on the transmitting side, and this is based on the signal sent from the transmitting side. *It is possible to secure the degree. However, since this technique is not limited to the scope of the present invention, a description thereof will be omitted.

As shown in (d), the correlation output on the receiving side is a signal synchronized with the frame on the transmitting side. However, this (0) is delayed by passing through filter 4, and the output of filter 4 is obtained at time 1s, which is delayed by 'rz from time 1 when the correlation output is obtained. This delay can be longer than the frame interval, and changes due to changes in filter performance due to changes in the fc control conditions.In such a state, which part of the demodulated output is It becomes impossible to determine whether it is the first frame, and it is also impossible to determine the initial timing of the first frame.

Therefore, in this invention, a signal near the initial timing of the first frame is output from the window control device 8 from the demodulated output of the information signal representing the position, taking into consideration the -M time of the filter and the variation in filter characteristics due to changes in environmental conditions. ing.

Generally, it is extremely difficult to accurately detect the initial timing when there is a large delay and this delay changes depending on environmental conditions. However, it is possible to estimate the first frame within one frame based on the demodulated output.
It is also possible to estimate the range in which the initial timing in the first frame exists from the variation in filter characteristics.

Therefore, as shown in FIG. 2 σ), the window control device 8 extracts the entire demodulated output of the portion where the initial timing of the first frame should exist. As described above, the initial timing is the timing at which all the pits of the pseudo-noise code become "1" level.

Therefore, if the signal containing the initial timing signal of the first frame outputted from the window control device 8 and the pseudo noise code are ANDed by the AND circuit 9, the result will be as shown in FIG. 2(r). Only the initial timing signal of the first frame can be detected accurately.

Using radio waves from four satellites based on this signal,
Three-dimensional information and time of measurement points can be accurately determined.

〔Effect of the invention〕

As explained above, the present invention outputs data near the initial timing of the first frame based on the information signal sent from the transmitting side, and performs a logical product of this output and the initial timing of the pseudo noise code on the receiving side. Therefore, even if the timing information is extracted from the filter output, the timing information can be accurately obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a time chart for explaining the operation. 2... e. Pseudo-random noise code generator, 3... φ. multiplier, 4...-filter, 8... window control device, 9... φ AND circuit.

Claims (1)

[Claims] Starting from the initial timing when all the pits of the signal output from the pseudo-random noise code generator that generates the M-sequence pseudo-random noise code consisting of multiple pits are in the "1" level state, the combination state of each pit is A pseudo-random noise code is generated by changing the In a correlation receiver that receives and demodulates a signal modulated by a noise code and an information signal, data near the initial timing of the target first frame of the demodulated output is output based on the information signal being demodulated. 1. A correlation receiver comprising: a window control device; and an AND circuit that obtains an AND signal of an output of the window control device and an initial timing in a pseudo-noise code on the receiving side.