JPH0712917A - Gps receiver - Google Patents

Abstract

PURPOSE:To receive radio waves of a plurality of GPS(global positioning system) satellites at a good timing stably with a simple circuitry. CONSTITUTION:An L1 carrier of a GPS satellite is converted to an IF signal with a mixer 23 and the IF signal is diffused reversely based on a code of a C/A (clear and acquisition) code generator 29 from a multiplier 28 and a PSK signal demodulated is obtained from a BPF 33. A carrier is reproduced with carrier reproduction circuits 52 and 46 from the PSK signal and a clock signal of the C/A code generator 29 is generated from the frequency of the carrier and a local oscillation frequency. The PSK signal is demodulated based on a reference frequency of a PLL circuit 54 to obtain a navigation message.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to GPS (Global Position
ioning system) relates to a GPS receiver that receives radio waves transmitted from a satellite to the earth.

[0002]

2. Description of the Related Art GPS satellites are satellites developed for military purposes, but some of them are open to civilian use and are used for positioning to detect the position of vehicles such as ground and ocean. The positioning device that receives this GPS radio wave has high positioning accuracy,
It has begun to be widely used for navigation systems for ships and cars, positioning systems for mobile phones, etc., but recently, the needs for mobile positioning systems and the like have been increasing, and their future potential and development are expected.

Radio waves transmitted from GPS satellites use two types of spreading codes, a publicly-known C / A (Clear and Acquisition) code and a military-use P (Precision) code. The navigation message is spread-modulated, and the obtained modulated signals are carrier-modulated and transmitted. Further, a plurality of GPS satellites have been launched, and the C / A code and P code used by each satellite are different.

When receiving radio waves transmitted from a plurality of GPS satellites toward the earth in this way, the radio waves of three or more satellites among them are simultaneously received, and the signals from each satellite reach the receiver. The current position can be obtained by calculating the distance from the time required for and the propagation velocity of the electromagnetic wave.

FIG. 2 shows a transmission circuit in a GPS satellite. This circuit is called the L1 carrier 1.575
42GHz and 1.2276GH called L2 carrier
A signal that is spread spectrum is transmitted by two carriers of z. As the atomic clock 1, a cesium atomic clock that performs very stable atomic vibration is used.
A reference frequency of 23 MHz is generated, and a carrier and each code are generated with reference to this frequency.

That is, the L1 carrier is a 154 multiplier 2.
Generated by the L1 carrier generator 3 (1.57542 GHz = 1.23 MHz × 15)
4), the L2 carrier is multiplied by the 120 multiplier 9 and generated by the L2 carrier generator 10 (1.227).
6 GHz = 10.23 MHz x 120). Also, C / A
The reference frequency of the code is divided by the 1/10 frequency divider 4 to generate a clock of 1.023 MHz. By supplying this clock to the C / A code generator 5, 1.
023 Mbps, spreading code with a period of 1023 (C / A
Code) is generated. The satellite-specific navigation message is generated as 50 bps data by dividing the reference frequency by the 1/204600 divider 6 and supplying it to the message generator 7, and the P code uses the reference frequency as it is as a clock signal. Generated by the P code generator 8. As described above, the spread code of the P code is not disclosed, but its code length is 6.18, which is about one week.
It is a very long code of 7104 × 10 12 chips.

The C / A code and the navigation message generated in this way are supplied to the EX-OR gate 11 to obtain a message in which the message is spread and modulated, and this signal is L
One carrier is multiplied by the carrier phase-shifted by 90 ° (13 and 14 in the figure) and supplied to the adder circuit 18.
Similarly, the P code is also EX-O along with the navigation message.
The signal is supplied to the R gate 12 to obtain a signal in which the message is spread and modulated, and this signal is multiplied by the L1 carrier (see FIG. 1).
5) and is supplied to the adder circuit 18.

Further, the outputs of the EX-OR gates 11 and 12 and the P code are the switches 1 controlled by the ground station.
Select via 6 and multiply with L2 carrier (shown 17)
It is then supplied to the adder circuit 18. In the adder circuit 18, the respective inputs are added, and the addition result is transmitted via the antenna 19.

In the receiving device for receiving the radio wave transmitted from this transmitter, the signal is converted to an intermediate frequency by the frequency circuit, and then despread and demodulated by the C / A code output from the demodulating C / A code generator. After that, the navigation message is demodulated by PSK demodulation. The navigation message thus obtained is taken into the microcomputer in the receiving section and various necessary information is reproduced. Also, the demodulation C
/ A code generator generates a code according to the receiving satellite,
The switching is controlled by a microcomputer, but the most important function of the receiving device is the C of the receiving satellite.
/ A code is generated in synchronization with the code.

Conventionally, in this type of GPS receiving device, a synchronous capturing device and a synchronous holding device are used to generate a code synchronized with a C / A code of a receiving satellite, and a delay locked loop is used as the synchronous holding device. Widely used.

[0011]

However, in the above-mentioned conventional GPS receiver, the circuit configuration of the synchronization capturing device and the synchronization holding device is complicated, and the delay lock loop used as the synchronization holding device is provided in each satellite. It is difficult to operate stably with respect to different received electric field strengths transmitted from the. Therefore, at present, it is general to use a synchronization holding device that operates at a certain reception electric field strength with a certain threshold, and although the circuit scale is large as a whole, the dynamic range of reception synchronization with respect to the reception electric field strength is low, and However, there is a problem that it is difficult to receive radio waves from a plurality of satellites in good timing depending on the orbital position of each satellite.

In view of the above problems of the prior art, it is an object of the present invention to provide a GPS receiver having a simple circuit configuration and capable of stably receiving radio waves of a plurality of GPS satellites at a good timing.

[0013]

In order to achieve the above object, the present invention reproduces a carrier wave by a PLL from a PSK signal detected from a radio wave received from a GPS satellite and uses a frequency of this carrier wave and a local oscillation frequency to generate a clock. A signal is generated and applied to the C / A code generating means. That is, according to the present invention, a C / A code generating means for generating a C / A code according to a target receiving GPS satellite based on a clock signal, and an electric wave received from the GPS satellite with an intermediate frequency signal at a local oscillation frequency. A conversion means for converting the PSK signal to a PSK signal by multiplying the intermediate frequency signal obtained by the conversion means by the C / A code generated by the C / A code generation means; Reproducing means for reproducing a carrier wave from the obtained PSK signal by a PLL; and means for generating a clock signal by the frequency of the carrier wave obtained by the reproducing means and the local oscillation frequency and applying it to the C / A code generating means. A means for demodulating GPS data from the frequency of the carrier wave obtained by the reproducing means and the PSK signal obtained by the detecting means. GPS receiver that is provided.

[0014]

In the present invention, the carrier is reproduced by the PLL from the PSK signal detected from the radio wave received from the GPS satellite, and the clock signal of the C / A code generating means is generated by the frequency of the carrier and the local oscillation frequency. Therefore,
The clock signal of the C / A code generating means is generated using the frequency of the carrier wave of the C / A code, and the effect of the local oscillation frequency not synchronized with the C / A code is canceled to generate the clock signal. Therefore, the synchronization holding performance of the PLL circuit for reproducing the carrier wave of the C / A code becomes the synchronization holding performance of the C / A code generating means, and the synchronization holding device such as the delay lock loop of the conventional example is not provided, and it is simple. With such a circuit configuration, it is possible to stably receive the radio waves of a plurality of GPS satellites with good timing.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a GPS receiving apparatus according to the present invention.

FIG. 1 shows an antenna 2 receiving an L1 carrier.
1 to C / A code synchronization generation. First, the L1 carrier of the GPS satellite received by the reception antenna 21 is supplied to the frequency conversion mixer 23 via the bandpass filter (BPF) 22, and the local conversion is performed. Oscillator (X
O) 24 and the multiplied local oscillation signal obtained by the frequency multiplier 25 and mixed to be converted into an intermediate frequency (IF) signal. Here, 20.321M generated by the local oscillator 24
1. Hz is multiplied by 77 by the frequency multiplier 25 and 1.
A local oscillation signal of 567472 GHz is generated and 1.5
Receive L1 carrier of 7542 GHz is 10.7 MHz
It is converted into an IF signal of (= 1.57542 GHz-1.56472 GHz) and output via the BPF 26.

The output signal of the BPF 26 is amplified by the automatic gain control (AGC) circuit 2 and shaped into a constant amplitude, and then supplied to the despreading multiplier 28 for reception C / A.
Despreading is performed based on the code generated by the code generator 29, and a demodulated PSK signal is obtained from the output of the BPF 33 at the next stage. This PSK signal is passed through the amplifier 34,
The multiplier 35, the BPF 36, the phase comparator 37, the DC amplifier 38, the loop filter (LF) 40, the voltage-controlled crystal oscillator (VCXO) 39, and the carrier recovery circuit 52 including the frequency divider 46 are supplied. To be done. The phase comparator 37, the DC amplifier 38, the loop filter (L
F) 40 and the voltage controlled crystal oscillator 39 constitute a PLL (phase locked loop) 54 circuit, and the oscillator 39 is 21.4M.
Generate a Hz signal.

Since the PSK signal has two phase changes of 0 and π, it is necessary to cancel the phase change when reproducing the carrier wave. In this embodiment, the PSK signal is multiplied by 2 by the multiplier 35. The π phase is 2π
Therefore, since 2π = 0, the phase change is canceled.
The output signal of the BPF 36 in which this phase change is canceled is
Since the frequency is a double frequency (21.4 MHz) in which the amplitude changes, the phase locked loop (PLL) circuit 54 shapes the constant double frequency signal.

The 21.4 MHz signal generated by the oscillator 39 of the PLL circuit 54 is halved by the frequency divider 46.
Is divided into a fundamental frequency of 10.7 MHz, which means that the carrier frequency itself of the PSK signal is reproduced. This reproduced carrier wave is divided into 1540 by the frequency divider 42.
The frequency is divided by one, converted to a frequency of 69.4805 kHz, and applied to the EX-OR gate 43.

The EX-OR gate 43 also divides the frequency of 20.321 MHz generated by the local oscillator 24 by 20 by the frequency divider 41 to 1.01605.
A frequency of MHz is applied, multiplication is performed by the EX-OR gate 43, and a signal of 1.023 MHz which is the sum frequency thereof is obtained from the output of the BPF 44 in the next stage. That is, since this frequency is equal to the frequency of the clock signal supplied to the receiving C / A code generator 29, the BPF 44
Output via the amplifier 45 and switch 31 for receiving C /
The C / A code generator 2 is supplied to the A code generator 29.
9 produces a C / A code equivalent to a GPS satellite and is despread by the multiplier 28.

The synchronization acquisition at the start of reception is performed by selecting 1.023 MHz + Δf output from the synchronization acquisition oscillator 30 by the switch 31 and supplying it to the C / A code generator 29. , Code synchronization flows at a frequency that is slightly different from the regular clock frequency by + Δf. That is, PSK of BPF33
The output becomes a large signal at the synchronization point (correlation point),
At the non-correlation point, it becomes a diffused signal of a small level 2
Since it is obtained as a value, the correlation point is detected by the amplifier 34 and the synchronization detector 32 in the next stage, and the switch 31 is detected at the correlation point.
Is switched to the regular clock signal side.

Further, the C / A code generator 29 is applied with a code switching control signal corresponding to the receiving satellite via the input terminal 50, so that the radio waves of a plurality of GPS satellites are selectively received. Further, the PLL frequency divided by half by the frequency divider 46 is multiplied by the PSK signal output from the amplifier 34 by the multiplier 47 to perform PSK demodulation, whereby PSK is output from the output of the LPF 48 of the next stage. A navigation message obtained by demodulating the signal is obtained, and output terminal 49
Is output via. The circuits 23 to 25 constitute a conversion means for converting an electric wave received from a GPS satellite into an intermediate frequency signal at a local oscillation frequency, and the circuits 28 and 33 are PSK.
A detection means for detecting a signal is configured. Furthermore, the circuit 30
32 to 41 to 45 constitute means for generating a clock signal by the frequency of the carrier wave obtained by the reproducing means and the local oscillation frequency and applying it to the C / A code generating means.
Reference numerals 7 and 48 constitute means for demodulating GPS data from the frequency of the carrier wave obtained by the reproducing means and the PSK signal obtained by the detecting means.

[0023]

As described above, according to the present invention, C
The clock signal of the C / A code generating means is generated by using the frequency of the carrier wave of the / A code, and the clock signal is generated by canceling the influence of the local oscillation frequency which is not synchronized with the C / A code. Therefore, the synchronization holding performance of the PLL circuit that reproduces the carrier wave of the C / A code becomes the synchronization holding performance of the C / A code generating means, and therefore, without providing a synchronization holding device such as the delay lock loop of the conventional example,
It is possible to stably receive radio waves from a plurality of GPS satellites with a simple circuit configuration and at a good timing.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a GPS receiver according to the present invention.

FIG. 2 is a block diagram showing a transmitter for a GPS satellite according to the present invention.

[Explanation of symbols]

 21 Antenna 22, 26, 33, 36, 44 BPF 23 Mixer 24 Local Oscillator (XO) 25 Frequency Multiplier 27 AGC Circuit 28 35, 47 Multiplier 29 C / A Code Generator (C / A Code Generator) 30 Oscillator 31 switch 32 synchronization detector 37 phase comparator 38 DC amplifier 39 voltage controlled crystal oscillator (VCXO) 40 loop filter (LF) 41, 42, 46 frequency divider 48 LPF 52 carrier recovery circuit (regeneration means) 54 PLL circuit

Claims (1)

[Claims] 1. A C / A code generating means for generating a C / A code according to a target receiving GPS satellite based on a clock signal, and a radio wave received from the GPS satellite is converted into an intermediate frequency signal by a local oscillation frequency. Converting means, the intermediate frequency signal obtained by the converting means, and the C / A
A detecting means for detecting a PSK signal by multiplying the C / A code generated by the code generating means, a reproducing means for reproducing a carrier wave by a PLL from the PSK signal obtained by the detecting means, and a reproducing means for reproducing the carrier wave. Means for generating a clock signal based on the frequency of the carrier wave and the local oscillation frequency and applying the clock signal to the C / A code generating means, and the frequency of the carrier wave obtained by the reproducing means and the PSK signal obtained by the detecting means. A GPS receiver having means for demodulating GPS data.