CN105717524B - A kind of Beidou navigation satellite system receiver pseudo range measurement improved method based on FPGA and DSP - Google Patents

Abstract

The invention discloses a kind of pseudo range measurement improved method of the Beidou navigation satellite system receiver based on FPGA and DSP, belong to technical field of satellite navigation.This method is directed to the non-GEO satellite of the Big Dipper for navigation message period of sub-frame with 6 seconds, with with 0.6 second Big Dipper GEO satellite for period of sub-frame, by detecting its subframe frame head respectively, the square-wave response that a cycle is 0.2 second is triggered respectively, counted by FPGA, the pseudo-time that satellite navigation signals are propagated in space is obtained, pseudorange value is calculated after reading this time by DSP, so as to realize positioning.This method can effectively avoid because Big Dipper GEO satellite and non-GEO satellite period of sub-frame is inconsistent or sequential amendment after, the phenomenon of caused pseudorange saltus step suddenly in position fixing process, so as to better profit from Beidou satellite navigation system, more accurate, stable navigation effect is realized.

Description

An improved method for pseudo-range measurement of Beidou navigation receiver based on FPGA and DSP

technical field

The invention relates to an improved pseudo-range measurement method of a Beidou navigation receiver based on FPGA (Field Programmable Gate Array) and DSP (Digital Signal Processor), and belongs to the technical field of satellite navigation.

Background technique

As we all know, the global satellite navigation system is a very important spatial information infrastructure. Satellite navigation systems can not only be used in military, disaster reduction and relief, and public safety fields, but also gradually play a huge role in many civilian fields such as personal navigation, traffic management, telecommunications, and fishery. In satellite navigation technology, the stability of receiver pseudorange solution has a crucial impact on continuous good positioning.

In the existing Beidou navigation receiver, in order to simultaneously use GEO satellites (geostationary orbit satellites) and non-GEO satellites for positioning, and to realize the calculation of pseudo-ranges, as shown in Figure 2, the subframe header of the non-GEO satellites is triggered A square wave with a period of 1 second causes the subframe header of the GEO satellite to trigger a square wave with a period of 0.6 seconds, and at the same time generates a TIC_1 signal with a period of 1 second (positioning observation data latch enable signal 1). The counter in the tracking channel, when encountering the rising edge of the square wave triggered by the subframe head, the counter starts counting; when encountering the rising edge of the TIC_1 signal, the counter stops counting, and puts the counting result into the buffer, using this The count result is multiplied by the speed of light to calculate the pseudorange value. Because the starting position of the rising edge of the TIC_1 signal is random, after the positioning is realized, the clock difference can be obtained, and the clock difference is used as the feedback amount, which is fed back to the FPGA to adjust the starting time of TIC_1, and so on, so that the clock difference iterates , Gradually become smaller.

The defect of this pseudorange calculation method is that since the period of the square wave triggered by the subframe head of the non-GEO satellite is 1 second, and the period of the square wave triggered by the subframe head of the GEO satellite is 0.6 seconds, it is necessary to use the GEO satellite at the same time To perform positioning with non-GEO satellites, corresponding timing adjustments must be made to their counter reading values. After the timing adjustment is made, there will be a jump phenomenon of the pseudo-range value at a certain moment in the positioning process, which will cause the positioning process to be unstable and affect the accuracy of the positioning result.

Contents of the invention

The present invention proposes a Beidou navigation receiver pseudo-range based on FPGA and DSP in order to overcome the problem that the pseudo-range value suddenly jumps in the positioning process caused by timing adjustment due to the different sub-frame periods of non-GEO satellites and GEO satellites. Measurement improvement method, suitable for satellite navigation positioning neighborhood.

The present invention adopts following technical scheme for solving its technical problem:

A method for improving pseudorange measurement of a Beidou navigation receiver based on FPGA and DSP, comprising the steps of:

Step 1: On the basis of capturing and tracking the Beidou navigation satellite signal, detect the subframe header "11100010010" of the signal;

Step 2: After the subframe header is detected, the subframe headers of the non-GEO satellite and the GEO satellite trigger their respective Frame_D1 and Frame_D2 square wave signals with a period of 0.2 seconds, and the 1 second period generated by the existing FPGA Based on the TIC_1 signal, frequency division generates a TIC_2 signal with a period of 0.2 seconds;

Step 3: When the counter in the FPGA gets the rising edge of the Frame_D1 or Frame_D2 square wave signal, it starts to count them at 1.023MHz, which is 32 times times, until the rising edge of the TIC_2 signal arrives, stop counting, and count the count value with Cache to the latch, waiting for DSP to read;

Step 4: DSP fetches count value from FPGA with , use the count value conversion to calculate the pseudorange value of the satellite in each channel, and then perform positioning calculation; the clock difference obtained after the calculation with , as the feedback value, returned to FPGA to adjust the starting moment of the rising edge of the TIC_2 signal until it is aligned with UTC, that is, the international coordinated time;

Step 5: Correct the clock error and pseudorange value of the receiver step by step through the multiple loop executions of the first step to the fourth step above.

In the 4th step, when DSP takes out the count value of non-GEO satellite and GEO satellite respectively from the latch of FPGA with After that, use the formula:

to get the pseudo-range value of the satellite; among them, when the satellite tracked in the channel is a non-GEO satellite, the value represent , when the satellite tracked in the channel is a GEO satellite, the value represent ; for the speed of light .

The beneficial effects of the present invention are as follows:

(1) This method is an improved research on the pseudo-range measurement method of Beidou navigation receiver based on FPGA and DSP, which can be used to improve the positioning effect of Beidou navigation receiver. Compared with the currently applied pseudo-range measurement method, this method can avoid the jump phenomenon of pseudo-range value, and make the receiver more perfect and stable to use Beidou non-GEO satellites and GEO satellites for positioning calculation.

(2) The method of the present invention can better evaluate the effectiveness of the algorithm by analyzing the positioning calculation results and pseudorange calculation values output by the serial port of the DSP.

Description of drawings

Fig. 1 is the overall flow chart of this method.

Figure 2 is a square wave diagram of timing signals generated by FPGA before modification and improvement.

Figure 3 is a square wave diagram of the timing signal generated by the FPGA after modification and improvement.

Figure 4 is a schematic diagram of the pseudo-range measurement.

detailed description

The invention will be described in further detail below in conjunction with the accompanying drawings.

The basis of the present invention is the FPGA and DSP hardware platform owned by the Deep Combination Research Group of the Navigation Research Center of Nanjing University of Aeronautics and Astronautics, and a complete set of Beidou receiver programs compiled by the research group. In order to enable Beidou non-GEO satellites and GEO satellites to participate in positioning calculations at the same time, it is necessary to solve the problem that the subframe period of non-GEO satellites is 6 seconds, while the subframe period of GEO satellites is 0.6 seconds. As mentioned in the background technology, the original method is to use FPGA counting to obtain the propagation time of two types of satellite signals, and adjust the timing of the two types of satellite signals through the objective logical relationship between the two propagation times, so as to achieve the Beidou Non-GEO satellites and GEO satellites participate in the positioning calculation at the same time. However, this method will lead to a large deviation jump in the pseudo-range result at a certain moment after the positioning is realized, which will affect the positioning accuracy and stability.

Therefore, consider modifying the periods of the square wave signals triggered by the subframe headers of non-GEO satellites and GEO satellites to 0.2 seconds. At the same time, add a TIC_2 signal (location observation data latch enable signal 2) with a period of 0.2 seconds to read the propagation time count value of each satellite signal. In this way, the integrity of satellite signal reading can be guaranteed (GEO satellite signal propagation time is about 120 milliseconds, and non-GEO satellite signal propagation time is about 70 milliseconds), while avoiding timing adjustments to prevent pseudo-range The occurrence of a jump in the evaluated value.

The overall flow chart of this method is shown in Figure 1. By capturing and tracking satellite signals, after stripping off the carrier and pseudo codes, the navigation message is obtained. After the frame header of the navigation message is detected, the frame information square wave is triggered. After obtaining the counter value of the pseudo-range propagation time, the pseudo-range is calculated for positioning solution. The following work needs to be done:

Subframe header detection

The synchronization code of the Beidou satellite navigation message subframe contains bits 1 to 11 of the telemetry code in the first word of each subframe, and the value is "11100010010". By detecting these 11 bits, the position of the subframe header can be determined. Since the subframe is cycled periodically, the frame header can also be recursively, that is, if the frame header is detected, after an integer multiple of the subframe cycle cycle, it should return to the frame header position and detect the frame header again to ensure Correctness of frame header detection.

Time Base Generation Module Design

There is a time base square wave signal TIC_1 with a period of 1 second in the system (a square wave signal with a period of 1 second). On the basis of this signal, a time-base square wave signal TIC_2 with a period of 0.2 seconds (a square wave signal with a period of 0.2 seconds) is obtained by dividing the frequency by five times.

Then, when the non-GEO satellite and the subframe header of the GEO satellite are detected, Frame_D1 (the square wave signal triggered by the subframe header of the non-GEO satellite) and Frame_D2 (the square wave signal triggered by the subframe header of the GEO satellite) and Frame_D2 (the square wave signal triggered by the subframe header of the GEO satellite) with the same period of 0.2 seconds are respectively triggered. wave signal) square wave signal. As shown in Figure 3. The reason why the subframe signal period of the two types of satellites is selected as 0.2 seconds is to find their least common factor between the subframe period of non-GEO satellites of 6 seconds and the subframe period of GEO satellites of 0.6 seconds, while satisfying The objective condition for GEO satellite signal propagation time is about 120 milliseconds. Taking these factors into consideration, we choose to set the period of the subframe signal to 0.2 seconds, which can not only get rid of timing adjustments, but also improve the accuracy of pseudorange calculation to a certain extent.

Satellites in different channels have their own counters. Let the rising edge of the signal triggered by the subframe header be used as the signal for the counter in the FPGA to clear the count value and restart counting, and let the rising edge of the time base square wave signal TIC_2 with a period of 0.2 seconds be used as the count in the read and latch counter value signal.

Pseudorange measurement principle

Pseudorange has a distance deviation, the distance between the user's measurement point and the satellite, which is the basic data for calculating the coordinates of the user's point.

As shown in FIG. 4 , it is the pseudo-range measurement method used in the present invention.

Initially, the starting position of the rising edge of the TIC_2 signal is arbitrary, and we assume that it is the moment when the satellite signal is sent from the space satellite. At the same time, it is assumed that the rising edge of the frame synchronization signal is the moment when the user receiver on the ground receives the corresponding frame signal sent by the satellite.

The 29-bit counter in the FPGA counts continuously at a frequency of 1.023MHz that is 32 times higher. When it is triggered by the rising edge of the Frame_D1 or Frame_D2 (that is, non-GEO satellite and GEO satellite subframe signal) signal, the counter in the counter The count value is cleared and starts counting from zero. When the counter is triggered by the rising edge of the TIC_2 signal, the current count value in the counter is latched into the latch.

DSP reads this count value from the latch (The count values of non-GEO satellites and GEO satellites are expressed as with ), then the pseudorange value That is:

(1)

in for the speed of light .

After obtaining the pseudorange value, the positioning solution can be performed. The three-dimensional position coordinates of the user's location and the clock difference of the receiver are obtained through positioning calculation. The clock error is fed back to the FPGA to adjust the position of the rising edge of the TIC_2 signal, so that the pseudo-range value is corrected again and again, and the positioning solution is performed in a cyclic iteration.

Through the experimental data sent from the serial port of the DSP, we can find that the jump of the pseudo-range value no longer occurs, and the receiver achieves a more stable and accurate positioning result.

Claims (2)

1. a method for improving pseudorange measurement of a Beidou navigation receiver based on FPGA and DSP, is characterized in that, comprises the steps: Step 1: On the basis of capturing and tracking the Beidou navigation satellite signal, detect the subframe header "11100010010" of the signal; Step 2: After the subframe header is detected, the subframe headers of the non-GEO satellite and the GEO satellite trigger their respective Frame_D1 and Frame_D2 square wave signals with a period of 0.2 seconds, and the 1 second period generated by the existing FPGA Based on the TIC_1 signal, frequency division generates a TIC_2 signal with a period of 0.2 seconds; Step 3: When the counter in the FPGA gets the rising edge of the Frame_D1 or Frame_D2 square wave signal, it starts to count them at 1.023MHz, which is 32 times times, until the rising edge of the TIC_2 signal arrives, stop counting, and count the count value with Cache to the latch, waiting for DSP to read; Step 4: DSP fetches count value from FPGA with , use the count value conversion to calculate the pseudorange value of the satellite in each channel, and then perform positioning calculation; the clock difference obtained after the calculation with , as the feedback value, returned to FPGA to adjust the starting moment of the rising edge of the TIC_2 signal until it is aligned with UTC, that is, the international coordinated time; Step 5: Correct the clock error and pseudorange value of the receiver step by step through the multiple loop executions of the first step to the fourth step above. 2. according to a kind of Beidou navigation receiver pseudorange measurement improvement method based on FPGA and DSP described in claim 1, it is characterized in that, in the described 4th step, when DSP takes out non-GEO from the latch of FPGA Count values for satellites and GEO satellites respectively with After that, use the formula: Get the pseudorange value of the satellite; where, when the satellite tracked in the channel is a non-GEO satellite, the value equal /(32*1.023MHz), when the satellite tracked in the channel is a GEO satellite, the value equal /(32*1.023MHz); for the speed of light .