技术领域technical field
本发明属于导航信号检测技术领域，特别涉及北斗信号捕获方法，可用于北斗弱信号捕获。The invention belongs to the technical field of navigation signal detection, in particular to a Beidou signal acquisition method, which can be used for Beidou weak signal acquisition.
背景技术Background technique
全球卫星定位系统（Global Navigation Satellite System，GNSS）信号是经过直接序列扩频调制的扩频信号，对经过直接扩频调制的卫星导航信号的捕获是GNSS系统需要解决的首要问题。而当信号条件不理想时，例如在室内、森林和城市环境条件下，遮挡、多径和干扰等现象较严重，能量有更多的削弱和衰落，接收信噪比有更大程度的恶化，普通的捕获方法将难以捕获和跟踪到导航卫星信号。目前串行/并行算法、快速分段算法、FFT/IFFT等捕获算法解决的主要问题是降低计算量、提高捕获速度。随大规模集成电路的发展，计算的瓶颈已经克服，而问题集中在低信噪比下信号的捕获上，即通过合适的算法来提高后测信噪比，达到对低信噪比信号的捕获。GNSS通过加长相干积分和非相干积分时间以提高信噪比,从而提高信号检测的灵敏度，但是，导航信号比特翻转、频偏引起的相干积分增益下降及码偏移、非相干积分的平方损失以及复杂信道对相干积分长度的限制，都会对高灵敏度接收机检测算法的设计和性能产生很大的影响。The Global Navigation Satellite System (GNSS) signal is a spread spectrum signal that has been modulated by direct sequence spread spectrum. The acquisition of the satellite navigation signal that has been modulated by direct spread spectrum is the primary problem that the GNSS system needs to solve. When the signal conditions are not ideal, such as indoors, forests and urban environments, the phenomenon of occlusion, multipath and interference is more serious, the energy is more weakened and fading, and the receiving signal-to-noise ratio is deteriorated to a greater extent. Ordinary acquisition methods will be difficult to capture and track navigation satellite signals. At present, the main problem solved by serial/parallel algorithm, fast segmentation algorithm, FFT/IFFT and other capture algorithms is to reduce the amount of calculation and improve the capture speed. With the development of large-scale integrated circuits, the bottleneck of calculation has been overcome, and the problem is focused on the capture of signals under low signal-to-noise ratio, that is, to improve the post-test signal-to-noise ratio through appropriate algorithms to achieve the capture of low signal-to-noise ratio signals . GNSS improves the signal-to-noise ratio by lengthening the time of coherent integration and non-coherent integration, thereby improving the sensitivity of signal detection. The limitation of the length of coherent integration by complex channels will have a great impact on the design and performance of detection algorithms for high-sensitivity receivers.
为了提高了信噪比进而提高了检测概率，克服导航数据调制所带来的比特翻转问题，同时减小非相干积分的平方损失，并提高频偏估计精度，提出差分相干累积结合频域频偏估计算法的方法。该方法采用在FPGA与DSP的环境下进行实现，具有很强的实际意义。In order to improve the signal-to-noise ratio and thus improve the detection probability, overcome the bit flipping problem caused by navigation data modulation, reduce the square loss of incoherent integration, and improve the accuracy of frequency offset estimation, a differential coherent accumulation combined with frequency domain frequency offset is proposed Method for estimating algorithms. This method is implemented under the environment of FPGA and DSP, which has strong practical significance.
发明内容Contents of the invention
为了解决上述问题，本发明一种弱信号环境下北斗信号捕获方法，其包括，In order to solve the above problems, the present invention provides a Beidou signal acquisition method in a weak signal environment, which includes,
S1下变频单元，对接受到的中频采样信号进行下变频处理；The S1 down-conversion unit performs down-conversion processing on the received intermediate frequency sampling signal;
S2分别将接收到的信号进行剥离NH码，并变换到频域，与本地码频域值的复工额相乘后再逆变换到时域；S2 respectively strips the received signal of the NH code, and transforms it into the frequency domain, multiplies it with the rework value of the frequency domain value of the local code, and then inversely transforms it into the time domain;
S3将目前时刻的相干累加值与前一时刻的相干累加值的共轭相乘并求和；S3 multiplies and sums the coherent accumulation value at the current moment and the conjugate of the coherent accumulation value at the previous moment;
S4对相干积分结果峰值两侧谱线的幅度差值作泰勒级数展开，导出了频率值与幅度差值的准线性关系，利用此线性关系求解得到频率估计值。In S4, the Taylor series expansion is performed on the amplitude difference of the spectral lines on both sides of the peak of the coherent integration result, and the quasi-linear relationship between the frequency value and the amplitude difference is derived, and the frequency estimation value is obtained by solving this linear relationship.
在上述技术方案的基础上，所述步骤S1包括：对接受到的中频采样信号r(n)进行下变频处理：On the basis of the above-mentioned technical solution, the step S1 includes: performing down-conversion processing on the received intermediate frequency sampling signal r(n):
其中s(n)为基带信号，P(n)为中频信号r(n)的噪声，f1为接收信号的中频载波频率，fIF为设定中频频率，△f为搜索步长，i为搜索次数。Where s(n) is the baseband signal, P(n) is the noise of the intermediate frequency signal r(n), f1 is the intermediate frequency carrier frequency of the received signal, fIF is the set intermediate frequency frequency, △f is the search step size, and i is Number of searches.
在上述技术方案的基础上，所述步骤S2包括：将L个1ms相关后的值对应相加，即完成L ms数据的相干积分，On the basis of the above technical solution, the step S2 includes: correspondingly adding L 1 ms correlated values, that is, completing the coherent integration of the L ms data,
然后完成多次Lms的相干积分，Then complete the coherent integration of multiple Lms,
其中FFT()表示取信号快速傅里叶变换，IFFT()表示求信号的快速傅里叶逆变换，conj()表示求信号的复共轭，si(n)表示根据numSKIPmax延迟后的基带采用信号，NHk(i)表示确定的NH码排序，c(n)表示本地产生的测距码。Ri(n)表示某1ms相干积分结果，Yi(n)表示第i个Lms相干积分结果。Among them, FFT() means to take the fast Fourier transform of the signal, IFFT() means to find the inverse fast Fourier transform of the signal, conj() means to find the complex conjugate of the signal, and si (n) means to delay according to numSKIPmax The baseband adopts signals, NHk (i) represents the determined NH code sorting, and c(n) represents the ranging code generated locally. Ri (n) represents a certain 1ms coherent integration result, and Yi (n) represents the ith Lms coherent integration result.
在上述技术方案的基础上，所述剥离NH码包括，On the basis of the above technical solution, the stripped NH code includes,
其中，其中FFT()表示取信号快速傅里叶变换，IFFT()表示求信号的快速傅里叶逆变换，conj()表示求信号的复共轭，si(n)表示基带采用信号，c(n)表示本地产生的测距码，numSKIP表示从采样数据开始延迟采样点数，其范围控制在1ms采样点数内，NHk(i)表示NH码的一次循环右移k位的排序结果，Ri(n)表示某1ms相干积分结果，表示第numSKIP个对应NH循环右移k位的排序结果的20ms相干积分结果，Among them, FFT() means to take the fast Fourier transform of the signal, IFFT() means to find the inverse fast Fourier transform of the signal, conj() means to find the complex conjugate of the signal, si (n) means to use the signal in the baseband, c(n) represents the ranging code generated locally, numSKIP represents the number of delayed sampling points from the sampling data, and its range is controlled within the number of sampling points within 1ms, NHk (i) represents the sorting result of a cyclic right shift of the NH code by k bits , Ri (n) represents a 1ms coherent integration result, Indicates the 20ms coherent integration result of the sorting result of the numSKIP corresponding to the NH cycle shifted right by k bits,
其中表示1ms数据的起始位置，kmax表示对应NH码排序标示。in Indicates the starting position of 1ms data, and kmax indicates the corresponding NH code sorting mark.
估计当前相邻两个相干累积值对应的导航数据位取值为±1的值的乘积，然后与差分累积相乘后进行相干累积，公式如下：Estimate the product of the navigation data bits corresponding to the current two adjacent coherent accumulation values with a value of ±1, and then multiply it with the differential accumulation to perform coherent accumulation. The formula is as follows:
其中，Y*i-1(n)表示前一时刻的相干累加值的共轭，Yi(n)表示为当前时刻的相干累加值，ai-1表示当前相邻两个相干累积值对应的导航数据位的值(取值为±1)的乘积，Z(n)表示差分相干累积结果。Among them, Y*i-1 (n) represents the conjugate of the coherent accumulation value at the previous moment, Yi (n) represents the coherent accumulation value at the current moment, ai-1 represents the corresponding two adjacent coherent accumulation values The product of the value of the navigation data bit (with a value of ±1), Z(n) represents the result of differential coherent accumulation.
在上述技术方案的基础上，对初始频率进行补偿，再重复进行迭代估计J次，最终得到高精度载波频率和码相位。On the basis of the above technical solution, the initial frequency is compensated, and then the iterative estimation is repeated J times, and finally the high-precision carrier frequency and code phase are obtained.
其中，表示中间变量估计值，D表示峰值左右两侧谱线幅度差值，Q表示相干累积的段数，QI表示FFT点数，即有Q个Lms相干积分，做点数为QI的FFT变换，G表示FFT的峰值，α1取4/π。fini表示差分相干所得到的频率估计值，Nc为扩频码周期长度，表示高精度载波估计值。in, Represents the estimated value of the intermediate variable, D represents the amplitude difference between the left and right sides of the peak, Q represents the number of coherent accumulation segments, QI represents the number of FFT points, that is, there are Q Lms coherent integrals, do the FFT transformation with the number of points QI , and G represents For the peak value of FFT, α1 takes 4/π. fini represents the frequency estimation value obtained by differential coherence, Nc is the period length of the spreading code, Indicates a high-precision carrier estimate.
与现有技术相比，本发明由于采用频域相关算法使本方法能一次相关计算所有码相位对应的相关值。并且使用相干累积与差分相干累积结合算法，提高信噪比进而提高了检测概率，减小非相干积分的平方损失；Compared with the prior art, the present invention enables the method to calculate correlation values corresponding to all code phases at one time due to the use of a frequency domain correlation algorithm. And the combination algorithm of coherent accumulation and differential coherent accumulation is used to improve the signal-to-noise ratio, thereby increasing the detection probability, and reducing the square loss of non-coherent integration;
同时本发明采用差分相干累积，估计了导航数据位跳变，克服导航数据调制所带来的比特翻转问题，提高了检测概率；采用基于Tayor展开的线形频偏估计模型，在低复杂度下进行二次捕获，有效提高了码相位和载波频偏估计精度。采用FPGA+DSP的模块进行实现，运算速度和精度都得到了保障，具有很强的稳定性和实用性。Simultaneously, the present invention adopts differential coherent accumulation to estimate navigation data bit hopping, overcomes the bit flipping problem brought by navigation data modulation, and improves detection probability; adopts a linear frequency offset estimation model based on Taylor expansion, and performs The secondary acquisition effectively improves the estimation accuracy of code phase and carrier frequency offset. The FPGA+DSP module is used to realize the operation speed and precision, and it has strong stability and practicability.
附图说明Description of drawings
图1是本发明的系统结构框图；Fig. 1 is a system structure block diagram of the present invention;
图2是本发明系统中的相干积分单元功能框图；Fig. 2 is a functional block diagram of the coherent integration unit in the system of the present invention;
图3是本发明系统中的差分相干单元功能框图；Fig. 3 is a functional block diagram of a differential coherent unit in the system of the present invention;
图4是本发明系统中的二次精捕获单元功能框图；Fig. 4 is the functional block diagram of the secondary fine capture unit in the system of the present invention;
图5是本发明系统中的实验环境单元功能框图。Fig. 5 is a functional block diagram of the experimental environment unit in the system of the present invention.
具体实施方式detailed description
请参考图1至图5对本发明做详细说明。Please refer to FIG. 1 to FIG. 5 to describe the present invention in detail.
请参考图1，本发明一种弱信号环境下北斗信号捕获方法包括以Please refer to Fig. 1, a Beidou signal acquisition method in a weak signal environment of the present invention includes the following
下步骤：Next steps:
S1下变频单元，对接受到的中频采样信号进行下变频处理；The S1 down-conversion unit performs down-conversion processing on the received intermediate frequency sampling signal;
步骤S1包括：对接受到的中频采样信号r(n)进行下变频处理：Step S1 includes: performing down-conversion processing on the received intermediate frequency sampling signal r(n):
其中s(n)为基带信号，P(n)为中频信号r(n)的噪声，f1为接收信号的中频载波频率，fIF为设定中频频率，△f为搜索步长，i为搜索次数。Where s(n) is the baseband signal, P(n) is the noise of the intermediate frequency signal r(n), f1 is the intermediate frequency carrier frequency of the received signal, fIF is the set intermediate frequency frequency, △f is the search step size, and i is Number of searches.
S2分别将接收到的信号进行剥离NH码，并变换到频域，与本地码频域值的复工额相乘后再逆变换到时域；S2 respectively strips the received signal of the NH code, and transforms it into the frequency domain, multiplies it with the rework value of the frequency domain value of the local code, and then inversely transforms it into the time domain;
其中步骤S2包括：将L个1ms相关后的值对应相加，即完成Lms数据的相干积分，Wherein, step S2 includes: correspondingly adding L values after 1ms correlation, that is, completing the coherent integration of the Lms data,
然后完成多次Lms的相干积分，Then complete the coherent integration of multiple Lms,
其中FFT()表示取信号快速傅里叶变换，IFFT()表示求信号的快速傅里叶逆变换，conj()表示求信号的复共轭，si(n)表示根据numSKIPmax延迟后的基带采用信号，NHk(i)表示确定的NH码排序，c(n)表示本地产生的测距码。Ri(n)表示某1ms相干积分结果，Yi(n)表示第i个Lms相干积分结果。Among them, FFT() means to take the fast Fourier transform of the signal, IFFT() means to find the inverse fast Fourier transform of the signal, conj() means to find the complex conjugate of the signal, and si (n) means to delay according to numSKIPmax The baseband adopts signals, NHk (i) represents the determined NH code sorting, and c(n) represents the ranging code generated locally. Ri (n) represents a certain 1ms coherent integration result, and Yi (n) represents the ith Lms coherent integration result.
所述剥离NH码包括，The stripped NH code includes,
其中，其中FFT()表示取信号快速傅里叶变换，IFFT()表示求信号的快速傅里叶逆变换，conj()表示求信号的复共轭，si(n)表示基带采用信号，c(n)表示本地产生的测距码，numSKIP表示从采样数据开始延迟采样点数，其范围控制在1ms采样点数内，NHk(i)表示NH码的一次循环右移k位的排序结果，Ri(n)表示某1ms相干积分结果，表示第numSKIP个对应NH循环右移k位的排序结果的20ms相干积分结果，Among them, FFT() means to take the fast Fourier transform of the signal, IFFT() means to find the inverse fast Fourier transform of the signal, conj() means to find the complex conjugate of the signal, si (n) means to use the signal in the baseband, c(n) represents the ranging code generated locally, numSKIP represents the number of delayed sampling points from the sampling data, and its range is controlled within the number of sampling points within 1ms, NHk (i) represents the sorting result of a cyclic right shift of the NH code by k bits , Ri (n) represents a 1ms coherent integration result, Indicates the 20ms coherent integration result of the sorting result of the numSKIP corresponding to the NH cycle shifted right by k bits,
其中numSKIPmax表示1ms数据的起始位置，kmax表示对应NH码排序标示。Among them, numSKIPmax represents the starting position of 1ms data, and kmax represents the corresponding NH code sorting mark.
S3将目前时刻的相干累加值与前一时刻的相干累加值的共轭相乘并求和；S3 multiplies and sums the coherent accumulation value at the current moment and the conjugate of the coherent accumulation value at the previous moment;
其包括，估计当前相邻两个相干累积值对应的导航数据位取值为±1的值的乘积，然后与差分累积相乘后进行相干累积，公式如下：It includes estimating the product of the navigation data bits corresponding to the current two adjacent coherent accumulation values with a value of ±1, and then multiplying the differential accumulation to perform coherent accumulation. The formula is as follows:
其中，Y*i-1(n)表示前一时刻的相干累加值的共轭，Yi(n)表示为当前时刻的相干累加值，ai-1表示当前相邻两个相干累积值对应的导航数据位的值(取值为±1)的乘积，Z(n)表示差分相干累积结果。Among them, Y*i-1 (n) represents the conjugate of the coherent accumulation value at the previous moment, Yi (n) represents the coherent accumulation value at the current moment, ai-1 represents the corresponding two adjacent coherent accumulation values The product of the value of the navigation data bit (with a value of ±1), Z(n) represents the result of differential coherent accumulation.
S4对相干积分结果峰值两侧谱线的幅度差值作泰勒级数展开，导出了频率值与幅度差值的准线性关系，利用此线性关系求解得到频率估计值。In S4, the Taylor series expansion is performed on the amplitude difference of the spectral lines on both sides of the peak of the coherent integration result, and the quasi-linear relationship between the frequency value and the amplitude difference is derived, and the frequency estimation value is obtained by solving this linear relationship.
其包括对初始频率进行补偿，再重复进行迭代估计J次，最终得到高精度载波频率和码相位。It includes compensating the initial frequency, and repeating iterative estimation for J times, finally obtaining high-precision carrier frequency and code phase.
其中，表示中间变量估计值，D表示峰值左右两侧谱线幅度差值，Q表示相干累积的段数，QI表示FFT点数，即有Q个Lms相干积分，做点数为QI的FFT变换，G表示FFT的峰值，α1取4/π。fini表示差分相干所得到的频率估计值，Nc为扩频码周期长度，表示高精度载波估计值。in, Represents the estimated value of the intermediate variable, D represents the amplitude difference between the left and right sides of the peak, Q represents the number of coherent accumulation segments, QI represents the number of FFT points, that is, there are Q Lms coherent integrals, do the FFT transformation with the number of points QI , and G represents For the peak value of FFT, α1 takes 4/π. fini represents the frequency estimation value obtained by differential coherence, Nc is the period length of the spreading code, Indicates a high-precision carrier estimate.
下面结合附图对本发明进一步说明。The present invention will be further described below in conjunction with the accompanying drawings.
1）实现环境1) Realize the environment
在室内采集北斗信号，作为原始信号进行处理。The Beidou signal is collected indoors and processed as the original signal.
2）参照图2，经过接收机得到中频的采样数据，以设定中频fIF作为基准，以△f为搜索步长，搜索范围是以fIF作为基准的±f，则共进行2f/△f次频率搜索，按照公式2) Referring to Figure 2, the sampling data of the intermediate frequency is obtained through the receiver, and the set intermediate frequency fIF is used as the reference, and △f is used as the search step, and the search range is ±f based on fIF , then a total of 2f/△ f frequency search, according to the formula
将中频信号降到基频进行相干积分处理。首先按照FFT-IFFT的方法在FPGA内快速完成每1ms的接收信号与本地信号的相关，取20ms数据完成NH码剥离，然后将Lms的相关结果对应相加，得到长度为Lms的相干积分结果。将所得结果通过FIFO传给DSP，在DSP中进行以下处理。The intermediate frequency signal is reduced to the fundamental frequency for coherent integration processing. Firstly, according to the FFT-IFFT method, the correlation between the received signal and the local signal of each 1ms is quickly completed in the FPGA, and the 20ms data is taken to complete the NH code stripping, and then the correlation results of Lms are correspondingly added to obtain the coherent integration result with a length of Lms. The obtained result is sent to DSP through FIFO, and the following processing is carried out in DSP.
3）参照图3，对从上一个功能单元得到的数据进行差分相干处理，公式如下3) Referring to Figure 3, perform differential coherent processing on the data obtained from the previous functional unit, the formula is as follows
其中，Y*i-1(n)表示前一时刻的相干累加值的共轭，Yi(n)表示为当前时刻的相干累加值，ai表示当前相邻两个相干累积值对应的导航数据位的值(取值为±1)的乘积，Z(n)表示差分相干累积结果。根据有用信号总是存在峰值中的原理，通过将相邻相干积分的峰峰值进行差与和的模进行比较，判定前后相邻相干积分之间的相位关系，估计ai的值，以避免由导航数据位的跳变引起相互抵消的现象，增大的信号的检测概率。同时采用差分累积法减小平方损耗。查找Z(n)的第一峰值与第二峰值，并得到峰值比，若该比值大于门限λ，则表明捕获到卫星然后进行下面处理，否则，当遍历完所有频率都没有达到门限值则表明没有捕获到，则换下一颗卫星进行捕获。Among them, Y*i-1 (n) represents the conjugate of the coherent accumulation value at the previous moment, Yi (n) represents the coherent accumulation value at the current moment, ai represents the navigation corresponding to the current two adjacent coherent accumulation values The product of the value of the data bit (the value is ±1), Z(n) represents the differential coherent accumulation result. According to the principle that there are always peaks in useful signals, by comparing the peak-to-peak values of adjacent coherent integrals with the modulus of the sum, the phase relationship between the adjacent coherent integrals before and after is determined, and the value of ai is estimated to avoid being caused by The jumps of the navigation data bits cause a phenomenon of mutual cancellation, increasing the detection probability of the signal. At the same time, the differential accumulation method is used to reduce the square loss. Find the first peak and the second peak of Z(n), and get the peak ratio, if the ratio is greater than the threshold λ, it means that the satellite is captured and then proceed to the following processing, otherwise, when all frequencies have not reached the threshold after traversing, then If it shows that it has not been captured, then the next satellite will be captured.
4）参照图4，经过前面的方法可以估算出GPS信号的码相位和载波频率，其中码相位的精度根据实际计算量和计算复杂度设定，载波频率的估计精度即△f，通过所得结果，对中频采样信号进行码相位和频率的补偿，然后进行Lms的相干积分，对Q个Lms相干积分结果进行QI点的FFT变换，通过公式4) Referring to Figure 4, the code phase and carrier frequency of the GPS signal can be estimated by the previous method. The accuracy of the code phase is set according to the actual calculation amount and computational complexity. The estimation accuracy of the carrier frequency is △f. Through the obtained results , carry out code phase and frequency compensation to the intermediate frequency sampling signal, then carry out the coherent integration of Lms, carry out the FFT transformation of QI point to Q Lms coherent integration results, through the formula
其中，表示中间变量估计值，D表示峰值左右两侧谱线幅度差值，Q表示相干累积的段数，QI表示FFT点数，即有Q个Lms相干积分，做点数为QI的FFT变换，G表示FFT的峰值，α1取4/π。fini表示差分相干所得到的频率估计值，Nc为扩频码周期长度，表示高精度载波估计值。进行频偏估计，然后对初次补偿后的数据进行第二次补偿，重新按照参照图4的方法进行J次迭代后，将最终捕获数据传输给弱信号跟踪环节，进行跟踪处理。in, Represents the estimated value of the intermediate variable, D represents the amplitude difference between the left and right sides of the peak, Q represents the number of coherent accumulation segments, QI represents the number of FFT points, that is, there are Q Lms coherent integrals, do the FFT transformation with the number of points QI , and G represents For the peak value of FFT, α1 takes 4/π. fini represents the frequency estimation value obtained by differential coherence, Nc is the period length of the spreading code, Indicates a high-precision carrier estimate. Perform frequency offset estimation, and then perform second compensation on the data after the first compensation, and then perform J iterations according to the method referring to Figure 4, and then transmit the final captured data to the weak signal tracking link for tracking processing.
本发明所使用的FPGA加DSP构建的嵌入式处理器，具体设计方案参照图5，通过天线接收“北斗二代”导航信号，经下变频模块将射频信号下变频到中频信号，然后采用十路的采样通道对信号进行采样，将采样后中频信号传输到FPGA模块，在该模块内完成从中频降到基频，NH码剥离和与本地信号进行相关实现相干积分，其中USB、RS232和Internet用于与上位机进行通信。将FPGA处理完的相干积分数据传入DSP中，由DSP完成完成差分相干的任务以及高精度频率估计，采用双DSP大大提高了运算速度降低了执行时间。DSP模块也可以使用其它具有类似功能的处理器实现，如ARM；本领域研究人员可以根据实际条件选择合适的器件。The embedded processor constructed by the FPGA and DSP used in the present invention, with reference to Figure 5 for the specific design scheme, receives the "Beidou II" navigation signal through the antenna, and down-converts the radio frequency signal to an intermediate frequency signal through the down-conversion module, and then adopts ten-way The sampling channel samples the signal, transmits the sampled intermediate frequency signal to the FPGA module, and completes the reduction from the intermediate frequency to the base frequency in the module, NH code stripping and correlation with the local signal to achieve coherent integration, among which USB, RS232 and Internet use To communicate with the host computer. The coherent integration data processed by the FPGA is transferred to the DSP, and the DSP completes the task of differential coherence and high-precision frequency estimation. The use of dual DSPs greatly improves the operation speed and reduces the execution time. The DSP module can also be implemented using other processors with similar functions, such as ARM; researchers in this field can choose suitable devices according to actual conditions.
综上所述，仅为本发明之较佳实施例，不以此限定本发明的保护范围，凡依本发明专利范围及说明书内容所作的等效变化与修饰，皆为本发明专利涵盖的范围之内。In summary, it is only a preferred embodiment of the present invention, and does not limit the protection scope of the present invention. All equivalent changes and modifications made according to the scope of the patent of the present invention and the content of the specification are all covered by the patent of the present invention. within.
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| CN201310654468.8ACN103645483B (en) | 2013-12-09 | 2013-12-09 | Beidou signal capturing method in weak signal environment |
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| CN201310654468.8ACN103645483B (en) | 2013-12-09 | 2013-12-09 | Beidou signal capturing method in weak signal environment |
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