JP4828308B2 - Phase modulation sequence playback device - Google Patents

Description

  The present invention relates to direct spread spectrum communication, and more particularly to a phase modulation sequence reproducing apparatus that acquires a phase modulation sequence of a spread code that is phase-modulated by a phase modulation sequence from a spread spectrum signal.

In the direct spread spectrum method, the signal is spread by using a spreading code on the transmitting side, and the receiving side uses the same spreading code as the transmitting side to despread the received signal at the timing synchronized with the transmitting side. Read the signal. In a GPS (Global Positioning System), a signal transmitted from a GPS satellite is a signal that has been directly spectrum spread using a spreading code called a C / A code (Coarse / Acquisition Code). Since the C / A code is determined for each GPS satellite, the reception side despreads the received signal using the C / A code of the GPS satellite to be received to obtain a signal from the desired GPS satellite.
In GPS, the distance between a GPS satellite and a GPS positioning device is measured using the delay time of a signal, and the position of the GPS positioning device is determined based on the distance from a plurality of GPS satellites. In the initial state, since the distance between the GPS satellite and the GPS positioning device is unknown, the delay time is also unknown. Therefore, the despread timing cannot be synchronized on the receiving side.

  In general, a pseudorandom code is used as a spreading code for direct spectrum spreading. The C / A code used for spreading the GPS signal is a pseudo-random code called a gold series. A signal directly spread using a pseudo-random code can be detected on the receiving side if the timing of despreading is synchronized. However, if the timing is shifted, the signal cannot be detected. In order to solve this problem, the receiving side shifts the despreading timing little by little and searches for the timing at which the signal can be detected, thereby synchronizing the despreading timing. That is, using the synchronization timing as a variable, the correlation value between the received signal and the spread code generated by itself is obtained (cross-correlation function CCF; hereinafter simply referred to as “correlation function”), and the absolute value of the correlation value is obtained. If the timing at which the value is maximized (spreading code start time) is obtained, the despreading timing can be synchronized.

By the way, when the GPS positioning device is in a weak place such as indoors, the S / N ratio (Signal / Noise Ratio) is small and the signal is buried in noise, so the timing of despreading is synchronized. Even if it is possible, the problem is that the absolute value of the correlation value is not always maximized. As a method for solving this, conventionally, correlation has been performed for a long time. The reason for this is that the direct spectrum spread signal is basically a repetition of the spreading code, so if correlation is made over multiple periods of the spreading code, the signals will synergize, noise will cancel each other, and the S / N ratio will improve. This is because the signal can be detected. However, the direct spectrum spread signal is not simply a repetition of the spreading code, but is phase-modulated by the information code at every predetermined period of the spreading code. For example, when a binary coded signal is directly spectrum spread, the repetition of the spreading code corresponds to “0” of the original signal and the polarity of the spreading code is reversed to “1” of the original signal. Corresponds. For example, in a GPS signal, one cycle of the C / A code is 1 millisecond. One unit of 20 C / A codes, which corresponds to 1 bit of navigation data. Therefore, there is a possibility that the polarity of the C / A code is reversed every 20 milliseconds.
If the correlation is taken across the boundary where the value of the original signal changes, the signals cancel each other because the polarity of the spreading code is reversed. As a result, signal detection becomes difficult.

  As a method for solving this problem, for example, there is a technique described in Patent Document 1. According to this technology, the headquarter server in a good reception state receives GPS signals and obtains navigation data. The GPS positioning device receives navigation data from the headquarter server when the radio wave is weak and it is difficult to synchronize the timing of despreading. The GPS positioning device uses the navigation data received from the headquarters server to invert the polarity of the received GPS signal and then take a correlation. This makes it possible to detect the despreading synchronization timing without canceling the signals even if the correlation over a long period of time exceeds the boundary where the value of the original signal changes.

JP 2001-349935 A

  In the conventional technique described in Patent Document 1, when the reception status of the GPS positioning device is poor, the headquarters server receives the navigation data instead, and the GPS positioning device detects the despreading synchronization timing using the navigation data. However, for that purpose, it is necessary to provide a headquarters server separately, and since the GPS positioning device and the headquarter server need to communicate with each other, the GPS positioning device has a communication function for that purpose. Need arises. As a result, the system becomes large and affects the manufacturing cost of the GPS positioning device. Moreover, since the GPS positioning device itself becomes heavier due to the addition of the communication function, portability deteriorates. Further, when communication with the headquarter server becomes impossible due to some kind of failure, there is a problem that the despreading synchronization timing cannot be detected.

  The present invention was made to solve the above problems, and even when the radio wave condition is poor and the S / N ratio is small, the synchronization timing of the despreading is efficiently detected from the direct spread spectrum signal, An object of the present invention is to obtain a phase modulation sequence reproducing apparatus that correctly estimates a navigation data bit sequence, that is, a phase modulation sequence.

  A phase modulation sequence reproducing device according to the present invention acquires a spread spectrum signal, divides a spread signal of a predetermined length into a plurality of continuous sections and stores the spread signal, and a code having the same format as the spread code of the spread signal A frequency shift for one continuation section of the spread signal acquired by the spread signal acquisition section, a spread code storage section for storing and outputting a plurality of phase modulation sequences of a predetermined length, However, a correlation function between the frequency-shifted signal and the spreading code output from the spreading code storage unit is calculated, a correlation processing unit that calculates the sum of the correlation functions, and a correlation function calculated by the correlation processing unit For the sum, after correcting the phase modulation according to the phase modulation sequence of a predetermined length in the phase modulation sequence storage unit, the spread code start time, frequency shift, phase modulation sequence, and phase modulation boundary are accumulated as variables. An integration processing unit that calculates the function, a detection unit that detects each candidate of the spread code start time, frequency shift, phase modulation sequence, and phase modulation boundary from the integrated correlation function calculated by the integration processing unit, and detection By combining the frequency optimum value calculation unit for calculating the optimum value of the frequency shift from the frequency shift candidates detected by the unit and the phase modulation sequence detected for each continuous section of the spread signal, A phase modulation sequence concatenation processing unit for generating a modulation sequence is provided, and the correlation processing unit correlates with the spread signal for the same one continuation period only in the vicinity of the optimum value of the frequency shift calculated by the frequency optimal value calculation unit. The integration processing unit performs the integration process again on the sum of the correlation functions obtained by the second correlation process, and the detection unit detects the integrated correlation function obtained by the second integration process. place Performed again, spread code start time obtained by again detecting process of detecting unit, a frequency shift and phase modulation series, and outputs it as data to be used in the phase modulation sequence connection section.

  According to the present invention, in consideration of polarity inversion of the repetitive signal in the spread spectrum signal, a plurality of possibilities are correlated to obtain an integrated correlation function, and unit signal start time candidates are determined based on the obtained integrated correlation function. Since it narrows down, it is not necessary to know in advance about polarity inversion of the repetitive signal. In addition, since the correlation function is added again using the optimum value of the frequency shift calculated from the narrowed candidates, the phase modulation sequence having the largest correlation value can be detected, so that the detected phase modulation sequence can be detected. Reduces the probability that is different from the true phase modulation sequence. Therefore, even when the radio wave condition is poor and the S / N ratio is small, it is possible to efficiently detect the despread synchronization timing directly from the spread spectrum signal and correctly estimate the navigation data bit sequence, that is, the phase modulation sequence. It becomes possible.

Embodiment 1 FIG.
The present invention relates to a phase modulation sequence reproducing apparatus that detects a spread code start time and a phase modulation sequence in spread spectrum communication, and can be used for CDMA communication and wireless LAN communication, for example. A GPS positioning apparatus to which the phase modulation series reproducing apparatus is applied will be described by taking a GPS signal as an example.
An example of the GPS signal format is shown in FIG. The GPS signal is a signal obtained by performing spread spectrum modulation on a CW (Continuous Wave) signal having a carrier center frequency of 1.57542 MHz using a C / A code that is a spread code (this is referred to as a spread spectrum signal). The C / A code is phase-modulated by an information code sequence called a navigation data bit sequence (mainly called a phase modulation sequence in this invention) with 20 periods as one unit. Therefore, the GPS receiver can obtain satellite orbit information by decoding this information code sequence. Also, by performing correlation calculation with the received GPS signal using the same spreading code as the C / A code generated inside the receiver, the spreading code start time (delay time) is known from the correlation function (peak position). Can do. In addition, positioning calculation can be performed by using the delay time of each satellite and the decoded satellite orbit information.

  In the first embodiment, the received GPS signal is divided into predetermined continuation sections, and the correlation function between the shifted signal and the spread code is calculated while frequency shifting the received GPS signals in the divided continuation sections, Thereafter, a round-robin search of the phase modulation sequence and a frequency shift search of the C / A code are performed, and correlation calculation and coherent integration processing are performed. Here, coherent integration means that a spread code (C / A code) of a received GPS signal is divided every C / A code period, and each divided C / A code and C / A generated inside the receiver. The cross-correlation function with the code is added within the continuation interval, and the addition result is accumulated by adding together the polarity based on the phase modulation sequence (navigation data) detected by itself or the navigation data received from the headquarters server. Say. Here, a description will be given by taking as an example a case where the continuous section, that is, the number of navigation data bits for performing coherent integration is 5 (= 100 milliseconds).

1 is a block diagram showing a functional configuration of a GPS positioning apparatus to which a phase modulation sequence reproducing apparatus according to Embodiment 1 of the present invention is applied.
The GPS positioning apparatus includes a GPS antenna 101, a receiving unit 102, an A / D (analog / digital) conversion unit 103, a data storage unit 104, a data reading unit 105, a spreading code generation unit (spreading code storage unit) 106, and a correlation processing unit. (Integrated correlation function calculation unit) 108, phase modulation sequence generation unit (phase modulation sequence storage unit) 107, integration processing unit (integrated correlation function calculation unit) 109, detection unit 110, data holding unit 111, frequency optimum value calculation unit 112 A phase modulation sequence concatenation processing unit 113, a positioning calculation unit 114, and a position display unit 115. Of these, the portion surrounded by a solid line is the phase modulation sequence reproducing device of the present invention, and the portion surrounded by a broken line is a spread signal acquisition unit.

Next, the operation will be described.
In FIG. 1, first, when a GPS signal is received by the GPS antenna 101, processing such as amplification and frequency conversion is performed by the reception unit 102, and then A / D conversion is performed by the A / D conversion unit 103 to obtain digital data ( (Spread spectrum signal as shown in FIG. 2). In addition, although the structure which performs A / D conversion after frequency-converting to IF (Intermediate Frequency) frequency is also considered, the structure which frequency-converts to a baseband and A / D-converts a baseband signal is demonstrated here. The A / D converted data is recorded in the data storage unit 104. In the data storage unit 104, in order to search for the navigation data bit boundary, the correlation calculation process is shifted every one cycle of the C / A code, and is performed up to 20 milliseconds. save. Further, the received spread signal data to be stored is further divided into a plurality of blocks (continuation sections) having a time length of 1 millisecond and stored. The data reading unit 105 reads the first block of the received spread signal stored in the data storage unit 104 and sends it to the correlation processing unit 108.

ここで、ｙ（ｑ，ｎ）はデータ読出し部１０５が送った受信拡散信号を表す。ｑは受信信号を１ミリ秒毎に分割したｑ番目の信号ブロックを示し、ｎはその信号ブロックにおけるｎ番目のサンプルデータを示す。ｖ（ｎ）は拡散符号発生部１０６で生成したＣ／Ａコード、ΔＴはＡ／Ｄ変換部１０３のサンプリング周期、Δｆは周波数ステップである。航法データビット系列の正確な推定のためにはコヒーレント積分時間をＴｃとして、１／２／Ｔｃ以下にΔｆを設定する必要がある。それはＴｃ時間内に信号位相がπ／２変化すると、航法データビット系列による位相変化と判別できなくなってしまうためである。ＮはＣ／Ａコード１周期（＝１ミリ秒）内に含まれるサンプル数（＝ｆ_s ／１０００）であり、ｉは相関関数のラグ、ｎ_f は周波数インデックスである。また、＊は複素共役を意味する。ここで、信号遅延時間は、ｒ_yv（ｑ，ｉ，ｎ_f ）の絶対値が最大となるときのラグｉ_peakを用いて、ｉ_peakΔＴとして計算される。以後、ｉをラグ、ｉ_peakΔＴを遅延時間と呼ぶ。 The spread code generation unit 106 generates a C / A code corresponding to the number of the GPS satellite to be received, and interpolates and stores the C / A code in one chip according to the sampling frequency. The stored code is sent to the correlation processing unit 108. In correlation processing section 108, the received spread signal for the first block sent from data reading section 105 is frequency-shifted, and the frequency-shifted signal and the C / A code sent from spreading code generating section 106 are compared. The correlation function r _yv (q, i, n _f ) is calculated using the following equation.

Here, y (q, n) represents the received spread signal sent by the data reading unit 105. q indicates a q-th signal block obtained by dividing the received signal every 1 millisecond, and n indicates n-th sample data in the signal block. v (n) is a C / A code generated by the spread code generator 106, ΔT is a sampling period of the A / D converter 103, and Δf is a frequency step. For accurate estimation of the navigation data bit sequence, it is necessary to set Δf to be equal to or less than 1/2 / Tc, where Tc is the coherent integration time. This is because if the signal phase changes by π / 2 within the Tc time, it cannot be distinguished from the phase change due to the navigation data bit sequence. N is the number of samples (= f _s / 1000) included in one C / A code period (= 1 millisecond), i is the lag of the correlation function, and n _f is the frequency index. * Means a complex conjugate. Here, the signal delay time is calculated as i _peak ΔT using the lag i _peak when the absolute value of r _yv (q, i, n _f ) is maximum. Hereinafter, i is called lag and i _peak ΔT is called delay time.

ここで、ｎ_b は航法データビット境界を探索するインデックスであり、Ｃ／Ａコード２０周期分までシフトさせれば、その中には境界が必ず含まれることになるので、ｎ_b は０〜１９までの整数である。
このようにして計算された相関関数の総和ｓ＿ｒ_yvは積分処理部１０９に送られる。 FIG. 3 shows a time-frequency plot of the correlation function r _yv (q, i, n _f ) at an arbitrary q when the S / N ratio is relatively high. As shown in the figure, it can be seen that a signal peak is obtained. However, in a low S / N ratio environment, a peak as shown in the figure cannot be detected, and therefore a subsequent coherent integration process is required.
Next, the correlation processing unit 108 calculates a total of 20 correlation functions corresponding to one bit of navigation data (an example of an integrated correlation function). However, the navigation data bit boundary is unknown, and there is a possibility that an integration loss due to the shift of the bit boundary may occur only by performing phase modulation and addition. Therefore, navigation data bit boundaries, i.e. while shifting the position to start addition of the correlation function, to compute the sum S_R _yv of 20 each of the correlation functions as follows.

Here, n _b is an index for searching the navigation data bit boundary, and if it is shifted up to 20 C / A codes, the boundary is necessarily included therein, so that n _b is 0-19. It is an integer up to.
Sum S_R _yv correlation function calculated in this way is sent to the integration processing unit 109.

ここで、０は０位相変調、１はπ位相変調を示す。
以下、Ｂ_s の各要素をｂ_s （ｎ_s ，ｐ）と表現する。ここで、ｎ_s およびｐは、それぞれＢ_s の行番号と列番号であり、またそれぞれ、位相変調系列の総当りインデックスと航法データビットのインデックスを表している。
位相変調系列発生部１０７は、以上のようにして発生させた位相変調系列を積分処理部１０９に送る。 The phase modulation sequence generation unit 107 generates and stores a phase modulation sequence having a predetermined length, that is, a phase modulation sequence corresponding to 5 bits of navigation data. Since the absolute value of the integration result by the inverted bit sequence is the same, the pattern of the phase modulation sequence to be generated becomes two ways ^4. The phase modulation sequence B _s for 5 bits of navigation data is shown below.

Here, 0 indicates 0 phase modulation and 1 indicates π phase modulation.
Hereinafter, representing each element of _{B s b s (n s,} p) and. Here, n _s and p are the row number and the column number of B _s , respectively, and represent the round-robin index of the phase modulation sequence and the index of the navigation data bit, respectively.
The phase modulation sequence generation unit 107 sends the phase modulation sequence generated as described above to the integration processing unit 109.

相関関数の積算動作の概略を図４に示す。このようにして積分処理部１０９で得られる集積相関関数ｇ＿ｒ_yvは、遅延時間、周波数インデックス、航法データビット境界インデックスおよび位相変調系列のインデックスの４つのパラメータを持つ関数であり、これら全てのインデックスを変化させて計算する。算出された集積相関関数ｇ＿ｒ_yvは検出部１１０に送られる。 The integration processing section 109, the sum S_R _yv correlation function calculated by the correlation processing unit _{108 (p, i, n f} , n b) with respect to the phase modulation sequence generation unit 107 phase modulation sequence B _s which is generated by After correcting the phase modulation according to the above, an integrated correlation function is calculated to improve sensitivity. In other words, it corrects a phase modulation to the 20 sum S_R _yv of the correlation function, to perform coherent integration span multiple navigation data bits. Obtained by coherent integration integrated correlation function _{g_r yv (i, n f,} n b, n s) is given by the following equation.

FIG. 4 shows an outline of the correlation function integration operation. In this way, the integration processing unit integrated correlation function G_r _yv obtained in 109, the delay time, frequency index is a function with four parameters of the index of the navigation data bit boundaries index and phase modulation series, all these indices Change to calculate. The calculated integrated correlation function G_r _yv is sent to the detection unit 110.

In the detection unit 110, first, among the absolute values of the integrated correlation function G_r _yv calculated by integration processing unit 109 detects a correlation value exceeding the threshold set. Instead of setting the threshold value, the number of correlation values to be detected may be set in advance, and the absolute values of the integrated correlation function may be detected in descending order until the set value is satisfied. Next, a delay time, a frequency shift index, a navigation data bit boundary index, and a navigation data bit sequence index are detected from the detected correlation value, sent to the data holding unit 111 and stored.
When L correlation values are detected, parameters are set as p ^(l) , i ^(l) , nf ^(l) , nb ^(l) (l = 1, 2,..., L). Correlation value at that time is G_r _yv a ^{(i (l), nf (} l), nb (l), ns (l)). Further, G_r correlation value when the absolute value of the l correlation value is maximized _yv put and ^{(i (lpeal), nf (} lpeak), nb (lpeak), ns (lpeak)). The absence of ^{noise, i (lpeal), nb (} lpeak), correlation values in the frequency axis direction in _{^{ns (lpeak) | g_r yv (}} i (lpeal), nf, nb (lpeak), ns (lpeak)) | is As shown in FIG. In this case, the correlation value is a ^sinc function with the frequency shift true value as the center, and n _f ^(lpeak) Δf is closest to the frequency shift true value. The phase modulation series ^{_{b s (n s (lpeak)}} , p) at this time coincides with the navigation data bit sequence the true value. However, when there is an influence of noise and the correlation value is disturbed, it becomes as shown in FIG. In this case, n _f ^(lpeak) Δf is not necessarily closest to the true value of the frequency shift. The phase is rotated by the frequency difference from the frequency shift true value, and the estimated phase modulation sequence b _s (n _s ^(lpeak) , p) may be different from the true value.

7 is a true value of the navigation data bit sequence 0,0,0,0, of the absence of noise ^{i (lpeal), nb (lpeak} ), the integrated correlation function in _{^{ns (lpeak) s_r yv (p}} , i ^(lpeal) , n _f ^(lpeak) , nb ^(lpeak) ) are shown on the complex plane. It can be seen that although there is a phase change due to the frequency difference as the navigation bits increase, the phase rotation is within π / 4, and 0, 0, 0, 0 is estimated as the phase modulation sequence at this time. On the other hand, FIG. 8 shows the integrated correlation function when there is noise on the complex plane. Compared to the case without noise, the difference between n _f ^(lpeak) Δf and the true value of the frequency offset increases, so the amount of phase rotation increases, and the third and fourth bits have a phase of π / 2 or more. It turns out that it is reversed. The phase modulation sequence estimated in this case is 0, 0, 1, 1.

Therefore, in order to obtain an accurate navigation data bit sequence, it is first necessary to know an accurate frequency shift. For this purpose, a frequency optimum value calculation unit 112 is provided. The frequency optimum value calculation unit 112 calculates the optimum value of the frequency shift from the L frequency shift candidates detected by the detection unit 110 stored in the data holding unit 111 as follows.
Since the frequency distribution of the integrated correlation function is symmetrical as shown in FIG. 5, the median value of the frequency shift detected by the detection unit 110 is expected to approach the true value. Specifically, the L frequency shifts detected are rearranged in descending order, and a value n _f ^(center) Δf having the ^{center in} the order is extracted, and this is set as the optimum value. As another method, a frequency shift that is significantly different from the median value n _f ^(center) Δf out of L frequency shifts is excluded, and the remaining frequency shifts are averaged to obtain a frequency close to the true value. The shift n _f ^(mean) Δf may be obtained and set as an optimum value. The optimum value of the frequency shift calculated in this way is passed to the correlation processing unit 108.

In the correlation processing unit 108, the optimal value of the frequency shift calculated by the frequency optimal value calculation unit 112, that is, a value n _f ^(center) Δf close to the true value of the frequency shift, for the received spread signal of the block processed first. Alternatively, the correlation process is performed again around n _f ^(mean) Δf. The frequency range in this case is set to n _f ^(center) Δf−0.5Δf to n _f ^(center) Δf + 0.5Δf, for example. With respect to the sum of the correlation functions calculated by the correlation processing unit 108, the integration correlation unit 109 calculates the integrated correlation function again, and the detection unit 110 also calculates the delay time, frequency offset, navigation data bit boundary, and A navigation data bit sequence is detected. In this case, the phase modulation sequence when the absolute value of the correlation value is maximized is estimated. Since the phase modulation sequence estimated in this way has a frequency shift close to a true value, phase rotation as shown in FIG. 8 does not occur, and the possibility that the phase data is a true value of the navigation data bit sequence increases. The delay time, frequency offset, navigation data bit boundary, and navigation data bit sequence obtained as described above are sent to the phase modulation sequence concatenation processing unit 113.
When the processing on the reception spread signal of the first block is completed, the data storage unit 104 stores the reception spread signal of the next block, that is, a signal of 80 to 200 milliseconds. Note that the next block overlaps the first block by 40 milliseconds. The same processing as described above is performed in the next block, and the calculated delay time, frequency shift, navigation data bit boundary, and navigation data bit sequence are sent to the phase modulation sequence concatenation processing unit 113.

  In the phase modulation sequence concatenation processing unit 113, the phase modulation sequence detected in the first block (continuation interval) of the received spread signal and the phase modulation sequence detected in the next block (continuation interval) are connected to each other for a long time. An information code sequence is generated. Specifically, the navigation data bit sequence detected in the first continuation interval 0 to 120 milliseconds and the navigation data bit sequence detected in the next continuation interval 80 to 200 milliseconds are connected. The navigation data bit sequence detected in the first continuation interval cannot simply be connected to the navigation data bit sequence detected in the next continuation interval. This is because there is a slight error between the true value of the frequency shift and the estimated frequency shift, and this error causes the phase of the GPS signal to change between the first continuous section and the next continuous section. This is because there is a possibility of inversion. Therefore, the phase modulation sequence concatenation processing unit 113 performs processing by overlapping the first continuation interval and the next continuation interval with one bit or a plurality of bits of the navigation data bit sequence, thereby completing the end of the first continuation interval. One bit or a plurality of bits coincides with the first one bit or a plurality of bits of the next continuation section. If the overlapping navigation data bit sequences match, the navigation data bit sequences of each other are connected together, while if the overlapping navigation data bit sequences are inverted, one of the navigation data bit sequences is reversed. Can be obtained by inverting and joining them to obtain a continuous long-time bit sequence. For example, an example in which the continuous section is overlapped by one navigation data bit will be described. If the navigation data bit sequence estimated in the first continuous section is 0, 1, 0, 1, 0 and the bit sequence estimated in the next section is 1, 1, 0, 0, 1, Since the overlapping navigation bits are inverted, the next bit sequence is inverted and connected, and the navigation data bits for two continuous sections of 0, 1, 0, 1, 0, 0, 1, 1, 0 A series can be obtained.

By repeating the above operation for at least four satellites for 30 seconds, a navigation data bit sequence for 30 seconds is obtained. In order to perform positioning calculation, orbit information of the satellite is necessary, but when no information is given, it is obtained by decoding the navigation data bit sequence. The satellite orbit information is called almanac, and is obtained by decoding the navigation data bit sequence for 30 seconds. Therefore, the navigation data bit sequence, delay time, frequency shift, and navigation bit boundary for 30 seconds of the obtained four satellites are sent to the positioning calculation unit 114. Also, after obtaining almanac information for one satellite, search for three or more satellites in good observation state, limit the frequency shift search range for that satellite, and perform the above correlation processing, integration processing, and detection processing But it ’s okay.
Next, the positioning calculation unit 114 performs positioning calculation using the satellite orbit information obtained by decoding the delay time and the navigation data bit sequence sent from the phase modulation sequence concatenation processing unit 113, and the GPS positioning device 100. And the position information obtained is sent to the position display unit 115 for display.

  As described above, according to the first embodiment, a correlation process for calculating the sum of correlation functions and an integrated correlation function are calculated for each of a plurality of continuous sections obtained by dividing the acquired spread spectrum signal having a predetermined length. The integration process and the detection process for detecting each candidate of the spread code start time, frequency shift, phase modulation sequence and phase modulation boundary are performed twice, and from among the frequency shift candidates obtained in the first detection process Since the optimum value of the frequency shift is calculated and the correlation process in the second process for the spread signal for the same one continuous section is performed only around the optimum value of the frequency shift obtained the first time, the correlation value is The largest phase modulation sequence can be detected. Therefore, even when the radio wave condition is poor and the S / N ratio is small, the synchronization timing of the despreading is efficiently detected directly from the spread spectrum signal, and the probability of error in the navigation data bit sequence, that is, the phase modulation sequence is reduced. It becomes possible.

Embodiment 2. FIG.
In the first embodiment, the median value of the frequency shift detected by the detection process is calculated, and the correlation process, the integration process, and the detection process are performed again around the median value, so that the detected phase modulation sequence becomes the navigation data. The possibility that it is the true value of the bit series is increased. However, if the number of frequency shifts when calculating the frequency shift median value is small, the difference between the median value and the true value becomes large, and the possibility that the phase modulation sequence estimated in the second detection process is erroneous will increase. End up. Alternatively, in the second detection process, when an erroneous peak that is not a signal is detected, the estimated phase modulation sequence is not a navigation data bit sequence. In the second embodiment, a method for solving this problem will be described.

FIG. 9 is a block diagram showing a functional configuration of a GPS positioning apparatus to which the phase modulation sequence reproducing apparatus according to Embodiment 2 of the present invention is applied. In the figure, the same reference numerals are given to the functional units corresponding to FIG. 1 of the first embodiment. The second embodiment has a configuration in which a start point optimum value calculation unit 901 and a phase modulation boundary optimum value calculation unit 902 are newly added to the configuration of the first embodiment.
The start point optimum value calculation unit 901 is a means for calculating the optimum value at the spread code start point from the spread code start point candidates detected by the detector 110. The phase modulation boundary optimum value calculation unit 902 is means for calculating the optimum value of the phase modulation boundary based on the phase modulation boundary candidate detected by the detection unit 110.
The data storage unit 104 stores, for example, data from 0 to 700 ms of the received spread signal. As in the first embodiment, the correlation processing, integration processing, and detection processing are performed every 100 ms, and data for 120 ms is handled as one block for navigation bit boundary search. For the phase modulation sequence concatenation processing unit 113, the data after the second block are overlapped by about 20 ms to 40 ms. For example, in the case of overlapping by 20 ms, 80 ms to 200 ms are stored as the second block, and a total of 6 blocks are stored.

  The data reading unit 105 reads the received spread signal of the first block (0 to 120 ms) from the data storage unit 104 and sends it to the correlation processing unit 108. Correlation processing unit 108, integration processing unit 109, and detection unit 110 perform the same operations as in the first embodiment. The correlation value, delay time, frequency shift, navigation data bit sequence, and navigation data bit boundary detected by the detection unit 110 are sent to and stored in the data holding unit 111. Next, the data reading unit 105 reads the received signal data of the second block (80 to 200 ms) from the data storage unit 104, and performs similar processing in the correlation processing unit 108, the integration processing unit 109, and the detection unit 110. The above operations are read and repeated for all six blocks, and the detected correlation value, frequency shift, navigation data bit sequence, and navigation data bit boundary of each block are stored in the data holding unit 111.

In the data holding unit 111, the frequency shift candidate detected in each block is the frequency optimum value calculation unit 112, the delay time candidate is the start time optimum value calculation unit 901, and the navigation data bit boundary is the phase modulation boundary optimum value calculation unit. Send to 902.
The frequency optimum value calculation unit 112 calculates a median value from the frequency shifts detected in all blocks sent from the data holding unit 111. If the frequency shift does not change between all blocks (500 ms), the median value n _f ^(center) Δf of the frequency shift is assumed to approach the true value, and this median value is set as the optimum value of the frequency shift. . Further, an optimum value may be obtained by calculating an average value n _f ^(mean) Δf obtained by averaging the frequency shifts of all blocks by excluding a frequency shift value greatly deviating from the ^center value n _f ^(center) Δf of the frequency shift. Good. The optimum value of the frequency shift calculated in this way is sent to the correlation processing unit 108.
The start time optimum value calculation unit 901 calculates a median value i ^(center) ΔT from the delay times (spread code start time candidates) detected in all blocks sent from the data holding unit 111. Since the delay time shifts due to the frequency shift between all blocks (700 ms), the median value of delay time i ^(center) ΔT is assumed to be an average value between all blocks. The median value of the delay time is set as the optimum value at the start of the spreading code. The optimum value at the spread code start time calculated in this way is sent to the correlation processing unit 108.

In the phase modulation boundary optimum value calculation unit 902, the value that is the mode value (the value that has been detected most frequently) among the navigation bit boundary values of all detected blocks sent from the data holding unit 111 is calculated. Calculate and set the optimum value of the navigation data bit boundary (phase modulation boundary). The navigation data bit boundary is an integer value from 0 to 19, and is constant regardless of the received signal data length. That is, it does not change with the data processing time. However, in a block having the same navigation data bit sequence (for example, when the navigation data bit sequence is 0, 0, 0, 0, 0), the absolute value of the integrated correlation value is no matter where the navigation bit boundary is set. Since the values are the same, the possibility that the detected navigation bit boundary is a true value is as low as 1/20. However, when the navigation data bit sequence is, for example, 1, 0, 1, 0, 1, the absolute value of the correlation value becomes 0 to 18/20 times due to a mistake in the navigation data bit sequence boundary, and is detected by the detection unit 110. There is a high possibility that the obtained bit sequence boundary is a true value. Therefore, it is possible to estimate the true value of the navigation bit boundary by using the navigation bit boundary detected in a plurality of blocks. Since the mode value of the navigation data bit boundary is assumed to approach the true value of the bit boundary, the mode value nb ^(mode) of the navigation bit boundary is set as the optimum value of the navigation data bit boundary. The optimal value of the navigation data bit boundary calculated in this way is sent to the integration processing unit 109.

Next, the data reading unit 105 reads the received signal data of the first block (0 to 100 ms) from the data storage unit 104 again and sends it to the correlation processing unit 108. In correlation processing section 108, the received spread signal of the first block sent is frequency-shifted around the optimum value of the frequency shift obtained from the first processing data in frequency optimum value calculating section 112, and the optimum value at the start point Within the delay time range (start time range) set based on the optimum value of the spread code start time obtained from the first processing data in the calculation unit 901, the correlation process with the spread code of the spread code generating unit 106 is performed again, the sum of the correlation function _{s_r yv (p, i, n} f, n b) is calculated. In this case, the optimum value of the frequency shift is the frequency shift median value n _f ^(center) Δf, the frequency shift average value n _f ^(mean) Δf, and the lag median value i ^(center). , (N _f ^(center) ± 0.5) Δf, and the delay time range is set to i ^(center) ΔT ± 1 μsec. Moreover, the structure which changes the range to search by the detected frequency shift may be sufficient.

The integration processing section 109, the sum S_R _yv correlation function calculated again by the processing of the correlation processing unit _{108 (p, i, n f} , n b) and phase modulation sequence B _s of the phase modulation series generator 107 and sent And the coherent integration between C / A code periods is performed again only around the optimum value of the navigation data bit boundary obtained from the first series of processing data by the phase modulation boundary optimum value calculation unit 902 as the navigation data bit boundary. , calculated integrated correlation function _{g_r yv (i, nf, nb} , ns) a.
In the detection unit 110 again integrated correlation function is calculated in the processing G_r _yv the integration processing section 109 (i, nf, nb, ns) when the absolute value of the maximum delay time estimates, frequency shift estimate Detecting navigation data bit boundaries and phase modulation sequences.
The above processing operation is repeated for the received spread signals of all blocks (0 to 700 ms), and the delay time estimated value, frequency shift estimated value, navigation bit boundary and phase modulation sequence detected for all blocks are stored in the data holding unit 111. Saved.

Next, the phase modulation sequence, delay time estimation value, frequency shift estimation value, and phase modulation boundary estimation value of all blocks stored in the data holding unit 111 are passed to the phase modulation sequence concatenation processing unit 113. The phase modulation sequence concatenation processing unit 113 concatenates the phase modulation sequences of all blocks in the same manner as in the first embodiment, and generates a navigation data bit sequence of 0 to 700 ms.
The above operation is performed on 1-second data stored in the data storage unit 104, and a delay time, a frequency shift, a navigation bit boundary, and a navigation data bit sequence for one second are acquired. These operations are repeated for other satellites, and the delay time, frequency shift, navigation bit boundary, and navigation data bit sequence of a total of four or more satellites are acquired. After acquiring each parameter of four or more satellites, the data storage unit 104 acquires reception signal data for the next one second.
The delay time, frequency shift, and navigation data bit sequence for 30 seconds regarding four or more satellites obtained by repeating the above operation are sent to the positioning calculation unit 115. The positioning calculation unit 115 demodulates the navigation message from the navigation data bit sequence, calculates the position from the demodulated navigation message and the delay time of each satellite, and calculates the position of the GPS positioning device.

  As described above, according to the second embodiment, the optimum value of the frequency shift, the optimum value of the delay time (spreading code start point), and the navigation bit boundary (phase modulation) in the first processing of all the blocks of the received spread signal Boundary) is calculated, and all blocks are processed again, and correlation processing is performed around the optimal value of the frequency shift and within the delay time range set based on the optimal value of the delay time, and the navigation bit boundary Since the integration process is performed only in the vicinity of the optimal value of, since unnecessary correlation peaks can be removed and only true correlation peaks can be detected, the estimated phase modulation sequence may become a true navigation data bit sequence. Increasingly, positioning is possible even at a lower signal-to-noise ratio such as indoors.

It is a block diagram which shows the function structure of the GPS positioning apparatus to which the phase modulation series reproducing | regenerating apparatus by Embodiment 1 of this invention is applied. It is a time chart which shows the structure of a GPS received signal. It is explanatory drawing which shows the time-frequency plot example of the correlation function computed with the correlation process part which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows the example of the integrated correlation function calculated with the integration process part which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows an example of the expression on the frequency axis of an integrated correlation function when there is no noise. It is explanatory drawing which shows an example of the expression on the frequency axis of an integrated correlation function in case there exists noise. It is explanatory drawing which shows an example of the expression on the complex plane of an integrated correlation function when there is no noise. It is explanatory drawing which shows an example of the expression on the complex plane of an integrated correlation function when there exists noise. It is a block diagram which shows the function structure of the GPS positioning apparatus to which the phase modulation series reproducing | regenerating apparatus by Embodiment 2 of this invention is applied.

Explanation of symbols

101 GPS antenna, 102 receiving unit, 103 A / D conversion unit, 104 data storage unit, 105 data reading unit, 106 spreading code generation unit (spreading code storage unit), 107 phase modulation sequence generation unit (phase modulation sequence storage unit) 108 correlation processing unit 109 integration processing unit 110 detection unit 111 data holding unit 112 frequency optimum value calculation unit 113 phase modulation sequence concatenation processing unit 114 positioning calculation unit 115 position display unit 901 start point optimum value Calculation unit, 902 Phase modulation boundary optimum value calculation unit.

Claims (9)

A spread signal acquisition unit that acquires a spread spectrum signal and divides and stores a spread signal of a predetermined length into a plurality of continuous sections;
A spreading code storage unit that stores and outputs a code of the same format as the spreading code of the spread signal;
A phase modulation sequence storage unit for storing and outputting a plurality of phase modulation sequences of a predetermined length;
While shifting the frequency of one continuation portion of the spread signal acquired by the spread signal acquisition unit, the correlation function between the frequency shifted signal and the spread code output from the spread code storage unit is calculated, A correlation processing unit for calculating the sum,
After correcting the phase modulation according to the phase modulation sequence of a predetermined length in the phase modulation sequence storage unit with respect to the sum of correlation functions calculated by the correlation processing unit, the spread code start time, frequency shift, phase An integration processing unit for calculating an integrated correlation function using a modulation sequence and a phase modulation boundary as a variable;
From the integrated correlation function calculated by the integration processing unit, a detection unit that detects each candidate of a spread code start time, a frequency shift, a phase modulation sequence, and a phase modulation boundary;
Among the frequency shift candidates detected by the detection unit, a frequency optimum value calculation unit that calculates an optimum value of the frequency shift;
A phase modulation sequence concatenation processing unit that connects phase modulation sequences detected for each continuation section of the spread signal and generates a phase modulation sequence for a long time,
The correlation processing unit performs correlation processing again only on the periphery of the optimum value of the frequency shift calculated by the frequency optimal value calculation unit for the same spread signal for one continuous section, and the integration processing unit The integration process is performed again on the sum of the correlation functions obtained by the correlation process, and the detection unit performs the detection process again on the integrated correlation function obtained by the second integration process. A phase modulation sequence reproducing apparatus that outputs a spread code start point, a frequency shift, and a phase modulation sequence obtained by the detection processing as described above as data used in the phase modulation sequence concatenation processing unit. Get the spectrum spread signal, a spread signal acquisition unit to store by dividing the spread signal of a predetermined length into a plurality of continuous sections,
A spreading code storage unit that stores and outputs a code of the same format as the spreading code of the spread signal;
A phase modulation sequence storage unit for storing and outputting a plurality of phase modulation sequences of a predetermined length;
Outputs the frequency-shifted signal and the spread code storage unit while frequency-shifting the spread signal of the continuous section to be processed for each continuous section of the spread signal of a predetermined length acquired by the spread signal acquisition unit A correlation processing unit that calculates a correlation function with the spread code, and calculates a sum of correlation functions for each continuous section;
After correcting the phase modulation in accordance with the phase modulation sequence of a predetermined length in the phase modulation sequence storage unit for each of the sum of correlation functions for each continuation interval calculated by the correlation processing unit, the spread code start point An integration processing unit that calculates an integrated correlation function for each continuous section using a frequency shift, a phase modulation sequence, and a phase modulation boundary as variables,
From the integrated correlation function for each continuation interval calculated by the integration processing unit, a detection unit that detects each candidate of the spread code start time, frequency shift, phase modulation sequence, and phase modulation boundary for each continuation interval;
A frequency optimum value calculating unit for calculating an optimum value of the frequency shift, from among frequency shift candidates of all the continuous sections of the spread signal of the predetermined length detected by the detection unit;
A start time optimum value calculating unit for calculating an optimum value of the spread code start time from among the spread code start time candidates of all the continuous sections of the spread signal of the predetermined length detected by the detection unit;
A phase modulation boundary optimum value calculating unit for calculating an optimum value of the phase modulation boundary from among candidates for phase modulation boundary of all the continuous sections of the spread signal of the predetermined length detected by the detection unit;
A phase modulation sequence concatenation processing unit that connects phase modulation sequences detected for each continuation section of the spread signal and generates a phase modulation sequence for a long time,
The correlation processing unit is arranged around the optimum value of the frequency shift calculated by the frequency optimum value calculating unit and for the start time optimum value calculating unit for each continuous section of the same spread signal processed first. The correlation processing is performed again within the start time range set based on the calculated optimum value of the spread code start time, and the integration processing unit performs phase modulation on the sum of each correlation function obtained by the second correlation processing. The integration process is performed again only around the optimum value of the phase modulation boundary calculated by the boundary optimal value calculation unit, and the detection unit performs the detection process again for each integrated correlation function obtained by the second integration process, A phase modulation sequence reproduction apparatus, characterized in that the spreading code start time, frequency shift, and phase modulation sequence obtained by re-detection processing are output as data used in the phase modulation sequence concatenation processing unit.   3. The phase according to claim 1, wherein the frequency optimum value calculation unit calculates a median value of the frequency shift candidates detected by the detection unit, and sets the median value as an optimum value of the frequency shift. Modulation sequence playback device.   The frequency optimum value calculating unit calculates a median value of the frequency shift candidates detected by the detecting unit, calculates an average value of frequency shift candidates around the median value, and sets the average value of the frequency shift as an optimum value. The phase modulation sequence reproducing device according to claim 1 or 2.   3. The start point optimum value calculating unit calculates a median value of the spread code start point candidates detected by the detection unit, and sets the median value as an optimum value at the spread code start point. Phase modulation sequence playback device.   3. The phase modulation boundary optimum value calculation unit calculates a mode value of phase modulation boundary candidates detected by the detection unit, and sets the mode value as an optimum value of the phase modulation boundary. Phase modulation sequence reproduction apparatus.   The detection unit compares the absolute value of the integrated correlation function with a predetermined threshold, and detects the spread code start time, frequency shift, phase modulation sequence, and phase modulation boundary from the integrated correlation function when the absolute value exceeds the threshold. The phase modulation sequence reproducing apparatus according to claim 1 or 2, wherein   The detection unit detects the absolute value of the integrated correlation function in descending order and until the integrated correlation function satisfies a predetermined number. From the detected integrated correlation function, the spread code start point, the frequency shift, the phase modulation sequence, and the phase modulation boundary are detected. The phase modulation sequence reproducing apparatus according to claim 1, wherein a candidate for the phase modulation sequence is detected.   The phase modulation sequence concatenation processing unit compares the phase modulation sequence detected in the predetermined continuation interval and the next continuation interval by the predetermined number of bits, and if the polarity of the compared bits is reversed, either The phase modulation sequence is inverted and connected. On the other hand, when the collated bits have the same polarity, the phase modulation sequences are connected as they are to obtain a phase modulation sequence for a long time. The phase modulation sequence reproducing device according to claim 1 or 2.

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