JP3577104B2 - Data transmission method - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a data transmission method for performing wireless data transmission between a transmitting station and a receiving station.
[0002]
[Prior art]
Various methods are known as modulation methods that can be used for wireless data transmission. For example, a method such as FSK (frequency shift keying) or MSK (minimum shift keying) is used for low power communication. This type of system has the advantage that the occupied frequency bandwidth is narrow, and is particularly suitable for applications with limited occupied bandwidth. In recent years, an SS (spread spectrum) scheme has attracted attention. This system is a system that enhances confidentiality and secures interference resistance by spreading a carrier spectrum using a PN (pseudo noise) code.
[0003]
[Problems to be solved by the invention]
However, each of the above modulation schemes has a problem. First, when a modulation scheme such as FSK or MSK is adopted, narrow band transmission can be realized, but the transmission distance is short due to the influence of S / N deterioration, and data errors are relatively easy to occur. There is a defect. In addition, when the SS is adopted, the transmittable distance is long, but the spectrum is spread, so that the occupied bandwidth is generally widened, which results in a result that goes against social demands for effective use of frequency resources.
[0004]
In particular, in order to perform synchronous transmission of data, the receiving station must ensure synchronization with the transmitting station. As a means for achieving this, frame synchronization has been widely used. That is, when data is framed, a synchronization pattern is added to this frame, and a clock (bit clock) for bit synchronization is inserted. The receiving station receives this frame, detects the frame synchronization pattern, and reproduces the bit clock to ensure synchronization with the transmitting station. When such synchronous transmission is performed while employing a modulation scheme such as FSK, MSK, etc., so-called out-of-synchronization occurs because synchronization information is more likely to be destroyed due to the occurrence of interference in a wireless transmission path than when SS is employed. The entire frame cannot be demodulated and reproduced normally.
[0005]
Therefore, conventionally, it has been difficult to perform synchronous transmission of data under low power or in a bad environment without increasing the occupied bandwidth due to the adoption of SS. Needless to say, if a high-precision synchronous clock is installed in each of the transmitting / receiving station and the receiving station, problems such as loss of synchronization due to poor transmission path quality will not occur, but such a clock can be realized at low cost. It is difficult.
[0006]
SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and has an effect of S / N deterioration despite using a modulation system with a narrow occupied frequency bandwidth such as FSK or MSK. It is an object of the present invention to realize a data transmission method that is less susceptible to data transmission, thereby extending a transmittable distance and reducing data errors. Another object of the present invention is to realize a data transmission method that does not require transmission and reception of synchronization information without mounting a high-precision clock synchronized with each other in the transmitting / receiving station and the receiving station.
[0007]
[Means for Solving the Problems]
To achieve the above object, engagement Lud over data transmission method of the present invention may generate in the transmitting station the PN code obtained by delaying the phase based on the value of the data, using a PN code generated as a modulated signal a step of wirelessly transmitting from a transmitting station narrowband signal modulated Te demodulates PN code from the received signal received in the narrow band receiving station a signal is detected at the receiving station the phase of the PN code demodulating Demodulating the data, and transmitting and receiving signals from GNSS ( Global Navigation Satellite System ) satellites at both transmitting and receiving stations located on the earth , detecting an absolute time based on the received signals, Securing synchronization based on the absolute time detected at both receiving stations; and determining the position of the own station based on the signal received from the GNSS satellite at the transmitting station. By adjusting the synchronization timing at the receiving station based on the position of the transmitting station included in the data transmitted from the transmitting station, including the position of the own station measured at the transmitting station in the data transmitted from the transmitting station to the receiving station by radio, Compensating for synchronization deviation due to radio propagation time between the station and the receiving station.
[0012]
[Action]
In engaging Lud over data transmission method of the present invention, first, data to be transmitted in the transmitting station is converted into a phase of the PN code. Further, a modulation process using a PN code having such a phase as a modulation signal is performed. The modulation method used at this time is a method capable of narrowing the band, such as FSK or MSK. The narrow-band signal obtained by the modulation is wirelessly transmitted from the transmitting station to the receiving station. The receiving station receives this signal and demodulates the PN code. The receiving station further detects the phase of the demodulated PN code. Since the phase of the PN code represents data, the data can be demodulated by detecting the phase. Therefore, in the first method according to the present invention, since the phase of the PN code is used at the time of data transmission, the influence of the S / N deterioration despite the use of the modulation method having a narrow occupied frequency bandwidth. A data transmission method that is less susceptible to noise is realized. As a result, the transmittable distance is extended, the service area is extended, and data errors are reduced. In the GNSS, a signal including data indicating a time (absolute time) which is a reference of the system is transmitted from the GNSS satellite to the earth. In the transmission method according to the present invention, signals from GNSS satellites such as GPS ( Global Positioning System ) and GLONASS ( Global Orbiting Navigation Satellite System ) are received at both the transmitting station and the receiving station disposed on the earth. , The absolute time is detected from this signal. Synchronization between the transmitting station and the receiving station is ensured based on the absolute time detected by each. Therefore, the method of the present invention realizes a data transmission method that does not require transmission and reception of synchronization information without mounting a high-precision clock synchronized with each other in the transmitting and receiving stations and the receiving station. In addition, since the error of the detected absolute time with respect to the true absolute time is within 1 microsecond, accurate synchronization is realized. Further, in the present invention, by transmitting the position of the transmitting station determined using GNSS as data to the receiving station, the synchronization deviation due to the radio propagation time between the transmitting station and the receiving station is compensated. That is, the transmitting station functions as a GNSS earth station and causes the receiving station to transmit its own position obtained by positioning as part of the data. The receiving station receives the position of the transmitting station transmitted from the transmitting station and adjusts the synchronization timing using the position. By doing so, the time required for data to be transmitted between the transmitting station and the receiving station is compensated, and synchronization is suitably ensured. Further, when the position data of the transmitting station is converted into the PN code phase and transmitted, this position data is also less likely to be affected by the deterioration of S / N.
[0017]
【Example】
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0018]
FIGS. 1 and 2 show the configurations of a transmitting station and a receiving station, respectively, which constitute a system according to an embodiment of the present invention. First, the transmitting station shown in FIG. 1 includes a GNSS receiver 10T, a data processing unit 12T, a synchronization clock generation unit 14T, a P / S conversion unit 16T, a frequency conversion / modulation unit 18T, and a power amplification unit 20T. And a GNSS antenna 22T and a ground antenna 24T. The transmitting station shown in FIG. 2 includes a GNSS receiver 10R, a data reproduction unit 12R, a synchronization clock generation unit 14R, an S / P conversion unit 16R, a frequency conversion / demodulation unit 18R, and a high frequency amplification unit 20R. And a GNSS antenna 22R and a ground antenna 24R.
[0019]
First, the GNSS receiver 10T receives a signal from the GNSS satellite S using the GNSS antenna 22T. The signal transmitted from the GNSS satellite carries clock data indicating the GNSS system time (absolute time) in addition to orbit data indicating the orbit of the GNSS satellite. The GNSS receiver 10T calculates the position of its own station using the orbit data received from three or four GNSS satellites and the pseudorange of the GNSS satellite obtained from synchronization information with the GNSS satellite, and generates position data. (Positioning calculation). For that purpose, it is actually necessary to receive signals from three or four signals, but FIG. 1 shows only one signal for simplification of the drawing. The GNSS receiver 10T compares the obtained position of the own station or the pseudo distance to the GNSS satellite S used for obtaining the position with the known position of the own station or the pseudo distance from the position to the GNSS satellite S. . That is, the transmitting station is configured as a DGNSS base station, and generates DGNSS correction data based on the result of the comparison. The DGNSS correction data indicates a position or pseudo-range error related to the positioning calculation. The GNSS receiver 10T further generates a time synchronization signal PPS (Pulse Per Second) indicating an absolute time based on the received and demodulated clock data. Among the data or signals obtained by the GNSS receiver 10T, the position data and the DGNSS correction data are supplied to the data processing unit 12T, and the PPS is supplied to the synchronization clock generation unit 14T.
[0020]
The data processing unit 12T converts transmission data provided from a user, in addition to the position data and DGNSS correction data supplied from the GNSS receiver 10T, into a PN code phase. FIG. 3 shows an example of the content of the data converted to the PN code phase, and FIG. 4 shows the content of the conversion process to the PN code phase in the data processing unit 12T.
[0021]
Here, as shown in FIG. 3, it is assumed that data A, B,... Z having values of L, M,. It is also assumed that the unmodulated PN code is a sequence as indicated by O in FIG. The data processing unit 12T gives a delay corresponding to the values L, M,... N of the data A, B,. For example, when converting data A whose value is L to a PN code phase, the unmodulated PN code O is delayed by TL = L × t (t: 1-bit length of the PN code). Similarly, when converting the data B whose value is M to the PN code phase, the PN code O is delayed by TM = M × t, and the data Z whose value is N is converted to the PN code phase. , The PN code O is delayed by TN = N × t. The PN code having such phases TL, TM,... TN is supplied to the P / S converter 16T. As shown in FIG. 5, when M1, M2,... Mn are prepared as unmodulated PN codes, the phase corresponding to the values L, M,. .. TN may be given to these PN codes M1, M2,. In that case, P / S conversion by the P / S conversion unit 12T and S / P conversion by the S / P conversion unit 12R described later are required.
[0022]
The synchronization clock generator 14T generates a bit clock and a frame synchronization signal based on the PPS supplied from the GNSS receiver 10T. That is, the synchronization clock generation unit 14T generates a bit clock that gives the bit phase of the PN code while compensating for the delay that occurs from when the signal is received by the GNSS receiver 10T to when the signal is transmitted from the terrestrial antenna 24T. Generated based on PPS. The phase zero of the PN code O is also given by this bit clock. The synchronization clock generator 14T further generates a frame synchronization signal used for P / S conversion in the P / S converter 16T based on the PPS. The bit clock and the frame synchronization signal are supplied to the P / S converter 16T.
[0023]
The P / S converter 16T supplies the PN code to the frequency converter / modulator 18T while securing the bit synchronization of the PN code with respect to the absolute time using the bit clock supplied from the synchronization clock generator 14T. A plurality of codes M1, M2,... Mn are prepared as unmodulated PN codes, and phases TL, TM,... TN corresponding to the values L, M,. If there is, the P / S conversion unit 16T further converts a frame in which these PN codes are arranged in parallel into a frame in which time is serially arranged (P / S conversion; see FIG. 5). The method of preparing a plurality of codes M1, M2,... Mn as unmodulated PN codes and performing P / S conversion is particularly preferable when the frame length of data A, B,. Conversely, when the frame length of the data A, B,... Z is relatively short, it is preferable to prepare only a single code O as an unmodulated PN code. Of course, both types can be used together.
[0024]
The frequency conversion / modulation unit 18T modulates a local oscillation signal of a predetermined frequency using the PN code supplied from the P / S conversion unit 16T as a modulation signal. As a modulation method, a method capable of narrowing the occupied frequency bandwidth of the obtained modulated wave, for example, a method such as FSK or MSK is used. The frequency conversion / modulation unit 18T further increases the frequency of the modulated wave to a radio frequency and supplies the frequency to the power amplification unit 20T. The power amplifying unit 20T power-amplifies the frequency-converted modulated wave, and transmits the modulated wave to a surrounding receiving station using the ground antenna 24T. This transmission may be performed as 1: a large number of broadcast-type transmissions.
[0025]
On the other hand, the GNSS receiver 10R shown in FIG. 2 receives a signal from the GNSS satellite S using the GNSS antenna 22R. The GNSS receiver 10R obtains the position of its own station in the same manner as the GNSS receiver 10T, and generates a PPS. Among the data or signals obtained by the GNSS receiver 10R, position data indicating the position of the receiving station is output to the data reproducing unit 12R (after DGNSS correction described later), and PPS is output to the data reproducing unit 12R and the clock for synchronization. This is supplied to the unit 14R. The synchronization clock generator 14R compensates for a delay that occurs from when a signal is received by the GNSS receiver 10R to when the signal is input to the synchronization clock generator 14R based on the PPS supplied from the GNSS receiver 10R. A bit clock that gives the bit phase of the PN code is generated based on the PPS. The phase zero of the PN code O is also given by this bit clock. The synchronization clock generator 14R further generates a frame synchronization signal used for S / P conversion in the S / P converter 16R based on the PPS. The bit clock and the frame synchronization signal are further corrected by the position data supplied from the data reproducing unit 12R as described later, and further supplied to the S / P converter 16R.
[0026]
The high frequency amplifying unit 20R receives the modulated wave transmitted from the transmitting station using the ground antenna 24R and amplifies the modulated wave. The high frequency-amplified modulated wave is frequency-converted to a baseband by a frequency conversion / demodulation unit 18R, and further demodulated (by a method such as FSK or MSK). The PN code obtained by the demodulation is supplied to the S / P converter 16R. The S / P converter 16R detects the bit synchronization of the PN code with respect to the absolute time using the bit clock supplied from the synchronization clock generator 14R, and supplies the result to the data reproducing unit 12R. That is, the correlation between the demodulated PN code and the unmodulated PN code O is detected while controlling the phase of the PN code O in synchronization with the bit clock. As a result of this processing, when the phase control amount of the PN code O coincides with the phases TL, TM,... TN provided by the data processing unit 12T, a correlation pulse having a high correlation at that time is generated as shown in FIG. Appears on the correlation waveform. The S / P conversion unit 16R gives the phase control amount of the PN code O at the time when such a correlation pulse is obtained to the data reproduction unit 12R as a detection result of the PN code phase. A plurality of codes M1, M2,... Mn are prepared as non-modulated PN codes, and phases TL, TM,... TN corresponding to the values L, M,. In this case, the S / P conversion unit 16R converts the serial frame of these PN codes into a parallel frame using a frame synchronization signal (S / P conversion; see FIG. 5). The correlation with the corresponding PN code M1, M2,... Mn is detected, and the phase control amount of the PN code O at the time when the correlation pulse is obtained is given to the data reproducing unit 12R as the PN code phase detection result.
[0027]
The data reproducing unit 12R reproduces the values L, M,... N of the data A, B,... Z by dividing the detected PN code phases TL, TM,. Of the reproduced data, the DGNSS correction data is supplied to the GNSS receiver 10R. The GNSS receiver 10R obtains higher-precision position data by correcting the position of the own station (directly a position or a pseudo distance) obtained by the positioning calculation using the DGNSS correction data. Among the data reproduced by the data reproducing unit 12R, position data indicating the position of the transmitting station obtained by the GNSS receiver 10T is supplied to the synchronization clock generating unit 14R. The synchronization clock generator 14R compares the position data obtained by the GNSS receiver 10R and indicating the position of the receiving station (however, DGNSS-corrected data is used) with the reproduced position data indicating the position of the transmitting station. , The difference between the two, that is, the distance between the transmitting station and the receiving station. The synchronization clock generator 14R adjusts the timing of the bit clock and the frame synchronization signal according to the obtained distance, thereby compensating for the influence of the signal propagation time from the transmitting station to the receiving station. The data reproducing unit 12R outputs high-precision position data to the user together with other data among the reproduced data. The data reproducing unit 12R extracts only data in the vicinity of the predicted value from the reproduced data having the property of predicting the value in advance, and removes an abnormal value (gate processing based on the predicted value).
[0028]
FIG. 7 shows an example of the sequence of the operation of the transmitting station and the receiving station in this embodiment. As shown in this figure, before transmitting the data converted to the PN code phase from the transmitting station to the receiving station (100T, 100R), the transmitting station transmits a line connection signal (102T), and the receiving station transmits Upon receiving this, the frequency of the carrier is detected (102R: carrier sense). The receiving station tunes the local oscillation frequency of the frequency conversion / demodulation unit 18R to the detected carrier frequency (104). On the other hand, the transmitting station transmits the initial value of the bit clock (106) and the initial value of the frame synchronization signal (108), and transmits an ID code for identifying each transmitting station (110). When transmitting the data converted to the PN code phase, the transmitting station transmits a predetermined start PN code indicating that transmission is to be started immediately before (112T), and immediately ends the transmission. The specified PN code for stop is transmitted (114T). The receiving station detects the start of data transmission by receiving the start PN code (112R), and detects the end by receiving the stop PN code (114R).
[0029]
Therefore, according to the present embodiment, the data is converted into the phase of the PN code and modulated into a narrow-band modulated wave, and this modulated wave is used for wireless transmission, so that data wireless transmission with a narrow occupied frequency bandwidth can be realized. . Further, since the PN code is used as the modulation signal, it is less susceptible to S / N deterioration of the wireless transmission path. Therefore, the transmittable distance is extended, the service area is extended, and data errors are reduced. Further, according to the present embodiment, since the GNSS system time is received at each station and synchronization is ensured by this, it is not necessary to transmit a bit clock or a frame synchronization signal for data reproduction. Further, it is not necessary to mount a high-precision clock synchronized with each other in the transmitting / receiving station and the receiving station. Further, since the error of the detected value with respect to the true system time is within 1 microsecond, accurate synchronization can be realized. Further, there is no possibility that the bit clock or the frame synchronization signal is destroyed and the synchronization is not lost.
[0030]
Further, according to the present embodiment, by transmitting the position of the transmitting station determined using GNSS to the receiving station as data, it is possible to compensate for the synchronization deviation due to the radio propagation time between the transmitting station and the receiving station. Further, according to the present embodiment, the transmitting station functions as a DGNSS base station, and the receiving station functions as a DGNSS mobile station. Since the position data of the transmitting station and the DGNSS correction data are transmitted after being converted into the PN code phase, these data are also less susceptible to S / N deterioration and the position of the mobile station (receiving station) in the DGNSS. Measurement accuracy is improved.
[0031]
As described above, according to the present embodiment, for example, a data transmission method suitable for telemetering, telecontrol, wireless transmission, and DGNSS in a low-power, bad environment application can be obtained.
[0032]
In the above description, the transmitting station and the receiving station are separated, but one station may have both the function of the transmitting station and the function of the receiving station.
[0033]
When the modulation scheme used between the transmitting and receiving stations is FSK, the transmission frequency shifts between two types of frequencies according to the value (1, 0) of the PN code. Frequency shift is also performed in frequency hopping (FH), which is a type of SS, but FSK in the present invention is completely different in function and effect from general FH. That is, in the case of FH, one of N waves is selected using m bits (where N = 2 ^m -1) in a PN code of length N and set as a transmission frequency, whereas in the case of FSK There are only two waves. In other words, in the case of FH, the spectrum is spread and narrowband transmission is difficult or impossible. However, such a problem does not occur when FSK is used in the present invention.
[0034]
【The invention's effect】
As described above, according to the present invention, the data to be transmitted is converted into the PN code phase, and the PN code phase is modulated and transmitted / received by a method capable of narrowing the band, such as FSK or MSK. By demodulating the PN code and detecting the phase, the data can be demodulated. In addition, since the phase of the PN code is used for data transmission, a data transmission method that is not easily affected by S / N degradation can be realized despite the use of a modulation method with a narrow occupied frequency bandwidth. The service area can be expanded by extending the possible distance, and data errors can be reduced.
[0035]
Further, according to the present invention, since both the transmitting station and the receiving station receive the absolute time from the GNSS satellite and secure synchronization based on the absolute time, a high-precision synchronous clock is mounted on each of the transmitting / receiving station and the receiving station. Thus, data transmission that does not require transmission and reception of synchronization information can be realized. Further, since the error of the detected absolute time with respect to the true absolute time is within 1 microsecond, accurate synchronization can be realized.
[0036]
Furthermore, according to the present invention, synchronization is ensured by the absolute time of the GNSS in data transmission using the PN code phase. Therefore, even in the case of low power transmission or poor transmission path conditions, there is no data error and synchronization loss. And synchronous transmission of data becomes possible.
[0037]
Further, according to the present invention, the position of the transmitting station determined using GNSS is transmitted to the receiving station as data, and the synchronization deviation due to the radio propagation time between the transmitting station and the receiving station is compensated. Synchronization can be suitably ensured irrespective of a change in distance between stations. In addition, due to the transmission using the PN code phase, this position data is also less susceptible to S / N degradation.
[0038]
According to the present invention, since the transmitting station is used as a DGNSS base station and the receiving station is used as a DGNSS mobile station, the service area of the DGNSS base station (transmitting station) can be expanded. Further, when the DGNSS correction data is converted into the PN code phase and transmitted, the mobile station position accuracy in the DGNSS is improved.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a transmitting station according to one embodiment of the present invention.
FIG. 2 is a block diagram illustrating a configuration of a receiving station according to one embodiment of the present invention.
FIG. 3 is a diagram illustrating an example of the content of data to be transmitted;
FIG. 4 is a diagram illustrating an outline of a conversion process to a PN code phase;
FIG. 5 is a diagram showing an outline of P / S conversion and S / P conversion processing.
FIG. 6 is a diagram showing an outline of synchronous reproduction of data.
FIG. 7 is a diagram showing an example of a data transmission sequence between a transmitting and receiving station.
[Explanation of symbols]
10T, 10R GNSS receiver 12T Data processing unit 12R Data reproduction unit 14T, 14R Synchronization clock generation unit 16T P / S conversion unit 16R S / P conversion unit 18T Frequency conversion / modulation unit 18R Frequency conversion / demodulation unit 20T Power amplification unit 20R High-frequency amplifier 22T, 22R GNSS antenna 24T, 24R Ground antennas A, B,... Z Data L, M,... N Data values O, M1, M2,.
TL, TM, ... TN PN code phase

Claims (1)

The PN code obtained by delaying the phase based on the value of the data is generated in the transmitting station, the steps of wirelessly transmitting a narrowband signal modulated with the PN code as a modulation signal from a transmission station that have occurred,
A step of demodulating data by receiving a narrowband signal at a receiving station, demodulating a PN code from the received signal, and detecting a phase of the demodulated PN code at the receiving station ;
Both the transmitting station and the receiving station arranged on the earth receive a signal from the GNSS satellite and detect an absolute time based on the received signal, and synchronize based on the absolute time detected at both the transmitting station and the receiving station. Securing process,
The transmitting station determines its own position based on the signal received from the GNSS satellite, and the data transmitted from the transmitting station to the receiving station includes the position of the own station measured by the transmitting station and is included in the data transmitted from the transmitting station. Adjusting the synchronization timing at the receiving station based on the position of the transmitting station to compensate for synchronization deviation due to radio propagation time between the transmitting station and the receiving station;
A data transmission method comprising:

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