JP4735550B2 - Code correlation processing method in receiver of spread spectrum communication system - Google Patents

Description

  The present invention relates to a code correlation processing method in a receiver of a spread spectrum communication system used, for example, when acquiring a satellite in a GPS receiver.

  For example, in a GPS system, spread spectrum communication with a frequency of 1.5 GHz band is used to transmit information from a GPS satellite to a user. At this time, a different spreading code (pseudo noise (PN) code) is assigned to each of the 32 GPS satellites, and the spreading code and navigation message data are transmitted. A publicly available spreading code (PN code) is called a C / A code, and has a chip rate of 1023 Hz and a code length of 1 ms. On the other hand, at the GPS receiver side, at least four usable satellites are captured, the pseudo distance to each satellite is measured, and its own position (latitude, longitude, altitude) and time are measured. Yes.

In capturing the satellite, it is necessary to establish code phase synchronization by despreading the spreading code received from each satellite and obtaining a correlation value with an internal code generated on the receiver side. In this case, a method of obtaining a code correlation in units of 1 ms (1 frame) using a shift register is generally used, and sequentially obtaining a code correlation value by shifting an internal code by one chip at a time. (1023 times) It repeats (for example, refer nonpatent literature 1). However, this process has a problem that it takes a relatively long time. For example, if processing is performed for all 32 satellites, 32 × 1023 × 1 ms = 32.736 (s) is required.
GPS Official Document Interface Specification (IS-GPS-200) (pages 30-34)

  By the way, in the GPS receiver, when the intensity of the received signal from the satellite is sufficiently high, the correlation can be obtained without performing the processing for one cycle. For example, in the field of mobile phones (CDMA wireless communication, etc.), a method of canceling the process for obtaining the correlation until the middle of one cycle has already been used. As a result, the time required for the correlation process can be shortened.

  However, in the method of canceling the process for obtaining the correlation in the middle of one cycle as described above, a code reset circuit and a function for initializing the correlation process usually performed in units of 1 ms in accordance with the reset are required. Needs to be rethought.

  The present invention has been made in view of the above circumstances, and an object thereof is a method for performing code correlation processing on a received signal to establish code phase synchronization, and changes the correlation processing in units of one code length. It is an object of the present invention to provide a code correlation processing method in a receiver of a spread spectrum communication system capable of shortening the time for performing code correlation processing without having to do so.

In order to achieve the above object, the code correlation processing method in the receiver of the spread spectrum communication system of the present invention is a method for synchronizing the spread code in the received signal with the internal code generated on the receiver side. And generating a code pattern in which a plurality of inner codes are evenly mixed in a frame of the number of chips corresponding to one repetition period of the spreading code, and the plurality of inner codes are applied to the spreading code in the received signal. A process of obtaining a code correlation using the mixed code pattern is executed , and a code pattern generated by mixing the plurality of internal codes is generated by using n internal codes (number of chips corresponding to one repetition period / n). It is characterized by being performed by taking out chips one by one and arranging them in order (Invention of Claim 1).

  According to this, since the correlation process can be performed in units of the number of chips corresponding to one repetition period of the spread code, the concept of the correlation process in units of one code length can be maintained, and the addition of the reset circuit and the correlation This can be done without changing the processing circuit. Then, if n internal codes are mixed by executing a process for obtaining a code correlation using a code pattern obtained by mixing a plurality of internal codes with respect to a spreading code included in the received signal, one internal code Since the time for the correlation processing relating to the code is about 1 / n, the time for performing the correlation processing for the code as a whole can be shortened.

Hereinafter, the present invention, for example a vehicle, a ship, an embodiment applied to a GPS receiver utilized in a navigation system such as an aircraft, will be described with reference to FIGS. FIG. 1 schematically shows an electrical configuration of a GPS receiver 1 in the present embodiment.

  Here, the GPS system will be briefly described. In GPS, spread spectrum communication with a frequency of 1.5 GHz band is used to transmit information from a GPS satellite to a user. At this time, a pseudo noise (PN) code different for each satellite is assigned to the 32 GPS satellites as a spreading code, and this PN code and navigation message data are transmitted. A PN code released for private use is called a C / A code, and has a chip rate of 1023 Hz and a code length of 1 ms.

  On the other hand, the GPS receiver 1 side captures at least four usable satellites, measures the pseudo distance to each satellite from the navigation data from each satellite, and determines its own position (latitude, longitude, altitude) and Time is measured. At this time, the cross-correlation between spreading codes (C / A codes) in each satellite is assumed to be small. In addition, the intensity of the radio signal received from the satellite to be captured is sufficiently high.

  As shown in FIG. 1, the GPS receiver 1 is roughly configured to include a wireless unit 2, a despreading processing unit (digital signal processing unit) 3, an arithmetic control unit 4, and the like. Among them, the radio unit 2 includes a GPS antenna 5, an RF unit 6, a ZF synchronization unit 7, and the like. The despreading processing unit 3 includes first to sixth multipliers 8 to 13, an NCO 14, first to fourth integrators 15 to 18, a PLL circuit 19, a DLL circuit 20, a bit synchronization unit 21, and the like. It is configured. Although not shown, the arithmetic control unit 4 includes a CPU, a memory, an internal PN code generation unit, and the like.

  Thus, the received signal received by the GPS antenna 5 is input as an input signal to the despreading processing unit 3 via the RF unit 6 and the ZF synchronization unit 7. The input signals are multiplied by two output signals different in phase by 90 degrees outputted from the NCO 14 in the first and second multipliers 8 and 9, respectively. The signals that have passed through the first and second multipliers 8 and 9 are used for despreading the delay zero (P) output from the arithmetic control unit 4 in the third and fourth multipliers 10 and 11, respectively. And the first and second integrators 15 and 16 for integration. Outputs from the first and second integrators 15 and 16 are input to the PLL circuit 19, and a signal from the second integrator 16 is input to the bit synchronization unit 21.

  The signal that has passed through the second multiplier 9 is delayed by ½ bit (chip) output from the arithmetic control unit 4 in the fifth and sixth multipliers 12 and 13, respectively (L). The inner code and 1/2 bit (chip) early (E) inner code are multiplied and further integrated by the third and fourth integrators 17 and 18. Outputs from the third and fourth integrators 17 and 18 are input to the DLL circuit 20. A control signal from the PLL circuit 19 is input to the NCO 14, and a code delay amount signal from the DLL circuit 20 is input to the arithmetic control unit 4. A navigation data signal is output from the bit synchronization unit 21.

  In the GPS receiver 1, the spreading code included in the received signal from the GPS satellite and the despreading pattern generated in the same pattern as the spreading code for each satellite, centering on the processing of the arithmetic control unit 4. Is established (acquired) in sequence with respect to a plurality of satellites, and necessary four satellites are selected, and then synchronization is maintained (tracked). Of these, the establishment of synchronization between the spread code and the internal code in the received signal is performed by sequentially performing code correlation processing for obtaining the correlation between the spread code and the internal code using a shift register while shifting the internal code by one chip at a time. This is done by running and detecting the peak.

  At this time, in this embodiment, the arithmetic control unit 4 generates a code pattern in which a plurality of internal codes are evenly mixed in a frame having the number of chips corresponding to one repetition period of the spread code, in this case, 1023 chips (1 ms). And the process which calculates | requires a code correlation is performed using the code pattern which mixed the said some internal code with respect to the spreading code in the said received signal. The process for obtaining the code correlation is performed by repeating the process of obtaining the code correlation value for one period (1023 times) while shifting the generated code pattern by one chip. Internal codes relating to all satellites are stored in advance in the memory of the arithmetic control unit 4.

FIG. 2 shows a reference example of a method for generating a code pattern in which a plurality of internal codes are evenly mixed. In this reference example, as shown in FIG. 2, the internal code related to the satellite 1 and the internal code related to the satellite 2 are sequentially nested one by one. That is, the internal code data related to the satellite 1 (first chip) is inserted into the first chip of the frame, the internal code data related to the satellite 2 (second chip) is inserted into the second chip, and the satellite 1 is related to the third chip. By sequentially repeating the insertion of the internal code data (third chip), a code pattern in which the two internal codes are mixed is generated. In the next frame, the internal code related to the satellite 3 and the internal code related to the satellite 4 are similarly mixed in order. Using the code pattern generated in this way, correlation processing is sequentially executed in 1 ms units.

  In this case, the cross-correlation between the spreading codes (internal codes) of each satellite is extremely small, and the intensity of the received signal from the GPS satellite is sufficiently high, so that even if the internal codes are mixed, the correlation is obtained. Is fully possible. However, since the despread gain is reduced by mixing, it is desirable not to increase the number of mixing (2 to 4). Even if the correlation is detected, it is impossible to determine which of the two satellites, and thereafter, the correlation for satellite identification is performed one code at a time.

According to the interphase processing method described above , there is a method for performing code correlation processing on a received signal to establish code phase synchronization, and a code pattern in which a plurality of internal codes are mixed is used. Thereby, since the correlation processing can be performed in units of the number of chips corresponding to one repetition period of the spreading code, the concept of the correlation processing in units of one code length can be maintained, and the addition of the reset circuit and the correlation processing circuit Can be done without incurring any changes. Then, it is assumed that n (2 to 4) inner codes are mixed by executing a process for obtaining code correlation using a code pattern in which a plurality of inner codes are mixed with the spreading code included in the received signal. For example, since the correlation processing time for one internal code is about 1 / n, the time for performing the correlation processing of the code as a whole can be shortened.

Figure 3 shows the actual施例of the present invention, the reference example differs from, is the method of generating a code pattern that mixes a plurality of internal code. That is, in the real施例, the internal code of n (e.g., four), by arranging the order is taken out one by chips (number of chips / n corresponding to 1 repetition period), a code pattern that mixes a plurality of internal code It is designed to generate.

Specifically, the internal code of satellite 1 is 256 chips (first 256 chips), the internal code of satellite 2 is 256 chips (from the 257th chip to the 512th chip), and the internal code of satellite 3 is 256 chips (513 chips) From the first to the 768th chip), the internal code of the satellite 4 is arranged in 255 chips (the last 255 chips), and a code pattern for 1 ms is generated. Even in such a configuration, it is possible to reduce the time for performing the code correlation process while eliminating the need to change the correlation process in units of one code length.

In the above embodiment, the present invention is applied to a GPS receiver. However, the present invention is not limited to GPS, but is a system using spectrum spread communication such as a mobile communication field such as a CDMA mobile phone. It can be applied in general. In addition, the present invention is not intended to be limited to the embodiments described above, but may be practiced by changing as appropriate within a range not departing from the Abstract.

The block diagram which shows one Example of this invention and shows the electrical structure of a GPS receiver roughly A figure showing a reference example for explaining the method of mixing internal code Figure 2 corresponds diagram showing an actual施例of the present invention

Explanation of symbols

  In the drawings, 1 is a GPS receiver, 2 is a radio unit, 3 is a despreading processing unit, 4 is an arithmetic control unit, 8 to 13 are multipliers, 14 is an NCO, 15 to 18 are integrators, 19 is a PLL circuit, Reference numeral 20 denotes a DLL circuit.

Claims (1)

In a correlation processing method for synchronizing a spread code included in a received signal and an internal code for despreading generated on the receiver side in a receiver of a spread spectrum communication system,
Generating a code pattern in which a plurality of internal codes are mixed evenly in a frame of the number of chips corresponding to one repetition period of the spreading code;
For the spreading code in the received signal, performing a process for obtaining a code correlation using a code pattern obtained by mixing the plurality of internal codes ,
Generating a code pattern by mixing the plurality of internal codes is performed by taking out n internal codes (number of chips corresponding to one repetition period / n) chips and arranging them in order. A code correlation processing method in a receiver of a communication system.

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