Data processing method for memory coding and GNSS receiver

Abstract

The present invention discloses a data processing method and a GNSS receiver for memory coding. The GNSS receiver includes a plurality of signal tracking channels, a query module, a management module and a storage module. Each signal tracking channel includes a pseudo-random code generator and a correlator. The memory code is pre-stored in the storage module. The data processing method includes: the management module receives query requests of all signal tracking channels; the management module calls the query module to process the query request in a preset order; the query module queries the coded data in the memory code according to the query request; the query module sends the coded data to the corresponding signal tracking channel; the signal tracking channel uses the pseudo-random code generator and the correlator to calculate the obtained coded data to track the satellite signal. The present invention can solve the problem that the memory coding in the GNSS receiver consumes a lot of storage resources. The memory coding occupies less storage space and the receiver has high computing efficiency.

Description

Technical Field

[0001] The invention relates to a data processing method for memory coding and a GNSS receiver. Background Art

[0002] Satellite navigation and positioning technology has basically replaced ground-based radio navigation, traditional geodetic and astronomical measurement navigation and positioning technology, and has promoted new developments in the fields of geodetic measurement and navigation and positioning. Today, the GNSS system is not only the infrastructure of national security and economy, but also an important symbol of the status of a modern great power and the country's comprehensive national strength. Due to its important significance in politics, economy, and military, the world's major military powers and economies are competing to develop independent satellite navigation systems.

[0003] GNSS (Global Navigation Satellite System) refers to the world's four major navigation and positioning systems, including the US GPS, Russia's GLONASS, Europe's Galileo, and my country's Beidou. It can provide users with uninterrupted, high-precision navigation signal resources with global coverage, thereby realizing all-weather real-time positioning, speed measurement and timing functions. GNSS is currently widely used in many fields such as navigation, mapping, disaster monitoring, scientific research, etc., and with the continuous improvement and development of GNSS technology, receivers or processing chips are expected to break through the limitations of cost, power consumption, size, etc., and be installed on various ground-based, air-based, and space-based intelligent terminals, which can greatly promote the development of positioning technologies such as autonomous driving, drones, and space vehicles. In these application scenarios, the dynamic nature of users, the openness of signal propagation, and the complexity of the receiving environment often lead to signal deterioration, which seriously damages the availability, reliability, continuity and other service performance of GNSS.

[0004] High-precision global satellite positioning system real-time tracking technology needs to track signals of multiple frequencies of different satellite systems, which means that the receiver needs to implement pseudo-random codes modulated by multiple satellite signals. These pseudo-random codes are mainly divided into two categories, Gold codes and codes based on memory code. With the continuous update of satellite signals, there are more and more codes based on memory code, such as Galileo E1 / E6, BDS B1C, GPS L1C, etc., and these new signals have become indispensable tracking signals for the new generation of high-precision GNSS receivers.

[0005] In the design of high-precision GNSS receiver baseband tracking algorithm, the code generator is used to generate the pseudo-random code used by the baseband signal, and perform correlation operation with the baseband data to calculate the code phase of the current signal to achieve the purpose of tracking the signal. Since the signals of the same frequency point of multiple satellites need to be tracked at the same time, in order to save hardware resources, the code generator is often used in a time-division multiplexing manner, and there is no need to design a set of special code generators and correlators for each satellite. Only 4-8 groups need to be designed.

[0006] However, this still means that 4-8 groups of code generators are required for each frequency point. For tracking Galileo E1 / E6, GPS L1C, and BDS B1C signals, the memory code capacity required for storage increases exponentially. When implementing ASIC, the amount of ROM will be greatly increased, thereby increasing the ASIC area.

[0007] As the number of signals tracked by receivers increases, the baseband algorithms of most receivers can only be completed using specialized FPGA chips or even ASIC chips. The memory resources of FPGA chips are very limited, while for ASIC chips, the chip area occupied by memory resources often exceeds 50%, or even close to 90%, which also means a significant increase in area cost. Therefore, minimizing the use of memory is particularly critical for the design of GNSS receiver baseband algorithms. Summary of the invention

[0008] The technical problem to be solved by the present invention is to overcome the defect that memory coding in GNSS receivers in the prior art consumes a lot of storage resources, and to provide a data processing method for memory coding and a GNSS receiver with memory coding occupying less storage space and high receiver operation efficiency.

[0009] The present invention solves the above technical problems through the following technical solutions:

[0010] A data processing method for memory coding is used for a GNSS receiver. The GNSS receiver includes a plurality of signal tracking channels, a query module, a management module and a storage module. Each signal tracking channel includes a pseudo-random code generator and a correlator. The memory code is pre-stored in the storage module. The data processing method includes:

[0011] The management module receives query requests for all signal tracking channels;

[0012] The management module calls the query module in a preset order to process the query request;

[0013] The query module queries the code data in the memory code according to the query request;

[0014] The query module sends the coded data to the corresponding signal tracking channel;

[0015] The signal tracking channel uses a pseudo-random code generator and a correlator to calculate the acquired coded data to track satellite signals.

[0016] Preferably, each query request includes a flag bit and a query address, and the management module calls the query module in a preset order to process the query request, including:

[0017] After receiving the query request, the management module latches the flag bit and the query address in the query request;

[0018] The state of the query module changes from the IDLE state to the Check state, and the management module generates an index information according to the query request, and the index information corresponds to the signal tracking channel that sends the valid query request.

[0019] Preferably, the data processing method comprises:

[0020] The management module imports the latched query address into the address input terminal of the storage module according to the current index information in the Check state, and generates a read valid signal to the en terminal of the storage module;

[0021] The management module determines whether the output of the storage module is valid. If so, the coded data output by the storage module is transmitted to the corresponding signal tracking channel according to the current index information, and an output valid signal is generated and transmitted back, and then the address information latched at the signal tracking channel port indicated by the current index information and the query valid information are cleared;

[0022] The query module enters the IDLE state.

[0023] Preferably, the data processing method comprises:

[0024] The pseudo-random code generator generates a query address in a corresponding query request according to the current code phase, wherein the query address increases by 1 each time it is queried, and automatically returns to an initial value after increasing to a maximum value, and the initial value is generated according to the satellite number and written into the status register.

[0025] Preferably, the pseudo-random code generator includes a two-level cache. After receiving the coded data, the pseudo-random code generator saves the latest received coded data into the second-level cache. The pseudo-random code generator and the correlator calculate the coded data in the first-level cache to track the satellite signal. The first-level cache reads the coded data in the second-level cache after the coded data calculation is completed. Then, the pseudo-random code generator generates the next query request after the first-level cache reads the coded data in the second-level cache.

[0026] Preferably, the data processing method comprises:

[0027] The pseudo-random code generator reads a chip from the first-level cache;

[0028] The pseudo-random code generator generates a pseudo-random code using the code chip;

[0029] Determine whether to read the second-level cache into the first-level cache, if yes, read the encoded data in the second-level cache into the first-level cache, if no, execute the step of reading a code piece from the first-level cache again;

[0030] The pseudo-random code generator generates the next query request;

[0031] Determine whether the coded data corresponding to the query request is received, and if so, save the latest received coded data to the second-level cache.

[0032] The present invention also provides a GNSS receiver, the GNSS receiver comprising a plurality of signal tracking channels, a query module, a management module and a storage module, each signal tracking channel comprising a pseudo-random code generator and a correlator, the storage module pre-stores a memory code,

[0033] The management module is used to receive query requests for all signal tracking channels;

[0034] The management module is used to call the query module in a preset order to process the query request;

[0035] The query module is used to query the coded data in the memory code according to the query request;

[0036] The query module is used to send the coded data to the corresponding signal tracking channel;

[0037] The signal tracking channel is used to track satellite signals by using the coded data obtained by calculating the pseudo-random code generator and the correlator.

[0038] Preferably, each query request includes a flag bit and a query address.

[0039] The management module is used to latch the flag bit and the query address in the query request after receiving the query request;

[0040] The query module is used to change the state from IDLE state to Check state after receiving the query request;

[0041] The management module is used to generate an index information according to the query request, and the index information corresponds to the signal tracking channel that sends the valid query request;

[0042] The management module is used to import the latched query address into the address input terminal of the storage module according to the current index information in the Check state, and generate a read valid signal to the en terminal of the storage module;

[0043] The management module is used to determine whether the output of the storage module is valid. If so, the coded data output by the storage module is transmitted to the corresponding signal tracking channel according to the current index information, and an output valid signal is generated and transmitted back, and then the address information latched at the signal tracking channel port indicated by the current index information and the query valid information are cleared;

[0044] The query module is used to enter the IDLE state after the management module clears the address information latched by the signal tracking channel port indicated by the current index information and the query valid information.

[0045] Preferably, the pseudo-random code generator is used to generate a query address in a corresponding query request according to a current code phase, wherein the query address is incremented by 1 each time it is queried, and automatically returns to an initial value after increasing to a maximum value, and the initial value is generated according to a satellite number and written into a status register, wherein the pseudo-random code generator includes a two-level cache, and after receiving the coded data, the pseudo-random code generator saves the latest received coded data into a second-level cache, and the pseudo-random code generator and the correlator calculate the coded data in the first-level cache to track satellite signals, and the first-level cache reads the coded data in the second-level cache after the coded data calculation is completed, and then the pseudo-random code generator generates a next query request after the first-level cache reads the coded data in the second-level cache.

[0046] Preferably, the pseudo-random code generator is used to read a chip from the first level cache;

[0047] The pseudo-random code generator is used to generate a pseudo-random code using the code chip;

[0048] The pseudo-random code generator is used to determine whether to read the second-level cache into the first-level cache, and if so, read the encoded data in the second-level cache into the first-level cache, and if not, perform the step of reading a code chip from the first-level cache again;

[0049] The pseudo-random code generator is used to generate the next query request;

[0050] The pseudo-random code generator is used to determine whether the coded data corresponding to the query request is received, and if so, save the latest received coded data to the second-level cache.

[0051] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0052] The positive and progressive effects of the present invention are:

[0053] The present invention can solve the problem that memory coding in a GNSS receiver consumes large storage resources, the memory coding occupies less storage space and the receiver has high computing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a schematic diagram of the structure of a GNSS receiver according to Embodiment 1 of the present invention.

[0055] Figure 2 This is a flow chart of the data processing method of embodiment 1 of the present invention.

[0056] Figure 3 This is another flow chart of the data processing method according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0057] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. Example

[0058] See also Figure 1 This embodiment provides a GNSS receiver, which includes a plurality of signal tracking channels 14, a query module 12, a management module 11 and a storage module 13.

[0059] Each signal tracking channel includes a pseudo-random code generator 141 and a correlator 142, and the memory code is pre-stored in the storage module.

[0060] The management module is used to receive query requests for all signal tracking channels;

[0061] The management module is used to call the query module to process the query request in a preset order, and the preset order can be the order of the requests.

[0062] The query module is used to query the coded data in the memory code according to the query request;

[0063] The query module is used to send the coded data to the corresponding signal tracking channel;

[0064] The signal tracking channel is used to track satellite signals by using the coded data obtained by calculating the pseudo-random code generator and the correlator.

[0065] Specifically, each query request includes a flag bit and a query address. The flag bit is used to inform the management module which signal tracking channel sends the query request, and the query address indicates the target data in the memory code required by the signal tracking channel.

[0066] The management module is used to latch the flag bit and the query address in the query request after receiving the query request;

[0067] The query module is used to change the state from IDLE state to Check state after receiving the query request;

[0068] The management module mainly completes the random read management function of several requests. When there are one or more query requests, the corresponding query operations are completed in a certain order and the queried data is returned. The queried data is returned according to the flag bit.

[0069] After receiving the query request, the management module will first latch the two pieces of information. Then any valid request status will trigger the query state machine to enter the Check state from the IDLE state, that is, to enter the query state from the standby state.

[0070] The management module is used to generate an index information according to the query request, and the index information corresponds to the signal tracking channel that sends the valid query request;

[0071] The management module generates the index information after acquiring the signal tracking channel according to the flag bit in the query request, and returns the data according to the index information after the coded data is queried.

[0072] The management module is used to import the latched query address into the address input terminal of the storage module according to the current index information in the Check state, and generate a read valid signal to the en terminal of the storage module;

[0073] The management module is used to determine whether the output of the storage module is valid. If so, the coded data output by the storage module is transmitted to the corresponding signal tracking channel according to the current index information, and an output valid signal is generated and transmitted back, and then the address information latched at the signal tracking channel port indicated by the current index information and the query valid information are cleared;

[0074] The query module is used to enter the IDLE state after the management module clears the address information latched by the signal tracking channel port indicated by the current index information and the query valid information.

[0075] In the Check state, according to the current index value (index information), the query address latched by the corresponding channel is imported into the address input terminal of the ROM, and a read valid signal is generated to the en terminal of the ROM (storage module), forming a many-to-one read request management function.

[0076] After the ROM output becomes valid, the ROM output result is sent to the corresponding channel output port according to the current index, and a corresponding output valid signal is generated and returned.

[0077] At the same time, the address information latched by the channel port indicated by the current index and the query validity information are cleared. Then the state machine returns to the IDLE state to wait for the next query request.

[0078] Furthermore, the pseudo-random code generator is used to generate a query address in a corresponding query request according to the current code phase, wherein the query address is incremented by 1 each time it is queried, and automatically returns to an initial value after increasing to a maximum value, and the initial value is generated according to the satellite number and written into the status register.

[0079] Specifically, the pseudo-random code generator includes a two-level cache. After receiving the coded data, the pseudo-random code generator saves the latest received coded data into the second-level cache. The pseudo-random code generator and the correlator calculate the coded data in the first-level cache to track the satellite signal. The first-level cache reads the coded data in the second-level cache after the coded data calculation is completed. Then, the pseudo-random code generator generates the next query request after the first-level cache reads the coded data in the second-level cache.

[0080] The pseudo-random code generator is the initiator of the query request and the receiver of the data, and then calculates the corresponding pseudo-random code based on the queried memorycode.

[0081] The query request needs to generate the corresponding query address according to the current code phase. The query address increases by 1 each time it is queried, and automatically returns to the initial value after it increases to the maximum value. The initial value is generated by software control according to the satellite number and written into the status register.

[0082] There are two levels of cache in the pseudo-random code generator to store the query data. After receiving the data returned by the query module, it is first saved in the second-level cache. When the data in the first-level cache is used up, the data in the second-level cache will be automatically read into the first-level cache. Then the code generator will initiate a new query operation to update the data in the second-level cache.

[0083] The calculation of the code slice can directly use the data in the L1 cache and perform other operations as needed.

[0084] For example, for Galileo E1b, E1c, E6b, and E6c signals, the data in the L1 cache is the code chip. For GPS L1C and BDS B1C signals, the memory code stores the Legendre sequence, and the corresponding bits need to be XORed again based on the data from two different addresses to generate the correct pseudo-random code.

[0085] Specifically, the function of the pseudo-random code generator is as follows:

[0086] The pseudo-random code generator is used to read a chip from the first-level cache;

[0087] The pseudo-random code generator is used to generate a pseudo-random code using the code chip;

[0088] The pseudo-random code generator is used to determine whether to read the second-level cache into the first-level cache, and if so, read the encoded data in the second-level cache into the first-level cache, and if not, perform the step of reading a code chip from the first-level cache again;

[0089] The pseudo-random code generator is used to generate the next query request;

[0090] The pseudo-random code generator is used to determine whether the coded data corresponding to the query request is received, and if so, save the latest received coded data to the second-level cache.

[0091] Using the above GNSS receiver, taking the GAL E1 signal as an example, in the common receiver baseband algorithm implementation structure, most of them use 4-channel correlators for tracking. Therefore, if the conventional method is used, each correlator has an independent code generator, which means that 4 sets of storage modules for storing memory codes are required, and each storage module contains E1c and E1b signals. The number of code chips of E1c / E1b signals is 9216 bits. Then the total storage module capacity is 4*2*9216 bits = 73728 bits.

[0092] In this embodiment, only one set of ROM needs to be implemented, so the total storage module capacity is 9216 bits*2=18432 bits.

[0093] It can greatly save the space occupied by the storage module.

[0094] See also Figure 2 , using the above GNSS receiver, this embodiment also provides a data processing method, including:

[0095] Step 100: the management module receives query requests for all signal tracking channels;

[0096] Step 101, the management module calls the query module in a preset order to process the query request;

[0097] Step 102, the query module queries the code data in the memory code according to the query request;

[0098] Step 103, the query module sends the coded data to the corresponding signal tracking channel;

[0099] Step 104: The signal tracking channel uses the pseudo-random code generator and the correlator to calculate the acquired coded data to track the satellite signal.

[0100] Furthermore, each query request includes a flag bit and a query address, and step 101 specifically includes:

[0101] Step 1011: After receiving the query request, the management module latches the flag bit and the query address in the query request;

[0102] Step 1012: the state of the query module changes from the IDLE state to the Check state, and the management module generates an index information according to the query request, and the index information corresponds to the signal tracking channel that sends the valid query request.

[0103] Step 1013: The management module imports the latched query address into the address input terminal of the storage module according to the current index information in the Check state, and generates a read valid signal to the en terminal of the storage module;

[0104] Then in step 102, the query module queries the code data in the memory code according to the query address;

[0105] Step 102 includes:

[0106] In step 1021, the management module determines whether the output of the storage module is valid. If so, step 103 is executed. If not, step 1021 is executed again.

[0107] Step 103 includes:

[0108] Step 1031: transmit the encoded data output by the storage module to the corresponding signal tracking channel according to the current index information, generate an output valid signal for transmission, and then clear the address information and query valid information latched at the signal tracking channel port indicated by the current index information;

[0109] Step 1032: The query module enters the IDLE state.

[0110] The data processing method comprises:

[0111] The pseudo-random code generator generates a query address in a corresponding query request according to the current code phase, wherein the query address increases by 1 each time it is queried, and automatically returns to an initial value after increasing to a maximum value, and the initial value is generated according to the satellite number and written into the status register.

[0112] The pseudo-random code generator includes two levels of cache. After receiving the coded data, the pseudo-random code generator saves the latest received coded data into the second-level cache. The pseudo-random code generator and the correlator calculate the coded data in the first-level cache to track the satellite signal. The first-level cache reads the coded data in the second-level cache after the coded data calculation is completed. Then, the pseudo-random code generator generates the next query request after the first-level cache reads the coded data in the second-level cache.

[0113] See also Figure 3 , for the pseudo-random code generator, during the execution of steps 100 to 104, the data processing method includes:

[0114] Step 200: The pseudo-random code generator reads a chip from the first-level cache;

[0115] Step 201: A pseudo-random code generator generates a pseudo-random code using the code chip;

[0116] Step 202, determine whether to read the second-level cache into the first-level cache, if yes, execute step 203, if no, execute step 200;

[0117] Step 203, read the encoded data in the second level cache into the first level cache;

[0118] Step 204: The pseudo-random code generator generates the next query request;

[0119] Step 205 , determine whether the coded data corresponding to the query request is received, if yes, execute step 206 , if no, execute step 205 again.

[0120] Step 206: Save the latest received coded data into the second-level cache.

[0121] Then step 200 is executed in a loop.

[0122] Although the specific embodiments of the present invention are described above, those skilled in the art should understand that these are only examples, and the protection scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A data processing method for memory coding, for use in a GNSS receiver, It is characterized in that The GNSS receiver includes a plurality of signal tracking channels, a query module, a management module and a storage module. Each signal tracking channel includes a pseudo-random code generator and a correlator. The storage module is pre-stored with memory codes. The data processing method includes: The management module receives query requests for all signal tracking channels; The management module calls the query module in a preset order to process the query request; The query module queries the code data in the memory code according to the query request; The query module sends the coded data to the corresponding signal tracking channel; The signal tracking channel uses a pseudo-random code generator and a correlator to calculate the acquired coded data to track satellite signals.

2. The data processing method according to claim 1, It is characterized in that Each query request includes a flag bit and a query address, and the management module calls the query module in a preset order to process the query request, including: After receiving the query request, the management module latches the flag bit and the query address in the query request; The state of the query module changes from the IDLE state to the Check state, and the management module generates an index information according to the query request, and the index information corresponds to the signal tracking channel that sends the valid query request.

3. The data processing method according to claim 2, It is characterized in that The data processing method comprises: The management module imports the latched query address into the address input terminal of the storage module according to the current index information in the Check state, and generates a read valid signal to the en terminal of the storage module; The management module determines whether the output of the storage module is valid. If so, the coded data output by the storage module is transmitted to the corresponding signal tracking channel according to the current index information, and an output valid signal is generated and transmitted back, and then the address information latched at the signal tracking channel port indicated by the current index information and the query valid information are cleared; The query module enters the IDLE state.

4. The data processing method according to claim 3, It is characterized in that The data processing method comprises: The pseudo-random code generator generates a query address in a corresponding query request according to the current code phase, wherein the query address increases by 1 each time it is queried, and automatically returns to an initial value after increasing to a maximum value, and the initial value is generated according to the satellite number and written into the status register.

5. The data processing method according to claim 4, It is characterized in that The pseudo-random code generator includes two levels of cache. After receiving the coded data, the pseudo-random code generator saves the latest received coded data in the second level cache. The pseudo-random code generator and the correlator calculate the coded data in the first level cache to track the satellite signal. The first level cache reads the coded data in the second level cache after the coded data calculation is completed. Then, the pseudo-random code generator generates the next query request after the first level cache reads the coded data in the second level cache.

6. The data processing method according to claim 5, It is characterized in that The data processing method comprises: The pseudo-random code generator reads a chip from the first-level cache; The pseudo-random code generator generates a pseudo-random code using the code chip; Determine whether to read the second-level cache into the first-level cache, if yes, read the encoded data in the second-level cache into the first-level cache, if no, execute the step of reading a code piece from the first-level cache again; The pseudo-random code generator generates the next query request; Determine whether the coded data corresponding to the query request is received, and if so, save the latest received coded data to the second-level cache.

7. A GNSS receiver, It is characterized in that The GNSS receiver includes a plurality of signal tracking channels, a query module, a management module and a storage module. Each signal tracking channel includes a pseudo-random code generator and a correlator. The storage module has a pre-stored memory code. The management module is used to receive query requests for all signal tracking channels; The management module is used to call the query module in a preset order to process the query request; The query module is used to query the coded data in the memory code according to the query request; The query module is used to send the coded data to the corresponding signal tracking channel; The signal tracking channel is used to track satellite signals by using the coded data obtained by calculating the pseudo-random code generator and the correlator.

8. The GNSS receiver according to claim 7, It is characterized in that Each query request includes a flag and a query address. The management module is used to latch the flag bit and the query address in the query request after receiving the query request; The query module is used to change the state from IDLE state to Check state after receiving the query request; The management module is used to generate an index information according to the query request, and the index information corresponds to the signal tracking channel that sends the valid query request; The management module is used to import the latched query address into the address input terminal of the storage module according to the current index information in the Check state, and generate a read valid signal to the en terminal of the storage module; The management module is used to determine whether the output of the storage module is valid. If so, the coded data output by the storage module is transmitted to the corresponding signal tracking channel according to the current index information, and an output valid signal is generated and transmitted back, and then the address information latched at the signal tracking channel port indicated by the current index information and the query valid information are cleared; The query module is used to enter the IDLE state after the management module clears the address information latched by the signal tracking channel port indicated by the current index information and the query valid information.

9. The GNSS receiver according to claim 8, It is characterized in that The pseudo-random code generator is used to generate a query address in a corresponding query request according to the current code phase, wherein the query address is incremented by 1 each time it is queried, and automatically returns to an initial value after increasing to a maximum value, and the initial value is generated according to the satellite number and written into a status register, wherein the pseudo-random code generator includes a two-level cache, and after receiving the coded data, the pseudo-random code generator saves the latest received coded data to the second-level cache, and the pseudo-random code generator and the correlator calculate the coded data in the first-level cache to track the satellite signal, and the first-level cache reads the coded data in the second-level cache after the coded data calculation is completed, and then the pseudo-random code generator generates the next query request after the first-level cache reads the coded data in the second-level cache.

10. The GNSS receiver according to claim 9, It is characterized in that The pseudo-random code generator is used to read a chip from the first-level cache; The pseudo-random code generator is used to generate a pseudo-random code using the code chip; The pseudo-random code generator is used to determine whether to read the second-level cache into the first-level cache, and if so, read the encoded data in the second-level cache into the first-level cache, and if not, execute the step of reading a code chip from the first-level cache again; The pseudo-random code generator is used to generate the next query request; The pseudo-random code generator is used to determine whether the coded data corresponding to the query request is received, and if so, save the latest received coded data to the second-level cache.

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