Data compression and transmission method for low-bandwidth wireless local area network

Abstract

The invention discloses a data compression and transmission method for a low-bandwidth wireless local area network, which belongs to the technical field of low-bandwidth wireless local area networks, and comprises the following steps of: 1, compressing received differential data in a main node; 2, subpackaging the compressed data, and broadcasting the subpackaged data to child nodes; and step 3, carrying out packet mixing and decompression on the data in the child nodes. In the process of the step 1, received differential data are compressed in a main node by using a lossless compression algorithm; according to the system, a main node and sub-nodes cooperatively work, and the main node is used for collecting and transmitting data, obtaining current positioning data, communicating with a differential service platform and obtaining corresponding differential correction data; and the main node compresses and packages the differential data, and sends the differential data to the sub-nodes in a broadcast mode. According to the method, the integrity and the real-time performance of the RTK data can be ensured, and the problems of data accumulation and delay are avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-bandwidth wireless local area networks, and in particular relates to a data compression and transmission method for low-bandwidth wireless local area networks. Background Art

[0002] RTK (Real Time Kinematic, real-time dynamic carrier phase differential technology) is a high-precision real-time dynamic positioning method based on carrier phase measurement and differential positioning, usually referred to as RTK technology in the industry. This technology is widely used in various scenarios that require high-precision positioning by improving the accuracy of satellite positioning systems. When applying RTK technology for positioning, the traditional method is to assign an independent account to each positioning device on the network RTK service platform, so that these devices can communicate directly with the platform to obtain correction data, thereby improving positioning accuracy. This method is particularly suitable for scenarios where positioning points are relatively scattered. However, when the number of positioning nodes is large within a certain range (for example, within 3 kilometers), the use of a one-to-one communication mode will lead to low efficiency and increased costs. In this scenario, a master node can communicate with the service platform to obtain differential calibration data. Then, the master node can provide differential data to surrounding sub-nodes in a broadcast form through a low-bandwidth wireless LAN (such as Bluetooth or LoRa, etc.) to achieve high-precision positioning. This method only requires one account to meet the needs of multiple nodes, which not only reduces equipment cost and terminal power consumption, but also extends the use time of the equipment and reduces the overall construction cost.

[0003] In the patent "A local real-time differential data multi-path broadcasting system" (publication number CN212540724U), a method for sending local RTK data from a master node to a sub-node in a wireless local area network is proposed, thereby achieving a higher-precision positioning service. However, when using RTK technology for positioning, the size of the differential data packet is usually between 3KB and 4KB, and since wireless local area networks (ZigBee, LoRa, Bluetooth) have the characteristics of long communication distance, relatively low data transmission rate and small single frame length, when using this method to transmit differential data, problems such as data accumulation and increased delay will be encountered. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a data compression and transmission method for a low-bandwidth wireless local area network, thereby solving the problems in the above-mentioned background technology.

[0005] The purpose of the present invention is achieved as follows: a data compression and transmission method for low-bandwidth wireless local area networks, which includes the following steps: step one, compressing the received differential data in the main node; step two, packetizing the compressed data and broadcasting it to the child nodes; step three, packetizing and decompressing the data in the child nodes.

[0006] In the process of step 1, the received differential data is compressed in the master node by using a lossless compression algorithm; the system is composed of a master node and a sub-node working together, the master node is used for data collection and transmission, obtains the current positioning data, communicates with the differential service platform, and obtains the corresponding differential correction data; the master node compresses and packages the differential data, and sends it to the sub-node by broadcasting;

[0007] The child node is used to receive the differential data packet broadcast by the master node. After receiving the data packet, the child node parses it and uses the parsed differential data for differential positioning to update its own location information. The master node uses the positioning module to obtain location data, extract valid positioning information, and upload the valid positioning information to the RTK server. The RTK server generates differential calibration data based on the location information and transmits it to the master node.

[0008] The lossless compression algorithm comprises the following steps:

[0009] First, arrange the received strings and store them in the buffer;

[0010] Second, initialize the sliding window and scanning window, point the sliding window to the beginning of the string, and the scanning window to the last bit of the sliding serial port;

[0011] Third, perform a hash operation on the string in the sliding window to determine whether the string exists in the current hash table;

[0012] Fourth, move the sliding window right and place it to the right of the matched string, return to step 3 and perform hash operation again until the end of the string;

[0013] Fifth, concatenate the hash table length, the hash table value, and the offset + length of each string into a hexadecimal data stream, store the data stream in the buffer, and end.

[0014] The third includes:

[0015] 3.1; if the string exists in the current hash table, the scanned serial port will be merged into the sliding window, shifted back one position, and hashed again until the longest string can be successfully matched, and then the index and length of the string in the hash table will be recorded.

[0016] 32; If the string does not exist in the current hash table, append the string to the end of the hash table, and then record the index and length of the string in the hash table.

[0017] After the child node successfully captures the data packet broadcast by the master node, it verifies the packet number and check bit of each individual data packet received. The specific process is as follows:

[0018] 1. First, identify the frame header and frame tail to obtain valid data;

[0019] 2. Secondly, identify the check bit to confirm the correctness of the packet during transmission;

[0020] 3. Read the data length and instruction to determine the packet type of this packet;

[0021] 4. Record the variable length read out, record the packet number and data content together, and put them into the buffer;

[0022] 5. Return to step 1 and read the data packet again until the data packet read out is the last packet, and then go to step 6;

[0023] 6. Combine several data packets to restore the original data sent by the master node.

[0024] After the verification combination is completed, the child node will splice and restore these data packets in order according to the packet number identifier. After completing the data splicing, the child node will use the decompression algorithm to decompress the compressed data. The specific decompression process is as follows:

[0025] (1) Read data blocks and reference information from the compression result;

[0026] (2) Same as the compression process, create a fixed-size buffer as a sliding window;

[0027] (3) For each data block, first read its literal part, then find and copy the matching string in the sliding window according to the reference information, and this process reconstructs the original string;

[0028] (4) Output the reconstructed original string to the decompression result;

[0029] (5) Finally, the differential data restored by the child node is used for positioning.

[0030] The beneficial effects of the present invention are as follows: a lossless compression algorithm is used to significantly reduce the amount of data, ensure the integrity and real-time performance of RTK data, and avoid data accumulation and delay problems. In addition, in order to adapt to the low-speed wireless LAN environment and improve the accuracy of data transmission, the compressed data is reasonably packetized. Each data packet is added with a header, a tail, and verification information, so that the child node can verify whether the data packet remains intact during the transmission process after receiving the data, thereby improving the overall data transmission efficiency and accuracy. Data is transmitted to child nodes in a broadcasting manner, and there is no limit on the number of child nodes. When the number of child nodes increases significantly, the communication efficiency within the system is less affected. The lossless compression algorithm has low resource requirements and is suitable for terminals with low computing power. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the steps of the present invention;

[0032] Figure 2 It is a schematic diagram of the lossless compression algorithm of the present invention. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with the accompanying drawings. It should be pointed out that it is only for the purpose of more clearly describing and explaining the present invention.

[0034] like Figure 1 and 2 As shown, this embodiment discloses a data compression and transmission method for low-bandwidth wireless local area networks. In view of the problem of large amount of differential data in RTK positioning, a method for data compression and transmission in a low-bandwidth wireless local area network is designed. The method first uses a lossless compression algorithm to quickly compress the received differential data in the main node, then divides the compressed data into packets and broadcasts them to the child nodes, and finally combines and decompresses the data in the child nodes.

[0035] In this method, the system consists of a master node and sub-nodes working together. The master node plays a core role in data collection and transmission. It first obtains the current positioning data, communicates with the differential service platform, and obtains the corresponding differential correction data. Subsequently, the master node efficiently compresses the differential data, reasonably divides it into packets, and sends it to the sub-nodes through broadcasting.

[0036] The tasks of the child nodes are relatively clear. They are mainly responsible for receiving the differential data packets broadcast by the master node. Once the data packets are received, the child nodes will immediately parse them and use the parsed differential data for differential positioning to update their own location information.

[0037] The master node uses the positioning module to obtain position data, extract valid positioning information, and upload the valid positioning information to the RTK server. The RTK server generates differential calibration data based on the position information and transmits it to the master node. The master node uses a lossless compression algorithm to compress the data. The specific calculation process is as follows:

[0038] 1: Arrange the received character string and store it in the buffer.

[0039] 2: Initialize the sliding window and scanning window, point the sliding window to the beginning of the string, and the scanning window to the last bit of the sliding serial port.

[0040] 3: Perform hash operation on the string in the sliding window to determine whether the string exists in the current hash table.

[0041] 3.1: If the string exists in the current hash table, the scanning serial port will be merged into the sliding window, and it will be shifted back one position, and the hash operation will be performed again until the longest string can be successfully matched, and then the index and length of the string in the hash table will be recorded.

[0042] 3.2: If the string does not exist in the current hash table, append the string to the end of the hash table, and then record the index and length of the string in the hash table.

[0043] 4: Move the sliding window right and place it to the right of the matched string. Return to step 3 and perform hash operation again until the end of the string.

[0044] 5: Connect the hash table length, hash table value, offset + length of each string into a hexadecimal data stream, store the data stream into the buffer, and end.

[0045] The master node compresses the original 3k-4k bytes of differential data to about 1k bytes through a lossless compression algorithm. Then, the master node splits the compressed data into multiple data packets suitable for transmission in the wireless LAN, and adds a frame header, data length, instruction, and packet number to the header of each data packet, and adds a checksum and frame tail to the end of each data packet, finally forming a complete data packet. The structure of the complete data packet is as follows:

[0046]

[0047] The instruction code for sending a differential data packet is 0x10, and the packet number is the first byte of the variable length. The packet number is divided into two parts by bit, where bit7 indicates whether this packet is the last packet. When bit7 is 0, it indicates that this packet is not the last packet. When bit7 is 1, it indicates that this packet is the last packet. Bit1 to bit6 indicate the packet number, ranging from 0 to 63. The wireless LAN broadcasts the data packet to the child nodes.

[0048] After the child node successfully captures the data packet broadcast by the master node, it verifies the packet number and check bit of each individual data packet received. The specific process is as follows:

[0049] 1: First, identify the frame header and frame tail to obtain valid data.

[0050] 2: Next, identify the check bit to confirm the correctness of the packet during transmission.

[0051] 3: Read the data length and instruction to determine the packet type of this packet.

[0052] 4: Record the variable length read out, record its packet number and data content together, and put them into the buffer.

[0053] 5: Return to step 1 and read the data packet again until the data packet read out is the last packet, and then go to step 6.

[0054] 6: Combine several data packets to restore the original data sent by the master node.

[0055] After the verification combination is completed, the child node will splice and restore these data packets in order according to the packet number identifier. After completing the data splicing, the child node will use the decompression algorithm to decompress the compressed data. The specific decompression process is as follows:

[0056] 1: Read data blocks and reference information from the compression result.

[0057] 2: Same as the compression process, create a fixed-size buffer as a sliding window.

[0058] 3: For each data block, first read its literal part, then find and copy the matching string in the sliding window according to the reference information. This process will reconstruct the original string.

[0059] 4: Output the reconstructed original string to the decompression result.

[0060] Finally, the child node will perform high-precision positioning on the restored differential data.

[0061] The invention creates and utilizes a lossless compression algorithm to reduce the amount of transmitted data, compensate for the defects of low data transmission rate and high delay of wireless local area network, and improve the real-time performance of data. A reliable data transmission mechanism is proposed, and data is adaptively packetized according to the characteristics of the wireless local area network to reduce the packet loss rate and improve the reliability of data transmission. In this method, data is transmitted to child nodes in a broadcasting manner. There is no limit on the number of child nodes. When the number of child nodes increases significantly, the communication efficiency in the system is less affected. The lossless compression algorithm has low resource requirements and is suitable for terminals with low computing power.

[0062] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A data compression and transmission method for low-bandwidth wireless local area networks, characterized in that: The following steps are involved: Step 1: compress the received differential data in the master node; Step 2: Sub-packaging the compressed data and broadcasting it to the child nodes; Step 3: Pack and decompress the data in the child node.

2. The data compression and transmission method for low-bandwidth wireless local area network according to claim 1, characterized in that: In the process of step 1, the received differential data is compressed in the master node by using a lossless compression algorithm; the system is composed of a master node and a sub-node working together, the master node is used for data collection and transmission, obtains the current positioning data, communicates with the differential service platform, and obtains the corresponding differential correction data; the master node compresses and packages the differential data, and sends it to the sub-node by broadcasting; The child node is used to receive the differential data packet broadcast by the master node. After receiving the data packet, the child node parses it and uses the parsed differential data for differential positioning to update its own location information. The master node uses the positioning module to obtain location data, extract valid positioning information, and upload the valid positioning information to the RTK server. The RTK server generates differential calibration data based on the location information and transmits it to the master node.

3. The data compression and transmission method for low-bandwidth wireless local area network according to claim 2, characterized in that: The lossless compression algorithm comprises the following steps: First, arrange the received strings and store them in the buffer; Second, initialize the sliding window and scanning window, point the sliding window to the beginning of the string, and the scanning window to the last bit of the sliding serial port; Third, perform a hash operation on the string in the sliding window to determine whether the string exists in the current hash table; Fourth, move the sliding window right and place it to the right of the matched string, return to step 3 and perform hash operation again until the end of the string; Fifth, concatenate the hash table length, the hash table value, and the offset + length of each string into a hexadecimal data stream, store the data stream in the buffer, and end.

4. The data compression and transmission method for low-bandwidth wireless local area network according to claim 3, characterized in that: The third includes: 3.1; if the string exists in the current hash table, the scanned serial port will be merged into the sliding window, shifted back one position, and hashed again until the longest string can be successfully matched, and then the index and length of the string in the hash table will be recorded.

5. The data compression and transmission method for low-bandwidth wireless local area network according to claim 4, characterized in that: The third includes: 32; If the string does not exist in the current hash table, append the string to the end of the hash table, and then record the index and length of the string in the hash table.

6. The data compression and transmission method for low-bandwidth wireless local area network according to claim 2, characterized in that: After the child node successfully captures the data packet broadcast by the master node, it verifies the packet number and check bit of each individual data packet received. The specific process is as follows:

1. First, identify the frame header and frame tail to obtain valid data; 2. Secondly, identify the check bit to confirm the correctness of the packet during transmission; 3. Read the data length and instruction to determine the packet type of this packet; 4. Record the variable length read out, record the packet number and data content together, and put them into the buffer; 5. Return to step 1 and read the data packet again until the data packet read out is the last packet, and then go to step 6; 6. Combine several data packets to restore the original data sent by the master node.

7. The data compression and transmission method for low-bandwidth wireless local area network according to claim 6, characterized in that: After the verification combination is completed, the child node will splice and restore these data packets in order according to the packet number identifier. After completing the data splicing, the child node will use the decompression algorithm to decompress the compressed data. The specific decompression process is as follows: (1) Read data blocks and reference information from the compression result; (2) Same as the compression process, create a fixed-size buffer as a sliding window; (3) For each data block, first read its literal part, then find and copy the matching string in the sliding window according to the reference information, and this process reconstructs the original string; (4) Output the reconstructed original string to the decompression result; (5) Finally, the differential data restored by the child node is used for positioning.

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