CN111538060B - A relative positioning method based on Lora network - Google Patents

Abstract

The invention discloses a relative positioning method based on the Lora network, which includes: gateway nodes and terminal nodes obtain satellite information through their GPS positioning modules at the agreed time at the same time, and obtain their own positioning coordinates; for the terminal node, if it If the number of duplicate satellites between the satellite sequence set S' in the acquired satellite information and the satellite sequence set S of the gateway node is greater than the preset threshold, then the terminal node uploads its positioning coordinates and the number of duplicate satellites to the gateway node; so The gateway node calculates the relative coordinates between itself and the corresponding terminal node based on its own positioning coordinates, the positioning coordinates uploaded by the terminal node, and the number of repeated satellites. The use of relative positioning can eliminate most system errors, thereby reducing the relative positioning error between nodes; while ensuring positioning accuracy without increasing the cost of hardware, it is suitable for precision agriculture, aquaculture, livestock tracking and other fields, and has good performance economic benefits and social value.

Description

A relative positioning method based on Lora network

Technical field

The invention relates to the field of communication technology, and in particular to a relative positioning method based on Lora network.

Background technique

Large-scale and refined modern aquaculture has become a trend, and low cost and high quality have become demands. The research and application of fishery Internet of things (IOT) technology are becoming more and more extensive. In addition to static monitoring points, the terminal nodes of the Fishery Internet of Things also have a large number of floating nodes using buoys, fish rafts, cages, etc. as carriers; therefore, how to obtain high-precision location information has become a hot topic in the current Fisheries Internet of Things research. one.

For long-distance IoT applications, the LoRa protocol is usually used for communication. LoRa (long range) is a low-power long-distance wireless communication technology, and its industry chain is currently very mature and complete. LoRa wireless communication technology has become an important basic technology for Internet of Things applications after being promoted globally by the LoRa Alliance composed of Semtech, Cisco, and IBM. Different from traditional wireless systems that use frequency shift keying modulation as the physical layer to achieve low power consumption, LoRa uses linear frequency modulation spread spectrum modulation, which has the same low power consumption characteristics as frequency shift keying modulation technology, and the transmission distance is also Significantly improved. The working frequency of LoRa is below 1GHz, including 109MHz, 433MHz, 866MHz and other frequencies. Thanks to LoRa's use of new spread spectrum modulation technology, users can customize different spreading factors and bandwidths to meet different distances and needs. In addition, the penetration capability of LoRa communication is enhanced due to the spread spectrum technology used, so it can be used in relatively complex environments. Therefore, LoRa technology has obvious advantages in low power consumption, wireless transmission distance, penetration capability, networking, etc. Therefore, this study uses low-power long-distance LoRa wireless communication technology as the data communication link in the relative positioning system.

Positioning is a basic requirement for IoT applications. Commonly used positioning methods are mainly divided into the following three types:

(1) Based on the received signal strength indicator (RSSI) measurement and positioning of the path loss model. This method requires the location of the gateway to be known in advance, and then the location of the end devices within the area can be roughly calculated. This method is greatly affected by the environment and obstacles, and the positioning error is as high as several hundred meters.

(2) Positioning based on time difference of arrival (TDOA). Positioning methods based on TDOA require time synchronization between nodes. The LoRa terminal device sends uplink packets to the LoRa gateway. Each gateway records the packet arrival time separately. A positioning server in the network calculates the time difference of arrival and then determines the location of the end device. This method requires multiple gateways to be deployed, and time synchronization between gateways is required. This method requires dedicated hardware and software to capture high-precision arrival times, and requires high equipment costs.

(3) GPS positioning is currently the most widely used positioning solution. The error of GPS single-point positioning is about 10 meters. Using differential technology can effectively improve positioning accuracy, but it requires support from ground base stations, and differential equipment is expensive. Therefore, It cannot be widely used in applications such as precision agriculture and aquaculture.

Contents of the invention

The purpose of the present invention is to provide a relative positioning method based on the LoRa network based on the above-mentioned shortcomings of the prior art. This method combines the LoRa network with GPS positioning to solve the cost and positioning problems of the Internet of Things positioning solution in the prior art. It is difficult to balance accuracy.

The purpose of the present invention is achieved by the following technical solutions:

A relative positioning method based on the Lora network, applied to the Lora network. The Lora network includes a gateway node and a large number of terminal nodes that are communicated with the gateway node through the Lora protocol; the gateway node and the terminal node both Including a GPS positioning module, the relative positioning method includes the following steps:

(S1) The gateway node and the terminal node simultaneously obtain satellite information through their GPS positioning modules at the agreed satellite sampling time t _SN , and obtain their own positioning coordinates;

(S2) For the terminal node, if the number of duplicate satellites between the satellite sequence set S′ in the satellite information it obtains and the satellite sequence set S of the gateway node is greater than the preset threshold, the terminal node will determine its positioning coordinates and the duplicate satellites. Upload the data to the gateway node;

(S3) The gateway node calculates the relative coordinates between itself and the corresponding terminal node based on its own positioning coordinates, the positioning coordinates uploaded by the terminal node, and the number of repeated satellites.

A further improvement of the present invention is that the relative positioning method operates with _TP as a period, and each period _TP is divided into a sampling period _TS , a command broadcast period _TB , and a terminal data upload period _TD according to time;

The gateway node and the terminal node obtain satellite information during the sampling period T _S and obtain their own positioning coordinates;

The gateway node sends a command packet B to each of the terminal nodes during the command broadcast period T _B. The command packet B includes the satellite sequence set S obtained by the gateway node;

The terminal data upload period _TD is divided into a plurality of time slots, the terminal node has a group number, and the time slot corresponds to the group number; the terminal node transmits data to the terminal node in its assigned time slot. The gateway node uploads the satellite sequence set S′ and positioning coordinates it has obtained.

A further improvement of the present invention is that,

The command package B also includes the group number of the terminal node participating in positioning in the next period TP ₊₁ and the agreed satellite sampling time t _SN ;

In the next period T _P+1 , only the terminal node corresponding to the group number included in the command packet B of the previous period T _P participates in relative positioning.

A further improvement of the present invention is that the terminal node and the gateway node each include a microcontroller; the gateway node and the terminal node perform time synchronization through the second pulse of the GPS positioning module.

A further improvement of the present invention is that in the terminal node and the gateway node, the serial port of the GPS positioning module is connected to the serial port of the microcontroller; the second pulse of the microcontroller and the GPS positioning module The signal pin is connected. When the GPS positioning module sends out a second pulse, the microcontroller responds to the interrupt signal and enters the second pulse interrupt response program;

When entering the second pulse interrupt response program for the first time, the microcontroller resolves the time message obtained by the GPS positioning module, obtains the time value therefrom, and saves the time value;

Each time the second pulse interrupt response program is entered thereafter, the microcontroller adds the number of seconds between the last second pulse interrupt and the current second pulse interrupt and its saved time value to obtain the current time value.

The advantages of the present invention are:

(1) Combining the Lora network with GPS positioning, using relative positioning can eliminate most system errors, thereby reducing the relative positioning error between nodes; it ensures positioning accuracy without increasing the cost of hardware, and is suitable for precision agriculture. , aquaculture, livestock tracking and other fields, with good economic benefits and social value;

(2) The process of transmitting data from the terminal node to the gateway node uses time division multiple access (TDMA) technology, which allocates different time slots to different terminal nodes, which can reduce the probability of channel collision while increasing the data delivery rate and increasing the capacity of the network.

Description of the drawings

Figure 1 is a flow chart of the operation mode of the gateway node;

Figure 2 is a flow chart of the operation mode of the terminal node;

Figure 3 is a schematic diagram of the data sending and receiving method in each cycle _TP in the relative positioning method;

Figure 4 is a schematic diagram of the data frame of command packet B;

Figure 5 is a schematic diagram of a data frame sent by a terminal node to a gateway node.

Detailed ways

As shown in Figures 1 to 5, embodiments of the present invention include a relative positioning method based on the Lora network, which method is applied to the Lora network. The Lora network includes gateway nodes and a large number of terminal nodes that communicate with the gateway nodes through the Lora protocol. Both the gateway node and the terminal node include GPS positioning modules.

As shown in Figures 1 to 3, the above-mentioned Lora network operates with T _P as a cycle. Each cycle T _P is divided into a sampling period T _S , a command broadcast period T _B , and a terminal data upload period T _D in time order. In each cycle, the relative positioning method includes the following steps:

(1) During the sampling period _TS , the gateway node and each terminal node obtain satellite information through its GPS positioning module at the agreed satellite sampling time t _SN (time t _s in Figure 3), and obtain its own positioning coordinates. The positioning coordinates here include longitude and latitude, and the error level is the same as that of ordinary GPS single-point positioning. The satellite information includes the satellite sequence set received by the GPS positioning module.

(2) In the command broadcast period T _B , the gateway node sends command packet B to each terminal node through the Lora protocol. The frame format of the command packet B is shown in Figure 4. The command packet B includes the satellite sequence set S obtained by the gateway node.

(3) During the terminal data upload period T _D , if the number of duplicate satellites between the satellite sequence set S′ in the satellite information obtained by a terminal node and the satellite sequence set S of the gateway node is greater than the preset threshold, then the terminal node Upload its positioning coordinates and the number of repeated satellites to the gateway node. The format of the uploaded data frame is shown in Figure 5.

As shown in Figure 3, the terminal data upload period TD is divided into a plurality of time slots θ, the terminal node has a group number, and the time slot corresponds to the group number; the terminal node in its assigned time slot θ _i The gateway node uploads the satellite sequence set S′ and positioning coordinates it has obtained.

(4) The gateway node calculates the relative coordinates between it and the corresponding terminal node based on its own positioning coordinates, the positioning coordinates uploaded by the terminal node, and the number of repeated satellites.

In this embodiment, relative coordinates are calculated only when the number of repeated satellites is greater than a preset threshold. The reason is that the purpose of calculating relative coordinates is to eliminate most system errors, thereby reducing relative positioning errors between nodes. Only when the terminal node and gateway node use the same satellite for positioning, will the positioning coordinates of the two contain similar systematic errors. The more repeated satellites there are, the higher the accuracy of the calculated relative coordinates.

The principle of calculating relative coordinates to reduce relative positioning errors is: During the GPS positioning process, positioning accuracy is usually affected by three parts of errors. The first part is common to every user receiver, such as satellite clock error, ephemeris error, etc. ; The second part is the propagation delay error that cannot be calculated by user measurement or correction model, such as ionospheric refraction and tropospheric delay; the third part is the error inherent in each user's receiver, such as internal noise, channel delay, multipath Effect etc.

Assume that the observed position of the gateway node is P _W =P _tW +P _eW , P _tW is the real position of the gateway node, and P _eW is the position error caused by the measurement error of the gateway node position. The position of the terminal node is P _N =P _tN +P _eN , P _tN is the real position of the gateway node, and P _eN is the position error caused by the gateway position measurement error. The relative position available is

The gateway node W obtains its observation position (coordinate) error in the earth-centered coordinate system (earth-centered, earth-fixed, ECEF) at time t _W , which can be expressed as Equation (1):

P _eW (t _W )=G _W (E _W ΔS _W (t _W )-Δρ _W (t _W )) (1)

In the formula, G _W and E _W are the azimuth characteristic matrices of node W and each satellite; P _eW (t _W ) is the satellite position deviation at time t _W caused by satellite clock difference, atmospheric delay, multipath deviation and receiver hardware deviation. ; Δρ _W (t _W ) is the pseudo-range error vector from node W to each satellite at time t _W .

As mentioned above, for the terminal node N, the observation position (coordinate) error in the ECEF coordinate system at time t _N can be obtained as shown in Equation (2):

P _eN (t _N )=G _N (E _N ΔS _N (t _N )-Δρ _N (t _N )) (2)

Observed relative position between onshore gateway node W and terminal node N As shown in formula (3):

make Where D _WN =P _tW (t _W )-P _tN (t _N ) is the true relative position between W and N, ΔD _WN is its relative position error, and combined with equations (1) to (3), we get W, The relative distance error between N is shown in equation (4):

After time synchronization, the gateway node W and the terminal node N obtain the GPS location information at the same time as agreed, that is: t _W =t _N =t. Within the same area, the gateway node W on the shore and the terminal node N in the monitoring waters are almost The same satellite combination can be observed, namely: S ^W =S ^N =S. In this way, when almost the same satellite combination is used for positioning calculations at the same time, the satellite position deviations caused by satellite clock differences, atmospheric delays, etc. are almost the same, that is: ΔS _W (t) = ΔS _N (t). Since the gateway node W on the shore is fixed and the node N is in the breeding waters, the position difference between the gateway node W and the node N can be ignored relative to the distance from the node to the satellite. The difference in direction angle between the two points and the satellite is very small. Therefore, The difference between their direction vectors is negligible, that is, G _W E _W ≈ G _N E _N . Then substitute equations (2) and (3) into equation (4) to get equation (5):

ΔD _WN ＝G _W Δρ _W (t)-G _N Δρ _N (t) (5)

Express the pseudorange error as: Δρ _Wi = B _Wi + V _Wi (i = 1, 2,..., 4), where B _Wi is the systematic random error, mainly caused by atmospheric delay, tropospheric and ionospheric effects, etc., V _Wi It is a random error, mainly caused by multipath deviation and receiver hardware. Then for the W and N nodes: Δρ _W =B _W +V _W , Δρ _N =B _N +V _N , substituted into equation (5) to represent the position error of the W and N nodes, as shown in equation (6):

ΔD _WN ＝G _W B _W -G _N B _N +G _W V _W -G _N V _N (6)

In the formula, the random errors V _W and V _N are independent of each other, and E{V _W }=E{V _N }=0,

Let ΔN=N _N -N _W and ΔG=G _N -G _W represent the difference of W and N node system errors and orientation matrices respectively. Substituting into equations (5) and (6), and ignoring the third-order small quantities, we can get The mathematical expectation of the position error of nodes W and N is shown in formula (7):

It can be seen from equation (7) that the relative position error between the gateway node and the terminal node is mainly related to the system error and the second-order small quantity of the orientation matrix difference, and the distance error caused by the hardware random error is usually related to the system error. Very small, so using relative positioning can eliminate most systematic errors, thereby reducing the relative positioning error between nodes.

In some actual cases, the terminal node is 100m away from the gateway node, the maximum relative positioning error is 2m, the minimum relative positioning error is 1.1m, and the average positioning error is 1.5m. Its positioning error level is far lower than the error of GPS single-point positioning. The positioning error is almost 1 times smaller than single-point positioning.

As shown in Figures 1, 2, and 3, in this embodiment, the terminal node does not participate in relative positioning every cycle _TP . The command package B also includes the group number of the terminal node participating in positioning in the next period T _P+1 and the agreed satellite sampling time t _SN . In the next period T _P+1 , only the terminal node corresponding to the group number included in the command packet B of the previous period T _P participates in relative positioning.

In the terminal data upload period T _D , the number of time slots can be smaller than the number of terminal nodes. In this case, the command packet B sent by the gateway node includes in addition to the group number of the terminal node participating in positioning in the next period T _P+1. The corresponding time slot number needs to be specified so that the corresponding terminal node uploads data in the specified time slot. In the embodiment of the present invention, the process of transmitting data from the terminal node to the gateway node uses time division multiple access (TDMA) technology to allocate different time slots to different terminal nodes, which can reduce the probability of channel collision while increasing the data delivery rate and improving the network efficiency. capacity.

In some implementations, microcontrollers are included in both the end node and the gateway node. The gateway node and the terminal node perform time synchronization through the second pulse of the GPS positioning module.

Specifically, in the terminal node and the gateway node, the serial port of the GPS positioning module is connected to the serial port of the microcontroller; the microcontroller is connected to the second pulse signal pin of the GPS positioning module. When the GPS positioning module sends out the second pulse, The microcontroller responds to the interrupt signal and enters the second pulse interrupt response program.

When entering the second pulse interrupt response program for the first time, the microcontroller interprets the time message obtained by the GPS positioning module. The message is sent through the serial port, contains the time value internally, and saves the time value. The resolution process of the message containing the time value transmitted through the serial port takes time, and the length of the resolution process is uncertain. Therefore, the time value is difficult to be directly used for time synchronization and is usually only used for initialization.

After the initial response to the interrupt signal, each time the second pulse interrupt response program is entered, the microcontroller adds the number of seconds between the last second pulse interrupt and the current second pulse interrupt and its saved time value to obtain the current time. value. The accuracy of the pulse per second (PPS) output by the GPS positioning module is 1μs, which can be used for high-precision time synchronization.

In addition, in each cycle, the command package B sent by the gateway node also includes the command type. Each terminal node will execute the above method only when the command type is positioning.

The above embodiments of the present invention do not limit the scope of protection of the present invention. Any modifications, substitutions and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims (3)

1. A relative positioning method based on the Lora network, applied to the Lora network, the Lora network includes a gateway node and a large number of terminal nodes that are communicated with the gateway node through the Lora protocol; the gateway node and the terminal Each node includes a GPS positioning module, which is characterized in that the relative positioning method includes the following steps: (S1) The gateway node and the terminal node simultaneously obtain satellite information through their GPS positioning modules at the agreed satellite sampling time t _SN , and obtain their own positioning coordinates; (S2) For the terminal node, if the number of duplicate satellites between the satellite sequence set S' in the satellite information it obtains and the satellite sequence set S of the gateway node is greater than the preset threshold, then upload its positioning coordinates and the number of duplicate satellites to the gateway node; (S3) The gateway node calculates the relative coordinates between itself and the corresponding terminal node based on its own positioning coordinates, the positioning coordinates uploaded by the terminal node and the number of repeated satellites; The relative positioning method operates with _TP as a cycle, and each cycle _TP is divided into a sampling period _TS , a command broadcast period _TB , and a terminal data upload period _TD according to time; The terminal data upload period _TD is divided into a plurality of time slots, the terminal node has a group number, and the time slot corresponds to the group number; the terminal node transmits data to all the time slots in its assigned time slot. The gateway node uploads the acquired satellite sequence set S′ and positioning coordinates; The gateway node and the terminal node obtain satellite information during the sampling period T _S and obtain their own positioning coordinates; The gateway node sends a command packet B to each of the terminal nodes during the command broadcast period T _B. The command packet B includes the satellite sequence set S obtained by the gateway node; The command package B also includes the group number of the terminal node participating in positioning in the next period TP ₊₁ and the agreed satellite sampling time t _SN ; During the terminal data upload period _TD , when the number of time slots is less than the number of terminal nodes, the command packet B sent by the gateway node includes in addition to the group number of the terminal node participating in positioning in the next period TP ₊₁ , and specifies the corresponding The time slot number; In the next period T _P+1 , only the terminal node corresponding to the group number included in the command packet B of the previous period T _P participates in relative positioning. 2. A relative positioning method based on the Lora network according to claim 1, characterized in that the terminal node and the gateway node each include a microcontroller; the gateway node and the terminal node use GPS The second pulse of the positioning module is time synchronized. 3. A relative positioning method based on Lora network according to claim 2, characterized in that, in the terminal node and the gateway node, the serial port of the GPS positioning module and the serial port of the microcontroller Connection; the microcontroller is connected to the second pulse signal pin of the GPS positioning module. When the GPS positioning module sends out the second pulse, the microcontroller responds to the interrupt signal and enters the second pulse interrupt response program; When entering the second pulse interrupt response program for the first time, the microcontroller resolves the time message obtained by the GPS positioning module, obtains the time value therefrom, and saves the time value; Each time the second pulse interrupt response program is entered thereafter, the microcontroller adds the number of seconds between the last second pulse interrupt and the current second pulse interrupt and its saved time value to obtain the current time value.