CN102014489A - Environment adaptive RSSI local positioning system and method - Google Patents

Abstract

The present invention proposes an environment-adaptive RSSI local positioning system and method. Positioning is based on signal energy strength. The signal can be a radio frequency signal or an underwater acoustic signal. The positioning steps include: during the positioning process, the reference node Measure the reference node path loss factor corresponding to each area in real time, and follow the database of the new loss factor according to the set frequency; when receiving the signal of the mobile node, use the three points with the strongest signal to determine the area where the mobile node is located; use Calculate the distance from the mobile node to the three reference nodes based on the loss factors of the reference nodes in the corresponding area; calculate the position of the mobile node by using the method of trilateration. The advantage of using this positioning technology is that in a changeable environment, such as a warehouse where goods often come in and out, it can solve the shortcomings of the existing RSSI positioning technology that is not high in accuracy due to environmental changes.

Description

Environment Adaptive RSSI Local Positioning System and Method

technical field

The present invention relates to a positioning method based on signal energy strength, in particular to an environment-adaptive RSSI local positioning system and method.

Background technique

Local positioning technology can be divided into three categories according to the principle: positioning technology based on time, positioning technology based on signal strength (RSSI, received signal strength indication), positioning technology based on signal angle (AOA), and positioning technology based on time can be divided into Time of Arrival (TOA) and Time Difference of Arrival (TDOA). TOA requires precise time synchronization between reference nodes; TDOA is limited by the short ultrashort wave transmission distance and the visibility of the environment; AOA requires additional hardware support. The hardware composition of the RSSI positioning system is shown in Figure 1, including: (1) 2 or more reference nodes, each node has the function of wireless reception and transmission, and the positions of these nodes are fixed and known. (2) The transmission protocol of the mobile node to be located is the same as that of the reference node, but it only has the function of wireless transmission. (3) A gateway/base station node, used to receive the RSSI information of the mobile node received by the reference node, and calculate the position of the mobile node through software.

The cost of RSSI positioning technology is low, the positioning accuracy can meet most applications, and it does not require additional hardware support, and the positioning can be realized by using the most basic transmission and reception of reference nodes and mobile nodes. However, in the prior art, the accuracy of the RSSI positioning system is limited due to the inconsistency of the performance of the receivers and antennas of each node, environmental factors and other multiple influences.

Local positioning technology is of great significance to industrial safety monitoring, such as coal mine safety and other issues. Of course, its application field is not limited to this. It can be used on industrial assembly lines to improve the efficiency of assembly lines. Taking the safety of underground work in coal mines as an example, once an accident occurs, how to quickly and accurately find the location of the personnel is of great help to the rescue work. Using wireless sensor network technology, a number of reference nodes with fixed positions can be pre-arranged in the monitoring environment, and these nodes can be used to receive signals from nodes carried by people, and then determine the location of people through certain algorithms.

Contents of the invention

The present invention mainly overcomes the deficiencies in the positioning accuracy of the prior art, and especially provides an environment-adaptive RSSI local positioning system and method for the environment that changes greatly with time, using the loss factor obtained in real time to calculate the distance .

According to the technical solution provided by the present invention, the environment-adaptive RSSI local positioning system includes no less than 4 reference nodes, each of which has wireless receiving and transmitting functions, and can communicate with each other through protocols. The antenna is isotropic, and the position of the reference node is known; one or more mobile nodes to be tested have wireless transmission function, and the transmission frequency and communication protocol are consistent with the reference node, and the transmission antenna of the mobile node is isotropic; It includes at least one base station, which is used to collect the RSSI information of the mobile node sent by each reference node, and then calculate the distance from the mobile node to each reference node by using the loss factor measured in the previous period and stored in the database, so as to calculate the position of the mobile node.

The environment adaptive RSSI local positioning method is: use the loss factor corresponding to the area updated in real time to calculate the distance from the mobile node to the reference node, that is, in the RSSI local positioning system, the loss factor of each reference node in different areas Factors use real-time measured values. There is a database of loss factor parameters in the monitoring software. The database is updated according to a settable frequency. During the positioning process, three reference nodes with the highest signal strength are used. According to the relationship between signal strength and distance, Find the location of the mobile node.

The signal strength refers to the strength of the radio frequency signal or the strength of the underwater acoustic signal.

The loss factor is calculated and obtained after regularly measuring the signal strength at the center of every four adjacent reference nodes, and then stored in the software database.

In the positioning process, the area to which the mobile node belongs should be judged according to the three reference nodes that receive the strongest signal strength of the mobile node, and then the corresponding loss factors of the three reference nodes in the area are used to calculate the distance between the mobile node and the three reference nodes. The distance of the reference node, and finally use the trilateration method to determine the position of the mobile node.

The advantages of the present invention are:

1. Easy to implement: the method proposed by the present invention can be directly completed by using the sending and receiving of the reference node and the mobile node.

2. Improve accuracy: It can reduce the errors caused by the inhomogeneity and time-varying characteristics of the monitoring area environment, and store various factors such as shielding in the form of loss factors in the distance measurement database and update them continuously, effectively improving the accuracy of positioning and tracking. precision.

3. Wide application range: the present invention is not affected by land and underwater environments, and can be widely used in industrial environments, civil environments, and military fields.

Description of drawings

Figure 1 is a schematic diagram of the composition of the positioning system.

Fig. 2 is a schematic diagram of the real-time loss factor measurement of the positioning system.

Figure 3 is a flow chart of the positioning system algorithm.

Figure 4 is an example of how the positioning system works.

Fig. 5 is a schematic diagram of the correction effect of the positioning system on environmental factors.

Detailed ways

The present invention will be further described below in conjunction with drawings and embodiments. In the RSSI positioning system, the present invention uses the loss factor corresponding to the area updated in real time to calculate the distance from the mobile node to the reference node, so that environmental factors can be reflected in the real-time loss factor calculation and improve the positioning accuracy. The use of the loss factor obtained in real time to calculate the distance means that in the application system of RSSI (Received Signal Strength Indication), the loss factor of each reference node in different areas adopts the value measured in real time, and there are loss factors in the monitoring software. A database of factor parameters, which is updated at a configurable frequency. The loss factor is calculated and obtained after regularly measuring the signal strength at the center of every four adjacent reference nodes, and then stored in the software database. In the positioning process, three reference nodes with the highest signal strength are used, and the position of the mobile node is obtained according to the relationship between signal strength and distance.

In the specific system construction process, every four adjacent reference nodes determine an area, test the loss factor of the corresponding reference node at the center of each area, and then store the data in the corresponding database, each area corresponds to a 4 The group loss factor database, in this way, is equivalent to taking environmental factors and the inconsistency of node transceiver performance into the loss factor. In the process of positioning, first determine which area the mobile node is in according to the three reference nodes with the strongest received signals, then determine which area parameters are used to calculate the distance to each reference node, and finally use the trilateration method to determine Calculate the location of the mobile node.

The signal strength in the present invention may be the strength of a radio frequency signal or the strength of an underwater acoustic signal. During the positioning process, the reference node measures the path loss factor of the reference node corresponding to each area in real time, and updates the database of the loss factor according to the set frequency; when receiving the signal of the mobile node, the three points with the strongest signal are used to determine The area where the mobile node is located; use the loss factor of the reference node in the corresponding area to calculate the distance from the mobile node to the three reference nodes; use the method of trilateration to calculate the position of the mobile node. The advantage of using this positioning technology is that it can solve the shortcoming of the existing RSSI positioning technology, which has low accuracy due to environmental changes, in a changeable environment (such as a warehouse where goods often come in and out).

See Figure 1. Among them, the black circle represents the mobile node, the hollow circle represents the reference node, and the two-way arrow represents the wireless communication. The most basic components of the system can be divided into: (1) No less than 4 reference nodes, each reference node has wireless receiving and transmitting functions, and can communicate with each other through a certain protocol, and its receiving antenna is isotropic, and the reference node The positions of the nodes are known. (2) One or more mobile nodes to be tested have wireless transmission function, the transmission frequency and communication protocol are consistent with the reference node, and the transmission antenna is isotropic. (3) At least one base station is required to collect the RSSI information of the mobile node sent by each reference node, and then use the loss factor measured in the previous period and stored in the database to calculate the distance from the mobile node to each reference node, and calculate the mobile node Location.

In the system using wireless energy positioning, the mobile node sends signals at regular intervals, and the time interval between transmissions is also related to the accuracy of the positioning system, and also related to the power consumption of the mobile node. In practical applications, since batteries are generally used for power supply, the requirements for accuracy and usage time should be considered, and then the sending interval and sending power should be selected.

See Figure 2. There are 9 hollow circles, which respectively represent 9 reference nodes, and they divide the entire positioning area into 4 areas: A, B, C, and D. The formula for known wireless signal transmission loss is as follows

                  公式一

formula one

In the measurement of the loss factor N, X represents the fixed loss when the distance between the reference node and the mobile node is 1 meter. It can be measured several times in advance and take the average value. P _Rec represents the received signal strength, and P _Send represents the transmitted signal strength. The signal strengths P ₁ , P 2 , P 4 , and P 5 received by the four reference nodes 1, ₂ , ₄ , and ₅ are measured at regular intervals. Given that d is the distance from the center to each reference node, the loss factors N _1a , N _2a , N _4a , and N _5a corresponding to the four reference nodes in Area A can be calculated respectively. Then, test the loss factors corresponding to the other three regional reference nodes, N _2b , N _3b , N _5b , N _6b , N _4c , N _5c , N _7c , N _8c , N _5d , N _6d , N _8d , N _9d , update the loss factor database according to the set frequency.

See Figure 3. In the workflow of the positioning system, firstly, ensure that each reference node has joined the network, and when ready, the mobile node starts to send signals. The reference nodes are sorted according to the received signal strength of the mobile node, find out the three reference points with the strongest received signal, and then determine the area where the mobile node is located. After the area is determined, the distances from the mobile node to the three reference nodes are calculated by using the loss factors of the area corresponding to the three reference nodes. Finally, the position of the mobile node is obtained by using the trilateration method.

In the positioning process using the wireless signal strength, the area to which the mobile node belongs is first judged according to the three reference nodes that receive the highest signal strength of the mobile node, and then the mobile node is calculated using the loss factors corresponding to the three reference nodes in the area. The distance from the node to these three reference nodes, and finally use the trilateration method to determine the position of the mobile node. Referring to Fig. 4, there are 2 mobile nodes, and the positioning process of mobile node 1 is in progress. First, since the signal strength of the mobile node received by reference nodes 1, 2, and 4 is the highest, it is determined to use these three reference nodes for positioning, and use the loss factor of area A. Then, using the above formula, in the case of knowing P _Rec , P _Send , N _1a , N _2a , N _4a , and X, calculate d ₁ , d ₂ , d ₄ respectively. Then the position of mobile node 1 is calculated by trilateration method.

The signal of mobile node 2 received by reference nodes 3, 5, and 6 is the strongest, and it is judged that mobile node 2 is in area B. Then, using Formula 1, d ₃ , d ₅ , and d ₆ are respectively calculated when P _Rec , P _Send , N _3b , N _5b , N _6b , and X are known. Then use the trilateration method to calculate the position of the mobile node 2 .

See Figure 5. In the area surrounded by reference nodes 1, 2, 3, and 4, due to the recently imported goods at reference nodes 2 and 4, in the real-time measurement of the loss factor, the signal strength received by reference nodes 2 and 4 is relatively small, that is, It is said that the calculated loss factor will be larger than that of the other two points. In the positioning process of the system, using a larger loss factor for reference nodes 2 and 4 can reduce the error in distance calculation due to cargo occlusion. Therefore, the use of non-uniform loss factors can overcome the positioning difficulties in changing environments and improve the accuracy of the positioning system.

Claims (5)

1. the RSSI local positioning system of environment self-adaption, it is characterized in that: comprise being no less than 4 reference nodes, each reference node has wireless receiving and emission function, can pass through protocol communication each other, the reception antenna of reference node is an isotropism, and the position of reference node is known; One or more mobile nodes to be measured have the wireless transmission function, and tranmitting frequency, communication protocol and reference node are consistent, and the transmitting antenna of mobile node is an isotropism; Also comprise at least one base station, be used to collect the RSSI information of the mobile node that each reference node sends over, calculate the distance of mobile node with the fissipation factor of measuring early stage that leaves in the database then, thereby calculate positions of mobile nodes to each reference node.

2. the RSSI local locating method of environment self-adaption, it is characterized in that: adopt the regional corresponding fissipation factor of real-time update to calculate the distance of mobile node to reference node, promptly, in the RSSI local positioning system, each reference node all adopts the value of real-time measurement in the fissipation factor of zones of different, the database of lossy factor parameter in the monitoring software, database upgrades according to the frequency that can set, in position fixing process, adopt the reference node of three signal strength signal intensity maximums, according to the relation of signal strength signal intensity and distance, draw the position of mobile node.

3. as the RSSI local locating method of environment self-adaption as described in the claim 2, it is characterized in that described signal strength signal intensity is meant the intensity of radio-frequency (RF) signal strength or underwater signal.

4. as the RSSI local locating method of environment self-adaption as described in the claim 2, it is characterized in that described fissipation factor is regularly to calculate to obtain, and leaves in the software database then after the measure signal intensity of the center of per four adjacent reference nodes.

5. as the RSSI local locating method of environment self-adaption as described in the claim 2, it is characterized in that in position fixing process, want earlier to judge zone under the mobile node according to three reference nodes of receiving mobile node signal strength signal intensity maximum, utilize these three reference nodes to calculate the distance of mobile node respectively then, utilize trilateration to determine the position of mobile node at last to these three reference nodes in the fissipation factor of this zone correspondence.

Images