CN102831456B - Indoor wireless positioning method based on RF (Radio Frequency) identification signal level - Google Patents

Abstract

The present invention proposes an indoor wireless positioning method based on the radio frequency identification signal level. First, the scene to be positioned is divided into grids, and the same active electronic tag is placed at the center of each square grid as a correction point; Establish the energy level correspondence table of the active electronic tag; then measure the RSS value of each calibration point with the RFID reader on the target to be located, and obtain the signal energy level of each active electronic tag at the target to be located, and the positioning of each active electronic tag area; finally locate through logical judgment. The present invention only needs one RFID reader, introduces the offline pre-learning stage, and uses the preset electronic tag signal energy level association to determine the position of the only RFID reader in the system.

Description

An Indoor Wireless Positioning Method Based on Radio Frequency Identification Signal Level

technical field

The invention relates to the technical field of wireless positioning in an indoor environment, in particular to an indoor wireless positioning method based on a radio frequency identification signal level.

Background technique

RFID applications are already common, ranging from asset tracking, service industries, logistics and manufacturing to supply chains. The large number of applications of RFID has made the price of RFID hardware drop significantly, and stable equipment for automatic identification has been developed. RFID has obvious advantages, such as non-contact identification, non-line-of-sight readability, and so on. It is because of these capabilities that RFID technology can be used as the first choice for indoor positioning, although it was not originally designed and developed for this purpose.

However, there are still many difficulties in using RFID positioning. First, the system requires a large number of devices to estimate position, and most devices do not have the capability to read RSSI. Furthermore, RFID can work at frequencies ranging from low frequency to microwave, and it is necessary to select a suitable working frequency. There are also many types of electronic tags, such as active tags, passive tags, and semi-active tags. The type of tag will also affect the positioning accuracy.

The most famous RFID positioning system is the LANDMARC positioning system. This technology introduces reference tags and arranges them at known locations as system landmarks. Because the reference tag and the tag to be positioned are in the same indoor environment, the dynamic change of the environment has little influence on the positioning accuracy. First, by calculating the Euclidean distance of the energy level vector, the reference tags adjacent to the tag to be located are determined, and the coordinates of these adjacent tags are weighted and averaged as the position of the tag to be located. By using reference tags instead of expensive RFID readers, LANDMARC uses fewer RFID readers to achieve higher positioning accuracy. Since more than 3 RFID readers are still required, the positioning cost is still high. Moreover, the system needs to consider all reference labels as neighboring label candidates, so a lot of unnecessary calculations are introduced.

Contents of the invention

technical problem to be solved

In order to solve the problems existing in the prior art, the present invention proposes an indoor wireless positioning method based on the radio frequency identification signal level, which only needs one RFID reader, introduces the offline pre-learning stage, and utilizes the preset energy level of the electronic tag signal Association determines the location of unique RFID interrogators in the system.

Technical solutions

Technical scheme of the present invention is:

The indoor wireless positioning method based on the radio frequency identification signal level is characterized in that: comprising the following steps:

Step 1: Divide the indoor scene to be positioned into N×M square grids, the side length of each square grid is a, and the same active electronic tag is placed at the center of each square grid as a calibration point;

Step 2: Establish the energy level correspondence table of active electronic tags offline:

The corresponding table of signal energy level and distance S is:

Signal energy level The distance S between the RFID reader and the active electronic tag L ₁ S≤a/4 L ₂ a/4＜S≤a/2 L ₃ a/2＜S≤a L ₄ S > a

On the three circles of S=a/4, S=a/2 and S=a, select no less than 10 different measurement points, and use an RFID reader to measure the RSS value of the active electronic tag at each point, And get the corresponding table of signal energy level and RSS value R after taking the average value respectively:

Signal energy level The distance S between the RFID reader and the active electronic tag RSS value R L ₁ S≤a/4 R≥R _a/4 L ₂ a/4＜S≤a/2 R _a/2 ≤ R < R _a/4 L ₃ a/2<S≤a R _a ≤ R < R _a/2 L4 S＞a R<R _a

Step 3: Use the RFID reader on the target to be located to measure the RSS value of each calibration point, and compare the active electronic tag energy level correspondence table established in step 2 to obtain the signal energy level of each active electronic tag at the target to be located, and The positioning area of each active electronic tag;

Step 4: Calculate the intersection of each active electronic tag positioning area obtained in step 3. If the obtained intersection is not an empty set, then use the obtained intersection area as the positioning area of the target to be located, and the geometric center of the intersection area is the location of the target to be located. Estimate the anchor point; if the obtained intersection is an empty set, go to step 5;

Step 5: From the signal energy levels of the active electronic tags obtained in step 3 at the target to be located, select active electronic tags with the same signal energy level, and calculate the positioning of each group of active electronic tags with the same signal energy level The intersection of the regions, the active electronic tags whose k group intersection is empty and the l group whose intersection is not empty active electronic tags are obtained;

Step 6: Find the intersection of the positioning areas of the active electronic tags whose intersection set l is not empty is Ω; find the intersection of the positioning area of each active electronic tag in the active electronic tags whose intersection set k is empty and Ω respectively, and obtain W intersection areas, where W is the number of k groups of active electronic tags whose intersections are empty, and w non-empty areas are obtained after removing the empty sets in the W intersection areas, then the estimated positioning point coordinates of the target to be located Where P _i is the geometric center of the i-th non-empty area among the w non-empty areas, and A _i is the area of the i-th non-empty area among the w non-empty areas.

Beneficial effect

An indoor wireless positioning method based on the radio frequency identification signal level proposed by the present invention only needs one RFID reader, introduces the offline pre-learning stage, and uses the preset electronic tag signal energy level correlation to determine the unique RFID reading and writing in the system location of the device. The test shows that under the same experimental environment, the average positioning error of LANDMARC is 1.7m and takes 2.03s, while the average positioning error of the method of the present invention is 0.7m and takes 0.3s.

Description of drawings

Figure 1: Schematic diagram of the energy level correspondence table of the active electronic tag in the embodiment;

Detailed ways

Describe the present invention below in conjunction with specific embodiment:

The positioning scene in this embodiment is a square scene. The adopted indoor wireless positioning method based on the radio frequency identification signal level includes the following steps:

Step 1: Divide the indoor scene to be positioned into 3×3 square grids, each square grid has a side length of 2m, and place the same active electronic tag at the center of each square grid as a calibration point.

Step 2: Establish the energy level correspondence table of active electronic tags offline:

The corresponding table of signal energy level and distance S is:

Signal energy level The distance S between the RFID reader and the active electronic tag L ₁ S≤0.5m L ₂ 0.5m＜S≤1m L ₃ 1m＜S≤2m L ₄ S＞2m

On the three circles of S=0.5m, S=1m and S=2m, select 10 different measurement points, and use an RFID reader to measure the RSS value of the active electronic tag at each point, and take the average value respectively Get the corresponding table of signal energy level and RSS value R:

Signal energy level The distance S between the RFID reader and the active electronic tag RSS value R L ₁ S≤0.5m R≥-45dBm L ₂ 0.5m＜S≤1m -52dBm≤R＜-45dBm L ₃ 1m＜S≤2m -67dBm≤R＜-52dBm L ₄ S＞2m R＜-67dBm

As shown in Figure 1, four areas are formed around each active electronic tag, corresponding to four signal energy levels, where L ₁ corresponds to a circular area with the active electronic tag as the center and a radius of 0.5m, and L ₂ corresponds to the active electronic tag. The electronic tag is the center of the circle, the inner diameter is 0.5m, and the outer diameter is 1m. L ₃ corresponds to the active electronic tag as the center of the circle, the inner diameter is 1m, and the outer diameter is 2m. L ₄ corresponds to the active electronic tag. The center of the circle, the area outside the circle with a radius of 2m.

Step 3: Use the RFID reader on the target to be located to measure the RSS value of each calibration point, and compare the active electronic tag energy level correspondence table established in step 2 to obtain the signal energy level of each active electronic tag at the target to be located, and The positioning area of each active electronic tag:

Tag ₁₁ =L ₄ Tag ₁₂ =L ₃ Tag ₁₃ =L ₃

Tag ₂₁ =L ₃ Tag ₂₂ =L ₂ Tag ₂₃ =L ₄ Tag ₃₁ =L ₄ Tag ₃₂ =L ₄ Tag ₃₃ =L ₄

For example, Tag ₁₁ = L ₄ , indicating that the signal energy level of the active electronic tag Tag ₁₁ measured at the target to be located is L ₄ , and the location area corresponding to the active electronic tag Tag ₁₁ is the area outside the circle with Tag ₁₁ as the center and a radius of 2m .

Step 4: Calculate the intersection of each active electronic tag positioning area obtained in step 3. If the obtained intersection is not an empty set, then use the obtained intersection area as the positioning area of the target to be located, and the geometric center of the intersection area is the location of the target to be located. Estimate the anchor point; if the obtained intersection is an empty set, go to step 5.

It can be seen from FIG. 1 that in this embodiment, the intersection of the positioning areas of active electronic tags is an empty set, so step 5 is entered.

Step 5: From the signal energy levels of the active electronic tags obtained in step 3 at the target to be located, select active electronic tags with the same signal energy level, and calculate the positioning of each group of active electronic tags with the same signal energy level The intersection of the regions, k groups of active electronic tags whose intersection is empty and l groups of active electronic tags whose intersection is not empty are obtained.

Compared with Fig. 1, there is only one active electronic tag at the _L2 level in this embodiment, and its intersection must not be empty, and there are five active electronic tags at the _L4 level, and its intersection is also not empty as seen in Fig. 1; However, there are 3 active electronic tags at level _L3 , and their intersection is empty; therefore, in this embodiment, there is 1 group of active electronic tags whose intersection is empty and 2 groups of active electronic tags whose intersection is not empty.

Step 6: Find the intersection of the positioning areas of the active electronic tags whose intersection set l is not empty is Ω; find the intersection of the positioning area of each active electronic tag in the active electronic tags whose intersection set k is empty and Ω respectively, and obtain W intersection areas, where W is the number of k groups of active electronic tags whose intersections are empty, and w non-empty areas are obtained after removing the empty sets in the W intersection areas, then the estimated positioning point coordinates of the target to be located Where P _i is the geometric center of the i-th non-empty area among the w non-empty areas, and A _i is the area of the i-th non-empty area among the w non-empty areas.

In this embodiment, the intersection of the positioning areas of the 6 active electronic tags in the 2 sets of active electronic tags whose intersection is not empty is Ω, and the positioning area of the 3 active electronic tags in the 1 group of active electronic tags whose intersection is empty is equal to Ω Calculate the intersection respectively, and get 3 intersection areas, including 1 empty set, and get 2 non-empty areas after removing the empty set, then the estimated positioning point coordinates of the target to be located Where P _i is the geometric center of the i-th non-empty area among the two non-empty areas, and A _i is the area of the i-th non-empty area among the two non-empty areas.

Claims (1)

1. A kind of indoor wireless positioning method based on radio frequency identification signal level, it is characterized in that: comprise the following steps: Step 1: Divide the indoor scene to be positioned into N×M square grids, the side length of each square grid is a, and the same active electronic tag is placed at the center of each square grid as a calibration point; Step 2: Establish the energy level correspondence table of active electronic tags offline: The corresponding table of signal energy level and distance S is: signal energy level Distance S between RFID reader and active electronic tag L ₁ S≤a/4 L ₂ a/4<S≤a/2 L ₃ a/2<S≤a L ₄ S > a On the three circles with the active electronic tag as the center and the radii of S=a/4, S=a/2 and S=a, select no less than 10 different measurement points, and use RFID reading at each point The RSS value of the active electronic tag is measured by the device, and the corresponding table of the signal energy level and the RSS value R is obtained after taking the average value: signal energy level Distance S between RFID reader and active electronic tag RSS value R L ₁ S≤a/4 R≥R _a/4 L ₂ a/4<S≤a/2 R _a/2≤R <R _a/4 L ₃ a/2<S≤a R _a ≤ R < R _a/2 L ₄ S > a R<R _a Step 3: Use the RFID reader on the target to be located to measure the RSS value of each calibration point, and compare the active electronic tag energy level correspondence table established in step 2 to obtain the signal energy level of each active electronic tag at the target to be located, and The positioning area of each active electronic tag where the target is located, the positioning area of the active electronic tag is composed of three circles with the active electronic tag as the center and a radius of S=a/4, S=a/2 and S=a The division is composed of four regions corresponding to different signal energy levels; Step 4: Find the intersection of each active electronic tag positioning area where the target to be located is obtained in step 3. If the obtained intersection is not an empty set, then use the obtained intersection area as the positioning area of the target to be located. The geometry of the intersection area The center is the estimated positioning point of the target to be positioned; if the obtained intersection is an empty set, go to step 5; Step 5: From the signal energy levels of the active electronic tags obtained in step 3 at the target to be located, select active electronic tags with the same signal energy level, and calculate the positioning of each group of active electronic tags with the same signal energy level The intersection of the regions, the active electronic tags whose k group intersection is empty and the l group whose intersection is not empty active electronic tags are obtained; Step 6: Find the intersection of the positioning areas of the active electronic tags whose intersection set l is not empty is Ω; find the intersection of the positioning area of each active electronic tag in the active electronic tags whose intersection set k is empty and Ω respectively, and obtain W intersection areas, where W is the number of k groups of active electronic tags whose intersections are empty, and w non-empty areas are obtained after removing the empty sets in the W intersection areas, then the estimated positioning point coordinates of the target to be located Where P _i is the geometric center of the i-th non-empty area among the w non-empty areas, and A _i is the area of the i-th non-empty area among the w non-empty areas.