RSSI positioning method based on frequency-hopping spread spectrum technology

Abstract

An RSSI positioning method based on frequency-hopping spread spectrum technology, comprising: calibration stage: measuring the RSSI values of a plurality of channels at fixed points, and recording and calculating the ranging parameters in an RSSI ranging model; system preparation: deploying a positioning anchor node, and realizing synchronization between a target node and the anchor node; conducting communication on the target node by respectively utilizing a plurality of channels to obtain the RSSI values; signal processing stage: processing the RSSI into signal strength amplitude and performing optimization; and positioning stage: calculating a distance and the target node position on a positioning server according to each of the signal strength. The present invention solves the problem that low RSSI positioning precision cannot satisfy the actual requirements because a traditional RSSI positioning method is limited to factors such as multipath signal transmission, co-channel interference, obstacle interference and low coordinate calculation precision of a trilateration method.

Claims

1. An RSSI positioning method based on frequency-hopping spread spectrum technology, comprising: measuring RSSI values of a plurality of channels at fixed points, and recording and calculating at least one ranging parameter in an RSSI ranging model; deploying a wireless sensor network and synchronizing between a target node and a plurality of anchor nodes in the wireless sensor network; communicating with the plurality of anchor nodes, via the target node, by respectively utilizing a plurality of channels, thereby obtaining the RSSI values; the plurality of anchor nodes eliminating the channels with relatively large RSSI value error from a frequency-hopping spread spectrum (FHSS) sequence according to the received position signal strength of the sending node in one FHSS cycle; and updating the FHSS sequence and adding the eliminated channels to a blacklist; processing the RSSI values into signal strength amplitudes and performing optimization; and calculating, for each anchor node in the plurality of anchor nodes, a distance value between the target node and the respective anchor node on a positioning server according to each of the signal strength amplitudes, and calculating the position coordinate of the target node, wherein said RSSI values are processed into signal strength amplitudes and optimized, comprising the following steps: converting the signal strength values RSSI into signal amplitudes according to:
A.sub.i=k*(10.sup.RSSI.sup.i).sup.0.5 wherein A.sub.i, is a signal amplitude, k is a constant coefficient, i is a channel label, and RSSI.sub.i is a measured signal strength value of the i.sup.th channel; calculating the central values A.sub.0 of the signal amplitudes A.sub.i repeatedly and converting A.sub.0 into an optimized RSSI value; and calculating the distance value between the target node and the respective anchor node according to the optimized RSSI value, wherein the central value A.sub.0 of said signal amplitude is calculated by, at least one of: i. solving for A.sub.0 according to $A_0=A_{1}l\sqrt{1+\frac{l^2}{l^2+{\left(2h\right)}^2}+2\frac{l}{\sqrt{l^2+{\left(2h\right)}^2}}\cos \left(\frac{2\left(\sqrt{l^2+{\left(2h\right)}^2}-l\right)}{}\right)},$ wherein l is the distance between the positioning anchor node and the target node, h is the height from the respective anchor node to the ground, and is the wavelength of a radio frequency signal; or ii. solving for an approximate value of A.sub.0 according to $A_0=\frac{A_{\max }+A_{\min }}{2},$ wherein the maximum A.sub.max and the minimum A.sub.min are values of the signal amplitude A.sub.i.

2. The RSSI positioning method based on frequency-hopping spread spectrum technology according to claim 1, wherein said RSSI ranging model is a constant-logarithm model, according to:
A=RSSI(d)+10*n*lg(d) wherein, A is signal received power at a distance of 1m, n is a propagation factor, d is a distance between the target node and the respective anchor node, and A and n are ranging parameters.

3. The RSSI positioning method based on frequency-hopping spread spectrum technology according to claim 2, wherein the ranging parameters in said RSSI ranging model are determined through repeated multi-channel communication experiments, comprising the following steps: calculating the measured values of A and n by measuring RSSI values of two sets of different d position; and averaging the obtained A and n as the values A and n by repeated multi-channel communication measurements.

4. The RSSI positioning method based on frequency-hopping spread spectrum technology according to claim 1, wherein said wireless sensor network is a multi-channel TDMA mesh network with time synchronization, and comprising anchor nodes, target nodes, the positioning server, and a network path auxiliary device.

5. The RSSI positioning method based on frequency-hopping spread spectrum technology according to claim 1, wherein the central value A.sub.0 of said signal amplitude is calculated by solving for an approximate value of A.sub.0 according to $A_0=\frac{A_{\max }+A_{\min }}{2}.$

6. The RSSI positioning method based on frequency-hopping spread spectrum technology according to claim 1, wherein said optimized RSSI value is calculated by using the central value A.sub.0 of the signal amplitude, specifically:
RSSI =2*log.sub.10(A/k) wherein k is a constant coefficient.

7. An RSSI positioning method based on frequency-hopping spread spectrum technology, comprising: measuring RSSI values of a plurality of channels at fixed points, and recording and calculating at least one ranging parameter in an RSSI ranging model; deploying a wireless sensor network and synchronizing between a target node and a plurality of anchor nodes in the wireless sensor network; communicating with the plurality of anchor nodes, via the target node, by respectively utilizing a plurality of channels, thereby obtaining the RSSI values; the plurality of anchor nodes eliminating the channels with relatively large RSSI value error from a frequency-hopping spread spectrum (FHSS) sequence according to the received position signal strength of the sending node in one FHSS cycle; and updating the FHSS sequence and adding the eliminated channels to a blacklist; processing the RSSI values into signal strength amplitudes and performing optimization; and calculating a distance value between the target node and each anchor node in the plurality of anchor nodes on a positioning server according to each of the signal strength amplitudes, and calculating the position coordinate of the target node, wherein a distance value between the target node and each anchor node in the plurality of anchor nodes is calculated based on substituting the central value A.sub.0 of the signal amplitude into the formula $d={10}^{\left(\frac{A-\mathrm{RSSI}\left(d\right)}{10n}\right)}$ to calculate a distance value d for each respective anchor node.

8. An RSSI positioning method based on frequency-hopping spread spectrum technology, comprising measuring RSSI values of a plurality of channels at fixed points, and recording and calculating at least one ranging parameter in an RSSI ranging model; deploying a wireless sensor network and synchronizing between a target node and a plurality of anchor nodes in the wireless sensor network; communicating with the plurality of anchor nodes, via the target node, by respectively utilizing a plurality of channels, thereby obtaining the RSSI values; the plurality of anchor nodes eliminating the channels with relatively large RSSI value error from a frequency-hopping spread spectrum (FHSS) sequence according to the received position signal strength of the sending node in one FHSS cycle; and updating the FHSS sequence and adding the eliminated channels to a blacklist; processing the RSSI values into signal strength amplitudes and performing optimization; and calculating a distance value between the target node and each anchor node of the plurality of anchor nodes on a positioning server according to each of the signal strength amplitudes, and calculating the position coordinate of the target node, wherein the calculation of said position coordinate of the target node on the positioning server according to each of the signal strength and the distance value comprises: calculating, for each anchor node of the plurality of anchor nodes, a distance value d between the respective anchor node and the target node; drawing, for each anchor node of the plurality of anchor nodes, a square using 2d as a width and using the respective anchor node as a central point; wherein the coordinate of a first anchor node of the plurality of anchor nodes (x.sub.a, y.sub.a); the RSSI value received by the first anchor node is used for calculating the estimated distance d.sub.abetween the first anchor node and the target node; a square is drawn around the first anchor node by using 2*.sup.da as a side length and using (x.sub.a, y.sub.a) as the center, such that the coordinates of four vertices of the square around the first anchor node are:
(x.sub.ad.sub.a, y.sub.ad.sub.a)(x.sub.a+d.sub.a, y.sub.a+d.sub.a) wherein the coordinates of the further anchor nodes of the plurality of anchor nodes are expressed as (x.sub.i, y.sub.i), with i representing the i.sup.th anchor node of the plurality of anchor nodes; the RSSI values received by the further anchor nodes are used for calculating respective estimated distances d.sub.i between the respective anchor nodes and the target node; and a respective square is drawn around each of the further anchor nodes by using, for each respective square, 2* .sup.d.sub.i as a side length and (x.sub.i, y.sub.i) as a center, such that the respective coordinates of the vertices of the further anchor nodes are:
(xd.sub.i, y.sub.id.sub.i)(x.sub.i+d.sub.i,y.sub.i+d.sub.i) wherein the target node is determined to be within an overlapping region of the drawn squares of the respective anchor nodes, the coordinates of four vertices of the overlapping region being:
[max(x.sub.id.sub.i),max(y.sub.id.sub.i)][min(x.sub.id.sub.i),min(y.sub.id.sub.i)]; and wherein the position coordinate of the target node is calculated as the central position of the overlapping region, with the coordinate as:
[(max(x.sub.id.sub.i)+min(x.sub.i+d.sub.i))/2,(max(y.sub.id.sub.i)+min(y.sub.i+d.sub.i))/2].

9. The RSSI positioning method based on frequency-hopping spread spectrum technology according to claim 1, wherein the central value A.sub.0 of said signal amplitude is calculated by solving for A.sub.0 according to $A_0=A_i/\sqrt{1+\frac{l^2}{l^2+{\left(2h\right)}^2}+2\frac{l}{\sqrt{l^2+{\left(2h\right)}^2}}\cos \left(\frac{2\left(\sqrt{l^2+{\left(2h\right)}^2}-l\right)}{}\right)}.$

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a structural diagram of basic composition of a positioning system of the present invention;

(2) FIG. 2 is a flow chart of a positioning algorithm of the present invention;

(3) FIG. 3 is a flow chart for obtaining ranging parameters of the present invention; and

(4) FIG. 4 is a schematic diagram of MinMax positioning method of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(5) The present invention will be further described in detail below in combination with the drawings and the embodiments.

(6) As shown in FIG. 1, the anchor node AP represents a reference node in a known position, a solid circle represents the target node, and a lightning symbol represents a wireless communications link. The system essentially comprises: (1) three and more anchor nodes, wherein the position information of each anchor node is known; the anchor nodes have wireless receiving and transmitting function and the layout directions of receiving antennas are consistent. (2) The target node to be measured has wireless transmitting function and has consistent transmitting frequency and communication protocol with the anchor nodes and the layout directions of receiving antennas are consistent. (3) The system at least includes one gateway mainly used for collecting RSSI informations of the target node transmitted by each anchor node and reporting the collected data to the positioning server. (4) The positioning server calculates the position informations of the target node through special software.

(7) The specific workflow is shown in FIG. 2:

(8) Step 1, calibration stage: measuring RSSI values of a plurality of channels at fixed points, and recording and calculating the ranging parameters in an RSSI ranging model, as shown in FIG. 3:

(9) The RSSI ranging model adopted in the present invention is a constant-logarithm model:
A=RSSI(d)+10*n*lg(d)

(10) wherein A and n are ranging parameters. The values of A and n can be calculated by measuring RSSI values of two sets of different d position. In the present invention, the values of A and n are calculated by selecting measured values at shorter transmission distances of 1 m and 3 m. The obtained A and n are averaged by repeated multi-channel communication experiments for reducing the random error;

(11) Step 2, system preparation: deploying a wireless sensor network and realizing synchronization between the target node and the anchor node;

(12) Step 3, the target node communicating with the positioning anchor node by respectively utilizing a plurality of channels to obtain the RSSI values; by adopting an automatic FHSS technology, the receiving node (i.e., the anchor node) eliminating a channel with larger RSSI value error in an FHSS sequence according to the position signal strength of a sending node received within one FHSS cycle through a channel cognitive blacklist technology; and updating the FHSS sequence and a blacklist;

(13) Step 4, signal processing stage: processing RSSI into a signal strength amplitude and performing optimization;

(14) The present invention adopts an indirect mode for calculating the central value of the signal amplitude, as follows:

(15) converting the signal strength value RSSI into a signal amplitude:
A.sub.i=k*(10.sup.RSSI.sup.i).sup.0.5

(16) wherein k is a constant coefficient, i is a channel label, and RSSI is a measured signal strength value;

(17) calculating the central value A.sub.0 of repeated signal amplitude result A.sub.i and converting A.sub.0 into RSSI value, i.e., an optimized RSSI value; and calculating the distance d according to the optimized RSSI value.

(18) The calculation method of the central value A.sub.0 of the signal amplitude is:

(19) $A_0=A_{1}l\sqrt{1+\frac{l^2}{l^2+{\left(2h\right)}^2}+2\frac{l}{\sqrt{l^2+{\left(2h\right)}^2}}\cos \left(\frac{2\left(\sqrt{l^2+{\left(2h\right)}^2}-l\right)}{}\right)}$

(20) wherein l is the distance between the positioning anchor node and the target node, h is the height from the anchor node to the ground, and is the wavelength of a radio frequency signal.

(21) Because positioning calculation occurs on a single chip microcomputer which calculation capability is weak; for solving the approximate value of A.sub.0 a special solution manner can be used to finish it; and the maximum A.sub.max and the minimum A.sub.min of A.sub.i are obtained to perform approximate calculation of the central value of the signal amplitude:

(22) $A_0=\frac{A_{\max }+A_{\min }}{2}$

(23) The optimized RSSI value is calculated by using the central value A.sub.0 of the signal amplitude, specifically:
RSSI=2*log.sub.10(A/k)
wherein k is a constant coefficient.

(24) The distance is calculated according to the optimized RSSI value and the ranging parameters, specifically:

(25) the central value A.sub.0 of the signal amplitude is substituted into the formula

(26) $d={10}^{\left(\frac{A-\mathrm{RSSI}\left(d\right)}{10n}\right)}$
to calculate the measured distance value.

(27) There are many advantages using this method for calculation: 1. noise generated by multipath reflection caused by environmental factors such as heights of the positioning anchor node and the target node, signal frequency, etc. is included, enhancing the adaptability to different environments; 2. the calculation of an overdetermined equation of the central value is avoided, reducing calculation complexity; 3. the central value method is used, effectively inhibiting noise spots from appearing and preventing a single datum that is off-center excessively from affecting the accuracy of a final result.

(28) Step 5, positioning stage: calculating the position coordinate of the target node on a positioning server according to each of the signal strength and the distance value.

(29) MinMax positioning algorithm is specifically:

(30) The calculated distance between the anchor node and the target node is d; then, a square is drawn by using 2d as width and using the anchor node as the central point; the target node is within the overlapping region of the squares of all beacon nodes around the target node.

(31) As shown in FIG. 4, the anchor node a is taken as an example, and the coordinate of a is (x.sub.a, y.sub.a); the RSSI value received at node a is used for calculating the estimated distance d.sub.a away from an unknown node; a squares is drawn by using 2*d.sub.a as side length and using (x.sub.a, y.sub.a) as the center, so the coordinates of four vertexes of the square are:
(x.sub.ad.sub.a,y.sub.ad.sub.a)(x.sub.a+d.sub.a,y.sub.a+d.sub.a)

(32) It can be known by analogy that the coordinates of the vertexes of the other anchor nodes are:
(x.sub.id.sub.i,y.sub.id.sub.i)(x.sub.i+d.sub.i,y.sub.i+d.sub.i)

(33) The coordinates of four vertexes of the final overlapping region of the squares are:
[max(x.sub.id.sub.i),max(y.sub.id.sub.i)][min(x.sub.id.sub.i),min(y.sub.id.sub.i)]

(34) Then, the estimated position of the target node is the central position of the overlapping region, and the coordinate thereof can be calculated according to the coordinates of four vertexes.
[(max(x.sub.id.sub.i)+min(x.sub.i+d.sub.i))/2,(max(y.sub.id.sub.i)+min(y.sub.i+d.sub.i))/2]