CN113766600B - Mobile target positioning method of multi-base station wireless sensor network - Google Patents

Mobile target positioning method of multi-base station wireless sensor network Download PDF

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CN113766600B
CN113766600B CN202111097902.8A CN202111097902A CN113766600B CN 113766600 B CN113766600 B CN 113766600B CN 202111097902 A CN202111097902 A CN 202111097902A CN 113766600 B CN113766600 B CN 113766600B
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positioning
array
base station
sequence number
signal intensity
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CN113766600A (en
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刘高平
宋执环
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Zhejiang Wanli University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/22—Communication route or path selection, e.g. power-based or shortest path routing using selective relaying for reaching a BTS [Base Transceiver Station] or an access point
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/04—Communication route or path selection, e.g. power-based or shortest path routing based on wireless node resources
    • H04W40/08—Communication route or path selection, e.g. power-based or shortest path routing based on wireless node resources based on transmission power
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/12—Communication route or path selection, e.g. power-based or shortest path routing based on transmission quality or channel quality
    • H04W40/16—Communication route or path selection, e.g. power-based or shortest path routing based on transmission quality or channel quality based on interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W64/00—Locating users or terminals or network equipment for network management purposes, e.g. mobility management
    • H04W64/003—Locating users or terminals or network equipment for network management purposes, e.g. mobility management locating network equipment
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W84/00—Network topologies
    • H04W84/18—Self-organising networks, e.g. ad-hoc networks or sensor networks
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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  • Computer Networks & Wireless Communication (AREA)
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Abstract

The invention relates to a method for positioning a moving target of a multi-base station wireless sensor network, wherein the signal intensity received by each base station forms an array P during the 1 st positioning; sequencing from big to small to obtain an array Q; then if the specified positioning base station exists, the specified base station is moved to the front of the array Q; the base station serial numbers of each element in the current array Q form an array M; finally, the signal intensity of the first k elements in the array M is subjected to positioning calculation; in the t-th positioning, updating the array P in the previous positioning by the signal intensity received by each base station in the current positioning, and sequencing the updated array P according to the sequence of the base station serial numbers in the array M in the previous positioning to obtain an array; and then sequencing the array Q in the t-th positioning according to a threshold value to generate a new array M, and finally performing positioning calculation on the signal intensities of the first k elements in the array M. The method can effectively eliminate the ping-pong effect generated during the handover.

Description

Mobile target positioning method of multi-base station wireless sensor network
Technical Field
The invention relates to the field of wireless communication, in particular to a mobile target positioning method of a multi-base station wireless sensor network.
Background
The development of the wireless sensor network provides a good means for high-precision positioning service. The moving range of the moving object is continuously enlarged, the whole coverage cannot be achieved by one or a plurality of base stations, a plurality of base stations are required to be set up, and the positioning of the moving object is only performed by a plurality of nearby base stations. A typical wireless sensor network architecture consisting of 20 base stations is shown in fig. 1, an arrow curve in fig. 1 represents a moving track of a moving object, a dotted circle is a maximum coverage area of a wireless signal of the moving object at a round point, and three positioning base stations in the circle form a positioning area. The mobile target sends wireless signals at fixed time in the moving process, the positioning base station receives the signals and then transmits information to the converging base station to transfer to the server, and the server calculates the position of the mobile target according to the positioning algorithm. However, when the moving object continues to move forward, some original positioning base stations cannot receive signals, other base stations can start to receive signals, the base stations capable of receiving signals form new positioning areas, and the moving object can be positioned, and the process of changing the positioning areas is called 'handover'. After the moving object is handed off, information is transmitted to the server through a new transmission channel.
The positioning ping-pong effect in the process of the handover occurs due to the interference in the actual environment, wherein the ping-pong effect means that the moving target is unidirectionally moved, but the wireless signal is subjected to the interference of the environment, the positioning is switched back and forth between two positioning areas in the process of the handover, and the communication link between the base station and the server can be repeatedly disconnected and reconnected, so that the information uploading delay and even loss of the moving target can be caused.
Regarding the problem of positioning of handover, there are several documents related to, for example, in document "zinois z.et al, handoff triggering for wireless sensor networks with performance needs [ C ].2013IEEE Symposium on Computers and Communications (ISCC). Split, croatia: IEEE xplore.2013,7:982-988 ], focusing on two easily found local values, namely, signal strength and local link loss, and selecting different thresholds for handover triggering to improve the success rate of handover, but the document does not describe in detail how to determine the thresholds and the handover procedure; the literature "Ma J, yang D, zhang H & Gidlund M.A Reliable Handoff Mechanism for Mobile Industrial Wireless Sensor Networks [ J ]. Sensors.2017,8,17 (8): 1797-1817." proposes an effective switching mechanism for an industrial wireless sensor network, wherein the mechanism is mainly judged by a plurality of measurement indexes, one of the indexes is the received signal strength of a base station, so that the "ping-pong effect" in the switching process is solved, but the process of judging the plurality of measurement indexes is complex; in the literature 'Gaosheng peace' indoor positioning technology research [ J ]. Land mine mapping, 2021,4 (1): 39-40 ], a Gaussian distribution method and an average method are adopted to process signal strength values during handover, but the method has great uncertainty and complex operation; document "Cao Jia, yan Peihui, liu Jianghua, zhang Chengyu, li Xiaoming. Laboratory article tracking management system design for high-precision low-power indoor and outdoor seamless positioning [ J ]. Laboratory research and exploration, 2019, 38 (06): 235-238+282 ", in order to reduce random volatility of real-time signals, a weighted sliding window is used to smooth the received signals, but signal strength jitter caused by abrupt environmental changes still cannot be eliminated; the invention of China with the application number of CN201710991805.0 discloses a method and a device for selecting a wireless positioning ranging base station, wherein the method adopts a method of horizontally projecting on a straight line, and judges and discards unsuitable base stations through preset values so as to achieve quick selection of the positioning base stations, but how to select the preset values is not introduced; the Chinese patent application No. CN201911221672.4 discloses a positioning base station selection method, which screens positioning base stations from each set according to the condition that the base stations are in each quadrant of a coordinate system, but the algorithm involves the opening angle of the base stations relative to a moving target, and the calculation is complex.
In summary, there is a certain research on the positioning of moving objects under the condition of multiple base stations, but two important problems still need to be further discussed, namely, quick selection of positioning base stations and elimination of the ping-pong effect during handover. Thus, further improvements are needed.
Disclosure of Invention
The first technical problem to be solved by the invention is to provide a mobile target positioning method of a multi-base station wireless sensor network aiming at the prior art, and the method can realize quick selection of positioning base stations.
The second technical problem to be solved by the invention is to provide a method for positioning a moving target of a multi-base station wireless sensor network according to the prior art, which can solve the ping-pong effect in the process of handover, thereby reducing the number of times of changing a transmission channel of information sent to a server.
The technical scheme adopted by the invention for solving the first technical problem is as follows: a method for positioning a moving target of a multi-base station wireless sensor network is characterized by comprising the following steps of: the method comprises the following steps:
step 1, carrying out 1 st positioning on a moving target, and forming an array P with the length of n by receiving the signal intensity of the moving target at the time corresponding to the 1 st positioning by each base station in the wireless sensor network;
wherein n is the total number of base stations in the wireless sensor network; the n elements in the array P are respectively: p0, P1, … P i, … P n-1, P0 is the signal intensity of the mobile object received by the base station with the sequence number 0 at the time corresponding to the 1 st positioning; p1 is the signal intensity of the mobile object received by the base station with the serial number 1 at the time corresponding to the 1 st positioning; the signal intensity of the moving target is received by the base station with the sequence number i at the time corresponding to the 1 st positioning; p [ n-1] is the signal intensity of the mobile target received by the base station with the sequence number of n-1 at the time corresponding to the 1 st positioning;
step 2, sequencing the signal intensity of all the base stations in the array P from big to small to obtain an array Q;
step 3, judging whether a base station appointed for positioning is preset, if so, shifting the signal intensity corresponding to b base stations appointed for positioning to the first b positions of an array Q, obtaining an updated array Q, and transferring to step 4; if not, turning to step 4;
step 4, forming an array M according to the base station serial numbers corresponding to each element in the array Q and the positions corresponding to each element in the array Q one by one;
step 5, positioning calculation is carried out on the signal intensity received by the base station corresponding to the first k elements in the array M, and the position of the moving target in the 1 st positioning process is obtained; k is less than or equal to n;
step 6, the mobile target is positioned for the t time, t is more than or equal to 2, the initial value of t is 2, the signal intensity of each base station receiving the mobile target at the time corresponding to the t time positioning updates the array P at the t-1 time positioning, and the array P at the t time positioning is obtained;
step 7, ordering the elements in the array P at the time of the t-th positioning according to the sequence of the base station serial numbers in the array M at the time of the t-1 th positioning to obtain an array Q at the time of the t-th positioning;
step 8, sequencing the array Q in the t positioning, and generating an array M in the t positioning from the base station serial numbers corresponding to each element in the sequenced array Q;
the specific steps of sequencing the array Q in the t-th positioning are as follows:
step 8-1, setting an initial value of m, wherein k is more than m and less than or equal to n; setting a threshold value corresponding to each base station corresponding to each element in the array Q in the t-th positioning, and forming all the threshold values into an array W;
step 8-2, setting j=1;
step 8-3, u=m-j;
8-4, judging whether Q [ u ] is larger than Q [ u-1] +Wu ], if so, exchanging the positions of Q [ u ] and Q [ u-1] in the array Q in the t-th positioning to obtain an updated array Q, exchanging the positions of W [ u ] and W [ u-1] in the array W to obtain an updated array W, and transferring to 8-5; if not, turning to the step 8-5;
wherein Q [ u ] is the u-th element in the array Q in the t-th positioning, Q [ u-1] is the u-1-th element in the array Q in the t-th positioning, W [ u ] is the threshold value corresponding to Q [ u ] and corresponds to the u-th element in the array W; w [ u-1] is a threshold corresponding to Q [ u-1], and corresponds to the (u-1) th element in the array W;
step 8-5, adding 1 to the j value as a new j value;
step 8-6, judging whether m-j is greater than 0, if so, switching to step 8-3; if not, turning to the step 8-7;
step 8-7, subtracting 1 from the m value to obtain a new m value;
step 8-8, judging whether m is larger than k, if so, switching to step 8-2; if not, ending to obtain an ordered array Q;
step 9, positioning calculation is carried out on the signal intensities received by the base stations corresponding to the first k elements in the array M in the t positioning process, and the position of the moving target in the t positioning process is obtained;
and step 10, adding 1 to the t value to serve as a new t value, and switching to step 6.
Preferably, in the step 5 and the step 9, a k-edge measurement positioning method is adopted for positioning calculation.
In order to enable rapid calculation, preferably, in step 8-1, when 2k is not less than n, the initial value of m is set to n; when 2k < n, the initial value of m is set to 2k.
The invention solves the second technical problem by adopting the technical proposal that: the setting method of the threshold value W [ i ] corresponding to the base station with the sequence number i in the step 8-1 is as follows:
the method is calculated by the following formula:
W[i]＝10lg(1+d[i])；
wherein d [ i ]]The base station with the sequence number i is interfered by interference factors of other adjacent base stations in the environment, i epsilon {0,1 … n-1},q[i，a]the signal strength, pi, a, transmitted by the adjacent a-th base station is actually received by the base station with the sequence number i]The base station with the sequence number i theoretically receives the signal strength transmitted by the adjacent a base station, p [ i, a ]]Calculated from the following formula: p (P) t -p[i，a]-P 0 ＝32.44+20lgr+20lgf，P t For the transmission power of the a-th base station adjacent to the base station with the sequence number i, P 0 For the loss of wireless signals in the air, r is the communication distance between the base station with the sequence number i and the adjacent a base station, f is the working frequency of the adjacent a base station with the sequence number i, s i The total number of the base stations which are adjacent to the base station with the sequence number i and participate in the interference factor calculation is smaller than or equal to the total number of the base stations which are adjacent to the base station with the sequence number i.
Compared with the prior art, the invention has the advantages that: and when the signal intensity received by a certain non-positioning base station is greater than the sum of the signal intensity received by a certain positioning base station and the threshold value thereof, the non-positioning base station meeting the conditions replaces the original positioning base station and is used for accurately positioning the subsequent moving target. Therefore, the method can rapidly select the base station for positioning the moving target, effectively eliminate the ping-pong effect generated during the handover, reduce the repeated connection times between the moving target and the server, and improve the stability of the system.
Drawings
FIG. 1 is a schematic diagram of a prior art wireless sensor network;
FIG. 2 is a flowchart of a method for locating a moving object according to an embodiment of the present invention;
FIG. 3 is a flowchart of sorting the array Q at the t-th positioning according to an embodiment of the present invention;
FIG. 4 is a schematic diagram illustrating a simulation of the positioning of a moving object according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of the present invention for locating a moving object in the presence of interference from the environment of FIG. 4;
FIG. 6 is a schematic diagram of the prior art bubbling algorithm used to rank and then locate a moving object in the case of interference in the environment of FIG. 4;
FIG. 7 is an enlarged view of a portion of FIG. 5;
fig. 8 is a partial enlarged view of fig. 6.
Detailed Description
The invention is described in further detail below with reference to the embodiments of the drawings.
As shown in fig. 2, the method for positioning a moving target of the multi-base station wireless sensor network in this embodiment includes the following steps:
step 1, carrying out 1 st positioning on a moving target, and forming an array P with the length of n by receiving the signal intensity of the moving target at the time corresponding to the 1 st positioning by each base station in the wireless sensor network;
wherein n is the total number of base stations in the wireless sensor network; the n elements in the array P are respectively: p0, P1, … P i, … P n-1, P0 is the signal intensity of the mobile object received by the base station with the sequence number 0 at the time corresponding to the 1 st positioning; p1 is the signal intensity of the mobile object received by the base station with the serial number 1 at the time corresponding to the 1 st positioning; the signal intensity of the moving target is received by the base station with the sequence number i at the time corresponding to the 1 st positioning; p [ n-1] is the signal intensity of the mobile target received by the base station with the sequence number of n-1 at the time corresponding to the 1 st positioning;
step 2, sequencing the signal intensity of all the base stations in the array P from big to small to obtain an array Q;
step 3, judging whether a base station appointed for positioning is preset, if so, shifting the signal intensity corresponding to b base stations appointed for positioning to the first b positions of an array Q, obtaining an updated array Q, and transferring to step 4; if not, turning to step 4;
step 4, forming an array M according to the base station serial numbers corresponding to each element in the array Q and the positions corresponding to each element in the array Q one by one;
step 5, positioning calculation is carried out on the signal intensity received by the base station corresponding to the first k elements in the array M, and the position of the moving target in the 1 st positioning process is obtained; k is less than or equal to n; wherein b is equal to or less than k in the optimal condition;
step 6, the mobile target is positioned for the t time, t is more than or equal to 2, the initial value of t is 2, the signal intensity of each base station receiving the mobile target at the time corresponding to the t time positioning updates the array P at the t-1 time positioning, and the array P at the t time positioning is obtained;
step 7, ordering the elements in the array P at the time of the t-th positioning according to the sequence of the base station serial numbers in the array M at the time of the t-1 th positioning to obtain an array Q at the time of the t-th positioning;
step 8, sequencing the array Q in the t positioning, and generating an array M in the t positioning from the base station serial numbers corresponding to each element in the sequenced array Q; the base station serial numbers in the array M are arranged in a one-to-one correspondence according to the positions of each element in the ordered array Q;
as shown in fig. 3, the specific steps for sorting the array Q at the time of the t-th positioning are as follows:
step 8-1, setting an initial value of m, wherein k is more than m and less than or equal to n; setting a threshold value corresponding to each base station corresponding to each element in the array Q in the t-th positioning, and forming all the threshold values into an array W; namely: each element in the array W is a threshold value of a base station corresponding to the corresponding element in the array Q;
step 8-2, setting j=1;
step 8-3, u=m-j;
8-4, judging whether Q [ u ] is larger than Q [ u-1] +Wu ], if so, exchanging the positions of Q [ u ] and Q [ u-1] in the array Q in the t-th positioning to obtain an updated array Q, exchanging the positions of W [ u ] and W [ u-1] in the array W to obtain an updated array W, and transferring to 8-5; if not, turning to the step 8-5;
wherein Q [ u ] is the u-th element in the array Q in the t-th positioning; q [ u-1] is the u-1 element in the array Q during the t-th positioning; w [ u ] is the threshold corresponding to Q [ u ], and corresponds to the u-th element in the array W; w [ u-1] is a threshold corresponding to Q [ u-1], and corresponds to the (u-1) th element in the array W;
step 8-5, adding 1 to the j value as a new j value;
step 8-6, judging whether m-j is greater than 0, if so, switching to step 8-3; if not, turning to the step 8-7;
step 8-7, subtracting 1 from the m value to obtain a new m value;
step 8-8, judging whether m is larger than k, if so, switching to step 8-2; if not, ending to obtain an ordered array Q;
step 9, positioning calculation is carried out on the signal intensities received by the base stations corresponding to the first k elements in the array M in the t positioning process, and the position of the moving target in the t positioning process is obtained;
and step 10, adding 1 to the t value to serve as a new t value, and switching to step 6.
In the step 2, an bubbling ordering algorithm can be adopted for automatic ordering; in the step 3, when the signal intensities corresponding to the b specified base stations for positioning are shifted to the first b positions of the array Q, the signal intensities received by the specified base stations and moving targets can be orderly sequenced from strong to weak at the first b positions of the array Q, or the signal intensities received by the specified b base stations and moving targets can be randomly distributed at the first b positions of the array Q, the specific mode is not limited, and other elements are shifted backwards according to the original sequence; in addition, the array P in the t-th positioning in the step 6 is also set according to the signal intensity of the moving target correspondingly received in the sequence from 0 to n-1 of the base station serial number; the purpose of the above step 7 is to select the base station used in the t-1 st positioning, and then the purpose of step 8 is to determine whether the base station used in the last positioning needs to be replaced or not in this positioning, so as to overcome the ping-pong effect of the handover.
The step 5 and the step 9 adopt a k-edge measurement positioning method to perform positioning calculation, the value of k is determined by the adopted positioning measurement method, and k=3 in the trilateration method and k=4 in the four-edge measurement method; this measurement method belongs to the prior art known to the person skilled in the art and is not described in detail here.
In the embodiment, in the selection of the initial value of m, when 2k is greater than or equal to n, the initial value of m is set as n; when 2k < n, the initial value of m is set to 2k, which is twice the number of base stations used for positioning last time, because the position of the moving object is continuously changed during the moving process, and even if a handover is generated, the last received signal strength is candidate in the base stations of the previous 2k, so that quick calculation can be realized.
In addition, the setting method of the threshold value W [ i ] corresponding to the base station with the sequence number i in the step 8-1 is as follows:
the method is calculated by the following formula:
W[i]＝10lg(1+d[i])；
wherein d [ i ]]The base station with sequence number i is subject to interference factors from other neighboring base stations in the environment, i e 0,1.q[i，a]The signal strength, pi, a, transmitted by the adjacent a-th base station is actually received by the base station with the sequence number i]The base station with the sequence number i theoretically receives the signal strength transmitted by the adjacent a base station, p [ i, a ]]Calculated from the following formula: p (P) t -p[i，a]-P 0 ＝32.44+20lgr+20lgf，P t For the transmission power of the a-th base station adjacent to the base station with the sequence number i, P 0 For the loss in air of the wireless signal transmitted by the a-th base station adjacent to the i-th base station, r is the communication distance between the i-th base station and the adjacent a-th base station, f is the adjacent a-th base stationOperating frequencies of a base stations s i The total number of the base stations which are adjacent to the base station with the sequence number i and participate in the interference factor calculation is smaller than or equal to the total number of the base stations which are adjacent to the base station with the sequence number i.
The selection principle of the threshold value is as follows: since the "ping-pong effect" in the handover process is caused by the wireless signal being interfered by the environment, the interference factor is considered when the threshold is selected in the embodiment; if the base station with the sequence number i receives the signal power x 'i of the mobile object transmission at a certain moment without signal interference, the power error s' i caused by interference in the actual environment is as follows:
s '[ i ] =x' [ i ] ×dj ] (formula 1)
Wherein di is the interference factor of the base station with the sequence number i affected by the environment;
the total signal strength y' [ i ] (unit: mW) received by the base station is:
y ' [ i ] =x ' [ i ] +x ' [ i ] ×dj ] (formula 2)
Converting the unit of the total signal intensity y' i from mW to dBm to obtain y i;
y [ i ] =x [ i ] +10lg (1+dj) (formula 3), where x [ i ] is a value of x' [ i ] converted from unit mW to dBm.
Taking the threshold value W [ i ] as the difference between the total signal intensity y [ i ] and the signal intensity x [ i ], namely:
wi=yi-xi=10lg (1+di) (equation 4)
In addition, in the process of selecting the threshold value, an interference factor parameter is adopted. The interference factor parameter can be obtained through calculation by a signal transmission method between adjacent base stations. The method comprises the following steps: if the base station with the sequence number e is adjacent to the base station with the sequence number i, the sequence number e selects a certain energy to send signals to the base station with the sequence number i at a certain moment, and the distance between the base station with the sequence number e and the base station with the sequence number i is known, so that the signal strength pi (unit: dBm) theoretically received by the base station with the sequence number i can be calculated according to the following formula 5;
ideally, the communication distance has the following relation with the transmission power, the reception sensitivity and the operating frequency:
Pt-Pr-p0=32.44+20lgr+20lgf (formula 5)
Wherein r is a transmission distance in km; f is the working frequency, and the unit is MHz; p (P) t The unit is dBm for transmitting power; p (P) r For received power, the unit is dBm; p (P) 0 The unit of the loss of the wireless signal in the air is dBm, and the unit is 10. The formula 5 is a common formula in the prior art.
P in the above equation 5 t The transmission power of the base station with the sequence number e corresponds to the signal strength pi which is theoretically received by the base station with the sequence number i and Pr corresponds to]R is the transmission distance between the base station with the sequence number e and the base station with the sequence number i, and f is the working frequency of the base station with the sequence number e.
Converting p [ i ] in dBm to power p' [ i ] in mW:
if the signal intensity actually received by the base station with the sequence number i is q [ i ] (unit: dBm), converting the signal intensity into power q' [ f ] with the unit of mW;
according to the formula 2, the formula 6 and the formula 7, the interference factors d [ i, e ] of the base station with the sequence number i, which are affected by the environment when receiving the wireless signal transmitted by the base station with the sequence number e, can be obtained as follows:
wherein q [ i, e ] is the signal strength of the adjacent base station with the sequence number e actually received by the base station with the sequence number i, and p [ i, e ] is the signal strength of the adjacent base station with the sequence number e theoretically received by the base station with the sequence number i.
In actual use, since there may be a plurality of base stations near the base station with the sequence number i, respective interference factors can be calculated from signals transmitted from the plurality of base stations near the base station with the sequence number i, and then the interference factor corresponding to the base station with the sequence number i is obtained by an averaging method. As a typical application, in this process, the base stations near the base station with the sequence number i select part or all of the base stations except the sequence number i in the positioning area.
In addition, in this embodiment, the interference factor represents the interference condition of signal transmission between the base stations, and is not consistent with the signal interference transmitted to the base stations by the moving target in theory, but because the environment and the signal strength of the transmission are approximately the same, the interference factor obtained in this section can be used for calculating the threshold value of equation 4 in practical application.
In order to verify the effectiveness of the algorithm, the signal intensity received by each base station in the moving process of the moving target must be obtained firstly, and the method adopted by the invention is as follows: a site 750 m long and 750 m wide is assumed to be covered by arranging 20 base stations, as shown in fig. 4. The initial position of the moving target is (0, 10), the moving target moves obliquely upwards at a speed of 3 meters per second and linearly moves, and the coordinates of the moving target in unit time are calculated by utilizing a trigonometric function relation, so that the moving target has 350 positioning points in total; simultaneously, the moving target transmits a wireless signal outwards at a rate of at least 3 times per second, and the transmission signal strength is 0dBm; the wireless sensitivity of the base station is-97 dBm, then the signal intensity received by each base station is obtained by using a formula 5, and when the calculated signal intensity is smaller than the sensitivity value, the signal intensity is recorded as- +. And finally, storing the obtained 350 positioning point coordinates and the signal intensities received by 20 base stations when the moving target is positioned at the positioning points in a database, wherein the data of the signal intensities correspond to the condition of no interference in the environment. And then according to the formula 3, the received signal strength under the condition that the base station has interference is calculated through simulation, and the data and the moving target index are correspondingly stored in a database.
The calculation of the received signal strength of each base station is specifically as follows:
assuming that the frequency point of the wireless sensing network is 868MHz, as the nearest distance between two adjacent base stations is 150 meters, the strength of the received signals of the adjacent base stations is-83.73 dBm according to the formula 5, namely p [ i ] = -83.73 (i E [0, 19 ]) in the formula 8. For simulation testing, random interference is artificially added to the signal strength. Substituting the randomly-changed interference factors into a formula 8, and obtaining the strength of the actually received signals of the adjacent base stations after transformation, wherein the strength is as follows:
q [ i ] =pi+101 g (1+ran [ i ]) (equation 9)
Wherein, ran [ i ] is a randomly varying interference factor, and ran [ i ] =Di×random (1), that is, ran [ i ] is a Random number uniformly distributed between [0, di ]); 10lg (1+di) is the maximum limit value of interference to the base station received signal with sequence number i. In this embodiment, each base station di is assumed to be 30% in the simulation test. It is noted that the ran i of each base station at the same time is a random number generated separately and is typically not equal.
Then, the ran [ i ] used in the formula 9 is substituted for d [ i ] and substituted into the formula 3, so that the signal intensity y [ i ] received by each base station under the interference condition can be obtained. And finally, q [ i ], y [ i ] of each base station when the moving target is at all positioning points are stored into a database for simulation test of the algorithm of the invention.
The simulation test assumes that the interference factor calculated by the base station is already obtained, i.e., the interference factor calculated by the above equation 9 is known. Thus, by substituting these interference factors into equation 4, the threshold value of each base station can be calculated, and when the interference factor is 30% (i.e., ran [ i ] takes the maximum value in equation (10)), the maximum value of W [ i ] (i e [0, 19 ]) is 1.1394. Taking k= =3, m=6, then using Java language programming to implement the sorting algorithm in fig. 3, obtaining 350 positioning coordinates under the condition of environmental interference, and plotting as shown in fig. 5.
To examine the effect of the algorithm herein, the above mentioned W [ i ] (i e [0, 19 ]) was set to 0, i.e. the sorting algorithm in fig. 3 was changed to a normal bubble sorting algorithm, 350 positioning coordinates were recalculated by the above software, and the plot is shown in fig. 6. Comparing the positioning track in fig. 5 and 6 with the preset track in fig. 4, it can be found that: the positioning points are scattered at the beginning and the end, and the positioning precision is low, because no base station exists near the moving point and is far away from the base station; in the middle section of the moving track, the positioning accuracy is higher, because a nearer base station is selected in the algorithm for positioning. The conclusion obtained by the formula (2) can be verified, namely, nearby positioning base stations are selected as much as possible for positioning the moving target, and the positioning accuracy can be improved.
Then, the local amplification of the base station 13 in fig. 5 and 6 is performed, and the occurrence probability of the ping-pong effect in the crossing region of the moving target under the two conditions is compared, so that the phenomenon of more ping-pong effect can be found when the moving target is positioned by adopting thresholdless calculation; with thresholded mobile object positioning, the "ping-pong effect" phenomenon may occur occasionally, but much less frequently than the thresholded result.
Fig. 7 and 8 are partial enlarged cases of the position of the base station 13 in fig. 5 and 6, respectively, 12 anchor points in fig. 8 move back and forth between the base stations 12, 13, 14 and 18 (base stations not shown in fig. 7 and 8), for example, anchor points 1 and 2 are located by the base stations 13, 18 and 12, anchor point 3 becomes located by the base stations 13, 18 and 14, and anchor point 4 becomes located by the base stations 13, 18 and 12, respectively, a "ping-pong effect" phenomenon occurs in the handover process, and moving target information is alternately transmitted to the server by the base station 12 or the base station 14, respectively. It can also be found that the positioning points 5, 6, 8-12 are positioned by the base stations 13, 18 and 14, and become positioned by the base stations 13, 18 and 12 when the positioning point 7 is positioned, and the ping-pong effect phenomenon is generated; in fig. 7, the first 4 positioning points are all positioned by the base stations 13, 18 and 12, the second 8 positioning points are all positioned by the base stations 13, 18 and 14, the whole process has no ping-pong effect, and the base station of the mobile target information sent to the server is changed for 1 time at most. Therefore, the algorithm in the invention can effectively solve the ping-pong effect in the process of the cross-zone, and reduce the change times of the transmission channel of the information sent to the server.

Claims (4)

1. A method for positioning a moving target of a multi-base station wireless sensor network is characterized by comprising the following steps of: the method comprises the following steps:
step 1, carrying out 1 st positioning on a moving target, and forming an array P with the length of n by receiving the signal intensity of the moving target at the time corresponding to the 1 st positioning by each base station in the wireless sensor network;
wherein n is the total number of base stations in the wireless sensor network; the n elements in the array P are respectively: p0, P1, … P i, … P n-1, P0 is the signal intensity of the mobile object received by the base station with the sequence number 0 at the time corresponding to the 1 st positioning; p1 is the signal intensity of the mobile object received by the base station with the serial number 1 at the time corresponding to the 1 st positioning; the signal intensity of the moving target is received by the base station with the sequence number i at the time corresponding to the 1 st positioning; p [ n-1] is the signal intensity of the mobile target received by the base station with the sequence number of n-1 at the time corresponding to the 1 st positioning;
step 2, sequencing the signal intensity of all the base stations in the array P from big to small to obtain an array Q;
step 3, judging whether a base station appointed for positioning is preset, if so, shifting the signal intensity corresponding to b base stations appointed for positioning to the first b positions of an array Q, obtaining an updated array Q, and transferring to step 4; if not, turning to step 4;
step 4, forming an array M according to the base station serial numbers corresponding to each element in the array Q and the positions corresponding to each element in the array Q one by one;
step 5, positioning calculation is carried out on the signal intensity received by the base station corresponding to the first k elements in the array M, and the position of the moving target in the 1 st positioning process is obtained; b is not less than k is not less than n;
step 6, the mobile target is positioned for the t time, t is more than or equal to 2, the initial value of t is 2, the signal intensity of each base station receiving the mobile target at the time corresponding to the t time positioning updates the array P at the t-1 time positioning, and the array P at the t time positioning is obtained;
step 7, ordering the elements in the array P at the time of the t-th positioning according to the sequence of the base station serial numbers in the array M at the time of the t-1 th positioning to obtain an array Q at the time of the t-th positioning;
step 8, sequencing the array Q in the t positioning, and generating an array M in the t positioning from the base station serial numbers corresponding to each element in the sequenced array Q;
the specific steps of sequencing the array Q in the t-th positioning are as follows:
step 8-1, setting an initial value of m, wherein k is more than m and less than or equal to n; setting a threshold value corresponding to each base station corresponding to each element in the array Q in the t-th positioning, and forming all the threshold values into an array W;
step 8-2, setting j=1;
step 8-3, u=m-j;
8-4, judging whether Q [ u ] is larger than Q [ u-1] +Wu ], if so, exchanging the positions of Q [ u ] and Q [ u-1] in the array Q in the t-th positioning to obtain an updated array Q, exchanging the positions of W [ u ] and W [ u-1] in the array W to obtain an updated array W, and transferring to 8-5; if not, turning to the step 8-5;
wherein Q [ u ] is the u-th element in the array Q in the t-th positioning, Q [ u-1] is the u-1-th element in the array Q in the t-th positioning, W [ u ] is the threshold value corresponding to Q [ u ] and corresponds to the u-th element in the array W; w [ u-1] is a threshold corresponding to Q [ u-1], and corresponds to the (u-1) th element in the array W;
step 8-5, adding 1 to the j value as a new j value;
step 8-6, judging whether m-j is greater than 0, if so, switching to step 8-3; if not, turning to the step 8-7;
step 8-7, subtracting 1 from the m value to obtain a new m value;
step 8-8, judging whether m is larger than k, if so, switching to step 8-2; if not, ending to obtain an ordered array Q;
step 9, positioning calculation is carried out on the signal intensities received by the base stations corresponding to the first k elements in the array M in the t positioning process, and the position of the moving target in the t positioning process is obtained;
and step 10, adding 1 to the t value to serve as a new t value, and switching to step 6.
2. The method for positioning a moving object in a multi-base station wireless sensor network according to claim 1, wherein: and in the step 5 and the step 9, a k-edge measurement positioning method is adopted for positioning calculation.
3. The method for positioning a moving object in a multi-base station wireless sensor network according to claim 1, wherein: in the step 8-1, when 2k is more than or equal to n, the initial value of m is set as n; when 2k < n, the initial value of m is set to 2k.
4. The method for positioning a moving object in a multi-base station wireless sensor network according to claim 1, wherein: the setting method of the threshold value W [ i ] corresponding to the base station with the sequence number i in the step 8-1 is as follows:
the method is calculated by the following formula:
W[i]＝10lg(1+d[i])；
wherein d [ i ]]The base station with the sequence number i is interfered by interference factors of other adjacent base stations in the environment, i epsilon {0,1 … n-1},q[i,a]the signal strength, pi, a, transmitted by the adjacent a-th base station is actually received by the base station with the sequence number i]The base station with the sequence number i theoretically receives the signal strength transmitted by the adjacent a base station, p [ i, a ]]Calculated from the following formula: p (P) t -p[i，a]-P 0 ＝32.44+20lgr+20lgf，P t For the transmission power of the a-th base station adjacent to the base station with the sequence number i, P 0 For the loss of wireless signals in the air, r is the communication distance between the base station with the sequence number i and the adjacent a base station, f is the working frequency of the adjacent a base station with the sequence number i, s i The total number of the base stations which are adjacent to the base station with the sequence number i and participate in the interference factor calculation is smaller than or equal to the total number of the base stations which are adjacent to the base station with the sequence number i.
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