CN104822158A - Method of optimizing position of base station in radio frequency charging wireless sensor network - Google Patents

Abstract

The invention discloses a method of optimizing a position of a base station in a radio frequency charging wireless sensor network. One feature that radio frequency waves emitted by two radio frequency base stations generate an interference phenomenon at one sensor node is combined, through overlay analysis on two columns of radio waves at the same charging waiting sensor node, a relationship between a position difference between the two radio frequency base stations and a charging efficiency of the charging waiting sensor node is obtained, and two base station positions with the optimized charging effects in the overall network are thus calculated. The method can be applied to the radio frequency charging wireless sensor network, the charging efficiency of the charging waiting node can be greatly improved, the service life of the overall wireless sensor network is prolonged, and the downtime of the overall system is reduced.

Description

The method for optimizing position of base station in a kind of radio frequency charging wireless sensor network

Technical field

The invention belongs to the technical fields such as wireless sensor network, radio frequency charging technique, radio frequency interference, relate to the method for optimizing position of base station in a kind of radio frequency charging wireless sensor network, particularly relate to the base station stop position method making whole network charging effect optimum in the radio frequency charging wireless sensor network of existence two base stations.

Background technology

Wireless sensor network forms primarily of sensor node, and sensor node has signal perception, calculates the functions such as storage, radio communication.Sensor node is deployed in needs to carry out the region of monitoring, this deployment is normally disseminated by aircraft, manually the mode such as embedding complete.Node forms network by self-organizing form, and passes through multihop routing mode by the transfer of data of monitoring to administrative center.User can be browsed by the server at Access Management Access center, inquires about, search for associated monitoring data.

Wireless sensor network is widely used, and mainly comprises the numerous areas such as environment measuring, industry and infrastructure monitoring, Smart Home, medical system and military affairs.Sensor network interior joint One's name is legion, and generally adopt powered battery, operable electricity is limited, in addition, nodes a large amount of in wireless sensor network is likely random scatter or is placed on the bad environments mankind and is difficult to the place of arrival or is embedded in building structure, change by manpower that battery difficulty is large, cost is high, limited energy problem becomes the key factor of restriction the type network Development.It how to be one of more effective supplementary electricity important research direction becoming wireless sensor network of sensor node.

Radio frequency charging technique a kind ofly supplements the emerging technology of electricity for sensor node, and in the art, base station is that the sensor node sending charge request supplements electricity by launching rf wave.

The team be engaged at present based on the wireless chargeable sensor network study of hardware of radio-frequency technique mainly contains Intel laboratory and PowerCast company.Intel laboratory and University of Washington have developed jointly RFID tag (Wireless Identification Sensing Platform WISP), this She Pin Shi Do label has sensing capability, do not use battery, adopt the direct current receiving the radio-frequency (RF) energy conversion that reader is launched as electric energy work.And the wireless chargeable sensor suite of PowerCast company exploitation comprises radio-frequency energy transmission part, energy receptor portions, microprocessor portion, Sensor section and radio frequency communication section.Energy-emitting portion is made up of radio frequency circuit for generating and antenna two parts, continue the electromagnetic wave launching 915MHz centre frequency, energy receptor portions is converted into high frequency voltage pulse after receiving electromagnetic wave by antenna, again by voltage doubling rectifing circuit by voltage amplification, electromagnetism good fortune is penetrated and is converted to available electric energy and powers to sensor node.

But, for how making the problem of whole network charging effect optimum in the wireless sensor network of existence two base stations still not can solve.

Simultaneously, because different base station is internodal apart from different from wait charge sensors, this phase difference rf wave that different base station can be caused to send produced because of range difference produces radio frequency electromagnetic interference at wait charge sensors Nodes, thus has influence on the charge efficiency of node to be charged.Radio frequency interference phenomenon how is well utilized to be the emphasis that the present invention studies to improve the charge efficiency of whole network.

Summary of the invention

For the technical problem of above-mentioned existence, the present invention proposes in the radio frequency charging wireless sensor network of a kind of existence two base stations and find the base station stop position method making whole network sensor node charging effect optimum.

The technical solution adopted in the present invention is: the method for optimizing position of base station in a kind of radio frequency charging wireless sensor network, is characterized in that, comprise the following steps:

Step 1: set two base stations as ET1, ET2, wait for that charge sensors node is S1, the distance of ET1 to S1 is r1, the distance of ET2 to S1 is r2, rf wave wavelength is λ, analyze in radio frequency charging wireless sensor network, when radio-frequency (RF) energy is launched in two base stations simultaneously, there is radio frequency constructive enhancing phenomenon or the blast phase relaxation phenomenon of radio frequency at S1 place;

Step 2: charge efficiency η and two base stations of analyzing S1 send electromagnetic wave at S1 point place phase difference relation;

Step 3: the optimum stop position analyzing base station in radio frequency charging wireless sensor network in following situation;

Situation one: if two base stations ET1, ET2 are that a sensor node S1 charges, then:

Only need control two base stations rests on the concentric circles that distance S1 is k λ; Wherein, λ is radio frequency electromagnetic wavelength, and k is integer, 1≤k≤65; Because the range difference being in two base stations on concentric circles and S1 node is just the integral multiple of wavelength, and the two row electromagnetic waves sent by two base stations respectively produce Constructive interaction at this point, and the energy making this place receive strengthens;

Situation two: if two base stations ET1, ET2 are two sensor node S1, S2 chargings, then:

Only need control two base stations to rest in distance S1 be k λ and distance S2 to be on the intersection point on the concentric circles of k λ; Because no matter two base stations be on intersection point are to S1 node or the integral multiple being wavelength to the range difference of S2 node, the two row electromagnetic waves sent by two base stations respectively produce Constructive interaction at these 2, and received energy is strengthened;

Situation three: if two base stations ET1, ET2 are three sensor node S1, S2, S3 chargings, then:

(1) if S1, S2, S3 conllinear, then only need to ensure that ET1 and ET2 is in the homonymy of three nodes and the range difference between two base stations is k λ, all the sensors Nodes just can be made to produce Constructive interaction, and charging effect is optimum;

(2) if S1, S2, S3 not conllinear, if the coordinate of S2, S3 is respectively, (0, d) with (0 ,-d), the coordinate of S1 node is (x1, y1); With S2, the line of S3 is Y-axis, with the perpendicular bisector of line for X-axis sets up plane right-angle coordinate, X-axis is found 2 symmetrical A (-c, 0) and B (c, 0), the difference of the distance of A to S1 and the distance of B to S1 is made to be k λ, if such two existence, two base stations rest on these 2 respectively, just can realize S1, S2, S3 place produces Constructive interaction simultaneously; Because now, the distance of ET1 and ET2 to S2 is equal, therefore strengthens for S2; The distance of ET1 and ET2 to S3 is equal, therefore strengthens for S3; The distance that the distance of ET1 to S1 deducts ET2 to S1 is k λ, therefore also strengthens for S1;

Situation four: if two base stations ET1, ET2 are the charging of N number of sensor node, N > 3, then:

(1) if N number of sensor node conllinear, then only need to ensure that ET1 and ET2 is in the homonymy of N number of node and the range difference between two base stations is k λ, all the sensors Nodes just can be made to produce Constructive interaction, and charging effect is optimum;

(2) if N number of sensor node not conllinear, node charge efficiency η formula is first derived, the corresponding value ε of each η value, and then between a corresponding distance regions [k λ-ε, k λ+ε]; If two base stations fall in this interval to wait charge sensors nodal pitch deviation, then the charge efficiency of this Nodes is at least η; In N number of node, optional three nodes, build plane right-angle coordinate according to the mode in above-mentioned situation three and calculate the stop position of two mobile base station ET1 and ET2, total plant and select, now, three the sensor node places chosen can realize Constructive interaction, can received energy significantly strengthen, again because select for each, two base station stop positions are k λ with the internodal range difference of wait charge sensors, k is variable, if the maximum of k is m; Therefore N number of node charging problems has the scheme of kind; Optional two schemes is wherein set to A, B, and for a remaining N-3 node, computing node is to the range difference of two base stations respectively, and carries out following judgement:

If the interstitial content >B scheme middle distance difference that A scheme middle distance difference falls into [k λ-ε, k λ+ε] falls into the interstitial content of [k λ-ε, k λ+ε], then A scheme is excellent;

If A scheme middle distance difference falls into [k λ-ε, k λ+ε] interstitial content=B scheme middle distance difference fall into [k λ-ε, k λ+ε] interstitial content, then compare in two schemes and fall into interval [k λ-ε, k λ+ε] in node to the range difference of two base stations absolute value to after wavelength remainder and value, and the little scheme of value is excellent;

After considering all schemes, try to achieve optimal solution.

As preferably, the radio frequency interference phenomenon described in step 1 comprises following situation:

As r1=r2=λ, now because two base stations are 0 to the range difference of S1, if two base station synchronizations, then consequent phase difference is that 0, two base stations produce the constructive enhancing phenomenon of radio frequency at S1 place;

When r1=r2=λ/2, now because two base stations are λ/2 to the range difference of S1, if two base station synchronizations, then consequent phase difference is π, and two base stations produce the blast phase relaxation phenomenon of radio frequency at S1 place.

As preferably, the specific implementation process of step 2 is: two two train waves establishing two base station ET1 and ET2 to send are in [-π, π] at the phase difference at S1 point place, and Δ r is the absolute value of two range differences, that is: Δ r=|r ₁-r ₂|.Get ε be range difference to wavelength remainder value, that is: ε=Δ r% λ (λ is radio frequency electromagnetic wavelength), if ε > λ/2, ε=λ-ε.Because phase difference and range difference exist linear relationship, for phase difference during ε, therefore:

If the vibration equation of the radio frequency electromagnetic that ET1, ET2 launch is respectively:

y1＝A1cos(wt)；

y2＝A2cos(wt)；

Then two train waves are A at S1 point place with amplitude:

Wherein A1 is that ET1 launches electromagnetic amplitude, A2 is that ET2 launches electromagnetic amplitude, and w is vibration frequency, and t is the time;

Due to intensity of wave be proportional to wave-amplitude square, and so the intensity after two train wave superpositions is:

In formula, I is the intensity after superposition, the intensity that I1 is amplitude when being A1, the length that I2 is amplitude when being A2; As I1=I2:

When time, I=4I1, S1 point place produces Constructive interaction;

When when not being 0, if S1 place charge efficiency η, then:

By learn: and then show that charge efficiency η and the two base stations absolute value to S1 range difference is to the relation of wavelength remainder value ε:

$\mathrm{\ϵ}=\frac{\mathrm{\λ}\arccos (2\mathrm{\η}-1)}{2\mathrm{\π}};$

When η=0.95, ε=0.0718 λ;

When η=0.90, ε=0.1025 λ;

When η=0.85, ε=0.1267 λ;

When η=0.80, ε=0.1477 λ.

As preferably, described in step 3 two base station ET1, an ET2 are three not conllinear sensor node S1, S2, S3 chargings, X-axis is found 2 symmetrical A (-c, 0) and B (c, 0), two mobile base stations rest on these 2 respectively, make the distance between ET1 to S1 and the range difference between ET2 to S1 be k λ; Its concrete computational process is:

$\sqrt{{(x1+c)}^2+{y1}^2}-\sqrt{{(x1-c)}^2+{y1}^2}=\mathrm{k\λ}$ ①；

$\frac{4\mathrm{cx}1}{\sqrt{{(x1+c)}^2+{y1}^2}+\sqrt{{(x1-c)}^2+y{1}^2}}=\mathrm{k\λ}$ ②；

Obtained by 2. formula:

$\sqrt{{(x1+c)}^2+{y1}^2}+\sqrt{{(x1-c)}^2+{y1}^2}=\frac{4x1}{\mathrm{k\λ}}c$ ③；

1.+3.:

$2\sqrt{{(x1+c)}^2+{y1}^2}=\mathrm{k\λ}+\frac{4x1}{\mathrm{k\λ}}c;$

$4({x1}^2+2\mathrm{cx}1+c^2+y{1}^2)=k^2{\mathrm{\λ}}^2+8x1c+\frac{16{x1}^2}{k^2{\mathrm{\λ}}^2}{c}^2;$

$c^2(\frac{16{x1}^2}{k^2{\mathrm{\λ}}^2}-4)=4{x1}^2+4{y1}^2-k^2{\mathrm{\λ}}^2;$

$\frac{{4c}^2(4x{1}^2-k^2{\mathrm{\λ}}^2)}{k^2{\mathrm{\λ}}^2}=4{x1}^2+4{y1}^2-k^2{\mathrm{\λ}}^2;$

Make above-mentioned equation have solution, then need to meet 4x ₁ ²– k ²λ ²>0;

If 4x ₁ ²– k ²λ ²during <=0, namely (-| k λ |/2) <x ₁< (| k λ |/2), now ∠ S2S1S3 is large obtuse angle, and ∠ S1S2S3 is little acute angle, and ∠ S1S3S2 is little acute angle; Under this situation, the optimum stop position in base station is as follows:

If S1 point is projected as T point in Y-axis, ET1 and ET2 is made to be distributed in T point both sides and distance between ET1 and T point, ET2 and T point is k λ/2.

The rf wave that the present invention launches in conjunction with two radio-frequency (RF) base station produces this feature of interference at same sensor node place, by the overlay analysis to same sensor node place two to be charged row electric wave, draw the alternate position spike of two radio-frequency (RF) base station and the relation of sensor node charge efficiency to be charged, and then calculate two base station locations of whole network charging effect optimum of sening as an envoy to.This invention is applied in radio frequency charging wireless sensor network, can improve the charge efficiency of node to be charged significantly, thus extend the life-span of whole wireless sensor network, reduce the downtime of whole system simultaneously.

Accompanying drawing explanation

Fig. 1: be the wireless sensor network structural representation with base station in the embodiment of the present invention;

Fig. 2: be in the embodiment of the present invention two base stations to a node charged condition schematic diagram;

Fig. 3: be in the embodiment of the present invention two base stations to two node charged condition schematic diagrames;

Fig. 4: be three sensor node conllinear situation schematic diagrames in the embodiment of the present invention;

Fig. 5: be three sensor nodes not conllinear and 4x in the embodiment of the present invention ₁ ²– k ²λ ²>0 situation schematic diagram;

Fig. 6: be three sensor nodes not conllinear and 4x in the embodiment of the present invention ₁ ²– k ²λ ²<=0 situation schematic diagram;

Concrete enforcement

Understand for the ease of those of ordinary skill in the art and implement the present invention, below in conjunction with drawings and Examples, the present invention is described in further detail, should be appreciated that exemplifying embodiment described herein is only for instruction and explanation of the present invention, is not intended to limit the present invention.

The method for optimizing position of base station in a kind of radio frequency charging wireless sensor network provided by the invention, comprises the following steps:

Step 1: set two base stations as ET1, ET2, wait for that charge sensors node is S1, the distance of ET1 to S1 is r1, the distance of ET2 to S1 is r2, rf wave wavelength is λ, analyze in radio frequency charging wireless sensor network, when radio-frequency (RF) energy is launched in two base stations simultaneously, the radio frequency interference phenomenon existed at S1 place;

As shown in Figure 1, the distance of ET1, ET2 to S1 is respectively λ, just be the length of a wavelength, now because two base stations are 0 to the range difference of S1, consequent phase difference is 0 (two base station synchronization), and two base stations produce the constructive enhancing phenomenon of radio frequency at sensor node place to be charged.

The distance of ET1 to S1 is λ, is the length of a wavelength just; The distance of ET3 to S1 is the length of λ/2, half wavelength, and now because two base stations are λ/2 to the range difference of S1, consequent phase difference is π (two base station synchronization), and two base stations produce blast phase relaxation phenomenon at sensor node place to be charged.

The present invention is based on how better application and construction is interfered, avoided blast phase interference thus make the charge efficiency optimum of whole network be that starting point is considered.

Step 2: charge efficiency η and the two base station phase differences of analyzing S1 relation;

If two train waves that two base station ET1 and ET2 send are in [-π, π] at the phase difference at S1 point place, Δ r is the absolute value of two range differences, that is: Δ r=|r ₁-r ₂|.Get ε be range difference to wavelength remainder value, that is: ε=Δ r% λ (λ is radio frequency electromagnetic wavelength), if ε > λ/2, ε=λ-ε.Because phase difference and range difference exist linear relationship, for phase difference during ε, therefore:

If the vibration equation of the radio frequency electromagnetic that ET1, ET2 launch is respectively:

y1＝A1cos(wt)；

y2＝A2cos(wt)；

Then two train waves are A at S1 point place with amplitude:

Wherein A1 is that ET1 launches electromagnetic amplitude, A2 is that ET2 launches electromagnetic amplitude, and w is vibration frequency, and t is the time.

Due to intensity of wave be proportional to wave-amplitude square, and so the intensity after two train wave superpositions is:

In formula, I is the intensity after superposition, the intensity that I1 is amplitude when being A1, the length that I2 is amplitude when being A2; As I1=I2:

When time, I=4I1; S1 point place produces Constructive interaction;

When when not being 0, if S1 place charge efficiency η, then:

By learn: and then show that charge efficiency η and the two base stations absolute value to S1 range difference is to the relation of wavelength remainder value ε:

$\mathrm{\&epsiv;}=\frac{\mathrm{\&lambda;}\arccos (2\mathrm{\&eta;}-1)}{2\mathrm{\&pi;}};$

When η=0.95, ε=0.0718 λ;

When η=0.90, ε=0.1025 λ;

When η=0.85, ε=0.1267 λ;

When η=0.80, ε=0.1477 λ.

Step 3: the optimum stop position analyzing base station in radio frequency charging wireless sensor network in following situation;

Situation one: if two base stations ET1, ET2 are that a sensor node S1 charges, then:

Ask for an interview Fig. 2, only need control two base stations and rest on the concentric circles that distance S1 is k λ (λ is radio frequency electromagnetic wavelength, and k is integer).Because the range difference being in two base stations on concentric circles and S1 node is just the integral multiple of wavelength, and the two row electromagnetic waves sent by two base stations respectively produce Constructive interaction at this point, and the energy making this place receive strengthens.

Situation two: if two base stations ET1, ET2 are two sensor node S1, S2 charging, then:

Ask for an interview Fig. 3, only need control two base stations to rest in distance S1 be k λ (λ is radio frequency electromagnetic wavelength, and k is integer) and distance S2 to be on the intersection point on the concentric circles of k λ.Because no matter two base stations be on intersection point are to S1 node or the integral multiple being wavelength to the range difference of S2 node, the two row electromagnetic waves sent by two base stations respectively produce Constructive interaction at these 2, and received energy is strengthened.

Situation three: if two base stations ET1, ET2 are three sensor node S1, S2, S3 chargings, then:

(1) ask for an interview Fig. 4, if S1, S2, S3 conllinear, then only need to ensure that ET1 and ET2 is in the homonymy of three nodes and the range difference between two base stations is k λ, all three Nodes just can be made all to produce Constructive interaction, and node charging effect is optimum.

(2) ask for an interview Fig. 5, if S1, S2, S3 not conllinear, if the coordinate of S2, S3 is respectively, (0, d) with (0 ,-d), the coordinate of S1 node is (x1, y1); With S2, the line of S3 is Y-axis, with the perpendicular bisector of line for X-axis sets up plane right-angle coordinate, X-axis is found 2 symmetrical A (-c, 0) and B (c, 0), two mobile base stations rest on these 2 respectively, make the distance between A (ET1) to S1 and the range difference between B (ET2) to S1 be k λ.Because the distance of ET1 and ET2 to S2 is equal, therefore strengthen for S2, the distance of ET1 and ET2 to S3 is equal, therefore strengthens for S3; The distance that the distance of ET1 to S1 deducts ET2 to S1 is k λ, therefore also strengthens for S1;

The concrete computational process of A, B 2 is:

$\sqrt{{(x1+c)}^2+{y1}^2}-\sqrt{{(x1-c)}^2+{y1}^2}=\mathrm{k\&lambda;}$ ①

$\frac{4\mathrm{cx}1}{\sqrt{{(x1+c)}^2+{y1}^2}+\sqrt{{(x1-c)}^2+y{1}^2}}=\mathrm{k\&lambda;}$ ②

Obtained by 2. formula:

$\sqrt{{(x1+c)}^2+{y1}^2}+\sqrt{{(x1-c)}^2+{y1}^2}=\frac{4x1}{\mathrm{k\&lambda;}}c$ ③

1.+3.:

$2\sqrt{{(x1+c)}^2+{y1}^2}=\mathrm{k\&lambda;}+\frac{4x1}{\mathrm{k\&lambda;}}c;$

$4({x1}^2+2\mathrm{cx}1+c^2+y{1}^2)=k^2{\mathrm{\&lambda;}}^2+8x1c+\frac{16{x1}^2}{k^2{\mathrm{\&lambda;}}^2}{c}^2;$

$c^2(\frac{16{x1}^2}{k^2{\mathrm{\&lambda;}}^2}-4)=4{x1}^2+4{y1}^2-k^2{\mathrm{\&lambda;}}^2;$

$\frac{{4c}^2(4x{1}^2-k^2{\mathrm{\&lambda;}}^2)}{k^2{\mathrm{\&lambda;}}^2}=4{x1}^2+4{y1}^2-k^2{\mathrm{\&lambda;}}^2;$

Make above-mentioned equation have solution, then need to meet 4x ₁ ²– k ²λ ²>0, because wavelength is decimeter grade, thus above-mentioned condition is easy to meet.

Ask for an interview Fig. 6, if 4x ₁ ²– k ²λ ²during <=0, namely (-| k λ |/2) <x ₁< (| k λ |/2), now ∠ S2S1S3 is large obtuse angle, and ∠ S1S2S3 is little acute angle, and ∠ S1S3S2 is little acute angle, and the base station stop position under this situation solves as follows:

If S1 point is projected as T point in Y-axis, make ET1 and ET2 be distributed in T point both sides, the distance between ET1 and T point, ET2 and T point is k λ/2.Now, the distance between ET1 and S1 equals the distance between ET2 and S1, and S1 point place produces Constructive interaction, and energy strengthens; Be k λ for the range difference between the distance between S2, ET2 to S2 and ET1 to S2, produce Constructive interaction; Be k λ for the range difference between the distance between S3, ET1 to S3 and ET2 to S3, produce Constructive interaction.

Situation four: if two base stations ET1, ET2 are the charging of N number of sensor node, N > 3, then:

(1) if N number of sensor node conllinear, then only need to ensure that ET1 and ET2 is in the homonymy of three nodes and the range difference between two base stations is that (k is integer to k λ, λ is radio frequency electromagnetic wavelength), all the sensors node charging effect just can be made optimum.

(2) if N number of sensor node not conllinear, node charge efficiency η formula is first derived, the corresponding value ε of each η value, and then between a corresponding distance regions [k λ-ε, k λ+ε].If two base stations fall in this interval to wait charge sensors nodal pitch deviation, then the charge efficiency of this Nodes is at least η.In N number of node, optional three nodes, build plane right-angle coordinate according to the mode in above-mentioned situation three and calculate the stop position of two mobile base station ET1 and ET2, total plant and select, now, three the sensor node places chosen can realize Constructive interaction, can received energy significantly strengthen, again because select for each, two base station stop positions are k λ with the internodal range difference of wait charge sensors, k is variable, if the maximum of k is m.Therefore N number of node charging problems has the scheme of kind.Optional two schemes is wherein set to A, B, and for a remaining N-3 node, computing node is to the range difference of two base stations respectively, and carries out following judgement:

If the interstitial content >B scheme middle distance difference that A scheme middle distance difference falls into [k λ-ε, k λ+ε] falls into the interstitial content of [k λ-ε, k λ+ε], then A scheme is excellent;

If A scheme middle distance difference falls into [k λ-ε, k λ+ε] interstitial content=B scheme middle distance difference fall into [k λ-ε, k λ+ε] interstitial content, then compare in two schemes and fall into interval [k λ-ε, k λ+ε] in node to the range difference of two base stations absolute value to after wavelength remainder and value, and the little scheme of value is excellent;

After considering all schemes, try to achieve optimal solution.

Should be understood that, the part that this specification does not elaborate all belongs to prior art.

Should be understood that; the above-mentioned description for preferred embodiment is comparatively detailed; therefore the restriction to scope of patent protection of the present invention can not be thought; those of ordinary skill in the art is under enlightenment of the present invention; do not departing under the ambit that the claims in the present invention protect; can also make and replacing or distortion, all fall within protection scope of the present invention, request protection range of the present invention should be as the criterion with claims.

Claims (4)

1. the method for optimizing position of base station in radio frequency charging wireless sensor network, is characterized in that, comprise the following steps:

Step 1: set two base stations as ET1, ET2, wait for that charge sensors node is S1, the distance of ET1 to S1 is r1, the distance of ET2 to S1 is r2, rf wave wavelength is λ, analyze in radio frequency charging wireless sensor network, when radio-frequency (RF) energy is launched in two base stations simultaneously, there is radio frequency constructive enhancing phenomenon or the blast phase relaxation phenomenon of radio frequency at S1 place;

Step 2: charge efficiency η and two base stations of analyzing S1 send electromagnetic wave at S1 point place phase difference relation;

Step 3: the optimum stop position analyzing base station in radio frequency charging wireless sensor network in following situation;

Situation one: if two base stations ET1, ET2 are that a sensor node S1 charges, then:

Only need control two base stations rests on the concentric circles that distance S1 is k λ; Wherein, λ is radio frequency electromagnetic wavelength, and k is integer, 1≤k≤65;

Situation two: if two base stations ET1, ET2 are two sensor node S1, S2 chargings, then:

Only need control two base stations to rest in distance S1 be k λ and distance S2 to be on the intersection point on the concentric circles of k λ;

Situation three: if two base stations ET1, ET2 are three sensor node S1, S2, S3 chargings, then:

(1) if S1, S2, S3 conllinear, then only need to ensure that ET1 and ET2 is in the homonymy of three nodes and the range difference between two base stations is k λ, all the sensors Nodes just can be made to produce Constructive interaction, and charging effect is optimum;

(2) if S1, S2, S3 not conllinear, if the coordinate of S2, S3 is respectively, (0, d) with (0 ,-d), the coordinate of S1 node is (x1, y1); With S2, the line of S3 is Y-axis, with the perpendicular bisector of line for X-axis sets up plane right-angle coordinate, X-axis is found 2 symmetrical A (-c, 0) and B (c, 0), the difference of the distance of A to S1 and the distance of B to S1 is made to be k λ, if such two existence, two base stations rest on these 2 respectively, just can realize S1, S2, S3 place produces Constructive interaction simultaneously;

Situation four: if two base stations ET1, ET2 are the charging of N number of sensor node, N > 3, then:

(1) if N number of sensor node conllinear, then only need to ensure that ET1 and ET2 is in the homonymy of N number of node and the range difference between two base stations is k λ, all the sensors Nodes just can be made to produce Constructive interaction, and charging effect is optimum;

(2) if N number of sensor node not conllinear, node charge efficiency η formula is first derived, the corresponding value ε of each η value, and then between a corresponding distance regions [k λ-ε, k λ+ε]; If two base stations fall in this interval to wait charge sensors nodal pitch deviation, then the charge efficiency of this Nodes is at least η; In N number of node, optional three nodes, build plane right-angle coordinate according to the mode in above-mentioned situation three and calculate the stop position of two mobile base station ET1 and ET2, total plant and select, now, three the sensor node places chosen can realize Constructive interaction, can received energy significantly strengthen, again because select for each, two base station stop positions are k λ with the internodal range difference of wait charge sensors, k is variable, if the maximum of k is m; Therefore N number of node charging problems has the scheme of kind; Optional two schemes is wherein set to A, B, and for a remaining N-3 node, computing node is to the range difference of two base stations respectively, and carries out following judgement:

If the interstitial content >B scheme middle distance difference that A scheme middle distance difference falls into [k λ-ε, k λ+ε] falls into the interstitial content of [k λ-ε, k λ+ε], then A scheme is excellent;

If A scheme middle distance difference falls into [k λ-ε, k λ+ε] interstitial content=B scheme middle distance difference fall into [k λ-ε, k λ+ε] interstitial content, then compare in two schemes and fall into interval [k λ-ε, k λ+ε] in node to the range difference of two base stations absolute value to after wavelength remainder and value, and the little scheme of value is excellent;

After considering all schemes, try to achieve optimal solution.

2. the method for optimizing position of base station in radio frequency according to claim 1 charging wireless sensor network, is characterized in that: the radio frequency interference phenomenon described in step 1 comprises following situation:

As r1=r2=λ, now because two base stations are 0 to the range difference of S1, if two base station synchronizations, then consequent phase difference is that 0, two base stations produce the constructive enhancing phenomenon of radio frequency at S1 place;

When r1=r2=λ/2, now because two base stations are λ/2 to the range difference of S1, if two base station synchronizations, then consequent phase difference is π, and two base stations produce the blast phase relaxation phenomenon of radio frequency at S1 place.

3. the method for optimizing position of base station in radio frequency according to claim 1 charging wireless sensor network, it is characterized in that, the specific implementation process of step 2 is:

If two train waves that two base station ET1 and ET2 send are in [-π, π] at the phase difference at S1 point place, Δ r is the absolute value of two range differences, that is: Δ r=|r ₁-r ₂|; Get ε be range difference to wavelength remainder value, that is: ε=Δ r% λ (λ is radio frequency electromagnetic wavelength), if ε > λ/2, ε=λ-ε; Because phase difference and range difference exist linear relationship, for phase difference during ε, therefore:

If the vibration equation of the radio frequency electromagnetic that ET1, ET2 launch is respectively:

y1＝A1 cos(wt)；

y2＝A2 cos(wt)；

Then two train waves are A at S1 point place with amplitude:

Wherein A1 is that ET1 launches electromagnetic amplitude, A2 is that ET2 launches electromagnetic amplitude, and w is vibration frequency, and t is the time;

Due to intensity of wave be proportional to wave-amplitude square, and so the intensity after two train wave superpositions is:

In formula, I is the intensity after superposition, the intensity that I1 is amplitude when being A1, the length that I2 is amplitude when being A2;

As I1=I2:

When time, I=4I1, S1 point place produces Constructive interaction;

When when not being 0, if S1 place charge efficiency η, then:

By learn: and then show that charge efficiency η and the two base stations absolute value to S1 range difference is to the relation of wavelength remainder value ε:

$\mathrm{\&epsiv;}=\frac{\mathrm{\&lambda;}\arccos (2\mathrm{\&eta;}-1)}{2\mathrm{\&pi;}};$

When η=0.95, ε=0.0718 λ;

When η=0.90, ε=0.1025 λ;

When η=0.85, ε=0.1267 λ;

When η=0.80, ε=0.1477 λ.

4. the method for optimizing position of base station in radio frequency according to claim 1 charging wireless sensor network, it is characterized in that, described in step 3 two base station ET1, an ET2 are three not conllinear sensor node S1, S2, S3 chargings, X-axis is found 2 symmetrical A (-c, 0) and B (c, 0), two mobile base stations rest on these 2 respectively, make the distance between ET1 to S1 and the range difference between ET2 to S1 be k λ; Its concrete computational process is:

$\sqrt{{(x1+c)}^2+{y1}^2}-\sqrt{{(x1-c)}^2+{y1}^2}=\mathrm{k\&lambda;}$ ①；

$\frac{4\mathrm{cx}1}{\sqrt{{(x1+c)}^2+{y1}^2}+\sqrt{{(x1-c)}^2+{y1}^2}}=\mathrm{k\&lambda;}$ ②；

Obtained by 2. formula:

$\sqrt{{(x1+c)}^2+{y1}^2}+\sqrt{{(x1-c)}^2+{y1}^2}=\frac{4x1}{\mathrm{k\&lambda;}}c$ ③；

1.+3.:

$2\sqrt{{(x1+c)}^2+{\mathrm{yl}}^2}=\mathrm{k\&lambda;}+\frac{4x1}{\mathrm{k\&lambda;}}c;$

$4({x1}^2+2\mathrm{cx}1+c^2+{y1}^2)=k^2{\mathrm{\&lambda;}}^2+8x1c+\frac{16{x1}^2}{k^2{\mathrm{\&lambda;}}^2}{c}^2;$

$c^2(\frac{16x{1}^2}{k^2{\mathrm{\&lambda;}}^2}-4)={4x1}^2+{4y1}^2-k^2{\mathrm{\&lambda;}}^2;$

$\frac{4c^2({4x1}^2-k^2{\mathrm{\&lambda;}}^2)}{k^2{\mathrm{\&lambda;}}^2}={4x1}^2+{4y1}^2-k^2{\mathrm{\&lambda;}}^2;$

Make above-mentioned equation have solution, then need to meet 4x ₁ ²– k ²λ ²>0;

If 4x ₁ ²– k ²λ ²during <=0, namely (-| k λ |/2) <x ₁< (| k λ |/2), now ∠ S2S1S3 is large obtuse angle, and ∠ S1S2S3 is little acute angle, and ∠ S1S3S2 is little acute angle; Under this situation, the optimum stop position in base station is as follows:

If S1 point is projected as T point in Y-axis, ET1 and ET2 is made to be distributed in T point both sides and distance between ET1 and T point, ET2 and T point is k λ/2.