阅读说明：本技术 无线传感器网络的定位优化方法、装置、设备和存储介质 (Positioning optimization method, device, equipment and storage medium of wireless sensor network ) 是由 谢宁 陈逸枞 李卓远 于 2020-06-04 设计创作，主要内容包括：本文公开了一种无线传感器网络的定位优化方法、装置、设备和存储介质,其中该方法包括：获取目标节点在接收挑战信号时提取的第一接收机噪声,以及锚点在接收响应信号时提取的第二接收机噪声；并确定锚点和目标节点的目标距离；根据设定误报概率上限值确定目标检测阈值；根据第一接收机噪声、第二接收机噪声以及目标检测阈值,确定测距增大攻击的检测结果；如果测距增大攻击的检测结果为不存在测距增大攻击,则根据目标距离对目标节点进行定位；否则,将目标距离丢弃。(Disclosed herein are a method, an apparatus, a device and a storage medium for location optimization of a wireless sensor network, wherein the method comprises: acquiring first receiver noise extracted by a target node when receiving a challenge signal and second receiver noise extracted by an anchor point when receiving a response signal; determining the target distance between the anchor point and the target node; determining a target detection threshold value according to a set upper limit value of the false alarm probability; determining a detection result of the ranging augmentation attack according to the first receiver noise, the second receiver noise and a target detection threshold; if the detection result of the ranging increase attack is that the ranging increase attack does not exist, positioning the target node according to the target distance; otherwise, the target distance is discarded.)

1. A positioning optimization method of a wireless sensor network comprises the following steps:

acquiring first receiver noise extracted by a target node when receiving a challenge signal and second receiver noise extracted by an anchor point when receiving a response signal; determining the target distance between the anchor point and the target node;

determining a target detection threshold value according to a set upper limit value of the false alarm probability;

determining a detection result of the ranging increase attack according to the first receiver noise, the second receiver noise and the target detection threshold;

if the detection result of the ranging increase attack is that no ranging increase attack exists, positioning the target node according to the target distance; otherwise, the target distance is discarded.

2. The method of claim 1, wherein said determining a target detection threshold from a set false positive probability upper limit value comprises:

and determining a target detection threshold according to the set upper limit value of the false alarm probability and a predetermined detection threshold expression.

3. The method of claim 2, wherein the detection threshold expression is:

4. The method of claim 3, wherein the target detection threshold comprises a detection threshold for both the presence and absence of the channel estimation error.

5. The method of claim 1, wherein determining a detection result of a ranging increase attack based on the first receiver noise, the second receiver noise, and the target detection threshold comprises:

determining a variance difference of the second receiver noise variance and the first receiver noise variance;

and determining the detection result of the ranging increase attack according to the variance difference and the comparison result of the target detection threshold.

6. The method of claim 5, wherein determining the detection result of the ranging-up attack according to the comparison result of the variance difference and the target detection threshold comprises:

if the variance difference is smaller than or equal to the target detection threshold, the detection result of the ranging increase attack is that no ranging increase attack exists; otherwise, the detection result of the ranging increase attack is that the ranging increase attack exists.

7. The method of claim 1, further comprising, prior to locating the target node according to the target distance:

determining a detection result of the ranging reduction attack;

if the detection result of the ranging increase attack is that no ranging increase attack exists and the detection result of the ranging reduction attack is that no ranging reduction attack exists, the target node is positioned according to the target distance; otherwise, the target distance is discarded.

8. A positioning optimization apparatus for a wireless sensor network, comprising:

the information acquisition module is arranged to acquire first receiver noise extracted by the target node when receiving the challenge signal and second receiver noise extracted by the anchor point when receiving the response signal; determining the target distance between the anchor point and the target node;

the detection threshold value determining module is used for determining a target detection threshold value according to a set upper limit value of the false alarm probability;

the attack detection module is set to determine the detection result of the ranging augmentation attack according to the first receiver noise, the second receiver noise and the target detection threshold;

the positioning module is set to position the target node according to the target distance if the detection result of the ranging increase attack is that the ranging increase attack does not exist; otherwise, the target distance is discarded.

9. An apparatus, comprising:

one or more processors;

a storage device arranged to store one or more programs;

when executed by the one or more processors, cause the one or more processors to implement a method for location optimization for a wireless sensor network as recited in any of claims 1-7.

10. A computer-readable storage medium, in which a computer program is stored which, when being executed by a processor, carries out a method for location optimization of a wireless sensor network according to any one of claims 1 to 7.

Technical Field

The embodiment of the application relates to the technical field of wireless network communication, for example, to a positioning optimization method, device, equipment and storage medium for a wireless sensor network.

Background

The wireless sensor network is widely applied to the military and civil fields, and the position information of the sensor node is very important for environment monitoring and target node tracking. Although the location information of the sensor node may be provided through a Global Positioning System (GPS), the performance of the GPS is very sensitive to the environment, and the cost is too high for a low-cost sensor node. Therefore, in some applications, the system locates the target node through wireless transmission between anchor target nodes, for example, based on Received Signal Strength (RSS), Time Of Arrival (ToA), Time difference Of Arrival (based on target radiation source), and Angle Of Arrival (AoA), etc.

Security of a wireless system is an important issue, and security holes caused by openness in the wireless system, distributed characteristics of a sensor positioning scheme, and the possibility of multiple attackers (especially cooperative attackers) make it challenging to ensure the security of the positioning scheme in a wireless sensor network. Attack defense schemes for positioning schemes tend to introduce higher communication overhead, the security of which depends on the capabilities of the attacker. The high communication overhead of the conventional scheme leads to the following limitations, first, the battery life of all sensor nodes needs to be sufficiently high; secondly, the storage space of each sensor node is large enough; thirdly, the timeliness is poor in the case of moving the sensor node. Furthermore, if the attacker has enough energy to launch more attacks, even if higher communication overhead is introduced, the conventional scheme fails. In summary, the solution for ensuring the positioning security in the wireless sensor network in the related art cannot meet the requirement of flexibility.

Disclosure of Invention

The embodiment of the application provides a positioning optimization method, a positioning optimization device and a storage medium of a wireless sensor network, so that a positioning optimization scheme of a wireless sensor is optimized, communication overhead is reduced, and flexibility is improved.

The embodiment of the application provides a positioning optimization method of a wireless sensor network, which comprises the following steps:

acquiring first receiver noise extracted by a target node when receiving a challenge signal and second receiver noise extracted by an anchor point when receiving a response signal; determining the target distance between the anchor point and the target node;

determining a target detection threshold value according to a set upper limit value of the false alarm probability;

determining a detection result of the ranging increase attack according to the first receiver noise, the second receiver noise and the target detection threshold;

if the detection result of the ranging increase attack is that no ranging increase attack exists, positioning the target node according to the target distance; otherwise, the target distance is discarded.

The embodiment of the present application further provides a positioning optimization device for a wireless sensor network, including:

the information acquisition module is used for acquiring first receiver noise extracted by the target node when receiving the challenge signal and second receiver noise extracted by the anchor point when receiving the response signal; determining the target distance between the anchor point and the target node;

the detection threshold value determining module is used for determining a target detection threshold value according to the set upper limit value of the false alarm probability;

the attack detection module is used for determining the detection result of the ranging augmentation attack according to the first receiver noise, the second receiver noise and the target detection threshold;

the positioning module is used for positioning the target node according to the target distance if the detection result of the ranging increase attack is that the ranging increase attack does not exist; otherwise, the target distance is discarded.

An embodiment of the present application further provides an apparatus, including:

one or more processors;

storage means for storing one or more programs;

when executed by the one or more processors, cause the one or more processors to implement a method for location optimization for a wireless sensor network as described above.

Embodiments of the present application further provide a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the method for location optimization of a wireless sensor network as described above.

According to the positioning optimization scheme of the wireless sensor, the first receiver noise extracted when the target node receives the challenge signal and the second receiver noise extracted when the anchor point receives the response signal are obtained; determining the target distance between the anchor point and the target node; determining a target detection threshold value according to a set upper limit value of the false alarm probability; determining a detection result of the ranging augmentation attack according to the first receiver noise, the second receiver noise and a target detection threshold; if the detection result of the ranging increase attack is that the ranging increase attack does not exist, positioning the target node according to the target distance; otherwise, the target distance is discarded. By adopting the technical scheme, the noise of the receiver is extracted in the wireless transmission process, the detection of ranging increase attack can be realized through one-time measurement according to the noise of the receiver and the upper limit value of the set false alarm probability, the wireless sensor node is positioned based on the detection result, and the upper limit value of the set false alarm probability can be flexibly adjusted based on the actual condition, so that the flexibility of the detection threshold value is improved, the communication overhead is saved on the basis of ensuring safe positioning, and the flexibility of the ranging increase attack detection is improved.

Drawings

Fig. 1 is a flowchart of a method for optimizing positioning of a wireless sensor network according to an embodiment of the present disclosure;

fig. 2 is a schematic diagram of a method for optimizing positioning of a wireless sensor network according to an embodiment of the present disclosure;

fig. 3 is a schematic diagram of a related art positioning method according to an embodiment of the present application;

fig. 4 is a schematic diagram of a ranging increase attack provided in an embodiment of the present application;

fig. 5 is a schematic view of positioning of a ranging augmentation attack according to an embodiment of the present application;

FIG. 6 is a schematic diagram of a bi-directional positioning system according to an embodiment of the present application;

fig. 7 is a flowchart of another method for optimizing location of a wireless sensor network according to an embodiment of the present disclosure;

fig. 8 is a schematic diagram of a wireless sensor network system according to an embodiment of the present application;

FIG. 9 is a comparative illustration of an experiment and theory provided in the examples of the present application;

fig. 10 is a schematic diagram illustrating a relationship between detection performance and measurement times according to an embodiment of the present disclosure;

fig. 11 is a schematic diagram illustrating a relationship between communication overhead and anchor point number according to an embodiment of the present application;

fig. 12 is a schematic diagram illustrating a relationship between communication overhead and measurement times according to an embodiment of the present application;

fig. 13 is a schematic diagram illustrating a relationship between a performance overhead ratio and a measurement frequency according to an embodiment of the present application;

fig. 14 is a schematic structural diagram of a positioning optimization apparatus of a wireless sensor network according to an embodiment of the present disclosure;

fig. 15 is a schematic structural diagram of an apparatus according to an embodiment of the present application.

Detailed Description

The present application will be described with reference to the accompanying drawings and examples. The specific embodiments described herein are merely illustrative of the present application and are not intended to be limiting of the present application. For the purpose of illustration, only some, but not all, of the structures associated with the present application are shown in the drawings.

Before discussing exemplary embodiments, it should be noted that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although a flowchart may describe the steps as a sequential process, many of the steps can be performed in parallel, concurrently or simultaneously. In addition, the order of the steps may be rearranged. The process may be terminated when its operations are completed, but may have additional steps not included in the figure. The processes may correspond to methods, functions, procedures, subroutines, and the like.

Fig. 1 is a flowchart of a positioning optimization method for a wireless sensor network according to an embodiment of the present disclosure, where the present embodiment is applicable to a situation where a secure positioning of a wireless sensor is implemented, and the method may be implemented by a positioning optimization apparatus of the wireless sensor network, where the positioning optimization apparatus may be implemented in software and/or hardware, and the apparatus may be configured in an electronic device, such as a server or a terminal device. As shown in fig. 1, the method may include:

s110, acquiring first receiver noise extracted by a target node when receiving a challenge signal and second receiver noise extracted by an anchor point when receiving a response signal; and determining a target distance between the anchor point and the target node.

The target node and the anchor point refer to sensor nodes in a wireless sensor network, and the anchor point is used for determining the position of the target node. The challenge signal is a signal sent to the target node by the anchor point, and the response signal is a signal returned to the anchor point after the challenge signal is received by the target node. The first receiver noise is the receiver noise extracted when the target node receives the challenge signal, and the second receiver noise is the receiver noise extracted when the anchor point receives the response signal.

In this embodiment, the anchor point may send a challenge signal to the target node, and after receiving the challenge signal, the target node extracts the noise of the first receiver at this time; the target node generates a response signal according to the first receiver noise and the challenge signal and sends the response signal to the anchor point; after the anchor point receives the response signal, the second receiver noise may be extracted. After the anchor point receives the response signal, the time interval may be recorded, and the target distance between the anchor point and the target node may be determined according to the time interval, that is, ranging is implemented. Or, the positioning optimization device of the wireless sensor network may also acquire the time interval of anchor point records, and further determine the target distance between the anchor point and the target node, i.e., implement ranging.

For example, referring to fig. 2, fig. 2 is a schematic diagram of a positioning optimization method for a wireless sensor network according to an embodiment of the present application. In FIG. 2, anchor point A sends a challenge signal to target node S, which is at time t₁Received challenge signal D, estimating first receiver noise

The target node S generates a response signal and returns the response signal to the anchor point A; anchor point A at t₂Receiving the response signal, recording for a time interval of tau_AS＝t₂-t₁For subsequent positioning and estimation of the second receiver noise

In the conventional scheme, a safety positioning scheme is proposed by continuously measuring a plurality of arrival times and storing a median value to estimate the distance between an anchor point and a target node, as shown in fig. 3. Fig. 3 is a schematic diagram of a related art positioning method provided in an embodiment of the present application, where a secret key K is assumed to be shared between all anchor nodes and a target node, and a message integrity code technique is used to ensure security, and a MIC encrypts information M using g_K(M), g (-) denotes a hash function and K is a key, the details of g (-) that an external attacker might know, but not the key K, doesThe use has two aspects: firstly, the source of M is determined, and secondly, the integrity of M is ensured to defend against tampering attack.

The traditional scheme requires L measurements, each consisting of three wireless transmissions, i.e., L ≧ 3, as shown in FIG. 3. In each measurement, firstly, an anchor point A sends a challenge signal consisting of an l-bit random number D to a target node S; target node S at time t₁Receiving the challenge signal, then extracting a random number D, sending a response signal of 2l-bit D | | | B to an anchor point A by a target node S, wherein the anchor point A sends the response signal to the anchor point A at time t₂Receiving a response signal, | | represents a message connection operator, and B is also a random number of l-bit; the anchor point A then records the elapsed time as τ_AS＝t₂-t₁And calculates t of the bidirectional ToA_AS. Meanwhile, anchor point a extracts D | | | B from the received response signal and calculates v | | g_KThe value of (D | | B); target node S sends MIC signal g_K(D | B) to anchor point A.

The conventional scheme detects a distance reduction and a ranging increase attack through two consecutive steps, and in the first step, if the received MIC and v have the same value, the detection of the distance reduction attack has passed; in the second step, after continuously measuring a plurality of toas, the prior scheme takes the median of the measurement times as the final measurement value to resist the ranging increase attack. The resistance of the traditional scheme to the ranging increase attack depends on the number M of times of attack initiation, and if M is less than or equal to (L-1)/2, the ranging increase attack can be successfully detected; otherwise, the security cannot be guaranteed. Although both types of attacks are detected, anchor point A may accept t_ASAs a valid ToA and stores it as useful positioning information to obtain the actual location of the target node. For one to include N_AThe wireless sensor network of each anchor point has the communication overhead of 3LN in the traditional scheme_AThe number 3 indicates that each measurement contains three radio transmissions and L indicates the number of measurements, so that when N_AOr L increases, the communication overhead of the conventional scheme increases. In addition, the flexibility of attack detection for distance measurement increase in the traditional scheme is low, the change of actual conditions is not considered, whether a measurement result is kept or not is determined simply according to the comparison of MIC and v of each measurement place, and then the measurement result is taken for multiple timesThe median of the measurements was taken as the final result. Based on the above technical problems, in this embodiment, it is considered that when an external attacker forwards an inquiry signal, extra receiver noise is inevitably introduced, attack detection before secure positioning is performed through the receiver noise, and secure positioning of a target node is performed based on an attack detection result, so that communication overhead is reduced, and flexibility is improved.

And S120, determining a target detection threshold according to the set upper limit value of the false alarm probability.

Wherein, suppose H₀Indicating the absence of a ranging increase attack, H₁Indicating the presence of a ranging increase attack, accepting the hypothesis H₁When H is present₀When true, it is called the false alarm Probability (PFA), P_fa＝P{H₁|H₀}. The upper limit value of the false alarm probability is set to be the upper limit value of the false alarm probability preset by a user according to the current actual requirement and the actual situation when the channel estimation error exists, and the upper limit value can be flexibly changed based on the selection of the user. The target detection threshold is used for detecting a threshold of the ranging increase attack, an incidence relation exists between the target detection threshold and the set upper limit value of the false alarm probability, and the target detection threshold can be determined based on the set upper limit value of the false alarm probability. Therefore, when the upper limit value of the false alarm probability is set flexibly according to the actual situation, the target detection threshold value is also flexibly changed.

In this embodiment, two cases are considered when determining the target detection threshold, one is a case where a channel estimation error exists, and the other is a case where the channel estimation error does not exist.

Determining the target detection threshold according to the set upper limit value of the false alarm probability may include: and determining a target detection threshold according to a set upper limit value of the false alarm probability and a predetermined detection threshold expression. In one embodiment, the detection threshold expression is:wherein, P_faRepresenting the false positive probability, theta represents the target detection threshold,representing the variance of the response signal or challenge signal,representing the variance of the channel estimation error.

The target detection threshold may be determined based on a false positive probability expression, which is:

wherein, P_faRepresenting false alarm probability, theta represents target detection threshold, H₁Indicating the presence of a ranging increase attack, H₀Indicating a situation without a ranging increase attack,representing the variance of the response signal or challenge signal,

representing the variance of the channel estimation error.

In the presence of channel estimation errors, the transmission power of the challenge signal and the response signal are assumed to be the same, i.e.All anchor and target nodes have the same receiver noise, i.e.However, the transmission power of the malicious node is different from the reception noise, which increases the hardware cost, and the transmission power of the malicious node is G_EDetermination of n_EHas a noise variance of

Wherein β represents the hardware performance of the malicious node, and β ═ 1 represents that the hardware performance of the malicious node is similar to that of the anchor node and the target node; beta is less than 1, which indicates that the malicious node has better hardware performance but higher hardware cost; beta > 1 indicates that the hardware performance of the malicious node is poor, but the hardware cost is low. Based on the first connection in S110Expressions for receiver noise and second receiver noise, representing variance of channel estimation error as

Andwhere α represents the performance of the channel estimation algorithm employed and the channel estimation error is determined by both the channel estimation algorithm employed and the receiver noise.

Target detection threshold may be determined based on a false positive probability expressionAfter determining the variance of the response signal or the challenge signal, the variance of the channel estimation error and setting the upper limit value of the false alarm probability, substituting the above formula to determine the target detection threshold.

Optionally, determining the target detection threshold according to the set upper limit value of the false alarm probability may include: and setting the upper limit value of the false alarm probability and the target detection threshold value to be zero under the condition that no channel estimation error exists. False positive probability P if all channel estimation errors are ignored_fa＝P{H₁|H₀When 0, the target detection threshold θ is 0.

In addition, when there is a channel estimation error, after determining the target detection threshold according to the set upper limit value of the false alarm probability and a predetermined detection threshold expression, the method further includes: and determining the detection probability according to the target detection threshold, the false alarm probability expression and the detection probability expression so as to verify the target detection threshold according to the detection probability.

Accepting hypothesis H₁When H is present₁When true, it is called the detection Probability (PD), i.e., P_d＝P{H₁|H₁}. The optimal threshold value of the detection probability can be determined by the neman-pearson theorem calculation. The detection probability expression may be

After the detection probability is determined according to the target detection threshold, the false alarm probability expression and the detection probability expression, the performance of the current target detection threshold can be verified to be better according to the detection probability and the optimal detection probability threshold, namely, the method adopted in the embodiment is determined to be suitable for the current environment.

S130, determining a detection result of the ranging increase attack according to the first receiver noise, the second receiver noise and the target detection threshold.

The positioning method adopted in the embodiment is a two-way Arrival Time (ToA) algorithm, and in the two-way ToA technology, two vulnerabilities Of a distance reduction attack and a distance measurement increase attack exist, and the embodiment is directed to the distance measurement increase attack. Two malicious nodes cooperatively launch an attack, as shown in fig. 4, fig. 4 is a schematic diagram of a ranging increase attack provided by the embodiment of the present application. Fig. 5 shows an attack effect, and fig. 5 is a schematic positioning diagram of a ranging increase attack provided in the embodiment of the present application. In FIGS. 4 and 5, S₁Is the actual location of the target node,

is the estimated position of the target node, A₁Representing anchor points, E₁And E₂And (4) representing a malicious node, wherein the purpose of the malicious node is to destroy a positioning process or reduce positioning precision.

In a range-finding augmented attack, as shown in FIG. 4, E₂There are different effects in the two stages. In the first stage, when A₁Sending challenge signalsE₂Transmitting an interference signal S₁Then E₁Receive from

Is shown as

In the second stage, E₂To maintain silence andE₁direct transmission

To give S₁Additional gain G_EReceiving a signal at S₁Is shown as

Is from E₁To S₁The channel response of (2). Then S₁Transmitting a response signal

To A₁. Thus A is₁The longer time required to receive the response signal, A₁A longer two-way ToA value will be obtained than when there is no attack. Thus A is₁An estimate of the increase in distance is obtained as shown in figure 5. Finally, S is estimated₁The error location of (2).

Determining a detection result of the ranging increase attack according to the first receiver noise, the second receiver noise, and the target detection threshold may include: determining a variance difference of the second receiver noise variance and the first receiver noise variance; and determining the detection result of the ranging increase attack according to the variance difference and the comparison result of the target detection threshold. In an embodiment, determining a detection result of the ranging augmentation attack according to the comparison result of the variance difference and the target detection threshold includes: if the variance difference is smaller than or equal to the target detection threshold, the detection result of the ranging increase attack is that the ranging increase attack does not exist; otherwise, the detection result of the ranging increase attack is that the ranging increase attack exists.

In this example, assume H₀Indicating the absence of a ranging increase attack, H₁Indicating a situation where a ranging boost attack is present. The challenge signal received by the target node S is at H₀And H₁Are respectively represented asAnd

at H₀The target node S passes through a channel estimation algorithm and a recovery message

Obtaining an estimated channel response

Since the recovered errors can be corrected by modulation and channel coding, it is assumed in this embodiment that the message can be completely recovered, i.e. thatTarget node S extracts receiver noise asThe target node S calculates its varianceAt H₁The target node S gets a channel response of

Extracted receiver noise is

The target node S calculates its variance

Then, in this embodiment, it is assumed that there is an attack when the anchor point a sends the challenge signal to the target node S, and there is no attack when the target node S returns the response signal, so that the anchor point a obtains a channel response ofExtracted receiver noise is

Anchor A calculates its variance

The variance difference may be Representing absolute value operators. In the presence of channel estimation errors, at H₀And H₁Are respectively rewritten as

And

wherein

Andbased on lemma 1, probability of false alarm

The maximum threshold for the false positive probability is calculated by setting a maximum value according to the Neumann-Pearson theorem, in this embodiment by the maximum threshold, P, representing the false positive probability_faIs less than or equal to. According to theorem 2, an expression of the detection probability can be obtained. In the absence of channel estimation error, at H₀And H₁Are respectively rewritten as

Anddue to the fact that|h_ES|²Is a parameter ofAn exponentially distributed random variable. Namely, it isTherefore, the target detection threshold is set to θ 0. Thus P_fa＝P{＞θ°|H ₀0 and

and when the distance is not more than theta, determining that the detection result of the distance measurement increasing attack does not exist, otherwise, determining that the detection result of the distance measurement increasing attack exists. Where θ represents the target detection threshold.

In this embodiment, each measurement includes two wireless transmissions, and by appropriately increasing the value of the duration of time after the last bit of the challenge signal reaches the antenna of the target node until the response signal of the first bit is transmitted from the antenna of the target node, a larger constant is obtained, which is large enough to complete all operations; and the attack detection method in this embodiment requires only one measurement. The communication overhead is 2N for one wireless sensor network_AIn which N is_AThe number of anchor points in the wireless sensor network. Thus, the present solution saves communication overhead compared to conventional solutions, especially in case of large scale wireless sensor networks or powerful external attackers. And when a channel estimation error exists, the set upper limit value of the false alarm probability can be flexibly set according to the actual situation, the target detection threshold value is flexibly changed, and the flexibility is improved on the basis of saving the communication overhead.

In the embodiment, while the detection result of the ranging increase attack is determined, the detection of the ranging decrease attack can be performed by introducing the noise variance of the receiver, so that the detection result of the ranging decrease attack is obtained.

S140, if the detection result of the ranging increase attack is that the ranging increase attack does not exist, positioning the target node according to the target distance; otherwise, the target distance is discarded.

If only the ranging increase attack is considered at present, the target node can be positioned according to the detection result of the ranging increase attack. If the attack detection result is that the distance measurement increasing attack does not exist, positioning the target node by adopting a two-way arrival time algorithm according to the target distance; and if the attack detection result is that the ranging increase attack exists, discarding the target distance. After the target distance is discarded, the wireless sensor network needs to be investigated for attacking malicious nodes to eliminate the ranging increase attack, and the target node is positioned until the attacking detection result shows that the ranging increase attack does not exist.

If the distance measurement increase attack and the distance reduction attack need to be considered at the same time at present, before the target node is located according to the target distance, the method may further include: determining a detection result of the ranging reduction attack; correspondingly, if the detection result of the ranging increase attack is that the ranging increase attack does not exist and the detection result of the ranging reduction attack is that the ranging reduction attack does not exist, positioning the target node according to the target distance is executed; otherwise, the target distance is discarded. If the attack detection result is that the distance reduction attack or the distance measurement increase attack exists, the wireless sensor network needs to be investigated to eliminate the attack of the attack malicious node, and the target node is positioned until the attack detection result is that the distance reduction attack or the distance measurement increase attack does not exist.

The two-way arrival time algorithm is an algorithm for locating sensor nodes in a wireless sensor network. Three types of sensor nodes may be included in a wireless sensor network: anchor points, target nodes and malicious nodes. The role of the anchor point is to determine the location of the target node, while the purpose of the malicious node is to disrupt the positioning process or reduce the positioning accuracy. In order to determine the two-dimensional position of the target node, the number of anchor points should be greater than 3. The more anchor points, the higher the corresponding positioning accuracy, but the communication overhead is increased, so the number of anchor points can be set according to the actual situation.

In a wireless sensor network, all sensor nodes are randomly deployed on a plane, and the positioning process of a target node is usually completed in a network initialization stage. Suppose there is N_AAn anchor point, denoted asN_SA target node represented asAnd N_EA malicious node represented asWherein N is_ANot less than 3. Suppose N_A＝3，N _S1 and N_E＝2，A₁At time t₁First a challenge signal is sent

To give S₁。S₁The received signal is represented as

WhereinAnd

are respectively A₁To S₁Channel response and S₁Extracted receiver-side noise, assuming all channel responses are modeled as zero-mean complex Gaussian Random Variables (RVs), i.e.Wherein

And d is the distance between the transmitter and the receiver, λ ═ c/f_cIs the wavelength of the transmitted signal, c is lightSpeed, f_cIs the carrier frequency of the transmitted signal. G_tAnd G_rRespectively transmit antenna gain and receive antenna gain. It is assumed that the receiver noise is also modeled as a zero-mean complex Gaussian random variable, e.g.

Is hardware based. The received Signal-to-Noise Ratio (SNR) is expressed asWherein P is_tIndicating the transmission power.

S₁Transmitting a response signalTo A₁The received signal is at A₁Is shown asWherein h is_S1A1Andare each S₁To A₁Channel response and A₁Of (d) noise, finally A₁The calculation of the two-way ToA, indicating that the last bit of the challenge signal was sent to a₁Time of complete decoding of the response signal;indicating the last bit of the response signal arrived at a₁After the antenna until the response signal is A₁Duration of full decoding;the last bit arrival S representing the challenge signal₁The response signal after the antenna up to the first bit is from S₁The duration of the antenna transmission; t is t_tranIndicating the time of transmission.Andis device-based, is constant in the positioning process, can be predetermined and preloaded at A₁For calibrating the time measurement to a certain accuracy. t is t_tran2l/b, l is the length of the transmitted signal and b is the bandwidth of the wireless sensor network.

Fig. 6 is a schematic diagram of a bidirectional positioning method according to an embodiment of the present application. Estimate A₁And S₁The distance between the two isLikewise, the distance S that other anchor points may estimate₁. Is represented by A_jAnd S_jIs located in two dimensions of

Andwithout loss of generality, assume a first anchor point A₁All positioning information is collected as a leader from other anchor points. Positioning information based on three anchor points, A₁The following equation is established and,

from this equation, the intersection point whose position is formed by the three circles is obtained as shown in fig. 6.

The positioning optimization method for the wireless sensor network provided by the embodiment has the following advantages: the ranging increase attack can be resisted according to the actual environment, and the flexibility is strong; the method has strong adaptability, and the safety of the sensor node under severe conditions is guaranteed, such as limited battery life of the sensor node, limited storage space of the sensor node, high mobility of the sensor node and the like; the security of the proposed scheme is not affected no matter how many times the external attacker launches the attack.

According to the positioning optimization scheme of the wireless sensor, the first receiver noise extracted when the target node receives the challenge signal and the second receiver noise extracted when the anchor point receives the response signal are obtained; determining the target distance between the anchor point and the target node; determining a target detection threshold value according to a set upper limit value of the false alarm probability; determining a detection result of the ranging augmentation attack according to the first receiver noise, the second receiver noise and a target detection threshold; if the detection result of the ranging increase attack is that the ranging increase attack does not exist, positioning the target node according to the target distance; otherwise, the target distance is discarded. By adopting the technical scheme, the noise of the receiver is extracted in the wireless transmission process, the detection of ranging increase attack can be realized through one-time measurement according to the noise of the receiver and the upper limit value of the set false alarm probability, the wireless sensor node is positioned based on the detection result, and the upper limit value of the set false alarm probability can be flexibly adjusted based on the actual condition, so that the flexibility of the detection threshold value is improved, the communication overhead is saved on the basis of ensuring safe positioning, and the flexibility of the ranging increase attack detection is improved.

In some embodiments, the lemma 1 above may be: if X and Y are parameters of

Independent identically distributed exponential random variables of, i.e.The Probability Density Function (PDF) of | X-Y | is

Cumulative distribution function (Cumulative distribution function) of X > 0, | X-Y |on, CDF) of

x is greater than 0. The certification process may be certified according to the related art and will not be described herein.

In some embodiments, the lemma 2 above may be: if X, Y and Z have different parameters

Andindependently distributed exponential random variables of, i.e.

And

then the PDF of | X-Y-Z | is

CDF of | X-Y-Z | is

The certification process may be certified according to the related art and will not be described herein.

Fig. 7 is a flowchart of another method for optimizing location of a wireless sensor network according to an embodiment of the present disclosure. On the basis of the above embodiments, the present embodiment optimizes the positioning optimization method of the wireless sensor network. Correspondingly, the method of the embodiment includes:

s210, acquiring first receiver noise extracted by a target node when receiving a challenge signal and second receiver noise extracted by an anchor point when receiving a response signal; and determining a target distance between the anchor point and the target node.

S220, determining a target detection threshold according to a set false alarm probability upper limit value and a predetermined detection threshold expression.

In this embodiment, two cases are considered when determining the target detection threshold, one is a case where a channel estimation error exists, and the other is a case where the channel estimation error does not exist. That is, the target detection threshold includes a detection threshold in both the presence and absence of channel estimation errors.

The detection threshold expression is:wherein, P_faRepresenting the false positive probability, theta represents the target detection threshold,representing the variance of the response signal or challenge signal,representing the variance of the channel estimation error.

Whether channel estimation errors need to be considered is determined according to the current actual situation, when the channel estimation errors exist, the set upper limit value of the false alarm probability can be flexibly set according to the actual situation, the target detection threshold value is also flexibly changed, and the flexibility is improved on the basis of saving the communication overhead; and under the condition that no channel estimation error exists, the false alarm probability and the target detection threshold value are both zero.

Optionally, in this embodiment, after determining the target detection threshold, the method may further include: and determining the detection probability according to the target detection threshold, the false alarm probability expression and the detection probability expression so as to verify the target detection threshold according to the detection probability.

After the detection probability is determined according to the target detection threshold, the false alarm probability expression and the detection probability expression, the performance of the current target detection threshold can be verified to be better according to the detection probability and the optimal detection probability threshold, namely, the method adopted in the embodiment is determined to be suitable for the current environment. The detection probability expression may be

And S230, determining a variance difference value of the second receiver noise variance and the first receiver noise variance.

S240, determining the detection result of the ranging augmentation attack according to the variance difference and the comparison result of the target detection threshold.

Determining a detection result of the ranging increase attack according to the comparison result of the variance difference and the target detection threshold, which may include: if the variance difference is smaller than or equal to the target detection threshold, the detection result of the ranging increase attack is that the ranging increase attack does not exist; otherwise, the detection result of the ranging increase attack is that the ranging increase attack exists.

S250, whether the detection result of the ranging increase attack is that no ranging increase attack exists or not is judged, and if yes, S260 is executed; otherwise, S280 is performed.

S260, whether the detection result of the ranging reduction attack is that no ranging reduction attack exists or not is judged, and if yes, S270 is executed; otherwise, S280 is performed.

In this embodiment, the detection of the ranging reduction attack may be implemented by using a method in the related art, which is not limited herein, and any method capable of detecting the ranging reduction attack may be applicable.

And S270, positioning the target node according to the target distance.

And positioning the target node by adopting a bidirectional arrival time algorithm according to the target distance. The positioning method is as described above, and is not described herein.

And S280, discarding the target distance.

After the target distance is discarded, the wireless sensor network can be subjected to investigation of attack malicious nodes to eliminate the attack, and the target node is positioned until the attack detection result shows that the ranging reduction attack and the ranging increase attack do not exist.

Next, the positioning optimization method of the wireless sensor network provided in this embodiment is tested through experimental simulation and analysisAnd (4) syndrome differentiation. The embodiment researches the experimental results of detecting the distance attack performance, and the conclusions are also suitable for the performance evaluation of the safety positioning scheme, which has two reasons, firstly, if all distance measurements are legal, the final positioning result is also legal; second, if the communication overhead in each range measurement is low, the overall overhead of the secure positioning scheme may be low. For the setting of the number of the sensor nodes, an experimental result under the simple condition of four nodes is provided, namely the number N of anchor points_A1, number of target nodes N _S1 and the number of malicious nodes N _E2. When the positions of the sensor nodes are set, assuming that all anchor points and malicious nodes are distributed on the same plane, the positions of the four nodes are set first, as shown in fig. 8, and fig. 8 is a schematic diagram of a wireless sensor network system provided in an embodiment of the present application. Then let E₁Moving on a 30m x 30m plane, setting the transmission power P_t1W and a transmit antenna gain and a receive antenna gain G_t＝G_r＝8。

In this embodiment, since randomness is introduced into both channel fading and receiver noise, the final results of a set number of independent experimental schemes may be used for averaging in this embodiment, for example, the set number may be 60000. In this embodiment, four performance indexes are taken as an example, and the first index is detection probability/false alarm probability (PD/PFA). The second index is Area Under the Curve (AUC), a Receiver Operating Characteristic (ROC) Curve is obtained according to Neyman Pearson (NP) theorem, and then the AUC corresponding to the ROC Curve is calculated. The third metric is the communication overhead, defined as the total number of bits transmitted in one range measurement. Due to the detection of Performance and Overhead conflicts, various schemes are compared by a fourth index, namely a Performance Overhead Ratio (POR), which is defined as a Ratio of AUC to communication Overhead.

This is illustrated by a comparison of the first indicators. Referring to fig. 9, fig. 9 is a schematic diagram for comparing experiments and theories provided by the embodiment of the present application, in which the detection performance of the scheme is dependent on the connection of malicious nodesNoise reception G_EAs shown in fig. 9, the signal-to-noise ratio γ is set to 10dB, the upper limit of the false alarm probability is set to 0.01, the performance α of the channel estimation algorithm used is 5%, and the hardware performance β of the malicious node is 100%. As shown in fig. 9, the closed form expression of PD and PFA completely matched the expected simulation results. And, if the estimation error cannot be ignored, then with G_EThe detection performance of the scheme can be improved by increasing the value. G_EThe value of (c) cannot be set too small by an external attacker, otherwise the signal received by the target node is low and even the target node cannot decode the challenge signal, making the distance attack meaningless.

The detection performance of the scheme is reduced along with the increase of the alpha value, alpha represents the performance of the adopted channel estimation algorithm, and G is set_EThe remaining conditions were analyzed as in fig. 9, 150. The detection performance is improved along with the increase of the value of beta, the beta represents the hardware performance of a malicious node, and G is set_EThe remaining conditions were analyzed as in fig. 9, 150. When the alpha and the beta are increased, the closed form expressions of PD and PFA are completely consistent with the expected simulation result

With the distance between the target node and the malicious node being reduced, the detection performance is improved, except G _E150 and E₁The conditions other than the position were analyzed in the same manner as in FIG. 9. However, if the estimation error cannot be ignored, the detection performance of the scheme improves as the distance between the target node and the malicious node decreases.

Next, this scheme will be explained by comparing the scheme provided in the present embodiment with the conventional scheme. The detection performance of the present solution is unrelated to the measurement times, as shown in fig. 10, fig. 10 is a schematic diagram of a relationship between the detection performance and the measurement times provided in the embodiment of the present application. Except that G_EThe remaining conditions except 150 and M-3 are the same as in fig. 9, and L indicates the number of measurements in the conventional scheme. As can be seen from fig. 10, the detection performance of the present scheme is independent, whereas the detection performance of the conventional scheme improves as the value of L increases. When L is more than or equal to 2M +1, the detection performance of the traditional scheme is better, namely AUC is 1; otherwise, the conventional scheme has poor detection performance,i.e. AUC equal to 0.5, which is equivalent to a random guess. In case of estimation error, the performance of the scheme is slightly degraded, i.e. AUC is 0.992.

For different numbers of anchor points, compared with the traditional scheme, the scheme can save the communication overhead by 72.8 percent and is independent of L. First, referring to fig. 11, fig. 11 is a schematic diagram illustrating a relationship between communication overhead and the number of anchor points according to an embodiment of the present application, and the remaining conditions except that L is 3 are the same as those in fig. 9. As can be seen from fig. 11, the communication overhead of both the present scheme and the conventional scheme is dependent on the number N of anchor points_AThe value increases. But this scheme has lower communication overhead than the conventional scheme. For example, if the IEEE 802.15.4 standard is adopted, for the case of 4 anchors, the communication overhead of the scheme is 1.067Kbytes lower than that of the conventional scheme; for the 10 anchor point case, the communication overhead of the scheme is 2.666Kbytes lower than that of the traditional scheme. Compared with the traditional scheme, the communication overhead of the scheme is saved by 72.8% for different numbers of anchor points.

Next, referring to fig. 12, fig. 12 is a schematic diagram of a relationship between communication overhead and measurement times provided in this embodiment, except that N_AThe rest conditions except 1 are the same as those in fig. 9. As can be seen from fig. 12, as the number of measurements L increases, the communication overhead of the conventional scheme increases, and the communication overhead of the present scheme is independent of L, which has a lower communication overhead than the conventional scheme, especially in the case of a larger L. For example, when L is 3, the communication overhead of the scheme is lower than that of the original scheme by 0.267 Kbytes; for L ═ 10, the communication overhead of this scheme is 1.121Kbytes lower than the original scheme.

The POR value of the scheme is much better than that of the traditional scheme, and the POR value is irrelevant to L. As shown in fig. 13, fig. 13 is a schematic diagram illustrating a relationship between a performance overhead ratio and a number of measurements according to an embodiment of the present application, where all conditions are the same as those in fig. 10. POR is defined as the ratio of AUC to communication overhead. As can be seen from fig. 13, the POR value of the present scheme is much better than that of the conventional scheme. The POR value of the scheme is irrelevant to L, while the POR value of the traditional scheme is reduced along with the increase of the L value, even if L is more than or equal to 2M + 1. Fig. 13 highlights the superiority of the present solution in terms of POR.

In conclusion, aiming at the safety problem of node positioning when two malicious nodes in a wireless sensor network cooperatively initiate attack, the scheme provides a lightweight safety positioning scheme by utilizing the noise characteristic of external distance attack. Compared with the traditional scheme, the scheme provides lower communication overhead and higher safety, and experimental results show the superiority of the scheme.

According to the positioning optimization scheme of the wireless sensor, the first receiver noise extracted when the target node receives the challenge signal and the second receiver noise extracted when the anchor point receives the response signal are obtained; determining the target distance between the anchor point and the target node; determining a target detection threshold value according to a set upper limit value of the false alarm probability and a predetermined detection threshold value expression, determining a variance difference value of a second receiver noise variance and a first receiver noise variance, determining a detection result of the ranging increase attack according to a comparison result of the variance difference value and the target detection threshold value, and determining a detection result of the ranging small attack if the detection result of the ranging increase attack is that the ranging increase attack does not exist; and if the detection result of the ranging reduction attack is that the ranging reduction attack does not exist, positioning the target node according to the target distance. By adopting the technical scheme, the noise of the receiver is extracted in the wireless transmission process, the detection of ranging increase attack can be realized through one-time measurement according to the noise of the receiver and the upper limit value of the set false alarm probability, the wireless sensor node is positioned based on the detection result, and the upper limit value of the set false alarm probability can be flexibly adjusted based on the actual condition, so that the flexibility of the detection threshold value is improved, the communication overhead is saved on the basis of ensuring safe positioning, and the flexibility of the ranging increase attack detection is improved.

Fig. 14 is a schematic structural diagram of a positioning optimization apparatus of a wireless sensor network according to an embodiment of the present disclosure, which is applicable to a situation of implementing secure positioning of a wireless sensor. The positioning optimization device of the wireless sensor network provided by the embodiment of the application can execute the positioning optimization method of the wireless sensor network provided by any embodiment of the application, and has corresponding functional modules and effects of the execution method. The device includes:

an information obtaining module 310, configured to obtain a first receiver noise extracted by the target node when receiving the challenge signal, and a second receiver noise extracted by the anchor point when receiving the response signal; determining the target distance between the anchor point and the target node; a detection threshold determining module 320, configured to determine a target detection threshold according to a set upper limit value of the false alarm probability; an attack detection module 330, configured to determine a detection result of a ranging increase attack according to the first receiver noise, the second receiver noise, and the target detection threshold; a positioning module 340, configured to, if the detection result of the ranging increase attack is that no ranging increase attack exists, position the target node according to the target distance; otherwise, the target distance is discarded.

According to the positioning optimization scheme of the wireless sensor, the first receiver noise extracted when the target node receives the challenge signal and the second receiver noise extracted when the anchor point receives the response signal are obtained; determining the target distance between the anchor point and the target node; determining a target detection threshold value according to a set upper limit value of the false alarm probability; determining a detection result of the ranging augmentation attack according to the first receiver noise, the second receiver noise and a target detection threshold; if the detection result of the ranging increase attack is that the ranging increase attack does not exist, positioning the target node according to the target distance; otherwise, the target distance is discarded. By adopting the technical scheme, the noise of the receiver is extracted in the wireless transmission process, the detection of ranging increase attack can be realized through one-time measurement according to the noise of the receiver and the upper limit value of the set false alarm probability, the wireless sensor node is positioned based on the detection result, and the upper limit value of the set false alarm probability can be flexibly adjusted based on the actual condition, so that the flexibility of the detection threshold value is improved, the communication overhead is saved on the basis of ensuring safe positioning, and the flexibility of the ranging increase attack detection is improved.

Optionally, the detection threshold determining module 320 is specifically configured to:

and determining a target detection threshold according to the set upper limit value of the false alarm probability and a predetermined detection threshold expression.

Optionally, the detection threshold expression is:

wherein, P_faRepresenting a false positive probability, theta represents the target detection threshold,representing a variance of the response signal or the challenge signal,

representing the variance of the channel estimation error.

Optionally, the target detection threshold includes a detection threshold in the presence of the channel estimation error and in the absence of the channel estimation error.

Optionally, the attack detection module 330 is configured to:

determining a variance difference of the second receiver noise variance and the first receiver noise variance; and determining the detection result of the ranging increase attack according to the variance difference and the comparison result of the target detection threshold.

Optionally, the attack detection module 330 is specifically configured to:

if the variance difference is smaller than or equal to the target detection threshold, the detection result of the ranging increase attack is that no ranging increase attack exists; otherwise, the detection result of the ranging increase attack is that the ranging increase attack exists.

Optionally, the apparatus further includes a ranging and ranging reduction attack module, specifically configured to:

determining a detection result of the ranging reduction attack before positioning the target node according to the target distance; correspondingly, if the detection result of the ranging increase attack is that no ranging increase attack exists and the detection result of the ranging reduction attack is that no ranging reduction attack exists, the target node is positioned according to the target distance; otherwise, the target distance is discarded.

The positioning optimization device of the wireless sensor network provided by the embodiment of the application can execute the positioning optimization method of the wireless sensor network provided by any embodiment of the application, and has corresponding functional modules and effects of the execution method.

Fig. 15 is a schematic structural diagram of an apparatus according to an embodiment of the present application. FIG. 15 illustrates a block diagram of an exemplary device 412 suitable for use in implementing embodiments of the present application. The apparatus 412 shown in fig. 15 is only an example and should not bring any limitations to the function and scope of use of the embodiments of the present application.

As shown in fig. 15, the device 412 is in the form of a general purpose device. The components of device 412 may include, but are not limited to: one or more processors 416, a storage device 428, and a bus 418 that couples the various system components including the storage device 428 and the processors 416.

Bus 418 represents one or more of any of several types of bus structures, including a memory device bus or memory device controller, a peripheral bus, an accelerated graphics port, and a processor or local bus using any of a variety of bus architectures. By way of example, such architectures include, but are not limited to, Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MAC) bus, enhanced ISA bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnect (PCI) bus.

Device 412 typically includes a variety of computer system readable media. Such media can be any available media that is accessible by device 412 and includes both volatile and nonvolatile media, removable and non-removable media.

Storage 428 may include computer system readable media in the form of volatile Memory, such as Random Access Memory (RAM) 430 and/or cache Memory 432. The device 412 may include other removable/non-removable, volatile/nonvolatile computer system storage media. By way of example only, storage system 434 may be used to read from and write to non-removable, nonvolatile magnetic media (not shown in FIG. 15, commonly referred to as a "hard drive"). Although not shown in FIG. 15, a magnetic disk drive for reading from and writing to a removable, nonvolatile magnetic disk (e.g., a "floppy disk") and an optical disk drive for reading from or writing to a removable, nonvolatile optical disk such as a Compact disk Read-Only Memory (CD-ROM), Digital Video disk Read-Only Memory (DVD-ROM) or other optical media may be provided. In these cases, each drive may be connected to bus 418 by one or more data media interfaces. Storage 428 may include at least one program product having a set (e.g., at least one) of program modules that are configured to carry out the functions of embodiments of the application.

A program/utility 440 having a set (at least one) of program modules 442 may be stored, for instance, in storage 428, such program modules 442 including, but not limited to, an operating system, one or more application programs, other program modules, and program data, each of which examples or some combination thereof may comprise an implementation of a network environment. The program modules 442 generally perform the functions and/or methods of the embodiments described herein.

The device 412 may also communicate with one or more external devices 414 (e.g., keyboard, pointing terminal, display 424, etc.), with one or more terminals that enable a user to interact with the device 412, and/or with any terminals (e.g., network card, modem, etc.) that enable the device 412 to communicate with one or more other computing terminals. Such communication may occur via input/output (I/O) interfaces 422. Further, the device 412 may also communicate with one or more networks (e.g., a Local Area Network (LAN), Wide Area Network (WAN), and/or a public Network, such as the internet) via the Network adapter 420. As shown in FIG. 15, network adapter 420 communicates with the other modules of device 412 over bus 418. It should be appreciated that although not shown in the figures, other hardware and/or software modules may be used in conjunction with the device 412, including but not limited to: microcode, end drives, Redundant processors, external disk drive Arrays, RAID (Redundant Arrays of Independent Disks) systems, tape drives, and data backup storage systems, among others.

The processor 416 executes programs stored in the storage device 428 to perform various functional applications and data processing, for example, to implement a method for optimizing the location of a wireless sensor network provided in an embodiment of the present application, the method including: acquiring first receiver noise extracted by a target node when receiving a challenge signal and second receiver noise extracted by an anchor point when receiving a response signal; determining the target distance between the anchor point and the target node; determining a target detection threshold value according to a set upper limit value of the false alarm probability; determining a detection result of the ranging increase attack according to the first receiver noise, the second receiver noise and the target detection threshold; if the detection result of the ranging increase attack is that no ranging increase attack exists, positioning the target node according to the target distance; otherwise, the target distance is discarded.

An embodiment of the present application further provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements a method for location optimization of a wireless sensor network, where the method includes: acquiring first receiver noise extracted by a target node when receiving a challenge signal and second receiver noise extracted by an anchor point when receiving a response signal; determining the target distance between the anchor point and the target node; determining a target detection threshold value according to a set upper limit value of the false alarm probability; determining a detection result of the ranging increase attack according to the first receiver noise, the second receiver noise and the target detection threshold; if the detection result of the ranging increase attack is that no ranging increase attack exists, positioning the target node according to the target distance; otherwise, the target distance is discarded.

The computer storage media of the embodiments of the present application may take any combination of one or more computer-readable media. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination of the foregoing. Examples (a non-exhaustive list) of the computer-readable storage medium include: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.

A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated data signal may take many forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may also be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

Computer program code for carrying out operations for aspects of the present application may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C + +, and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or terminal. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet service provider).