CN101945474B - RSSI-based positioning method for wireless sensor network - Google Patents

Abstract

The present invention relates to a positioning method based on RSSI in a wireless sensor network. First, a receiving node in the wireless sensor network receives a radio frequency signal sent by a transmitting node in radio frequency mode, and then, the receiving node passes the received The multipath fading radio frequency signal is demodulated and filtered to obtain the corresponding baseband signal, and then each chip in the baseband signal is oversampled, and then the first sampling point of each chip is correlatively despread to obtain different The bit-level information interfered by intra-chip multipath, and finally, calculate the RSSI value according to the obtained bit-level information to determine the distance between itself and the transmitting node, thereby realizing positioning. It can be seen that the method is simple, easy to implement, and can reduce the impact of multipath interference on positioning.

Description

In wireless sense network based on the localization method of RSSI

Technical field

The present invention relates to the wireless sensor network positioning field, particularly in a kind of wireless sense network based on the localization method of RSSI.

Background technology

Wireless sensor network (Wireless Sensor Network, WSN) " intelligence " network that is formed by the microsensor node with radio communication, perception and computing capability, it relates to that multidisciplinary height intersects, knowledge height integrated hot research field, forward position, now has been widely used in the various fields such as military affairs, agricultural, environment measuring, health care, industry, intelligent transportation.In wireless sensor network was used, the positional information of node was very important, in great majority are used, did not know sensing station and the data of perception are nonsensical.The moment sensor network positions is used and is mainly faced two subject matters: the one, and positioning accuracy, the 2nd, location cost.Owing to need not to increase extra hardware facility, simple and convenient based on the range finding of RSSI (received signal strength indicator), now be widely used in the location of wireless sensor network.Range finding based on RSSI is by received signal strength (RSS, received signal strength), obtain the power loss between transmitting-receiving node, contrast transmission of wireless signals distance obtains the transmitting-receiving node spacing with the relation of power attenuation, obtain to pass through again the coordinate position that network using three limits or triangle relation are obtained unknown node after range information by RSS, position.Yet in actual range finding, the RSSI value is subjected to the multipath interference effect larger, makes range accuracy reduce and then has reduced the precision of location.

research for range finding at present mainly is divided into two aspects, be to utilize the RSSI value that communication chip provides to carry out a large amount of actual environment tests on the one hand, and the methods such as average, Gauss model match, calculus of differences of getting according to fading channel model reduce range error, to study for the RSSI algorithm that improves physical layer on the other hand, a kind of ad hoc approach for measuring RSSI of IEEE802.15.4 standard with no authorized, only that the accumulated time length of asking for RSSI has been done certain standard, utilize the signal accumulation of 8 data bit lengths to obtain the RSSI value, there is algorithm to adopt FFT to carry out obtaining again the RSSI value after channel estimating, also have some by the interference of screening singular signal and process FIR and IIR filtering minimizing instantaneous interference and noise, yet these algorithms are not all considered multipath and are disturbed, the RSSI value that they draw all is subjected to multi-path influence.

Therefore, in wireless sensor network based on RSSI positioning accuracy problem, propose a kind of RSSI of minimizing positioning accuracy and be subjected to the method for multipath interference effect to become the technical task that those skilled in the art need to be resolved hurrily.

Summary of the invention

The technical problem to be solved in the present invention is to provide in a kind of wireless sense network the localization method based on RSSI, in order to improve the precision of RSSI value, reduces the impact of multipath interference.

The invention provides in a kind of wireless sense network based on the localization method of RSSI, comprise the following steps:

1) receiving node in wireless sense network receives the radiofrequency signal that a transmitting node sends with RF-wise;

What 2) described receiving node will receive carries out demodulation filtering in order to obtain corresponding baseband signal through the radiofrequency signal of multipath fading, and wherein, described baseband signal is made of a plurality of chips;

3) described receiving node carries out over-sampling to each chip in described a plurality of chips;

4) described receiving node is correlated with despreading to obtain not being subjected to the less bit-level information of multipath interference in the outer multipath interference of sheet and sheet to first sampled point of each chip in described a plurality of chips;

5) described receiving node calculates the RSSI value according to the bit-level information that obtains, so determine self with described transmitting node between distance, thereby realize locating.

Preferably, n bit-level data that obtain step 4) are: Wherein A is the amplitude of line of sight; N ₀₁Be the outer multipath number of the sheet that comprises in first sampled point; α _lBe that l bar multipath signal is with respect to the amplitude fading factor of line of sight; { d _nBe input traffic, d _n∈ 1 ,+1};

Be the phase place of l bar multipath component, l=1,2 ..., L-1; Y _{1, n}The bit-level data that obtain for despreading; M is the pseudo-code code length.

Described step 5) calculate the RSSI value in and be according to following formula the absolute value of 8 described line of sight component information is carried out square, adds up, is averaging, obtain.

$\mathrm{RSSI}=\frac{1}{8}\underset{n=1}{\overset{8}{\mathrm{\Σ}}}{\left|Y_{1,n}\right|}^2$

Beneficial effect of the present invention is:

1. the present invention utilizes the data-signal after despreading to calculate RSSI value, has eliminated sheet multipath interference effect outward.

2. the present invention carries out the despreading computing by first sampled point that extracts each chip, and then extracts the RSSI value, has reduced multipath interference effect in sheet, can isolate more accurately line of sight.

3. there is no a large amount of computings in the localization method based on RSSI in a kind of wireless sense network provided by the present invention, realize simply, be fit to very much the application scenarios of energy constraint, computing capability is limited, storage resources is limited and communication capacity is limited four large limited wireless sensor networks.

Description of drawings

In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, the below will do to introduce simply to the accompanying drawing of required use in embodiment or description of the Prior Art, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skills, under the prerequisite of not paying creative work, can also obtain according to these accompanying drawings other accompanying drawing.

Fig. 1 is based on the structural representation of the applied wireless sense network of localization method of RSSI in wireless sense network of the present invention.

Fig. 2 is based on the flow chart of the localization method of RSSI in wireless sense network of the present invention.

Embodiment

Below in conjunction with the accompanying drawing in the embodiment of the present invention, the technical scheme in the embodiment of the present invention is clearly and completely described, obviously, described embodiment is only the present invention's part embodiment, rather than whole embodiment.Based on the embodiment in the present invention, those of ordinary skills belong to the scope of protection of the invention not making all other embodiment that obtain under the creative work prerequisite.

For making the purpose, technical solutions and advantages of the present invention clearer, below in conjunction with accompanying drawing, the present invention is described in detail.

The invention provides in a kind of wireless sense network the localization method based on RSSI, below with reference to relevant accompanying drawing, a specific embodiment of the present invention in wireless sensor network is used is elaborated.

Seeing also Fig. 1 is the structural representation of wireless sense network, and it adopts DSSS (direct sequence spread spectrum, direct sequence spread spectrum) to communicate.

In described wireless sense network, the data flow { d that a transmitting node is to be sent _n, d _n∈ 1 ,+1}; Pseudo-code is { c _n, c _n∈ 1, and+1}, the pseudo-code code length is M, M＞＞1;

$c\left(t\right)=\underset{i=0}{\overset{M-1}{\mathrm{\Σ}}}{c}_{i}p\left(\frac{t-{\mathrm{iT}}_c}{T_c}\right)$

What c (t) represented is the pseudo-code data of one-period, is continuous signal; P (t) represents a square wave, is used for discrete signal is expressed as continuous signal.S emission signal s (t) is:

$s\left(t\right)=\underset{n=-\∞}{\overset{+\∞}{\mathrm{\Σ}}}{d}_{n}c(t-{\mathrm{nT}}_b)e^{{\mathrm{jw}}_{o}t}---\left(2\right)$

W wherein ₀Be modulation angular frequency, e ^jwtWhat represent is rf modulations, T _cBe chip period, T _bBe data bit period, satisfy T _b=MT _c

After the multidiameter fading channel transmission, the radiofrequency signal that receiving node receives is:

$r\left(t\right)=\mathrm{As}\left(t\right)+\underset{l=1}{\overset{L-1}{\mathrm{\Σ}}}{\mathrm{\α}}_1\mathrm{As}(t-{\mathrm{\τ}}_l)+n\left(t\right)---\left(3\right)$

Wherein A is the amplitude of line of sight; Suppose to exist L-1 bar multipath, α _lBe l bar multipath signal with respect to the amplitude fading factor of line of sight, 0＜α is arranged _l＜1, l=1,2 ..., L-1; τ _lBe the propagation delay time of multipath with respect to line of sight; α _lAnd τ _lBe stochastic variable, but remain unchanged in the time at frame data, n (t) is white Gaussian noise.The base band data that obtains after radio demodulating filtering is m (t).

Be illustrated in figure 2 as the flow chart of the inventive method:

At first, the receiving node in wireless sense network receives the radiofrequency signal that a transmitting node sends with RF-wise; Be that the radiofrequency signal that receiving node receives is:

Then, the radiofrequency signal through multipath fading that described receiving node will receive is carried out demodulation filtering in order to obtain corresponding baseband signal m (t), and wherein, described baseband signal is made of a plurality of chips, that is:

Wherein

It is the phase place of l bar multipath component; L=1,2 ..., L-1; The note Gaussian noise

As can be known

Obeying the random of [0,2 π] evenly distributes.

Then, described receiving node carries out over-sampling to each chip, in the present embodiment, the baseband signal of the simulation that demodulates is carried out N times of over-sampling, and the sampling period is T _s, satisfy T _c=NT _s, wherein N is that over-sampling is counted, N 〉=2.First do not consider the impact of Gaussian noise, the data of p the sampled point of q chip that obtains after sampling are:

(5)

Wherein, N _IpFor being in multipath number in p the sheet in sample, satisfy N _I1≤ N _I2≤ ... ≤ N _INN _OpFor being in the outer multipath number of p the sheet in sample; τ _{L, p}Be that the interior multipath of l silver is at the multidiameter delay of p sample, m _{τ, q, p}Be non-zero integer value; P ∈ 1,2 ..., N}, q ∈ 1,2 ..., M}.Find out that from formula (5) each sampled point has comprised the line of sight component, the outer multipath component of multipath component and sheet in sheet.For formula (5), extract first sampled point of each chip, analysis obtains:

(6)

The condition that formula (6) is set up is T _s→ 0, as long as in fact satisfy T _s＜min (τ l), l=1,2 ..., L-1, formula (6) just can be set up.That is:

(7)

Can find out from formula (7), this chip samples point only contains line of sight component and the outer multipath component of sheet.Therefore, as long as being extracted the despreading of be correlated with of first sampled point, each chip just can obtain not being subjected to the bit-level information of multipath interference in sheet.

Then, according to above-mentioned analysis, described receiving node is correlated with despreading to obtain not being subjected to the bit-level information that in sheet, multipath disturbs to first sampled point of each chip in described a plurality of chips.If the information of each first sampled point of chip after despreading is designated as Y _{1, n}, n represents n Bit data:

Found out Y by formula (8) _{1, n}Only has the outer multipath interference components of line of sight component and sheet.Due to M＞＞1, so the outer multipath of sheet disturbs and can ignore.

At last, described receiving node calculates the RSSI value according to the bit-level information that obtains, so determine self with described transmitting node between distance, thereby realize locating.In the present embodiment, by cumulative being averaged of 8 line of sight components square obtained the RSSI value,

And after receiving node obtained RSSI, the method for determining the distance between self and transmitting node is known to those skilled in the art knowing, therefore be not described in detail in this.

In sum, the present invention carries out the despreading computing by first sampled point that extracts each chip and obtains RSSI, so, can eliminate the impact that the outer multipath of sheet disturbs, reduce that multipath in sheet disturbs and impact, isolate comparatively accurately line of sight; And method operand of the present invention is few, realizes simply can using multiple radio sensing network.

Above embodiment is the unrestricted technical scheme of the present invention in order to explanation only.Any modification or partial replacement that does not break away from spirit and scope of the invention all should be encompassed in the middle of claim scope of the present invention.

Claims (2)

1. a positioning method based on RSSI in a wireless sensor network, for the wireless sensor network adopting direct sequence spread spectrum communication, it is characterized in that, comprising steps: 1) A receiving node in the wireless sensor network receives a radio frequency signal sent by a transmitting node in radio frequency mode; 2) The receiving node demodulates and filters the received radio frequency signal that has undergone multipath fading to obtain a corresponding baseband signal, wherein the baseband signal is composed of multiple chips; 3) The receiving node oversamples each chip in the plurality of chips; 4) The receiving node correlates and despreads the first sampling point of each chip among the plurality of chips to obtain the corresponding bit-level information; if the first sampling point of each chip after despreading The information of is denoted as Y _1,n , and n represents the nth bit data, then the obtained nth bit-level data is:

Among them, A is the amplitude of the direct path; N ₀₁ is the number of off-chip multipath contained in the first sampling point; α _l is the amplitude attenuation factor of the first multipath signal relative to the direct path; {d _n } is the input data flow, d _n ∈ {-1,+1};

is the phase of the lth multipath component, l=1,2,...,L-1; Y _{1, n} is the bit-level data obtained by despreading; M is the code length of the pseudo code; 5) The receiving node calculates the RSSI value according to the obtained bit-level information, and then determines the distance between itself and the transmitting node, thereby realizing positioning. 2. the positioning method based on RSSI in the wireless sensor network according to claim 1, is characterized in that: according to $\mathrm{RSSI}=\frac{1}{8}\underset{\mathrm{no}=1}{\overset{8}{\mathrm{\Σ}}}{\left|Y_{1,\mathrm{no}}\right|}^2$ Calculate the RSSI value.

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