CN101945474A - RSSI-based positioning method for wireless sensor network - Google Patents

Abstract

The invention relates to an RSSI-based positioning method for a wireless sensor network, which comprises the following steps of: firstly, receiving a radio-frequency signal sent in a radio-frequency mode by a transmitting node through a receiving node in the wireless sensor network, then, demodulating and filtering the received radio-frequency signal subjected to multi-path fading to acquire a corresponding base band signal through the receiving node, over-sampling each code chip in the base band signal, performing related despreading on a first sampling point of each code chip to acquire bit information which is not subjected to multi-path interference in the chip, and finally, calculating the RSSI value according to the acquired bit information to determine the distance between the receiving node and the transmitting node so as to realize positioning. Therefore, the method is simple and easy to implement, and can reduce the influence of the multi-path interference on positioning.

Description

In the wireless sense network based on the localization method of RSSI

Technical field

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

Background technology

Wireless sensor network (Wireless Sensor Network, WSN) " intelligence " network of forming by microsensor node with radio communication, perception and computing capability, it relates to, and multidisciplinary height intersects, the integrated hot research field, forward position of knowledge height, now has been widely used in 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.Because it is 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 intensity (RSS, received signal strength), obtain the power loss between transmitting-receiving node, the relation of contrast transmission of wireless signals distance and power attenuation obtains distance between transmitting-receiving node, obtain to pass through the coordinate position that network using three limits or triangle relation are obtained unknown node again after the range information by RSS, position.Yet the RSSI value is subjected to the multipath interference effect bigger in the actual range finding, makes range accuracy reduce and then reduce locating accuracy.

Research at range finding at present mainly is divided into two aspects, be that the RSSI value of utilizing communication chip to provide is carried out a large amount of actual environment tests on the one hand, and get methods such as average, Gauss model match, calculus of differences according to fading channel model and reduce range error; Be to study on the other hand at the RSSI algorithm that improves physical layer, the IEEE802.15.4 standard is not authorized a kind of ad hoc approach that is used for measure R SSI, only be 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 the RSSI value again after the channel estimating, also have some to reduce instantaneous interference and interference of noise by the screening singular signal and through FIR and IIR filtering, yet these algorithms are not all considered multipath and disturb that the RSSI value that they draw all is subjected to multi-path influence.

Therefore, in the 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 provides in a kind of wireless sense network the localization method based on RSSI, so that improve the precision of RSSI value, reduces the influence of multipath interference.

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

1) receiving node in the 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 so that 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 to first sampled point of each chip in described a plurality of chips, and multipath disturbs less bit-level information in outer multipath interference of sheet and the sheet not to be subjected in despreading;

5) described receiving node goes out the RSSI value according to the bit-level information calculations that is obtained, so determine self with described transmitting node between distance, thereby realize locating.

Preferably, n bit-level data that obtained in the 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 the amplitude fading factor of l bar multipath signal with respect to 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.

Calculate RSSI value in the described step 5) and be according to following formula the absolute value of 8 described line of sight component information is carried out square, adds up, asks on average, 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 the 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 the sheet, can isolate line of sight more accurately.

3. there is not 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 big limited wireless sensor networks.

Description of drawings

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

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

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

Embodiment

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

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

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

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 ,+1}, pseudo-code code length are M to ∈, 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 the amplitude fading factor of l bar multipath signal, 0＜α is arranged with respect to line of sight _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 a 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 the 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 so that 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

Obey evenly distributing at random of [0,2 π].

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.Do not consider earlier the influence 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 the sample, satisfy N _I1≤ N _I2≤ ... ≤ N _INN _OpFor being in the outer multipath number of p the sheet in the sample; τ _{L, p}Be the multidiameter delay of the interior multipath of l silver at 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 the sheet.At 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 satisfy T in fact _s＜min (τ l), l=1,2 ..., L-1, formula (6) just can be set up.That is:

(7)

From formula (7) as can be seen, 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 be subjected to the bit-level information of the interference of multipath in the sheet.

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

Find out Y by formula (8) _{1, n}Has only the outer multipath interference components of line of sight component and sheet.Because M＞＞1, so the outer multipath of sheet disturbs and can ignore.

At last, described receiving node goes out the RSSI value according to the bit-level information calculations that is obtained, so determine self with described transmitting node between distance, thereby realize locating.In the present embodiment,, 8 line of sight components obtain the RSSI value by square being added up to be averaged,

And after receiving node obtains RSSI, determine known to those skilled in the art the knowing of method of the distance between self and transmitting node, so 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 influence that the outer multipath of sheet disturbs, reduce that multipath in the sheet disturbs and influence, isolate line of sight comparatively accurately; 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 the claim scope of the present invention.

Claims (3)

1. In the wireless sense network based on the localization method of RSSI, be used to adopt the wireless sense network of direct sequence spread spectrum communication, it is characterized in that, comprise step:

   1) receiving node in the 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 so that 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 corresponding bits level information to first sampled point of each chip in described a plurality of chips;

   5) described receiving node goes out the RSSI value according to the bit-level information calculations that is obtained, so determine self with described transmitting node between distance, thereby realize locating.
2. 2. based on the localization method of RSSI, it is characterized in that in the wireless sense network according to claim 1: n bit-level data that obtained in the 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 the amplitude fading factor of l bar multipath signal with respect to 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.
3. 3. based on the localization method of RSSI, it is characterized in that in the wireless sense network according to claim 2: according to

   

   Calculate the RSSI value.

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