Zero-configuration, Robust Indoor Localization: Theory and Experimentation

Transcription

1 Zero-confguraton, Robust Indoor Localzaton: Theory and Expermentaton Hyuk Lm, Lu-Chuan Kung, Jennfer Hou, Hayun Luo Unversty of Illnos at Urbana Champagn

2 Indoor Localzaton Fne-graned ndoor localzaton and trackng of 802.-enabled devces wth exstng 802. WLAN deployments. Locaton-aware applcatons: Ubqutous offce/home, vstor gudance, network management/resource plannng, and wreless network attacker localzer.

3 Exstng Methods Receved sgnal strengths (RSSs) pattern-matchng approach 9 7 For each cell, S < s,s2, s3 > For a clent to be localzed, S c < s c,s c 2,s c 3 > Pck a cell that gves the m nmum dstance between S and S c as the locaton of the clent. - Requres offlne calbraton process. - Good f the RSSs do not change dramatcally.

4 Tme-varyng sgnal strength: Receved sgnal strengths (RSSs) fluctuate due to RF fadng, human moblty, and other dynamc changes of the ndoor envronment. One day One week Larger varaton durng offce hours Confguraton overhead: Frequent full-scale, on-ste survey and tranng are expensve. ex) 5 mnutes x 64 cells 5.3 hours

5 Exstng Methods (cont d) Path loss model based approach Inaccurate due to ansotropy of sgnal attenuaton: RF sgnals are attenuated dfferently along dfferent drectons. weaker dstance d dstance d Dedcated hardware based approach: Localzaton system usually employs expensve and specalzed hardware. ex) Ubsense wth UWB technology

6 Our Approach Zero confguraton Our localzaton system auto-confgures tself on-lne and adapts to the tme-varyng envronmental dynamcs. Robustness We compensate for nosy and tme-varyng 802. sgnal strength measurements wth the truncated sngular value decomposton. Accuracy We acheve an accuracy of 2.5m (medan error) for ndoor localzaton. Cost Our system s grounded on the nnovaton that turns the off-theshelf 802.-enabled devces (Lnksys WRT54G) nto wreless montors. These routers are nexpensve ($50 per router).

7 Algorthm Basc dea Gven: locatons of APs & dstances between APs, Contnuously montor RSSs between APs and detect dynamc envronmental changes n the area. Our APs measure RSSs from other APs as well as clents to be localzed!

8 Sgnal-Dstance Map (SDM) Construct sgnal-dstance map (SDM) from RSS measurements between APs. Obtan a lnear mappng n logarthm scale of both RSS and dstance: ex) RSS [n db unt] P 0 + α log (dstance) Least square soluton: TDS T (SS T ) -, where S and D are RSS and dstance matrces. s -30dBm, d 20m 3 d0 log d d 0 s0 T s s 0 where d 0 and s 0 are self-dstance and self-rss. s 2-40dBm, d 2 0m s 3-50dBm, d 3 5m T s 3x3 matrx, and T j represents the effect of RSS to j th AP on dstance to th AP. 2

9 Robust Computaton of SDM Matrx nverson ncurred by T DS T (SS T ) - Sngular value decomposton (SVD) Truncated pseudo-nverson technque Dscardng components correspondng to small (near-zero) sngular values by truncatng terms at an earler ndex γ < w. Cumulatve percentage method for selectng γ (τ * 0.98). T W T - - T T v u σ U Σ V ) (SS S T V Σ U S ),σ, dag(σ Σ W [ ] [ ] M M,v, v V,u, u U T v u σ D T γ * W σ σ ) ( τ γ τ γ

10 Locaton Estmaton for Clents Sgnal to dstance transformaton s d s 2 s c [20,40,30] T T d 2 d c d d d exp(t 40 ) 30 s 3 [30,50,s 0 ] T d 3 log[20,5,d 0 ] T sgnal strength space dstance space Dstance to locaton transformaton Use trangular methods: calculate the locaton wth the locatons of and the estmated dstances to APs.

11 Implementaton Localzaton Server Lnux machne runnng Ksmet server, Localzaton algorthm, and Graphcal user nterface (GUI). Montor Lnksys WRT54G wreless routers (v2.2) wth a thrd-party frmware (Sveasoft, Alchemy pre7a) Ksmet (802. layer2 wreless network snffer) drone for MIPS machnes.

12 Implementaton (cont d) Area 600 m Montors

13 Experments Wreless network setups Montor: Lnksys WRT54 wth IEEE 802. b/g, channel 2/7, and power (28/56 mw). Clent: Sharp Zaurus PDA (OS: Lnux) wth Lnksys WCF-2 CF wreless card. Localzaton algorthms for comparson Proposed sgnal-dstance map (SDM) based algorthm. Proxmty n Sgnal Space (PSS) proposed by Gwon and Jan [MobWac:04]. Measurement drecton Clent-asssted: Clent measures RSSs from APs and localzes tself. Montor-asssted : Montors measure RSSs from a clent whle t s transmttng wreless packets.

14 Performance wrt RSS Samplng Preprocessng RSS measurements Sample RSS measurements at an nstance wth the medan flter wth an nterval T s, whch determnes the maxmum estmaton delay. s(t) medan(s( τ) t Ts < τ t) We set T s 60 s for our experments

15 Localzaton Performance IEEE 802.b / Channel 2 / Power 28 mw / # of Montors 5, 6 SDM method outperforms PSS. Clent-asssted approach gves the better accuracy. The more montors gve the better accuracy.

16 Performance wrt Parameters Channel 7 Power 56 mw IEEE 802. g SDM method acheves robust performance to wreless network parameter settngs. The ncrease of tx power does not help for accuracy.

17 Trackng Performance The acheved accuracy for moble user s ±3m. Walkng trajectory Accuracy depends on the speed & the packet transmttng rate of moble users.

18 Summary Robust and accurate localzaton performance wthout manual confguratons. Value-added servce n W-F network nfrastructure for free. As future work, we wll nvestgate () where to place or select wreless montors for better performance, () how to desgn the flter for sgnal strength measurements wrt packet transmsson rate and movement speed for better trackng performance.