Results of an indoor deployment Yann-A el Le Borgne, Mathieu Van - PowerPoint PPT Presentation

Range based localization with CC2420 Results of an indoor deployment Yann-A¨ el Le Borgne, Mathieu Van Der Haegen, Gianluca Bontempi Machine Learning Group, Universit´ e Libre de Bruxelles Brussels - Belgium June 4, 2007 NOTERE - WSN workshop (Marrakech) Localization with CC2420 radio June 4, 2007 1 / 13

Machine Learning Group Wireless sensor networks Main research axes : Use of prediction/compression techniques to reduce the amount of data generated by the network More particularly : Time series prediction at the sensor level 1 Spatial/temporal in-network compression with PCA (Principal 2 component analysis) In-network feature extraction with PCA for network-wide prediction 3 task Localization : Multidimensional Scaling (close to PCA) 4 Experimental platforms : ◮ 22 TMote Sky (MoteIV) ◮ 8 TMote Invent 8 MHz microcontroller 48KB + 10KB RAM + 1MB memory CC2420 256kbps radio Strong energy constraints NOTERE - WSN workshop (Marrakech) Localization with CC2420 radio June 4, 2007 2 / 13

Agenda Range based localization 1 CC2420 distance indicators 2 Comparison RSSI/LQI 3 Impact of the power level 4 Conclusion 5 NOTERE - WSN workshop (Marrakech) Localization with CC2420 radio June 4, 2007 3 / 13

Range based localization Let consider a set of N sensors in a 2D space with : ◮ p i ∈ R 2 , 1 ≤ i ≤ N , be the coordinates of sensor i ◮ d ij = || p i − p j || be the euclidean distance between sensors i and j ◮ There exists geometrical relations betwen p i and d ij NOTERE - WSN workshop (Marrakech) Localization with CC2420 radio June 4, 2007 4 / 13

Range based localization Range based localization is a two stage process : 1 Internode distance estimation : ˆ d ij = f ( I ij ) ◮ I ij is an indicator of distance ◮ f is a the function transforming the indicator into a distance ◮ The set of all distance estimates is stored in a ˆ D ij = [ˆ d ij ] matrix p i } = argmin { φ i } L (ˆ 2 Position derivation : { ˆ D ij , { φ i } ) ◮ For example L (ˆ i , j (ˆ d ij − || φ i − φ j || ) 2 ) D ij , { φ i } ) = � Accuracy of the localization is given by 1 � N p i − p i ) 2 i =1 (ˆ N NOTERE - WSN workshop (Marrakech) Localization with CC2420 radio June 4, 2007 5 / 13

CC2420 CC2420 : Chipcon radio, 802.15.4 IEEE compliant, featured by TMote (MoteIV) MICAz (Crossbow) TelosB (Crossbow) IMote 2 (Intel) Operates in 2.4GHz GSM band, same as Wifi 16 channels, data rate of 256 kbps Two indicators of signal quality : ◮ RSSI : Received Signal Strength ◮ LQI : Link quality indicator NOTERE - WSN workshop (Marrakech) Localization with CC2420 radio June 4, 2007 6 / 13

Radio link quality indicators RSSI : Received Signal Strength Indicator ◮ Benefits from a theoretical basis : P ( d ) = β d − α ◮ However, it is depreciated in practice because of a high variability ◮ In CC2420 : computed over eight 4 bits symbol periods : P=RSSI VAL-45 (in dBm) NOTERE - WSN workshop (Marrakech) Localization with CC2420 radio June 4, 2007 7 / 13

Radio link quality indicators RSSI : Received Signal Strength Indicator ◮ Benefits from a theoretical basis : P ( d ) = β d − α ◮ However, it is depreciated in practice because of a high variability ◮ In CC2420 : computed over eight 4 bits symbol periods : P=RSSI VAL-45 (in dBm) LQI : Link Quality Indicator ◮ Chip error rate, i.e. number of bits flipped, computed over two 4 bits symbol periods ◮ Featured by CC2420 radios (TMote, TelosB, Micaz), and assumed to be more reliable to estimate link quality ◮ Ranging from 50 to 110 (Minimum and maximum quality frames, respectively) NOTERE - WSN workshop (Marrakech) Localization with CC2420 radio June 4, 2007 7 / 13

Radio link quality indicators RSSI : Received Signal Strength Indicator ◮ Benefits from a theoretical basis : P ( d ) = β d − α ◮ However, it is depreciated in practice because of a high variability ◮ In CC2420 : computed over eight 4 bits symbol periods : P=RSSI VAL-45 (in dBm) LQI : Link Quality Indicator ◮ Chip error rate, i.e. number of bits flipped, computed over two 4 bits symbol periods ◮ Featured by CC2420 radios (TMote, TelosB, Micaz), and assumed to be more reliable to estimate link quality ◮ Ranging from 50 to 110 (Minimum and maximum quality frames, respectively) Srinastava and Levis (IPSN-06) stressed : ◮ The lack of public experiments comparing RSSI and LQI with CC2420 ◮ Showed that RSSI was better for determining link quality NOTERE - WSN workshop (Marrakech) Localization with CC2420 radio June 4, 2007 7 / 13