School of Electrical, Computer and Energy Engineering
PhD Final Oral Defense
Localization in Wireless Sensor Networks
by
Xue Zhang
03/18/2016
1pm
GWC409
Committee:
Dr. Cihan Tepedelenlioglu (co-chair)
Dr. Andreas Spanias (co-chair)
Dr. Kostas Tskalis
Dr. Visar Berisha
Abstract
In many applications, measured sensor data is meaningful only when the location of sensors is accurately known. Therefore, the localization accuracy is crucial. In this dissertation, both location estimation and location detection problems are considered.
In location estimation problems, sensor nodes at known locations, anchors, transmit signals to sensor nodes at unknown locations, nodes, and use these transmissions to estimate the location of the node. Specifically, the location estimation in the presence of fading channels using time of arrival (TOA) measurements with narrowband communication signals is considered. Meanwhile, the Cramer-Rao lower bound (CRLB) for localization error under different assumptions is derived. The analytical results show that the loss in performance due to Rayleigh fading with known phase is about 5dB compared to the case with no fading. Unknown phase causes an additional 1dB loss. Also, maximum likelihood estimators (MLEs) for these assumptions are also derived.
In large WSNs, distributed location estimation algorithms are more efficient than centralized algorithms. A sequential localization scheme, which is one of distributed location estimation algorithms, is considered. Also, different localization methods, such as TOA, received signal strength (RSS), time difference of arrival (TDOA), direction of arrival (DOA), and large aperture array (LAA) are compared. Simulation results show that DOA is the preferred scheme at the low SNR regime and the LAA localization algorithm provides better performance for network discovery at high SNRs. Meanwhile, the CRLB for the localization error using the TOA method is also derived. Analytical results show that the sequential localization algorithm degrades the localization performance comparing to the non-sequential localization algorithm. Meanwhile, the SNR loss due to Rayleigh fading using the sequential algorithm is also 5dB. The unknown phase gives additional 1dB SNR loss.
In location detection problem, a distributed location detection scheme, which allows each anchor makes a decision as whether the node is active or not is proposed. Once an anchor makes a decision, a bit is transmitted to a fusion center (FC). The fusion center combines all the decisions and uses a design parameter K to make the final decision. Three scenarios are considered in this dissertation. Firstly, location detection at a known location is considered. Secondly, detecting a node in a known region is considered. Thirdly, location detection in the presence of fading is considered. The optimal thresholds are derived and the total probability of false alarm and detection under different scenarios are derived. Simulation results show that none of the K values outperforms others for all probability of false alarm, and the choice of K depends on the probability of false alarm values.