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Description:
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Recent years have seen a tremendous growth in the development of small sensing
devices capable of data processing and wireless communication through their embed -
ded processors and radios . Wireless Sensor Networks (WSNs ) are ad hoc networks
consisting of such devices gaining importance due to their emerging applications . For
a meaningful processing of the information sensed by WSN nodes , the clocks of these
individual nodes need to be matched through some well de¯ned procedures . This
dissertation focuses on deriving e±cient estimators for the clock parameters of the
network nodes for synchronization with the reference node and the estimators variance
thresholds are obtained to lower bound the maximum achievable performance .
For any general time synchronization protocol involving a two way message ex -
change mechanism , the BLUE -OS and the MVUE of the clock o®set between them is
derived assuming both symmetric and asymmetric exponential network delays . Next ,
with the inclusion of clock skew in the model , the joint MLE of clock o®set and skew
under both the Gaussian and the exponential delay model and the corresponding al -
gorithms for ¯nding these estimates are presented . Also , for applications where even
clock skew correction cannot maintain long -term clock synchronization , a closed -form expression for the joint MLE for a quadratic model is obtained .
Although the derived MLEs are not computationally very complex , two compu -
tationally e±cient algorithms have been proposed to estimate the clock o®set and
skew regardless of the distribution of the delays . Afterwards , extending the idea of
having inactive nodes in a WSN overhear the two -way timing message communication
between two active (master and slave ) nodes , the MLE , the BLUE -OS , the MVUE
and the MMSE estimators for the clock o®sets of the inactive nodes located within
the communication range of the active nodes are derived , hence synchronizing with
the reference node at a reduced cost .
Finally , focusing on the the one -way timing exchange mechanism , the joint MLE
for clock phase o®set and skew under exponential noise model and the Gibbs Sampler
for a receiver -receiver protocol is formulated and found via a direct algorithm . Lower
and upper bounds for the MSE of JMLE and Gibbs Sampler are introduced in terms
of the MSEs of the MVUE and the conventional BLUE , respectively . |