Estimators for RBS-Based Time Synchronization in Heterogeneous Wireless Networks
A general scenario for using reference broadcast synchronization (RBS) in heterogeneous multihop wireless networks is deﬁned, together with an appropriate model allowing to directly derive maximum likelihood estimators (MLE) to the skew and oﬀset between communicating nodes. The model captures nodes heterogeneity that may cause diﬀerences in the reception delays. It also eliminates the need for synchronizing to the reference and enables direct relative synchronization. This accurately eliminates sender’s delays from the critical path, which faithfully reﬂects RBS features and the receiver/receiver paradigm. It will be shown that state-of-the-art RBS estimators for the joint skew/oﬀset problem fail to eliminate sender’s delay. Appropriate MLEs are accordingly proposed. The Cramer-Rao lower bounds (CRLBs) are calculated, then the proposed estimators are numerically analyzed. Results show the estimators quadratically converge to the CRLB as the sample size rises, and that the precession is uninﬂuenced by the degree of heterogeneity (increase of delay diﬀerences). In a summary, the contribution of this paper is threefold; i) considering usage of RBS in heterogeneous and multi-hop networks, ii) deﬁning an appropriate model and- accordinglythe maximum likelihood estimators for relative skew/oﬀset between communicating nodes, iii) deﬁning theoretical bounds for the estimators and numerically analyzing their convergence.
Synchronization, Estimation, Wireless sensor nework