Clock skew and offset estimations for channel rendezvous in cognitive radio networks

In a Dynamic Spectrum Access (DSA) environment, how can cognitive radios (CRs) initially rendezvous their opportunistic channels to setup a network without causing interference to primary users (SUs) or other secondary users (SUs) is still an open problem in literature. In this paper, this problem is solved by a proposed network-wide clock synchronization scheme, which is implemented along with the initial channel rendezvous procedures. Not much resource consumption is assumed. The clock parameters of skew and offset are estimated on all nodes of a CR network except for the reference one. The timing message transmission delays in CR network are modeled by the exponential models. Two Maximum-Likelihood Estimation (MLE) algorithms and a quasi-MLE algorithm are proposed in three statuses of channel rendezvous respectively. The results of numeric simulations show that the proposed methods improve the mean square errors (MSE) of clock parameters estimations progressively, and the four-way based timing message exchanging based estimator outperforms classical one-way and two-way timing messages exchanging based estimators.