Gholami, M. R.Gezici, SinanStröm, E. G.2016-02-082016-02-082012-04-131053-587Xhttp://hdl.handle.net/11693/21409This paper addresses the problem of positioning multiple target nodes in a cooperative wireless sensor network in the presence of unknown turn-around times. In this type of cooperative networks, two different reference sensors, namely, primary and secondary nodes, measure two-way time-of-arrival (TW-TOA) and time-difference-of-arrival (TDOA), respectively. Motivated by the role of secondary nodes, we extend the role of target nodes such that they can be considered as pseudo secondary nodes. By modeling turn-around times as nuisance parameters, we derive a maximum likelihood estimator (MLE) that poses a difficult global optimization problem due to its nonconvex objective function. To avoid drawbacks in solving the MLE, we linearize the measurements using two different techniques, namely, nonlinear processing and first-order Taylor series, and obtain linear models based on unknown parameters. The proposed linear estimator is implemented in three steps. In the first step, a coarse position estimate is obtained for each target node, and it is refined through steps two and three. To evaluate the performance of different methods, we derive the Cramér-Rao lower bound (CRLB). Simulation results show that the cooperation technique provides considerable improvements in positioning accuracy compared to the noncooperative scenario, especially for low signal-to-noise-ratios.EnglishCooperative positioningCramér-Rao lower bound (CRLB)Linear estimatorMaximum-likelihood estimator (MLE)Time-difference-of-arrival (TDOA)Time-of-arrival (TOA)Two-way time-of-arrival (TW-TOA)Wireless sensor networkCooperative positioningLinear estimatorsLower boundsMaximum-likelihood estimator (MLE)Time-difference-of-arrivalTime-of-arrivalMaximum likelihood estimationWireless sensor networksSensor nodesArticle10.1109/TSP.2012.2194705