The term D2 is a delay in response, δ2(k) indicates a second time offset at the time point t(k) in the second sequence of TDOAs, and term (d_4u?d_3u)/c indicates a relative propagation time of a reference signal, which is a difference between transmission times from each network node 110C, 110D in the second pair to the wireless device 120. The second time offset δ2(k) varies along time. A time difference between a maximum second time offset and a minimum second time offset which may be zero is called a second sawtooth offset Δ2 herein. In other words, the second sawtooth offset Δ2 is a time duration between the maximum and minimum levels of variation in the sawtooth. The d_3u is a distance from the wireless device 120 to the network node 110C, d_4u is a distance from the wireless device 120 to the network node 110D. The term d_4u?d_3u is the relative distance indicating difference between distances from the wireless device 120 to each network node 110C, 110D in the second pair.

As shown in FIG. 6, the wireless device 120 listens to the reference signal exchanges between the network node 110A and the network node 110B, and between the network node 110B and a network node 110C or between network nodes 110C and 110D.

Thus, the wireless device 120 obtains two sawtooth waveforms from two sequences of TDOAs. From each individual sawtooth waveform, the wireless device 120 can estimate the clock asynchronization between network nodes.

Action A432