A method comprising: determining a first time difference, the first time difference being the difference between a transmission time when a packet was transmitted by a first wireless device and a reception time when a packet transmitted by a third wireless device was received by the first wireless device, based on a first clock associated with the first wireless device; determining a second time difference, the second time difference being the difference between a reception time when the packet transmitted by the first wireless device was received by a second wireless device and a reception time when the packet transmitted from the third wireless device was received by the second wireless device, based on a second clock associated with the second wireless device; determining a relative clock frequency difference between the first clock associated with the first wireless device and the second clock associated with the second wireless device, the relative clock frequency difference optionally being estimated as f CLK 1 f CLK 2 + f Err f nom, where f CLK 1 denotes a clock frequency of the first clock, f CLK 2 denotes a clock frequency of the second clock, f Err denotes a frequency estimation error term, and f nom denotes a nominal or expected clock frequency; determining a product, the product being the product of the relative clock frequency difference and the second time difference; and determining a time difference of arrival for the packet transmitted by the third wireless device from a difference between the first time difference and the product; wherein a propagation delay between the first wireless device and second wireless device is known. determining a first time difference, the first time difference being the difference between a transmission time when a packet was transmitted by a first wireless device and a reception time when a packet transmitted by a third wireless device was received by the first wireless device, based on a first clock associated with the first wireless device; determining a second time difference, the second time difference being the difference between a reception time when the packet transmitted by the first wireless device was received by a second wireless device and a reception time when the packet transmitted from the third wireless device was received by the second wireless device, based on a second clock associated with the second wireless device; determining a relative clock frequency difference between the first clock associated with the first wireless device and the second clock associated with the second wireless device, the relative clock frequency difference optionally being estimated as f CLK 1 f CLK 2 + f Err f nom, where f CLK 1 denotes a clock frequency of the first clock, f CLK 2 denotes a clock frequency of the second clock, f Err denotes a frequency estimation error term, and f nom denotes a nominal or expected clock frequency; determining a product, the product being the product of the relative clock frequency difference and the second time difference; and determining a time difference of arrival for the packet transmitted by the third wireless device from a difference between the first time difference and the product; wherein a propagation delay between the first wireless device and second wireless device is known.