The time difference of arrival for a signal received at two or more receiving
sites as transmitted from a wireless communications device, is determined by a
frequency domain technique. The constituent frequencies of the signals received
at the two or more receiving sites are determined, including the phase, or a value
representative of the phase, of each frequency component. The phase values for
the same frequency are subtracted to yield a phase difference values as a function
of frequency. The slope of the function represents the time difference of arrival
for the wireless communications device signal as received at the two receiving
sites. To determine the mobile location based on the determined time difference
of arrival values, a seed or initial location is first assumed for the wireless
communications device and the distance difference of arrival (the time difference
of arrival multiplied by the speed of light) is calculated. The calculated time
difference of arrival is then used to adjust the distance difference of arrival
by continuously iterating the position of the wireless communications device until
the calculated distance of arrival and the calculated time difference of arrival
(as multiplied by the speed of light) are within a predetermined margin.
