DETERMINING POSITION OF A PORTABLE DEVICE

摘要

A positioning system comprises a set of transmitter stations (Tx1-Tx4) which are arranged to transmit at predetermined time intervals with respect to each other and to a common timing reference (20, 21 ) such that the time intervals can identify each of the transmitter stations. Each pair of transmitted signals can be spaced by a time interval which is different from any other pair of transmitted signals from stations (Tx1-Tx4) or a sequence of time intervals separating a sub-set of the group of transmitted signals can be different from a sequence of time intervals for any other sub-set of transmitted signals from (Tx1-Tx4). Assistance information (38) distributed to portable devices (15) associates time intervals between transmitted signals to identity and location of transmitter stations in the system. Portable devices (15) determine pseudo- ranges of the portable device from the transmitter stations and determine the position of the portable device using a triangulation technique which uses the locations of the transmitter stations and pseudo-ranges.