POSITION DETERMINING SYSTEM DETERMINING DOPPLER-INDUCED CODE PHASE DEVIATION

A system is provided for determining the position of a mobile receiver unit (7) in an environment (1). The system comprises a plurality of transmitter units (2, 3, 4, 5) which transmit a respective phase-modulated transmitter-unit identifier, a mobile receiver unit (7), arranged to receive a signal from a transmitter unit (2, 3, 4, 5), and a processing subsystem (205; 9). The processing subsystem (205; 9) is configured to sample received signals to generate sampled data, wherein the identifier spans a transmitter-unit-identifier-bearing portion of the sampled data, obtain template data corresponding to the identifier, analyse the sampled data to determine a Doppler-induced phase deviation, adjust the template or the sampled data to change one or more phase shifts by an amount depending on the determined deviation, cross-correlate the template with the sampled data, determine a time-of-arrival of the signal, decode the identifier from the sampled data, and use the time-of-arrival and the decoded identifier to determine information relating to the position