Positioning system

A positioning system comprising one or more transmitters configured to transmit transmissions including positioning data, wherein the system is configured to synchronize the transmission with a reference time. The transmissions are formed using a repeating pseudorandom number (PRN) code comprising a plurality of chips. The system is configured to determine a timing bias between the first transmission and the reference time. The system is configured to change the number of chips in one or more of said transmissions such that the timing bias of a subsequent pseudorandom number (PRN) code is reduced.