A method for providing assistance to a roving position receiver in a location system consisting of a Global Navigation Satellite System (GNSS) and at least one positioning-unit device (101-1, 101-2), said at least one positioning-unit device (101-1, 101-2) being in a known location and providing a network time and a network frequency, said method comprising: a) providing at least one positioning unit device (101-1, 101-2) processing GNSS signals in order to determine assistance data relative to said network time and said network frequency of said at least one positioning unit device (101-1, 101-2), said assistance data including: i) the time-of-arrival of GNSS signals relative to said network time, and; ii) the frequency of GNSS signals relative to said network frequency; b) said at least one positioning unit device (101-1, 101-2) transmitting positioning signals (104-1, 104-2) incorporating said determined assistance data; c) said roving position receiver extracting said determined assistance data; characterised in that d) the location system comprises a plurality of positioning-unit devices (101-1, 101-2) forming a synchronised network of positioning-unit devices (101-1, 101-2) providing a synchronised network time and synchronised network frequency and chronologically synchronised positioning signals; e) said roving position receiver calculates a single point position solution from said chronologically synchronised positioning signals provided by said synchronised network of positioning-unit devices (101-1, 101-2) to determine said synchronised network time and determines said synchronised network frequency; and f) said roving position receiver searches for GNSS signals in a time range responsive to said extracted assistance data and said determined synchronised network time, and in a frequency range responsive to said extracted assistance data and said determined synchronised network frequency to more quickly acquire GNSS signals. a) providing at least one positioning unit device (101-1, 101-2) processing GNSS signals in order to determine assistance data relative to said network time and said network frequency of said at least one positioning unit device (101-1, 101-2), said assistance data including: i) the time-of-arrival of GNSS signals relative to said network time, and; ii) the frequency of GNSS signals relative to said network frequency; i) the time-of-arrival of GNSS signals relative to said network time, and; ii) the frequency of GNSS signals relative to said network frequency; b) said at least one positioning unit device (101-1, 101-2) transmitting positioning signals (104-1, 104-2) incorporating said determined assistance data; c) said roving position receiver extracting said determined assistance data; d) the location system comprises a plurality of positioning-unit devices (101-1, 101-2) forming a synchronised network of positioning-unit devices (101-1, 101-2) providing a synchronised network time and synchronised network frequency and chronologically synchronised positioning signals; e) said roving position receiver calculates a single point position solution from said chronologically synchronised positioning signals provided by said synchronised network of positioning-unit devices (101-1, 101-2) to determine said synchronised network time and determines said synchronised network frequency; and f) said roving position receiver searches for GNSS signals in a time range responsive to said extracted assistance data and said determined synchronised network time, and in a frequency range responsive to said extracted assistance data and said determined synchronised network frequency to more quickly acquire GNSS signals.