A method and system for finding the position of a mobile unit with respect to
the
satellites of a satellite network such as the Global Positioning System and with
respect to the base stations of a wireless communications network. Each satellite
transmits a signal that consists of a series of frames of a pseudonoise sequence.
The frames of a signal received from the satellite network by the mobile unit are
arranged as columns of a matrix and are processed coherently to provide estimated
pseudoranges and estimated rates of change of pseudoranges for in view satellites.
The coherent processing includes performing an orthogonal transform on the rows
of the matrix, multiplying the elements of the matrix by Doppler compensation factors,
and then, for each satellite in view, convolving the columns of the matrix with
the pseudonoise sequence of that satellite. Other pseudoranges are inferred from
synchronization burst sequences received by the mobile unit from one or more base
stations. If the base stations are not mutually synchronized, reference units are
provided to determine the time offsets between the base station clocks and the
satellite network clock and to transmit these time offsets to the mobile unit,
so that all the pseudoranges include the same bias relative to the satellite network
clock. The pseudoranges are processed and reconciled by a dynamic estimator that
includes a linear optimal estimator such as a Kalman filter, to produce successive
estimates of the location of the mobile unit as the mobile unit moves.