Determination of multipath tracking error
AssigneeTrimble Navigation Limited
InventorJohn F. Schipper
Life of this patent
Estimating the term…
Abstract
Methods for estimating the tracking error in estimated time of arrival of a composite incoming signal that contains a known, digital, spread spectrum signal S.sub.d (t) and that may contain one or more multipath signals whose source is the known signal. Some methods use linear, quadratic or other approximations for the measured correlation function AC(.tau.) for the early and late regions of the time shift variable .tau. (separated by a punctual value .tau.=t.sub.P). Other methods require only knowledge of the measured correlation function AC(.tau.) for one or two time shift values in the early region .tau.<t.sub.P.
Claims17
A method for estimating the correlation tracking error for a received composite signal that includes a distortion-free reference signal, the method comprising the steps of:
- receiving an incoming signal s(t) that includes a known, distortion-free, digital reference signal S.sub.d (t) having a selected bit value interval of .DELTA.t.sub.chip, and that may include at least one signal that distorts the reference signal;
- forming a measured correlation function AC(.tau.) between the incoming signal s(t) and the known signal S.sub.d (t+.tau.), where .tau. is a selected time shift value of the reference signal relative to the incoming signal;
- selecting a first time shift value .tau.=.tau.1 for which there exists at least a second time shift value .tau.'>.tau.1 satisfying AC(.tau.')>AC(.tau.1);
- approximating the measured correlation function AC(.tau.) by a function f(.tau.) that satisfies f(.tau.)=0 at a determinable value .tau.=t.sub.E ;
- approximating a reference correlation function AC(.tau.;0) for the distortion-free signal for time shift values .tau.<.tau.' by the relation AC(.tau.;0).apprxeq.a+b.tau., where b is a selected slope value and a is a selected number;
- and
- estimating a tracking error .DELTA.t.sub.P for the incoming signal s(t) from the parameters a, b, .tau.1, .tau.' and a knowledge of the function f(.tau.).
A method for estimating the correlation tracking error for a received composite signal that includes a distortion-free reference signal, the method comprising the steps of:
- receiving an incoming signal s(t) that includes a known, distortion-free, digital reference signal S.sub.d (t) having a selected bit value interval of .DELTA.t.sub.chip, and that may include at least one signal that distorts the reference signal;
- forming a measured correlation function AC(.tau.) between the incoming signal s(t) and the known signal S.sub.d (t+.tau.), where .tau. is a selected time shift value of the reference signal relative to the incoming signal;
- selecting a first time shift value .tau.=.tau.1 and a second time shift value .tau.2 for which there exists at least one third time shift value .tau.' satisfying .tau.1<.tau.'<.tau.2, AC(.tau.')>AC(.tau.1) and AC(.tau.')>AC(.tau.2);
- approximating the measured correlation function AC(.tau.) for .tau.<.tau.' by a first function f(.tau.;E);
- approximating the measured correlation function AC(.tau.) for .tau.>.tau.' by a second function f(.tau.;L);
- determining at least one time shift value .tau.=t'.sub.P satisfying .tau.1<t'.sub.P <.tau.2 for which f(t'.sub.P ;E)=f(t'.sub.P ;L);
- approximating a reference correlation function AC(.tau.;0) for the distortion-free signal for time shift values .tau. near a third time shift value .tau.1'<.tau.' by the relation AC(.tau.;0).apprxeq.a+b.tau., where b is a selected slope value and a is a selected number;
- and
- estimating a tracking error .DELTA.t.sub.P for the incoming signal s(t) from the parameters a, b, .tau.1, .tau.2, .tau.', t'.sub.P and knowledge of at least one of the functions f(.tau.;E) and f(.tau.;L).
Dependencies are inferred from the claim text.