Complex maximum likelihood range estimator in a multipath environment

摘要

In ranging systems such as GPS, radar, and the like, accuracy of the ranging information recovered depends on the phase linearity of the ranging receiver, generally implemented as a superheterodyne radio. Superheterodyne radios use bandpass filters in their Intermediate Frequency (IF) amplifiers to accomplish suppression of adjacent channel signal interference. Depending on the ratio of IF center-frequency to signal-bandwidth, such filters evidence phase non-linearity affecting the signal group delay response. This generally manifests in coupling of the in-phase and quadrature detected signals during signal modulation changes in state. If this effect is ignored, reduced accuracy in the recovery of ranging information can be expected. One solution is to incorporate in the ranging receiver a phase non-linearity compensation structure, but this has an adverse economic impact. On study, it has been determined that real-time Maximum Likelihood estimates of signal parameters in a multipath environment is both tractable and efficacious. The subject of this invention is means to obtain Maximum Likelihood estimates of the amplitude, carrier phase, and delay parameters of the direct and secondary path signals arising in a multipath environment when the receiver signal modulation is complex-valued, an appropriate signal model when phase non-linearity is operating. An algorithmic solution to the problem of ranging receiver induced phase non-linearity is a preferred solution, since there is little to no economic impact.