The sixth sentence is eliminated the ambiguity error. In order to determine the frequency guided sign, all subimages were processed to correct the problem of ambiguity sign.
When the process is finished for all the subimages, (13) corrects the ambiguity error. Figure 4 shows the diagram of the demodulation process for each pixel applying HSO and FSD.
Caption: Figure 5: FSD-HSO algorithm applied to demodulate synthetic and real interferograms: (a) normalized interferograms; (b) direct phases of interferograms; (c-d) calculated frequencies along (x, y) axis, respectively; (e) demodulated phases with ambiguity errors; and (f) correct demodulated phases without ambiguity error.
The phase errors in the other correlators will have no effect unless the phase margin is exceeded, producing an ambiguity error. Errors in the long delay correlator appear directly as output frequency measurement errors.
In addition, since each correlator produces the same peak phase error over frequency, frequency combinations exist where the correlator phase error exceeds the error correction algorithm limit, producing an ambiguity error.
The 45 [degrees] phase margin implies that any or all correlator video outputs can be randomly in error by [+/-] 45 [degrees] without causing ambiguity errors in the measurement.
Delay line ratios of 2:1 provide the phase margins necessary for minimizing frequency ambiguity errors
. In use, receivers employing multiple wideband DFDs can provide instantaneous frequency measurements over a 2- to 18-GHz range.
The added phase margin allows for operation at 3 dB SNR with an RMS frequency accuracy of 1 MHz with no ambiguity errors
. A system sensitivity of -80 dBm with 200 MHz instantaneous bandwidth using a tuner with an 8 dB noise figure can be achieved.
There are four basic contributions to ambiguity errors: low SNR, simultaneous signals, correlator-phase linearity and errors in precise delay-line lengths.
With a gaussian distribution of phase error, the 2:1 ratio system will produce ambiguity errors with probability 0.00023%; the 4:1 system produces ambiguity errors with probability of 1.20%.
When measuring the frequency of a spread spectrum signal, the IFM will exhibit two types of errors, least significant bits (LSB) errors and ambiguity errors. Although any error is undesirable, ambiguity errors, which are the result of the inability of the shorter delay lines to resolve the ambiguity of the longest delay line, are large and occur suddenly as the phase margin is exceeded.
If the error exceeds the margin, ambiguity errors will occur.