Phase, frequency and frequency derivative are parameters independent of energy of the input signal (i.e., non-energy parameters). There are known methods of estimating signal non-energy parameters based on processing of variables received from a phase-lock loop (PLL).
U.S. Pat. No. 7,869,554, entitled “Phase/frequency estimator-based phase locked loop”, discloses an apparatus and methods described in use a PLL and provided a phase estimation of the input signal from which signal frequency is estimated by a derivative function and low pass filtering.
U.S. Pat. No. 3,895,294, entitled “Phase change measuring circuit”, discloses a device for measuring the phase change of an input signal over a specified period comprising a phase-locked tracking filter including a high frequency voltage-controlled oscillator (VCO), a frequency divider to give local oscillator signal at the same frequency as the input signal and a counter counting cycles of the VCO whose phase change in any period is N times the input phase change to allow 1/N period resolution, N being an arbitrary integer. The phase change measuring circuit thus allows phase measurement with a resolution within a small fraction of one cycle.
U.S. Pat. No. 7,222,035, entitled “Method and apparatus for determining changing signal frequency”, discloses a method and apparatus which include a PLL having a numerically controlled oscillator (NCO) and a filter of frequency estimates (FFE). The PLL tracks the changing signal frequency and outputs non-smoothed frequency estimates into the FFE. The FFE then smoothes noise in the signal to produce a more accurate smoothed frequency estimate of the input signal.
US Patent Publication No. 20140072084, entitled “Digital system and method of estimating quasi-harmonic signal non-energy parameters using a digital Phase Locked Loop”, discloses a digital system and method of measuring (estimating) non-energy parameters of the signal (phase, frequency and frequency rate) received in additive mixture with Gaussian noise. The first embodiment of the measuring system consists of a PLL system tracking variable signal frequency, a block of NCO full phase computation (OFPC), a block of signal phase preliminary estimation (SPPE) and a first type adaptive filter filtering the signal from the output of SPPE. The second embodiment of the invention has no block SPPE, and NCO full phase is fed to the input of a second type adaptive filter.
A DPLL described in U.S. Pat. No. 4,771,250 generates signal phase which is an approximation of the phase of the received signal with a linear estimator. The effect of a complication associated with non-zero transport delays related to the DPLL is then compensated by a predictor. The estimator provides recursive estimates of phase, frequency, and higher order derivatives, while the predictor compensates for transport lag inherent in the loop.
However, the above references, as well as other conventional methods of measuring non-energy signal parameters using PLL are not adaptive to the jerking motion (when, for example, the acceleration varies linearly in time) of the receiver, or adapt to it by expanding the bandwidths of PLL or using smoothing filters. It is not possible to completely eliminate the dynamic measurement errors using conventional methods.
Unlike the methods above, the present invention enables to obtain accurate phase estimates of the input signal and its derivatives by correcting the preliminary estimates at sites with jerking motion and by an additional filtering of phase estimates at sites without such jerking motion.
The present invention can be used in receivers of various navigation systems, such as GPS, GLONASS and GALILEO, which provide precise measurements of signal phase at different rates of frequency change, as well as systems using digital PLLs for speed measurements.
Accordingly, the present invention is related to a system of estimating quasi-harmonic signal non-energy parameters using a digital Phase Locked Loop that substantially obviates one or more of the disadvantages of the related art.
In one embodiment, a system for estimating parameters of an input signal includes (a) a digital phase locked loop (PLL) that tracks the input signal and includes:
C
φ=1−αLF/2+βLF/12+γLF/24,
Cω=(αLF−βLF/2−γLF/6)/Tc, and
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.
In the drawings:
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.
In embodiments of the present invention, adaptation to the nature of the movement of the receiver is made not by changing the parameters of FAP, but by changing the algorithm for estimating the signal parameters. For this purpose, corrections that compensate for the dynamic measurement errors during jerking motion are produced.
where Ac is the amplitude of the signal,
Signal phase φc(t), signal frequency ωc(t) and frequency derivative {dot over (ω)}c(t) should be estimated (measured).
A loop filter (LF) operates with a control period Tc on the basis of recurrence equations:
where αLF, βLF, γLF are constant transfer coefficients,
zid is the PD output;
φir is the phase code for NCO,
fir is the frequency code for NCO,
ΔφNCO is the phase step size (radian) in the NCO,
ΔωNCO is the frequency step size (radian/s) in the NCO,
round( ) is the operation of a numerical rounding.
A numerically controlled oscillator (NCO) (104) has frequency and phase control. The phase input of the NCO is connected to the phase output φir of the loop filter (LF) and the frequency input of the NCO is connected to the frequency output fir of the LF (103); wherein a complex output of a NCO connected to a reference input of a PD (102).
where ANCO is the sample amplitude, and φnw,NCO is the wrapped phase (i.e., 0≦φnw,NCO<+2π) of NCO in radians. Multiplication results
are fed to the input of low-pass filters, which are typically the reset accumulators Σ↓ with frequency Fc<<fs. The reset frequency of the accumulators Fc is the control frequency in the PLL, for example, Fc=50 Hz . . . 1000 Hz; fs=10 MHz . . . 100 MHz. The outputs of the reset accumulators are
The output of a phase discriminator is
zid=arctan(Qi/Ii) [in radians].
Further, the signal zid from the PD output is inputted to the loop filter (LF) (
where αLF, βLF, γLF are constant transfer coefficients,
zid is the PD output;
φir is the phase code for the NCO,
fir is the frequency code for the NCO,
ΔφNCO is the phase step size (radian) in the NCO,
ΔωNCO is the frequency step size (radian/s) in the NCO, and
round(.) is the operation of a numerical rounding.
Digital phase samples φir are fed to the NCO phase control input and abruptly change its phase by the corresponding value ΔφiNCO=φir·ΔφNCO, where ΔφNCO is the phase step size. Samples fir (frequency codes) are delivered to the NCO frequency input and determine its frequency ωiref=fir·ΔωNCO, where ΔωNCO is the frequency step size [radian/s] in the NCO.
The measuring system (see
block (105) for calculation of full phase (CFP) of NCO, coupled with the LF outputs, operates on the basis of equation
φiNCO=φi-1NCO+φir·ΔφNCO+fi-1r·ΔωNCO·Tc;
block (106)—a low-pass filter (LPF) coupled with an output zid of a PD;
block (107)—a block for preliminary estimation of signal parameters (PESP) coupled by its inputs with:
the phase output φiNCO of a block for CFP of a NCO,
the frequency output fir of the loop filter,
the output siγ of the loop filter;
where a block for PESP operates on the basis of equations:
{circumflex over (φ)}ic,E=φiNCO+siγ/12,
{circumflex over (ω)}ic,E=2π·fir−siγ/(2·Tc),
{dot over ({circumflex over (ω)})}ic,E=siγ/Tc2;
where
block (108) is a threshold unit coupled with an output ziA of a LPF; where an output Ji of a threshold unit is given by the formula:
Ji=true, if ziA>TA,
Ji=false, if ziA≦TA,
here TA is a threshold; the threshold value is set equal to (3 . . . 5)·RMS(ziA).
block (109)—a block for jerk-corrections of preliminary estimates (JCPE) coupled with an output ziA of a LPF and with an output Ji of a threshold unit; where the block JCPE operates on the basis of equations:
Block (309) for jerk-corrections of preliminary estimates (JCPE) coupled with an output ziA of a LPF and operates on the basis of equations:
where {circumflex over (φ)}ic,J, {circumflex over (ω)}ic,J, {dot over ({circumflex over (ω)})}ic,J are, respectively, estimates with jerk-corrections for a phase [in radians], frequency [in radian/s] and frequency derivative [radian/s2] of a signal.
Block (309) for jerk-corrections of preliminary estimates (JCPE) reduces dynamic error of estimates due to frequency spurts, but it increases fluctuation errors of estimates. The measuring system, see
z
i
T=φiNCO−
where αT, βT, γT are constant transfer coefficients of the TFP.
Block (311) decides on which group of estimates for signal parameters should be taken; this block takes the estimates from the TFP block when there is no jerk, otherwise, it takes the estimates from the JCPE (when there is jerk), i.e.
where
{circumflex over (φ)}ic is the estimate for a signal phase [in radians],
{circumflex over (ω)}ic is the estimate for a signal frequency [in radian/s],
{dot over ({circumflex over (ω)})}ic is the estimate for a signal frequency derivative [in radian/s2].
Having thus described a preferred embodiment, it should be apparent to those skilled in the art that certain advantages of the described apparatus have been achieved.
It should also be appreciated that various modifications, adaptations, and alternative embodiments thereof may be made within the scope and spirit of the present invention. The invention is further defined by the following claims.
Filing Document | Filing Date | Country | Kind |
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PCT/RU2015/000043 | 1/26/2015 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2016/122341 | 8/4/2016 | WO | A |
Number | Name | Date | Kind |
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4771250 | Statman et al. | Sep 1988 | A |
8271221 | Sato | Sep 2012 | B2 |
8891687 | Zhodzishsky | Nov 2014 | B1 |
Entry |
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Search Report in PCT/RU/2015/000043, dated Nov. 12, 2015. |
Number | Date | Country | |
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20160315759 A1 | Oct 2016 | US |