Method and apparatus for joint data-pilot tracking of navigation signal

A method for joint data-pilot tracking of a navigation signal, the method comprising:

• 1) accomplishing carrier removal by:
• multiplying a digital intermediate frequency (IF) signal of the navigation signal with an inphase branch of a local carrier to yield an inphase-branch signal I, and multiplying the digital IF signal with a quadrature branch of the local carrier to yield a quadrature-branch signal Q;
• wherein the digital IF signal comprises a data-channel component and a pilot-channel component that have the same frequency and a constant phase difference;
• the local carrier is generated by a local-carrier generator that is controlled by a carrier numerically controlled oscillator (NCO);
• and the inphase branch of the local carrier is derived from a cosine mapping of the local carrier, and the quadrature branch of the local carrier is derived from a sine mapping of the local carrier;
• 2) accomplishing code removal by:
• 2a) multiplying an early instance, a prompt instance, and a late instance of a data baseband signal with the inphase-branch signal I to yield an inphase-early data signal, an inphase-prompt data signal, and an inphase-late data signal, respectively;
• wherein the early instance of the data baseband signal is generated by a data-baseband-signal generator that is controlled by a code NCO;
• and the prompt instance and the late instance of the data baseband signal are generated by delaying the early instance of the data baseband signal by a first delay time and a second delay time with a data time delayer, respectively;
• 2b) multiplying the early instance, the prompt instance, and the late instance of the data baseband signal with the quadrature-branch signal Q to yield a quadrature-early data signal, a quadrature-prompt data signal, and a quadrature-late data signal, respectively;
• 2c) obtaining a phase-shifted inphase signal I′ by shifting a phase of the inphase-branch signal I by a phase that is equal to the constant phase difference;
• and multiplying an early instance, a prompt instance, and a late instance of a pilot baseband signal with the phase-shifted inphase signal I′ to yield an inphase-early pilot signal, an inphase-prompt pilot signal, and an inphase-late pilot signal, respectively;
• wherein the early instance of the pilot baseband signal is generated by a pilot-baseband-signal generator that is controlled by the code NCO;
• and the prompt instance and the late instance of the pilot baseband signal are generated by delaying the early instance of the pilot baseband signal by a third delay time and a fourth delay time with a pilot time delayer, respectively;
• and
• 2d) obtaining a phase-shifted quadrature signal Q′ by shifting a phase of the quadrature-branch signal Q by the phase;
• and multiplying the early instance, the prompt instance, and the late instance of the pilot baseband signal with the phase-shifted quadrature signal Q′ to yield a quadrature-early pilot signal, a quadrature-prompt pilot signal, and a quadrature-late pilot signal, respectively;
• 3) obtaining coherent integration results by:
• 3a) processing the inphase-early data signal, the inphase-prompt data signal, and the inphase-late data signal with first integration-and-dump units to obtain a data inphase-early coherent integration result IDE, a data inphase-prompt coherent integration result IDP, and a data inphase-late coherent integration result IDL, respectively;
• 3b) processing the quadrature-early data signal, the quadrature-prompt data signal, and the quadrature-late data signal with second integration-and-dump units to obtain a data quadrature-early coherent integration result QDE, a data quadrature-prompt coherent integration result QDP, and a data quadrature-late coherent integration result QDL, respectively;
• 3c) processing the inphase-early pilot signal, the inphase-prompt pilot signal, and the inphase-late pilot signal with third integration-and-dump units to obtain a pilot inphase-early coherent integration result IPE, a pilot inphase-prompt coherent integration result IPP, and a pilot inphase-late coherent integration result IPL, respectively;
• and
• 3d) processing the quadrature-early pilot signal, the quadrature-prompt pilot signal, and the quadrature-late pilot signal with fourth integration-and-dump units to obtain a pilot quadrature-early coherent integration result QPE, a pilot quadrature-prompt coherent integration result QPP, and a pilot quadrature-late coherent integration result QPL, respectively;
• 4) using prompt-instance coherent integration results of the coherent integration results to obtain a data-bit-flip-detection output Flip=sign(IPP×IDP+QPP×QDP) so to accomplish a data-bit flip detection;
• wherein prompt-instance coherent integration results comprise IDP, QDP, IPP, and QPP, sign denotes a signbit function, and sign (x) provides an output +1 when x is greater than or equal to 0 and an output −1 when x is less than 0;
• 5) using a power ratio between the data-channel component and the pilot-channel component to calculate a power-weighting factor
• α
• 1
• =
• P
• 1
• P
• 2
• ,
• where, P1 and P2 denote a power of the data-channel component and a power of the data-channel component, respectively;
• 6) using the prompt-instance coherent integration results to calculate a probability-weighting factor α2;
• wherein α2 and a correction-probability of the data-bit flip detection are decreased along with an increase of an angle between a first vector (IDP, QDP) and a second vector (IPP, QPP) when the angle is between the range 0-90°;
• and α2 and the correction-probability of the data-bit flip detection are increased along with an increase of the angle between the first vector (IDP, QDP) and the second vector (IPP, QPP) when the angle is between the range 90-180°;
• 7) calculating an inphase-prompt coherent integration result IP and a quadrature-prompt coherent integration result QP by using the prompt-instance coherent integration results according to formulas as follows:
• IP=IPP+Flip×IDP×α1 QP=QPP+Flip×QDP×α1
• performing phase-discrimination to the inphase-prompt coherent integration result IP and the quadrature-prompt coherent integration result QP to obtain a phase-discrimination output Δφ, multiplying the phase-discrimination output Δφ with the probability-weighting factor α2 and performing loop-filtering to obtain a data-pilot joint carrier tuning-amount;
• feeding the data-pilot joint carrier tuning-amount back to the carrier NCO, and tuning the carrier NCO to realize data-pilot joint signal carrier tracking;
• 8) calculating an inphase-early coherent integration result IE, an inphase-late coherent integration result IL, a quadrature-early coherent integration result QE and a quadrature-late coherent integration result QL by using early-instance coherent integration results and late-instance coherent integration results of the coherent integration results according to formulas as follows:
• IE=IPE+Flip×IDE×α1 IL=IPL+Flip×IDL×α1
• QE=QPE+Flip×QDE×α1 QL=QPL+Flip×QDL×α1
• wherein, the early-branch coherent integration results comprise IDE, QDE, IPE, and QPE, and the late-branch coherent integration results comprise IDL, QDL, IPL, and QPL;
• performing phase-discrimination by using the inphase-early coherent integration result IE, the inphase-late coherent integration result IL, the quadrature-early coherent integration result QE and the quadrature-late coherent integration result QL to obtain a phase-discrimination result Δτ;
• multiplying the phase-discrimination result Δτ with the probability-weighting factor α2 and performing loop-filtering to obtain a data-pilot joint code tuning-amount;
• feeding the data-pilot joint code tuning-amount back to the code NCO, and tuning the code NCO to realize baseband signal tracking.