Variable update rate carrier tracking loop for time‐hopping DSSS signals

To overcome the near‐far problem, the time‐hopping direct sequence spread spectrum (TH‐DSSS) signal structure is often adopted in pseudolite positioning systems. The time‐hopping characteristics of this type of signal causes the estimating interval of both frequency and phase to be non‐uniform in the tracking loop. However, the existing TH‐DSSS signal tracking loops adopt the continuous DSSS tracking architecture directly, ignoring the influence of such non‐uniform characteristics, which results in a jitter degradation. Here, a TH‐DSSS signal tracking model with variable update rate is established based on the quantitative analyses of the intrinsic mechanism of the TH‐DSSS signal frequency and carrier phase tracking. From this analysis, a Kalman filter (KF)‐based modified TH‐DSSS signal tracking loop is proposed. Wired transmitting and receiving tests show that, compared with the existing TH‐DSSS tracking loops, the proposed tracking loop has a significant improvement in tracking accuracy and convergence.