Subcarrier Aided Code Tracking Of High Order Boc Signals

High order BOC signals pose significant challenges for tracking. Their correlation functions have multiple side peaks, which makes false peak tracking a common problem. Another issue, less commonly addressed in tracking loops, is the potential for divergence between the code and the subcarrier. The Double Estimator (DE) tracking strategy is one approach to overcome these issues, through the use of both code and subcarrier locked loops, which treat the code and subcarrier delays as separate entities to be tracked.In this work we show that the dynamics of the code/subcarrier divergence are very low, and so the more robust subcarrier tracking loop can be used as a source of aiding for the code tracking loop, analogous to the use of carrier aiding of the code tracking loop in traditional GPS receivers. Based on recent results on frequency dispersive effects on high order BOC signals, we show that the ionosphere is not a significant contributor to code/subcarrier dynamics. This permits the use of extremely low tracking bandwidths in the code loop, thereby optimally combining the benefits of the subcarrier (better tracking) and the code (unambiguous measurements).To demonstrate the validity of the proposed approach the subcarrier aiding concept has been implemented in two different tracking strategies: the DE and VEML strategies. Results are presented for a number of simulations based on the Galileo E1 Public Regulated Service (PRS) signal in a variety of multipath fading channels. The results are compared with the traditional Bump Jumping (BJ) algorithm. The results clearly show the advantage of subcarrier aiding under the simulated conditions.