2008 ION: Generation of third code and phase signals based on dual-frequency...
Bofeng Li
Future Global Navigation Satellite Systems (GNSS) will transmit three or more frequency signals, which can potentially benefit rapid and reliable phase ambiguity resolution. Due to the lack of third frequency data, current studies using multiple GNSS signals, such as Three Carrier Ambiguity Resolution (TCAR), are limited to the theoretical analysis based on purely simulated three frequency signals. The problem is that the simulated GNSS data sets, regardless of being generated by an expensive signal generator or a software tool, are not realistic representation of the real world situations. Signals are simulated and data generated based on various assumptions for signal delays, error sources, and uncertainty levels. Thus, these data sets could be very different to that experienced in the real world. In this paper, a new so-called semi-simulation method for generating the third requency double differenced GPS signals is proposed. The key of this method is the separation between ionospheric biases and geometric errors consisting of three main procedures. In step 1, the integer ambiguities at two frequencies are fixed to their integer values and the geometric and ionospheric biases are separated by means of corresponding combined measurements. This idea is similar to that of the networkbased RTK processing. In the second procedure, a new multiple-difference based method is introduced to assess the uncertainties of code and phase measurements as well as the cross correlation between L1 and L2 phase signals for long distance baselines. These stochastic characteristics will be utilized in the generation of random noise components for the new signals. Finally, the third frequency signals are generated according to the proposed procedures based on the separated biases and their stochastic characteristics obtained from the real dualfrequency GPS measurements. The third frequency GPS data sets are generated with baselines of 15, 53 and 78 km in length and further employed for ambiguity resolution and position estimation analysis. The results from these testing baselines have shown consistency with the theoretical analysis. The semi-simulation method is a convenient and efficient alternative for generating the new double differenced third frequency signal based on the existing dual-frequency GPS signals. It will provide benefits to researches and developments for future generation GNSS technology and applications.
