Unambiguous Tracking Technique for Multicarrier Modulation Signals in the Framework of Cognitive Receivers

Abstract

With the continuous construction and improvement of global navigation satellite systems (GNSSs), the number of navigation signals broadcast by GNSSs has increased significantly, and the spectrum resources are becoming increasingly scarce. In order to solve the contradiction between limited spectrum resources and the growing demand for positioning, navigation and timing services, some scholars have proposed a multicarrier modulation scheme which multiplexes narrow-band signals in several adjacent spectrum slots into a composite wide-band signal. On the one hand, multicarrier modulation signals can make full use of the spectrum resources, and on the other hand such signals can provide diversified processing strategies. Based on the idea of cognitive receivers and the inherent characteristics of multicarrier signals, we propose two different unambiguous tracking techniques named energy aggregation method and multi-dimensional loop tracking method respectively. In the first method, the energy of different signal components is aggregated, which can improve the positioning performance while maintaining the unimodal characteristic of the correlation function. In the second method, the potential high-precision ranging performance of high-frequency subcarriers in the multicarrier signal is further exploited. By introducing additional subcarrier loop, the one-dimensional correlation function is extended to two-dimensional. In the dimension of subcarrier, the correlation function is sharper and still has the characteristic of multiple correlation peaks, but in the dimension of pseudo-random noise (PRN) code, the correlation function presents the unimodal characteristic, so it can assist the subcarrier loop to eliminate ambiguity. The proposed tracking methods can be embedded in the architecture of cognitive receivers, where GNSS receivers can flexibly configure the receiving parameters according to the internal and external environment, and select proper receiving strategy. For example, in scenarios where the requirement in positioning precision is moderate, the system could select single-component receiving and processing strategy. In scenarios with high requirement for positioning performance, the system will choose multicomponent receiving mode. Simulation results show that in the above two methods, multicomponent wideband reception can improve the ranging accuracy successfully. Besides, the ranging accuracy of the second method is much better than that of the first method.