TH-DS-CDMA-Based Robust Frequency-Domain Signal Processing for GNSS Pseudolite Correlators

Abstract

In order to build a seamless national PNT infrastructure based on Beidou system, the absence of Beidou in indoor environments has to be dealt with. Although there are other sensors and approaches to indoor positioning, they cannot be merged into Beidou system smoothly. As a ground transmitter that broadcasts GNSS-like signals, pseudolite has a promising future. Despite these superiorities, pseudolite signals more often than not suffer from joint effects of radio frequency interference and near-far problems. Previous work suggests frequency-domain interference mitigation can suppress jamming effectively while Time-Hopped Direct Sequence Code Division Multiple Access (TH-DS-CDMA) signaling is effective in near-far problem. However, there is little research considering both interference and near-far problem in pseudolite. For the purpose of solving these two problems simultaneously, a frequency-domain interference mitigation method based on TH-DS-CDMA within receiver correlators is proposed in this paper. An adaptive interference detection and mitigation method enabled by thresholding is used to separate the interference and signal in terms of signal power effectively. And the synchronization of TH sequence method called Time-Hopping Starting Index (THSI) is achieved according to the time interval of CDMA signals in different subframe. Simulation shows that the proposed interference mitigation method in frequency domain based on TH-DS-CDMA can effectively provide a stop gap for the combined influence of interference and near-far problem, and the receiver can complete signal acquisition and sequence synchronization successfully, which verifies the validity of the proposed algorithm.