Method for eliminating pseudolite near-far effect based on orthogonal subspace projection

Receivers in ground-based pseudolite systems are often affected by the near-far effect, causing failure acquisition of far-field pseudolite signals. An optimization method based on orthogonal subspace projection is introduced in this paper, which is applied to code division multiple access (CDMA) pseudolite signals. Firstly, strong-signal code phases and Doppler frequencies are obtained through conventional sliding correlation to calculate the orthogonal projection operator. Then the weak-signal space is obtained by the received signal subtracting its projection in the strong-signal space. Finally, the re-acquisition is done in the weak-signal space to eliminate of the interference of strong signals. The experimental result indicates that the orthogonal subspace projection can effectively improve weak-signal acquisition performance in the power ratio range of lower than 30 dB, which is of great importance to widen the effective working range of ground-based pseudolite systems and the limitation of pseudolite receivers’ signal power ratio tolerance.