A cross-correlation mitigation method based on subspace projection for GPS receiver

As the cross-correlation peak between the GPS C/A codes is non-zero, it will degrade the performance of the detection probability and increase the bit error rate of the weak signals when coexisting strong ones. In this paper, the basic principle of the cross-correlation mitigation method based on subspace projection is analyzed and the architecture of suppressor is presented. The corresponding subspace matrix for strong signals can be constructed after the receiver acquiring the code phases, carrier frequencies and data-bit modulation of all strong signals. The projection of the input signals onto the strong signal subspace is the sum of the strong signals and the projection of the noise. Then the projection can be used as an estimate of the strong signals. After subtracting the estimated strong signals from the input signals, the result consists of weak signals, noises and the residue error resulted from the projection operation. Then the acquisition and tracking of the weak signals can be implemented. Two kinds of receiver structure have been proposed for two different scenarios. One is for that the strengths of the strong signals are almost the same. And the other is under that the strengths of the strong signals are largely different. In comparison with the direct interference cancellation technique, only the code phases, carrier frequencies and data-bit modulation of strong signals are required and the method is independent of the carrier phases of the strong signals with complex signal processing. The simulation results indicate that the method can suppress the cross-correlation interference effectively and ADC requires 4-bit quantization at least when the weak signal to the strong signal ratio is -20 dB.