Research and Implementation of Carrier and Code NCO in GPS Signal Simulator

The system architecture and function of the carrier NCO(numerically controlled oscillator) and code NCO in GPS signal simulator are described.A model for DDS(direct digital synthesizer) is established based on the multi-rate signal processing theory,and the signal spectrum analysis is given.The compression efficiency based on Taylor approximation compression algorithm for mapping from phase to sine amplitude DDS for carrier NCO is discussed,which provides additional improvements in compression.The parameter updating method for code NCO is presented as well.With the Xilinx'ISE6.3 development tool and FPGA using Verilog,the design and simulation of the carrier NCO and the code NCO is implemented.By the procedure simulating and system testing,it is shown that the module specifications of the carrier NCO and code NCO meet the requirement of GPS signal simulator.