BeiDou B1I Signal Spreading Code Generation and Simulation

Generation and Simulation of BeiDou B1I Signal Spreading Codes

The BeiDou Navigation Satellite System's B1I signal employs direct sequence spread spectrum technology, with its core lying in the generation and modulation of spreading codes. The B1I signal's spreading code is constructed from Gold sequences, which exhibit excellent autocorrelation and cross-correlation properties. These characteristics enable effective differentiation between satellite signals and suppression of multipath interference.

Spreading Code Generation Principles The B1I signal's spreading code is generated using Gold sequences based on two Linear Feedback Shift Registers (LFSRs). Through specific tap configurations and initial phase settings, a pseudo-random code with a period of 1023 chips can be generated. The implementation requires: - LFSR Initialization: Determining initial phases according to satellite PRN numbers - Modulo-2 Addition: Performing XOR operations on outputs from both LFSRs - Chip Rate Control: Typically generating codes at 2.046 MHz chip rate

Key Signal Simulation Components - Baseband Modulation: Implementing spread spectrum through modulo-2 addition of navigation data and spreading codes - Carrier Modulation: Using BPSK to modulate baseband signals onto 1575.42 MHz carriers - Channel Modeling: Incorporating channel effects like Doppler shift and additive white Gaussian noise

Receiver Simulation Essentials The receiver must perform acquisition and tracking: - Coarse Acquisition: Determining approximate signal position through time-frequency 2D search - Fine Synchronization: Implementing code phase tracking using Delay Locked Loops (DLL) - Carrier Removal: Eliminating carrier frequency offset with Costas Loops (PLL)

The simulation requires attention to how Gold sequence periodicity affects correlation peaks and how navigation data bit transitions limit coherent integration time. By adjusting signal-to-noise ratio parameters, demodulation performance under different environmental conditions can be evaluated.