Mutation-Aided RTL Design of a Four-Phase Code Generator for Low-Correlation Spread Spectrum Sequences

In modern spread spectrum communication and radar systems, the performance of signal acquisition and interference resistance is significantly influenced by the quality of the spreading codes. This project presents a hardware-centric approach for generating 4-phase polyphase codes using a mutation-aided evolutionary process. The proposed design utilizes a 13-bit index to generate a 52-bit polyphase sequence composed of 13 symbols, each encoded in one of four discrete phase levels (0°, 90°, 180°, 270°). A mutation logic is applied to explore sequence diversity, and a simple fitness comparator selects the optimal sequence based on index-derived metrics. All components, including the sequence generator, mutation module, and fitness evaluator, are implemented using Verilog HDL and verified through RTL simulation. A synchronous Finite State Machine (FSM) controls the sequence of operations for mutation-aided optimization. Additionally, MATLAB was used to perform Autocorrelation Function (ACF) analysis on sequences of varying lengths, including the final 52-symbol output. These evaluations confirmed that the generated codes maintained a sharp correlation peak with suppressed sidelobes, supporting their effectiveness for spread spectrum use. The design demonstrates a scalable and synthesizable solution for generating low-correlation polyphase sequences, suitable for use in secure, interference-resilient communication systems.