Research and Implementation of Onboard BTM Demodulation OQPSK Based on FPGA

• Published in: 2022 4th International Academic Exchange Conference on Science and Technology Innovation (IAECST) pp. 1297 - 1302
• Main Authors: Jiang, Genzhu, Xu, Qing
• Format: Conference Proceeding
• Language: English
• Published: IEEE 09.12.2022
• Subjects: BTM demodulation; Carrier synchronization; FPGA; Frequency shift keying; Frequency synchronization; Interpolation; Mathematical models; Phase shift keying; Stability analysis; Synchronization; Timing synchronization; Train-ground communication
• DOI: 10.1109/IAECST57965.2022.10062080

The point type equipment (transponder) used for vehicle ground communication of rail transit adopts frequency shift keying (FSK) signal with center frequency of 4.24MHZ and phase shift keying (PSK) signal with a center frequency of 9.032MHz. In order to make the vehicle-ground communication in the high-speed data transmission can be more rapid and accurate, Then the OQPSK signal is proposed, The modulation and demodulation of OQPSK signal is explained, And then compared with FSK signal , It has better advantages in spectrum and bit error rate. But when the on-board BTM demodulation OQPSK signal will appear due to the practical work in the process of signal amplitude, cycle, burr caused by the effects of such factors as the carrier and clock errors, For this shortcoming Costas loop algorithm and the interpolation algorithm is proposed to eliminate the error , Carrier synchronization take Costas loop can restrain carrier signal tracking of low SNR, Guarantees the carrier of the input and output of the carrier to keep the smaller frequency difference and difference, The interpolation algorithm to obtain the optimum interpolation time sampling by interpolation value signal, Which ensures the local clock frequency synchronization with the data sampling rate , The symbol synchronization can ensure the stability of the signal, In the Matlab simulation results show the algorithm can correct the error, The algorithm optimization can make the OQPSK signal demodulated by vehicle-mounted BTM more accurate. Quartus and Modelsim are combined to verify the correctness of the whole demodulation system, The results show that the OQPSK signal can be demodulated by FPGA, Which proves the feasibility of vehicle-borne BTM demodulation OQPSK signal based on FPGA.