Carrier Recovery In Low-SNR Condition

The request of high speed data transmission in TDRSS (Track and Data Relay Satellite System) to transmission rate continuously rises. Communication systems have to adopt higher-alphabet-size modulations and more-efficient codes. When the power and bandwidth is limited at the same time, carrier recovery in low-SNR (Signal Noise Ratio) condition is one of problems which need to be researched and solved, otherwise it will be a bottleneck to signal receiving and demodulating.Firstly, the SNR threshold of different modulations especially of TCM-8PSK is analyzed, and the problem of carrier recovery in low-SNR condition is put forward. Then, parameter estimation algorithms in carrier recovery are researched, and an improved project is proposed to reduce the SNR threshold. Finally, based on the FPGA of the Virtex-IV series of Xilinx company, a carrier recovery system in 8PSK digital receiver for high speed data transmission in TDRSS is designed.Simulation result indicates that: The SNR threshold of the improved carrier frequency offset estimation algorithm is reduced to be as low as 5dB. The carrier recovery system proposed can work well under the situation of 6dB SNR, and the request that the BER performance comes down to 10^-5 in 6dB SNR condition for TCM-8PSK signal can be satisfied.