Research On MSD And TPC Technologies Of Spacecraft Telemetry And Realization

Pulse Code Modulation/Frenquency Modulation(PCM/FM) is widely used for spacecraft telemetry, and a demodulator based on discriminator is conventionally adopted at the receiver. However, with the constant increase of telemetry data rate and transmission distance, the threshold effect of the discriminator and low efficiency problems are becoming prominent. Therefore, how to effectively improve PCM/FM telemetry system performance is mainly investigated in this dissertation. The main work is as follows:Firstly, according to the shortage of the discriminator, multi-symbol detection(MSD) algorithm was studied based on introducing the relevant theories of PCM/FM telemetry system. The simulation results show that it can enhance the demodulation performance of PCM/FM signal about 3dB if the observation intervals are 5 symbols. There are deficiency such as high computational complexity and engineering issues in classical MSD algorithm, a low-complexity MSD algorithm is proposed by using several segment correlators instead of the long correlator. Thus, the complexity of correlation calculation is reduced. Studies have shown that the amount of multiplication and addition are 10% and 14.5% of the baseband MSD with 0.1dB performance loss if the observation intervals are 5 symbols.In addition, Turbo product code(TPC) was analyzed on the basis of deeply comprehending the relevant theories of TPC encoding and decoding. Simulation results show that the demodulation performance can be improved about 6dB by using such error correction coding technique. Aiming at the high computational complexity of conventional Chase iterative decoding, a joint Chase decoding algorithm is proposed. This algorithm firstly uses parity making a hard decision to decide whether to have subsequent soft decoding. The computation of algebraic decoding is decreased by about 50% while the decoding speed is improved by the proposed joint Chase decoding algorithm. What’s more, exploiting the second largest correlation codeword instead of the competition codeword can avoid complex calculation, which further reduces the complexity of the algorithm.Moreover, both the low-complexity MSD algorithm and the joint Chase decoding algorithm were applied to the PCM/FM telemetry system. Simulation results show that the performance is enhanced about 7.7dB. Although the demodulation performance is with 1.8dB loss, the computation complexity has substantially decreased. A better trade-off between demodulation performance and computational complexity is achieved.Finally, the hardware implementation of low-complexity MSD algorithm and TPC decoding algorithm were given on the basis of the theoretical research.