Coded Modulation For Deep Space Communications Algorithms And Implementation

Deep space detection is the main tool of human being for exploring outer space so that it's one of the most important human spaceflight activities. As one of the main component of the exploration, deep space communication has characteristices such as remote and complicated environment and low power efficiency, thus higher requirement aimed at the thchniques such as coding and modulation has been proposed. In order to meet the need of development of the deep space instrumentation system, we considered use the FQPSK modulation and the LDPC code into deep space communication system. Then their respective performances are analysed. The result shows that they can meet the need of design and implementation of circuit.This paper firstly introduces operating principles of several basic coding methods in communication systems, focus on LDPC code and a semi-random LDPC codes structure, then analyzes the problem of implementation process of LDPC decoder based on original LDPC decoding algorithm. Then we introduce a new decoder which is called sequence decoder and series of concepts such as stochastic computation, internal and edge memory, asynchronous pipeline, structure of the whole decoder especially the node structure in the decoder. Finally details of the implementation of sequence decoder are given and the simulations are performed to verify the performance of sequence decoder. the result shows that: sequence decoder has nearly 0.25 dB performance loss comparing with traditional decoder, but it obtains clear gain in the implementation, which provides the strong indication of the practicability in deep space communication.In the last part, we introduce the FQPSK modulation and demodulation mechanism. For the modulation principle, we analyze the evolution beginning from QPSK. The main improvements are: the grid coding operation; 16 kinds of baseband waveforms as the mapping output. For demodulation, the attention is mainly related to MAP demodu- lation, which bring soft information processing and iteration in the demodulation algorithm. Subsequently we finish the circuit design of FQPSK modem based-on FPGA with Virtex-4 chips of Xilinx Company. Combining with its performance simulation, we find that FQPSK modulation algorithm and its corresponding MAP demodulation have significant performance improvement with viable circuit load conditions. Results of the paper can provide reference for application implementation of LDPC codes and FQPSK in both sides of the transceiver.