Research On Design Method Of Inter-Satellite Communication System For Formation Small Satellite

The formation flying system distributes the tasks which conventionally taking by one satellite into several small satellites. This scheme can enhance the anti-jamming or anti-destruction of the space systems and shorten the design period with lower cost. However, this scheme causes the problem of satellites communication networking. How to build up reliable inter-satellite links and form a space communication network with satellites as its nodes is a significant problem which includes the order of the formation, inter-satellite links, communication technology, the modulation and demodulation scheme, the multiple-access scheme and the channel coding scheme etc. This dissertation analyzes the need of the communication systems in formation flying and designs a simulation system of the inter-satellite communication system. Based on these, a system design approach is proposed.In order to deal with Doppler shift and satisfy the requirements of the repaid acquisition of spread-spectrum code, a new accumulation acquisition approach which is fit for low-orbit satellite is proposed by making trade-off on the computation complexity and performance. This approach is based on serial slippage correlation acquisition. The main improvement is that the delay T is introduced to judge the chip period deviation caused by Doppler shift. An accumulation approach is applied here to improve the SNR in acquisition loop. And a multi-branch accumulation scheme is used to avoid the chip slippage problem. Due to all the adapted mechanism above, the acquisition is achieved in high dynamic scenario with low SNR and big Doppler shift.In order to address the issues of the conventional BP decoder with huge computation, the dissertation proposed an improved BP decoding algorithm by considering the feature of inter-satellite communication. In this algorithm only the information of the bits which may be error is updated instead of all bits information. Due to this, the efficiency and the delay of the decoder are improved much. Based on the proposed algorithm, a parallel high speed decoder is designed. The simulations are done in Gauss channel by comparing LDPC codes with various code length and iterative times. The result illustrates that the proposed BP decoding algorithm reduces the computation complexity obviously with little performance sacrificed, and the improved decoder can achieve high decoding rate.In order to solve the confliction between system power and data transmission rate, a variable date rate communication scheme is proposed. And the mathematic simulation validates the performance of this variable date rate scheme. In this scheme, the data rate is low when the quantity of exchanged data is small, while in the case that the exchanged data is huge, the date rate would turn to be high. For inter-satellite communication in the long-term stable formation flying, the dissertation proposes a space roundness formation order based on improved genetic algorithm, and build a direct sequence spread spectrum (DSSS) communication system with reference signals. Those can also support the simulations of formation flying and inter-satellite communication.To satisfy the requirements of inter-satellite communication, a simulation platform is proposed which is based on Petri network. The platform, which combines the space environment and attitude and orbit sub-systems, focuses on the simulation of encoder/decoder module and spread spectrum module of the inter-satellite communication system. Based on these, this dissertation proposes a design approach of inter-satellite communication system which considers the features of several relative disciplines. The application simulation result shows that the inter-satellite communication platform based on Petri network can obviously improve the design efficiency, shorten the duration of simulation and increase the precise of the result.