Studies On Cross-layer Resource Optimization Techniques Of An AOS-based Space Communication System

With the development of space shuttle, manned spacecraft and space station, research on space communication systems is becoming a hot spot. In order to solve the data processing problems of space missions, and adapt new systems (including manned space station, unmanned space platforms and free aircraft etc) and the development of new space mission, the conventional recommendation is expanded and Advanced Orbiting System (AOS) recommendation including flexible and diverse data processing service is proposed by Consultative Committee for Space Data System(CCSDS).Based on analyzing the CCSDS AOS, with the theme of cross-layer resource optimization techniques of AOS space communication system, remote sensing image transmission technique in application layer and virtual channels multiplexing algorithm in data link layer are studied in this dissertation.Firstly, in the AOS space communication system application layer, aim to the problem of the high bit error rate of space-to-ground communications, based on the wavelet coefficients hierarchical algorithm remote sensing image transmission scheme and based on wavelet coefficients sub-block algorithm remote sensing image transmission are proposed by source encoding and research of synchronization, bitstream service encapsulation, and optimum data block length design, improved throughput of remote sensing image transmission system and quality of restructured images. In the bit error rate(ber<10-4), the wavelet coefficients hierarchical algorithm can achieve maximal throughput. In the wavelet coefficients sub-block algorithm, the wavelet coefficients are separated into small blocks and encoded based on character of the wavelet coefficients and principle of the SPIHT, and the synchronization codes and sequence number are added to the front of block. The proposed scheme provides higher character of resisted error and higher PSNR than traditional algorithm, in the same bit error rate (ber<10-3). The PSNR can be improved about4dB.Secondly, in the AOS space communication system data link layer, in order to adapt diverse data transmission and improve systems performance, a novel AOS virtual channels scheduling algorithm based on the separate evaluation of virtual channels and frames is proposed. In the proposed algorithm, the transmission time slots are divided into synchronous ones and asynchronous ones. For synchronous time slots the virtual channels are scheduled in a polling manner; for asynchronous time slots, virtual channels urgent degree and frame urgent degree are first considered separately, and then joined together to form a new urgent degree function, which satisfies the transmission demand of various data sources. Extensive simulation experiments are conducted and showed that the proposed algorithm provides much lower average scheduling delay and maximal scheduling delay of the important virtual channels than the traditional dynamic priority scheduling algorithm, without deteriorating frame loss rates and channel utilization rate.Finally, with joining the application layer, data link layer and physical layer, a cross-layer resource optimization architecture based on QoS is proposed. Based on the architecture, a dynamic cross-layer scheme for QoS Services is proposed, solved the problem of information interaction in application layer, data link layer and physical layer, decreased total transmission delay of data frame, and improved system performance. To solve the problem of efficiency and robustness between application layer and data link layer, an optimized link adaptation scheme based on virtual modulation and coding is proposed. With the criterion of time domain normalized spectrum efficiency, link adaptation and hybrid automatic repeat request are jointly optimized. Theoretical analysis and simulation results show that the proposed scheme achieves better performance for wireless transmissions than conventional schemes.Consequently, the application layer and data link layer techniques are joined by adopting cross-layer resource optimization techniques in the AOS space communication system, decreased total transmission delay of data frame, and improved system performance, which are meaningful to improve research of AOS space communication system performance.