Research On Source Channel Encoding And Joint Rate Allocation For Deep Space Image Transmission

In the deep space exploration,the image can accurately reflect the unknown deep space,so it is very important to get them accurately and efficiently.The characteristics of deep space communication environment are the asymmetric of uplink and downlink resources,the communication link changeable with time,and high error of link.So,it puts forward higher requirements for deep space image transmission system.This paper focuses on the research of the key parts of the image transmission system,the source coding methods and the channel coding methods.This paper mainly includes two aspects,one is based on the source channel separation system,analyzed and compared the source and channel encoding methods and combined with the characteristics of deep space communication are preferred suggestions;the second is based on the joint source channel encoding theory research the source compression rate and channel encoding rate joint optimization assignment aim to improve the image quality.This paper specific includes the following work.Firstly,we introduce and analyze the source compression coding methods in current image transmission system,and then compare their performance and choose the set partitioning in hierarchical trees division algorithm as source encoding algorithm through simulation.Then we analyze the channel coding methods,including the low density parity check code and the polar code that can achieve the Shannon limit in the theory.We compare their decoding performance by simulations and select the polar code as the channel coding method in deep space communication system.Secondly,the source coding and channel coding separately,when the total rate of system is fixed,the rate of source coding and channel coding also is fixed in traditional image transmission systems,Because of the tradition image transmission system can't adaptive adjustment in deep space,so the quality of transmission image is difficult to achieve the optimal point.According to the joint source channel coding theory,this paper put forward a new scheme that can jointly achieve the source compression rate and channel encoding rate optimization assignment,and can adaptive adjustment rate.Further,taking into account the feature of the progressive scalability of image compression stream,the proposed scheme is also designed based on unequal error protection technology.Put the standard deep space images as the simulation objects.In the same conditions,the traditional separation encoding transmission system and the scheme based on unequal error protection technology as well as the scheme based on rate allocation technology and the joint rate allocation scheme are simulated.The simulation results show that image transmission scheme based on joint rate allocation than the traditional separated coding scheme in image quality restoration on average 3 dB-5 d B improvements.