Research On Capacity And Rateless Coding Strategy Of Time Varying Dying Channel

With the continuous development of space exploration,deep space communication,which guarantee its smooth implementation,has been concerned by more and more countries.However,because the space environment is complex and changeable,conventional communication methods which suit for ground communication cannot meet the request of validity and reliability in deep space communication.Thus,a new transmission strategy which is able to deal with long delay and no feedback is awaiting to be studied.Due to the characteristics of deep space communication,we propose a “dying” channel model which is block fading,then we analyze its power allocation and transmission strategy to improve the effectiveness of deep space communication link without feedback and a relatively long time-delay.The research details are as follows:A dying channel model which has random channel length is proposed.Due to the classic Shannon capacity does not apply to the channel,outage capacity and outage probability of dying channel are studied and related formulas are given.Subsequently,we optimize the frame length and the power allocation scheme in order to approach the bound of outage capacity.According to simulation results,the power allocation scheme proposed obviously outperforms the uniform power distribution.Targeting non-feedback point-to-point communication,a semi-Markov dying erasure channel(SMDEC)model is introduced.We propose a heuristic approach for rateless coding degree distributions to achieve high recovery probabilities in the SMDEC.Then,the optimal code length for the maximum average throughput of the SMDEC under different channel conditions is derived and analyzed.Simulation results have shown that the proposed rateless coding strategy outperforms existing conventional rateless codes with significantly better performance.Spatial information networks(SIN)links are suffered by periodic time-varying channel noise because of the periodic motion orbit of the space nodes and planets.Moreover,SIN communications may have a probability to fail at random times,such as severe rain attenuation on Ka band downlinks,or solar scintillation during the superior/inferior solar conjunction.We propose a time-vary dying channel with finite channel-length,and we give the expression of outage capacity is given,moreover,the upper and lower bounds of outage capacity are given.Besides,we propose a sub-optimal degree distribution rateless coding scheme by using a heuristic method.Simulation results show that,the proposed coding scheme has an outperform improvement of throughput compared with traditional LT and Raptor codes.It also provides a practical inspiration for further studies on deep space communication.