Research On Transmission Strategy Based On Systematic Lt Code In Deep Space Time-varying Channel

Deep space exploration has great scientific value and economic significance, which means a country’s level of technological development and comprehensive national strength. The normal operation of the communication system is one significant guarantee of success in the deep space exploration mission. Meanwhile, in order to cope with the increasing number of the deep space exploration missions, deep- space communication will employ K a-band for future exploration missions. Although, Ka-band increases the throughput of the down- link data information transfer, it faces the problem that Ka-band link is more susceptible to fluctuating weather conditions and decreases the transmission efficiency. Therefore, in order to cope with the channel bit error rate changes, our work intends to propose an adaptive rate transmission scheme to ensure the continuity of the communications link and increase Ka-band downlink system throughput. Above all, designing an adaptive transmission scheme based on deep space Ka-band downlink channel modeling and channel state forecast. However, compared to the actual cha nnel condit ions, predictions of channels exist error. So there requires the receiving end feedback and forward erasure technology to reduce forecast error of the system throughput impact. The main research work focuses on how to further improve the system throughput.In this paper, in order to avoid the further reduces of weak signal in the deep space, a two state Markov chain Gilbert- Elliot channel model on transport layer over Ka-band link noise temperature is proposed, which apparently reflects the characteristics of rain attenuation and equivalent noise temperature from the weather condit ions of ground station area. Based on the GE channel, it calculate a complete characterization of the thresholds for each policy and design the best threshold policy in deep space GE channel, which provides the platform for channel forecast algorithm combined with transmission protocol for next step.In order to minimize the prediction steps, the ground station receiving terminal need to feedback the weather conditions regularly. While the deep space has the characteristic of intermittent connectivity, high error rate, and long delay. Delay tolerant network(DTN) is introduced into the deep space communication. In order to increase the overall throughput of Ka-band downlink, this paper proposed a transition mode combined with asynchronous LTP/BP to feedback current weather state. First, the LTP transmission model is described completely, then, a theoretical model of LTP timer is established, finally, design a weather state forecast model, combined GE channel model with asynchronous LTP/BP transmission mode.Forward erasure technology fountain code system was introduced, the system code is a rateless code, no fixed transmission rate, so when channel conditions are "good" condition, the sender choose to use a high transfer rate transmission; when the channel when condit ions are "bad" state, the selection of low transmission rate transmission. According to the impact of weather changes on the state of the Ka-band downlink packet loss rate of change, adaptive rate adjustment system fountain codes, thus ensuring Ka-band data link capable of continuous communication and effectively improve the K a-band downlink throughput.