基于系统码的深空时变信道传输策略研究

发布时间：2018-12-15 06:46

【摘要】：深空探测具有十分重要的科学价值与经济意义,其中深空通信的有效进行是保障深空探测任务成功的关键。随着深空通信任务的日益艰巨,未来将选用具备更高传输速度和更宽带宽的Ka波段。但是Ka波段尽管能够增加通信下行链路的数据吞吐量,却容易受到天气变化的影响继而导致传输过程的有效性降低。由于近地天气的动态变化,使得Ka波段下行链路呈时变信道。针对于时变信道而言,使用传统的固定传输速率的链路方案使得链路的有效吞吐量受限甚至链路中断,所以本论文拟提出自适应传输速率方案以应对时变信道的误码率变化,在保证通信链路连续性的同时,深空Ka波段下行链路的系统吞吐量也会增加。设计自适应传输方案首先需要基于深空Ka波段下行链路进行信道建模,在信道模型的基础上,对信道进行预测。然而信道的预测结果相较于实际信道状态会存在误差,因此需要接收端反馈与前向纠删技术来降低预测误差对于系统吞吐量的影响,本文重点关注如何进一步提高系统吞吐量。本文为了减少由于近地天气变化所带来的下行链路吞吐量损耗,结合近地大气雨衰参数与等价噪声温度,建立时变信道预测模型——Gilbert-Elliot模型。同时基于此信道模型,计算出两种信道阈值策略中的阈值,在深空背景下设计出具有最优阈值策略的GE信道模型,为下一步设计结合传输协议的信道预测算法提供平台。为了避免由于预测步长过长而引起预测误差过大的问题,本课题采用能够处理间断传输,大时延,高误码率的LTP/BP协议反馈地面天气状态,从而避免了预测步长过长的问题。本文提出基于异步LTP/BP(Licklider Transmission Protocol/Bundle Protocol)协议的文件传输模式,并结合LTP传输模式特点,设计一种基于Ka波段的信道状态预测模型,从而提高Ka波段下行链路的全局吞吐量。在前向纠删技术中引入了系统喷泉码,系统码是无码率码,没有固定的传输速率,因此当信道条件为“好”状态时,发送端选择用高传输码率传输;当信道条件为“坏”状态时,则选用低传输码率传输。根据天气状态转变对Ka波段下行链路丢包率变化的影响,自适应的调节系统喷泉码码率,从而保证Ka波段的数据链路能够连续通信并且有效的提高Ka波段下行链路吞吐量。
[Abstract]:Deep space exploration has very important scientific value and economic significance, among which the effective implementation of deep space communication is the key to ensure the success of the deep space exploration mission. With the increasingly arduous task of deep space communication, Ka band with higher transmission speed and wider bandwidth will be selected in the future. However, although Ka band can increase the data throughput of the downlink, it is vulnerable to the weather change, which leads to the decrease of the efficiency of the transmission process. Because of the dynamic change of near-earth weather, the downlink of Ka band is time-varying channel. For the time-varying channel, the traditional fixed transmission rate link scheme is used to limit the effective throughput of the link and even interrupt the link, so this paper proposes an adaptive transmission rate scheme to deal with the change of BER in time-varying channel. At the same time, the system throughput of deep space Ka band downlink will be increased. The design of adaptive transmission scheme requires channel modeling based on deep space Ka band downlink and channel prediction based on channel model. However, compared with the actual channel state, the channel prediction results will have errors, so the receiver feedback and forward erasure techniques are needed to reduce the impact of prediction errors on the system throughput. This paper focuses on how to further improve the system throughput. In order to reduce the downlink throughput loss caused by the variation of near-Earth weather, a time-varying channel prediction model, Gilbert-Elliot model, is established by combining the rain decline parameters and equivalent noise temperature of the near-Earth atmosphere. At the same time, based on this channel model, the threshold of two channel threshold strategies is calculated, and the GE channel model with optimal threshold strategy is designed under the background of deep space, which provides a platform for the next design of channel prediction algorithm combined with transmission protocol. In order to avoid the problem that the prediction error is too large because the prediction step is too long, the LTP/BP protocol, which can deal with discontinuous transmission, large delay and high bit error rate, is adopted to feedback the ground weather state, thus avoiding the problem of long prediction step. In this paper, a file transfer mode based on asynchronous LTP/BP (Licklider Transmission Protocol/Bundle Protocol) protocol is proposed. Combining the characteristics of LTP transmission mode, a channel state prediction model based on Ka band is designed to improve the global throughput of downlink in Ka band. The system fountain code is introduced into the forward erasure technology. The system code is no bit rate code and has no fixed transmission rate. Therefore, when the channel condition is "good", the sender chooses to transmit at high transmission rate. When the channel condition is "bad" state, select low transmission rate transmission. According to the influence of weather state change on the downlink packet loss rate of Ka band, the fountain code rate of the system can be adjusted adaptively to ensure the continuous communication of the Ka band data link and improve the downlink throughput of Ka band effectively.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN927.3

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