Modeling and Verification of File Delivery Delay for LTP in Complex Deep Space Networks
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摘要: 针对简化场景下建立的LTP（Licklider Transmission Protocol）传递时延模型无法直接应用于复杂场景的问题，提出了一种复杂深空通信网络的LTP传递时延理论模型。已有研究多关注于一到两跳的简化场景或 bundle 保管开启状态下多跳场景数据传输模型的建立，然而其结果在复杂深空通信网络中，对于在 bundle 保管关闭状态下的深空通信并不适用。本文对LTP在复杂深空通信网络中的传输机制进行了分析，基于此分析对LTP在复杂深空通信网络中的传递时延进行了理论建模，搭建了仿真验证平台，仿真分析了模型的正确性及优势。结果表明，该模型计算结果与实验结果较为吻合，相比基于简化场景建立的理论模型，本文所提出的模型更加适用于复杂深空通信网络。Abstract: Aiming at the problem that the models of file delivery time for Licklider Transmission Protocol (LTP) established in simplified scenarios can’t be directly applied to complex scenarios, a theoretical model of file delivery time for LTP in complex deep space networks is proposed. Previous research has focused mainly on establishment of a data transmission model for LTP in simplified scenarios with one to two hops or multihop scenarios with a custody mechanism of the Bundle Protocol (BP). However, the research results are not applicable to communications in complex deep space networks without the custody mechanism of BP that is more suitable for deep space communications with LTP. Firstly, the transmission mechanism of LTP in complex deep space networks is analyzed. Then, the theoretical model of file delivery time for LTP in complex deep space networks is established based on the analysis of the transmission mechanism before. Finally, a simulation verification platform is built to analyze the correctness and advantages of the model. The results show that the calculated results of the model are in good agreement with the experimental results, and the model proposed is more suitable for complex deep space networks than the models based on simplified scenarios.
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Key words:
- Complex deep space networks /
- LTP /
- Delivery delay /
- Theoretical model
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图 1 复杂深空通信网络LTP详细传输过程
Figure 1. Detailed transmission process of LTP in a complex deep space network
图 2 不同链路环境下仿真结果与模型计算结果对比
Figure 2. Comparison of simulation results and model calculation results with different link environments
图 3 三种理论模型在不同链路环境下的MAPE对比
Figure 3. MAPE comparison of three theoretical models with different communication environments
表 1 模型验证的实验参数配置
Table 1. Experiment parameter settings for model verification
各段链路下行速率/(Byte·s–1) 探测器−UNICON：7500
UNICON卫星之间：250
UNICON-GEO：7500
GEO-地面站：1250000信道速率非对称比(下行\上行) 1∶1，100∶1，500∶1 BP托管机制 关闭 bundle尺寸/kByte 50 文件尺寸/MByte 1 LTP block尺寸 1 bundle LTP session 24 LTP segment尺寸/Byte 1400 LTP segment数据链路层尺寸/Byte ${L_{{\rm{seg}}\_{\rm{payload}}} } + 100$ 误码率 10–7, 10–6, 10–5, mul mul ${N_{\rm{U}}} = $ 3 [10–6, 10–5, 10–5, 10–6, 10–7]
${N_{\rm{U}}} = $ 2 [10–6, 10–5, 10–6, 10–7]
${N_{\rm{U}}} = $ 1 [10–6, 10–6, 10–7]三种链路情况的单程延时/s ${N_{\rm{U}}} = $ 3 358+725×2+285+0.125=2093.125
${N_{\rm{U}}} = $ 2 296+725+273+0.125=1294.125
${N_{\rm{U}}} = $ 1 245+241+0.125=486.125实验次数 10 
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表 2 计算MAPE的实验参数设置
Table 2. Parameter settings of experiments for calculating MAPEs
标号 数据传输
路径情况BER CR a NU =2 10−7 500∶1 b NU =2 10−6 500∶1 c NU =2 10−5 500∶1 d NU =2 10−5 100∶1 e NU =2 10−5 1∶1 f NU =3 10−5 500∶1 g NU =1 10−5 500∶1
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