To support the emergent freshness-critical applications in the satellite-integrated IoT, information must be transmitted timely and reliably. A significant limitation of the upcoming satellite-integrated IoT era is the non-trivial propagation latency because of long-distance communication. To realize timely information delivery, the hybrid automatic repeat request (HARQ) strategy with frequent feedback is not fit anymore, since the reliability of the HARQ strategy needs multiple retransmission of the obsolete packets, which inevitably result in information staleness in the satellite-integrated IoT. In this paper, we design a two-layer coding strategy that uses error-correction codes within each packet in the physical-layer (PHY) and erasure-correction codes across the packets in the packet-layer. Then, we formulate an AoI-optimal redundancy-allocation problem to find the redundancy compromise between error-correction codes and erasure-correction codes. By solving the redundancy-allocation problem for the designed two-layer coding strategy, we derive explicit expressions of the AoI-optimal two-layer coding rates. Inspired by this, we explore the optimal reliability of the physical channel. Numerical results and analysis prove that making the physical channel suitably unreliable is beneficial to the timeliness of the system. And the simulation results indicate that the combination of erasure-correction codes and relative lossy error-correction codes achieves AoI-improvement over the ultra-reliable PHY-only coding scheme. The simulation results also show that the choice of AoI-optimal coding rates depends heavily on the channel characteristics, such as the signal-to-noise ratio, fade duration and channel fading parameters.

中文翻译：

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实现卫星集成物联网中的年龄最佳传输：两层编码方法


为了支持卫星集成物联网中新兴的新鲜关键应用，信息必须及时可靠地传输。即将到来的卫星集成物联网时代的一个重大限制是长距离通信带来的巨大传播延迟。为了实现及时的信息传递，频繁反馈的混合自动重传请求（HARQ）策略已经不再适用，因为HARQ策略的可靠性需要对过时的数据包进行多次重传，这不可避免地导致卫星集成物联网中的信息陈旧。 。在本文中，我们设计了一种两层编码策略，该策略在物理层（PHY）的每个数据包内使用纠错码，并在数据包层的数据包之间使用纠删码。然后，我们制定了 AoI 最优冗余分配问题，以找到纠错码和纠删码之间的冗余折衷。通过解决所设计的两层编码策略的冗余分配问题，我们导出了 AoI 最佳两层编码率的显式表达式。受此启发，我们探索物理通道的最优可靠性。数值结果和分析证明，将物理通道设置为适当的不可靠有利于系统的时效性。仿真结果表明，纠删码和相对有损纠错码的组合相对于超可靠的纯 PHY 编码方案实现了 AoI 改进。仿真结果还表明，AoI 最佳编码率的选择在很大程度上取决于信道特性，例如信噪比、衰落持续时间和信道衰落参数。