Related Work

Satellite Networking: Previous work in the satellite networking domain has mostly focused on satellite ground station architectures [25, 42, 69], RF link prediction [17, 27, 72], and orbital and power modeling [21, 28, 32, 55], as well as analyzing large-scale constellations [44, 45, 65]. However, the majority of this prior work focuses on broadband satellites, which have much fewer constraints than IoT picosats in terms of coordination and data communication. In contrast, previous work specifically on IoT satellite networking is limited and tends to focus on improving networks around individual satellites [22, 31, 33, 37, 56, 71].

卫星网络

先前在卫星网络领域的工作主要集中在卫星地面站架构 [25, 42, 69]、射频链路预测 [17, 27, 72]、轨道与功率建模 [21, 28, 32, 55]，以及对大规模星座的分析 [44, 45, 65]。然而，这些先前工作中的绝大多数都聚焦于宽带卫星，与物联网微型卫星相比，宽带卫星在协调和数据通信方面受到的限制要少得多。相比之下，专门针对物联网卫星网络的研究则较为有限，且倾向于关注如何改进单个卫星周边的网络 [22, 31, 33, 37, 56, 71]。

Uplink Protocols: Due to current hardware constraints on both IoT devices and picosats, complex network medium access control cannot be used. Therefore, data uplink to picosats can only be done using random access MAC protocols [15]. State-of-the-art uplink protocols are limited to Alohabased schemes because other random access protocols, such as CSMA, would be difficult to implement without direct coordination among IoT devices. These Aloha variants typically modify IoT device transmit backoff time by calculating the number of devices within range and estimating the trajectory/link variation of a single satellite [70]. In contrast to terrestrial networks, where Aloha with overlapping cells has been explored to a much more limited extent [53], the satellite network case is largely different because the cells are constantly moving. CosMAC is a MAC layer solution that can be easily integrated with various popular PHY layer approaches. For example, recent work [15, 51, 67] has discussed long-range frequency hopping spread spectrum (LR-FHSS) as a mechanism to improve long-range uplink performance in satellite networks at the PHY layer.

上行链路协议

由于物联网设备和微型卫星当前都存在硬件限制，复杂的网络介质访问控制（MAC）协议无法使用。因此，向微型卫星的数据上行只能通过随机接入MAC协议 [15] 来完成。 当前最先进的上行链路协议仅限于基于Aloha的方案，因为其他随机接入协议（如CSMA）在物联网设备之间缺乏直接协调的情况下难以实现 。这些Aloha的变体通常通过计算覆盖范围内的设备数量，并估算单个卫星的轨迹/链路变化来调整物联网设备的传输退避时间 [70]。与地面网络中对重叠蜂窝下的Aloha协议探索程度有限的情况 [53] 相比，卫星网络的情形大相径庭，因为其蜂窝是持续移动的。CosMAC是一个MAC层解决方案，可以轻松地与各种流行的物理层（PHY）方法集成。例如，近期的工作 [15, 51, 67] 已经讨论了将远距离跳频扩频技术（LR-FHSS）作为一种在物理层上提升卫星网络远距离上行链路性能的机制。

Downlink Scheduling: Although there has been significant research on downlink scheduling for satellite ground station links, much of this work does not account for the real-world complexity of time-varying wireless links [18, 35, 64]. The few studies that address this complexity primarily focus on broadband satellites that can beamform and enable one-to-one scheduling of satellites and ground station nodes [29, 69]. In contrast, CosMAC’s scheduling approach is tailored for picosats and addresses interference in the satellite network resulting from omnidirectional antennas used for downlink.

下行链路调度

尽管在卫星与地面站链路的下行调度方面已有大量研究，但其中许多工作并未考虑到时变无线链路在真实世界中的复杂性 [18, 35, 64]。少数解决了这一复杂性的研究主要关注能够进行波束成形并实现卫星与地面站节点一对一调度的宽带卫星 [29, 69]。与此不同，CosMAC的调度方法是为微型卫星量身定制的，并解决了因下行链路使用全向天线而导致的卫星网络干扰问题。