Abstract: Satellite Internet of Things (IoT) is a promising way to provide seamless coverage to a massive number of devices all over the world, especially in remote areas not covered by cellular networks, e.g., forests, oceans, mountains, and deserts. In general, satellite IoT networks take low Earth orbit (LEO) satellites as access points, which solves the problem of wide coverage, but leads to many challenging issues. We first give an overview of satellite IoT, with an emphasis on revealing the characteristics of IoT services. Then, the challenging issues of satellite IoT, i.e., massive connectivity, wide coverage, high mobility, low power, and stringent delay, are analyzed in detail. Furthermore, the possible solutions to these challenges are provided. In particular, new massive access protocols and techniques are designed according to the characteristics and requirements of satellite IoT. Finally, we discuss several development trends of satellite IoT to stimulate and encourage further research in such a broad area.

卫星物联网：挑战、方案和发展趋势

[1]Ahmed N, De D, Hussain I, 2018. Internet of Things (IoT) for smart precision agriculture and farming in rural areas. IEEE Internet Things J, 5(6):4890-4899.

[2]Briskman R, 1984. Domestic satellite services for rural areas. IEEE Commun Mag, 22(3):35-38.

[3]Cao XL, Yang B, Shen YL, et al., 2023. Edge-assisted multi-layer offloading optimization of LEO satellite-terrestrial integrated networks. IEEE J Sel Areas Commun, 41(2):381-398.

[4]Caus M, Perez-Neira A, Mendez E, 2021. Smart beamforming for direct LEO satellite access of future IoT. Sensor, 21(14):4877.

[5]Centenaro M, Vangelista L, Saur S, et al., 2017. Comparison of collision-free and contention-based radio access protocols for the Internet of Things. IEEE Trans Commun, 65(9):3832-3846.

[6]Chen XM, 2019. Massive Access for Cellular Internet of Things Theory and Technique, Springer, Singapore.

[7]Chen XM, Zhang ZY, Zhong CJ, et al., 2018. Fully non-orthogonal communication for massive access. IEEE Trans Commun, 66(4):1717-1731.

[8]Chen XM, Ng DWK, Yu W, et al., 2021. Massive access for 5G and beyond. IEEE J Sel Areas Commun, 39(3):615-637.

[9]Chen ZL, Sohrabi F, Liu YF, et al., 2019. Covariance based joint activity and data detection for massive random access with massive MIMO. Proc IEEE Int Conf on Communications, p.1-6.

[10]Chu JH, Chen XM, Zhong CJ, et al., 2021. Robust design for NOMA-based multibeam LEO satellite Internet of Things. IEEE Internet Things J, 8(3):1959-1970.

[11]Cisco, 2019. Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update. 2017–2022 White Paper.

[12]De Sanctis M, Cianca E, Araniti G, et al., 2016. Satellite communications supporting Internet of Remote Things. IEEE Internet Things J, 3(1):113-123.

[13]Di BY, Song LY, Li YH, et al., 2019. Ultra-dense LEO: integration of satellite access networks into 5G and beyond. IEEE Wirel Commun, 26(2):62-69.

[14]Fengler A, Caire G, Jung P, et al., 2019. Massive MIMO unsourced random access. https://arxiv.org/abs/1901.00828

[15]Hassan NUL, Huang CW, Yuen C, et al., 2020. Dense small satellite networks for modern terrestrial communication systems: benefits, infrastructure, and technologies. IEEE Wirel Commun, 27(5):96-103.

[16]Islam SMR, Kwak D, Kabir MH, et al., 2015. The Internet of Things for health care: a comprehensive survey. IEEE Access, 3:678-708.

[17]Jiao J, Sun YY, Wu SH, et al., 2020. Network utility maximization resource allocation for NOMA in satellite-based Internet of Things. IEEE Internet Things J, 7(4):3230-3242.

[18]Joroughi V, Vázquez MÁ, Pérez-Neira AI, et al., 2017. Onboard beam generation for multibeam satellite systems. IEEE Trans Wirel Commun, 16(6):3714-3726.

[19]Kaur H, Sood SK, 2020. Energy-efficient IoT-fog-cloud architectural paradigm for real-time wildfire prediction and forecasting. IEEE Syst J, 14(2):2003-2011.

[20]Kodheli O, Andrenacci S, Maturo N, et al., 2019. An uplink UE group-based scheduling technique for 5G mMTC systems over LEO satellite. IEEE Access, 7:67413-67427.

[21]Kuang LL, Jiang CX, Qian Y, et al., 2018. Terrestrial-Satellite Communication Networks—Transceivers Design and Resource Allocation, Springer, Cham, Switzerland.

[22]Liu L, Larsson EG, Yu W, et al., 2018. Sparse signal processing for grant-free massive connectivity: a future paradigm for random access protocols in the Internet of Things. IEEE Signal Process Mag, 35(5):88-99.

[23]Qiu T, Zhao Z, Zhang T, et al., 2020. Underwater Internet of Things in smart ocean: system architecture and open issues. IEEE Trans Ind Inform, 16(7):4297-4307.

[24]Qu ZC, Zhang GX, Cao HT, et al., 2017. LEO satellite constellation for Internet of Things. IEEE Access, 5:18391-18401.

[25]Shao XD, Chen XM, Jia RD, 2020. A dimension reduction-based joint activity detection and channel estimation algorithm for massive access. IEEE Trans Signal Process, 68:420-435.

[26]Statista Research Department, 2016. Internet of Things (IoT) Connected Devices Installed Base Worldwide from 2015 to 2025 (in Billions).

[27]Tian FY, Chen XM, 2019. Multiple-antenna techniques in nonorthogonal multiple access: a review. Front Inform Technol Electron Eng, 20(12):1665-1697.

[28]Vázquez MÁ, Pérez-Neira A, Christopoulos D, et al., 2016. Precoding in multibeam satellite communications: present and future challenges. IEEE Wirel Commun, 23(6):88-95.

[29]Wang WJ, Liu A, Zhang Q, et al., 2018. Robust multigroup multicast transmission for frame-based multi-beam satellite systems. IEEE Access, 6:46074-46083.

[30]Xu LD, He W, Li SC, 2014. Internet of Things in industries: a survey. IEEE Trans Ind Inform, 10(4):2233-2243.

[31]Ying M, Chen XM, Shao XD, 2023. Exploiting tensor-based Bayesian learning for massive grant-free random access in LEO satellite Internet of Things. IEEE Trans Commun, 71(2):1141-1152.

[32]You L, Liu A, Wang WJ, et al., 2019. Outage constrained robust multigroup multicast beamforming for multi-beam satellite communication systems. IEEE Wirel Commun Lett, 8(2):352-355.

[33]You L, Li KX, Wang JH, et al., 2020. Massive MIMO transmission for LEO satellite communications. IEEE J Sel Areas Commun, 38(8):1851-1865.

[34]You XH, Wang CX, Huang J, 2021. Towards 6G wireless communication networks: vision, enabling technologies, and new paradigm shifts. Sci China Inform Sci, 64:110301.

[35]Zanella A, Bui N, Castellani A, et al., 2014. Internet of Things for smart cities. IEEE Internet Things J, 1(1):22-32.

[36]Zhang ZJ, Li Y, Huang CW, et al., 2020. User activity detection and channel estimation for grant-free random access in LEO satellite-enabled Internet of Things. IEEE Internet Things J, 7(9):8811-8825.

[37]Zhang ZY, Wang XB, Zhang Y, et al., 2016. Grant-free rateless multiple access: a novel massive access scheme for Internet of Things. IEEE Commun Lett, 20(10):2019-2022.

[38]Zheng G, Chatzinotas S, Ottersten B, 2012. Generic optimization of linear precoding in multibeam satellite systems. IEEE Trans Wirel Commun, 11(6):2308-2320.