The traditional ground industrial Internet of Things (IIoT) cannot supply wireless interconnections anywhere due to its small-scale communication coverage. In this article, a multibeam satellite IIoT in Ka-band is proposed to realize wide-area coverage and long-distance transmissions, which uses nonorthogonal multiple access (NOMA) for each beam to improve transmission rate. To guarantee Quality of Service (QoS) for the satellite IIoT, the beam power is optimized to match the theoretical transmission rate with the service rate. The NOMA transmission rate for each beam is maximized by optimizing the power allocation proportion of each node subject to the constraints of the total power for the beam and the minimal transmission rate for each node within the beam. Satellite-ground integrated IIoT is proposed to use the ground cellular network to supplement the satellite coverage in the blocked areas. The power allocation and network selection for the integrated IIoT are proposed to decrease the transmission cost. Simulation results are provided to validate the superiority of employing NOMA in the satellite IIoT and show higher transmission performance for the QoS-guarantee resource allocation.

QoS-Guarantee Resource Allocation for Multibeam Satellite Industrial Internet of Things With NOMA

Satellite communication system is expected to play a vital role for realizing various remote Internet-of-Things (IoT) applications in sixth-generation vision. Due to unique characteristics of satellite environment, one of the main challenges in this system is to accommodate massive random access (RA) requests of IoT devices while minimizing their energy consumptions. In this article, we focus on the reliable design and detection of RA preamble to effectively enhance the access efficiency in high-dynamic low-earth-orbit (LEO) scenarios. To avoid additional signaling overhead and detection process, a long preamble sequence is constructed by concatenating the conjugated and circularly shifted replicas of a single root Zadoff–Chu (ZC) sequence in RA procedure. Moreover, we propose a novel impulse-like timing metric based on length-alterable differential cross-correlation (LDCC), that is immune to carrier frequency offset (CFO) and capable of mitigating the impact of noise on timing estimation. Statistical analysis of the proposed metric reveals that increasing correlation length can obviously promote the output signal-to-noise power ratio, and the first-path detection threshold is independent of noise statistics. Simulation results in different LEO scenarios validate the robustness of the proposed method to severe channel distortion, and show that our method can achieve significant performance enhancement in terms of timing estimation accuracy, success probability of first access, and mean normalized access energy, compared with the existing RA methods.

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Energy-Efficient Random Access for LEO Satellite-Assisted 6G Internet of Remote Things

The Internet of Things (IoT) is expected to bring new opportunities for improving several services for the Society, from transportation to agriculture, from smart cities to fleet management. In this framework, massive connectivity represents one of the key issues. This is especially relevant when IoT systems are expected to cover a large geographical area or a region not reached by terrestrial network connections. In such scenarios, the usage of satellites might represent a viable solution for providing wide area coverage and connectivity in a flexible and affordable manner. Our paper presents a survey on current solutions for the deployment of IoT services in remote/rural areas by exploiting satellites. Several architectures and technical solutions are analyzed, underlining their features and limitations, and real test cases are presented. It has been highlighted that low-orbit satellites offer an efficient solution to support long-range IoT services, with a good trade-off in terms of coverage and latency. Moreover, open issues, new challenges, and innovative technologies have been focused, carefully considering the perimeter that current IoT standardization framework will impose to the practical implementation of future satellite based IoT systems.

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A Survey on Technologies, Standards and Open Challenges in Satellite IoT

Reasonable design and effective detection of the random access preamble has become a challenging task due to the unique characteristics of mobile satellite communications. To tackle this challenge, we first design a universal long sequence structure by concatenating multiple short Zadoff–Chu sequences that are insensitive to carrier frequency offset (CFO), and then propose the new principles of parameter selection for short sequences to ensure the minimum utilization of root sequence and the independence of the cyclic shift offset on the beam radius. To further reduce the detection complexity and improve the multi-user access performance, a fast timing detection approach is also presented by leveraging the piecewise cumulative detection and the multi-peaks joint estimation to obtain an accurate timing advance for each access user. Simulation results and complexity analysis validate the effectiveness of the new preamble in a typical satellite communication environment, and reveal that the proposed timing detection can achieve the robustness to CFO and offer outstanding performance improvements especially in multi-user scenarios while having a notably reduced computational complexity.

Random Access Preamble Design and Detection for Mobile Satellite Communication Systems

In Satellite Internet of Things (SIoT), satellite constellation design is used to satisfy more communication demands with fewer satellites by optimizing satellite orbits in specific areas. However, the diversity of user demands and satellite resource poses a great challenge in evaluating the Quality of Experience (QoE) of the satellite constellation. In this article, a QoE-aware satellite constellation design scheme is proposed to enhance the user satisfaction by constructing QoE factors. First, an SIoT network model is established with low-Earth-orbit (LEO) satellites and ground Internet of Things (IoT) devices, and the problem is formulated to calculate the QoE for different areas after analyzing the dynamic network topology. Then, the QoE factors are defined to assess QoE by taking into account the coverage performance, communication fluency, regional demand capacity, and profitability. Following that, an intelligent optimization algorithm named multilayer tabu search (MLTS) is designed to obtain reasonable satellite orbits with the best QoE, which provides orbit parameters for satellite constellation configuration. The simulation results demonstrate that the designed satellite constellation can effectively improve the users QoE by optimizing the various QoE factors.

QoE-Aware Intelligent Satellite Constellation Design in Satellite Internet of Things

Timing advanced estimation with Zadoff-Chu sequences is sensitive to the frequency offset, especially for satellite systems with large Doppler shift and oscillator uncertainties. In this letter, Timing Advanced Estimation with Symmetric Zadoff-Chu sequences (TAE-SZC) is proposed to deal with the integer and fractional frequency offset, respectively. By adopting TAE-SZC, the effect of integer frequency offset can be resolved by the symmetric properties of Zadoff-Chu sequences, and an iterative compensation method is used to mitigate the effect of fractional frequency offset. Simulation results show that TAE-SZC outperforms the conventional timing advanced estimation methods without incurring additional consumption of time/frequency resource.

Enhanced Timing Advanced Estimation With Symmetric Zadoff-Chu Sequences for Satellite Systems

Satellite communication networks suffer from heterogeneous and varying propagation delay, which makes slotted random access (RA) protocols being no longer favorable, especially in the multi-receiver scenario. Different from other train of thoughts for RA algorithms, an asynchronous RA scheme named asynchronous cooperative Aloha (ACA) is introduced to benefit from the heterogeneous and varying propagation delay in satellite communication networks. A specific packet is transmitted only once with the concept of spatial diversity, and multiple receivers are used to receive the packets. Cooperative interference cancellation technique combined with sliding correlation scheme is adopted to efficiently resolve packet collisions at the gateway. The performance of ACA scheme is evaluated via mathematical analysis and simulations. Simulation results show that ACA outperforms the conventional asynchronous RA scheme in terms of throughput and packet loss ratio.

Asynchronous Cooperative Aloha for Multi-Receiver Satellite Communication Networks

In satellite communication system, the large Doppler frequency shift and the accumulated oscillator uncertain frequency offset will influence the accuracy of timing advanced estimation with Zadoff-Chu sequence. In order to mitigate the adverse impacts of frequency offset for timing advanced estimation, a novel estimation algorithm is put forward in this paper. This novel proposed algorithm utilizes the symmetric properties of Zadoff-Chu sequences and applies Discrete Fourier Transform (DFT) spectrum analysis at the receiver to find out the indices of peaks which are related to the frequency offset. By executing operation on the obtained peak indices, it can not only eliminate the frequency offset, but also determine the value of transmission delay. Simulation results show that this proposed timing advanced estimation scheme can achieve better performance than the conventional methods with low complexity.

A novel timing advanced estimation algorithm for eliminating frequency offset in satellite system

As a fundamental and significant stage of satellite networks which play an important role in global communications, a design of satellite constellations with inter-satellite links(ISLs) becomes necessary. An optimization method is proposed to determine both satellite elements and constellation elements using the multi-objective genetic algorithm(GA) in this paper. The objectives to be optimized, which are determined by the elements to be designed, are divided into performance objectives and cost objectives. The former consist of the coverage rate, the ISL range and the minimum elevation while the latter contain the total satellite count, the orbital altitude and the orbital inclination. With the aim of maximizing the performance minimizing the cost, the proposed method tries to achieve a balance among multi objectives and design specific satellite constellations considered in different conditions. Then the constellations designed in different schemes are compared with each other to demonstrate the correctness and effectiveness of the method.

Design of satellite constellation with inter-satellite links for global communication using genetic algorithm

The invention provides a method for adjusting a random access sequence format and a user terminal. The method comprises the steps that the user terminal acquires location information of a spot beam center of an area in which the user terminal is; according to the location information, delay inequality deviation of transmission of the random access sequence from the spot beam center to the user terminal is determined; according to a false dismissal probability and a false alarm probability, the time duration of a preamble of the random access sequence is determined; a sampling frequency of the random access sequence is acquired, and the length of the random access sequence is determined according to the sampling frequency and the time duration of the preamble; according to the delay inequality deviation, the time duration of the preamble and the length of the random access sequence, the cyclic shift number is determined; and the user terminal adjusts the random access sequence according to the delay inequality deviation, the time duration of the preamble, the length of the random access sequence and the cyclic shift number. The method readjusts relevant parameters of the random access sequence, thereby effectively lowering testing number of times, improving success rate of first access, and meeting the communication requirement of high speed, reliability and large capacity.

Pengxu Li

Papers

Enhanced Timing Advanced Estimation With Symmetric Zadoff-Chu Sequences for Satellite Systems

Asynchronous Cooperative Aloha for Multi-Receiver Satellite Communication Networks

A novel timing advanced estimation algorithm for eliminating frequency offset in satellite system

Design of satellite constellation with inter-satellite links for global communication using genetic algorithm

Method for adjusting random access sequence and user terminal