Providing ubiquitous connectivity to diverse device types is the key challenge for 5G and beyond 5G (B5G). Unmanned aerial vehicles (UAVs) are expected to be an important component of the upcoming wireless networks that can potentially facilitate wireless broadcast and support high rate transmissions. Compared to the communications with fixed infrastructure, UAV has salient attributes, such as flexible deployment, strong line-of-sight (LoS) connection links, and additional design degrees of freedom with the controlled mobility. In this paper, a comprehensive survey on UAV communication towards 5G/B5G wireless networks is presented. We first briefly introduce essential background and the space-air-ground integrated networks, as well as discuss related research challenges faced by the emerging integrated network architecture. We then provide an exhaustive review of various 5G techniques based on UAV platforms, which we categorize by different domains including physical layer, network layer, and joint communication, computing and caching. In addition, a great number of open research problems are outlined and identified as possible future research directions.

UAV Communications for 5G and Beyond: Recent Advances and Future Trends

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Клініко-епідеміологічні особливості спалаху кору в м. Суми у 2014 році

The Internet of Underwater Things (IoUT) is an emerging communication ecosystem developed for connecting underwater objects in maritime and underwater environments. The IoUT technology is intricately linked with intelligent boats and ships, smart shores and oceans, automatic marine transportations, positioning and navigation, underwater exploration, disaster prediction and prevention, as well as with intelligent monitoring and security. The IoUT has an influence at various scales ranging from a small scientific observatory, to a mid-sized harbor, and to covering global oceanic trade. The network architecture of IoUT is intrinsically heterogeneous and should be sufficiently resilient to operate in harsh environments. This creates major challenges in terms of underwater communications, whilst relying on limited energy resources. Additionally, the volume, velocity, and variety of data produced by sensors, hydrophones, and cameras in IoUT is enormous, giving rise to the concept of Big Marine Data (BMD), which has its own processing challenges. Hence, conventional data processing techniques will falter, and bespoke Machine Learning (ML) solutions have to be employed for automatically learning the specific BMD behavior and features facilitating knowledge extraction and decision support. The motivation of this article is to comprehensively survey the IoUT, BMD, and their synthesis. It also aims for exploring the nexus of BMD with ML. We set out from underwater data collection and then discuss the family of IoUT data communication techniques with an emphasis on the state-of-the-art research challenges. We then review the suite of ML solutions suitable for BMD handling and analytics. We treat the subject deductively from an educational perspective, critically appraising the material surveyed. Accordingly, the reader will become familiar with the pivotal issues of IoUT and BMD processing, whilst gaining an insight into the state-of-the-art applications, tools, and techniques. Finally, we analyze the architectural challenges of the IoUT, followed by proposing a range of promising direction for research and innovation in the broad areas of IoUT and BMD. Our hope is to inspire researchers, engineers, data scientists, and governmental bodies to further progress the field, to develop new tools and techniques, as well as to make informed decisions and set regulations related to the maritime and underwater environments around the world.

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Internet of Underwater Things and Big Marine Data Analytics—A Comprehensive Survey

Reliable data transfer aims to guarantee that the destination node can successfully receive what have been sent to it, and the basic mechanisms extensively for this purpose in radio frequency (RF) networks include redundancy and retransmission. However, this issue becomes much more challenging in underwater acoustic (UWA) networks in comparison with RF networks due to the following peculiar features of UWA channels: poor quality and high dynamics of UWA channels, much smaller channel capacity and much larger propagation delay, as well as asymmetric connectivity of UWA links. These features either limit extensive application of redundancy mechanisms or influence the performance of retransmission mechanisms. Therefore, many research results have been reported in the literature, with several different design strategies and various proposals available. This paper conducts a survey on many schemes proposed from the data link layer to the transport layer, and discusses challenging issues necessary for further research.

On Reliable Data Transfer in Underwater Acoustic Networks: A Survey From Networking Perspective

The inter-satellite links (ISLs) will play an increasingly important role in improving the service performance and enhancing the survivability of global navigation satellite systems. The current signal transmission schemes in ISLs primarily employ constant coded modulation to guarantee a high reliable communication even for the worst channel status, and the adaptive coded modulation (ACM) schemes, such as binary low-density parity-check (LDPC) coded quadrature phase shift keying or $M$ -ary quadrature amplitude modulation ( $M$ QAM) have been introduced to improve spectral efficiency over inter-satellite channels recently. However, the phase discontinuity of the above modulations will widen frequency spectrum and cause the high-voltage transient of transmitter, and the $M$ QAM signal through high power amplifier onboard will result in non-linear distortion because of non-constant envelope. In this paper, the association between non-binary LDPC codes and high-order partial response continuous phase modulation with iterative detection is presented as the source of ACM schemes, which effectively inhibits information loss in the process of conversion between bit and symbol probabilities. According to the constellation of BeiDou navigation satellite system in 2020, an open loop ACM control mechanism based on inter-satellite distance is introduced, and implemented by the target bit error rate (BER) and the maximum ratio between the throughput and bandwidth algorithms. Simulation results show that the proposed ACM scheme can reduce the BER and improve the power efficiency in the requirement of target BER limit, and provide a higher spectral efficiency under the same transmitting power compared with the existing ACM scheme.

Adaptive Coded Modulation Based on Continuous Phase Modulation for Inter-Satellite Links of Global Navigation Satellite Systems

Frequency allocations in the L band suitable for global navigation satellite system (GNSS) services are getting crowded and system providers face an ever tougher job when they try to bring in new signals and services while maintaining radio frequency compatibility. With the successive opening of the S and C bands to GNSS service, the multi-band combined navigation is predicted to become a key technology for future high-precision positioning navigation systems, and a single modulation scheme satisfying the requirements in each band is a promising solution for reducing user terminal complexity. A universal modulation scheme based on the continuous phase modulation (CPM) family suitable for the above bands’ demands is proposed. Moreover, this paper has put forward two specific CPM signals for the S and C bands, respectively. Then the proposed modulation schemes, together with existing candidates, are comprehensively evaluated. Simulation results show that the proposed CPM signals can not only satisfy the constraint condition of compatibility in different bands well and reduce user terminal complexity, but also provide superior performance in terms of tracking accuracy, multi-path mitigation and anti-jamming compared to other candidate modulation schemes.

https://www.mdpi.com/1424-8220/15/6/13184/pdf

CPM Signals for Satellite Navigation in the S and C Bands.

With L band frequency allocations for satellite navigation getting more crowded, S band (2483.5–2500 MHz) is already allocated for navigation services, where Globalstar broadcasts downlink communications to user terminals. The Indian Regional Navigation Satellite System (IRNSS) is transmitting navigation signals and Galileo exploits some potential signals in S band. Also, several candidate S band signals based on binary offset carrier (BOC), binary phase shift keying (BPSK), continuous phase modulation (CPM) and minimum shift keying-BOC (MSK-BOC) are suggested for BeiDou system (BDS). In quite narrow S band, mutual interference among these systems is inevitable, thus the compatibility issue is particularly significant for S band signal design. To explore desired S band signals for BDS, the paper firstly describes a comprehensive compatibility evaluation methods based on effective carrier-to-noise ratio degradation for acquisition and code tracking. Then a real simulation is established using space constellations, modulation schemes and received power. Finally, the worst mutual interference of BDS candidate signals with Galileo, IRNSS and Globalstar is calculated and compared. The results indicate that CPM signal is easier to allow peaceful coexistence of other systems with minimal mutual interference in S band compared to other BDS candidates.

Radio Frequency Compatibility Evaluation of S Band Navigation Signals for Future BeiDou.

In underwater wireless sensor networks (UWSNs), the sensor nodes are sparsely deployed over a large sea area due to their high design cost and high manufacturing cost. Opportunistic routing protocols are a promising forwarding technique for various UWSNs. However, many opportunistic routing protocols suffer from the void problem in sparse underwater scenarios. Hop count-based opportunistic routing protocols inherently alleviate this problem by periodically maintaining the topological information of sensor node. Nevertheless, the robustness of these protocols degrades due to channel variation and node movement in UWSNs. In this paper, we propose a coding-aware opportunistic routing method for sparse UWSNs (CORS). In CORS, we use topological information to adaptively expand the candidate set. On this basis, a forwarding with opportunistic coding strategy is developed to join interflow network coding and opportunistic forwarding in CORS. In addition, we design a sliding window-based coding algorithm to provide effective coding gains with low coding overhead. Then, a sliding window-based decoding algorithm is designed to reduce decoding overhead. Simulation results show that CORS significantly improves upon the network performances of existing protocols in various scenarios.

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Coding-Aware Opportunistic Routing for Sparse Underwater Wireless Sensor Networks

In this paper, a transmission redundancy optimization strategy for fountain codes that uses an adaptive filtering technique as well as recent results concerning the upper bound of the source packet erasure probability for fountain codes over finite fields is proposed. The performance of the proposed strategy was evaluated in static and simulated realistic underwater acoustic channel environments simulated by a recently proposed statistical underwater acoustic channel model. The goal of this investigation is to improve the communication efficiency of underwater acoustic sensor networks that use communication protocols based on fountain codes. The performance of the proposed strategy is compared with the recently proposed approaches of discrete stochastic approximation (DSA) and the joint power and rate control (JPR) schemes. The simulation results demonstrate that the strategy proposed in this paper performs better than the existing schemes in both static and simulated realistic environments. The proposed strategy is 4.75 times better than the DSA in the static convergence performance evaluation. Further analysis shows that in the presence of a simulated realistic environment, compared to DSA and JPR, the strategy proposed in this paper reduces the overall transmission redundancy by approximately 11.4% and 52.6%, respectively. It also improves the average communication efficiency by 1.3% and 12.5%, respectively. The average optimization error relative to optimal redundancy is improved by approximately 62.1% and 92.5%, respectively. These numerical results are obtained by employing the specific simulation parameters and the simulated environment mentioned in this paper.

Danfeng Zhao

Papers

CPM Signals for Satellite Navigation in the S and C Bands.

Radio Frequency Compatibility Evaluation of S Band Navigation Signals for Future BeiDou.

Coding-Aware Opportunistic Routing for Sparse Underwater Wireless Sensor Networks

Optimal Redundancy Control Strategy for Fountain Code-Based Underwater Acoustic Communication

Novel joint encoding/decoding algorithms of fountain codes for underwater acoustic communication