Unmanned aerial vehicles (UAVs) have found numerous applications and are expected to bring fertile business opportunities in the next decade. Among various enabling technologies for UAVs, wireless communication is essential and has drawn significantly growing attention in recent years. Compared to the conventional terrestrial communications, UAVs’ communications face new challenges due to their high altitude above the ground and great flexibility of movement in the 3-D space. Several critical issues arise, including the line-of-sight (LoS) dominant UAV-ground channels and induced strong aerial-terrestrial network interference, the distinct communication quality-of-service (QoS) requirements for UAV control messages versus payload data, the stringent constraints imposed by the size, weight, and power (SWAP) limitations of UAVs, as well as the exploitation of the new design degree of freedom (DoF) brought by the highly controllable 3-D UAV mobility. In this article, we give a tutorial overview of the recent advances in UAV communications to address the above issues, with an emphasis on how to integrate UAVs into the forthcoming fifth-generation (5G) and future cellular networks. In particular, we partition our discussion into two promising research and application frameworks of UAV communications, namely UAV-assisted wireless communications and cellular-connected UAVs, where UAVs are integrated into the network as new aerial communication platforms and users, respectively. Furthermore, we point out promising directions for future research.

Accessing From the Sky: A Tutorial on UAV Communications for 5G and Beyond

Unmanned aerial vehicles (UAVs) have attracted great interest in rapid deployment for both civil and military applications. UAV communication has its own distinctive channel characteristics compared to the widely used cellular or satellite systems. Accurate channel characterization is crucial for the performance optimization and design of efficient UAV communication. However, several challenges exist in UAV channel modeling. For example, the propagation characteristics of UAV channels are under explored for spatial and temporal variations in non–stationary channels. Additionally, airframe shadowing has not yet been investigated for small size rotary UAVs. This paper provides an extensive survey of the measurement methods proposed for UAV channel modeling that use low altitude platforms and discusses various channel characterization efforts. We also review from a contemporary perspective of UAV channel modeling approaches, and outline future research challenges in this domain.

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A Survey of Channel Modeling for UAV Communications

In recent years, there has been a dramatic increase in the use of unmanned aerial vehicles (UAVs), particularly for small UAVs, due to their affordable prices, wide availability, and relative ease of operability. Existing and future applications of UAVs include remote surveillance and monitoring, relief operations, package delivery, and communication backhaul infrastructure. Additionally, UAVs are envisioned as an important component of 5G wireless technology and beyond. The unique application scenarios for UAVs necessitate accurate air-to-ground (AG) propagation channel models for designing and evaluating UAV communication links for control/non-payload as well as payload data transmissions. These AG propagation models have not been investigated in detail, relative to terrestrial propagation models. In this paper, a comprehensive survey is provided on available AG channel measurement campaigns, large and small scale fading channel models, their limitations, and future research directions for UAV communication scenarios.

A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles

The scalable video coding (SVC) standard as an extension of H.264/AVC allows efficient, standard-based temporal, spatial, and quality scalability of video bit streams. Scalability of a video bit stream allows for media bit rate as well as for device capability adaptation. Moreover, adaptation of the bit rate of a video signal is a desirable key feature, if limitation in network resources, mostly characterized by throughput variations, varying delay or transmission errors, need to be considered. Typically, in mobile networks the throughput, delay and errors of a connection (link) depend on the current reception conditions, which are largely influenced by a number of physical factors. In order to cope with the typically varying characteristics of mobile communication channels in unicast, multicast, or broadcast services, different methods for increasing robustness and achieving quality of service are desirable. We will give an overview of SVC and its relation to mobile delivery methods. Furthermore, innovative use cases are introduced which apply SVC in mobile networks.

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Mobile Video Transmission Using Scalable Video Coding

Unmanned aerial vehicles (UAVs) have found numerous applications and are expected to bring fertile business opportunities in the next decade. Among various enabling technologies for UAVs, wireless communication is essential and has drawn significantly growing attention in recent years. Compared to the conventional terrestrial communications, UAVs' communications face new challenges due to their high altitude above the ground and great flexibility of movement in the three-dimensional (3D) space. Several critical issues arise, including the line-of-sight (LoS) dominant UAV-ground channels and resultant strong aerial-terrestrial network interference, the distinct communication quality of service (QoS) requirements for UAV control messages versus payload data, the stringent constraints imposed by the size, weight and power (SWAP) limitations of UAVs, as well as the exploitation of the new design degree of freedom (DoF) brought by the highly controllable 3D UAV mobility. In this paper, we give a tutorial overview of the recent advances in UAV communications to address the above issues, with an emphasis on how to integrate UAVs into the forthcoming fifth-generation (5G) and future cellular networks. In particular, we partition our discussions into two promising research and application frameworks of UAV communications, namely UAV-assisted wireless communications and cellular-connected UAVs,where UAVs serve as aerial communication platforms and users, respectively. Furthermore, we point out promising directions for future research and investigation.

Accessing From The Sky: A Tutorial on UAV Communications for 5G and Beyond

The LMMSE (linear minimum mean square error) algorithm is one of the best linear receivers for DS-CDMA (direct sequence-code division multiple access). However, for the case of MIMO/BLAST (multiple input, multiple output/Bell Laboratories layered space time) with high loading, the perceived complexity of the LMMSE receiver is taken as too big, and thus other types of receivers are employed, yielding worse results. In this paper, we investigate the complexity of the solution to the MIMO LMMSE receiver's equations using block-Fourier algorithms, for both steady and unsteady channel situations.

Employing the Block Fourier Algorithm for Solving the LMMSE Receiver Equation Under Variable Channel Conditions

In this paper, we present a probabilistic MonteCarlo method to simulate the electromagnetic field in multiple interface problems based on transmission lines We present numerical results for the simplest case of the propagation of gaussian pulses and sinusoidal sources in lossy and lossless dielectric slabs which demonstrate the applicability of the method to solve network problem in microwave theory We also present a methodology to obtain the amplitude and phase associated with every point in the domain without resorting to fourier transformations This method is an important achievement in the development of our Monte-Carlo method because otherwise we would have to integrate the field over time to achieve similar results, which would be unpractical for a Monte-Carlo method Finally, we compare our results with well established theory to validate the methods

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Application of a Mesh Free Monte-Carlo Method to the Analysis of Dielectric Slabs in Electromagnetics

The concept of cooperative Multiple-Input-Multiple-Output (MIMO), also referred to as network MIMO, or as Coordinated Multi-Point Transmission (CoMP), was standardized in 3GPP Release 11. The goal of CoMP is to improve the coverage of high data rates and cell-edge throughput, and also to increase system throughput. In this paper we analyze only the latter scenario, using system level simulations in accordance with 3GPP guidelines. It is shown that the use of joint coordinated multipoint transmission achieves additional throughput gains. However, the gains depend on the scheduling type. This paper also indicates that the criterion of fairness is an important parameter when the number of users is high.

Coordinated Multi-Point MIMO Processing for 4G

In this paper, a low-complexity iterative detector with frequency domain equalization is proposed for generalized spatial modulation (GSM) aided single carrier (SC) transmissions in frequency selective channels. The detector comprises three main separate tasks namely, multiple-input multiple-output (MIMO) equalization, active antenna detection and symbol wise demodulation. This approach makes the detector suitable for a broad range of MIMO configurations, which includes single-user and multiuser scenarios, as well as arbitrary signal constellations. Simulation results show that the receiver can cope with the intersymbol interference induced by severe time dispersive channels and operate in difficult underdetermined scenarios where the total number of transmitter antennas is substantially larger than the number of receiver antennas.

Iterative Signal Detection with Frequency Domain Equalization for Generalized Spatial Modulation Aided Single-Carrier Systems

In recent years there has been a growing interest in reconfigurable intelligent surfaces (RISs) as enablers for the realization of smart radio propagation environments which can provide performance improvements with low energy consumption in future wireless networks. However, to reap the potential gains of RIS it is crucial to jointly design both the transmit precoder and the phases of the RIS elements. Within this context, in this paper we study the use of multiple RIS panels in a parallel or multi-hop configuration with the aim of assisting a multi-stream multiple-input multiple-output (MIMO) communication. To solve the nonconvex joint optimization problem of the precoder and RIS elements targeted at maximizing the achievable rate, we propose a novel iterative algorithm based on the monotone accelerated proximal gradient (mAPG) method which includes an extrapolation step for improving the convergence speed and monitoring variables for ensuring sufficient descent of the algorithm. Based on the sufficient descent property we then present a detailed convergence analysis of the algorithm which includes expressions for the step size. Simulation results in different scenarios show that the use of multiple RIS panels combined with the proposed algorithm can be an effective solution for improving the achievable rates.

https://ieeexplore.ieee.org/ielx7/8782661/8901158/10146011.pdf

Nuno Souto

Papers

Employing the Block Fourier Algorithm for Solving the LMMSE Receiver Equation Under Variable Channel Conditions

Application of a Mesh Free Monte-Carlo Method to the Analysis of Dielectric Slabs in Electromagnetics

Coordinated Multi-Point MIMO Processing for 4G

Iterative Signal Detection with Frequency Domain Equalization for Generalized Spatial Modulation Aided Single-Carrier Systems

Joint Beamforming Algorithm for Multi-Stream MIMO Systems Assisted by Multiple Reconfigurable Intelligent Surfaces