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.

/pdf/a-survey-of-channel-modeling-for-uav-communications-dsksrzxhfd.pdf

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.

/pdf/mobile-video-transmission-using-scalable-video-coding-4uti9fdg6x.pdf

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

Whenever there is a collision involving several transmitted packets, the traditional approach for MAC (Medium Access Control) protocols is to discard all packets involved and request their retransmission, with a consequent loss in the overall throughput. Based on conventional Multiple Input Multiple Output (MIMO) techniques, in this paper we propose a multipacket detector for OFDM schemes (Orthogonal Frequency Division Multiplexing) that allows an efficient packet separation in the presence of collisions and can achieve high throughputs. We show that reliable detection is possible as long as different interleavers are used for different retransmissions. We also include a method to estimate the users involved in the collision, as well as well as the corresponding channel characteristics.

Efficient Detection Technique for Multiple Packet Collisions in OFDM Systems

A coordinated multi-resolution and multi-point MIMO transmission method for the LTE-Advanced is presented considering the Evolved-Multimedia Broadcast/Multicast Service (E-MBMS). Fixed relays with MIMO and different adaptive frequency reuse schemes are considered in the proposed scheme to improve the E-MBMS spectral efficiency at the cell borders and/or to save transmission power from the base stations and relays. In order to provide additional diversity over Rayleigh multi-path fading channels, a signal space diversity based on Complex Rotation Matrices (CRM) is used, associated to MIMO, as a multi-resolution technique. The decoding of these signals are facilitated with the use of Maximum Likelihood Soft Output (MLSO) criterion, included in the proposed receiver. The link performance of the MIMO system turbo-coded with hierarchical constellations and CRM is analyzed in terms of bit and block error rate (BER/BLER). The corresponding system level coverage and throughput gains are also evaluated associated to the presence or not of fixed relays and measuring the maximum spectral efficiencies at cell borders of single cell point-to-multipoint or single frequency network. The influence of the cell radius in the performance of the previous cellular topologies with coordinated MIMO transmissions is also evaluated.

/pdf/on-the-multi-resolution-techniques-for-lte-advanced-px4m3s2eqz.pdf

On the Multi-Resolution Techniques for LTE-Advanced

In this paper we describe parallel concatenations of two convolutional encoders based on nonlinear cyclic codes with codewords of length n=2m, m being a positive integer. The resulting turbo codes have a very low coding rate, which makes them especially suitable for spread spectrum systems where they can be used for achieving simultaneously error correction and bandwidth expansion. Due to the cyclic properties and codeword length of the component codes, branch metrics can be efficiently computed using the Fast Fourier Transform, which enables simple implementation of the encoder and decoder for the component convolutional coding schemes. Among the possible base nonlinear cyclic codes, special attention is given to the TCH (Tomlinson-Cercas-Hughes) codes family due to their good autocorrelation properties, which enables the resulting turbo codes to achieve good BER performance. These schemes, similarly to the superorthogonal turbo codes, usually perform better than the traditional turbocodes at the cost of bandwidth expansion. Simulation results are presented both for the AWGN and for the uncorrelated Rayleigh fading channels. One of the advantages of the presented solution over the traditional turbo superorthogonal codes is its ability to improve the synchronization process at the receiver due to the good autocorrelation properties of the available nonlinear codes (specially TCH codes).

Low rate turbo codes based on nonlinear cyclic codes

Recent studies have determined the performance of TCH(n,k) (Tomlinson, Cercas, Hughes) codes in different environments, namely for mobile satellite channels for which TCH codes of small length n (e.g. 16) present some advantages when compared with TCH codes of higher length (e.g. 256). However, the correlation characteristics of TCH codes of small length present some peaks that deteriorate its performance. In this paper we present a method to properly bit-map the incoming data bits to the code words so as to minimize this effect. The improvement in performance was obtained by simulation and is compared with previous known results.

Optimum bit-mapping of TCH codes

HSDPA is the already standardized evolution of UMTS to significantly increase the data rate achieving peak values over 10 Mbit/s. This paper addresses the performance improvement of the HSDPA in multipath fading channels when using several transmitting antennas at the BS. 3GPP specifications define several transmit diversity schemes for two antennas, namely the standardized closed loop modes 1 and 2 and the open loop space time transmit diversity (STTD). This paper studies these techniques but also other transmitting schemes such as open loop modes using space time block codes (STBC) for 4 and 8 transmitting antennas, selective transmit diversity (STD) and hybrid modes combining space time block codes and STD. The performance impact of all these techniques is compared and evaluated using a HSDPA link level simulator.

Nuno Souto

Papers

Efficient Detection Technique for Multiple Packet Collisions in OFDM Systems

On the Multi-Resolution Techniques for LTE-Advanced

Low rate turbo codes based on nonlinear cyclic codes

Optimum bit-mapping of TCH codes

Transmit diversity schemes for high speed downlink packet access in 3.5G cellular systems