In this paper, we consider a novel mobile relaying technique, where the relay nodes are mounted on unmanned aerial vehicles (UAVs) and hence are capable of moving at high speed. Compared with conventional static relaying, mobile relaying offers a new degree of freedom for performance enhancement via careful relay trajectory design. We study the throughput maximization problem in mobile relaying systems by optimizing the source/relay transmit power along with the relay trajectory, subject to practical mobility constraints (on the UAV’s speed and initial/final relay locations), as well as the information-causality constraint at the relay. It is shown that for the fixed relay trajectory, the throughput-optimal source/relay power allocations over time follow a “staircase” water filling structure, with non-increasing and non-decreasing water levels at the source and relay, respectively. On the other hand, with given power allocations, the throughput can be further improved by optimizing the UAV’s trajectory via successive convex optimization. An iterative algorithm is thus proposed to optimize the power allocations and relay trajectory alternately. Furthermore, for the special case with free initial and final relay locations, the jointly optimal power allocation and relay trajectory are derived. Numerical results show that by optimizing the trajectory of the relay and power allocations adaptive to its induced channel variation, mobile relaying is able to achieve significant throughput gains over the conventional static relaying.

Throughput Maximization for UAV-Enabled Mobile Relaying Systems

Introduction. Principles, Methods and Performance Limits. Carrier Frequency Recovery with Linear Modulations. Carrier Frequency Recovery with CPM Modulations. Carrier Phase Recovery with Linear Modulations. Carrier Phase Recovery with CPM Modulations. Timing Recovery in Baseband Transmission. Timing Recovery with Linear Modulations. Timing Recovery with CPM Modulations. Index.

https://www.springer.com/productFlyer_978-0-306-45725-8.pdf?SGWID=0-0-1297-33351749-0

Synchronization Techniques for Digital Receivers

Orthogonal frequency division multiple access (OFDMA) has recently attracted vast research attention from both academia and industry and has become part of new emerging standards for broadband wireless access. Even though the OFDMA concept is simple in its basic principle, the design of a practical OFDMA system is far from being a trivial task. Synchronization represents one of the most challenging issues and plays a major role in the physical layer design. The goal of this paper is to provide a comprehensive survey of the latest results in the field of synchronization for OFDMA systems, with tutorial objectives foremost. After quantifying the effects of synchronization errors on the system performance, we review some common methods to achieve timing and frequency alignment in a downlink transmission. We then consider the uplink case, where synchronization is made particularly difficult by the fact that each user's signal is characterized by different timing and frequency errors, and the base station has thus to estimate a relatively large number of unknown parameters. A second difficulty is related to how the estimated parameters must be employed to correct the uplink timing and frequency errors. The paper concludes with a comparison of the reviewed synchronization schemes in an OFDMA scenario inspired by the IEEE 802.16 standard for wireless metropolitan area networks.

Synchronization Techniques for Orthogonal Frequency Division Multiple Access (OFDMA): A Tutorial Review

The main characteristic of Reconfigurable Computing is the presence of hardware that can be reconfigured to implement specific functionality more suitable for specially tailored hardware than on a simple uniprocessor. Reconfigurable computing systems join microprocessors and programmable hardware in order to take advantage of the combined strengths of hardware and software and have been used in applications ranging from embedded systems to high performance computing. Many of the fundamental theories have been identified and used by the Hardware/Software Co-Design research field. Although the same background ideas are shared in both areas, they have different goals and use different approaches.This book is intended as an introduction to the entire range of issues important to reconfigurable computing, using FPGAs as the context, or "computing vehicles" to implement this powerful technology. It will take a reader with a background in the basics of digital design and software programming and provide them with the knowledge needed to be an effective designer or researcher in this rapidly evolving field.

· Treatment of FPGAs as computing vehicles rather than glue-logic or ASIC substitutes
· Views of FPGA programming beyond Verilog/VHDL
· Broad set of case studies demonstrating how to use FPGAs in novel and efficient ways

Reconfigurable Computing: The Theory and Practice of FPGA-Based Computation

DVB-S2 is the second-generation specification for satellite broad-band applications, developed by the Digital Video Broadcasting (DVB) Project in 2003. The system is structured as a toolkit to allow the implementation of the following satellite applications: TV and sound broadcasting, interactivity (i.e., Internet access), and professional services, such as TV contribution links and digital satellite news gathering. It has been specified around three concepts: best transmission performance approaching the Shannon limit, total flexibility, and reasonable receiver complexity. Channel coding and modulation are based on more recent developments by the scientific community: low density parity check codes are adopted, combined with QPSK, 8PSK, 16APSK, and 32APSK modulations for the system to work properly on the nonlinear satellite channel. The framing structure allows for maximum flexibility in a versatile system and also synchronization in worst case configurations (low signal-to-noise ratios). Adaptive coding and modulation, when used in one-to-one links, then allows optimization of the transmission parameters for each individual user,dependant on path conditions. Backward-compatible modes are also available,allowing existing DVB-S integrated receivers-decoders to continue working during the transitional period. The paper provides a tutorial overview of the DVB-S2 system, describing its main features and performance in various scenarios and applications.

/pdf/dvb-s2-the-second-generation-standard-for-satellite-broad-1hexqkf3ux.pdf

DVB-S2: The Second Generation Standard for Satellite Broad-Band Services

In this chapter we investigate timing recovery in PAM baseband transmission. Additional features that arise with modulated signals will be explored in Chapters 8 and 9 for PAM and CPM modulations, respectively. The reason for first concentrating on baseband signals is motivated by the need of avoiding any distractions caused by modulation matters. As we shall see in the later chapters, such matters are easily taken into account when the basic concepts relevant to baseband systems are understood.

Timing Recovery in Baseband Transmission

This chapter lays the groundwork for the material in the book and addresses three major themes. Section 2.2 describes synchronization functions in a digital receiver and indicates methods to pinpoint design limits on the synchronization errors. Section 2.3 is an overview of maximum likelihood parameter estimation theory, with emphasis on synchronization applications. A distinction is made between wanted and unwanted parameters, the former being those of interest in a given situation and with respect to which the maximum of a likelihood function is to be sought. The computation of likelihood functions for wanted parameters is investigated. Section 2.4 establishes limits to the performance of practical synchronizers. The most popular limit is the Cramer-Rao bound to the variance of unbiased estimators. It is argued that this limit is difficult to compute in most practical cases. A simpler limit is the modified Cramer-Rao bound, which is used as a benchmark in performance evaluations throughout the book.

Principles, Methods and Performance Limits

Continuous phase modulation (CPM) encompasses a class of signaling schemes that conserve and reduce signal energy and bandwidth at the same time. Furthermore, the signals in this class have a constant envelope and therefore are very attractive in radio channels employing low-cost non-linear power amplifiers. Notwithstanding these favorable features, current CPM applications are still limited to a few simple modulation schemes (basically, MSK and its generalizations) because of implementation complexity and synchronization problems [1]. Research efforts are under way and advances in these areas are expected in the near future.

Carrier Frequency Recovery with CPM Modulations

In this chapter we investigate algorithms for carrier phase estimation with linear modulations. As with frequency recovery, ML estimation methods will play a central role in our study. We shall see that various approximations to the ML formulation are possible, leading to different estimation methods. Thus, a rather disparate set of synchronization schemes is anticipated. This is also a consequence of the many scenarios that can be thought of, depending on the specific modulation format and the availability of data/clock information. In this regard the following categories may be envisaged: 

(i)

Modulation format: 


Modulation may be either offset or non-offset.








(ii)

Additional knowledge: 


Clock information may be available or not.


Information symbols may be known or not. When they are, they may come either from a known preamble (data-aided schemes) or from the detector output (decision-directed schemes)








(iii)

Estimator topology: 


Estimators may be either open loop or closed loop.

Carrier Phase Recovery with Linear Modulations

In this chapter we consider carrier phase recovery for CPM signaling. By and large the presentation follows the same route taken with linear modulations. In particular, data-aided (DA) estimation is considered first, then we concentrate on decision-directed (DD) methods and, finally, on non-data-aided (NDA) techniques (either clock-aided or non-clock-aided).

Aldo N. D’Andrea

Papers

Timing Recovery in Baseband Transmission

Principles, Methods and Performance Limits

Carrier Frequency Recovery with CPM Modulations

Carrier Phase Recovery with Linear Modulations

Carrier Phase Recovery with CPM Modulations