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

We propose an algorithm for joint carrier phase and timing estimation with offset quadriphase modulation (OQPSK) signaling. The derivation is based on maximum-likelihood arguments and leads to a feedforward structure that operates on signal samples taken at the bit rate. Phase and timing algorithms operate in parallel-not sequentially-and provide their estimates in a fixed time. The synchronizer is readily implemented in digital form and is particularly suitable for burst mode transmissions. Its performance is analytically assessed and verified by simulations. Comparisons are made with other methods described in the literature.

Feedforward joint phase and timing estimation with OQPSK modulation

This paper presents a novel technique for cross-layer adaptive modulation and coding, suited for bit interleaved turbo-coded OFDM packet transmission, and aimed at maximizing the goodput (i.e., the number of data bits delivered without error per unit of time). The optimization problem is formalized through an accurate modeling on the link performance, and a greedy iterative solution is derived. Simulation results demonstrate that performance improvement provided by the proposed method amount to 4 dB with respect to static transmission and about 1.2 dB with respect to adaptive transmission with uniform bit allocation.

A greedy algorithm for goodput-oriented AMC in turbo-coded OFDM

Feedforward algorithms are investigated for estimating carrier frequency, carrier phase and symbol timing in MSK-type modulations. Their derivation is based on maximum likelihood criteria and leads to synchronization schemes that are suitable for full digital implementation. The operation of these algorithms is decoupled, meaning that the frequency parameter is measured first and independently of the others. Subsequently, phase and timing are computed through simple formulas. The performance of the proposed algorithms is investigated analytically and by simulation and the results are compared with Cramer-Rao bounds. It turns out that the estimation accuracy is very close to the theoretical limits. The frequency estimation range is in the order of 20% of the symbol rate for MSK and 10% for GMSK. A frequency estimation threshold lower that 4 dB is achieved with fairly short observation windows.

Feedforward Synchronization Schemes for MSK‐Type Signals

A frequency recovery system accomplishes two basic functions: (i) it derives an estimate v of the carrier frequency offset; (ii) it compensates for this offset by counter-rotating the received waveform r(t) at an angular speed 2πv. In the ensuing discussion we distinguish between two major cases [1]: 

(i)

the offset is much smaller than 1/T,




(ii)

the offset is on the order of the symbol rate 1/T.

Aldo N. D’Andrea

Papers

Synchronization Techniques for Digital Receivers

Feedforward joint phase and timing estimation with OQPSK modulation

A greedy algorithm for goodput-oriented AMC in turbo-coded OFDM

Feedforward Synchronization Schemes for MSK‐Type Signals

Carrier Frequency Recovery with Linear Modulations