Signals satisfying low Peak-to-Average-Power Ratio (PAPR) properties are desirable in order to ensure the efficient operation of power amplifiers (PA) and to enhance the uplink (UL) coverage for user equipment. Building on the Discrete-Fourier-Transform spread Orthogonal Frequency Division Multiplexing (DFT-s-OFDM) waveform, we investigate in this paper a novel communication scheme capable of achieving significant PAPR gains for higher order modulations based on controlling the transition probabilities between time domain symbols. The design draws its inspiration from probabilistic amplitude shaping (PAS) with the use of a distribution matcher (DM) to generate sequences of symbols approximating the desired transitions. The performance is evaluated according to the PAPR and cubic metric (CM) as measures for a 16-QAM modulation order. The bit-error-rate (BER) performance curves are also assessed in comparison with the 16-QAM baseline scheme.

Technology advances have enabled unmanned aerial vehicles (UAV) to stay afloat in the stratosphere for several months as base station platforms with the communication payload powered by solar energy. These UAV-based High Altitude Platform Stations (HAPS) can provide i) connectivity for remote areas not served by terrestrial networks, ii) global coverage for IoT devices, and iii) services for public safety and transportation industries. At a typical altitude of 20 Km, an HAPS can cover a large service area with a higher throughput and a lower latency compared to satellite links.In this paper, we present a reference design of a New Radio (NR) HAPS communication system comprised of both service and feeder links that can serve multiple cells within a large coverage area. The use of an adaptive antenna array with beam steering enables the system to continuously serve users from the same cell while the aircraft conducts a repetitive flight pattern above the fixed service area. Achievable capacity and coverage of the service link design at a sub-6 GHz carrier frequency are first estimated in a link budget analysis and then evaluated through Monte Carlo simulations. We observe that good spectral efficiency and coverage can be expected for outdoor line-of-sight users in the downlink, while the uplink performance is limited by the transmit power and antenna gain of the user terminal. We also demonstrate that 5G NR in the mmWave band can be used for the feeder link and can satisfy the throughput and availability requirement.

We generalize probabilistic amplitude shaping (PAS) with binary codes [1] to the case of non-binary codes defined over prime finite fields. Firstly, we introduce probabilistic shaping via time sharing where shaping applies to information symbols only. Then, we design circular quadrature amplitude modulations (CQAM) that allow to directly generalize PAS to prime finite fields with full shaping.

We consider spatially coupled low-density parity-check codes with finite smoothing parameters. A finite smoothing parameter is important for designing practical codes that are decoded using low-complexity windowed decoders. By optimizing the amount of coupling between spatial positions, we show that we can construct codes with excellent thresholds and small rate loss, even with the lowest possible smoothing parameter and large variable node degrees, which are required for low error floors. We also establish that the decoding convergence speed is faster with non-uniformly coupled codes, which we verify by density evolution of windowed decoding with a finite number of iterations. We also show that by only slightly increasing the smoothing parameter, practical codes with potentially low error floors and thresholds close to capacity can be constructed. Finally, we give some indications on protograph designs.

We consider non-binary product codes with MDS components and their iterative row-column algebraic decoding on the erasure channel. Both independent and block erasures are considered in this paper. A compact graph representation is introduced on which we define double-diversity edge colorings via the rootcheck concept. An upper bound of the number of decoding iterations is given as a function of the graph size and the color palette size M. Then, we propose a differential evolution edge coloring algorithm that produces colorings with a large population of minimal rootcheck order symbols. The complexity of this algorithm per iteration is o(Mℵ), for a given differential evolution parameter ℵ, where Mℵitself is small with respect to the huge cardinality of the coloring ensemble. Stopping sets of a product code are defined in the context of MDS components and a relationship is established with the graph representation. A full characterization of these stopping sets is given up to a size (d + 1)2, where d is the minimum Hamming distance of the MDS component code. The performance of MDS-based product codes with and without double-diversity coloring is analyzed in presence of both the block and the independent erasures. In the latter case, ML and iterative decoding are proven to coincide at small channel erasure probability. Furthermore, numerical results show excellent performance in presence of unequal erasure probability due to double-diversity colorings.

Stopping sets for MDS-based product codes under iterative row-column algebraic decoding are analyzed in this paper. A union bound to the performance of iterative decoding is established for the independent symbol erasure channel. This bound is tight at low and very low error rates. We also proved that the performance of iterative decoding reaches the performance of Maximum-Likelihood decoding at vanishing channel erasure probability. Numerical results are shown for product codes at different coding rates.

A new method for spatial coupling of low-density parity-check ensembles is proposed. The method is inspired from overlapped layered coding. Edges of local ensembles and those defining the spatial coupling are separately built. The new method allows the construction of non-uniform coupling chains with near-Shannon spatially-varying thresholds under iterative decoding. A direct application of non-uniform spatial coupling is unequal error protection of information.