5G will have to cope with a high degree of heterogeneity in terms of services and requirements. Among these latter, the flexible and efficient use of non-contiguous unused spectrum for different network deployment scenarios is considered a key challenge for 5G systems. To maximize spectrum efficiency, the 5G air interface technology will also need to be flexible and capable of mapping various services to the best suitable combinations of frequency and radio resources. In this work, we propose a comparison of several 5G waveform candidates (OFDM, UFMC, FBMC and GFDM) under a common framework. We assess spectral efficiency, power spectral density, peak-to-average power ratio and robustness to asynchronous multi-user uplink transmission. Moreover, we evaluate and compare the complexity of the different waveforms. In addition to the complexity analysis, in this work, we also demonstrate the suitability of FBMC for specific 5G use cases via two experimental implementations. The benefits of these new waveforms for the foreseen 5G use cases are clearly highlighted on representative criteria and experiments.

During the past few years, we are witnessing the emergence of 5G and its high-level performance targets. Waveform (WF) design is one of the important aspects for 5G that received considerable attention from the research community in recent years. To find an alternative to the classical Orthogonal Frequency Division Multiplexing (OFDM), several multicarrier approaches addressing different 5G technical challenges, have been proposed. In this paper, we focus on Critical Machine-Type Communications (C-MTC) which is one of the key features of the foreseen 5G system. We provide a comparative performance study of the most promising multicarrier waveforms. We consider several C-MTC Key Performance Indicators (KPIs): Out-of-band radiations, spectral efficiency, End-to-End Physical layer latency, robustness to time and frequency synchronization errors, power fluctuation and transceiver complexity. The investigated multicarrier WFs are classified into three groups based on their ability to keep the orthogonality: in the complex domain e.g. most of the OFDM-inspired WFs, in the real domain like Offset-QAM based techniques and non-orthogonal WFs like Generalized Frequency Division Multiplexing (GFDM) and Filter Bank-based MultiCarrier (FBMC)-QAM. Finally, performances of these WFs are thoroughly discussed in order to highlight their pros and cons and permit a better understanding of their capabilities in the context of C-MTC.

Relaxed synchronization and access to fragmented spectrum are considered for future generations of wireless networks. Frequency division multiple access for filter bank multicarrier (FBMC) modulation provides promising performance without strict synchronization requirements contrary to conventional orthogonal frequency division multiplexing (OFDM). The architecture of a FBMC receiver suitable for this scenario is considered. Carrier frequency offset (CFO) compensation is combined with intercarrier interference (ICI) cancellation and performs well under very large frequency offsets. Channel estimation and interpolation had to be adapted and proved effective even for heavily fragmented spectrum usage. Channel equalization can sustain large delay spread. Because all the receiver baseband signal processing functionalities are proposed in the frequency domain, the overall architecture is suitable for multiuser asynchronous transmission on fragmented spectrum.

The radio spectrum above 90GHz offers opportunities for huge signal bandwidths, and thus unprecedented increase in the wireless network capacity, beyond the performance defined for the 5G technology. This spectrum is essentially exploited for scientific services, but attracts nowadays many interest within the wireless telecommunications research community, following the same trend as in previous network generations. The BRAVE project that was launched at early 2018, aims at the elaboration of new waveforms able to efficiently operate in the 90-200 GHz spectrum. The researches rely on three complementary works: the definition of relevant communications scenarios (spectrum usage, application, environment, etc); the development of realistic models for the physical layer (propagation channel and RF equipments); and the elaboration of a single-carrier modulation compliant with the propagation channel properties, and allowing improvement on the spectral and energy efficiency. The motivation for this work, and the preliminary results on the waveform definition, are exposed in the present paper.

To meet the requirements of beyond 5G networks, the significant amount of unused spectrum in sub-TeraHertz frequencies is contemplated for high-rate wireless communications. Yet, the performance of sub-TeraHertz systems is severely degraded by strong oscillator phase noise. We investigate in this paper the design of digital communications robust to phase noise. This problem is addressed in three steps: the characterization of the phase noise channel, the design of the optimum receiver, and the optimization of the modulation scheme. This paper proposes a joint performance and implementation optimization. First, we address the design of the demodulation scheme for phase noise channels and propose the polar metric, a soft-decision rule for symbol detection. It is shown that performance gains are achieved for coded and uncoded systems with valuable complexity reductions of the receiver. Second, we investigate the optimization of the modulation scheme for phase noise. We demonstrate that using a constellation defined upon a lattice in the amplitude-phase domain leads to significant performance gains and a low-complexity implementation. Thereupon, we propose the Polar-QAM scheme with efficient binary labeling and demodulation. Numerical simulation results show that the proposed modulation and demodulation schemes offer valuable solutions to achieve high-rate communications on systems strongly impaired by phase noise.