Waveform Design for 5G and beyond Systems

5G traffic has very diverse requirements with respect to data rate, delay, and reliability. The concept of using multiple OFDM numerologies adopted in the 5G NR standard will likely meet these multiple requirements to some extent. However, the traffic is radically accruing different characteristics and requirements when compared with the initial stage of 5G, which focused mainly on high-speed multimedia data applications. For instance, applications such as vehicular communications and robotics control require a highly reliable and ultra-low delay. In addition, various emerging M2M applications have sparse traffic with a small amount of data to be delivered. The state-of-the-art OFDM technique has some limitations when addressing the aforementioned requirements at the same time. Meanwhile, numerous waveform alternatives, such as FBMC, GFDM, and UFMC, have been explored. They also have their own pros and cons due to their intrinsic waveform properties. Hence, it is the opportune moment to come up with modification/variations/combinations to the aforementioned techniques or a new waveform design for 5G systems and beyond. The aim of this Special Issue is to provide the latest research and advances in the field of waveform design for 5G systems and beyond

Orthogonal transmultiplexers : extensions to digital subscriber line (DSL) communications

An orthogonal transmultiplexer which unifies multirate filter bank theory and communications theory is investigated in this dissertation. Various extensions of the orthogonal transmultiplexer techniques have been made for digital subscriber line communication applications. It is shown that the theoretical performance bounds of single carrier modulation based transceivers and multicarrier modulation based transceivers are the same under the same operational conditions. Single carrier based transceiver systems such as Quadrature Amplitude Modulation (QAM) and Carrierless Amplitude and Phase (CAP) modulation scheme, multicarrier based transceiver systems such as Orthogonal Frequency Division Multiplexing (OFDM) or Discrete Multi Tone (DMT) and Discrete Subband (Wavelet) Multicarrier based transceiver (DSBMT) techniques are considered in this investigation. The performance of DMT and DSBMT based transceiver systems for a narrow band interference and their robustness are also investigated. It is shown that the performance of a DMT based transceiver system is quite sensitive to the location and strength of a single tone (narrow band) interference. The performance sensitivity is highlighted in this work. It is shown that an adaptive interference exciser can alleviate the sensitivity problem of a DMT based system. The improved spectral properties of DSBMT technique reduces the performance sensitivity for variations of a narrow band interference. It is shown that DSBMT technique outperforms DMT and has a more robust performance than the latter. The superior performance robustness is shown in this work. Optimal orthogonal basis design using cosine modulated multirate filter bank is discussed. An adaptive linear combiner at the output of analysis filter bank is implemented to eliminate the intersymbol and interchannel interferences. It is shown that DSBMT is the most suitable technique for a narrow band interference environment. A blind channel identification and optimal MMSE based equalizer employing a nonmaximally decimated filter bank precoder / postequalizer structure is proposed. The performance of blind channel identification scheme is shown not to be sensitive to the characteristics of unknown channel. The performance of the proposed optimal MMSE based equalizer is shown to be superior to the zero-forcing equalizer

Enhanced Multicarrier Techniques for Professional Ad-Hoc and Cell-Based Communications (EMPhAtiC) Document Number D3.3 Reduction of PAPR and non linearities effects

Livrable d'un projet Européen EMPHATICLike other multicarrier modulation techniques, FBMC suffers from high peak-to-average power ratio (PAPR), impacting its performance in the presence of a nonlinear high power amplifier (HPA) in two ways. The first impact is an in-band distortion affecting the error rate performance of the link. The second impact is an out-of-band effect appearing as power spectral density (PSD) regrowth, making the coexistence between FBMC based broad-band Professional Mobile Radio (PMR) systems with existing narrowband systems difficult to achieve. This report addresses first the theoretical analysis of in-band HPA distortions in terms of Bit Error Rate. Also, the out-of band impact of HPA nonlinearities is studied in terms of PSD regrowth prediction. Furthermore, the problem of PAPR reduction is addressed along with some HPA linearization techniques and nonlinearity compensation approaches

Communication Subsystems for Emerging Wireless Technologies

The paper describes a multi-disciplinary design of modern communication systems. The design starts with the analysis of a system in order to define requirements on its individual components. The design exploits proper models of communication channels to adapt the systems to expected transmission conditions. Input filtering of signals both in the frequency domain and in the spatial domain is ensured by a properly designed antenna. Further signal processing (amplification and further filtering) is done by electronics circuits. Finally, signal processing techniques are applied to yield information about current properties of frequency spectrum and to distribute the transmission over free subcarrier channels

Multiantenna Interference Mitigation Schemes and Resource Allocation for Cognitive Radio

Maximum and efficient utilization of available resources has been a central theme of research on various areas of science and engineering. Wireless communication is not an exception to this. With the rapid growth of wireless communication applications, radio frequency spectrum has become a valuable commodity. Supporting very high demands for data rate and throughput has become a challenging problem which requires innovative solutions. Dynamic spectrum sharing (DSS) based cognitive radio (CR) is envisioned as a promising technology for future wireless communication systems, such as fifth generation (5G) further development and sixth generation (6G). Extensive research has been done in the areas of CRs and it is considered to mitigate the spectral crowding problem by introducing the notion of opportunistic spectrum usage. Spectrum sensing, which enables CRs to identify spectral holes, is a critical component in CR technology. Furthermore, improving the efficiency of the radio spectrum use through spectrum sensing and dynamic spectrum access (DSA) is one of the emerging trends. In the first part of this thesis, we focus on enhancing the spectrum usage of CR’s using interference cancellation methods that provides considerable performance gains with realistic computational complexity, especially, in the context of the widely used multicarrier waveforms. The primary focus is on interference rejection combining (IRC) methods, applied to the black-space cognitive radio (BS-CR). Earlier studies on the BS-CR in the literature were focused on using CRs as repeaters for the primary transmitter to guarantee that the CR is not causing significant interference to nearby primary users’ receivers. This kind of approaches are transmitter-centric in nature. In this thesis, receiver-centric approaches such as multi-antenna diversity combining, especially enhanced IRC methods, are considered and evaluated. IRC methods have been widely studied and adopted in several practical wireless communication systems. We focus on developing such BS-CR schemes under strong interference conditions, which has not been studied in the CR literature so far. Spatial covariance matrix estimation under mobility and high carrier frequencies is found to be the most critical part of such scheme. Algorithms and methods to mitigate these effects are developed in this thesis and they are evaluated under realistic BS-CR receiver operating conditions. We use sample covariance estimation approach with silent gaps in the CR transmisison. Covariance interpolation between silent gaps improves greatly the robustness with time-varying channels. Good link performance can be reached with low mobility at carrier frequency considered for the TV white-spaced case. The proposed BS-CR scheme could be feasible at below 6 GHz frequencies with pedestrian mobilities. The second part of this thesis investigates the effect of radio frequency (RF) impairments on the performance of the cognitive wireless communication. There are various unavoidable imperfections, mainly due to the limitations of analog high-frequency transmitter and receiver circuits. These imperfections include power amplifier (PA) non-linearities, receiver nonlinearities, and carrier frequency offset (CFO), which are considered in this study. These effects lead to significant signal distortion and, as a result of this, the wireless link quality may deteriorate. In multicarrier communications such signal distortions may lead to additional interference, and it is important to evaluate their effects on spectrum sensing quality and on the performance of the proposed BS-CR scheme. This part of the thesis provides critical analysis and insights into such issues caused by RF imperfections and demonstrates the need for designing proper compensation techniques required to avoid/reduce such degradations. It is found that the transmitter’s PA nonlinearities affect in the same way as in basic OFDM systems and BS-CR receiver’s linearity requirements are similar to those for advanced DSP-intensive software defined radios. The CR receiver’s CFO with respect to the PU has the most critical effect. However, synchronizing the CR with the needed high accuracy is considered achievable due to the PU signal’s high-power level. The final part of the thesis briefly looks at alternate waveforms and techniques that can be used in CRs. The filter bank multicarrier (FBMC) waveforms are considered as an alternative to the widely used OFDM schemes. Here the core idea is interference avoidance, targeting to reduce the interference leakage between CRs and the primary systems, by means of using a waveform with good spectrum localization properties. FBMC system’s performance is compared with OFDM based system in the context of CRs. The performance is compared from a combined spectrum sensing and resource allocation point of view through simulations. It is found that well-localized CR waveforms improve the CR link capacity, but with poorly localized primary signals, these possibilities are rather limited

An enhanced multicarrier modulation system for mobile communications

PhD ThesisThe recent revolution in mobile communications and the increased demand on more efficient transmission systems influence the research to enhance and invent new modulation techniques. Orthogonal frequency division multiplexing with offset quadrature amplitude modulation (OFDM/OQAM) is one of the multicarrier modulations techniques that overcomes some of the weaknesses of the conventional OFDM in term of bandwidth and power efficiencies. This thesis presents a novel multicarrier modulation scheme with improved performance in mobile communications context. Initially, the theoretical principles behind OFDM and OFDM/OQAM are discussed and the advantages of OFDM/OQAM over OFDM are highlighted. The time-frequency localization of pulse shapes is examined over different types of pulses. The effect of the localization and the pulse choice on OFDM/OQAM performance is demonstrated. The first contribution is introducing a new variant of multicarrier modulation system based on the integration of the Walsh-Hadamard transform with the OFDM/OQAM modulator. The full analytical transmission model of the system is derived over flat fading and frequency selective channels. Next, because of the critical requirement of low implementation complexity in mobile systems, a new fast algorithm transform is developed to reduce the implementation complexity of the system. The introduced fast algorithm has demonstrated a remarkable 60 percent decrease in the hardware requirement compared to the cascaded configuration. Although, the problem of high peak to average power ratio (PAPR) is one of the main drawbacks that associated with most multicarrier modulation techniques, the new system achieved lower values compared to the conventional systems. Subsequently, three new algorithms to reduce PAPR named Walsh overlapped selective mapping (WOSLM) for a high PAPR reduction, simplified selective mapping (SSLM) for a very low implementation complexity and Walsh partial transmit sequence (WPTS), are developed. Finally, in order to assess the reliability of the presented system in this thesis at imperfect environments, the performance of the system is investigated in the presence of high power amplifier, channel estimation errors, and carrier frequency offset (CFO). Two channel estimations algorithms named enhanced pair of pilots (EPOP) and averaged enhanced pair of pilots (AEPOP), and one CFO estimator technique called frequency domain (FD) CFO estimator, are suggested to provide reliable performance.Ministry of Higher Education and Scientific Research (MOHSR) of Ira

D13.1 Fundamental issues on energy- and bandwidth-efficient communications and networking

Deliverable D13.1 del projecte europeu NEWCOM#The report presents the current status in the research area of energy- and bandwidth-efficient communications and networking and highlights the fundamental issues still open for further investigation. Furthermore, the report presents the Joint Research Activities (JRAs) which will be performed within WP1.3. For each activity there is the description, the identification of the adherence with the identified fundamental open issues, a presentation of the initial results, and a roadmap for the planned joint research work in each topic.Preprin

Multiple-Input Multiple-Output Detection Algorithms for Generalized Frequency Division Multiplexing

Since its invention, cellular communication has dramatically transformed personal lifes and the evolution of mobile networks is still ongoing. Evergrowing demand for higher data rates has driven development of 3G and 4G systems, but foreseen 5G requirements also address diverse characteristics such as low latency or massive connectivity. It is speculated that the 4G plain cyclic prefix (CP)-orthogonal frequency division multiplexing (OFDM) cannot sufficiently fulfill all requirements and hence alternative waveforms have been in-vestigated, where generalized frequency division multiplexing (GFDM) is one popular option. An important aspect for any modern wireless communication system is the application of multi-antenna, i.e. MIMO techiques, as MIMO can deliver gains in terms of capacity, reliability and connectivity. Due to its channel-independent orthogonality, CP-OFDM straightforwardly supports broadband MIMO techniques, as the resulting inter-antenna interference (IAI) can readily be resolved. In this regard, CP-OFDM is unique among multicarrier waveforms. Other waveforms suffer from additional inter-carrier interference (ICI), inter-symbol interference (ISI) or both. This possibly 3-dimensional interference renders an optimal MIMO detection much more complex. In this thesis, weinvestigate how GFDM can support an efficient multiple-input multiple-output (MIMO) operation given its 3-dimensional interference structure. To this end, we first connect the mathematical theory of time-frequency analysis (TFA) with multicarrier waveforms in general, leading to theoretical insights into GFDM. Second, we show that the detection problem can be seen as a detection problem on a large, banded linear model under Gaussian noise. Basing on this observation, we propose methods for applying both space-time code (STC) and spatial multiplexing techniques to GFDM. Subsequently, we propose methods to decode the transmitted signals and numerically and theoretically analyze their performance in terms of complexiy and achieved frame error rate (FER). After showing that GFDM modulation and linear demodulation is a direct application of Gabor expansion and transform, we apply results from TFA to explain singularities of the modulation matrix and derive low-complexity expressions for receiver filters. We derive two linear detection algorithms for STC encoded GFDM signals and we show that their performance is equal to OFDM. In the case of spatial multiplexing, we derive both non-iterative and iterative detection algorithms which base on successive interference cancellation (SIC) and minimum mean squared error (MMSE)-parallel interference cancellation (PIC) detection, respectively. By analyzing the error propagation of the SIC algorithm, we explain its significantly inferior performance compared to OFDM. Using feedback information from the channel decoder, we can eventually show that near-optimal GFDM detection can outperform an optimal OFDM detector by up to 3dB for high SNR regions. We conclude that GFDM, given the obtained results, is not a general-purpose replacement for CP-OFDM, due to higher complexity and varying performance. Instead, we can propose GFDM for scenarios with strong frequency-selectivity and stringent spectral and FER requirements

6G for vehicle-to-everything (V2X) communications: Enabling technologies, challenges, and opportunities

We are on the cusp of a new era of connected autonomous vehicles with unprecedented user experiences, tremendously improved road safety and air quality, highly diverse transportation environments and use cases, and a plethora of advanced applications. Realizing this grand vision requires a significantly enhanced vehicle-to-everything (V2X) communication network that should be extremely intelligent and capable of concurrently supporting hyperfast, ultrareliable, and low-latency massive information exchange. It is anticipated that the sixth-generation (6G) communication systems will fulfill these requirements of the next-generation V2X. In this article, we outline a series of key enabling technologies from a range of domains, such as new materials, algorithms, and system architectures. Aiming for truly intelligent transportation systems, we envision that machine learning (ML) will play an instrumental role in advanced vehicular communication and networking. To this end, we provide an overview of the recent advances of ML in 6G vehicular networks. To stimulate future research in this area, we discuss the strength, open challenges, maturity, and enhancing areas of these technologies