Time-Domain N-continuous GFDM

Generalized frequency division multiplexing (GFDM) has been a candidate multicarrier scheme in the 5th generation cellular networks for its flexibility of transmitter filter in time and frequency. However, for the circularly shaped transmitter filter, GFDM provides limited performance gain of sidelobe suppression. In this paper, we propose a scheme, called time-domain N-continuous GFDM (TD-NC-GFDM), to reduce the discontinuities caused by the GFDM transmitter filter and achieve promising sidelobe suppression gain. Based on time-domain N-continuous orthogonal frequency devision multiplexing (TD-NC-OFDM), TD-NC-GFDM signal can be obtained by superposing a smooth signal in the time domain. The smooth signal is linearly combined by basis signals in a new basis set related to GFDM transmitter waveform. To eliminate the interference caused by the smooth signal, two solutions are proposed. Firstly, a signal recovery algorithm for reception is adopted at the cost of high complexity. Thus, secondly, to simplify the TD-NC-GFDM receiver, a low-interference TD-NC-GFDM is proposed by redesigning the basis signals. A soft truncation of the basis signals in TD-NC-GFDM is given to design the basis signals in the low-interference TD-NC-GFDM. Then, the smooth signal is aligned with the beginning of the GFDM symbol and is added in the front part of the GFDM symbol. Moreover, for a big number of GFDM subsymbols, theoretical analysis proves that the signal-to-interference ratio (SIR) in TD-NC-GFDM is much higher than that in TD-NC-OFDM. Simulation results shows that TD-NC-GFDM can obtain significant sidelobe suppression performance as well as the low-interference TD-NC-GFDM, which can achieve the same BER performance as the original GFDM.Comment: single column, 19 pages, 10 figure

Fundamental Limits on Performance for Cooperative Radar-Communications Coexistence

abstract: Spectral congestion is quickly becoming a problem for the telecommunications sector. In order to alleviate spectral congestion and achieve electromagnetic radio frequency (RF) convergence, communications and radar systems are increasingly encouraged to share bandwidth. In direct opposition to the traditional spectrum sharing approach between radar and communications systems of complete isolation (temporal, spectral or spatial), both systems can be jointly co-designed from the ground up to maximize their joint performance for mutual benefit. In order to properly characterize and understand cooperative spectrum sharing between radar and communications systems, the fundamental limits on performance of a cooperative radar-communications system are investigated. To facilitate this investigation, performance metrics are chosen in this dissertation that allow radar and communications to be compared on the same scale. To that effect, information is chosen as the performance metric and an information theoretic radar performance metric compatible with the communications data rate, the radar estimation rate, is developed. The estimation rate measures the amount of information learned by illuminating a target. With the development of the estimation rate, standard multi-user communications performance bounds are extended with joint radar-communications users to produce bounds on the performance of a joint radar-communications system. System performance for variations of the standard spectrum sharing problem defined in this dissertation are investigated, and inner bounds on performance are extended to account for the effect of continuous radar waveform optimization, multiple radar targets, clutter, phase noise, and radar detection. A detailed interpretation of the estimation rate and a brief discussion on how to use these performance bounds to select an optimal operating point and achieve RF convergence are provided.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

QoS-Aware Precoder Optimization for Radar Sensing and Multiuser Communications Under Per-Antenna Power Constraints

In this work, we concentrate on designing the precoder for the multiple-input multiple-output (MIMO) dual functional radar-communication (DFRC) system, where the dual-functional waveform is designed for performing multiuser downlink transmission and radar sensing simultaneously. Specifically, considering the signal-independent interference and signal-dependent clutter, we investigate the optimization of transmit precoding for maximizing the sensing signal-to-interference-plus-noise ratio (SINR) at the radar receiver under the constraint of the minimum SINR received at multiple communication users and per-antenna power budget. The formulated problem is challenging to solve due to the nonconovex objective function and nonconvex per-antenna power constraint. In particular, for the signal-independent interference case, we propose a distance-majorization induced algorithm to approximate the nonconvex problem as a sequence of convex problems whose optima can be obtained in closed form. Subsequently, our complexity analysis shows that our proposed algorithm has a much lower computational complexity than the widely-adopted semidefinite relaxation (SDR)-based algorithm. For the signal-dependent clutter case, we employ the fractional programming to transform the nonconvex problem into a sequence of subproblems, and then we propose a distance-majorization based algorithm to obtain the solution of each subproblem in closed form. Finally, simulation results confirm the performance superiority of our proposed algorithms when compared with the SDR-based approach. In conclusion, the novelty of this work is to propose an efficient algorithm for handling the typical problem in designing the DFRC precoder, which achieves better performance with a much lower complexity than the state-of-the-art algorithm

Joint Communications and Sensing Employing Multi- or Single-Carrier OFDM Communication Signals: A Tutorial on Sensing Methods, Recent Progress and a Novel Design

Joint communications and sensing (JCAS) has recently attracted extensive attention due to its potential in substantially improving the cost, energy and spectral efficiency of Internet of Things (IoT) systems that need both radio frequency functions. Given the wide applicability of orthogonal frequency division multiplexing (OFDM) in modern communications, OFDM sensing has become one of the major research topics of JCAS. To raise the awareness of some critical yet long-overlooked issues that restrict the OFDM sensing capability, a comprehensive overview of OFDM sensing is provided first in this paper, and then a tutorial on the issues is presented. Moreover, some recent research efforts for addressing the issues are reviewed, with interesting designs and results highlighted. In addition, the redundancy in OFDM sensing signals is unveiled, on which, a novel method is based and developed in order to remove the redundancy by introducing efficient signal decimation. Corroborated by analysis and simulation results, the new method further reduces the sensing complexity over one of the most efficient methods to date, with a minimal impact on the sensing performance.</jats:p

Bandwidth Compressed Waveform and System Design for Wireless and Optical Communications: Theory and Practice

This thesis addresses theoretical and practical challenges of spectrally efficient frequency division multiplexing (SEFDM) systems in both wireless and optical domains. SEFDM improves spectral efficiency relative to the well-known orthogonal frequency division multiplexing (OFDM) by non-orthogonally multiplexing overlapped sub-carriers. However, the deliberate violation of orthogonality results in inter carrier interference (ICI) and associated detection complexity, thus posing many challenges to practical implementations. This thesis will present solutions for these issues. The thesis commences with the fundamentals by presenting the existing challenges of SEFDM, which are subsequently solved by proposed transceivers. An iterative detection (ID) detector iteratively removes self-created ICI. Following that, a hybrid ID together with fixed sphere decoding (FSD) shows an optimised performance/complexity trade-off. A complexity reduced Block-SEFDM can subdivide the signal detection into several blocks. Finally, a coded Turbo-SEFDM is proved to be an efficient technique that is compatible with the existing mobile standards. The thesis also reports the design and development of wireless and optical practical systems. In the optical domain, given the same spectral efficiency, a low-order modulation scheme is proved to have a better bit error rate (BER) performance when replacing a higher order one. In the wireless domain, an experimental testbed utilizing the LTE-Advanced carrier aggregation (CA) with SEFDM is operated in a realistic radio frequency (RF) environment. Experimental results show that 40% higher data rate can be achieved without extra spectrum occupation. Additionally, a new waveform, termed Nyquist-SEFDM, which compresses bandwidth and suppresses out-of-band power leakage is investigated. A 4th generation (4G) and 5th generation (5G) coexistence experiment is followed to verify its feasibility. Furthermore, a 60 GHz SEFDM testbed is designed and built in a point-to-point indoor fiber wireless experiment showing 67% data rate improvement compared to OFDM. Finally, to meet the requirements of future networks, two simplified SEFDM transceivers are designed together with application scenarios and experimental verifications

Mimo Communication Systems with Reconfigurable Antennas

RÉSUMÉ Les antennes reconfigurables sont capables d'ajuster dynamiquement les caractéristiques de leur diagramme de rayonnement, par exemple, la forme, la direction et la polarisation, en réponse aux conditions environnementales et exigences du système. Ces antennes peuvent aussi être utilisées en conjonction avec des systèmes à entrées multiples sorties multiples (MIMO) pour améliorer davantage la capacité et la fiabilité des systèmes sans fil. Cette thèse étudie certains des problèmes dans les systèmes sans fil équipés d'antennes reconfigurables et propose des solutions pour améliorer la performance du système. Dans les systèmes sans fil utilisant des antennes reconfigurables, la performance atteignable par le système dépend fortement de la connaissance de la direction d'arrivée (DoA) des signaux souhaités et des interférences. Dans la première partie de cette thèse, nous proposons un nouvel algorithme d'estimation de la DoA pour les systèmes à entrer simple et sortie simple (SISO) qui possèdent un élément d'antenne reconfigurable au niveau du récepteur. Contrairement à un système utilisant un réseau d'antennes conventionnelles à diagramme de rayonnement fixe, où la DoA est estimée en utilisant les signaux reçus par plusieurs éléments, dans le réseau d'antennes avec l'algorithme proposé, la DoA est estimée en utilisant des signaux reçus d'un élément d'antenne unique pendant qu'il balai un ensemble de configurations de diagramme de rayonnement. Nous étudions aussi l'impact des différentes caractéristiques des diagrammes de rayonnement utilisés, tels que la largeur du faisceau de l'antenne et le nombre d'étapes de numérisation, sur l'exactitude de la DoA estimée. Dans la deuxième partie de cette thèse, nous proposons un système de MIMO faible complexité employant des antennes reconfigurables sur les canaux sélectifs en fréquence pour atténuer les êtes de trajets multiples et donc éliminer l'interférence entre symboles sans utiliser la technique de modulation multiplexage orthogonale fréquentiel (OFDM). Nous étudions aussi l'impact de la propagation et de l'antenne angulaire largeur de faisceau sur la performance du système proposé et faire la comparaison avec la performance du système MIMO-OFDM. Dans la troisième partie de cette thèse, nous fournissons des outils analytiques pour analyser la performance des systèmes sans _l MIMO équipés d'antennes reconfigurables au niveau du récepteur. Nous dérivons d'abord des expressions analytiques pour le calcul de la matrice de covariance des coefficients des signaux reçus empiétant sur un réseau d'antennes reconfigurables en tenant compte de plusieurs caractéristiques de l'antenne tels que la largeur du faisceau, l'espacement d'antenne, l'angle de pointage ainsi que le gain de l'antenne. Dans cette partie, nous considérons un récepteur MIMO reconfigurable où le diagramme de rayonnement de chaque élément d'antenne dans le réseau peut avoir des caractéristiques différentes. Nous étudions également la capacité d'un système MIMO reconfigurable en utilisant les expressions analytiques dérivées.----------ABSTRACT Reconfigurable antennas are able to dynamically adjust their radiation pattern characteristics, e.g., shape, direction and polarization, in response to environmental conditions and system requirements. These antennas can be used in conjunction with multiple-input multiple-output (MIMO) systems to further enhance the capacity and reliability of wireless networks. This dissertation studies some of the issues in wireless cellular systems equipped with reconfigurable antennas and offer solutions to enhance their performance. In wireless systems employing reconfigurable antennas, the attainable performance improvement highly depends on the knowledge of direction-of-arrival (DoA) of the desired source signals and that of the interferences. In the first part of this dissertation, we propose a novel DoA estimation algorithm for single-input single-output (SISO) system with a reconfigurable antenna element at the receiver. Unlike a conventional antenna array system with fixed radiation pattern where the DoA is estimated using the signals received by multiple elements, in the proposed algorithm, we estimate the DoA using signals collected from a set of radiation pattern states also called scanning steps. We, in addition, investigate the impact of different radiation pattern characteristics such as antenna beamwidth and number of scanning steps on the accuracy of the estimated DoA. In the second part of this dissertation, we propose a low-complexity MIMO system employing reconfigurable antennas over the frequency-selective channels to mitigate multipath effects and therefore remove inter symbol interference without using orthogonal frequency division multiplexing (OFDM) modulation. We study the impact of angular spread and antenna beamwidth on the performance of the proposed system and make comparisons with that of MIMO-OFDM system equipped with omnidirectional antennas. In the third part of this dissertation, we provide an analytical tool to analyze the performance of MIMO wireless systems equipped with reconfigurable antennas at the receiver. We first derive analytical expressions for computing the covariance matrix coefficients of the received signals impinging on a reconfigurable antenna array by taking into account several antenna characteristics such as beamwidth, antenna spacing, antenna pointing angle, and antenna gain. In this part, we consider a reconfigurable MIMO receiver where the radiation pattern of each antenna element in the array can have different characteristics. We, additionally, study the capacity of a reconfigurable MIMO system using the derived analytical expressions