Since past few decades different types of cellular networks were launched and went successful on the radio links such as WiMAX, that became very popular because of its high data rate (70Mbps) and support for providing wireless internet services over 50km distance. The UMTS Long Term Evolution (LTE) is an emerging technology in the evolution of 3G cellular services. LTE runs on an evolution of the existing UMTS infrastructure already used by over 80 percent of mobile subscribers globally. We have very limited resources in cellular technologies and it is important to utilize them with high efficiency. Single Carrier Frequency Division Multiple Access (SC-FDMA) & Orthogonal Division Multiple Access (OFDMA) are major part of LTE. OFDMA was well utilized for achieving high spectral efficiency in communication system. SC-FDMA is introduced recently and it became handy candidate for uplink multiple access scheme in LTE system that is a project of Third Generation Partnership Project (3GPP). The Multiple Access Scheme in Advanced Mobile radio system has to meet the challenging requirements for example high throughput, good robustness, efficient Bit Error Rate (BER), high spectral efficiency, low delays, low computational complexity, low Peak to Average Power Ratio (PAPR), low error probability etc. Error probability is playing vital role in channel estimation and there are many ways to do channel estimation, like Wiener Channel Estimation, Bayesian Demodulation etc. In our thesis, we investigate the performance of SC-FDMA and OFDMA of LTE physical layer by considering different modulation schemes (BPSK, QPSK, 16QAM and 64QAM) on the basis of PAPR, BER, power spectral density (PSD) and error probability by simulating the model of SC-FDMA & OFDMA. We use Additive White Gaussian Noise (AWGN) channel and introduce frequency selective (multipath) fading in the channel by using Rayleigh Fading model to evaluate the performance in presence of noise and fading. A set of conclusions is derived from our results describing the effect of higher order modulation schemes on BER and error probability for both OFDMA and SC-FDMA. The power spectral densities of both the multiple access techniques (OFDMA and SC-FDMA) are calculated and result shows that the OFDMA has high power spectral density. The considered modulation schemes also have a significant impact on the PAPR of both OFDMA and SC-FDMA such that the higher order modulations increase PAPR in SC-FDMA and decrease PAPR in OFDMA. However, the overall value of PAPR is minimum in SC-FDMA for all modulation schemes. The PSD calculation results also support the remarks given on PAPR. / Author 01: Abdul Samad Shaikh, Phone # 0046-760915236 Author 02 : Khatri Chandan Kumar, Phone # 0046-762649745

Support of many different services, approximately 1000x increase of current data rates, ultra-reliability, low latency and energy/cost efficiency are among the demands from upcoming 5G standard. In order to meet them, researchers investigate various potential technologies involving different network layers and discuss their trade-offs for possible 5G scenarios. Waveform design is a critical part of these efforts and various alternatives have been heavily discussed over the last few years. Besides that, wireless technology is expected to be deployed in many critical applications including the ones involving with daily life activities, health-care and vehicular traffic. Therefore, security of wireless systems is also crucial for a reliable and confidential deployment. In order to achieve these goals in future wireless systems, physical layer (PHY) algorithms play a vital role not only in waveform design but also for improving security. In this dissertation, we draft the ongoing activities in PHY in terms of waveform design and security for providing spectrally efficient and reliable services considering various scenarios, and present our algorithms in this direction. Regarding the waveform design, orthogonal frequency division multiplexing (OFDM) is mostly considered as the base scheme since it is the dominant technology in many existing standards and is also considered for 5G new radio. We specifically propose two approaches for the improvement of OFDM in terms of out-of-band emission and peak to average power ratio. We also present how the requirements of different 5G RAN scenarios reflect on waveform parameters and explore the motivations behind designing advanced frames that include multiple waveforms with different parameters, referred to as numerologies by the 3GPP community, as well as the problems that arise with such coexistence. On the security aspect, we firstly consider broadband communication scenarios and propose practical security approaches that suppress the cyclic features of OFDM and single carrier-frequency domain equalization based waveforms and remove their vulnerability to the eavesdropping attacks. Additionally, an authentication mechanism in PHY is presented for wireless implantable medical devices. Thus, we address the security issues for two critical wireless communication scenarios in PHY to contribute a confidential and reliable deployment of wireless technologies in the near future.

La technique Orthogonal Frequency Division Multiplexing (OFDM) a été adoptée par plusieurs systèmes de télécommunications et de diffusion pour sa robustesse, sa capacité à transmettre de hauts débits dans des canaux radiomobiles et pour son efficacité spectrale. Cependant, les signaux OFDM sont caractérisés par des fluctuations importantes, mesurées par le rapport de la puissance crête sur la puissance moyenne (Peak to Average Power Ratio – PAPR) du signal, qui génèrent des distorsions à la sortie de l’amplificateur non-linéaire de puissance (High Power Amplifier - HPA) et ne permettent pas de l’utiliser dans sa zone optimale afin de diminuer sa consommation énergétique. La deuxième génération de la norme Digital Video Broadcasting (DVB-T2) a notamment adopté la technique Tone Reservation (TR) de réduction du PAPR. Son principe consiste à créer un noyau, à partir d’un ensemble de sous-porteuses réservées, qui est ensuite ajouté d’une manière itérative au signal OFDM de façon à réduire les pics du signal et donc son PAPR. Dans la première partie de la thèse, différents algorithmes permettant d’améliorer les performances de cette solution TR DVT-T2 sont proposés. Un premier groupe de solutions, reposant sur la même définition du noyau, comprend : la technique Partial Oversampling and Fractional Shifted Kernels (POFSK) reposant sur un sur-échantillonnage partiel du signal, la technique Dynamic Threshold (DT) qui effectue un calcul dynamique du seuil de troncature et la technique Enhanced Peak Selection (EPS) qui améliore la sélection des pics à réduire. Le deuxième groupe de solutions comprend tout d’abord la technique Individual Carrier Multiple Peaks (ICMP) qui repose sur une nouvelle définition du noyau et utilise un calcul de phase différent permettant la réduction de plusieurs pics en même temps. La technique GICMP est une version optimisée de la technique ICMP qui, en parallélisant les opérations, permet de réduire le délai de traitement et le nombre total d’itérations. Les résultats de simulations et les mesures effectuées sur une plateforme de transmission réelle montrent que, par rapport à la version TR de DVB-T2, l’algorithme GICMP offrait notamment un gain de l’ordre de 2.5 dB en termes de Modulation Error Rate – MER ou permettait une réduction de 10 % de l’énergie consommée par l’amplificateur de puissance à performances identiques. [...] / Orthogonal Frequency Division Multiplexing (OFDM) has been adopted by many telecommunication and broadcasting systems for its robustness, high transmission rates, mobility and bandwidth efficiency. However, OFDM signals are characterized by high power fluctuations, measured by the Peak to Average Power Ratio (PAPR), which cause distortions at the output of the non-linear High Power Amplifier (HPA) and prevent the radio frequency designer to feed the signal at the optimal point of the HPA specifications in order to reduce the energy consumption. The second generation of Digital Video Broadcasting (DVB-T2) adopted two PAPR reduction techniques, one of them is Tone Reservation (TR). TR creates a Kernel from a reserved set of subcarriers. The kernel is then iteratively added to the OFDM signal in such a way to reduce its peaks thus reducing its PAPR. In the first part of the thesis, different algorithms offering better performances compared to the DVB-T2 TR solution are proposed. A first group of solutions introduces changes and enhancements to the TR algorithm adopted in DVB-T2 TR but keeps the same kernel definition. This group includes: the Partial Oversampling and Fractional Shifted Kernels (POFSK) technique which is based on a partial oversampling of the signal, the Dynamic Threshold (DT) technique which allows better algorithm convergence by dynamically computing the PAPR reduction threshold for every OFDM symbol, and the Enhanced Peak Selection (EPS) technique which provides additional PAPR reduction by choosing the appropriate signal peaks to reduce and the peaks to skip. The second group of solutions includes the Individual Carrier Multiple Peaks (ICMP) technique which is based on a special kernel definition that changes from one algorithm iteration to another and uses a different phase calculation approach that allows the reduction of multiple peaks at a time. GICMP is an optimized version of ICMP that allows the parallelization of iterations in such a way to reduce the processing delay and the number of algorithm iterations. The simulation results and real hardware platform measurements of the proposed algorithms showed that, compared to the DVB-T2 TR version, the GICMP algorithm allows a Modulation Error Rate – MER gain of up to 2.5 dB or a 10 % reduction in HPA consumed energy with the same performances.

Radio frequency (RF) spectrum congestion motivates the search for alternative communication techniques to complement radio systems. Visible light communications (VLC) is an emerging technology that exploits the recent and ever-growing increase in the usage of energy-efficient light emitting diodes (LEDs) to imperceptibly modulate the optical power output of LEDs to enable communication and augment RF networks. Orthogonal frequency-divison multiplexing (OFDM) has been proposed as a modulation scheme for VLC due to its high spectral efficiency, ease of channel estimation and equalization, resistance to inter-symbol interference (ISI) and frequency-selective fading, efficient implementation using the Fast Fourier Transform (FFT), and compatibility with RF and power-line communication (PLC) standards that use OFDM. One of the major drawbacks of conventional OFDM techniques is the high peak-to-average power ratio (PAPR) of OFDM signals. The peaks of the OFDM signals are clipped due to the limited dynamic range of the LED, which translates the high PAPR of the OFDM signal into non-linear distortion (NLD). This signal distortion causes bit-error rate (BER) performance degradation, especially at high optical signal-to-noise ratios (SNRs) typical of indoor VLC scenarios. In this thesis, a new family of modulation techniques, termed spatial optical OFDM (SO-OFDM), is proposed with the aim of reducing the PAPR of conventional DC-biased optical OFDM (DCO-OFDM) by making use of the large number of LEDs typically available in indoor lighting settings. Each LED group signal is a narrowband signal consisting of a small number of subcarriers, and thus has a smaller PAPR than the original OFDM signal. Firstly, SO-OFDM is introduced and its two key concepts of frequency-to-space mapping and spatial summing are explained. Frequency-to-space mapping is achieved by allocating a subset of OFDM subcarriers to each LED. Each LED group signal is a narrowband signal consisting of a small number of subcarriers, and thus has a smaller PAPR than the original OFDM signal. Several design variations of the subcarrier assignment to LEDs are introduced and are shown through simulations, to reduce PAPR, and NLD noise due to clipping, and improve the BER performance at high SNRs as compared to DCO-OFDM. In addition, luminous efficacy is identified as an important lighting design parameter that is impacted by modulation. Relative luminous efficacy is defined as the ratio of the luminous efficacy of a modulated LED to that of an LED driven by a DC signal, and is introduced as a metric to assess the impact of modulation on LED lighting. Relative luminous efficacy links communication parameters such as signal variance to lighting design requirements. Secondly, a low-complexity amplify-and-forward (AF) scheme is proposed for an integrated power-line communication/visible-light communication (PLC/VLC) where SO-OFDM is used for the VLC link. Frequency translation of the incoming PLC signal is used to increase the usable bandwidth of the LED. The use of both frequency translation and SO-OFDM leads to capacity gains over DCO-OFDM in the high SNR regime. Finally, a low-complexity variant of SO-OFDM, termed square-wave SO-OFDM (SW-SO-OFDM), is proposed. Square-wave SO-OFDM uses square-wave carriers instead of sinusoidal waves to modulate a single OFDM subcarrier signal per LED. By using square-wave carriers, SW-SO-OFDM eliminates the need for digital-to-analog converters (DACs), digital predistortion (DPD), and the FFT operation. Squarewave SO-OFDM is also shown, through simulations, to achieve BER performance gains over SO-OFDM and DCO-OFDM. In addition, an experimental demonstration of SW-SO-OFDM with 64 QAM modulation on subcarriers is described. / Thesis / Doctor of Philosophy (PhD) / Visible-light communications (VLC) is an emerging technology that exploits the increasingly widespread use of light-emitting diodes (LEDs) for indoor lighting, and modulates the optical power output of the LED for data transmission. Among the various modulation techniques that have been proposed for VLC, orthogonal frequency-division multiplexing (OFDM) offers high data rates, resistance to channel impairments, and simple channel estimation and equalization. However, OFDM signals suffer from a high peak-to-average power ratio (PAPR) which degrades the efficiency of the power amplifier in the transmitter and hinders the communication performance. In this thesis, a new multiple-LED modulation technique, termed spatial optical OFDM (SO-OFDM), is proposed to reduce the PAPR. Using a frequency-to-space mapping, SO-OFDM divides the wideband high-PAPR OFDM signal into multiple narrowband low-PAPR signals and assigns each signal to a group of LEDs. Spatial summing of the transmitted signals occurs at the receiver allowing for the use of a conventional OFDM receiver. Several variations of SO-OFDM are introduced and are shown, using simulations, to reduce the PAPR, combat non-linear distortion (NLD), and improve the bit-error rate (BER) performance at high signal-to-noise ratios (SNRs), typical of VLC systems. Spatial optical OFDM is also applied to a practical scenario where its PAPR reduction capability is used to improve the overall capacity of a proposed system that integrates power-line communication (PLC) and VLC. A low-complexity variant of SO-OFDM, that uses square-wave carriers and simplifies the transmitter design by eliminating the need for digital predistortion (DPD) and digital-to-analog converters (DACs) is also proposed, and tested experimentally.

No description available.

Les futurs systèmes de radiocommunications devront proposer des services nécessitant des transferts de données à haut débit, tout en garantissant une grande mobilité aux utilisateurs. Pour y parvenir, de nouvelles techniques de traitement de signal doivent être mises en oeuvre. Une de ces approches constituant actuellement un axe important de la recherche dans ce domaine est la technique MC-CDMA. Cette dernière repose sur la combinaison de deux techniques : les modulations à porteuses multiples et l'étalement de spectre. Les travaux de recherche présentés dans cette thèse ont pour buts l'étude et l'optimisation des systèmes de communications mettant en oeuvre cette technique MC-CDMA.<br /><br />Après une présentation générale des différentes façons de combiner les techniques de modulations à porteuses multiples et d'étalement de spectre, les performances des systèmes MC-CDMA sont présentées sur des canaux de Rayleigh et BRAN dans le cas de détection mono-utilisateur et multi-utilisateur.<br /><br />Puis, l'influence des codes d'étalement sur la variation de la dynamique de l'enveloppe du signal émis, et sur l'interférence produite par la cohabitation des données de plusieurs utilisateurs sur les mêmes ressources fréquentielles et temporelles est étudiée. Pour cela, nous nous sommes intéressés aux variations de l'enveloppe des sisgnaux MC-CDMA à travers l'étude du facteur de crête et du facteur de crête global. Ces quantités permettent d'estimer les fluctuations du signal transmis respectivement en voie montante et descendante. En ce qui concerne la minimisation de l'interférence d'accès multiple, une technique reposant sur l'allocation des séquences d'étalement est décrite et plusieurs critères de sélection des codes d'étalement sont proposés.<br /><br />Enfin, une attention particulière est portée à l'optimisation de la voie montante des systèmes MC-CDMA. Afin d'éviter l'insertion de Nu jeux de sous-porteuses pilotes servant à estimer les Nu canaux de la voie montante, une solution reposant sur le principe de la réciprocité du canal radiomobile est ici proposée. Cette alternative consiste à effectuer une prédistorsion du signal utile dans le terminal avant son émission. Deux variantes sont envisagées, la première repose sur un multiplexage temporel des voies montante et descendante alors que la seconde repose sur un multiplexage fréquentiel de ces deux voies.

In the last decade, there has been an explosive growth in different applications of wireless technology, due to users' increasing expectations for multi-media services. With the current trend, the present systems will not be able to handle the required data traffic. Lattice codes have attracted considerable attention in recent years, because they provide high data rate constellations. In this thesis, the applications of implementing lattice codes in different communication systems are investigated. The thesis is divided into two major parts. Focus of the first part is on constellation shaping and the problem of lattice labeling. The second part is devoted to the lattice decoding problem. In constellation shaping technique, conventional constellations are replaced by lattice codes that satisfy some geometrical properties. However, a simple algorithm, called lattice labeling, is required to map the input data to the lattice code points. In the first part of this thesis, the application of lattice codes for constellation shaping in Orthogonal Frequency Division Multiplexing (OFDM) and Multi-Input Multi-Output (MIMO) broadcast systems are considered. In an OFDM system a lattice code with low Peak to Average Power Ratio (PAPR) is desired. Here, a new lattice code with considerable PAPR reduction for OFDM systems is proposed. Due to the recursive structure of this lattice code, a simple lattice labeling method based on Smith normal decomposition of an integer matrix is obtained. A selective mapping method in conjunction with the proposed lattice code is also presented to further reduce the PAPR. MIMO broadcast systems are also considered in the thesis. In a multiple antenna broadcast system, the lattice labeling algorithm should be such that different users can decode their data independently. Moreover, the implemented lattice code should result in a low average transmit energy. Here, a selective mapping technique provides such a lattice code. Lattice decoding is the focus of the second part of the thesis, which concerns the operation of finding the closest point of the lattice code to any point in N-dimensional real space. In digital communication applications, this problem is known as the integer least-square problem, which can be seen in many areas, e.g. the detection of symbols transmitted over the multiple antenna wireless channel, the multiuser detection problem in Code Division Multiple Access (CDMA) systems, and the simultaneous detection of multiple users in a Digital Subscriber Line (DSL) system affected by crosstalk. Here, an efficient lattice decoding algorithm based on using Semi-Definite Programming (SDP) is introduced. The proposed algorithm is capable of handling any form of lattice constellation for an arbitrary labeling of points. In the proposed methods, the distance minimization problem is expressed in terms of a binary quadratic minimization problem, which is solved by introducing several matrix and vector lifting SDP relaxation models. The new SDP models provide a wealth of trade-off between the complexity and the performance of the decoding problem.

In the last decade, there has been an explosive growth in different applications of wireless technology, due to users' increasing expectations for multi-media services. With the current trend, the present systems will not be able to handle the required data traffic. Lattice codes have attracted considerable attention in recent years, because they provide high data rate constellations. In this thesis, the applications of implementing lattice codes in different communication systems are investigated. The thesis is divided into two major parts. Focus of the first part is on constellation shaping and the problem of lattice labeling. The second part is devoted to the lattice decoding problem. In constellation shaping technique, conventional constellations are replaced by lattice codes that satisfy some geometrical properties. However, a simple algorithm, called lattice labeling, is required to map the input data to the lattice code points. In the first part of this thesis, the application of lattice codes for constellation shaping in Orthogonal Frequency Division Multiplexing (OFDM) and Multi-Input Multi-Output (MIMO) broadcast systems are considered. In an OFDM system a lattice code with low Peak to Average Power Ratio (PAPR) is desired. Here, a new lattice code with considerable PAPR reduction for OFDM systems is proposed. Due to the recursive structure of this lattice code, a simple lattice labeling method based on Smith normal decomposition of an integer matrix is obtained. A selective mapping method in conjunction with the proposed lattice code is also presented to further reduce the PAPR. MIMO broadcast systems are also considered in the thesis. In a multiple antenna broadcast system, the lattice labeling algorithm should be such that different users can decode their data independently. Moreover, the implemented lattice code should result in a low average transmit energy. Here, a selective mapping technique provides such a lattice code. Lattice decoding is the focus of the second part of the thesis, which concerns the operation of finding the closest point of the lattice code to any point in N-dimensional real space. In digital communication applications, this problem is known as the integer least-square problem, which can be seen in many areas, e.g. the detection of symbols transmitted over the multiple antenna wireless channel, the multiuser detection problem in Code Division Multiple Access (CDMA) systems, and the simultaneous detection of multiple users in a Digital Subscriber Line (DSL) system affected by crosstalk. Here, an efficient lattice decoding algorithm based on using Semi-Definite Programming (SDP) is introduced. The proposed algorithm is capable of handling any form of lattice constellation for an arbitrary labeling of points. In the proposed methods, the distance minimization problem is expressed in terms of a binary quadratic minimization problem, which is solved by introducing several matrix and vector lifting SDP relaxation models. The new SDP models provide a wealth of trade-off between the complexity and the performance of the decoding problem.

Selected mapping (SLM) is a well-known technique used to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. Although SLM scheme can reduce PAPR efficiently, the side information (SI) must be transmitted to the receiver to indicate the candidate signal that generates the OFDM signal with the lowest PAPR. Robust channel coding schemes are typically adopted to prevent erroneous decoding of SI, leading to the lower bandwidth efficiency. To reduce PAPR efficiently and avoid the bandwidth efficiency loss caused by the transmission of SI, two novel PAPR reduction methods are proposed in SFBC MIMO-OFDM systems with two transmitter antennas that employs the Alamouti coding. The candidate signals are constructed in the frequency-domain and time-domain in the first proposed scheme and the second proposed scheme, respectively. In addition, the orthogonality of the space frequency block code is preserved resulting in the data recovery and the corresponding SI can be easily obtained from the conventional Alamouti detection method for both transmission methods. Simulation results show that the BER performance of a SFBC MIMO-OFDM system with the proposed SI detection algorithm is very close to that of perfect SI detection if the extension factor is larger than 1.3.

In multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system which was used space frequency block coding (SFBC) method. It order to reduce the peak-to-average power ratio in several transmit antennas. We proposed two new architectures to simply the computational complexity on transmitter. According to the characteristics of SFBC structure which have M transmitter antennas. We can decomposed the interleaving subcarrier groups by used conversion vector to circular convolution with signal vector and shrink the inverse fast Fourier transform (IFFT) points. Therefore it can do the SFBC coding operation in time domain. By using combination of different cyclic shifts and phase rotations in U subcarrier groups can generate the P candidate signals. And it wouldn¡¦t increase the number of IFFT. The proposed transmitter architectures can improve the major drawback of high computational complexity in traditional selected mapping (SLM). The traditional SLM generate the P candidate signals needs MP IFFT units. Then in the condition of lose a little PAPR reduction performance, we can save the most of computational complexity.