Scalable System Design for Covert MIMO Communications

In modern communication systems, bandwidth is a limited commodity. Bandwidth efficient systems are needed to meet the demands of the ever-increasing amount of data that users share. Of particular interest is the U.S. Military, where high-resolution pictures and video are used and shared. In these environments, covert communications are necessary while still providing high data rates. The promise of multi-antenna systems providing higher data rates has been shown on a small scale, but limitations in hardware prevent large systems from being implemented

AN OFDM platform for wireless systems testing: alamouti 2x1 MIMO example

In this paper, we present a real-time implementation of an OFDM hardware platform. The platform is based on HW blocks that can be put together to configure a wireless system based on OFDM modulation. The platform can be easily upgraded to test pre-coding cooperation algorithms. We evaluate the platform to implement a diversity Alamouti 2×1 MIMO scheme wireless system. The testbed is implemented using Field- Programmable Gate Array (FPGAs) through Xilinx System Generator for DSP. Blocks for time-domain synchronization and channel estimation are key components necessary in transmission system that require good time synchronization and channel estimation for efficient demodulation

HARDWARE IMPLEMENTATION OF MISO ON ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING PLATFORM WITH THE HELP OF ALAMOUTI ALGORITHM

Many software based OFDM techniques were proposed from last half decade to improve the performance of the system. This paper tried to implement the same with Hardware implementation. We created Hardware based MISO platform with OFDM. We implemented Alamouti algorithm on this test bed. The test bed is implemented with the help of Field Programmable Gate Array (FPGA). The test bed is functionalized with the help of FPGA through Xilinx based system generator for DSP. In this paper we considered the 2×1 MISO implementation with Alamouti algorithm. The simulation results showed that BER and SNR are considerably high for MISO than SISO. The results also proved that proposed OFDM based Alamouti implementation for MISO is excellent in all performance criterionsMany software based OFDM techniques were proposed from last half decade to improve the performance of the system. This paper tried to implement the same with Hardware implementation. We created Hardware based MISO platform with OFDM. We implemented Alamouti algorithm on this test bed. The test bed is implemented with the help of Field Programmable Gate Array (FPGA). The test bed is functionalized with the help of FPGA through Xilinx based system generator for DSP. In this paper we considered the 2×1 MISO implementation with Alamouti algorithm. The simulation results showed that BER and SNR are considerably high for MISO than SISO. The results also proved that proposed OFDM based Alamouti implementation for MISO is excellent in all performance criterion

Review of Recent Trends

This work was partially supported by the European Regional Development Fund (FEDER), through the Regional Operational Programme of Centre (CENTRO 2020) of the Portugal 2020 framework, through projects SOCA (CENTRO-01-0145-FEDER-000010) and ORCIP (CENTRO-01-0145-FEDER-022141). Fernando P. Guiomar acknowledges a fellowship from “la Caixa” Foundation (ID100010434), code LCF/BQ/PR20/11770015. Houda Harkat acknowledges the financial support of the Programmatic Financing of the CTS R&D Unit (UIDP/00066/2020).MIMO-OFDM is a key technology and a strong candidate for 5G telecommunication systems. In the literature, there is no convenient survey study that rounds up all the necessary points to be investigated concerning such systems. The current deeper review paper inspects and interprets the state of the art and addresses several research axes related to MIMO-OFDM systems. Two topics have received special attention: MIMO waveforms and MIMO-OFDM channel estimation. The existing MIMO hardware and software innovations, in addition to the MIMO-OFDM equalization techniques, are discussed concisely. In the literature, only a few authors have discussed the MIMO channel estimation and modeling problems for a variety of MIMO systems. However, to the best of our knowledge, there has been until now no review paper specifically discussing the recent works concerning channel estimation and the equalization process for MIMO-OFDM systems. Hence, the current work focuses on analyzing the recently used algorithms in the field, which could be a rich reference for researchers. Moreover, some research perspectives are identified.publishersversionpublishe

Convergence of millimeter-wave and photonic interconnect systems for very-high-throughput digital communication applications

In the past, radio-frequency signals were commonly used for low-speed wireless electronic systems, and optical signals were used for multi-gigabit wired communication systems. However, as the emergence of new millimeter-wave technology introduces multi-gigabit transmission over a wireless radio-frequency channel, the borderline between radio-frequency and optical systems becomes blurred. As a result, there come ample opportunities to design and develop next-generation broadband systems to combine the advantages of these two technologies to overcome inherent limitations of various broadband end-to-end interconnect systems in signal generation, recovery, synchronization, and so on. For the transmission distances of a few centimeters to thousands of kilometers, the convergence of radio-frequency electronics and optics to build radio-over-fiber systems ushers in a new era of research for the upcoming very-high-throughput broadband services. Radio-over-fiber systems are believed to be the most promising solution to the backhaul transmission of the millimeter-wave wireless access networks, especially for the license-free, very-high-throughput 60-GHz band. Adopting radio-over-fiber systems in access or in-building networks can greatly extend the 60-GHz signal reach by using ultra-low loss optical fibers. However, such high frequency is difficult to generate in a straightforward way. In this dissertation, the novel techniques of homodyne and heterodyne optical-carrier suppressions for radio-over-fiber systems are investigated and various system architectures are designed to overcome these limitations of 60-GHz wireless access networks, bringing the popularization of multi-gigabit wireless networks to become closer to the reality. In addition to the advantages for the access networks, extremely high spectral efficiency, which is the most important parameter for long-haul networks, can be achieved by radio-over-fiber signal generation. As a result, the transmission performance of spectrally efficient radio-over-fiber signaling, including orthogonal frequency division multiplexing and orthogonal wavelength division multiplexing, is broadly and deeply investigated. On the other hand, radio-over-fiber is also used for the frequency synchronization that can resolve the performance limitation of wireless interconnect systems. A novel wireless interconnects assisted by radio-over-fiber subsystems is proposed in this dissertation. In conclusion, multiple advantageous facets of radio-over-fiber systems can be found in various levels of end-to-end interconnect systems. The rapid development of radio-over-fiber systems will quickly change the conventional appearance of modern communications.PhDCommittee Chair: Gee-Kung Chang; Committee Member: Bernard Kippelen; Committee Member: Shyh-Chiang Shen; Committee Member: Thomas K. Gaylord; Committee Member: Umakishore Ramachandra

Tecnologias coerentes para redes ópticas flexíveis

Next-generation networks enable a broad range of innovative services with the best delivery by utilizing very dense wired/wireless networks. However, the development of future networks will require several breakthroughs in optical networks such as high-performance optical transceivers to support a very-high capacity optical network as well as optimization of the network concept, ensuring a dramatic reduction of the cost per bit. At the same time, all of the optical network segments (metro, access, long-haul) need new technology options to support high capacity, spectral efficiency and data-rate flexibility. Coherent detection offers an opportunity by providing very high sensitivity and supporting high spectral efficiency. Coherent technology can still be combined with polarization multiplexing. Despite the increased cost and complexity, the migration to dual-polarization coherent transceivers must be considered, as it enables to double the spectral efficiency. These dual-polarization systems require an additional digital signal processing (DSP) subsystem for polarization demultiplexing. This work seeks to provide and characterize cost-effective novel coherent transceivers for the development of new generation practical, flexible and high capacity transceivers for optical metro-access and data center interconnects. In this regard, different polarization demultiplexing (PolDemux) algorithms, as well as adaptive Stokes will be considered. Furthermore, low complexity and modulation format-agnostic DSP techniques based on adaptive Stokes PolDemux for flexible and customizable optical coherent systems will be proposed. On this subject, the performance of the adaptive Stokes algorithm in an ultra-dense wavelength division multiplexing (U-DWDM) system will be experimentally evaluated, in offline and real-time operations over a hybrid optical-wireless link. In addition, the efficiency of this PolDemux algorithm in a flexible optical metro link based on Nyquist pulse shaping U-DWDM system and hybrid optical signals will be assessed. Moreover, it is of great importance to find a transmission technology that enables to apply the Stokes PolDemux for long-haul transmission systems and data center interconnects. In this work, it is also proposed a solution based on the use of digital multi-subcarrier multiplexing, which improve the performance of long-haul optical systems, without increasing substantially, their complexity and cost.As redes de telecomunicações futuras permitirão uma ampla gama de serviços inovadores e com melhor desempenho. No entanto, o desenvolvimento das futuras redes implicará vários avanços nas redes de fibra ótica, como transcetores óticos de alto desempenho capazes de suportar ligações de muito elevada capacidade, e a otimização da estrutura da rede, permitindo uma redução drástica do custo por bit transportado. Simultaneamente, todos os segmentos de rede ótica (metropolitanas, acesso e longo alcance) necessitam de novas opções tecnológicas para suportar uma maior capacidade, maior eficiência espetral e flexibilidade. Neste contexto, a deteção coerente surge como uma oportunidade, fornecendo alta sensibilidade e elevada eficiência espetral. A tecnologia de deteção coerente pode ainda ser associada à multiplexação na polarização. Apesar de um potencial aumento ao nível do custo e da complexidade, a migração para transcetores coerentes de dupla polarização deve ser ponderada, pois permite duplicar a eficiência espetral. Esses sistemas de dupla polarização requerem um subsistema de processamento digital de sinal (DSP) adicional para desmultiplexagem da polarização. Este trabalho procura fornecer e caracterizar novos transcetores coerentes de baixo custo para o desenvolvimento de uma nova geração de transcetores mais práticos, flexíveis e de elevada capacidade, para interconexões óticas ao nível das futuras redes de acesso e metro. Assim, serão analisados diferentes algoritmos para a desmultiplexagem da polarização, incluindo uma abordagem adaptativa baseada no espaço de Stokes. Além disso, são propostas técnicas de DSP independentes do formato de modulação e de baixa complexidade baseadas na desmultiplexagem de Stokes adaptativa para sistemas óticos coerentes flexíveis. Neste contexto, o desempenho do algoritmo adaptativo de desmultiplexagem na polarização baseado no espaço de Stokes é avaliado experimentalmente num sistema U-DWDM, tanto em análises off-line como em tempo real, considerando um percurso ótico hibrido que combina um sistema de transmissão suportado por fibra e outro em espaço livre. Foi ainda analisada a eficiência do algoritmo de desmultiplexagem na polarização numa rede ótica de acesso flexível U-DWDM com formatação de pulso do tipo Nyquist. Neste trabalho foi ainda analisada a aplicação da técnica de desmultiplexagem na polarização baseada no espaço de Stokes para sistemas de longo alcance. Assim, foi proposta uma solução de aplicação baseada no uso da multiplexagem digital de múltiplas sub-portadoras, tendo-se demonstrado uma melhoria na eficiência do desempenho dos sistemas óticos de longo alcance, sem aumentar significativamente a respetiva complexidade e custo.Programa Doutoral em Engenharia Eletrotécnic

Adaptive Modulation Schemes for Underwater Acoustic OFDM Communication

High data rate communication is challenging in underwater acoustic (UA) communication as UA channels vary fast along with the environmental factors. A real-time Orthogonal frequency-division multiplexing (OFDM) based adaptive UA communication system is studied in this research employing the National Instruments (NI) LabVIEW software and NI CompactDAQ device. The developed adaptive modulation schemes enhance the reliability of communication, guarantee continuous connectivity, ensure maximum performance under a fixed BER at all times and boost data rate

Space-time-frequency methods for interference-limited communication systems

textTraditionally, noise in communication systems has been modeled as an additive, white Gaussian noise process with independent, identically distributed samples. Although this model accurately reflects thermal noise present in communication system electronics, it fails to capture the statistics of interference and other sources of noise, e.g. in unlicensed communication bands. Modern communication system designers must take into account interference and non-Gaussian noise to maximize efficiencies and capacities of current and future communication networks. In this work, I develop new multi-dimensional signal processing methods to improve performance of communication systems in three applications areas: (i) underwater acoustic, (ii) powerline, and (iii) multi-antenna cellular. In underwater acoustic communications, I address impairments caused by strong, time-varying and Doppler-spread reverberations (self-interference) using adaptive space-time signal processing methods. I apply these methods to array receivers with a large number of elements. In powerline communications, I address impairments caused by non-Gaussian noise arising from devices sharing the powerline. I develop and apply a cyclic adaptive modulation and coding scheme and a factor-graph-based impulsive noise mitigation method to improve signal quality and boost link throughput and robustness. In cellular communications, I develop a low-latency, high-throughput space-time-frequency processing framework used for large scale (up to 128 antenna) MIMO. This framework is used in the world's first 100-antenna MIMO system and processes up to 492 Gbps raw baseband samples in the uplink and downlink directions. My methods prove that multi-dimensional processing methods can be applied to increase communication system performance without sacrificing real-time requirements.Electrical and Computer Engineerin

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

Roadmap of optical communications

© 2016 IOP Publishing Ltd. Lightwave communications is a necessity for the information age. Optical links provide enormous bandwidth, and the optical fiber is the only medium that can meet the modern society's needs for transporting massive amounts of data over long distances. Applications range from global high-capacity networks, which constitute the backbone of the internet, to the massively parallel interconnects that provide data connectivity inside datacenters and supercomputers. Optical communications is a diverse and rapidly changing field, where experts in photonics, communications, electronics, and signal processing work side by side to meet the ever-increasing demands for higher capacity, lower cost, and lower energy consumption, while adapting the system design to novel services and technologies. Due to the interdisciplinary nature of this rich research field, Journal of Optics has invited 16 researchers, each a world-leading expert in their respective subfields, to contribute a section to this invited review article, summarizing their views on state-of-the-art and future developments in optical communications