Otimização do fronthaul ótico para redes de acesso de rádio (baseadas) em computação em nuvem (CC-RANs)

Doutoramento conjunto (MAP-Tele) em Engenharia Eletrotécnica/TelecomunicaçõesA proliferação de diversos tipos de dispositivos moveis, aplicações e serviços com grande necessidade de largura de banda têm contribuído para o aumento de ligações de banda larga e ao aumento do volume de trafego das redes de telecomunicações moveis. Este aumento exponencial tem posto uma enorme pressão nos mobile operadores de redes móveis (MNOs). Um dos aspetos principais deste recente desenvolvimento, é a necessidade que as redes têm de oferecer baixa complexidade nas ligações, como também baixo consumo energético, muito baixa latência e ao mesmo tempo uma grande capacidade por baixo usto. De maneira a resolver estas questões, os MNOs têm focado a sua atenção na redes de acesso por rádio em nuvem (C-RAN) principalmente devido aos seus benefícios em termos de otimização de performance e relação qualidade preço. O standard para a distribuição de sinais sem fios por um fronthaul C-RAN é o common public radio interface (CPRI). No entanto, ligações óticas baseadas em interfaces CPRI necessitam de uma grande largura de banda. Estes requerimentos podem também ser atingidos com uma implementação em ligação free space optical (FSO) que é um sistema ótico que usa comunicação sem fios. O FSO tem sido uma alternativa muito apelativa aos sistemas de comunicação rádio (RF) pois combinam a flexibilidade e mobilidade das redes RF ao mesmo tempo que permitem a elevada largura de banda permitida pelo sistema ótico. No entanto, as ligações FSO são suscetíveis a alterações atmosféricas que podem prejudicar o desempenho do sistema de comunicação. Estas limitações têm evitado o FSO de ser tornar uma excelente solução para o fronthaul. Uma caracterização precisa do canal e tecnologias mais avançadas são então necessárias para uma implementação pratica de ligações FSO. Nesta tese, vamos estudar uma implementação eficiente para fronthaul baseada em tecnologia á rádio-sobre-FSO (RoFSO). Propomos expressões em forma fechada para mitigação das perdas de propagação e para a estimação da capacidade do canal de maneira a aliviar a complexidade do sistema de comunicação. Simulações numéricas são também apresentadas para formatos de modulação adaptativas. São também considerados esquemas como um sistema hibrido RF/FSO e tecnologias de transmissão apoiadas por retransmissores que ajudam a alivar os requerimentos impostos por um backhaul/fronthaul de C-RAN. Os modelos propostos não só reduzem o esforço computacional, como também têm outros méritos, tais como, uma elevada precisão na estimação do canal e desempenho, baixo requisitos na capacidade de memória e uma rápida e estável operação comparativamente com o estado da arte em sistemas analíticos (PON)-FSO. Este sistema é implementado num recetor em tempo real que é emulado através de uma field-programmable gate array (FPGA) comercial. Permitindo assim um sistema aberto, interoperabilidade, portabilidade e também obedecer a standards de software aberto. Os esquemas híbridos têm a habilidade de suportar diferentes aplicações, serviços e múltiplos operadores a partilharem a mesma infraestrutura de fibra ótica.The proliferation of different mobile devices, bandwidth-intensive applications and services contribute to the increase in the broadband connections and the volume of traffic on the mobile networks. This exponential growth has put considerable pressure on the mobile network operators (MNOs). In principal, there is a need for networks that not only offer low-complexity, low-energy consumption, and extremely low-latency but also high-capacity at relatively low cost. In order to address the demand, MNOs have given significant attention to the cloud radio access network (C-RAN) due to its beneficial features in terms of performance optimization and cost-effectiveness. The de facto standard for distributing wireless signal over the C-RAN fronthaul is the common public radio interface (CPRI). However, optical links based on CPRI interfaces requires large bandwidth. Also, the aforementioned requirements can be realized with the implementation of free space optical (FSO) link, which is an optical wireless system. The FSO is an appealing alternative to the radio frequency (RF) communication system that combines the flexibility and mobility offered by the RF networks with the high-data rates provided by the optical systems. However, the FSO links are susceptible to atmospheric impairments which eventually hinder the system performance. Consequently, these limitations prevent FSO from being an efficient standalone fronthaul solution. So, precise channel characterizations and advanced technologies are required for practical FSO link deployment and operation. In this thesis, we study an efficient fronthaul implementation that is based on radio-on-FSO (RoFSO) technologies. We propose closedform expressions for fading-mitigation and for the estimation of channel capacity so as to alleviate the system complexity. Numerical simulations are presented for adaptive modulation scheme using advanced modulation formats. We also consider schemes like hybrid RF/FSO and relay-assisted transmission technologies that can help in alleviating the stringent requirements by the C-RAN backhaul/fronthaul. The propose models not only reduce the computational requirements/efforts, but also have a number of diverse merits such as high-accuracy, low-memory requirements, fast and stable operation compared to the current state-of-the-art analytical based approaches. In addition to the FSO channel characterization, we present a proof-of-concept experiment in which we study the transmission capabilities of a hybrid passive optical network (PON)-FSO system. This is implemented with the real-time receiver that is emulated by a commercial field-programmable gate array (FPGA). This helps in facilitating an open system and hence enables interoperability, portability, and open software standards. The hybrid schemes have the ability to support different applications, services, and multiple operators over a shared optical fiber infrastructure

Separation of Digital Audio Signals using Least-Mean-Square (LMS) Adaptive Algorithm

Adaptive filtering is one of the fundamental technologies in digital signal processing (DSP) in today’s communication systems and it has been employed in a wide range of applications such as adaptive noise cancellation, adaptive equalization, and echo cancellation.Signal separation remains a task that has called for attention in digital signal processing and different techniques have been employed in order to achieve efficient and accurateresult. Implementation of adaptive filtering can separate wanted and interference signals so as to improve performance of communication systems. In the light of this, this paper usesa least-mean-square (LMS) adaptive algorithm for separation of audio signals.The simulated results show that the designed LMS based adaptive filtering techniqueconverge faster than conventional LMS adaptive filter.DOI:http://dx.doi.org/10.11591/ijece.v4i4.621

Link Adaptation for Microwave Link using both MATLAB and Path-Loss Tool

The inherent multipath transmission on wireless channels usually leads to signal fading which eventually degrades the system performance. In mitigating this problem, link adaptation has been identified as a promising scheme that helps in maximizing the system spectral efficiency (SE) in dispersive wireless channels. In this paper, link adaptation based on adaptive modulation and coding was used to study the performance of M-ary quadrature amplitude modulation radio system subjected to multipath fading. MATLAB® scripts and Simulink model were developed to compare the effect of wireless channel on different constellation sizes. Also, transmission link on Federal University of Technology Akure campus’ path terrain was designed with the aid of path-loss® tool application software in order to further analysis the effect of using different modulation formats on the system performance. The results show that, employment of link adaptation scheme offers better performance regarding the system availability and S

Voice-Based Door Access Control System Using the Mel Frequency Cepstrum Coefficients and Gaussian Mixture Model

Access to an area or environment can be controlled by conventional and electronic keys, identity cards, personal identification numbers (PINs) pads and smartcards.  Due to certain limitations of existing door access schemes deployed for security in buildings, this paper presents speaker recognition for building security as a better means of admission into important places. This is proposed due mainly to the fact that speech cannot be stolen, copied, forgotten, lost or guessed with accuracy. This paper, therefore presents design of an affordable voice activated door control system for building security. The proposed system uses the Mel Frequency Cepstrum and the Gaussian Mixture Model for feature extraction and template pattern matching respectively. The analysis of the result which is based on the false acceptance and rejection rates indicate a system accuracy of more than 80%.DOI:http://dx.doi.org/10.11591/ijece.v4i5.644

Spatial Light Modulation as a Flexible Platform for Optical Systems

Spatial light modulation is a technology with a demonstrated wide range of applications, especially in optical systems. Among the various spatial light modulator (SLM) technologies, e.g., liquid crystal (LC), magneto-optic, deformable mirror, multiple quantum well, and acoustic-optic Bragg cells, the ones based on liquid crystal on silicon (LCoS) have been gaining importance and relevance in a plethora of optical contexts, namely, in telecom, metrology, optical storage, and microdisplays. Their implementation in telecom has enabled the development of high-capacity optical components in system functionalities as multiplexing/demultiplexing, switching and optical signal processing. This technology combines the unique light-modulating properties of LC with the high-performance silicon complementary metal oxide semiconductor properties. Different types of modulation, i.e., phase, amplitude or combination of the two, can be achieved. In this book chapter, we address the most relevant applications of phase-only LCoS SLM for optical telecom purposes and the employment of SLM technology in photonic integrated circuits (PICs) (e.g., field-programmable silicon photonic (SiP) circuits and integrated SLM application to create versatile reconfigurable elements). Furthermore, a new SLM-based flexible coupling platform with applications in spatial division multiplexing (SDM) systems (e.g., to efficiently excite different cores in MCF) and characterization/testing of photonic integrated processors will be described

Optical signal phase retrieval with low complexity DC-value method

We propose a novel method to reconstruct the optical signal phase information using direct detection. The method is suitable for minimum phase signals and it enables low complexity, low latency, and low tone power operation. Moreover, the proposed method offers low optical complexity solution for the short-reach links compared with the concurrent phase retrieval techniques. We apply the method to M-ary signals with the transmitted power of as low as 3 dBm, and we are able to reach 70 km for 100 Gb/s quadrature phase shift keying (QPSK) system without optical amplification. Our method is based on the single sideband (SSB) and DC-Value property of the minimum phase signal. The SSB and DC-Value properties are iteratively imposed on the amplitude signal in the frequency domain to recover the full complex field from a directly detected optical signal. The normalized mean square error (NMSE) value between the available amplitude information and reconstructed minimum phase signal amplitude decreases after each iteration, providing global minimum convergence. A constant scaling factor is exploited to improve the convergence speed. The scaling factor provides 6 dB, 4.5 dB, and 2.5 dB error vector magnitude (EVM) gains with 4, 5, and 8 iterations, respectively.publishe

Enhancement of Speech Communication Technology Performance Using Adaptive-Control Factor Based Spectral Subtraction Method, Journal of Telecommunications and Information Technology, 2013, nr 2

This paper presents speech enhancement technique based on Spectral Subtraction (SS) method. SS is a renowned noise reduction technique that works on the principle that noise spectrum estimate over the entire speech spectrum can be subtracted from the noisy signal. On the contrary, most of the noise encountered in the real-world conditions is majorly colored. Unlike Additive White Gaussian Noise (AWGN), colored noise does not affect the speech signal uniformly over the entire spectrum. To mitigate effects of colored noise on the processed signal, we propose a Multi-Band Spectral Subtraction (MBSS) method using novel Adaptive-Control Factor (ACF). The spectrum is divided into frequency sub bands based on a nonlinear multi-band frame and various signal-to-noise ratios (SNRs) are considered. The proposed scheme results in better system performance with quality signal and unlike the basic SS method. It mitigates the effects of anomaly known as “musical” tones artifacts in the processed signal thatresult in residual noise and speech distortion. The computational complexity involved is minimal. Furthermore, simulation results show that the proposed algorithm removes more colored noise without removing the relatively low amplitude speech signal over the entire speech spectrum. Subjective listening tests, with clean speech signals and different noise levels, show discernable performance of our proposed method when compared with the conventional SS approach

Challenges and Opportunities of Optical Wireless Communication Technologies

In this chapter, we present various opportunities of using optical wireless communication (OWC) technologies in each sector of optical communication networks. Moreover, challenges of optical wireless network implementations are investigated. We characterized the optical wireless communication channel through the channel measurements and present different models for the OWC link performance evaluations. In addition, we present some technologies for the OWC performance enhancement in order to address the last-mile transmission bottleneck of the system efficiently. The technologies can be of great help in alleviating the stringent requirement by the cloud radio access network (C-RAN) backhaul/fronthaul as well as in the evolution toward an efficient backhaul/fronthaul for the 5G network. Furthermore, we present a proof-of-concept experiment in order to demonstrate and evaluate high capacity/flexible coherent PON and OWC links for different network configurations in the terrestrial links. To achieve this, we employ advanced modulation format and digital signal processing (DSP) techniques in the offline and real-time mode of the operation. The proposed configuration has the capability to support different applications, services, and multiple operators over a shared optical fiber infrastructure

Enabling Optical Wired and Wireless Technologies for 5G and Beyond Networks

The emerging fifth-generation mobile communications are envisaged to support massive number of deployment scenarios based on the respective use case requirements. The requirements can be efficiently attended with ultradense small-cell cloud radio access network (C-RAN) approach. However, the C-RAN architecture imposes stringent requirements on the transport networks. This book chapter presents high-capacity and low-latency optical wired and wireless networking solutions that are capable of attending to the network demands. Meanwhile, with optical communication evolutions, there has been advent of enhanced photonic integrated circuits (PICs). The PICs are capable of offering advantages such as low-power consumption, high-mechanical stability, low footprint, small dimension, enhanced functionalities, and ease of complex system architectures. Consequently, we exploit the PICs capabilities in designing and developing the physical layer architecture of the second standard of the next-generation passive optical network (NG-PON2) system. Apart from being capable of alleviating the associated losses of the transceiver, the proposed architectures aid in increasing the system power budget. Moreover, its implementation can significantly help in reducing the optical-electrical-optical conversions issue and the required number of optical connections, which are part of the main problems being faced in the miniaturization of network elements. Additionally, we present simulation results for the model validation

Trends in Cloud Computing Paradigms: Fundamental Issues, Recent Advances, and Research Directions toward 6G Fog Networks

There has been significant research interest in various computing-based paradigms such as cloud computing, Internet of Things, fog computing, and edge computing, due to their various associated advantages. In this chapter, we present a comprehensive review of these architectures and their associated concepts. Moreover, we consider different enable technologies that facilitate computing paradigm evolution. In this context, we focus mainly on fog computing considering its related fundamental issues and recent advances. Besides, we present further research directions toward the sixth generation fog computing paradigm