Radio over fiber broadband access networks architectures based on wavelength division multiplexing techniques

The recent remarkable growth in bandwidth of both wired optical and wireless access networks supports a burst of new high bandwidth Internet applications such as: peer-topeer file sharing, cloud storage, on-line gaming, video streaming, etc. Within this scenario, the convergence of fixed and wireless access networks offers significant opportunities for network operators to satisfy user demands, and simultaneously reduce the cost of implementing and running separated wireless and wired networks. The integration of wired and wireless network can be accomplished within several scenarios and at several levels. In this thesis we will focus on converged radio over fiber architectures, particularly on two application scenarios: converged optical 60 GHz wireless networks and wireless overlay backhauling over bidirectional colorless wavelength division multiplexing passive optical networks (WDM-PONs). In the first application scenario, optical 60 GHz signal generation using external modulation of an optical carrier by means of lithium niobate (LiNbO3) Mach- Zehnder modulators (MZM) is considered. The performance of different optical modulation techniques, robust against fiber dispersion is assessed and dispersion mitigation strategies are identified. The study is extended to 60 GHz carriers digitally modulated with data and to systems employing subcarrier multiplexed (SCM) mm-wave channels. In the second application scenario, the performance of WDM-PONs employing reflective semiconductor optical amplifiers (RSOAs), transmitting an overlay orthogonal frequency-division multiplexing (OFDM) wireless signal is assessed analytically and experimentally, with the relevant system impairments being identified. It is demonstrated that the intermodulation due to the beating of the baseband signal and wireless signal at the receiver can seriously impair the wireless channel. Performance degradation of the wireless channel caused by the RSOA gain modulation owing to the downstream baseband data is also assessed, and system design guidelines are provided.Universidade do Algarve, Faculdade de Ciências e Tecnologi

Radio over fiber broadband access networks architectures based on wavelength division multiplexing techniques

The recent remarkable growth in bandwidth of both wired optical and wireless access networks supports a burst of new high bandwidth Internet applications such as: peer-topeer file sharing, cloud storage, on-line gaming, video streaming, etc. Within this scenario, the convergence of fixed and wireless access networks offers significant opportunities for network operators to satisfy user demands, and simultaneously reduce the cost of implementing and running separated wireless and wired networks. The integration of wired and wireless network can be accomplished within several scenarios and at several levels. In this thesis we will focus on converged radio over fiber architectures, particularly on two application scenarios: converged optical 60 GHz wireless networks and wireless overlay backhauling over bidirectional colorless wavelength division multiplexing passive optical networks (WDM-PONs). In the first application scenario, optical 60 GHz signal generation using external modulation of an optical carrier by means of lithium niobate (LiNbO3) Mach- Zehnder modulators (MZM) is considered. The performance of different optical modulation techniques, robust against fiber dispersion is assessed and dispersion mitigation strategies are identified. The study is extended to 60 GHz carriers digitally modulated with data and to systems employing subcarrier multiplexed (SCM) mm-wave channels. In the second application scenario, the performance of WDM-PONs employing reflective semiconductor optical amplifiers (RSOAs), transmitting an overlay orthogonal frequency-division multiplexing (OFDM) wireless signal is assessed analytically and experimentally, with the relevant system impairments being identified. It is demonstrated that the intermodulation due to the beating of the baseband signal and wireless signal at the receiver can seriously impair the wireless channel. Performance degradation of the wireless channel caused by the RSOA gain modulation owing to the downstream baseband data is also assessed, and system design guidelines are provided.Universidade do Algarve, Faculdade de Ciências e Tecnologi

Optimised Radio over Fibre Links for Next Generation Radio Access Networks

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonOptical fibre has become the dominant theme of transmission in long haul, high data rate communication systems due to its tremendous bandwidth and low loss. Radio over Fibre (RoF) technology facilitates the seamless integration between wireless and optical communication systems and found to be the most promising solution to meet the exponential bandwidth demands expected for the upcoming years. However, the main bit-rate/distance limitation in RoF systems is the chromatic dispersion. In this thesis, the two generations of RoF technologies, namely Analogue RoF (ARoF) and Digital RoF (DRoF) are investigated. The overall aim of this research is to optimise the optical bandwidth utilisation of these two approaches for a typical transmission of the fronthaul link proposed in the next generation Centralised Radio Access Network (C-RAN). Consequently, a number of physical layer design scenarios for the optimised transmission of the Radio Frequency (RF) signals over a Standards Single Mode Fibre (SSMF) are demonstrated. Firstly, for an ARoF transmission, where the analogue RF signals are transported over SSMF using an optical carrier, a bidirectional link transmitting four Downlink/Uplink channels in a chromatic dispersion limited scenario is designed. Simulation results have shown a clear constellation diagram of a 2.5 Gb/s RF signal transmission over 120 km fibre length. Secondly, a DRoF system with reduced optical bandwidth occupancy is proposed. This system employs an optical Duobinary transmission to the digitised RF signal at the transmitter side to reduce its spectrum and to address the chromatic dispersion effect, simultaneously. Simulation results demonstrate the capability of the proposed system to maintain high-quality transmission of the digitised signals over 70 km of fibre distance without dispersion compensation requirements. Finally, an advanced DRoF transmission link based on integrating digital Optical Single Sideband (OSSB) transmission with Duobinary encoding scheme is designed. Simulation results have clearly verified system’s robustness against transmission impairments and have better performances in terms of the obtained BER and EVM with respect to the 3GPP standardised values. Moreover, the results show that both transmission distance and power budget are furtherly improved in comparison with two other digital transmission scenarios

Enabling Technologies for Distribution of Broadband Radio over Fiber

RÉSUMÉ La radio sur fibre (RoF) a été considérée comme une technologie prometteuse qui concurrencera de manière indisputable comme solution viable pour la distribution des systèmes de communication sans fil à bande large actuels et futurs. La technologie RoF emploie la modulation d'onde sous-porteuse (SCM) pour moduler la lumière par un signal RF, qui à son tour sera transmise par la fibre. Malheureusement, la transmission du signal RF sur la fibre est sujette à un certain nombre de défauts. Ces défauts incluent le faible rendement de la conversion optique en électrique, à la dispersion chromatique de la fibre, et à la non-linéarité de l’émetteur optique. L'objectif de cette thèse est de développer des technologies de pointe pour la radio sur fibre à large bande. Les conceptions proposées devraient adresser la déformation non linéaire induite par l'émetteur optique, combattre le problème de l’affaiblissement de la puissance optique induit par la dispersion chromatique de la fibre, et améliorer l'efficacité de modulation optique au petit signal sans augmenter de manière significative le cout et la complexité du système RoF. Pour le signal RF à large bande, nous considérons le signal à bande ultra large utilisant le multiplexage par répartition orthogonale de la fréquence (ULB MB-MROF), qui a été proposé comme solution pour le réseau de secteur personnel sans fil d’IEEE 802.15.3a (WPAN). D'abord, la performance de la transmission de l'ULB MB-MROF par la fibre est étudiée en considérant l'impact de modulation et démodulation optique. L'analyse théorique de l'effet de la dispersion de la fibre, de la réponse de l'émetteur optique et du récepteur optique sur la performance du système est effectuée en considérant la distorsion de la phase et de l'amplitude. Des expériences sont réalisées pour vérifier notre analyse théorique et une bonne concordance est obtenue. Il est constaté que l'index de modulation RF de ~4% est optimum pour l'émetteur optique avec le modulateur de Mach-Zehnder, et le récepteur optique avec la réponse de Tchebychev-II est le meilleur pour l'ULB MB-MROF sur fibre. Aussi, la performance de la transmission sans fil est limitée par la sensibilité du récepteur ULB MB-MROF. Il est aussi trouvé qu’une haute puissance optique reçue est exigée pour la transmission du signal de l'ULB MB-MROF sur fibre.----------ABSTRACT Radio over fiber (RoF) has been considered as a very promising technology that will indisputably compete as a viable solution for the distribution of current and future broadband wireless communication systems such as IEEE 802.15.3a WPAN using Multiband-Orthogonal Frequency Division Multiplexing Ultra-Wideband (MB-OFDM UWB) signal. The RoF technology makes use of subcarrier modulation (SCM) to modulate an RF signal on light, which in turn will be transmitted by optical fiber. Unfortunately, the transmission of RF signal over fiber is subject to a number of impairments. These impairments include: low optical to electrical conversion efficiency, fiber chromatic dispersion, and nonlinearity of the optical front end, etc.. The objective of this thesis is to develop enabling technologies for broadband RoF systems. The proposed design platforms and techniques should address nonlinear distortion induced by the optical transmitter; combat optical power fading issue induced by the chromatic dispersion; and improve modulation efficiency of the optical small-signal modulation without significantly adding excessive expense and complexity to the RoF system. First of all, the performance of MB-OFDM UWB wireless over fiber transmission system is investigated considering optical modulation and demodulation aspects. Theoretical analysis of the effects of fiber chromatic dispersion, relative intensity noise (RIN), optical transmitter and optical receiver response on system performance is carried out considering amplitude and phase distortion. Experiments are conducted, which have verified our theoretical analysis and a good agreement is obtained. It is found that low RF modulation index (4%) for optical transmitter with Mach-Zehnder modulator (MZM), and optical receiver with Chebyshev-II response is the best for MB-OFDM UWB over fiber. The wireless transmission performance is limited by the UWB receiver sensitivity. Moreover, a high received optical power is required for transmission of MB-OFDM UWB signal over fiber. It is also found that the parameters like laser output power, laser linewidth and fiber dispersion that control RIN, will critically affect the overall performance of a UWB over fiber system

Advanced Technique and Future Perspective for Next Generation Optical Fiber Communications

Optical fiber communication industry has gained unprecedented opportunities and achieved rapid progress in recent years. However, with the increase of data transmission volume and the enhancement of transmission demand, the optical communication field still needs to be upgraded to better meet the challenges in the future development. Artificial intelligence technology in optical communication and optical network is still in its infancy, but the existing achievements show great application potential. In the future, with the further development of artificial intelligence technology, AI algorithms combining channel characteristics and physical properties will shine in optical communication. This reprint introduces some recent advances in optical fiber communication and optical network, and provides alternative directions for the development of the next generation optical fiber communication technology

Optical generation of mm-wave signals for use in broadband radio over fiber systems

In future cellular radio networks Radio over Fiber (RoF) is a very attractive technology to deliver microwave and millimeter-wave signals containing broad band multimedia services to numerous base stations of the network. The radio signals are placed on an optical carrier and distributed by means of an optical fiber network to the base stations (BS). In the BS the optical signals heterodyne in a photodiode to produce the radio signals which are then sent via a wireless link to the mobile units (MU). The optical fiber network provides high frequency, wideband, low loss and a means of signal distribution immune to electromagnetic interference. In this thesis, different methods of electrooptical upconversion were investigated. The generation of an optical double-sideband with suppressed carrier (DSB-SC) signal is a straightforward method due to the fact that only one optical modulator driven at half the millimeter-wave frequency is required. One or both sidebands were ASK-modulated with baseband data rates of up to 10 Gbps. Optical single sideband modulation proves to be dispersion resilient as error free transmission was demonstrated after 53 km of single mode fiber transmission for data rates up to 10 Gbps. Wireless links up to 7 m were also demonstrated, proving the feasibility of this approach for broadband wireless inhouse access systems.Für zukünftige zellulare Funknetze ist „Radio over Fiber (RoF)“ eine sehr attraktive Technologie, um breitbandige Multimedia-Dienste mit Mikro- und Millimeterwellen zu übertragen. Die Funksignale werden dabei auf eine optische Trägerwelle aufmoduliert und mittels eines optischen Fasernetzes zu den Basisstationen (BS) verteilt. In den BS erfolgt die Überlagung der optischen Signale durch eine Fotodiode, um die Funksignale zu erzeugen. Diese werden dann über eine drahtlose Verbindung zu den beweglichen Multimedia-Endgeräten geschickt. Vorteile des optischen Fasernetzes sind Breitbandigkeit, geringe Dämpfung und eine gegenüber elektromagnetischen Störungen immune Signalverteilung. In dieser Arbeit werden verschiedene Methoden der elektrooptischen Aufwärtskonversion erforscht und die wichtigsten Eigenschaften dieser untersucht. Die Erzeugung eines optischen Zweiseitenbandsignales mit unterdrücktem Träger (DSB-SC) ist eine einfache Methode, da nur ein optischer Modulator, betrieben mit der halben elektrischen Trägerfrequenz, benötigt wird. Eine oder beide Seitenbänder konnten mit Bitraten bis zu 10 Gbps amplitudenmoduliert werden. Optische Einseitenbandmodulation ist extrem tolerant bezüglich der chromatischen Dispersion der Faser, wie die fehlerfreie Übertragung nach 53 km Glasfaser beweist. Drahtlose Links bis zu 7 m wurden realisiert und zeigen die Möglichkeit dieser Verfahren für breitbandige drahtlose Inhouse-Zugangssysteme

Digital Processing for an Analogue Subcarrier Multiplexed Mobile Fronthaul

In order to meet the demands of the fifth generation of mobile communication networks (5G), such as very high bit-rates, very low latency and massive machine connectivity, there is a need for a flexible, dynamic, scalable and versatile mobile fronthaul. Current industry fronthaul standards employing sampled radio waveforms for digital transport suffer from spectral inefficiency, making this type of transport impractical for the wide channel bandwidths and multi-antenna systems required by 5G. On the other hand, analogue transport does not suffer from these limitations. It is, however, prone to noise, non-linearity and poor dynamic range. When combined with analogue domain signal aggregation/multiplexing, it also lacks flexibility and scalability, especially at millimetre wave frequencies. Measurements (matched in simulation) of analogue transport at millimetre wave frequencies demonstrate some of these issues. High data rates are demonstrated employing wide bandwidth channels combined using traditional subcarrier multiplexing techniques. However, only a limited number of channels can be multiplexed in this manner, with poor spectral efficiency, as analogue filter limitations do not allow narrow gaps between channels. To this end, over the last few years, there has been significant investigation of analogue transport schemes combined with digital channel aggregation/ de-aggregation (combining/ separating multiple radio waveforms in the digital domain). This work explores such a technique. Digital processing is used at the transmitter to flexibly multiplex a large number of channels in a subcarrier multiplex, without the use of combiners, mixers/ up-converters or Hilbert transforms. Orthogonal Frequency Division Multiplexing (OFDM) - derived Discrete Multi-Tone (DMT) and Single Sideband (SSB) modulated channels are integrated within a single Inverse Fast Fourier Transform (IFFT) operation. Channels or channel groups are mapped systematically into Nyquist zones by using, for example, a single IFFT (for a single 5G mobile numerology) or multiple IFFTs (for multiple 5G mobile numerologies). The analogue transport signal generated in this manner is digitally filtered and band-pass sampled at the receiver such that each corresponding channel (e.g. channels destined to the same radio frequency (RF)/ millimetre wave (mmW) frequency) in the multiplex is presented at the same intermediate frequency, due to the mapping employed at the transmitter. Analogue or digital domain mixers/ down-converters are not required with this technique. Furthermore, each corresponding channel can be readily up-converted to their respective RF/mmW channels with minimal per-signal processing. Measurement results, matched in simulation, for large signal multiplexes with both generic and 5G mobile numerologies show error-vector magnitude performance well within specifications, validating the proposed system. For even larger multiplexes and/or multiplexes residing on a higher IF exceeding the analogue bandwidth and sampling rate specifications of the ADCs at the receiver, the use of a bandwidth-extension device is proposed to extend the mapping to a mapping hierarchy and relax the analogue bandwidth and sampling rate requirements of the ADCs. This allows the receiver to still use digital processing, with only minimal analogue processing, to band-pass sample smaller blocks of channels from the larger multiplex, down to the same intermediate frequency. This ensures that each block of channels is within the analogue bandwidth specification of the ADCs. Performance predictions via simulation (based on a system model matched to the measurements) show promising results for very large multiplexes and large channel bandwidths. The multiplexing technique presented in this work thus allows reductions in per-channel processing for heterogeneous networking (or multi-radio access technologies) and multi-antenna configurations. It also creates a re-configurable and adaptable system based on available processing resources, irrespective of changes to the number of channels and channel groups, channel bandwidths and modulation formats

Análise de redes de rádio sobre fibra óptica

Mestrado em Engenharia Electrónica e TelecomunicaçõesEste trabalho teve como objectivo a implementação e simulação de dois sistemas óptico-analógicos possíveis para a transmissão de sinais rádio sobre fibra óptica. O primeiro utilizando modulação externa, e o segundo modulação directa. Foram implementados modelos necessários para a modelação/transmissão de sinais rádio, bem como a sua desmodulação/recepção. Estes modelos foram adaptados ao software de simulação óptica OSIP, de modo a permitir a simulação de Rádio sobre Fibra. Para validar os resultados, foram utilizados valores obtidos de simulações com o software VPI, assim como medidas experimentais. ABSTRACT: The objective of the presented work was to implement and simulate two different analog optical systems for the transmission of radio signals over optical fiber. The first one with external modulation, and the second with direct modulation. In order to make this possible, were implemented necessary models to the modulation/transmission of radio signals, as well as the respective demodulator/receiver. Those models were adapted to the optical simulation software OSIP, to allow the Radio over Fiber simulation. To validate the results were used experimental measurements, as well as results from VPI, another simulation software

All-optical processing systems based on semiconductor optical amplifiers

Doutoramento em Engenharia ElectrotécnicaNesta tese investigam-se e desenvolvem-se dispositivos para processamento integralmente óptico em redes com multiplexagem densa por divisão no comprimento de onda (DWDM). O principal objectivo das redes DWDM é transportar e distribuir um espectro óptico densamente multiplexado com sinais de débito binário ultra elevado, ao longo de centenas ou milhares de quilómetros de fibra óptica. Estes sinais devem ser transportados e encaminhados no domínio óptico de forma transparente, sem conversões óptico-eléctrico-ópticas (OEO), evitando as suas limitações e custos. A tecnologia baseada em amplificadores ópticos de semicondutor (SOA) é promissora graças aos seus efeitos não-lineares ultra-rápidos e eficientes, ao potencial para integração, reduzido consumo de potência e custos. Conversores de comprimento de onda são o elemento óptico básico para aumentar a capacidade da rede e evitar o bloqueio de comprimentos de onda. Neste trabalho, são estudados e analisados experimentalmente métodos para aumentar a largura de banda operacional de conversores de modulação cruzada de ganho (XGM), a fim de permitir a operação do SOA para além das suas limitações físicas. Conversão de um comprimento de onda, e conversão simultânea de múltiplos comprimentos de onda são testadas, usando interferómetros de Mach-Zehnder com SOA. As redes DWDM de alto débito binário requerem formatos de modulação optimizados, com elevada tolerância aos efeitos nefastos da fibra, e reduzida ocupação espectral. Para esse efeito, é vital desenvolver conversores integramente ópticos de formatos de modulação, a fim de permitir a interligação entre as redes já instaladas, que operam com modulação de intensidade, e as redes modernas, que utilizam formatos de modulação avançados. No âmbito deste trabalho é proposto um conversor integralmente óptico de formato entre modulação óptica de banda lateral dupla e modulação óptica de banda lateral residual; este é caracterizado através de simulação e experimentalmente. Adicionalmente, é proposto um conversor para formato de portadora suprimida, através de XGM e modulação cruzada de fase. A interligação entre as redes de transporte com débito binário ultra-elevado e as redes de acesso com débito binário reduzido requer conversão óptica de formato de impulso entre retorno-a-zero (RZ) e não-RZ. São aqui propostas e investigadas duas estruturas distintas: uma baseada em filtragem desalinhada do sinal convertido por XGM; uma segunda utiliza as dinâmicas do laser interno de um SOA com ganho limitado (GC-SOA). Regeneração integralmente óptica é essencial para reduzir os custos das redes. Dois esquemas distintos são utilizados para regeneração: uma estrutura baseada em MZI-SOA, e um método no qual o laser interno de um GC-SOA é modulado com o sinal distorcido a regenerar. A maioria dos esquemas referidos é testada experimentalmente a 40 Gb/s, com potencial para aplicação a débitos binários superiores, demonstrado que os SOA são uma tecnologia basilar para as redes ópticas do futuro.This thesis investigates and develops all-optical processing devices for wavelength division multiplexing networks (DWM) of the future. The ultimate goal of optical networks is to transport and deliver a densely multiplexed spectrum, populated by ultra-high bit rate signals over hundreds or thousands of kilometers of optical fiber. Such signals should be transported and routed transparently in the optical domain, without recurring to optic-electro-optic (OEO) conversions, avoiding its limitations and costs. Semiconductor optical amplifier (SOA) based technology is a promising building block due to its inherent ultra-fast and efficient non-linear effects, potential for integration, low power consumption and cost. Wavelength converters are the basic optical functionality to increase the network throughput and avoid wavelength blocking. Methods to increase the operation bandwidth of cross-gain modulation (XGM) converters are studied and experimentally assessed to enable operation beyond the physical constraints of SOA. Single and multi-wavelength conversion exploiting crossphase modulation (XPM) in Mach-Zehnder interferometer with semiconductor optical amplifiers (MZI-SOA) is tested. High bit rate DWDM networks require optimized modulation formats with enhanced tolerance to fiber impairments and reduced spectral tolerance. As a consequence, it is crucial to develop all-optical modulation formats between legacy on-off-keying networks and networks employing advanced modulation formats. An all-optical format converter between optical double sideband (ODSB) and optical vestigial sideband (OVSB) based on SOA self-phase modulation is proposed and thoroughly characterized by simulations and experimental tests. A converter, which uses a mix of XGM and XPM to allow simultaneous pulse and modulation format conversion to the carrier suppressed format, is proposed. The interface between ultra-high bit rate transport networks and lower bit rate access networks requires optical pulse format conversions between return-tozero (RZ) and non-return-to-zero (NRZ). Two different structures are proposed and investigated. The first is based on detuned filtering of XPM converted signal; while the second uses the dynamics of the internal laser of a gainclamped SOA. All-optical regeneration is one of the most sought functionalities to reduce network costs. Regeneration is achieved in this work through two simple setups: a MZI-SOA based structure, and a method in which the internal laser from a GC-SOA is modulated with the input distorted signal. Most applications are experimentally validated at 40 Gb/s, with potential for even higher bit rates, demonstrating that SOA can be one of the key elements for the next generation of optical networks