WDM-PON has been considered a promising solution for future fronthaul links concerning new mobile networks applications. However, in order to avoid inventory problems and reduce operation costs, there is a need for colorless sources, where the same basic optical source can be used regardless of the desired wavelength. Also, the digital RoF scheme, which has been employed so far, might require a bandwidth that is prohibitive even for optical fiber links. In this paper, we propose and numerically investigate a bidirectional colorless WDM-PON fronthaul transporting analog RoF signals as an alternative to meet these demands. All simulations were performed using a framework calibrated with experimental data. For the downstream, we employ a double-cavity self-seeding technique, while the upstream is performed by a cascaded-RSOAs carrier-reuse approach. BER and EVM simulation analysis are presented for various data rates, modulations formats and RF bands ranging from 1 to 5 GHz, demonstrating the feasibility of our proposed topology as a novel fronthaul approach.
Wavelength‐division multiplexing passive optical network (WDM‐PON) is a promising solution to cope with the exponential data traffic growth, particularly regarding future mobile fronthaul. WDM‐PON schemes, based on self‐seeded wavelength agnostic transmitters using reflective semiconductor optical amplifiers (RSOAs), are seen as an option to provide an analog radio‐over‐fiber (A‐RoF) alternative to the current digital fronthaul. Although these A‐RoF have been already successfully demonstrated, it was observed that the arrayed waveguide grating (AWG)‐filtering characteristics affect both the optical seed generation and the radio signal integrity, requiring a design optimization. In order to do so, in this article, we optimize the A‐RoF transmission performance by comparing Bessel, Gaussian, and flat‐top AWG‐filter formats. The impact of seed linewidth and red‐shift on the signal error‐vector magnitude (EVM) and phase rotation is also investigated. We have found that EVM performance for BPSK and 16QAM transmission provided an improvement of 45% when compared to our previous results, with a phase offset of 0.8°, indicating little to no distortion, as a result of the selection of the optimal AWG filtering response.
Resumo A implementação de atividades práticas que envolvam cores constitui uma estratégia poderosa para estimular o interesse de crianças e adolescentes para a Ciência. Devido ao seu forte apelo visual e presença no cotidiano, as cores despertam a curiosidade dos estudantes e propiciam o aprendizado de conceitos fundamentais no campo da óptica, tais como reflexão, transmissão e refração. Nesse trabalho, descrevemos um programa de atividades desenvolvido para ensinar conceitos de óptica presentes na formação de cores a partir de materiais simples, baratos e acessíveis. Através de demonstrações abertas e discussões autônomas por parte dos estudantes, elucidamos o processo de formação de cores por reflexão e transmissão, bem como a razão pela qual se pode visualizar objetos incolores. As atividades aqui descritas foram apresentadas num evento de divulgação científica direcionado a crianças e adolescentes com idade entre 8 e 17 anos.
The introduction of 5G mobile systems poses significant challenges to the design of the fronthaul structure. The dense coverage, comprising several small cells operating in the millimeter‐wave range, with an enormous number of antennas, makes conventional digital‐radio‐over‐fiber unfeasible. On the other hand, the centralized architecture of the optical fronthaul is well‐suited for the passive optical network (PON) topology, with WDM‐PON as a strong contender due to its capability to establish logical point‐to‐point optical links to each cell site. However, the large‐scale deployment of WDM‐PON requires the availability of colorless transmitters, where the same hardware is able to generate any wavelength needed by the network. In this context, this paper investigates an analog fronthaul configuration over a colorless WDM‐PON for 5G and beyond, employing the techniques of self‐seeding in the downlink and carrier reuse in the uplink. We numerically evaluated the EVM when transmitting 1.25 Gbps at 3.5 GHz and 10 Gbps at 26 GHz in a 20 km optical link. The results are within the 3GPP requirements, demonstrating the feasibility of the proposed fronthaul.
Future radio access networks, such as the fifth generation mobile network (5G), are introducing and consolidating disruptive technologies, such as millimeter wave operation, dense picocell coverage and massive use of antennas for spatial and temporal diversity. These new technologies present a challenge for the capacity of the links that are present on these networks, including backhaul and fronthaul. In the latest cellular network generations, the fronthaul was typically implemented by Digital Radio-over-Fiber (D-RoF) technique. However, in this future context, the digitalization process would require a prohibitive bandwidth and the analog transmission of RF signals over the fiber can be a more attractive solution when compared to D-RoF. At the same time, Wavelength-Division-Multiplexing PON (WDM-PON) is prominent alternative for the future of PONs, especially considering its use as fronthaul. In order to avoid employing numerous distinct transmitters, several self-seeding techniques have been proposed to achieve colorless optical sources. This dissertation presents a numerical study of double-cavity self-seeding topologies to serve as analog fronthaul for future radio access networks. Numerical simulations using the software Optisystem demonstrate the feasibility of these topologies in various scenarios envisioned for these access networks, especially considering operation in millimeter waves. Successful transmission was achieved for ASK, M-PSK and M-QAM signals at microwave (1.25, 2.5 and 5 GHz) and millimeter wave (38 and 60 GHz) frequencies with throughput of 155 Mbps to 10 Gbps using direct and external modulation.
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