Towards high bandwidth communication systems: from multi-gbit/s over si-pof in home scenarios to 5g cellular networks over smf

• Autores: Fahad Al Zubaidi
• Directores de la Tesis: Carmen Vázquez García (dir. tes.), David Sanchez Montero (codir. tes.)
• Lectura: En la Universidad Carlos III de Madrid ( España ) en 2021
• Idioma: español
• Tribunal Calificador de la Tesis: Beatriz Ortega Tamarit (presid.), Guillermo Carpintero del Barrio (secret.), Óscar Esteban Martínez (voc.)
• Programa de doctorado: Programa de Doctorado en Ingeniería Eléctrica, Electrónica y Automática por la Universidad Carlos III de Madrid
• Materias:
  • Ciencias tecnológicas
    • Tecnología electrónica
• Enlaces
  • Tesis en acceso abierto en: e-Archivo
• Resumen

  • The thesis analyses high bandwidth communication links using different types of optical fibers to cope with the rapid growth of the data traffic in parallel with the integration of power over fiber (PoF) technology in these systems. We implement novel simulations designs for different network architectures from the end user at home scenarios to the service provider through the mobile cellular network. For the home scenario, large core step-index (SI) plastic optical fiber (POF) has been recognized as a strong candidate for in-home networking due to many advantages such as inexpensive, easy installation and high bending tolerance in comparison with multimode silica fibers. The large core area for this kind of fiber (1 mm) opens the possibility to be changed or adapted even by final user at home. This large core diameter also attracts the use of light emitting diodes (LED) to achieve low cost links with the additional advantages of less eye damage risk for indoor free-space optics. Communication system with multi Gbit/s data transmission capability based on wavelength-division-multiplexing (WDM) over SIPOF is achieved. A real-time data link at a data rate of 1 Gbit/s with BER of < 1×10-10 over 10 m SI-POF link is implemented experimentally simultaneously with the energy delivery of several mW through PoF technology. The transmission capacity can be expanded up to 5 Gbit/s utilizing previously design and implemented multiplexer/demultiplexer (MUX/DEMUX) devices. The impact of simultaneous transmission for both PoF signal at 405 nm (blue channel) and data signal at 650 nm (red channel) on data signal quality is thoughtfully studied both theoretically and by experiments. We model Signal to Noise ratio (SNR) of the data signal affected by this simultaneous transmission. A detailed comparison to the state of the art of SI-POF based home networks is presented. The designed system outperforms previous works in terms of adding energy delivery while keeping both transmission efficiency and power per bit figures of merit. We show the designed system capability to optically powering multiple devices for specific in-home applications and Internet-of-Things (IoT) ecosystems, which can help to integrate smart homes automation. The proposed system can integrate the future 5G indoor architectures where each room within the home can be equipped with high connectivity provided by SI-POF, and simultaneously offering reliable optically feeding IoT solutions. Different examples for low power consumption IoT sensors that can monitor different environmental conditions such as temperature, humidity and pressure are provided. We present shared- and dedicated- fiber scenarios over SI-POF to integrate our PoF solution in the POF communication link where no impact on the data traffic neither on transmission efficiency is noticed. Design rules on the required crosstalk on the DEMUX at the receiver stage are also provided. The analysis shows that for 10 mW of optical power delivered at the remote node, there is a need of a device having a crosstalk of 23 dB. The scalability of the system is analyzed showing the PoF feeding capabilities for different case studies that fulfill smart IoT in-home ecosystem needs. We calculate the energy system efficiency (SEE) in different powering scenarios. We show the difference of considering different channels for optical powering (PoF channel) as the attenuation loss of the optical fiber varies with wavelength in the visible range. Apart from that, the conversion efficiency of Photovoltaic (PV) cells is of great importance too. Including the impact of considering different PV cell efficiencies for different channels (wavelengths). As a conclusion, the proposed system is able to transmit 4 Gbit/s in parallel with delivering 0.5 mW of electrical power after conversion at 10 m link distance (4 channels for data, 1 channel for PoF). We show the potential of this power to integrate 16 sensor nodes each one with a power consumption of 150 µW. This power can be enough to feed different IoT sensors with power consumptions in the µW range. The feeding capability can be increased up to 6.36 mW with 1 Gbit/s data transmission by using 4 channels for PoF purposes and 1 channel for data. In this scenario, the number of powered nodes increases from 16 to 42. The thesis also focuses on the power limits in PoF technology over Single Mode Fibers (SMFs) in mobile cellular networks due to fiber non-linear effects. Efficient fiber media is very important in PoF systems. For longer distances to achieve optically powered networks, SMFs working in the third window, are preferred over Multi- Mode Fibers (MMF) due to the higher attenuation of the latter being of around 3 dB/km at 850 nm compared to 0.2 dB/km for SMF at 1550 nm. In recent years and with research focus on developing energy efficient networks with low power consumption components, a new niche for PoF technology appears.

    Utilizing the currently installed SMF to integrate PoF can save costs and provide more reliability for the designed systems. However, due to the small core area of SMFs, this can limit the maximum amount of PoF levels transmitted over these fibers due to non-linear fiber effects that may arise at high power levels and introduce losses in the PoF systems. Those high power levels may also lead to fiber damage; being 2.5 MW/cm2 the fiber damage power threshold reported in literature. We analyze in details the power losses due to these effects including Stimulated Raman Scattering (SRS) and Stimulated Brillouin Scattering (SBS). The study considers different powering scenarios including shared scenario; i.e both data and PoF signals are transmitted on the same fiber and dedicated scenario; where each data or PoF signal is transmitted alone in the fiber. The study can help to choose the proper High Power Laser (HPL) characteristics of the PoF source. This part of the thesis contains extensive simulations studies based on the powerful software tool, Virtual Photonic Instrumentation (VPI), along with some experimental results.

    We show that working with HPL (PoF source) linewidth of 100 GHz and beyond can suppress SBS effect in SMF for different transmission distances up to 20 km and injected optical powers up to 5 W. For SRS impact we show how the link length, number of data channels, wavelength of data channels and injected power levels can limit the PoF system performance. The analysis shows how critical is the consideration of data channels frequencies within C-band as working with (1530-1540) nm band for example can save noticeable power level of PoF channel at remote side compared with (1550-1560) nm. This behavior is due to SRS as Raman gain is expected to increase in the latter due to the frequency difference between HPL signal and data channels. 25 data channels can be successfully transmitted without affecting PoF efficiency due to non-linear effects with injected power levels up to 2 W and 1.4 W for 10 km and 20 km SMF links respectively. Some simulation cases show the difference between co-propagating and counter-propagating for SMF showing that higher gains are achieved when both signals are transmitted in the forward direction. The counter-propagating analysis is important for powering scenarios when both data signals and PoF signal are transmitted in opposite directions. For example, when data are sent back from remote node to the central office while PoF is located in the central office. This scheme can also provide more protection to the photodiode.

    The impact on data signal quality due to PoF transmission have been studied which show the potential of the transmission of data signals with acceptable BER for tens of kilometers with hundreds of mW of optical power for feeding purposes. This is done by performing different VPI simulations considering BER for data traffic signal transmitted with 1.25 Gbit/s in different fibers and for different powering scenarios. The analysis shows that both signals (PoF and data traffic signals) can be transmitted with no problem. The analysis also shows that no impact on data signal quality is noticed by adding Relative Intensity Noise (RIN) up to -130 dB/Hz for the PoF channel in the shared scenario. On the other hand, the thesis also discusses the potential of Analog Radio over Fiber (ARoF) technology in future centralized (C-RAN). ARoF based C-RAN for 5G front-haul can be an optimal solution to meet with the bandwidth requirements. ARoF is a promising candidate for the future 5G mobile front-haul due to its important advantages like low transmission loss and the simplicity required at the Remote Radio Units (RRU). An extensive simulation study is performed to address the design parameters for this technology in a specific configuration. Different carrier Frequencies beyond Sub-6 GHz band are considered in the simulation study to meet with the bandwidth requirements of future 5G networks. We focus mainly on SMFs as there is a considerable interest by the operators in the reuse of the already deployed broadband fiber networks, being SMFs the most popular and widely used mean for these optical fiber-based infrastructures. CP-OFDM (Cyclic Prefix-Orthogonal Frequency Division Multiplexing) is considered in the simulation as the operators selected those type of waveforms for 5G access networks. This is due to the different key performances that this waveform has such as high spectral efficiency, powerful to cope with channel frequency selectivity which is expected in high bandwidth signals causing fading due to multipath transmission, well localized in time domain and robust to timing synchronization errors. The simulation study discusses the impact of chromatic dispersion of the fiber on the transmitted radio signals. 5G New Radio (NR) signal format is considered with different modulation formats (256QAM, 64QAM, 16QAM and QPSK) and for different link lengths. All the results within this part are compared with the standard requirements of 5G. The Error Vector Magnitude (EVM) is used for this purpose. Other metrics are also used to evaluate the designed system performance such as frequency response, constellation diagrams and recovered electrical spectrum for the transmitted radio signals. The simulation results show the importance of considering the impact of fiber impairments, mainly chromatic dispersion when considering 5G mm-wave carrier frequencies and ARoF transmission. For instance, at 30 GHz of carrier frequency the results show that the RF power fading due to chromatic dispersion of the fiber is expected to occur at 4 km with periodic notches at 12 km thus leading to EVM values beyond the limits imposed by the 5G standard and meaning an unfeasible high-speed data fiber link design. While for 20 GHz, the power fading occurs around 9.4 km with periodic notches at 27 km for fiber chromatic dispersion of 17 ps/nm/km. We also show by simulations the impact of considering different fiber chromatic dispersion values, the results show a shift of these critical distances where power fading occurs. When working close to these distances, even chromatic dispersion variations of 0.05 ps/nm/km can greatly affect data signal quality and the system performance. We also show the impact of using the Dispersion Compensation Fiber (DCF) to shift these notches due to RF power fading to longer distances. In some special cases, the non-linear effects like Kerr effect is also of great importance. The simulation results show the impact of the input optical power for laser data channel especially when working near critical length (i.e distances where RF power fading dominate due to fiber chromatic dispersion). Increasing this power and working with longer distances can give rise for non-linear effects to dominate. Some of the simulations results are supported by experimental characterizations and measurements. The impact of temperature on chromatic dispersion of the fiber is briefly studied too. The analysis shows that the increment in temperature can cause chromatic dispersion variations. This behavior comes from the linear changing of the zero dispersion wavelength because of the temperature increment being of around 0.025 nm/◦C according to the literature. These variations might be of most importance when working with RF frequencies near their critical lengths as we show with the results presented in this section of the thesis. For example, 1◦C increment in temperature can cause chromatic dispersion variation of 0.0022 ps/nm/km/◦C.

    Apart from that, we show that PoF can be applied to improve data signal quality utilizing fiber nonlinearity with HPL high power levels. This is done by presenting a simulation study that discusses the impact of non-linear effects such as Self Phase Modulation (SPM) and Cross Phase Modulation (XPM). The thesis discusses the importance of considering the interaction between these effects and the chromatic dispersion of the fiber especially at PoF power levels higher than 1 W. These analyses are also supported by simulations of RoF-PoF transmission over other kinds of fibers that have different trade-off between its chromatic dispersion and SPM and XPM. We choose Large Effective Area Fiber (LEAFTM) which is one of Non-Zero dispersion shifted fibers (NZDSF) and has low chromatic dispersion (2 to 4 ps/nm/km) compared to SMF (17 ps/nm/km at 1550 nm). We discuss the difference in PoFRoF system performance over these two fibers due to non-linear effects. Our analysis shows that SMF is preferred over Large Effective Area fiber for PoF levels of 1 W and beyond as with these power levels, EVM in Large Effective Area fibers exceeds the standard limits. The thesis also briefly discusses the importance of considering the instabilities that PoF source may have; especially at high power levels and its impact on data signal quality. A case of study is also presented to discuss the potential ARoF with PoF integration in access networks for 5G front-haul. Different example of low power consumption small radio cells and IoT vision sensors are provided. As a brief summary from the thesis work presented here, two main conclusions can be summarized as follow. Firstly, the feasibility of SI-POF to provide high bandwidth connectivity in parallel with optical feeding capability to integrate smart homes with different 5G services such as Internet of Things has been demonstrated. Second, the possibility of utilizing currently installed front-haul solutions over SMF to transmit 5G New Radio signals over tens of kilometers with data signal quality following 5G standard requirements has been also proved. And this is in parallel with delivering hundreds of mW of electrical energy for feeding purposes.

    Some issues related with the research topics presented in this thesis can represent open lines for future research lines. For example, increasing the optical feeding capability inside home networks based SI-POF by using high output power LD sources. From that, the long term stability of the SI-POF would be an interesting topic to be investigated. These high power levels may increase fiber temperature that can cause aging problems specially when applying to the blue channel (405 nm) which have been used for Power over Fiber channel in this work. Other conditions that can affect the performance of the Analog Radio over Fiber link are the environmental conditions, and especially the temperature. The HPL power levels used in the experiments may increase the fiber temperature. Some studies have reported that changing the fiber temperature in Single Mode Fibers may lead to fluctuations in the fiber chromatic dispersion parameter that is a very important design parameter as we show in this work. Additional research on the fiber temperature and its effect on data signal quality by changing the chromatic dispersion of the fiber will be an interesting topic to be considered in the future. Also implement more studies about the resulted optical crosstalk in Multi-Core Fibers due to Power over Fiber transmission in such fibers and its impact on the data signal quality in the shared powering scenario would be an interesting topic too