Dynamic Bandwidth Allocation for NG-PONs with channel bonding

Channel bonding is a recently proposed technique to provide higher aggregated line rates in NG-PONs by allowing ONUs to operate simultaneously in multiple wavelengths. On the other hand, the Dynamic Bandwidth Allocation (DBA) algorithm allocates to each ONU the grant time interval on each upstream frame that the ONU can use to transmit its data in the upstream direction. Channel bonding imposes a new challenge in the DBA algorithm as the grant time interval allocated to a ONU must be the same in all its channel-bonded wavelengths. In this work, we propose a new DBA algorithm for NG-PONs supporting data services which is a combination of a proportional fairness strategy and a max-min fairness strategy and guarantees the constraints imposed by channel bonding. We illustrate the merits of the new algorithm with two cases based on simulation. The results show that channel bonding can provide better QoS performance to data services even in cases where it is not strictly required.publishe

WDM/TDM PON bidirectional networks single-fiber/wavelength RSOA-based ONUs layer 1/2 optimization

This Thesis proposes the design and the optimization of a hybrid WDM/TDM PON at the L1 (PHY) and L2 (MAC) layers, in terms of minimum deployment cost and enhanced performance for Greenfield NGPON. The particular case of RSOA-based ONUs and ODN using a single-fibre/single-wavelength is deeply analysed. In this WDM/TDM PON relevant parameters are optimized. Special attention has been given at the main noise impairment in this type of networks: the Rayleigh Backscattering effect, which cannot be prevented. To understand its behaviour and mitigate its effects, a novel mathematical model for the Rayleigh Backscattering in burst mode transmission is presented for the first time, and it has been used to optimize the WDM/TDM RSOA based PON. Also, a cost-effective, simple design SCM WDM/TDM PON with rSOA-based ONU, was optimized and implemented. This prototype was successfully tested showing high performance, robustness, versatility and reliability. So, the system is able to give coverage up to 1280 users at 2.5 Gb/s / 1.25 Gb/s downstream/upstream, over 20 Km, and being compatible with the GPON ITU-T recommendation. This precedent has enabled the SARDANA network to extend the design, architecture and capabilities of a WDM/TDM PON for a long reach metro-access network (100 km). A proposal for an agile Transmission Convergence sub-layer is presented as another relevant contribution of this work. It is based on the optimization of the standards GPON and XG-PON (for compatibility), but applied to a long reach metro-access TDM/WDM PON rSOA-based network with higher client count. Finally, a proposal of physical implementation for the SARDANA layer 2 and possible configurations for SARDANA internetworking, with the metro network and core transport network, are presented

Towards Higher Speed Next Generation Passive Optical Networks

L'abstract è presente nell'allegato / the abstract is in the attachmen

Communications with spectrum sharing in 5g networks via drone-mounted base stations

The fifth generation wireless network is designed to accommodate enormous traffic demands for the next decade and to satisfy varying quality of service for different users. Drone-mounted base stations (DBSs) characterized by high mobility and low cost intrinsic attributes can be deployed to enhance the network capacity. In-band full-duplex (IBFD) is a promising technology for future wireless communications that can potentially enhance the spectrum efficiency and the throughput capacity. Therefore, the following issues have been identified and investigated in this dissertation in order to achieve high spectrum efficiency and high user quality of service. First, the problem of deploying DBSs is studied. Deploying more DBSs may increase the total throughput of the network but at the expense of the operation cost. The droNe-mounted bAse station PlacEment (NAPE) problem with consideration of IBFD communications and DBS backhaul is then formulated. The objective is to minimize the number of deployed DBSs while maximizing the total throughput of the network by incorporating IBFD-enabled communications for both access links and backhaul links via DBSs as relay nodes. A heuristic algorithm is proposed to solve the NAPE problem, and its performance is evaluated via extensive simulations. Second, the 3-D DBS placement problem is investigated as the communication efficiency is greatly affected by the positions of DBSs. Then, the DBS placement with IBFD communications (DSP-IBFD) problem for downlink communications is formulated, and two heuristic algorithms are proposed to solve the DSP-IBFD problem based on different DBS placement strategies. The performance of the proposed algorithms are demonstrated via extensive simulations. Third, the potential benefits of jointly optimizing the radio resource assignment and 3-D DBS placement are explored, upon which the Drone-mounted Base Station Placement with IBFD communications (DBSP-IBFD) problem is formulated. Since the DBSP-IBFD problem is NP-hard, it is then decomposed into two sub-problems: the joint bandwidth, power allocation and UE association problem and the DBS placement problem. A 1/2(1-/2^{l}})-approximation algorithm is proposed to solve the DBSP-IBFD problem based on the solutions to the two sub-problems, where l is the number of simulation runs. Simulation results demonstrate that the throughput of the proposed approximation algorithm is superior to benchmark algorithms. Fourth, the uplink communications is studied as the mobile users need to transmit and receive data to and from base stations. The Backhaul-aware Uplink communications in a full-duplex DBS-aided HetNet (BUD) problem is investigated with the objective to maximize the total throughput of the network while minimizing the number of deployed DBSs. Since the BUD problem is NP-hard, it is then decomposed into three sub-problems: the joint UE association, power and bandwidth assignment problem, the DBS placement problem and the problem of determining the number of DBSs to be deployed. The AA-BUD algorithm is proposed to solve the BUD problem with guaranteed performance based on the solutions to the three sub-problems, and its performance is demonstrated via extensive simulations. The future work comprises two parts. First, a DBS can be used to provide both communications and computing services to users. Thus, how to minimize the average latency of all users in a DBS-aided mobile edge computing network requires further investigation. Second, the short flying time of a drone limits the deployment and the performance of DBSs. Free space optics (FSO) can be utilized as the backhaul link and the energizer to provision both communication and energy to a DBS. How to optimize the charging efficiency while maximizing the total throughput of the network requires further investigation

Monolithic 1.3 μm InAs/GaAs Quantum Dot Lasers on Silicon: Simulation and Experiment

1.3 μm quantum dot (QD) lasers epitaxially grown on silicon have attracted great interest as light source for silicon photonics and other optical communication applications. This work focuses on improving the understanding of the physical mechanisms limiting the performance of these devices, and on studying the laser dynamics with respect to data transmission potential through simulation and experiment. Dislocation-induced carrier loss is a major concern for the performance of QD lasers on silicon. Part of this work aims, therefore, at identifying the processes degrading the laser characteristics as well as on understanding the performance disparity between silicon-based QD and quantum well (QW) devices. By using two specially extended types of rate equation travelling-wave models it is found that enhanced carrier loss at higher dislocation densities leads to a much larger laser threshold increase in QW than in QD lasers. The QD laser’s increased tolerance to dislocations can be explained based on efficient and ultrafast carrier capture into the QDs, where high energy barriers prevent them from migrating into defects. The carrier density reduction in the higher energy continuum layers is eventually reflected in a lower current injection efficiency and thus reduced light-current slope, confirming experimentally observed trends of 1.3 μm QD lasers on silicon. In particular, a large minority carrier diffusion length is identified as a key parameter inhibiting laser operation in QW-based devices. The other part of this work focuses on investigating the QD lasers’ dynamics by means of gain switching, small-signal and large-signal modulation. 150 ps short gain-switched pulses, modulation bandwidths of 1.6 GHz to 2.3 GHz, and optical eyes at 1.5 Gb/s are obtained from 2.5 mm long ridge-waveguide lasers grown and fabricated at University College London. Numerical simulations reveal that the observed high-speed limitations are a result of limited gain and a long photon lifetime, whereas suitability for 10 Gb/s operation is predicted in an optimised laser design. It was, furthermore, found that neither dislocation-induced carrier loss nor optical loss limit the modulation characteristics fundamentally. The reduced carrier lifetime is, however, reflected in stronger damping of the small-signal modulation curves. Apart from that, the overall device dynamics remain governed by the QD physics.Qualcomm Inc. School of Technology PhD scholarshi

Software Defined Applications in Cellular and Optical Networks

abstract: Small wireless cells have the potential to overcome bottlenecks in wireless access through the sharing of spectrum resources. A novel access backhaul network architecture based on a Smart Gateway (Sm-GW) between the small cell base stations, e.g., LTE eNBs, and the conventional backhaul gateways, e.g., LTE Servicing/Packet Gateways (S/P-GWs) has been introduced to address the bottleneck. The Sm-GW flexibly schedules uplink transmissions for the eNBs. Based on software defined networking (SDN) a management mechanism that allows multiple operator to flexibly inter-operate via multiple Sm-GWs with a multitude of small cells has been proposed. This dissertation also comprehensively survey the studies that examine the SDN paradigm in optical networks. Along with the PHY functional split improvements, the performance of Distributed Converged Cable Access Platform (DCCAP) in the cable architectures especially for the Remote-PHY and Remote-MACPHY nodes has been evaluated. In the PHY functional split, in addition to the re-use of infrastructure with a common FFT module for multiple technologies, a novel cross functional split interaction to cache the repetitive QAM symbols across time at the remote node to reduce the transmission rate requirement of the fronthaul link has been proposed.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Measurement-Driven Algorithm and System Design for Wireless and Datacenter Networks

The growing number of mobile devices and data-intensive applications pose unique challenges for wireless access networks as well as datacenter networks that enable modern cloud-based services. With the enormous increase in volume and complexity of traffic from applications such as video streaming and cloud computing, the interconnection networks have become a major performance bottleneck. In this thesis, we study algorithms and architectures spanning several layers of the networking protocol stack that enable and accelerate novel applications and that are easily deployable and scalable. The design of these algorithms and architectures is motivated by measurements and observations in real world or experimental testbeds. In the first part of this thesis, we address the challenge of wireless content delivery in crowded areas. We present the AMuSe system, whose objective is to enable scalable and adaptive WiFi multicast. AMuSe is based on accurate receiver feedback and incurs a small control overhead. This feedback information can be used by the multicast sender to optimize multicast service quality, e.g., by dynamically adjusting transmission bitrate. Specifically, we develop an algorithm for dynamic selection of a subset of the multicast receivers as feedback nodes which periodically send information about the channel quality to the multicast sender. Further, we describe the Multicast Dynamic Rate Adaptation (MuDRA) algorithm that utilizes AMuSe's feedback to optimally tune the physical layer multicast rate. MuDRA balances fast adaptation to channel conditions and stability, which is essential for multimedia applications. We implemented the AMuSe system on the ORBIT testbed and evaluated its performance in large groups with approximately 200 WiFi nodes. Our extensive experiments demonstrate that AMuSe can provide accurate feedback in a dense multicast environment. It outperforms several alternatives even in the case of external interference and changing network conditions. Further, our experimental evaluation of MuDRA on the ORBIT testbed shows that MuDRA outperforms other schemes and supports high throughput multicast flows to hundreds of nodes while meeting quality requirements. As an example application, MuDRA can support multiple high quality video streams, where 90% of the nodes report excellent or very good video quality. Next, we specifically focus on ensuring high Quality of Experience (QoE) for video streaming over WiFi multicast. We formulate the problem of joint adaptation of multicast transmission rate and video rate for ensuring high video QoE as a utility maximization problem and propose an online control algorithm called DYVR which is based on Lyapunov optimization techniques. We evaluated the performance of DYVR through analysis, simulations, and experiments using a testbed composed of Android devices and o the shelf APs. Our evaluation shows that DYVR can ensure high video rates while guaranteeing a low but acceptable number of segment losses, buffer underflows, and video rate switches. We leverage the lessons learnt from AMuSe for WiFi to address the performance issues with LTE evolved Multimedia Broadcast/Multicast Service (eMBMS). We present the Dynamic Monitoring (DyMo) system which provides low-overhead and real-time feedback about eMBMS performance. DyMo employs eMBMS for broadcasting instructions which indicate the reporting rates as a function of the observed Quality of Service (QoS) for each UE. This simple feedback mechanism collects very limited QoS reports which can be used for network optimization. We evaluated the performance of DyMo analytically and via simulations. DyMo infers the optimal eMBMS settings with extremely low overhead, while meeting strict QoS requirements under different UE mobility patterns and presence of network component failures. In the second part of the thesis, we study datacenter networks which are key enablers of the end-user applications such as video streaming and storage. Datacenter applications such as distributed file systems, one-to-many virtual machine migrations, and large-scale data processing involve bulk multicast flows. We propose a hardware and software system for enabling physical layer optical multicast in datacenter networks using passive optical splitters. We built a prototype and developed a simulation environment to evaluate the performance of the system for bulk multicasting. Our evaluation shows that the optical multicast architecture can achieve higher throughput and lower latency than IP multicast and peer-to-peer multicast schemes with lower switching energy consumption. Finally, we study the problem of congestion control in datacenter networks. Quantized Congestion Control (QCN), a switch-supported standard, utilizes direct multi-bit feedback from the network for hardware rate limiting. Although QCN has been shown to be fast-reacting and effective, being a Layer-2 technology limits its adoption in IP-routed Layer 3 datacenters. We address several design challenges to overcome QCN feedback's Layer- 2 limitation and use it to design window-based congestion control (QCN-CC) and load balancing (QCN-LB) schemes. Our extensive simulations, based on real world workloads, demonstrate the advantages of explicit, multi-bit congestion feedback, especially in a typical environment where intra-datacenter traffic with short Round Trip Times (RTT: tens of s) run in conjunction with web-facing traffic with long RTTs (tens of milliseconds)