In a hybrid PON xDSL access network, multiple customer premise equipment (CPE) nodes connect over individual digital subscriber lines (DSLs) to a drop-point device. The drop-point device, which is typically reverse powered from the customer, is co-located with an optical network unit (ONU) of the passive optical network (PON). We demonstrate that the drop-point experiences very high buffer occupancies when no flow control or standard Ethernet PAUSE frame flow control is employed. In order to reduce the buffer occupancies in the drop-point, we introduce two gated flow control protocols that extend the polling-based PON medium access control to the DSL segments between the CPEs and the ONUs. We analyze the timing of the gated flow control mechanisms to specify the latest possible time instant when CPEs can start the DSL upstream transmissions so that the ONU can forward the upstream transmissions at the full PON upstream transmission bit rate. Through extensive simulations for a wide range of bursty traffic models, we find that the gated flow control mechanisms, specifically, the ONU and CPE grant sizing policies, enable effective control of the maximum drop-point buffer occupancies.
Two physical-layer systems to bridge VDSL signals over a fiber access network were proposed in @cite_22 . Individual VDSL signals are converted to be spectrally stacked into a composite signal that modulates an optical carrier. In the first system the optical carrier is supplied by a laser at the ONU and in the second system the optical carrier is supplied by a laser in the OLT that is reflected and modulated by a Reflective Semiconductor Optical Amplifier (RSOA) at the ONU. The optical carrier provides 1 GHz of spectral width accommodating 40 VDSL lines without guard bands and 25 VDSL lines with guard bands. Although, this approach to a hybrid PON xDSL allows the drop-point device to avoid buffering as well as contain simple logic by pulling the DSLAM functionality into the OLT, the design requires the PON to carry the full bandwidth of each VDSL line even when idle. Designs that operate at the link layer rather than physical layer can avoid transmission of idle data on the PON thereby increasing the number of subscribers that can be supported by capitalizing on statistical multiplexing gains.
@cite_22
2044354677
Feature Issue on Optical Access Networks (OAN) We describe two schemes developed to carry very-high-data-rate DSL (VDSL) signals over a fiber to the cabinet architecture for the upgrade of legacy copper networks. The first technique exploits the subcarrier bandwidth of uncooled semiconductor lasers for the transmission of multiple VDSL signals by using inexpensive interfacing hardware in the optical network unit (ONU). With a hybrid fiber-copper link comprising 100 m of twisted-pair copper cable and as much as 45 km of single-mode fiber, data transmission comparable with that for fiber to the home is achieved. In an extension to this design we demonstrate a system using a reflective semiconductor optical amplifier in a carrierless remote ONU configuration. Such a design might provide wavelength agility in the fiber access network for signal routing or active bandwidth allocation. Preface to the Second Edition. Preface to the First Edition. 1 Ray Optics. 2 Wave Optics. 3 Beam Optics. 4 Fourier Optics. 5 Electromagnetic Optics. 6 Ploarization Optics. 7 Photonic-Crystal Optics. 8 Guided-Wave Optics. 9 Fiber Optics. 10 Resonator Optics. 11 Statistical Optics. 12 Photon Optics. 13 Photon and Atoms. 14 Laser Amplifiers. 15 Lasers. 16 Semiconductor Optics. 17 Semiconductor Photon Sources. 18 Semiconductor Photon Detectors. 19 Acousto-Optics. 20 Electro-Optics. 21 Nonlinear Optics. 22 Ultrafast Optics. 23 Optical Interconnects and Switches. 24 Optical Fiber Communications. A Fourier Transform. B Linear Systems. C Modes of Linear Systems. Symbols and Units. Authors. Index. We present different mechanisms for downstream transmissions in the coax segment of Ethernet Passive Optical Network (EPON) Protocol over Coax (EPoC). EPoC is the transparent extension of EPON over a cable operator's Hybrid Fiber-Coax network. For managing and controlling such a hybrid network, a network operator prefers to have a unified scheduling, management, and quality of service environment that includes both the optical and coax portions of the network. In EPoC, this is achieved by extending the EPON Medium Access Control to run over the coax physical layer, to have a centralized end-to-end network control from the cable head-end to the end users premises. In this paper, we focus on the downstream transmissions in EPoC. We study three different framing approaches for downstream coax frames based on how sub-carriers in an orthogonal frequency division multiplexed symbol are modulated. We discuss the merits and demerits of each approach and then compare them based on their control overheads and the maximum average data transmission rates each of them can achieve. We analyze how different parameters such as modulation profile, symbol duration, number of sub-carriers and length of resource blocks affect the data rates and the performance of downstream transmissions. We present simulation results to examine the implications of these factors on packet-level performance, such as delay. The results indicate that dynamic and hybrid framing approaches tend to perform better than static approaches, when traffic and usage pattern are identical to those in real-world scenarios. Finally, we outline the important engineering and research problems in this area which can be topics of future research. As optical networks evolve towards more dynamicity and an ever more efficient and elastic spectrum utilization, a more integrated, fault tolerant and system efficient design is becoming critical. To increase efficiency of spectral resource in bit rate per Hz (bit s Hz), high-level modulation formats are used, challenged by the accompanying optical impairments and the resulting limitation of optical reach. Previous work has addressed the issue of optical reach and transmission fault tolerance in the physical layer by deploying various FEC schemes and by a careful design of optical transceivers and links. This paper uses a different approach, applicable to link and networking layers. We propose a novel theoretical framework, whereby a randomized linear network coding (LNC) is applied to the main optical path, and in parallel, an auxiliary optical path is used at much lower transmission speeds, i.e., in addition to the main path. With the reception of the auxiliary path, as we analytically show, the system is highly tolerant to bit errors and packet loss caused by optical impairments in the main path, whereby alleviating the constraints on optical transmission quality and indirectly achieving better optical reach and spectral efficiency. The results are shown for a case study of high-speed Ethernet end-system transmitted over optical OFDM networks, which due to the inherent system-level parallelism in both networks, present one of the most interesting candidate technologies for the proposed method to yield best performance. A novel media access control (MAC) protocol named carrier sense multiple access with idle detection (CSMA ID) is proposed to handle variable-length packets over an all-optical ring network. To evaluate optimal utilization of channel bandwidth, we study packet scheduling based on three transmitting queue discipline (TQD) architectures and four idle space allocation (ISA) algorithms with regard to their impact on performance. For numerical evaluation of performance, an analytical model is developed by a preclassification queue with weighted round-robin (PCQWRR) architecture and a random algorithm. Moreover, three related MAC protocols are examined and compared, namely, multitoken, carrier sense multiple access collision avoidance (CSMA CA) and carrier sense multiple access collision preemption (CSMA CP). Simulation results indicate that, of the TQDs, better performance is obtained by PCQWRR compared with first-in-first-out and preclassification queues. The first fit space (FFS) algorithm has the best performance of the ISAs. The 12 combinations of TQDs-ISAs are then considered. It is found that the combination of PCQWRR with FFS provides the greatest efficiency and has the lowest packet latency, providing better throughput than three different MAC protocols under either symmetric or asymmetric traffic load on all-optical ring networks. Abstract The concept of physical-layer network coding (PNC) was proposed in 2006 for application in wireless networks. Since then it has developed into a subfield of network coding with wide implications. The basic idea of PNC is to exploit the mixing of signals that occurs naturally when electromagnetic (EM) waves are superimposed on one another. In particular, at a receiver, the simultaneous transmissions by several transmitters result in the reception of a weighted sum of the signals. This weighted sum is a form of network coding operation by itself. Alternatively, the received signal could be transformed and mapped to other forms of network coding. Exploiting these facts turns out to have profound and fundamental ramifications. Subsequent works by various researchers have led to many new results in the domains of (1) wireless communication, (2) information theory, and (3) wireless networking. The purpose of this paper is fourfold. First, we give a brief tutorial on the basic concept of PNC. Second, we survey and discuss recent key results in the three aforementioned areas. Third, we examine a critical issue in PNC: synchronization. It has been a common belief that PNC requires tight synchronization. Recent results suggest, however, that PNC may actually benefit from asynchrony. Fourth, we propose that PNC is not just for wireless networks; it can also be useful in optical networks. We provide an example showing that the throughput of a passive optical network (PON) could potentially be raised by 100 with PNC. Orthogonal frequency-division multiplexing (OFDM) is a modulation technology that has been widely adopted in many new and emerging broadband wireless and wireline communication systems. Due to its capability to transmit a high-speed data stream using multiple spectral-overlapped lower-speed subcarriers, OFDM technology offers superior advantages of high spectrum efficiency, robustness against inter-carrier and inter-symbol interference, adaptability to server channel conditions, etc. In recent years, there have been intensive studies on optical OFDM (O-OFDM) transmission technologies, and it is considered a promising technology for future ultra-high-speed optical transmission. Based on O-OFDM technology, a novel elastic optical network architecture with immense flexibility and scalability in spectrum allocation and data rate accommodation could be built to support diverse services and the rapid growth of Internet traffic in the future. In this paper, we present a comprehensive survey on OFDM-based elastic optical network technologies, including basic principles of OFDM, O-OFDM technologies, the architectures of OFDM-based elastic core optical networks, and related key enabling technologies. The main advantages and issues of OFDM-based elastic core optical networks that are under research are also discussed. Software-defined networking (SDN) has been proposed as a next-generation control and management framework, facilitating network programmability to address emerging dynamic application requirements. The separation of control and data planes in SDN demands the synergistic operation of the two entities for globally optimized performance. We identify the collaboration of the control plane and the data plane in software-defined optical transmission systems as a cyber-physical interdependency where the "physical" fiber network provides the “cyber” control network with means to distribute control and signaling messages and in turn is itself operated by these "cyber" control messages. We focus on the cyber-physical interdependency in SDN optical transmission from a network robustness perspective and characterize cascading failure behaviors. Our analysis suggests that topological properties pose a significant impact on failure extensibility. We further evaluate the effectiveness of optical layer reconfigurability in improving the resilience of SDN controlled optical transmission systems. The emerging high-speed Ethernet is expected to take full advantage of the currently deployed optical infrastructure, i.e., optical transport network over wavelength division multiplexing (OTN WDM) networks. Parallel transmission is a viable option towards this goal, as exemplified by several IEEE and ITU-T standards. The optical virtual concatenation protocol in the OTN layer defined in ITU-T G.709 enables high-speed Ethernet signals to be decoupled into low rate virtual containers. The multiple lane distribution layer defined in IEEE 802.3ba facilitates the optical parallel transmission by stripping Ethernet signals into multiple low rate lanes which can be mapped onto optical channels. In this paper, we propose a new optimization framework for parallel transmission in OTN WDM networks to support high-speed Ethernet. We formulate the parallel transmission optimization as an integer linear programming problem encompassing three sub-problems: parallel wavelength routing and assignment, usage of electronic buffering for skew compensation, and bufferless parallel transmission. To reduce computational complexity, we deploy multi-objective evolutionary optimization. The numerical results show that parallel transmission in OTN WDM networks is feasible, and optimal solutions can be obtained with minimum resource consumption and bufferless system design. We investigate optical network unit (ONU) grant scheduling techniques for multichannel Ethernet passive optical networks (EPONs), such as wavelength division multiplexed (WDM) EPONs. We take a scheduling theoretic approach to solving the grant scheduling problem. We introduce a two-layer structure of the scheduling problem and investigate techniques to be used at both layers. We present an extensive ONU grant scheduling simulation study that provides: 1) insight into the nature of the ONU grant scheduling problem and 2) indication of which scheduling techniques are best for certain conditions. We find that the choice of scheduling framework has typically the largest impact on average queueing delay and achievable channel utilization. An offline scheduling framework is not work conserving and consequently wastes channel resources while waiting for all ONU REPORT messages before making access decisions. An online scheduling framework, although work conserving, does not provide the best performance since scheduling decisions are made with the information contained in a single ONU REPORT. We propose a novel online just-in-time (JIT) scheduling framework that is work conserving while increasing scheduling control by allowing the channel availability to drive the scheduling process. In online JIT, multiple ONU REPORTs can be considered together when making scheduling decisions, resulting in lower average queueing delay under certain conditions and a more effective service differentiation of ONUs. The hybrid wireless-optical broadband-access network (WOBAN) is a promising architecture for future access networks. Recently, the wireless part of WOBAN has been gaining increasing attention, and early versions are being deployed as municipal access solutions to eliminate the wired drop to every wireless router at customer premises. This architecture saves on network deployment cost because the fiber need not penetrate each end-user, and it extends the reach of emerging optical-access solutions, such as passive optical networks. This paper first presents an architecture and a vision for the WOBAN and articulates why the combination of wireless and optical presents a compelling solution that optimizes the best of both worlds. While this discussion briefly touches upon the business drivers, the main arguments are based on technical and deployment considerations. Consequently, the rest of this paper reviews a variety of relevant research challenges, namely, network setup, network connectivity, and fault-tolerant behavior of the WOBAN. In the network setup, we review the design of a WOBAN where the back end is a wired optical network, the front end is managed by a wireless connectivity, and, in between, the tail ends of the optical part [known as optical network unit (ONU)] communicate directly with wireless base stations (known as ldquogateway routersrdquo). We outline algorithms to optimize the placement of ONUs in a WOBAN and report on a survey that we conducted on the distribution and types of wireless routers in the Wildhorse residential neighborhood of North Davis, CA. Then, we examine the WOBAN's routing properties (network connectivity), discuss the pros and cons of various routing algorithms, and summarize the idea behind fault-tolerant design of such hybrid networks. Abstract Underwater wireless communications can be carried out through acoustic, radio frequency (RF), and optical waves. Compared to its bandwidth limited acoustic and RF counterparts, underwater optical wireless communications (UOWCs) can support higher data rates at low latency levels. However, the severe aquatic channel conditions (e.g., absorption, scattering, turbulence, etc.) pose great challenges for UOWCs and significantly reduce the attainable communication ranges, which necessitates efficient networking and localization solutions. Therefore, we provide a comprehensive survey on the challenges, advances, and prospects of underwater optical wireless networks (UOWNs) from a layer by layer perspective which includes: (1) Physical layer issues including propagation characteristics, channel modeling, and modulation techniques (2) Data link layer problems covering link configurations, link budgets, performance metrics, and multiple access schemes; (3) Network layer topics containing relaying techniques and potential routing algorithms; (4) Transport layer subjects such as connectivity, reliability, flow and congestion control; (5) Application layer goals, and (6) Localization and its impacts on UOWN layers. Finally, we outline the open research challenges and point out the prospective directions for underwater optical wireless communications, networking, and localization studies. In this paper, we propose a novel wireless indoor events detection system, TRIEDS. By leveraging the time-reversal technique to capture the changes of channel state information (CSI) in the indoor environment, TRIEDS enables low-complexity single-antenna devices that operate in the ISM band to perform through-the-wall indoor multiple events detection. The multipath phenomenon denotes that the electromagnetic signals undergo different reflecting and scattering paths in a rich-scattering environment. In TRIEDS, each indoor event is detected by matching the instantaneous CSI to a multipath profile in a training database. To validate the feasibility of TRIEDS and to evaluate the performance, we build a prototype that works on ISM band with carrier frequency being 5.4 GHz and 125 MHz bandwidth. Experiments are conducted to detect the states of the indoor wooden doors. Experimental results show that with a single receiver access point and transmitter (client), TRIEDS can achieve a detection rate higher than 96.92 and a false alarm rate smaller than 3.08 under either line-of-sight (LOS) or non-LOS transmission. In this paper we consider an IEEE 802.15.4-based Wireless Body Area Network, where wearable sensor devices are distributed on a body and have to send the measured data to a coordinator. The Carrier Sense Multiple Access with Collision Avoidance algorithm defined by the standard is used as Medium Access Control protocol, whereas different modulation schemes are assumed to be available at the physical layer. We propose a novel Link Adaptation (LA) strategy, where nodes select the modulation scheme according to the experienced channel quality and level of interference. The novelty lays in the fact that in case of large Signal-to-Noise Ratio and low Signal-to-Interference Ratio nodes increase the bit rate, instead of reducing it, as largely done in the works present in the literature. The reduction of the bit rate, in fact, allows to decrease the time the channel is occupied and, therefore, the collision probability. Performance is evaluated in terms of packet error rate and results achieved with and without LA are compared. Results show that the proposed strategy improves performance. This paper develops a deep learning framework for the design of on-off keying (OOK) based binary signaling transceiver in dimmable visible light communication (VLC) systems. The dimming support for the OOK optical signal is achieved by adjusting the number of ones in a binary codeword, which boils down to a combinatorial design problem for the codebook of a constant weight code (CWC) over signal-dependent noise channels. To tackle this challenge, we employ an autoencoder (AE) approach to learn a neural network of the encoder-decoder pair that reconstructs the output identical to an input. In addition, optical channel layers and binarization techniques are introduced to reflect the physical and discrete nature of the OOK-based VLC systems. The VLC transceiver is designed and optimized via the end-to-end training procedure for the AE. Numerical results verify that the proposed transceiver performs better than baseline CWC schemes. There is a growing awareness that the utilized bandwidth of deployed optical fiber is rapidly approaching its maximum limit. Given the possibility for such capacity crunch, the research community has focused on seeking solutions that make the most out of the scarce network resources (such as the fiber bandwidth) and allow accommodating the ever-increasing traffic demands. In such context, new spectrum efficient optical networking techniques have been introduced as a way to offer efficient utilization of the available optical resources. "Flexible", "elastic", "tunable", "gridless" or "adaptive" are few examples of the terms used in literature to describe solutions that migrate from the fixed WDM single line rate systems to systems that provide support for the most efficient bandwidth utilization. In this paper, we review the recent developments on the research topic of flexible elastic networking and we highlight the future research challenges. A Laser-based Structured Light System (LbSLS) has been designed to perform underwater close-range 3D reconstructions even with high turbidity conditions and outperform conventional systems. The system uses a camera and a 532 nm green laser projector. The optical technique used is based on the projection of a pattern obtained placing a Diffractive Optical Element (DOE) in front of the laser beam. In the experiments described in this manuscript, the DOE used diffracts the laser beam in 25 parallel lines providing enough information in a single camera frame to perform a 3D reconstruction. Software defined networking in the optical physical layer is complicated by transmission control used to both optimize performance and stabilize optical signals across multiple nodes. Different approaches are emerging to address these problems. Fiber optic cables are the workhorses of today's Internet services. Operators spend millions of dollars to purchase, lease and maintain their optical backbone, making the efficiency of fiber essential to their business. In this work, we make a case for adapting the capacity of optical links based on their signal-to-noise ratio (SNR). We show two immediate benefits of this by analyzing the SNR of over 2000 links in an optical backbone over a period of 2.5 years. First, the capacity of 80 of IP links can be augmented by 75 or more, leading to an overall capacity gain of 145 Tbps in a large optical backbone in North America. Second, at least 25 of link failures are caused by SNR degradation, not complete loss-of-light, highlighting the opportunity to replace link failures by link flaps wherein the capacity is adjusted according to the new SNR. Given these benefits, we identify the disconnect between current optical and networking infrastructure which hinders the deployment of dynamic capacity links in wide area networks (WANs). To bridge this gap, we propose a graph abstraction that enables existing traffic engineering algorithms to benefit from dynamic link capacities. We evaluate the feasibility of dynamic link capacities using a small testbed and simulate the throughput gains from deploying our approach. Achieving multi-gigabit per second data rates, millimeter wave communication promises to accommodate future and current demands for very high speed wireless data transmission. However, the mandatory use of directional antennas brings significant challenges for the design of efficient MAC layer mechanisms. In particular, IEEE 802.11ad for the 60 GHz band lacks omni-directional transmissions and carrier sensing. This prevents stations from overhearing the actions of other stations, the so called “deafness” problem, which substantially impairs the efficiency and fairness of CSMA CA medium access. Most existing solutions to this problem depend on properties of lower frequency bands and thus do not apply to 60 GHz. In this paper, we propose a dual-band MAC protocol combining 60 GHz communication with co-existing 5 GHz interfaces. By broadcasting control messages on 5 GHz frequencies, we solve the deafness problem and can use the 60 GHz band exclusively for high rate data transmission. While our approach occupies air time on the 5 GHz band for control messages, it does achieve a net throughput gain (over both bands) of up to 65.3 compared to IEEE 802.11ad. In addition, our simulation results show an improvement of MAC fairness of up to 42.8 over IEEE 802.11ad.