Showing papers by "Pin-Han Ho published in 2014"

Energy efficiency in TDMA-based next-generation passive optical access networks

Abstract: Next-generation passive optical network (PON) has been considered in the past few years as a cost-effective broadband access technology. With the ever-increasing power saving concern, energy efficiency has been an important issue in its operations. In this paper, we propose a novel sleep-time sizing and scheduling framework for the implementation of green bandwidth allocation (GBA) in TDMA-PONs. The proposed framework leverages the batch-mode transmission feature of GBA to minimize the overhead due to frequent ONU on–off transitions. The optimal sleeping time sequence of each ONU is determined in every cycle without violating the maximum delay requirement. With multiple ONUs possibly accessing the shared media simultaneously, a collision may occur. To address this problem, we propose a new sleep-time sizing mechanism, namely Sort-And-Shift (SAS), in which the ONUs are sorted according to their expected transmission start times, and their sleep times are shifted to resolve any possible collision while ensuring maximum energy saving. Results show the effectiveness of the proposed framework and highlight the merits of our solutions .

Transmission Scheduling and Game Theoretical Power Allocation for Interference Coordination in CoMP

Abstract: In 3GPP LTE-A, Coordinated Multi-Point (CoMP) is adopted to enhance the transmission rates of edge users To maximize the total downlink throughput of all edge users, it is crucial to properly determine the set of simultaneously served users in each physical resource block (PRB) and the cooperative base stations (BSs) for each scheduled user, as well as the transmit power of the BSs Based on the reference signal receiving power (RSRP) of each edge user, we first propose two simple and integrated transmission scheduling algorithms, one distributed and the other centralized, to choose cell-edge users and cooperative BSs in each PRB With the scheduling results, the classic Water-Filling (WF) algorithm is carried out over all PRBs at each BS to get an initial single cell power allocation To take the interference among different cooperative BS sets into account, we further formulate a non-cooperative power allocation game to adjust the initial power allocation for interference coordination, where the initial power allocation provides the strategy space of the game for each BS This increases the total downlink throughput of edge users over all BSs We prove that the game has a unique Nash Equilibrium (NE), and design an algorithm to find the NE Performance gain is then demonstrated through extensive simulation studies

Joint Design on DCN Placement and Survivable Cloud Service Provision over All-Optical Mesh Networks

Abstract: Cloud services based on data center networks (DCNs) require a transmission infrastructure with high-capacity, low-latency, low-cost and high-availability, which can be offered by survivable optical networks. DCN placement is a fundamental issue in supporting cloud services in optical networks. It concerns not only the cost of providing cloud services, but also the service availability against failures via proper service replicas. In this paper, we jointly optimize DCN placement with service routing and protection to minimize the network cost, while ensuring fast protection of all services against any single link failure or service failure at a particular DCN. An ILP (Integer Linear Program) is first formulated to achieve optimal joint design. It integrates p-cycle (preconfigured protection cycle) for fast protection against a single link failure, and DCN replicas and fast service rerouting against a service failure. To make the design more scalable, a two-step heuristic is then proposed for large-size network scenarios. The first step separately solves the DCN placement and service routing problem in the failure-free scenario, and the second step takes fast service protection into account. The proposed design is validated by extensive numerical experiments.

Achieving Secure Communications over Wiretap Channels via Security Codes from Resilient Functions

Abstract: By manipulating both binary and non-binary resilient functions, a novel approach for generating security codes is introduced and their threshold probabilities are derived, which provides the security condition proof for the proposed security codes. In particular, by taking advantage of matrix general inverse algorithms the encoding method of the proposed security codes is derived and is practically implementable due to low complexity. Experiments are conducted to examine the proposed security codes and the security system over Binary Symmetric Channel (BSC).

On signaling-free failure dependent restoration in all-optical mesh networks

Abstract: Failure dependent protection (FDP) is known to achieve optimal capacity efficiency among all types of protection, at the expense of longer recovery time and more complicated signaling overhead. This particularly hinders the usage of FDP in all-optical mesh networks. As a remedy, this paper investigates a new restoration framework that enables all-optical fault management and device configuration via state-of-the-art failure localization techniques, such as the FDP restoration process. It can be implemented without relying on any control plane signaling. With the proposed restoration framework, a novel spare capacity allocation problem is defined and is further analyzed on circulant topologies for any single link failure, aiming to gain a solid understanding of the problem. By allowing reuse of monitoring resources for restoration capacity, we are particularly interested in the monitoring resource hidden property, where less or even no monitoring resources are consumed as more working traffic is in place. To deal with general topologies, we introduce a novel heuristic approach to the proposed spare capacity allocation problem, which comprises a generic FDP survivable routing scheme followed by a novel monitoring resource allocation method. Extensive simulation is conducted to examine the proposed scheme and verify the proposed restoration framework.

Fair packet scheduling in Wireless Mesh Networks

Abstract: In this paper we study the interactions of TCP and IEEE 802.11 MAC in Wireless Mesh Networks (WMNs). We use a Markov chain to capture the behavior of TCP sessions, particularly the impact on network throughput due to the effect of queue utilization and packet relaying. A closed form solution is derived to numerically determine the throughput. Based on the developed model, we propose a distributed MAC protocol called Timestamp-ordered MAC (TMAC), aiming to alleviate the unfairness problem in WMNs. TMAC extends CSMA/CA by scheduling data packets based on their age. Prior to transmitting a data packet, a transmitter broadcasts a request control message appended with a timestamp to a selected list of neighbors. It can proceed with the transmission only if it receives a sufficient number of grant control messages from these neighbors. A grant message indicates that the associated data packet has the lowest timestamp of all the packets pending transmission at the local transmit queue. We demonstrate that a loose ordering of timestamps among neighboring nodes is sufficient for enforcing local fairness, subsequently leading to flow rate fairness in a multi-hop WMN. We show that TMAC can be implemented using the control frames in IEEE 802.11, and thus can be easily integrated in existing 802.11-based WMNs. Our simulation results show that TMAC achieves excellent resource allocation fairness while maintaining over 90% of maximum link capacity across a large number of topologies.

Signaling free localization of node failures in all-optical networks

Abstract: Network-wide local unambiguous failure localization (NL-UFL) has been demonstrated as an interesting scenario of monitoring trails (m-trails). It attempts to enable every node to autonomously localize any failure event in the network in a distributed and all-optical manner by inspecting a set of m-trails traversing through the node. This paper investigates the m-trail allocation problem under the NL-UFL scenario by taking each link and node failure event into consideration. Bound analysis is performed using combinatorial group testing (CGT) theory and this is followed by the introduction of a novel heuristic on general topologies. Extensive simulation is conducted to examine the proposed heuristic in terms of the required cover length and the number of m-trails to achieve NL-UFL.

Multi-link failure localization via monitoring bursts

Abstract: This paper introduces a novel monitoring trail (m-trail) allocation method for achieving local unambiguous failure localization under the monitoring burst (m-burst) framework, in which a single monitoring node (MN) can localize any multi-link failure with up to d links in a (d + 1)-connected network by inspecting the optical bursts traversing through it Specifically, the proposed m-trail allocation method ensures that any healthy link is traversed by at least one uninterrupted m-trail during a multi-link failure, which can be achieved by launching no more than (d + 1)-link-disjoint m-trails per link originating from the MN Based on such a sufficient condition, we study the performance of the m-burst framework by solving an integer linear program (ILP) and a novel heuristic, and implement the method for up to three link failures To avoid high computation complexity in solving the ILP, a heuristic algorithm is developed for deriving (d + 1)-link-disjoint m-trails between the MN and each link of the network Numerical results show that the proposed methods yield significantly better performance than previous methods in the reference backbone network topologies

Guest Editorial Energy-Efficiency in Optical Networks

Abstract: THE increasing concern for environmental and cost issues has made energy efficiency in telecom networks an important theme. According to a recent report [1], today’s networks are wasting a lot of energy by consuming 10,000 times more energy than what is really needed. The Internet currently consumes about 0.4% of the total electricity in broadband-enabled countries and is foreseen to quickly reach 1% with the current trend of data transmission rate increase [2]. These numbers have triggered tremendous efforts and collaborations between industry and academia to address this epidemic and challenging problem. Consequently in 2010, Green Touch [3]—a consortium of leading Information and Communications Technology (ICT) industry, academic and non-governmental research experts, was launched aiming to make communications networks 1,000 times more energy-efficient within five years. The joint effort to reach this goal would not only reduce the world’s carbon emissions directly contributed by the ICT sector (which is estimated to be around 2%), but also lower the remaining 98% of the carbon emissions contributed by all the other sectors directly and indirectly affected by ICT [3]. Optical communication and networking technologies have been widely applied to both access networks and Internet optical backbone, and further incorporated with other wired and wireless systems in order to enable an end-to-end serviceprovisioning platform and to support specific application scenarios. This leads to a design paradigm of integrated optical networks, which targets better exploration of user experiences, network/carrier economics, and control/management flexibility by way of heterogeneous system integration, end-to-end considerations, and global optimization. Such a design paradigm has driven the emergence of many exciting research topics and applications, such as Long-Reach Passive Optical Networks (LR-PONs), translucent optical networks, Fiber-Wireless (FIWI) integration, and Radio-over-Fiber (RoF).

Internet Optical Infrastructure: Issues on Monitoring and Failure Restoration

Abstract: This book covers the issues of monitoring, failure localization, and restoration in the Internet optical backbone, and focuses on the progress of state-of-the-art in both industry standard and academic research. The authors summarize, categorize, and analyze the developed technology in the context of Internet fault management and failure recovery under the Generalized Multi-Protocol Label Switching (GMPLS), via both aspects of network operations and theories.

A Novel Energy-Efficient Transmission Scheme in CO-OFDM Elastic Optical Networks

Abstract: The use of orthogonal frequency division multiplexing (OFDM) technology enables an optical transmission system to break the limitation of wavelength grids due to legacy of wavelength division multiplexing. This constructs a flexible and elastic transmission paradigm so as to achieve high spectrum efficiency and flexibility of fiber resource usage. This paper introduces a novel adaptive transmission strategy in elastic coherent optical OFDM transmission systems, aiming to optimize the system operation in terms of energy and spectrum consumptions for a transmission demand with a required data rate. By jointly considering the nonlinear effects of Mach–Zehnder modulator and amplified spontaneous emission noise from optical amplifiers, as well as the performance impairment due to high peak-to-average-power ratio (PAPR) in the electronic domain, we first provide an analytical model on the bit error rate performance for a single-elastic optical transmission line. To achieve an efficient PAPR reduction, we introduce a new method called simplified null switching, which is considered very suitable in the elastic optical transmission systems due to lower computation complexity and little dependence on the channel side information. Based on the analytical model, an optimization problem is formulated based on the proposed analytical model and solved via mathematical programming. Case studies via extensive numerical experiments are conducted to verify the proposed analytical model and gain better understanding on the solutions of formulated optimization problem.

Fault localization in all-optical linear networks

Abstract: The paper investigates single-link fault localization in all-optical networks in a line topology in which a single monitoring node (MN) can localize shared risk link group (SRLG) faults by inspecting the optical bursts traversing through it. We investigate relevant problems in the proposed fault monitoring approach, including m-trail allocation, burst launching time scheduling, and node switch fabric configuration, where constructions are developed to derive optimal solutions and are further examined in numerical experiments.

SRLG failure localization using nested M-trails

Abstract: This paper introduces a novel technique called nested m-trail method in all-optical mesh networks for failure localization of any shared risk link group (SRLG) with up to d undirected links. The proposed method decomposes each network topology that is at least d-connected into virtual cycles and trails, in which sets of m-trails that traverse through a common monitoring node (MN) can be obtained. The nested m-trails are used in the monitoring burst (m-burst) framework, in which the MN can localize any SRLG failure by inspecting the optical bursts traversing through it. An integer linear program (ILP) and a heuristic are proposed for the network decomposition, which are further verified by numerical experiments. We show that the proposed method significantly reduces the required fault localization latency compared to the existing methods.

Superposition transmission of layered encoded sources over non-orthogonal amplify-forward relay networks

Abstract: The paper investigates the broadcast of n-layered source codes over a single-relay network using a half-duplex nonorthogonal amplify-forward (HD-NAF) relaying protocol. Taking the distortion exponent, (i.e., the SNR exponent of the average end-to-end distortion) as the performance metric, we consider system operation in the high SNR regime. We first prove that the HD-NAF relay network with an n-layer code is subject to the successively refinable Diversity Multiplexing Tradeoff (DMT) curve, which is exercised to derive a closed-form expression for an achievable upper bound of the system distortion exponent. Rate allocation optimization is conducted to analyze and gain insight into system behavior. Numerical evaluations are performed based on derived analytical formulations, and the performance advantage of single-relay HD-NAF networks is justified in terms of the distortion exponent versus its conventional counterparts. Furthermore, it is observed that increases in the number of encoded layers increases system performance.

Fault localization in all-optical ring networks

Abstract: The paper investigates dual-link fault localization in all-optical ring networks using optical probes (called monitoring bursts). By defining a single monitoring node (MN) in the ring that initiates and terminates a set of monitoring trails (m-trails), the MN can localize any dual-link fault by inspecting the on-off status of the launched optical bursts. We investigate relevant problems in the proposed fault monitoring approach, including m-trail allocation, burst launching time scheduling, and node switch fabric configuration, where constructions are developed to derive optimal solutions and are further examined in numerical experiments. 2(|Ej| − 1) m-trails and at most (2δ + L)(|E| − 1) + δ(|E| − 2) of monitoring delay are required for dual-link fault localization from a single MN in a ring with|E| links, where δ is the burst propagation delay along a unidirectional link and L is the burst length.

Optimized BS assignment and resource allocation in cooperative OFDM networks

Abstract: Cooperative transmission (CT) and orthogonal frequency division multiple (OFDM) are promising technologies for extending coverage and increasing throughput in broadband wireless access (BWA) networks. Therefore, we propose a novel BWA network architecture, that can set up inter-cell collaboration using physical layer cooperative transmissions among distributed wired access networks with a powerful coordination capability at the central office. However, conventional base station (BS) assignment and resource allocation schemes cannot be used directly because a user can be serviced by more than one BS with cooperative transmission technology. This study proposes a novel framework of BS assignment and resource allocation in a cooperative OFDM network. We provide three approaches of resource allocation for minimizing bandwidth usage, minimizing transmission power consumption, and balancing resource costs respectively. An optimized resource allocation scheme can be implemented by flexibly choosing one of these approaches based on network load. The simulation results show the efficiency of the proposed mathematical formulations and linearization approach of our scheme. The performance benefit of CT technology on the bandwidth saving is demonstrated by comparing the new BS assignment and resource allocation scheme with conventional non-cooperative transmission.