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Abstract?Hybrid fiber-wireless (FiWi) networks, which benefit from high bandwidth and ubiquitous access of optical and wireless networks, have been identified as a promising technology candidate for next-generation broadband access. As various component/fiber failures may occur in hybrid FiWi networks, thus affecting huge numbers of end users, survivability has become one of the key important deployment considerations in such networks. This paper focuses on developing optimal network planning strategies to achieve survivable hybrid FiWi networks. In particular, to address the additional cost involved in deploying backup fibers in previously proposed redundancy strategies against distribution fiber failures, we propose the use of wireless routing through the ubiquitous wireless coverage of end users in a hybrid FiWi network. We present an optimization framework to optimally plan and deploy a survivable hybrid FiWi network, where traffic from an affected optical network unit (ONU) can be effectively rerouted to backup ONUs through wireless connections in the event of a distribution fiber failure. However, focusing only on the resilience of a network without considering its cost, and ignoring the resultant capacity, latency, and coverage under normal and protection operating conditions, is impractical. Our proposed framework therefore ensures maximum end-user coverage whilst satisfying survivability, connectivity, delay, and capacity constraints of the network, by optimizing the placement of passive optical splitters, ONUs, and wireless routers in conjunction with fiber and wireless connections. Moreover, we demonstrate the feasibility of our framework in the context of an urban deployment under different deployment scenarios. In particular, our results provide insight into how survivable FiWi networks can be deployed without compromising on the latency, coverage, and capacity requirements of such networks. [ABSTRACT FROM PUBLISHER]

Due to the massive deployment of electrical network devices, Fiber-Wireless (FiWi) access network has to suffer from the challenge of high energy consumption. With the ever-increasing eager for green communication infrastructure, the issue of high energy consumption may become one of the major barriers for the advance of FiWi access network. Previous works proposed for green FiWi access network cover three aspects, including the optimized deployment of network devices such as optical network units (ONUs), the energy-efficient bandwidth allocation of ONUs with QoS guarantee, and the dynamic power states scheduling of ONUs (i.e., active/sleep) according to their traffic profile. However, these works did not take the energy-saving design of wireless subnetwork into account simultaneously. In fact, when some ONUs in the optical subnetwork are switched into sleep states, part of the radio interfaces originally forwarding traffic to the sleep ONUs would be idle or low-loaded. This provides a potential opportunity for energy-saving in wireless subnetwork by switching off the idle or low-loaded radios. This paper focuses on the design of green multi-radio FiWi access network by integrating the energy-savings of optical and wireless subnetworks. To support the energy-efficient design, the new power states are defined for ONUs and radios, respectively. Aiming at dynamic traffic profile, the heuristic algorithms are proposed for the energy saving of integrated wireless front-end and optical back-end of FiWi access network. First, the Energy-saving algorithm with ONU sleep mechanism (EAS) is proposed to dynamically schedule the power states of ONUs by judging their traffic profile with load thresholds. Then, the Energy-saving algorithm based on Radios Off (ERO) is proposed to reconfigure the topology of wireless subnetwork by controlling the power states of radios dynamically. Moreover, wireless rerouting is employed in both EAS and ERO to guarantee the QoS provisioning ability of network. Finally, a comprehensive energy-saving scheme called EE is proposed by combining the EAS and ERO algorithms strategically. Simulation results show that with the reasonable setting of parameters, the proposed EE scheme can save the energy of 33.14% to 64.35% and 8.56% to 36.42% in a wide range of traffic load compared to the No-energy-saving and QoS-aware energy-saving scenarios, respectively. [ABSTRACT FROM PUBLISHER]

High energy consumption in Ethernet Passive Optical Networks (EPONs) has caused intense research on energy-saving methods in recent years. The most common method for EPON energy saving is to cause optical network units (ONUs) to sleep which are idle or low loaded. With the popularity of multimedia applications, the ONUs carry not only unicast traffic but also more and more multicast traffic. However, existing studies mainly focus on ONUs that support only unicast traffic. The many differences between multicast traffic and unicast traffic make it necessary to design novel energy-saving methods. This paper proposes a multicast-traffic-oriented energy-saving algorithm for EPONs, called the energy-saving algorithm for multicast traffic (ESMT). To save as much energy as possible, the proposed algorithm uses a hybrid sleep mode (composed of a deep sleep state and an independent sleep mode) in which not only can ONU enter a deep sleep state, but also the ONU transmitter and receiver can sleep independently. Simulation results show that the proposed algorithm, which is oriented to multicast traffic in EPONs, is more energy efficient than other algorithms. [ABSTRACT FROM AUTHOR]

The current Passive Optical Network (PON) has faced many challenges when heterogeneous access techniques and multiple resource multiplexing ways are involved. Thus, we require a unified control and management of time, spectrum and mode, which is a necessary standardization for PONs. For this end, the multi-dimensional and flexible PON (Mflexi-PON) will emerge as an ideal solution of supporting the heterogeneous access with different resource multiplexing ways. But a high-efficient Mflexi-PON has its own problem. In term of the physical layer of Mflexi-PONs, some signals include a series of orthogonal subcarriers, or transmission modes should have the orthogonal property. Once multiple subcarriers have the same phase, the instantaneous power of a signal will exceed the average value, thus leading to a high Peak-to-Average Power Ratio (PAPR). Furthermore, the signal or transmission mode must be kept strictly orthogonal so that it can be correctly demodulated by the receiver side, which results in the high sensitivity of frequency offset and phase noise. In addition, we need to solve these problems under various resource multiplexing approaches. Thus in this paper, we first review previous solutions for the next-generation PON and discuss some challenging issues for Mflexi-PONs. Next, some promising solutions are proposed for optimization mechanisms in this new networking paradigm, mainly including system architecture, MAC (Media Access Control) layer allocation of multi-dimensional resources, physical-layer performance improvement, and cross-layer optimization. [ABSTRACT FROM AUTHOR]

Abstract: With increasing network sizes, the energy consumption of Passive Optical Networks (PONs) has grown significantly. Therefore, it is important to design effective energy-saving schemes in PONs. Generally, energy-saving schemes have focused on sleeping the low-loaded Optical Network Units (ONUs), which tends to bring large packet delays. Further, the traditional ONU sleep modes are not capable of sleeping the transmitter and receiver independently, though they are not required to transmit or receive packets. Clearly, this approach contributes to wasted energy. Thus, in this paper, we propose an Energy-Saving scheme that is based on downstream Packet Scheduling (ESPS) in Ethernet PON (EPON). First, we design both an algorithm and a rule for downstream packet scheduling at the inter- and intra-ONU levels, respectively, to reduce the downstream packet delay. After that, we propose a hybrid sleep mode that contains not only ONU deep sleep mode but also independent sleep modes for the transmitter and the receiver. This ensures that the energy consumed by the ONUs is minimal. To realize the hybrid sleep mode, a modified GATE control message is designed that involves 10 time points for sleep processes. In ESPS, the 10 time points are calculated according to the allocated bandwidths in both the upstream and the downstream. The simulation results show that ESPS outperforms traditional Upstream Centric Scheduling (UCS) scheme in terms of energy consumption and the average delay for both real-time and non-real-time packets downstream. The simulation results also show that the average energy consumption of each ONU in larger-sized networks is less than that in smaller-sized networks; hence, our ESPS is better suited for larger-sized networks. [Copyright &y& Elsevier]

Abstract: Fiber-Wireless (FiWi) broadband access network is a promising “last mile” access technology, because it integrates wireless and optical access technologies in terms of their respective merits, such as high capacity and stable transmission from optical access technology, and easy deployment and flexibility from wireless access technology. Since FiWi is expected to carry a large amount of traffic, numerous traffic flows may be interrupted by the failure of network components. Thus, survivability in FiWi is a key issue aiming at reliable and robust service. However, the redundant deployment of backup resource required for survivability usually causes huge energy consumption, which aggravates the global warming and accelerates the incoming of energy crisis. Thus, the energy-saving issue should be considered when it comes to survivability design. In this paper, we focus on the green survivability in FiWi, which is an innovative concept and remains untouched in the previous works to our best knowledge. We first review and discuss some challenging issues about survivability and energy-saving in FiWi, and then we propose some instructive solutions for its green survivability design. Therefore, our work in this paper will provide the technical references and research motivations for the energy-efficient and survivable FiWi development in the future. [Copyright &y& Elsevier]

Abstract: In passive optical network (PON), the existing energy-saving algorithms are implemented only with one kind of PON. However, as far as Ethernet PON (EPON), good performances cannot be reached simultaneously in both 10G-EPON and 1G-EPON. Although 10G-EPON can provide higher throughput and lower delay than 1G-EPON, it consumes more energy. Currently, there are four types of optical network unit (ONU) sleep modes which are specified by ITU-T. If transmitter and receiver can be turned off independently without upstream traffic or downstream traffic, additional energy can be saved. Therefore, in this paper, to obtain high throughput and low delay with low energy consumption, we propose a new energy saving mechanism based on double-sleep-state and dynamic double-threshold receiver selection (EDDS) with the combination of 1G-EPON and 10G-EPON techniques. In EDDS, ONU's receiver not only can be switched between 1Gbps receiver and 10Gbps receiver according to the downstream traffic, but also can be put into sleep state independently when possible. Hereby, EDDS can provide higher throughput and lower delay than 1G-EPON while consume less energy than 10G-EPON. To support EDDS, new structures for optical line terminal (OLT) and ONU are introduced. Simulation results show that EDDS achieves better performances than the traditional schemes. [Copyright &y& Elsevier]