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As a promising modulation technology for optical communication, Orthogonal Frequency Division Multiplexing (OFDM) is now increasingly used and a lot of ways of improving the optical efficiency of Intensity Modulated/ Direct Detection (IM/DD) systems have been proposed. And real and non-negative OFDM signals are required in this kind of system. Asymmetrically clipped DC biased Optical OFDM (DCO-OFDM), Asymmetrically Clipped Optical OFDM (ACO-OFDM) and Asymmetrically clipped DC biased Optical OFDM (ADO-OFDM) can satisfy this requirement. In this paper, we analysis the properties and performance orderly of the above three systems and simultaneously compare their performance. The simulation results show that DCO-OFDM is efficient in terms of bandwidth while the ACO-OFDM is efficient in terms of optical power. More importantly, ADO-OFDM is both power-efficient and bandwidth-efficient. At the same time, a developmentally proposal for the future OFDM in IM/DD systems is put forward.

As one of promising "last mile" scheme for broadband access network, Fiber-Wireless (FiWi) access network has the advantages of high capacity, long distance, low cost etc because it is the integration of optical back-end and wireless front-end. At the same time, energy consumption of FiWi access network is an important factor that limits the development of networks. A number of ONU sleep states such as ONU power shedding state, ONU doze state, ONU deep sleep state and ONU fast sleep state have been proposed to obtain low-power ONU state, which indirectly reduce energy consumption of networks. However, these low-power states of ONU are born to coordinate to green Passive Optical Network (PON), of which the function of ONU is different from FiWi. In this paper, two low power ONU sleep mechanisms called Static ONU Sleep (SOS) mechanism and Dynamic ONU Sleep (DOS) mechanism, respectively, are proposed and embedded into FiWi access network. By simulation and analysis based on OPNET 14.5, this paper shows that the DOS mechanism has a better performance than SOS, and both of them can save energy of FiWi access network.

The wireless ultraviolet (UV) communication technology has received great attention for either short-range high data-rate services or medium-to-large range low-rate sensing applications. However, performance of an UV link is limited by multiple constraints from the current UV laser source and detector technology, and atmospheric link conditions. In this paper, we have designed a model of UV communication system using OPTISYSTEM simulator to establish a FSO link between transmitter and receiver by a distance of 500m at data rate of 2.5 Gbps which is no reported in previous investigated works.

This paper addresses the fault-tolerant mechanisms in Wireless mesh networks (WMNs), and designs a C++ based simulation platform to measure the performance of different fault-tolerant mechanisms. A comprehensive performance evaluation of network coding tree algorithm (NCT), 1+1 scheme and 1: N scheme in WMNs is conducted. Performance metrics, such as packet delivery ratio, resource redundancy degree, end-to-end delay, and useful throughput ratio, are investigated. The simulation results and performance analysis reveal that how wireless channel quality can influence the performance of WMNs and how different fault-tolerant mechanisms can be efficient and effective for latency-sensitive applications in WMNs. The results can also provide the enlightening insights for efficient design of fault-tolerant routing protocols for many-to-one traffic pattern in WMNs.

Survivability is one of the key issues in Fiber-Wireless (FiWi) access network since a single network component failure may cause enormous data loss. This paper focuses on survivability of citywide FiWi access network and proposes a scheme using Integer Linear Programming (ILP) to tolerate the failures of distribution fiber and WiFi routers considering coverage problem. Simulation shows good performance of this scheme. When WiFi routers and ONUs are places in suitable potential sites, the maximal coverage of uses and survivability of FiWi access network are realized.

Considering the high throughput requirement in Wireless Mesh Networks (WMNs), a novel network coding based routing (NCBR) protocol is presented in this paper. The NCBR protocol could actively create potential coding opportunities in the process of path establishment, which attempts to choose an appreciated route with more coding benefits among available path candidates. After this paper gives the proposed coding condition, it describes the working principle of NCBR protocol in detail. Based on NS-2 platform, average end-to-end throughput is measured to evaluate the effectiveness of NCBR by varying the offered load and number of flows. The simulation results demonstrate that the proposed NCBR protocol performs better in enhancing average end-to-end throughput than traditional AODV and AODV+COPE schemes. In particular, average end-to-end throughput could be improved by 11% compared with the AODV+COPE case.

In order to solve the green energy saving problem with the wireless routing technology, a new energy-efficient survivable routing protocol, called Energy-efficient Survivable AODV (ES-AODV) for unicast demand in green Wireless Mesh Networks (WMNs), is proposed in this paper. The routing protocol uses the hop penalty strategy and flooding delaying strategy to improve the performances of traditional AODV routing protocol. This paper uses QualNet to simulate and verify the performances of proposed ES-AODV. The simulation results show that, compared with the traditional AODV, the energy utilization of ES-AODV is more efficient than AODV by 13%. At the same time, ES-AODV is more load-balancing to reduce the number of energy depletion nodes and postpone the appearance of the first energy depletion node, and thus it effectively improves the network survivability.