This article provides an up-to-date survey of hybrid fiber-wireless (FiWi) access networks that leverage on the respective strengths of optical and wireless. A definitive objective of Fiber-Wireless (FiWi) systems is the meeting of different optical and wireless innovations under a solitary base keeping in mind the end. Survey Smoothly Fiber-Wireless (FiWi) Accessing Wireless Networks: Convergence and Challenges. Naseer Hwaidi Alkhazaali, Raed Abduljabbar Aljiznawi.
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This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Furthermore, we discuss service, application, business, and operation related aspects, which motivate access technology to move into a substantially different direction in the long run than continued capacity provisioning.
Given that most 4G cellular mobile network researches so far have been focusing on the achievable performance gains in the wireless front-end only without looking into the details of backhaul implementations and possible backhaul bottlenecks, we identify open key research challenges for FiWi broadband access networks.
According to the Federal Communications Commission FCCbroadband enables individuals and enterprises to access a wide range of resources, services, and products related to education, culture, entertainment, telemedicine, e-commerce, public safety, and homeland security.
In a detailed study carried out by the Organisation for Economic Cooperation and Development OECD [ 1 ] it was shown that the impact of providing residential and business subscribers with broadband access is manifold. Among others, broadband enables the emergence of business models, processes, and inventions as well as improved goods and services.
Furthermore, broadband increases competitiveness and flexibility in the economy by the increased diffusion of information at lower cost and by improving market access to increasingly larger markets. Figure 1 a shows the fixed wired and wireless access technologies used by broadband subscribers in However, this situation is changing rapidly.
Clearly, this figure illustrates that an increasing percentage of broadband subscribers rely on fiber access technologies at the expense of legacy DSL solutions. This trend is expected to become even more pronounced over the next couple of decades.
In the short-to midterm, current state-of-the-art very high bit-rate DSL VDSL may be superseded by next-generation copper based solutions supported by deep fiber access networks getting increasingly closer to subscribers. We are currently witnessing a strong worldwide deployment of deep fiber access solutions to push optical fiber closer to individual homes and businesses and to help realize FTTx networks, whereby x denotes the discontinuity between optical fiber and some other transmission medium [ 3 ].
FTTCab is also used by cable network operators to build hybrid fiber-coax HFC networks, where the drop lines are realized through coax cables instead of twisted pairs.
Bringing fiber all the way to buildings gives rise to FTTB networks.
Typically, FTTB networks use a multidwelling unit MDU optical network unit ONU in the basement of the building to terminate the optical signal coming from the CO and distribute the converted signal across a separate network inside the building.
Finally, paving all the way to the home with optical fiber leads to FTTH networks, which come in two flavors: Deep fiber access is a challenging mix of technology choices, business models, and regulatory issues. According to recent market data by ABI Research, the number of fixed broadband subscribers will rise to million by the end ofof which million will subscribe to services delivered via fiber. Toward this goal, fiber together with next-generation wireless broadband technologies will play an increasingly vital role in future broadband access networks.
This is already witnessed by installed state-of-the-art VDSL equipment, which is almost exclusively based on optical fiber backhaul solutions. While copper will certainly continue to play an important role in current and near-term broadband access networks, it is expected that FTTH deployment volume will keep increasing gradually and will eventually become the predominant fixed wireline broadband technology by [ 5 ].
Optical fiber provides an unprecedented bandwidth potential that is far in excess of any other known transmission medium and offers significantly longer ranges without requiring any active devices.
Optical access networks provide transparency against data rate and signal format, which eased carriers worldwide into deploying future-proof PON outside plants that can be flexibly upgraded as new technologies mature or new standards evolve [ 7 ].
Arguing that due to its unique properties optical fiber is likely to entirely replace copper wires in the near-to midterm, we will elaborate on the final frontier of optical networks, namely, the convergence with their wireless counterparts. Optical and wireless technologies can be thought of as quite complementary and will expectedly coexist over the next decades.
Future broadband access networks will be bimodal, capitalizing on the respective strengths of both technologies and smartly merging them in order to realize future-proof fiber-wireless FiWi networks that strengthen our information society while avoiding its digital divide. By combining the capacity of optical fiber networks with the ubiquity and mobility of wireless networks, FiWi networks form a powerful platform for the support and creation of emerging as well as future unforeseen applications and services, for example, telepresence [ 8 ].
In this paper, we provide a comprehensive overview of the beginnings, state of the art, and latest developments of FiWi broadband access networks. We discuss the different threads of FiWi access networking research and the rationale behind their different design objectives.
After describing recent progress, we elaborate on the role of FiWi access networks in the dawning age of convergence and outline some exciting research directions for future FiWi access networks. The remainder of this paper is structured as follows. Section 2 describes related research topics and defines FiWi access networks as a new research area. In Section 3we review the state of the art of FiWi broadband access networks, while recent progress is described in Section 4.
Section 5 provides an outlook and outlines the road ahead for future FiWi access networks. Finally, we draw some conclusions in Section 6. Traditionally, wireless and optical fiber networks have been designed separately from each other. Wireless networks aimed at meeting specific service requirements while coping with particular transmission impairments and optimizing the utilization of the system resources to ensure cost-effectiveness and satisfaction for the user.
In optical networks, on the other hand, research efforts rather focused on cost reduction, simplicity, and future proofness against legacy and emerging services and applications by means of optical transparency. Wireless and optical access networks can be thought of as complementary.
Optical fiber does not go everywhere, but where it does go, it provides a huge amount of available bandwidth. Wireless access networks, on the other hand, potentially go almost everywhere but provide a highly bandwidth-constrained transmission channel susceptible to a variety of impairments. Future broadband access networks not only have to provide access to information when we need it, where we need it, and in whatever format we need it, but also, and arguably more importantly, have to bridge the digital divide and offer simplicity and user-friendliness based on open standards in order to stimulate the design of new applications and services.
Toward this end, future broadband access networks must leverage on both optical and wireless technologies and converge them seamlessly, giving rise to FiWi access networks [ 9 ]. FiWi access networks are instrumental in strengthening our information society while avoiding its digital divide. By combining the capacity of optical fiber networks with the ubiquity and mobility of wireless networks, FiWi networks form a powerful platform for the support and creation of emerging as well as future unforeseen applications and services.
FiWi networks hold great promise to change the way we live and work by replacing commuting with teleworking. This not only provides more time for professional and personal activities for corporate and our own personal benefit but also helps reduce fuel consumption and protect the environment; issues that are becoming increasingly important in our lives. Due to the difficulty and prohibitive costs of supplying optical fiber to all end-user premises as well as the spectrum limitations of wireless access networks, bimodal FiWi access networks are more attractive than relying on either stand-alone access solution.
To better understand the rationale behind the vision of FiWi access networks, we first describe related research topics and then define FiWi access networks as a new research area in the following. According to the European Telecommunications Standardization Institute ETSIFMC is concerned with developing network capabilities and supporting standards that may be used to seamlessly offer a set of consistent services via fixed or mobile access to fixed or mobile, public or private networks, independently of the access technique [ 10 ].
FMC can be done at different levels, for example, business or service provisioning level.
Fiber-wireless (FiWi) access networks: A survey – Semantic Scholar
Note, however, that FMC does not necessarily imply the physical convergence of networks. In fact, the convergence at the network facilities level, where an operator uses the same physical network infrastructure with common transmission and switching systems to provide both mobile and wurvey services, is more accurately referred to as fixed mobile integration FMI [ 11 ].
Current copper based access network technologies such as DSL and HFC face serious challenges to meet the requirements of future broadband access networks. While DSL suffers from severe distance and noise limitations, HFC falls short fier-wireless efficiently carry data traffic due to its upstream noise and crosstalk accumulation. Recent progress in optical fiber technologies, especially the maturity of integration and new packaging technologies, has rendered optical fiber access networks a promising low-cost broadband solution.
OWI aims at integrating PONs and other optical fiber access technologies with broadband wireless access technologies, for fibef-wireless, WiMAX, in order to increase the capacity of wireless access networks and reduce access point complexity fibet-wireless centralized management [ 12 ]. It is important to note that there is a difference between OWI and free-space optical wireless OW communications.
OW communications links operate at much higher carrier frequencies than their RF counterparts.
OW may be deployed as a temporary backbone for rapidly deployable mobile wireless communication infrastructure, especially in densely populated urban areas. Note, however, that unlike OWI networks, OW links and networks do not involve any wired fiber infrastructure. RoF networks have been studied for many years as an approach to integrate optical fiber and wireless networks. In RoF networks, RFs are carried over optical fiber links between the CO and multiple low-cost remote antenna units RAUs in support of a variety of wireless applications, for example, microcellular radio systems [ 14 ].
However, inserting an optical distribution system in wireless networks may have a major impact on the performance of medium access control MAC protocols [ 15 ]. As a consequence, wireless MAC frames do not have to travel along the optical fiber to be processed at the CO but simply traverse their associated wireless access point and remain in the wireless front-end, thus avoiding the negative impact of fiber propagation delay on the network performance. By simultaneously providing wired and wireless services over the same infrastructure, FiWi access networks are able to consolidate optical and wireless access networks that are usually run independently of each other, thus potentially leading to major cost savings.
Fiber-wireless (FiWi) access networks: A survey
FiWi networking research deals with the OWI of optical and wireless broadband access technologies, for example, wireless mesh network WMN.
FiWi research focuses on the physical PHYMAC, and fiber-wirelees layers with the goal to develop and investigate low-cost enabling FiWi technologies as well as layer-2 and layer-3 protocols and algorithms. FiWi research inquires new methods of optical RF generation exploiting fiber nonlinearities and various modulation techniques. Specifically, to avoid the electronic bottleneck, the generation of RF signals is survvey done optically.
According to [ 17 ], external intensity and phase modulation schemes are the most practical solutions for all-optical RF generation due to their low cost, simplicity, and long-distance transmission performance.
Furthermore, FiWi research also includes the study of different remodulation schemes for the design of colorless i. A number of different remodulation schemes have been proposed and investigated, for example, differentiated phase-shift keying DPSK for downstream and on-off-keying OOK for upstream, optical carrier suppression OCS for downstream and reused for upstream, or PM for downstream and directly modulated semiconductor optical amplifier SOA for upstream. The use of a colorless SOA as an amplifier and modulator for upstream transmission provides a promising low-cost RoF solution that is easy to maintain [ 17 ].
While significant progress has been made at the PHY layer of FiWi and in particular RoF transmission systems, FiWi networking research on layer-2 and layer-3 related issues has begun only recently. Beside cell-based RoF networks, a number of FiWi network architectures were proposed, which can be classified based on their wireless access technologies: As we will see shortly, different challenges were addressed such as routing and wireless channel assignment, which can be performed completely either in the wireless domain by the base station BS or access netwlrks APor by an optical network element, for example, CO or optical line terminal OLT.
The level of provided quality-of-service QoS largely depends on the performance of the implemented routing and resource management algorithms, including bandwidth allocation and flber-wireless assignment algorithms with absolute or relative QoS assurances. Cellular networks used for fast moving users, for example, train passengers, suffer from frequent handovers when hopping from one BS to another one.
The frequent handovers may cause numerous packet losses, resulting in a significantly decreased network throughput. An interesting approach to solve this problem is the use of an RoF network installed along the rail tracks in combination with the so-called moving cell concept [ 20 ].
Recently, the moving extended cell concept was proposed to provide connectivity for any possible direction [ 21 ]. The fiber optic network becomes a means for speedy handoff between base stations that serve the mobile users. The extended cell is adaptively restructured when the user enters a new cell. RoF networks are attractive since they provide transparency against modulation techniques and are able to support various digital formats and wireless standards in a cost-effective manner.
Diber-wireless single-mode fibers SMFs are typically found in outdoor optical networks, many buildings have preinstalled multimode fiber MMF cables. Apart from realizing low-cost microcellular radio networks, optical fibers can also be used to support a wide variety of other radio signals.
In [ 22 ], a low-cost MMF network was experimentally tested to demonstrate the feasibility of indoor radio-over-MMF networks for the in-building coverage of second-generation and third-generation cellular radio networks as well as IEEE According to [ 23 ], the following four architectures can be used. This type of FiWi network architecture interconnects the CO with multiple WiFi-based wireless APs by means of an optical unidirectional fiber ring [ 24 ].
The CO is responsible for managing the transmission of information between mobile client nodes MCNs and their associated APs as well as acting as a gateway to fiber-wirelews networks.
All MCNs take part in the topology discovery, whereby each MCN periodically sends the information about the beacon power received from its neighbors to its associated AP. Multihop relaying is used to extend the range.
To enhance the reliability of the wireless link, the CO sends ntworks to two different APs path diversity.
The proposed implementation can support advanced path diversity techniques that use a combination of transmission via several APs and multihop relaying, for example, cooperative diversity or multihop diversity. Consequently, the CO must be able to assign channels quickly and efficiently by using one or more wavelength channels on the fiber ring to accommodate multiple services such as WLAN and cellular radio network. In this architecture, the CO interconnects remote nodes RNs via a dual-fiber ring.
For protection, the CO is equipped with two sets of devices normal and standby.