Passive optical networks (PONs) are currently evolving into next-generation PONs (NG-PONs) which aim at achieving higher data rates, wavelength channel counts, number of optical network units (ONUs), and extended coverage compared to their conventional counterparts. Due to the increased number of stages and ONUs, NG-PONs face significant challenges to provide the same level of survivability like conventional PONs without exceeding the budget constraints of cost-sensitive access networks. Toward this end, partial optical protection, in combination with interconnecting a subset of ONUs through a wireless mesh network (WMN) front-end, are promising solutions to render NG-PONs survivable in a cost-effective manner. In this paper, we present a probabilistic analysis of the survivability of NG-PONs and hybrid fiber-wireless (FiWi) access networks, taking both optical and wireless protection into account. In addition, we propose different selection schemes to wirelessly upgrade a subset of ONUs, and investigate their performance for a wide range of fiber link failure scenarios and different NG-PON topologies.

Survivability Analysis of Next-Generation Passive Optical Networks and Fiber-Wireless Access Networks

The fastest ever 11.25Gb/s real-time FPGA-based optical orthogonal frequency division multiplexing (OOFDM) transceivers utilizing 64-QAM encoding/decoding and significantly improved variable power loading are experimentally demonstrated, for the first time, incorporating advanced functionalities of on-line performance monitoring, live system parameter optimization and channel estimation. Real-time end-to-end transmission of an 11.25Gb/s 64-QAM-encoded OOFDM signal with a high electrical spectral efficiency of 5.625bit/s/Hz over 25km of standard and MetroCor single-mode fibres is successfully achieved with respective power penalties of 0.3dB and -0.2dB at a BER of 1.0 x 10(-3) in a directly modulated DFB laser-based intensity modulation and direct detection system without in-line optical amplification and chromatic dispersion compensation. The impacts of variable power loading as well as electrical and optical components on the transmission performance of the demonstrated transceivers are experimentally explored in detail. In addition, numerical simulations also show that variable power loading is an extremely effective means of escalating system performance to its maximum potential.

Experimental demonstration of a record high 11.25Gb/s real-time optical OFDM transceiver supporting 25km SMF end-to-end transmission in simple IMDD systems.

Fiber to the home is the future-proof technology for broadband access networks. Several fiber access network architectures have been developed (e.g., point-to-point, active optical network, and passive optical network). PON is considered the most promising solution due to the relatively low deployment cost and high resource efficiency. Meanwhile, because of the growing demand for reliable service delivery, fault management is becoming more significant in all parts of communications networks. However, there is a trade-off between the cost of protection and the level of service reliability. Since economical aspects are most critical in the access part of networks, improving reliability performance by duplication of network resources (and capital expenditures) could be too expensive. Therefore, recent work has focused on PON protection schemes with reduced CAPEX. The future trend will probably migrate toward minimizing operational expenditures during the access network lifetime. The main contributions of this article include providing a general method for CAPEX and OPEX analysis that can be applied to any type of fiber access network with consideration of changed component cost in time and variable take rates, and comparing the total cost (i.e., sum of CAPEX and OPEX) for the selected representative architectures with and without protection for business and residential users in relation to reliability performance. The aim is to give a guideline for the design of the most cost-effective protection schemes, while maintaining acceptable service reliability.

Cost vs. reliability performance study of fiber access network architectures

Next-generation access networks are expected to provide mobility, large data bandwidth, high quality of service (QoS), and ubiquitous coverage. Hybrid optical-wireless access networks will support these complementary features through high-capacity fiber subnetworks and flexible wireless subnetworks. As wireless access technologies progress, increased demand for access bandwidth and QoS will require a rapid evolution of fiber subnetworks and a tighter integration of the two technologies. This paper presents both radio-over-fiber transport technologies and novel architectures and technologies for hybrid optical-wireless networking. Basic optical systems for radio signals' transport use intensity modulation and direct detection. Advanced transport systems may utilize amplified links, coherent links, subcarrier transport, and digitized transport. They can be used to support powerful access solutions. On the networking side, diverse alternatives for hybrid access architectures are presented. Two wavelength division multiplexing (WDM)-based architectures, MARIN and GROWNet, are analyzed in detail. Both architectures dynamically support next-generation wireless access network traffic employing reconfigurable WDM technologies. MARIN is more technologically conservative and so is more suitable for near-future implementation. GROWNet is more technologically aggressive and is substantially more flexible and more powerful. Using hybrid network simulations, we demonstrate these architectures' capabilities to dynamically balance wireless traffic and to coordinate wireless transmission. We also review other research efforts in this field including ACCORDANCE, FiWi, FUTON, and WOBAN. Remaining challenges and research topics are also discussed to motivate further investigations into optical-wireless access networks.

Hybrid Optical–Wireless Access Networks

The design and measurement of two optical receivers with integrated photodiode in 130 nm CMOS is presented. The low bandwidth, which is typical for photodiodes in CMOS technologies, is circumvented by a differential photodiode topology on the one hand and by including an optimized equalizer in the receiver chain on the other hand. The low responsivity of a CMOS photodiode is compensated by a very low-noise design for the differential TIA. The disadvantage of such a low-noise design is its high power consumption. Therefore, a design strategy is presented where part of the circuit is biased in weak inversion. Doing so, the power consumption is decreased from 138 mW for the standard design to only 74.16 mW. Both designs are measured optically with 850 nm modulated light and are able to operate at 4.5 Gbit/s with a BER lower than 10-12. The sensitivities for this BER and speed are - 3.8 dBm and -3.4 dBm respectively. The receivers even work up to 5 Gbit/s for BER values around 10-9.

High-Speed Optical Receivers With Integrated Photodiode in 130 nm CMOS

Fiber has been envisioned for delivering broadband services to the residential customer for over 30 years, yet it has only recently entered the mainstream. Currently, fiber-to-the-home (FTTH) is being installed in many countries at remarkable rates (even though it still constitutes only a fraction of all broadband lines in most countries). Other lightwave transmission technologies have progressed far faster. What has held FTTH up for so long? What improvements along the way have occurred? What recent changes have made it successful? This article follows the progress in moving fiber toward the home and major architectural changes that have reduced costs while increasing capabilities to meet today's needs.

P.W. Shumate

Papers

Fiber-to-the-Home: 1977–2007