Wei-Tao Shaw

Next-Generation Optical Access Networks

The last mile continues to be a major bottleneck in the Internet. Its low bandwidth and flexibility prevents the deployment of new services and the development of new applications. In this paper we present a summary of current efforts in access networks research, focusing in particular on fiber optic solutions. We present the Stanford University aCCESS (SUCCESS) initiative within the Photonics & Networking Research Laboratory (PNRL). As part of this initiative, two novel network architectures have been developed, SUCCESS-HPON and SUCCESS-DWA, which propose a smooth migration path from current TDM-PONs to future higher bandwidth, cost-efficient, scalable WDM-PONs. In addition, we present SUCCESS-LCO, a spectral-shaping line coding technique that enables a cost-effective shorter-term capacity upgrade of existing TDM-PONs. We discuss as well what we believe are the main open research areas in optical access networks.

Hybrid Architecture and Integrated Routing in a Scalable Optical–Wireless Access Network

We propose a hybrid optical-wireless access network that consists of reconfigurable optical backhaul and wireless mesh networks (WMNs). The complementary characteristics of wireless and optical networks are combined to provide a broadband and ubiquitous last-mile connection. Wireless mesh routers are deployed to penetrate the vicinity of end users for a flexible and ubiquitous connection. It eliminates massive and geographically scattered deployment of physical infrastructure to reach the end users. The broadband optical backhaul consists of optical ring and multiple tree networks, connecting the central hub and WMNs. The ends of the optical tree networks connect to the wireless gateway routers of WMNs. A hybrid time-division-multiplexing (TDM)/wavelength-division-multiplexing (WDM) optical backhaul is realized by wavelength-multiplexing multiple TDM-passive-optical-network streams. This hybrid architecture provides graceful scalability, cost effectiveness, and bandwidth efficiency. To adapt to a change of the overall demand in different districts, reconfigurability is implemented in the optical backhaul utilizing tunable optical transceivers. An experimental test bed is implemented to evaluate the reconfigurable scheme. Given the synergy of the optical backhaul and WMNs, we propose an integrated-routing algorithm to achieve load balancing on this hybrid architecture. The simulation using NS2 shows an approximately 25% throughput improvement with load balancing.

Homodyne Phase-Shift-Keying Systems: Past Challenges and Future Opportunities

Homodyne phase-shift-keying systems can achieve the best receiver sensitivity and the longest transmission distance among all optical communication systems. This paper reviews recent research efforts in the field and examines future possibilities that might lead toward potential practical use of these systems. Additionally, phase estimation techniques based on feed-forward phase recovery and digital delay-lock loop approaches are examined, simulated, and compared

Next Generation Optical Access Networks

The last mile continues to be a major bottleneck in the Internet. Its low bandwidth and flexibility prevents the deployment of new services and the development of new applications. In this paper we present a summary of current efforts in access networks research, focusing in particular on fiber optic solutions. We present the Stanford University aCCESS (SUCCESS) initiative within the Photonics & Networking Research Laboratory (PNRL). As part of this initiative, two novel network architectures have been developed, SUCCESS-HPON and SUCCESS-DWA, which propose a smooth migration path from current TDM-PONs to future higher bandwidth, cost-efficient, scalable WDM-PONs. In addition, we present SUCCESS-LCO, a spectral-shaping line coding technique that enables a cost-effective shorter-term capacity upgrade of existing TDM-PONs. We discuss as well what we believe are the main open research areas in optical access networks.

Success PON demonstrator: experimental exploration of next-generation optical access networks

The deployment of passive optical networks for broadband access has been largely recognized as a promising solution to open the first-/last-mile bottleneck. We propose and demonstrate a new hybrid TDM/WDM PON architecture that jointly serves multiple physical PONs to enjoy statistical multiplexing gain as well as cost sharing. This article describes design and implementation issues of the key building blocks, including fast tunable lasers, burst-mode receivers, and scheduling algorithms with quality of service support. A prototype testbed is constructed, and transmission experiments are performed to show the effectiveness of the integrated system. Coexistence with current PONs and future evolutional paths are described as well. Experimental explorations of the new network architecture involve advanced photonic and electronic subsystems, which inspires developments of the next-generation optical access networks.

SUCCESS-DWA: a highly scalable and cost-effective optical access network

Passive optical networks have been identified as promising access solutions that can open the first-mile bottleneck, bringing gigabits-per-second data rates to end users. Current TDM PONs enjoy low cost by sharing resources in time, but suffer from limited capacity. In the future, WDM technology may be employed to achieve high performance. In this article we introduce a novel PON employing dynamic wavelength allocation to provide bandwidth sharing across multiple physical PONs. Tunable lasers, arrayed waveguide gratings, and coarse/fine filtering combine to create a flexible new optical access solution. The networks excellent scalability can bridge the gap between conventional TDM PONs and WDM PONs. The powerful architecture is a promising candidate for next-generation optical access networks.

Smooth upgrade of existing passive optical networks with spectral-shaping line-coding service overlay

A simple and cost-effective upgrade of existing passive optical networks (PONs) is proposed, which realizes service overlay by novel spectral-shaping line codes. A hierarchical coding procedure allows processing simplicity and achieves desired long-term spectral properties. Different code rates are supported, and the spectral shape can be properly tailored to adapt to different systems. The computation can be simplified by quantization of trigonometric functions. DC balance is achieved by passing the dc residual between processing windows. The proposed line codes tend to introduce bit transitions to avoid long consecutive identical bits and facilitate receiver clock recovery. Experiments demonstrate and compare several different optimized line codes. For a specific tolerable interference level, the optimal line code can easily be determined, which maximizes the data throughput. The service overlay using the line-coding technique leaves existing services and field-deployed fibers untouched but fully functional, providing a very flexible and economic way to upgrade existing PONs.

OPN01-6: Enabling Security Countermeasure and Service Restoration in Passive Optical Networks

In this paper, we introduce a novel passive and wavelength selective remote node specifically designed to enable security countermeasure in PONs. The central office could physically isolate problem makers from the network without disrupting regular links by issuing a wavelength specific control signal to this device. With its wavelength selective nature, the countermeasure-enabled passive device is also a natural candidate to a WDM-PON remote node. To demonstrate its feasibility, a discrete version of the device is implemented. In addition to enable countermeasure capability, a new kind of PON restoration technique that employs a hybrid optical-wireless network is proposed. Finally, cost and performance considerations are discussed in an 8-channel planer lightwave circuit example.

MARIN Hybrid Optical-Wireless Access Network

A novel hybrid optical-wireless access network is proposed for metropolitan area. This novel architecture consists of wireless mesh networks and a reconfigurable optical backhaul and aggregation network based on TDM-PON technology.

Reconfigurable Optical Backhaul and Integrated Routing Algorithm for Load Balancing in Hybrid Optical-Wireless Access Networks

Various wireless and optical access technologies have been developed to address different issues in access networks. By combining the complementary characteristics of wireless and optical networks, a hybrid optical-wireless access network will enable broadband, ubiquitous, and cost-effective last-mile service to the users. In this paper, a reconfigurable optical backhaul leveraging both the standard Time Division Multiplexing Passive Optical Network (TDM-PON) technology and wavelength division multiplexed (WDM) ring is proposed to achieve a higher bandwidth efficiency than simply using point-to-point backhaul links. Furthermore, an integrated routing algorithm which can adapt to the change of overall demand among different service districts by taking advantage of the proposed optical backhaul is also proposed. An experimental testbed is implemented to evaluate the reconfigurable scheme and its feasibility. Also, simulation results show that the proposed integrated routing with load balancing can improve the performance in hybrid optical and wireless networks.