This study discusses two key technologies used in radio-over-fiber (RoF) systems, namely, the generation and transmission of millimeter-wave signals and optical modulation schemes capable of carrying vector signal formats and utilizing the continuous performance improvements offered by digital signal processing. A cost-effective frequency-quadrupling technique capable of generating millimeter-wave signals up to 72 GHz is proposed. The generated optical millimeter-wave signals have very high quality, with an optical carrier and harmonic distortion suppression ratio exceeding 36 dB. An optical modulation scheme that can support a 64-QAM, 16 Gbits/s orthogonal frequency-division multiplexing RoF system is also demonstrated. Results of this study demonstrate that both methods offer realistic solutions to support future wireless systems.
Following the approach of a prior integer linear programming network design model to provide specified dual-failure restorability levels, we develop a new model that allows for an enhanced dual-failure restorability approach. We observe that some dual-failure scenarios affecting a single p-cycle can, in fact, be partially restorable, contravening the typical understanding of p-cycle network restorability. We show that a p-cycle network that utilizes this enhanced dual-failure restorability can be designed more cost-effectively than one without it, saving as much as 20.01% in capacity design costs and averaging 7.93% over the test cases we studied. (C) 2008 Optical Society of America
Presented is a fuzzy-logic-based scheduling algorithm for passive optical networks (PONs) that considers four different metrics to allocate an upstream bandwidth to optical network units (ONUs). The metrics considered are the delay of the head-of-the-line packets at the ONUs, the importance level of the packets, the relative ONU's buffer fullness, and the level of the power fluctuation from one ONU to another. One of the advantages of a fuzzy controller is the fact that, regardless of the design complexity, the controller can be implemented as a simple look-up table, which makes it ideal for high-speed operation. Further facilitation of implementation was achieved by realization of the fuzzy algorithm through a two-stage hierarchal architecture. Moreover, linear predictive filters have been used to predict the traffic arrival rate and the packet delay at the ONUs. Compared with the round-robin scheduling algorithm, the results show significant performance improvement in terms of the overall packets delay as well as jitter when the proposed algorithm in employed. Furthermore, using this algorithm would reduce the average level of power fluctuations in a PON system and will also provide high-level service differentiation between packets of different importance. (C) 2009 Optical Society of America
This paper addresses the problem of providing bandwidth and delay guarantees in passive optical networks. To resolve this problem we propose an algorithm that provides absolute bandwidth and delay bound guarantees. Simulation results show that the proposed algorithm does not breach bandwidth and delay bounds for guaranteed service traffic even under the highest loads. Additionally, we analyze the lower bound for providing delay guarantees.
The main challenge for present and future personal communication systems and personal communication networks stems from the exponentially growing user demand. Radio over fiber (RoF), the combination of optical and wireless technologies, has many advantages and a wide range of applications. The 3G wireless communication technology uses wideband code division multiple access (WCDMA) standards to support the broadband services, and RoF technology will be an appropriate candidate in such environments. This paper presents what is believed to be a novel double-spreading mechanism, both in the wireless and optical domains for the cascaded RoF systems. Although a star configuration is the most popular because of its easy maintenance, the cascade or bus configuration can reduce the fiber counts and is hence cost-effective. Simulation studies on bit-error-rate performance for different numbers of users using orthogonal variable spread factor (OVSF) codes in the wireless domain and Walsh-Hadamard codes for optical code division multiple access (OCDMA) in the optical domain have been carried out. Hence, in view of less system complexity and cost, the proposed double-spreading technique would be an ideal solution for WCDMA-based wireless systems and the upcoming 4G with backbone cascaded RoF networks. (C) 2009 Optical Society of America
This paper describes recent research activities and results in the area of photonic switching carried out within the framework of the EU-funded e-Photon/ONe + network of excellence, Virtual Department on Optical Switching. Technology aspects of photonics in switching and, in particular, recent advances in wavelength conversion, ring resonators, and packet switching and processing subsystems are presented as the building blocks for the implementation of a high-performance router for the next-generation Internet. (C) 2009 Optical Society of America
What we believe to be a novel system for the distribution of high-definition video streams in a residential environment is demonstrated. The system utilizes impulse radio ultrawideband (IR-UWB) technology integrated with a fiber-based distribution network. The pulses are directly generated in the optical domain, and the receiver is implemented with a carrier recovery system for the demodulation. The system was built and tested to demonstrate error-free operation of the distribution network and the receiver. Spectrum shaping by varying the pulse position within the bit slot to optimize system performance is also examined.
Passive optical networks (PONs) are being aggressively pursued as a means of delivering access network solutions. The cost benefits resulting from a reduction in the number of interfaces between nodes has enabled increasing deployment of a PON delivering fiber to the home and fiber to the curb. However, in many cases, the need for high split ratios or an extended-reach requires amplification to overcome additional losses. Erbium-doped amplifiers have a limited use in PONs since the operational wavelengths typically include backhaul at 1.3 mu m. Semiconductor optical amplifiers (SOAs) offer a cost-effective solution with a migration path toward integration; deployment options include its use as a preamplifier, booster, or midspan amplifier. We present a theoretical treatment that analyzes the amplified system operational requirements and justifies this analysis through the experiment. The analysis considers for the first time to our knowledge the dc offset that is introduced into the receiver as a result of the significant amplified spontaneous emission powers present in amplified PONs, where filter widths are typically 20 nm or greater. (C) 2009 Optical Society of America
Some of the work carried out within the European integrated project Integrated Photonic mm-Wave Functions for Broadband Connectivity (IPHOBAC) on the development of photonic components and radio-over-fiber technologies for broadband wireless communication is reviewed. In detail, 60 GHz outdoor radio systems for >10 Gbits/s and 60 GHz indoor wireless systems offering >1 Gbit/s wireless transmission speeds are reported. The wireless transmission of uncompressed high-definition TV signals using the 60 GHz band is also demonstrated.
We propose a dynamic light-path establishment method for using wavelengths effectively. In our proposed method, a proportional, integral, derivative (PID) controller is implemented in each edge node. The edge node determines the amount of data to be transmitted with PID control so that a constant amount of data can be stored in the buffer. In addition, light paths are established and released dynamically by comparing the output signal of the PID controller with the maximum amount of data that can be transmitted with the established light paths. Because data can be stored in the buffer for a short time, it is expected that the number of established light paths decreases. We evaluate the performance of the proposed method and investigate the impact of the setting parameters. The effectiveness of the proposed method is shown through a comparison with the conventional method. (C) 2009 Optical Society of America
This paper introduces a novel fiber-wireless (FiWi) network architecture, called SuperMAN, and investigates the optical-wireless integration of a resilient packet ring (RPR) and WiMAX networks. We propose a novel hierarchical integrated scheduling algorithm that significantly improves the throughput-delay performance and triple-play quality-of-service support for fixed and mobile users. By means of extensive simulations we show in a benchmark comparison that the proposed hierarchical scheduler clearly outperforms the widely deployed weighted fair queuing (WFQ) scheduler in terms of mean aggregate throughput and mean delay as well as robustness for voice, video, and data traffic under realistic wireless channel conditions.
We indicate that the frequency drift of WDM light sources for uplink transmission in carrier-distributed WDM-based access networks severely impacts the loss budget. To prevent this, we propose a multifrequency monitoring stabilization technique that simplifies the configuration of WDM light sources. To achieve more precise frequency stabilization the bias current used to drive each laser diode is dithered. The key techniques are adding an offset bias to the detected error signal and offsetting the center frequency of the array waveguide grating port against the ITU-T grid frequency to achieve effective frequency stabilization. Experiments show that the relative frequency deviation of +/- 25 GHz can be suppressed to better than +/- 2.5 GHz. (C) 2009 Optical Society of America
The development of airports such as the recently inaugurated Heathrow Terminal 5, as well as the increasing number of people using these facilities every day for business reasons or just for pleasure, reveals the importance of adequate and reliable communication facilities in this context. This environment is characterized by multiservice, multistandard wireless technologies and a highly variable traffic demand in space and time due to passenger flow, behavior, and usage from the terminal's entrance to the corresponding boarding gate, ruled by flight departure schedules, in the indoor environment. The Intelligent Airport (TINA) project establishes its objective as the creation of a seamless hybrid wireless and wired infrastructure capable of providing users with a wide range of services, based on radio-over-fiber (RoF) networks, anticipating the deployment of multiple air interfaces within 4G networks. In this paper the spatial and temporal traffic demand is analyzed and modeled through simulation, as a means of selecting the optimum location for the base stations/antenna units (BSs/AUs) in the network. A load-balancing technique is applied to ease the load on congested cells using strategically located fixed relay nodes, and the network's behavior is analyzed for different BS properties. (C) 2009 Optical Society of America
The problem of routing traffic on multihop clear optical channels and deciding the virtual topology of optical channels to form on a physical network of fibers to minimize the cost of electronic switching equipment has become known as traffic grooming in optical networks. Traffic grooming is recognized as an important research area, because the joint opto-electric routing problem is a hard one, yet necessary because of the large cost of pure electronic switching. This problem has been shown to be NP-complete (nondeterminstic polynomial complete) even for very simple practical topologies such as a path network. In previous work, we have shown that at least the subproblem of routing traffic on a given virtual topology to minimize electronic switching (NP-hard for path networks with arbitrary traffic matrices) becomes polynomial when the traffic on the path is restricted to be egress traffic, that is, all traffic requests are destined for a single egress node. In that work, the objective was to minimize the raw OEO (opto-electro-optic) metric (number of bits electronically switched per second) totaled over all network nodes. Of late, it has become clear that electronic switching equipment cost is best counted in quantized units, e.g., in the number of transceiver interfaces at network nodes. In this paper, we consider the traffic grooming problem in unidirectional, WDM path networks with the goal of minimizing the number of transceivers. We conclusively show that the problem is NP-hard, even under the restriction of the egress traffic model. In the case of egress traffic, we give a simple heuristic that will never be worse than twice the optimal.
As Internet traffic continues to grow unabated at an exponential rate, it is unclear whether the existing packet-routing network architecture based on electronic routers will continue to scale at the necessary pace. On the other hand, optical fiber and switching elements have demonstrated an abundance of capacity that appears to be unmatched by electronic routers. In particular, the simplicity of circuit switching makes it well suited for optical implementations. We present what we believe to be a new approach to optical networking based on a paradigm of coarse optical circuit switching by default and adaptive rerouting over circuits with spare capacity. We consider the provisioning of long-duration quasi-static optical circuits between edge routers at the boundary of the network to carry the traffic by default. When the provisioned circuit is inadequate, excess traffic demand is rerouted through circuits with spare capacity. In particular, by adaptively load balancing across circuits with spare capacity, excess traffic is routed to its final destination without the need to create circuits on the fly. Our evaluations on two separate real, large Internet service provider point-of-presence-level topologies, Abilene and GEANT, show that only a very small amount of excess traffic needs to be rerouted even during peak traffic hours when the circuit configurations are carefully chosen and that this excess traffic could always be accommodated using our adaptive rerouting approach. We also demonstrate that our adaptive load-balancing approach is robust to sudden unexpected traffic changes by demonstrating its ability to reroute traffic under a number of hot-spot scenarios.
A novel media access control (MAC) protocol named carrier sense multiple access with idle detection (CSMA/ID) is proposed to handle variable-length packets over an all-optical ring network. To evaluate optimal utilization of channel bandwidth, we study packet scheduling based on three transmitting queue discipline (TQD) architectures and four idle space allocation (ISA) algorithms with regard to their impact on performance. For numerical evaluation of performance, an analytical model is developed by a preclassification queue with weighted round-robin (PCQ_WRR) architecture and a random algorithm. Moreover, three related MAC protocols are examined and compared, namely, multitoken, carrier sense multiple access/collision avoidance (CSMA/CA) and carrier sense multiple access/collision preemption (CSMA/CP). Simulation results indicate that, of the TQDs, better performance is obtained by PCQ_WRR compared with first-in-first-out and preclassification queues. The first fit space (FFS) algorithm has the best performance of the ISAs. The 12 combinations of TQDs-ISAs are then considered. It is found that the combination of PCQ_WRR with FFS provides the greatest efficiency and has the lowest packet latency, providing better throughput than three different MAC protocols under either symmetric or asymmetric traffic load on all-optical ring networks. (C) 2009 Optical Society of America
A scalable photonic interconnection network architecture is proposed whereby a Clos network is populated with broadcast-and-select stages. This enables the efficient exploitation of an emerging class of photonic integrated switch fabric. A low distortion space switch technology based on recently demonstrated quantum-dot semiconductor optical amplifier technology, which can be operated uncooled, is used as the base switch element. The viability of these switches in cascaded networks is reviewed, and predictions are made through detailed physical layer simulation to explore the potential for larger-scale network connectivity. Optical signal degradation is estimated as a function of data capacity and network size. Power efficiency and physical layer complexity are addressed for high end-to-end bandwidth, nanosecond-reconfigurable switch fabrics, to highlight the potential for scaling to several tens of connections. The proposed architecture is envisaged to facilitate high-capacity, low-latency switching suited to computing systems, backplanes, and data networks. Broadband operation through wavelength division multiplexing is studied to identify practical interconnection networks scalable to 100 Gbits/s per path and a power consumption of the order of 20 mW/(Gbits/s) for a 64×64 size interconnection network.
Some of the work carried out within the EU Network of Excellence ISIS on radio-over-fiber systems for the support of current and emerging wireless networks is reviewed. Direct laser modulation and externally modulated links have been investigated, and demonstrations of single-mode fiber and multimode fiber systems are presented. The wireless networks studied range from personal area networks (such as ZigBee and ultrawideband) through wireless local area networks to wireless metropolitan area networks (WiMAX) and third-generation mobile communications systems. The performance of the radio-over-fiber transmission is referenced to the specifications of the relevant standard, protocol operation is verified, and complete network demonstrations are implemented.
Spectral and waveform reshaping schemes can enhance the transmission distance of fiber links that use directly modulated lasers as transmitters. We prove the feasibility of using a simple Fabry-Perot (FP) etalon as the spectral reshaper for applications in wavelength division multiplexing (WDM) access networks. The transient chirp and adiabatic chirp of a directly modulated laser are analyzed in detail by using the time-resolved chirp measurement. The effects of the original extinction ratio and the adiabatic chirp on the spectral reshaping are clarified to obtain the optimal operation conditions. It is shown that placing a single-cavity FP etalon filter after multiple 10 Gbits/s directly modulated lasers can extend their transmission distances from <10 to <50 km in the 1.55 mu m wavelength window. Due to the limited filtering capability of the etalon, the choice of the original extinction ratio and finesse of the etalon is discussed in detail from the experiments and simulation. (C) 2009 Optical Society of America
Hybrid fiber-wireless networks for fixed wireless access operating in the millimeter-wave (mm-wave) frequency region have been actively pursued to provide ultrahigh bandwidth for untethered connectivity. Moving the radio operating frequency into the mm-wave region overcomes the spectral congestion in the lower microwave region and is also capable of providing high-capacity broadband wireless services in a picocellular or microcellular architecture. Optical fiber backhaul provides the broadband interconnectivity between a centralized location and a large number of high-throughput antenna base stations necessary in such an architecture. The transportation of mm-wave wireless signals within the hybrid network is subject to numerous impairments ranging from low conversion efficiency to fiber chromatic dispersion and also to signal degradation due to nonlinearity along the link. One of the major technical challenges in implementing these networks lies in the mitigation of these impairments that the wireless signals experience while traversing the links. In this paper, we present an overview of the different techniques and schemes to overcome some of the impairments for transporting mm-wave signals over optical fibers.
