Ahmad Fallahpour

Energy Efficient Routing and Spectrum Assignment With Regenerator Placement in Elastic Optical Networks

In this paper, we present a dynamic energy efficient routing and spectrum assignment algorithm with regenerator placement (RP) capability for elastic optical networks. In this algorithm, a virtual graph is considered for a given network topology graph, whereby the cost functions of virtual graph is computed according to the energy consumption of the corresponding links and intermediates routers. Furthermore, the arrived connection request is served by finding the most energy-efficient path among the possible candidate paths. Then, the quality of transmission (QoT) of the selected path is evaluated in terms of bit error rate. If the estimated QoT is higher than a predetermined threshold, the designated path is assigned to the incoming request, otherwise, the RP algorithm is utilized to place a regenerator at the most energy-efficient position. In addition, the demanded transmission rate and required QoT are fulfilled by assessing different modulation formats and selecting appropriate modulation format in terms of power consumption and blocking probability (BP). We evaluate the proposed algorithms through extensive numerical simulations. The results of simulations reveal that the proposed algorithms have better performance than other existing schemes in terms of network total energy consumption and acceptable BP.

Energy-Efficient Manycast Routing and Spectrum Assignment in Elastic Optical Networks for Cloud Computing Environment

In this paper, we present an energy-efficient manycast routing and spectrum assignment (EEM-RSA) algorithm in elastic optical networks supporting cloud computing applications. The proposed EEM-RSA is adapted for both static and dynamic scenarios. First, an integer linear programing formulation is derived for energy-efficient manycasting and spectrum assignment; then, the corresponding heuristic methods are proposed. To reduce the energy consumption, inactive (idle) elements are turned off, and in the proposed energy-efficient manycasting heuristic, the number of activated elements are minimized. The power consumption of network elements is modeled by considering a constant overhead for the element activation and a variable traffic-dependent term for the element operation. Furthermore, two types of data centers based on their power supply, renewable (green) or nonrenewable (brown), are considered to explore the capability of the proposed algorithms in decreasing green house gases emission. To investigate the impact of renewable energy sources, two approaches are utilized in the destination selection (DS) phase of the EEM-RSA, namely green-energy aware-DS and green-energy unaware-DS. All heuristic algorithms are evaluated by using an event-driven simulator based on the Poisson traffic model. The simulation results reveal that by applying the proposed energy-aware heuristic algorithm, the network energy consumption is reduced at the cost of increasing the blocking probability. However, by designating the shortest path, instead of the path with the lowest power consumption, the blocking probability is reduced, whereas increasing the energy consumption. Thus, we introduce an intermediate solution, referred to as blocking-aware energy-efficient manycasting, which compromises between the power consumption and blocking probability performance metrics.

Design concepts and performance analysis of multicarrier CDMA for indoor visible light communications

In this paper, we present a design methodology with implementational insight and evaluate the performance of a multicarrier code-division multiple access (MC-CDMA) system using intensity modulation/direct detection scheme suitable for an indoor visible light communication (VLC) environment. The proposed system is a CDMA system based on an orthogonal frequency division multiplexing (OFDM) platform. To overcome the light-dimming issue, we use a newly proposed methodology, namely, polarity reversed optical OFDM (PRO-OFDM). A unipolar signal is either added to the minimum current or subtracted from the maximum current in the LED linear current range to provide various amounts of dimming. The CDMA part employs Hadamard sequences to provide synchronous resource sharing. Combining the robustness of orthogonal modulation with the flexibility of CDMA schemes makes the proposed system a viable candidate for future indoor wireless communications such as VLC. The performance of the proposed MC-CDMA is evaluated, and mathematical formulations for the proposed system are derived. For example, closed-form equations for the signal-to-interference-plus-noise ratio and bit error rate (BER) performance are obtained. Furthermore, the analytical formulations are used in numerical analysis to verify the BER performance achieved in simulation results.

Resource Allocation and Multicast Routing in Elastic Optical Networks

In this paper, we formulate an integer linear programming (ILP) to perform multicast routing and spectrum assignment (MRSA) in elastic optical networks, which serves jointly a set of multicast requests. In this formulation, all physical layer restrictions including modulation level assignment, maximum number of multicast capable nodes (MCNs), and maximum splitting degree (MSD) of MCNs, are considered. In addition, we modify the proposed joint ILP to serve multicast requests one-by-one, which is referred to as a separate ILP. Furthermore, we present three heuristic algorithms for MRSA, namely distance-based MRSA (DMRSA), congestion-based MRSA (CMRSA), and mixed CMRSA/DMRSA, which are applicable in both static and dynamic operation scenarios. In CMRSA and DMRSA, the link length and the amount of occupied spectrum are considered as the cost function of multicast routing, respectively; and in mixed CMRSA/DMRSA, a combination of normalized link length and normalized occupied spectrum is considered as the cost function. The comparison of ILPs and heuristic algorithms in static operation reveals that the joint ILP, as the benchmark, gives the optimum solution while has the most computational complexity. Furthermore, the separate ILP has lower complexity at the cost of consuming slightly more spectrum. Unless the DMRSA method, which has the worst performance, the gap between the other two heuristic algorithms and the ILPs is negligible. Furthermore, simulation results of dynamic operation scenarios reveal that mixed CMRSA/DMRSA outperforms other two heuristics algorithms in terms of blocking probability.

Precision optical navigation guidance system

We present the new precision optical navigation guidance system approach that provides continuous, high quality range and bearing data to fixed wing aircraft during landing approach to an aircraft carrier. The system uses infrared optical communications to measure range between ship and aircraft with accuracy and precision better than 1 meter at ranges more than 7.5 km. The innovative receiver design measures bearing from aircraft to ship with accuracy and precision better than 0.5 mRad. The system provides real-time range and bearing updates to multiple aircraft at rates up to several kHz, and duplex data transmission between ship and aircraft.

Spectrum-usage-aware resource allocation and multicast routing in elastic optical networks

In this paper, dynamic resource allocation and multicast routing algorithms are proposed for elastic optical networks (EONs). The proposed algorithms find the shortest path trees by modeling either the amount of free spectrum in each link or the link length as the cost function of routing method. The proposed algorithms are simulated in the dynamic operation scenario over the so called US Backbone topology. Simulation results reveal that by considering the cost function of routing algorithm based on the available spectrum in each link will improve the blocking probability while reduce the spectrum efficiency. On the other hand, by considering link length as the cost function, the blocking probability get worsen whereas the bandwidth efficiency is improved. Consequently, in order to compromise the benefits of both algorithms, we consider a mixed cost function based on the normalized cost function of each method and employing a weighting coefficient to trade-off between blocking probability and spectrum efficiency.

Experimental demonstration of tunable homodyne detection of WDM and dual-polarization PSK channels by automatically locking the channels to a local pump laser using nonlinear mixing

This Letter proposes a method for tunable automatically locked homodyne detection of wavelength-division multiplexing (WDM) dual-polarization (DP) phase-shift keyed (PSK) channels using nonlinear mixing. Two stages of periodically poled lithium niobate (PPLN) waveguides and an LCoS filter enable automatic phase locking of the channels to a local laser.

Experimental demonstration of phase-sensitive regeneration of a binary phase-shift keying channel without a phase-locked loop using Brillouin amplification

All-optical phase regeneration of a binary phase-shift keying signal is demonstrated at 10-30 Gb/s without a phase-locked loop in a phase-sensitive amplification-based system using Brillouin amplification of the idler. The system achieves phase noise reduction of up to 56% and up to 11 dB OSNR gain at 10-5 bit error rate for the 10 Gb/s signal. The systems sensitivity to different parameters and stability is also evaluated.

Optical signal processing using coherent optical frequency combs

Optical signal processing using coherent optical frequency combs could have various potential applications for optical communications. In the beginning, an approach to achieve a tunable optical high-order QAM generation based on multichannel aggregation is discussed. Then, an all-optical pilot-tone based self-homodyne-detection scheme is demonstrated under two scenarios: (i) multiple WDM channels with sufficient power of pilot tones, and (ii) a single channel with a low-power pilot tone. Finally, a fragmented bandwidth allocation enabled by reconfigurable channel slicing and stitching is presented, in which a single optical channel could be redistributed into fragmented frequency slots and ultimately recovered at the receiver side.

Reconfigurable Channel Slicing and Stitching for an Optical Signal to Enable Fragmented Bandwidth Allocation Using Nonlinear Wave Mixing and an Optical Frequency Comb

A scheme for reconfigurable channel slicing and stitching is proposed and experimentally demonstrated. By employing optical nonlinear wave mixing and a coherent frequency comb, a single channel spectrum is sliced and redistributed into fragmented frequency slots, which can be stitched together to recover the original channel at the receiver. This approach is verified through a single channel experiment with the modulation formats of quadrature phase-shift keying and 16 quadrature amplitude modulation. The system exhibits less than 1.5% error-vector-magnitude deterioration and no more than 2-dB optical signal-to-noise ratio penalty, compared to a back-to-back baseline. To demonstrate robustness of the scheme, different parameters of the channel slices are varied, such as relative phase offset, relative amplitude, and the number of slices. A 10-km transmission experiment is also conducted and the additional system penalty is negligible. This scheme is used to experimentally demonstrate fragmented channel bandwidth allocation in a dense 6-channel wavelength-division-multiplexing system. The incoming 20-Gbaud optical channel is successfully reallocated into two fragmented frequency slots and reconstructed at the receiver.