Design and optimization of optical links based on VHDL-AMS modeling

In distance learning, web-based software may provide an alternative to installation of expensive software on the student computer, or an alternative to expensive laboratory equipment. This paper describes the original web-based e-learning software, which enables teaching and learning of the optical link design. Optical link design is an iterative process involving trade-offs to achieve the desired performance: bit error rate, transmission distance, etc., at minimal cost. Fundamental elements of an optical fiber transmission link are the optical transmitter, the optical fiber with associated splices and connectors, and the optical receiver. The student must select appropriate devices from a set of available optical components to meet a given set of system requirements. Data concerning optical equipment that can be used for specific optical link design are stored in a database, that was created for the purpose of this software.

Experiments were conducted to evaluate the viability of commercial-off-the-shelf (COTS) technology in the design of high-performance optical intersatellite communications links. The optical links were operated at 155, 622 and 2488 Megabits per second (Mbps) and at 1550 nm wavelength. Communications components were evaluated against performance parameters for on-off keyed (OOK) systems. Transmitters, receivers, optical amplifiers, and filters, used to minimize the impact of amplified spontaneous emission (ASE), were characterized individually and within system configurations. Bit error rate (BER) as a function of photons per bit was characterized for several system configurations. Extinction ratio analysis experiments were conducted to determine the limiting factors on the systems performance. Widely varying optical powers in space (for low earth orbit) imply a robust receiver dynamic range requirement. Dynamic range of COTS receivers was examined and resulted in sufficient performance. In addition, gamma radiation tests on fiber amplifiers were also evaluated in a system context.

A perspective for future high data-rate communication systems are quasi-geostationary high altitude platform (HAP) systems, where communications platforms are placed in the stratosphere at altitudes between 20 and 30 km and are kept stationary. Situated over congested urban areas they will be capable of handling high data rate traffic like a geostationary satellite. Due to the specific altitudes of these platforms, communications cross links between either two platforms are not as severely affected by Earth´s atmosphere, as near-ground links are. Hence this scenario is very well-suited for optical inter-platform communications. Nevertheless such optical links suffer from various atmospheric influences that we will discuss here. In particular this paper addresses intensity fluctuations due to atmospheric turbulence, atmospheric attenuation due to absorption and scattering, and background radiation. Platform vibrations and according mispointing and –tracking losses are regarded as well. It turns out that possible links distances are very much limited by vibrations, scintillations and background light. The terminal design is generally a trade-off between those effects. From an extensive investigation of all influence factors, hints for the design of optical cross links in HAP systems will be given in terms of suitable transmitter divergence angles and receiver field of view. Link budget calculations clearly prove the feasibility of optical cross links. However, they as well show the limitations to optical communications in this particular application.

We describe a numerical, wave optics approach for simulating the propagation of a partially coherent beam. The approach requires the application of a succession of phase screens at the transmit end of the link and the summation of the resulting intensity profiles at the receiving end. To test the approach, a phase screen formulation for a Gaussian Schell-model beam was derived using a Gaussian random phase screen where its parameters are related to a form of the spatial coherence function for the transmittance. The numerical model was applied to several cases of propagation through vacuum and atmospheric turbulence and the resulting average beam intensity profile is shown to be nearly identical to the profile predicted by analytical results for the Gaussian Schell-model beam. Finally, the scintillation index of a coherent beam was investigated and the numerical result was found to generally follow the theoretical result, especially for source sizes that are relatively small or relatively larger. The model developed in this paper can be applied to analysis and design of free space optical laser links that utilize various partially coherent beams.

As the number of active OWC installations is growing fast, the standards for compatibility of co-existing neighbouring systems are being developed. The paper addresses the Laser Safety (IEC standards), ITU-T Study Group 15 standards (G.640 Co-location longitudinally compatible interfaces for free space optical systems), ITU-Radiocommunication Sector standards (P.1817-1 Propagation data required for the design of terrestrial free-space optical links), and the IEEE Work in Progress - standardization activity on Visible Light Communications. International standards of FSO communications have been reviewed and discussed. ITU, IEC, and IEEE International standards for Free-Space Optical links have been reviewed. The system reliability and availability as well as security issues will be addressed as well in the talk.

분산 제어 (DM; dispersion management)은 파장 분할 다중 (WDM; wavelength division multiplexed) 채널의 고품질 전송을 위해 광섬유의 그룹 속도 분산 (GVD; group velocity dispersion)과 비선형 효과의 상호 작용에 의해 왜곡되는 신호의 보상할 수 있는 대표적 기술이다. DM이 적용된 광전송 링크의 유연한 구성에 필요한 중계 구간 (fiber span)을 구성하는 단일 모드 광섬유 (SMF; single mode fiber)의 길이와 중계 구간 당 잉여 분산 (RDPS; residual dispersion per span)을 랜덤하게 분포시키는 구조와 인위적으로 분포시키는 구조에서의 최적 전체 잉여 분산 (NRD; net residual dispersion)의 최적치와 유효 입사 전력 범위를 도출하였다. 고려한 SMF의 길이와 RDPS 분포 패턴 모두 precompensation으로 NRD를 조절하는 경우에서는 +10 ps/nm, postcompensation으로 NRD를 조절하는 경우에서는 -10 ps/nm이 최적 NRD라는 것을 알 수 있었다. 그리고 NRD가 상기 값으로 설정된 경우 중계 구간이 증가할수록 SMF 길이를 감소시키고, RDPS를 증가시키는 인위적인 분포의 전송 링크에서의 시스템 성능이 가장 양호하여 균일한 분포의 링크에 비해 유효 입사 전력 범위가 2 dB 정도 신장되는 것을 확인하였다. Dispersion management (DM) is the typical technique compensating for the distorted signals due to interaction of group velocity dispersion (GVD) and optical nonlinear effects for transmitting wavelength division multiplexed (WDM) channel with the excellent performance. Optimal net residual dispersion (NRD) and effective launching power range of optical transmission links with random distribution and artificial distribution of single mode fiber (SMF) length and residual dispersion per span (RDPS) required to flexibly design of optical links in DM. It is confirmed that optimal net residual dispersion (NRD) are +10 ps/nm and -10 ps/nm controlled by precompensation and postcompensation, respectively, in both of the considered distribution patterns of SMF length and RDPS. And, in optimal NRD, system performance in optical links with the descending distribution of SMF length and the ascending distribution of RDPS among the artificial distribution patterns are more improved, consequently, effective launching power range is expanded by almost 2 dB than those in optical links with the uniform distribution.

Optical links and photonic integrated circuits require integration of photonic and electronic devices at chip, module, or board level. The complexity of such systems is motivating a need for system level CAD tools which can simulate electronic and photonic devices and circuits simultaneously and at multiple levels of abstraction. Furthermore integrating photonic devices into conventional electronic computer and communication systems needs to be justified in terms of cost, performance, and portability of existing computer software and hardware. Thus system level analysis of optoelectronic interconnect system is clearly necessary to ensure that an overall functional and performance requirements are met. The proposed approach for system level modeling is to integrate photonic device simulations into the established electronic design automation environment, particularly VHDL-based one. VHDL description of photonic devices will provide benefits such as portability of individual design, system level performance analysis before building a real system, and synthesis capability for a rapid- prototyping. This paper demonstrates the use of basic VHDL entities of various passive optical waveguide components and a special VHDL package (`Optical_Package') defining physical photonic parameters to verify the feasibility of this approach. It includes modeling and simulation of global signal distribution network on MCMs using optical interconnect and wavelength division (de)multiplexing-based optical link.

Topology modeling is a challenging topic in the design and development of tools that simulate the behavior of interconnection networks. During the last years we have seen the birth of several simulation tools and frameworks modeling interconnects, some of them doing brilliant efforts to do the code re-usable and extensible. The main differences among these simulation tools and frameworks is the level of granularity and abstraction of their network models. Different network models may generate duplicated efforts in modeling certain aspects of them, such as the network topology or the routing algorithm. If the topology generation and routing algorithm modeling were separated from the modeling of other network aspects, then the simulator developers could focus on developing non-existing models and new functionality, without wasting time in doing a work previously done by other simulation tool developers. In this paper we describe TopGen, an external library that can be integrated with any tool that simulates interconnection networks. TopGen provides a compendious of well-known network topologies that can be used to interconnect the network components, such as end nodes, channels, switches and routers. It also provides the corresponding knowledge to apply a compendious of routing algorithms to the modeled network topologies. TopGen also supports the definition of customized topologies that are not the standard ones, thanks to a special interface used for this purpose. We also provide details on how to integrate TopGen with a network simulator, by means of a simple API. Finally, we describe several use cases of the TopGen library.

This paper presented a versatile smart antenna simulation tool which implements both direction finding and adaptive beamforming algorithms. The developed tool can be used for modelling of adaptive antenna arrays to improve and accelerate the design of wireless networks. The developed tool can also be used for computer-aided learning of modern communication systems that utilize smart antennas.

The way towards thermonuclear fusion simulators

Photovoltaic power generation is growing at a rapid rate. Most new PV installations are grid-connected small-scale system. The impact of these installations on the grid operation need to be carefully studied to investigated. This paper presents the development of simulation tools required for such interconnection studies. The simulation tools were developed in the popular electromagnetic transient simulation program PSCAD/EMTDC and include a PV array model, maximum power point tracking controller model, and a grid connected inverter. An example of an interconnection study using the developed simulation tools is presented.

A new controller has recently been developed, belonging to the generalized class of PID regulators. This article discusses a simulation tool whose role is to promote the use of the developed controller. The advantage of the new controller consists in the fact that the filtration has been taking into account during the controller design process that has enabled to use also higher derivatives degrees. The paper summarizes the development of PID controllers with higher derivative degree in a general way. The corresponding developed simulation tool can run offline or online. The simulation tool provides a comparison of setpoint and disturbance step responses in the control circuit with the first order time-delayed controlled system influenced by a noise. Generally, the simulation tool is an easy way for all potential users from the control field who want to become familiar with the new control design technique that extends classical PID control by higher derivative degrees.

This paper presents a modeling and simulation tool for the design and development of a Quad-Rotor UAV, which is capable of indoor flight with the aid of MEMS-based sensors and ultrasonic rangefinders. The vehicle requires an attitude stabilizing controller to allow it to be flown indoors without a high degree of operating skill. Attitude estimations are difficult without GPS aiding and expensive inertial sensors. An Extended Kalman Filter (EKF) is proposed to estimate the attitude states with the aid of rangefinders, but the system must be thoroughly tested in simulation. The paper presents a dynamics model and simulation tool for design and validation of the controller and state estimator prior to flight test. The simulation is performed under Mathworks’ Matlab/Simulink environment. A method for real-time simulation and visualization is also developed.

Progress on the Development of Generic Tools for Real-Time Simulation and Control of Complex Systems

For testing new methods of network security or new algorithms of security analytics, we need the experimental environments as well as the testing data which are much as possible similar to the real-world data. Therefore, the researchers are always trying to find the best approaches and recommendations of creating and simulating testbeds, because the issue of automation of the testbed creation is a crucial goal to accelerate research progress. One of the ways to generate data is simulate the user behavior on the virtual machines, but the challenge is how to describe what we want to simulate. In this paper, we present a new approach of describing user behavior for the simulation tool. This approach meets requirements of simplicity and extensibility. And it could be used for generating user behavior scenarios to simulate them on Windows-family virtual machines. The proposed approached is applied to our developed simulation tool that we use for solving a problem of the lack of data for research in network security and security analytics areas by generating log dataset that could be used for testing new methods of network security and new algorithms of security analytics.