The proposal addresses the wireless optical broadband access networks architecture by deploying mesh network structure, which could be the alternatives to FTTx (home or node, etc) architecture. Instead of fiber used as the transmission medium in the distribution plant, here we suggest to use the free space optic links to construct the optical mesh network. The practical connections are depending on the services provided. For Video-on-Demand (VoD) service, the final connection could use twisted pair by integrated VDSL technology. The distributed bandwidth can reach 25-32 Mbps per end user. In this paper we give some comments for designing a broadband access network using optical mesh network structure. It includes the traffic estimation, transmission network design and access node design suggestions.
A conceptual analysis of contemporary technological approaches for Free Space Optical (FSO) systems is presented, with cost drivers and installation requirements outlined. Major cost and installation drawbacks for typically packaged FSO systems include the number of opto-electronic (OE) interfaces needed to establish a link, rooftop or outdoor power utility requirements, and the mounting structures required to overcome wind loading and system weight. The paper describes an alternative to the traditional approach through the use of fiber coupled transceivers that separate the electronic packages away from the outdoor optical antenna. In this approach, weight and wind loading are minimized, the number of OE interfaces are reduced and special outdoor power utility requirements are eliminated. The fiber-coupled system is inherently low-maintenance and simple to upgrade and provides the low-cost core technology for a metropolitan area network deployment of point-to-multipoint FSO.
Eye safety, link performance, and technology infrastructure issues related to Optical Wireless (OW), also known as Free Space Optics (FSO), communication systems are examined relative to wavelength dependence. It is found that 1550 nm systems have compelling advantages over 800nm systems in the areas of laser eye safety, reduced solar background radiation, and existing technology infrastructure. 1550nm has somewhat better receiver sensitivity for PIN detectors, while 800nm has somewhat better sensitivity for APDs. Overall, the factor of 50 greater eye-safe laser power at 1550 nm provides up to 17 dB additional margin for higher data rates or penetrating fog at longer ranges. The availability of high power, low cost semiconductor lasers at 1550 nm allows these advantages to be exploited in commercially available systems.
This paper compares two emerging broadband access methodologies, Free Space Optics (FSO) and Local Multipoint Distribution System (LMDS) and the atmospheric propagation characteristics of each when exposed to a dynamically changing channel. The comparison focuses on bandwidth, availability, and distance requirements for the new broadband market and how LMDS and FSO can be used to meet these requirements. Possible network topologies and their associated costs are examined. This comparison takes into account the total cost of deployment, including equipment costs, installation fees, access fees, and spectrum licensing fees. LMDS and FSO are compared on speed of deployment, scalability, aggregate bandwidth, and bandwidth per customer. Present and projected capabilities of each technology are considered for their suitability in different locations in the network, from the Wide Area Network (WAN), to the Metropolitan Area Network (MAN), all the way to Last Mile Access. There is a discussion on the relative performance of LMDS and FSO, focusing on the different factors that can affect link availability. Since network design is a large factor in assuring overall reliability, the flexibility of each technology with regard to network design is compared. LMDS and FSO are both line of sight, space-propagated technologies, and as such, they are both susceptible to path impediments and atmospheric attenuation, dispersion, scattering, and absorption. LMDS and FSO are affected very differently by different meteorological phenomena. Problematic atmospheric conditions are, specifically scintillation, rainfall, and fog, are examined. In addition to a discussion of these conditions, various techniques for minimizing atmospheric and environmental effects are investigated. The paper concludes with a summary of findings and recommendations for a number of broadband wireless applications.
In this paper, we report design and implementation scenarios for a gigabit-capacity and high-data-rate fixed wireless access technology research demonstrator. The all weather survivable system is based on broadband wireless access concept and implementation techniques utilizing RF/microwave/millimeter-wave as well as free-space optical wireless high speed links. The demonstration platform provides broadband last mile access and networking solutions to Internet users in densely populated areas with homes and businesses (e.g., downtown building-centric and inner city- environment) in need of high bandwidth not served with fiber infrastructure. The focus of this investigation is radio link design, access network architecture, and system integration. Hybrid fiber radio and WDM optical wireless solutions are implemented to interface and complement the existing ATM fiber and satellite core networks in support of all wireless infrastructure for Next Generation Internet (NGI).
The Kruse formula was originally devised to relate visibility to optical attenuation, from the visible to the near infrared (IR), for dust and small particle aerosols with dimensions much smaller than the wavelength. Application of this formula to attenuation in fog is not appropriate since fogs consist mainly of particles much larger than optical wavelengths. Mie scattering calculations, transmission measurements and simple observations indicate that attenuation from the visible to the near IR is virtually independent of wavelength. The Kruse formula is also shown to be questionable apart form its wavelength dependence; it does not account for scattering into the field of view and does not consider background illumination. In the derivation presented here the visibility is linked to near-forward scattering, not explicitly to attenuation. We conclude that attenuation in fog should be treated as virtually wavelength independent from the visible to the near IR and a more appropriate formula is (Gamma) (V;(lambda) )=(kappa) divided byV(dB/km) where V is the visual range and 8.5dB,(kappa) <17dB.
The test methods and results are discussed for fSONA Communications SONAbeam 155-M product - a free-space-optics system that operates at 1550 nm. Results include environmental qualification testing and field testing of system performance over test ranges of 450 and 5000 meters. The SONAbeam 155-M is representative of a family of products that range from 34 to 1244 Mbps. This product line emphasizes very robust performance.
Free Space Optics (FSO) has become a viable, high-bandwidth wireless alternative to fiber optic cabling. The primary advantages of FSO over fiber are its rapid deployment time and significant cost savings. The disadvantage of FSO over fiber is that laser power attenuation through the atmosphere is variable and difficult to predict, since it is weather airports, the link availability as a function of distance can be predicted for any FSO system. These availability curves provide a good indication of the reasonable link distances for FSO systems in a particular geographical area. FSO link distances can vary greatly from desert areas like Las Vegas to heavy-fog cities like St. Johns NF. Another factor in determining FSO distance limitations is the link availability expectation of the application. For enterprise applications, link availability requirements are generally greater than 99%. This allows for longer FSO link ranges, based on the availability curves. The enterprise market is where the majority of FSO systems have been deployed. The carriers and ISPs are another potential large user of FSO systems, especially for last-mile metro access applications. If FSO systems are to be used in telecommunication applications, they will need to meet much higher availability requirements. Carrier-class availability is generally considered to be 99.999% (5 nines). An analysis of link budgets and visibility-limiting weather conditions indicates that to meet carrier-class availability, FSO links should normally be less than 140m (there are cities like Phoenix and Las Vegas where this 99.999% distance limitation increases significantly). This calculation is based on a 53 dB link budget. This concept is extended to the best possible FSO system, which would have a 10 W transmitter and a photocounting detector with a sensitivity of 1 nW. This FSO system would have a 100 dB link margin, which would only increase the 99.999% link distance to 286 m. A more practical solution to extending the high availability range would be to back up the FSO link with a lower data rate radio frequency (RF) link. This hybrid FSO/RF system would extend the 99.999% link range to longer distances and open up a much larger metro/access market to the carriers. It is important to realize that as the link range increases, there will be a slight decrease in overall bandwidth. To show the geographical dependence of FSO performance, the first map of FSO availabilities contoured over North America is presented. This map is the first step to developing an attenuation map for predicting FSO performance, which could be used in similar fashion to the International Telecommunication Union (ITU)/Crane maps for predicting microwave performance.
The internet has been the mantra in last decade and digital convergence is the latest talk on the tech streets. Features that once clearly discerned a mobile phone from a PDA or a PDA from a laptop are being replaced with multi-functional overlapping features and there is a growing need for wireless access and interoperability. Infrared communications has been addressing these needs for quite some time. The technology has matured through standardization efforts of IrDA (Infrared Data Association) and is widely used in PDAs, mobile phones, laptops, printers and digital cameras to name a few. This paper explores some new application scenarios for an IrDA transceiver. The first part of the paper describes a reference architecture for using infrared wireless communication for MP3 file exchange and the various possible user models. The second part of the paper discusses various configurations for implementing an ambient light detection scheme using IrDA transceivers, to turn off the backlighting of a LCD panel of a PDA or mobile phone in the presence of ambient light. The third part of the paper discusses various techniques of enabling extended link distance operation of IrDA transceivers for toy and remote control applications.
Diffuse wireless optical communications offer more robust optical links in terms of coverage and shadowing than line-of-sight links. However, they are more susceptible to multipath distortion, limiting high-speed performance. Angle diversity receivers can be used to combat the effects of multipath distortion albeit, at the cost of an increased path loss. The performance of an angle diversity receiver with 18-degree field-of-view receiver elements is reported. We have developed a channel simulation system capable of providing angularly resolved channel impulse response data. This is integrated with a receiver design model that allows path loss, dispersion and coverage to be calculated for various receiver topologies. The resulting bit error rate (BER) for different operating conditions are reported. Currently, we are developing a measurement system that will allow us to gather high-resolution angularly resolved channel data and this real data will then be integrated to the receiver design simulation system. In this paper we describe the use of simulated and measured channel data in designing angle diversity receiver structures.
With ever increasing requirements for bandwidth in communications and the trend towards the use of wireless technologies for increased mobility and convenience, greater interest is being directed towards optical wireless as a potential alternative to radio for some applications. The use of a transmitting antenna consisting of more than one optical source can mitigate some of the disadvantages of both line-of-sight and diffuse systems. Each source illuminates a coverage cell, providing greater coverage area than a line-of-sight system and no requirement for pointing, whilst also retaining the potential for higher bandwidths than a diffuse system. The use of a segmented receiver, on the other hand, results in a reduced photodiode capacitance penalty and, due to the possibility of signal processing on the multiple received signals, the potential for improved gain. In this paper we present a test-bed system that incorporates features of both the diffuse and line-of-sight architectures by employing multi-element transmitter and receiver structures. We demonstrate that the combination of such a transmitter and receiver, in conjunction with some focusing optics can provide information about direction of signal arrival, allowing tracking of the optical signal.
Diffuse and quasi-diffuse optical wireless systems have the potential to offer wireless coverage that is robust to any particular path between transmitter and receiver being blocked. The disadvantages of such systems are that links suffer from high path loss and multipath dispersion. Prediction of the magnitudes of these effects is crucial to the design of such systems, and simulation of these effects has been studied extensively. Measurements of the channel characteristics are also required, in order to verify the simulation results, and allow key effects to be identified. In this paper we describe a measurement system with the potential to provide link loss and frequency response of optical channels up to 1GHz. The system uses a narrow field of view receiver that is scanned through a complete range of angles, so that complete angular resolution of the multipaths is achieved. The paper details system design and configuration, data processing and preliminary results up to a bandwidth of 200MHz.
The widespread use of Optical LANs is dependent on the ability to fabricate low cost transceiver components. These are usually complex, and fabrication involves the integration of optoelectronic and electronic devices, as well as optical components. A number of UK universities are currently involved in a project to demonstrate integrated optical wireless transceiver subsystems that can provide eyesafe line of sight in-building communication at 155Mbit/s and above, using 1550nm eyesafe emitters. The system uses two-dimensional arrays of novel microcavity LED emitters, and arrays of detectors integrated with custom CMOS integrated circuits to implement tracking transceiver components. The project includes design and fabrication of the optoelectronic devices, transimpedance amplifiers and optical systems, as well as flip-chip bonding of the optoelectronic and CMOS integrated circuits to create components scaleable to the large numbers of sources and detectors required. In this paper we report initial results from the first seven channel demonstrator system. Performance of individual components, their limitations and future directions are detailed.
The purpose of this work is to develop integrated CMOS designs for optical transceivers at 1.55um wavelength that both meet the current system specification of 155Mb/s and provide a viable upgrade path to higher bit-rates. We present the design and implementation of an integrated multi-channel CMOS transceiver for use in a cellular 155Mb/s Manchester-coded optical wireless link. The receiver is an angle-diversity design and consists of multiple sectors with relatively small field of view; each driving an individual pre-amplifier channel. An on-chip selector selects signals to be passed to the combiner depending on the signal level and external control signals. The outputs of all the selected channels are combined using a current summing junction, implemented using a transconductance-transimpedance approach. In order to achieve a receiver design that will be robust in the face of process variations, an on-chip circuit is provided to maintain the operating point of the amplifier chain. The design has been optimized to achieve -30dBm sensitivity at a BER of 10-9. The CMOS transmitter circuit is tailored to match the electro-optic response of the resonant cavity LEDs being used. The transmitter driver incorporates current-peaking and charge-extraction circuitry using a novel timing generator, and has been designed to achieve rise and fall times of better than 0.2ns. Considerable effort is being directed towards the development of integrated designs which do not require significant numbers of discrete components. The prototype designs are being realised in a 0.7μm commodity mixed-signal CMOS process by Alcatel Microelectronics. We report results from the first prototype multi-channel demonstrator system and discuss future research directions.
Study on high speed indoor wireless optical LAN system enabling 100Mbps signal transmission with low bit error rate (10-9) is presented. To realize the optical LAN system handling 100 Mbps signal, a directed line of sight (LOS) system is adopted as the optical receiver sensitivity for a bit error rate of 10-9 for 100 Mbps signals is fairly large. In the system, new approaches are introduced: WDM technology which enables bi-directional transmission in full duplex manner is applied using a 1.3 micrometers laser diode for down-link and 0.65 micrometers red laser diode for up-link light sources. As the wavelengths of the two lasers are quite separated from each other, this WDM technology brings an advantage that two kind of semiconductor materials can be used for detectors; GaInAs is used for down-link while Si is applied for up-link. GaInAs PD cannot detect the up-link laser light of 0.65 micrometers and Si PD or APD cannot detect the down-link laser light of 1.3micrometers . Therefore full duplex transmission can be achieved in this configuration. In the indoor wireless optical LAN system, one of the critical points is the transmitter configuration for down- link which enables to deliver optical power enough for 100 Mbps transmission to user areas as wide as possible with inexpensive prices. To realize the point, a special 1.3micrometers laser diode, a spot-size converter integrated laser (SS-LD), is introduced in company with convex lens and an object lens to deliver optical power to areas as wide as possible. As the far-field patterns of the SS-LD are fairly narrow, most of the output power of the LD could be collected to and spread wide by the object lens of 40 magnifications. Using the device, 3m diameter circle area in the plane 2m apart from the 1.3micrometers SS-LD emitting 20 mW optical power, could receive optical power above the receiver sensitivity for a bit error rate of 10-9 for 100 Mbps signals. The visible red light is convenient for not only position setting but also eye-safety problem. Although maximum permissible exposure value at 0.65micrometers is lower than those at longer wavelength, winking response of human eyes for the visible laser light results in higher exposure value. Using 0.65 micrometers visible laser light of 1 mW output power for up- link light source and Si APD for detectors, reasonable area which can receive optical power above the receiver sensitivity for a bit error rate of 10(superscript -9 for 100 Mbps signals was obtained.
This contribution describes a new kind of ranging system based on a recently developed optical sensor called the Photonic Mixer Device (PMD). This new device combines fast optical sensing and modulation of incoherent light signals in one component part by its unique and powerful principle of operation. Due to this, the device is blind for any kind of uncorrelated light. An line or array of these smart sensors provides a multi-dimensional ranging system as will be shown in our contribution. We propose the advantages of this new approach, including the useful qualities of using a PN-code sequence. Especially the results of the extremely high resolution ranging system, including a new kind of PMD elements, are the main focus of this contribution.
Free space optical communication systems deployed in office buildings are subject to transmission loss through windows. Window attenuation varies between 0.4 and more than 15 dB. Window attenuation values are required to calculate communications link power budget and availability. But direct measurement of window attenuation in high-rise buildings is difficult since it requires access to both sides of the window. In this paper, we present a method of measuring optical attenuation from the interior side of a window. This method is based on measuring back reflections of a laser beam propagating through a semi-transparent dielectric medium, thus eliminating the need for access to the exterior of a building. In this system, a laser beam is launched at 45 degree(s) to normal incidence in order for the user to discriminate between the various reflections from the dielectric interfaces within the medium. A photodetector is then moved through the plane of incidence and the intensities of reflections from interfaces within the medium are measured. A simple formula is used to calculate total transmission of the optical system based on the relative intensities of the incident light beam and all resulting reflections. In this approach, it is assumed that the reflectivities of the first and final interfaces are identical. The index of refraction for glass from one commercial fabricator varies little; hence the reflectivity of uncoated air-glass interfaces in a particular window is the same. The intensity of the reflection from the final interface is attenuated by the entire medium twice. By comparison of the incident, first, and final reflected intensity a transmitted intensity can be determined. The same equation is used for a medium with any number of dielectric interfaces. A measurement of optical loss through a window without access to both sides of the medium is now possible. This method has been demonstrated to be accurate (+/- 1dB) through various windows with optical losses of up to 12dB.
Based on analysis of the meteorological visibility statistical data, the probability P of degradation (unavailability) of a free-space optical communication (FSOC)link caused by the light scattering in fog and precipitation versus distance of communication D has been investigated. It has been found that for a variety of geographical locations, P(D) dependence averaged over entire year is nearly proportional. Such linear dependence is valid for a wide range of communication distances, from tens of meters to kilometers. It can be shown that the averaged P(D) function is linear if the density of the light scattering partices number statistics is driven by Pareto distribution, and the distribution of particle sizes does not depend on the density of particles number. It is important that averaging of the unavailability data for any separate month of a year gives non-linear and significantly different for different months P(D)functions.