Telecommunications – Transmitter and receiver at separate stations – Near field
Reexamination Certificate
2002-05-24
2004-08-03
Ahmed, Samir (Department: 2663)
Telecommunications
Transmitter and receiver at separate stations
Near field
C455S517000, C455S063100, C455S067140
Reexamination Certificate
active
06771932
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wireless networks and more particularly to a method for determining lines of sight between two nodes in a wireless infrared mesh network.
BACKGROUND OF THE INVENTION
In many areas of the world the World Wide Web (WWW), or Internet, has become a significant medium for the exchange of information including everything from casual electronic mail (e-mail) to legal and business documents to entertainment media. Much of the material exchanged over the Internet comprises very large electronic files, for example large documents, music, video and even full-length motion pictures are available for exchange and distribution over the Internet.
While commercial services often choose fast but expensive high-speed Internet connections for business purposes, consumer connections typically use relatively slow telephone modems. For example, a typical commercial T1 connection will yield in the range of 1,544 kilobits per second (Kbps) or 1.544 megabits per second (Mbps) data communications rate at a monthly cost in the range of $1,000 to $2,000. In contrast, a typical consumer telephone modem connection will provide a 56 Kbps data communications rate at a cost of in the range of $10-$30 month.
As commercial services provide richer content for consumer use, data file sizes increase. For example, a typical audio music file may be in the range of 3-5 Megabytes and take anywhere from 5 minutes to an hour for a consumer to download over a standard telephone modem. A typical audio/video file, for example a full-length movie, may run in the thousands of mega bytes size range and take a significant part of a day for a consumer to download over a regular telephone modem. High-bandwidth applications such as on-demand television and Web pages filled with multimedia effects may be impossible to use with a standard telephone modem connection.
It is obvious that the ability of commercial services to provide rich, large media files is rapidly outstripping the typical consumer's ability to receive those files.
Recently, several affordable, high-speed alternatives have become available to the traditional telephone modem. Cable modems use the cable television infrastructure to provide Internet connections having a maximum speed of about 1,500 Kbps, over 25 times the speed of a telephone modem. DSL modems use conventional telephone lines to provide Internet connections also having a maximum speed of about 1,500 Kbps. Both cable and DSL modems are priced at approximately twice the cost of telephone modem services, with slightly higher costs for equipment.
The higher speed cable and DSL connections are geographically limited, however, by the underlying infrastructure. Many areas of the United States include regions not serviced by cable television or where the cable television network has not and will not be upgraded to support high-speed data modems. Similarly, DSL service is not available in many geographic areas. Numerous reasons exist for the limited availability of cable and DSL services, including high-cost of infrastructure upgrade, technological limitations, physical geographical limitations and, in some areas, low demand. As with many types of commercial services, the incremental costs of extending infrastructure become increasingly higher, sometimes by multiples or even exponentially, as attempts are made to expand those infrastructures to every last consumer.
There thus exists a real demand for high-speed Internet connections in areas that cable and/or DSL service providers may never serve. This demand will increase as more content is provided and more business is executed over the Internet.
Some providers have attempted to expand service coverage while avoiding the high costs associated with physically expanding the broadband network infrastructure. The ability to extend a network to individual businesses or homes that would not otherwise be able to be connected is called “Last-mile technology”, which is basically the infrastructure at the neighborhood level. Last-mile technology carries signals from the broad telecommunications network along the relatively short distance to and from a home or business.
One method of accomplishing Last-mile technology is through use of a wireless network that extends from an access point in the wired infrastructure. Wireless networks may be installed without the need for the wired infrastructure. In a wireless network, electromagnetic waves, rather than some form of wire, carry the signal over part or all of the communication path.
One type of wireless technology uses radio frequency (RF) components to transmit data in the radio frequency spectrum. RF networks however cannot provide a level of security that is required by many broadband users. Another type of wireless network uses infrared (IR) devices to convey data via IR radiation.
Infrared radiation is electromagnetic energy at a wavelength or wavelengths somewhat longer than those of red light. The shortest wavelength IR borders visible red in the electromagnetic radiation spectrum, the longest wavelength IR borders radio waves. IR wireless systems implement devices that convey data through IR radiation
IR systems typically operate in either “diffuse mode” or “line-of-sight” mode. In diffuse mode, the system can function when the source and destination are not directly visible to each other, e.g. a television remote. In line-of-sight (LOS) mode, there must be a visually unobstructed straight line through space between the transmitter and receiver. Unlike RF wireless links, IR wireless cannot pass through walls or other physical obstructions. However, unlike RF wireless links, a line-of-sight IR system offers a level of security comparable to hard-wired systems, due to the nature of the invisible and narrow beams used to connect a line-of-sight IR transmitter and receiver.
Free-space optics (FSO) refers to the transmission of modulated visible or infrared beams through the atmosphere to obtain broadband communications. Laser beams are generally used, although non-lasing sources such as light-emitting diodes (LEDs) or IR-emitting diodes (IREDs) may also be used. FSO works similarly to fiber optic transmission. The difference is that the energy beam is collimated and sent through clear air or space from the source to the destination, rather than guided through an optical fiber. At the source, the visible or IR energy is modulated with the data to be transmitted. At the destination, the beam is intercepted by a photodetector, the data is extracted from the beam (demodulated), and the resulting signal is amplified and sent to the hardware.
FSO systems can function over distances of several kilometers. As long as there is a clear line of sight between the source and the destination, communication is theoretically possible. Even if there is no direct line of sight, strategically placed mirrors can be used to reflect the energy.
Because air, not fiber, is the transport medium, FSO systems are cost-effective and easy to deploy. Unlike fiber, there are no heavy capital investments for buildout and there is no long provisioning delay to set up a FSO network. In addition, FSO works in an unregulated frequency spectrum with little or no traffic currently in this range. Another advantage to FSO networks is that FSO network architecture needn't be changed when other nodes are added; customer capacity can be easily increased by changing the node numbers and configurations.
However, for a number of reasons, FSO systems have generally not been used as a solution to the last-mile-access problem in the past. While lasers are a cost-effective high-speed communications medium, they require very highly aligned line-of-sight paths. More specifically, existing FSO systems have very narrow beam divergence parameters requiring precision alignment. For this reason, laser components tend to be expensive and laser systems tend to require high levels of maintenance and service. In addition, FSO systems can be limited by rain, dust, snow, fog or smog that can block the tr
Caminiti Lorenzo
Di Bernardo Enrico
Goncalves Luis
Moursund Carter
Ahmed Samir
Brandt Jeffrey L.
Omnilux, Inc.
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