Optical communications – Optical communication over freee space – Transceivers
Reexamination Certificate
2002-01-22
2004-03-02
Negash, Kinfe-Michael (Department: 2633)
Optical communications
Optical communication over freee space
Transceivers
C398S045000, C398S118000, C398S135000
Reexamination Certificate
active
06701092
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wireless telecommunications networks, and more particularly to a broadband telecommunication system and network which employs atmospheric (i.e. free-space) laser transmission.
DESCRIPTION OF THE RELATED ART
Broadband communications applications such as interactive television, video telephony, video conferencing, video messaging, video on demand, high definition television (HDTV) and high-speed data services require a broadband communications network between and to the various subscribers. The current telecommunications network, referred to as the Public Switched Telephone Network (PSTN) or the plain old telephone system (POTS), is presently the only wired network that is accessible to almost the entire population. This system, although ideally suited and designed for point-to-point transmission and any-to-any connectivity, has become nearly overloaded with the use of voice, fax and data communications.
The PSTN today primarily comprises digital switching systems, and transmission over the local loop is typically by either T
1
feeder copper-based systems or fiber optic cable systems. However, the subscriber loop is still primarily copper unshielded twisted pair (UTP) wiring, which has a limited capacity. Therefore, the physical nature of the system is severely bandwidth limited, with data transmissions typically in the 9,600-28,800 bits per second range. Thus, high speed broadband applications cannot feasibly be based on POTS technology.
New hard-wired systems, such as ISDN (Integrated Services Digital Network) and fiber optic networks, offer high speed bidirectional communications available to many individuals. However, ISDN itself may not provide sufficient bandwidth for many broadband communications applications. In addition, ISDN requires that most subscribers be connected with upgraded copper wire. A fiber based network, such as fiber to the curb (FTTC) and fiber to the home (FTTH), requires that new fiber optic cable be run to every subscriber. The cost of implementing a fiber optic network across the United States would be very expensive. Other alternatives for increasing the capacity of existing networks include ADSL (Asymmetric Digital Subscriber Line), SDSL (Symmetric Digital Subscriber Line), and HFC (Hybrid Fiber Coax), among others.
An alternative to hard wired network solutions is a wireless-based solution. Most currently existing methods for wireless telecommunications are based upon broadcast methodology in the electromagnetic spectrum. One example of a wireless broadcast medium is the Direct Broadcast Satellite (DBS) system, such as “DirecTV”. In general, broadcast systems are widespread and numerous. However, available bandwidth is increasingly limited by the sheer volume of subscribers, especially with the rapid growth in the cellular phone market. The result of this “crowding of the bands” is that the wireless electromagnetic systems are unable to meet the voracious need of the public for high speed data communications.
Another method for broadband point-to-point communications employs lasers in a point-to-point system that establishes a single continuous, high-speed, bi-directional, multi-channel, atmospheric connection. Laser based wireless systems have been developed for establishing point-to-point, bi-directional and high speed telecommunications through the atmosphere. The range for such systems is typically 0.5 to 1.2 miles, with some having a range of 4 miles or more. The longest atmospheric communications path achieved with a point-to-point system exceeded 100 miles. These single path systems require a laser and transceiver optics at each end of the connection. The connections are capable of maintaining high speed bidirectional communications in some of the most severe inclement weather conditions. The cost of such systems are typically in the $10,000 to $20,000 dollar range however, making them unsuitable for most home and business use.
Therefore, a wireless, laser based telecommunications system is desired that enables a number of subscribers to share a communications path to a great number of subscribers. A wireless, laser based telecommunications system is further desired which reduces the cost to each subscriber, yet still provides high speed, bi-directional, broadband, wide area telecommunications. A system is desired which does not require huge installation costs of ISDN and fiber optics, and which does not require any of the electromagnetic broadcast bands of the mobile communication systems. Such a network could be employed in a wide variety of applications such as telephony, data communications such as the Internet, teleconferencing, radio broadcast, and various television applications such as cable television, HDTV and interactive TV.
SUMMARY OF THE INVENTION
The present invention comprises a point-to-multipoint bi-directional wide area telecommunications network employing atmospheric optical communication. The network comprises a primary transceiver unit, an optical router, and a plurality of subscriber transceiver units. The primary transceiver unit generates a first light beam which includes first modulated data. The optical router receives the first light beam and demodulates the first data. The optical router modulates the first data onto a second light beam and transmits the second light beam to the subscriber transceiver units. The optical router demodulates, modulates and transmits to each of the subscriber transceiver units in a time-multiplexed fashion.
The subscriber transceiver units receive the second light beam and demodulate the first data. Each subscriber transceiver unit comprises an optical antenna or other optical receiver/transmitter. The optical antenna is preferably coupled to an input/output device such as a set-top box or display system, e.g., a computer or television, by a fiber optic cable.
In the other direction, the subscriber transceiver units atmospherically transmit a third light beam which includes second modulated data to the optical router. The optical router demodulates the second data, modulates the second data on a fourth light beam, and transmits the fourth light beam to the primary transceiver unit. The primary transceiver unit receives and demodulates the second data. The optical router demodulates, modulates and transmits to each of the subscriber transceiver units in a time-multiplexed fashion. Thereby, bi-directional communication channels between the primary transceiver unit and the plurality of subscriber transceiver units are established for transferring data in each direction.
The preferred embodiment of the optical router comprises a secondary transceiver unit, a plurality of transceiver modules and an electronic router for routing data between the secondary transceiver unit and the plurality of transceiver modules to establish the communication channels between the primary transceiver unit and the plurality of subscriber transceiver units. The secondary transceiver unit transceives light beams including data with the primary transceiver unit and the transceiver modules transceives light beams including data with the subscriber transceiver units. The transceiver modules comprise an X-Y beam deflector for deflecting the light beams to a portion of the subscriber transceiver units in a time-multiplexed fashion.
In an alternate embodiment of the optical router, the optical router simply redirects the light beams between the primary transceiver unit and the subscriber transceiver units in a time-multiplexed fashion rather than demodulating and re-modulating the data. The alternate optical router employs a mirror and lens set to redirect the light beams.
Therefore, the present invention comprises a laser-based atmospheric communication network which provides broadband bi-directional communications to a plurality of subscribers. The present invention provides a bi-directional broadband optical communication network with significantly reduced infrastructure costs. A network of such networks comprising multiple optical routers and mu
Doucet Mark A.
Panak David L.
Brightwell Mark K.
Dominion Lasercom, Inc.
Hood Jeffrey C.
Meyertons Hood Kivlin Kowert & Goetzel P.C.
Negash Kinfe-Michael
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