WO2001003241A1

WO2001003241A1 - Free space fixed and mobile optical communication system

Info

Publication number: WO2001003241A1
Application number: PCT/US2000/018147
Authority: WO
Inventors: Joseph R. Child
Original assignee: Child Joseph R
Priority date: 1999-07-01
Filing date: 2000-06-30
Publication date: 2001-01-11
Also published as: AU5910100A; WO2001003242A1; AU6063400A

Abstract

This invention is a broadband digital communication system that uses a multiplicity of interconnected base stations (20) with multi-beam antennas. The multi-beam antennas consist of lenses (47) and reflectors (40) with an array of optical transmitters (48) and receivers (46) at the focal surface (46) of the antenna. The invention enables local optical coverage of an area with broadband communications through free space. Individual users can purchase end user optical communications link equipment and connect to the system by attaching an end user antenna to a fixed mount and pointing the antenna at a base station nearby. The User then logs onto the system using a computer and an industry standard Internet browser interface. The invention includes simplified installation procedures and service subscription processes. These result in the delivery of cost effective broadband services requiring little or no effort on the part of the system operator to add new customers. The invention provides broadband communications services using multi-point distribution of optical signals through free space and using base station (20) that are small, easy to install, low power, and inexpensive. Each base station provides coverage for a small segment of the system's coverage area with a wide view optical antenna, and providing connectivity for fixed location customer equipment to all manner of telecommunications systems and services. Mobile User can also operate over the system, which automatically tracks and compensates for User movement.

Description

FREE SPACE FIXED AND MOBILE OPTICAL COMMUNICATION SYSTEM

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on the Provisional Patent Application filed on July 1, 1999 entitled "Low Cost Broadband Wireless Access System" by inventor Joseph R. Child with Serial Number: 60/141861.

FIELD OF THE INVENTION

The present invention is in the field of optical communication arts and relates more particularly to a optical communication system that uses a multi-directional antenna for point-to- point and point-to-multi-point communications.

BACKGROUND OF THE INVENTION

The demand for higher data rates in telecommunications is growing rapidly as is often noted. Many industry experts note that future demands for data transmission cannot be met with existing or anticipated systems. The capacity of ever faster computers will remain largely unexploited unless transmission facilities become available supporting much higher data rates than currently available. Fiber optics systems were perceived as an answer, but after decades of fiber deployments, only 3% of the nation's largest 750,000 commercial buildings have fiber passing by. Many of them do not, and may never, have taps into that fiber for numerous reasons related to the construction efforts required.

Historically, obtaining broadband services involved considerable cost and time. The process of deploying service is complex and involves extensive business decision processes, negotiations with carriers and real estate arrangements for trenching to install cabling or installation of expensive radio systems. This costly, time consuming process becomes unnecessary with the introduction of this invention. Likewise, a complex business process is replaced by trivial consumer purchases and costs for services drop as competition increases.

SUMMARY OF THE INVENTION

This invention is a broadband digital commumcation system that uses a multiplicity of interconnected base stations with multi-beam antennas for communicating through free space. The system consists of multiple base stations in a geographic area, such as a city, and multiple User locations within the coverage area. In the system, modulated optical signals are transmitted

-1- between adjacent base stations and between base stations and equipment located at a multiplicity of end user locations. End users communicate with each other through base stations or through a network of local interconnected base stations. Links are formed between Users in one geographic area and Users in a distant location via external digital connections links between base stations in the two geographic areas. The multi-beam antennas are wide angle antennas with an array of optical transmitter and receiver elements at the focal surface of the antenna.

A geographic area to be served is populated with base stations that use wide angle antennas mounted primarily on or near building tops so as to be able to illuminate the intended service area. This enables local optical coverage over a wide area. The invention provides the means for communicating through free space using a multiplicity of point-to-multi-point base stations. Each base station provides coverage for a small segment of the system's overall coverage area. The base stations use optical wide angle antenna, providing connectivity for fixed location Users.

The antennas form optical images of the surrounding area on the focal surface of the antenna in some ways similar to the way a camera forms an image on a flat film surface. At the focal surface is an array of detectors or optical receivers. Each detector senses the incoming signal from a particular distant point within view of the base station antenna. An incoming optical signal originating at that point is focused on the particular point on the array. The density of detectors is selected so each few square feet or less of illuminated building surface at a distance is detected by a detector. Adjacent to each detector is a transmitter element that supports transmission of optical energy back toward the same distant point.

User terminals are equipped with electronic identification numbers. This allows Users to move terminals. If a User terminal antenna moves, the image of the User's signal on the receiving antenna's array moves. The system tracks User movement by detecting the image as it moves from one detector to the next. This allows the system to automatically track signals when buildings sway or the Users move. If a User is operating in a mobile mode, using an antenna that continues to aim at the base station, the base station tracks the User as long as it remains within the base station antenna's field of view. Each time the image of the User's signal moves to another detector, the system redirects the base station's outgoing signal to a transmit element associated with the latest detector in use. This allows the system to continuously communicate with a mobile User as the User moves. This feature allows the system to map each user's location and track the users as they move. The process of redirecting the transmitted signals on both ends of the link is used to compensate for any movement or changes in orientation of the antenna at either ends. The system is able to track multiple mobile Users simultaneously. When more than one user is within a single spot beam, multi-user protocols are used to distinguish one User from the other as described herein.

By placing optical energy emitters, called transmitter elements, next to each detector at an antenna's focal surface, it is feasible to send optical signals back to the distant point where the incoming signal originated. By using detectors associated with specific transmitter elements, the system supports bidirectional communication with many separate locations within the view of the antenna. Signals arriving at different receiver elements contain packet information that is used by the base stations and associated routing electronics to direct the signals to the intended end user.

A base station antenna consists of one or more optical focusing device, each containing an array of signal receiver and transmitter elements at its focal surface. An antenna focusing device is a lens or parabolic reflector that optically forms an image on the focusing device's focal surface. The operation of a focusing device is enhanced with one or more reflectors which direct signal energy to the focusing device. The additional reflectors provide the antenna with wider coverage without increasing the number of receiver and transmitter elements in the focal surface. There are several types of reflectors used. One is a single flat mirror. The reflector is positioned so incoming optical signal energy impinges on the focal surface of the antenna where no other useful signals are likely to be focused. For example, if an antenna's vision includes open sky where no fixed customer locations exist, a reflector is located in the direction of the open sky that aims signal energy from buildings behind the antenna at the antenna gathering element. Another type of reflector is a set of mirrors aimed in separate directions forming separate images on different portions of the focal surface.

Another type of reflector is a concave reflector, which provides the antenna with improved signal gathering in a specific direction. In this case, the configuration of elements is functioning in a manner similar to a telescope. Several detector designs are used at the focal surface. One is an opto-electrical converter which converts optical energy into electrical energy. Another is a signal collection element such as a small lens that focuses optical energy into a fiber optic cable. Another is large diameter fiber optic cable with its end formed convexly so as to collect incident optical energy and transfer it into the fiber. User antennas are similar to base station antennas in that they have a signal gathering element and an array of receivers and transmitters at the focal surface. The angle of view subtended by the array is smaller than on a base station since the User antenna is used to view only one spot at a time, that being the base station with which it communicates.

The view of the directional antennas of this invention are narrow. Their beams are therefore referred to as a spot beams.

-3- A new customer initiates service by first mounting an end user antenna device at a window or on the outside of a building or other structure and aiming a small antenna at one of the base stations within line of sight. The User then activates service by registering on-line using a browser interface. The process employs automated use of credit card information as is common with e-commerce or other suitable financial transactions. The process requires little or no human intervention on the part of the service provider. Once registered, a User contends for service with other Users within the same spot beam. There are a variety of industry standard protocols for sharing communications links that are used such as time division multiple access. Alternatively, Users subscribes to have a spot beam assigned on a dedicated basis. The technique is more applicable where Users require broadband digital telecommunications services at cost effective rates that are not cost effectively available via other means. The base stations of the present invention are installed expeditiously at multiple locations.

The invention is configured to support data rates as high as fiber optics cabling systems. Fiber optics systems experience failures caused by construction workers digging up cables and this invention provides back up services for such fiber systems. No existing radio technology, approved for use by telecommunications carriers, is able to meet the high data rates required to provide this type of service. The invention is also used to provide backup services for other, lower data rate wireless systems such as LMDS, MMDS, and other telecommunications related technologies.

The system supports telephony, wireless cable TV, video-on-demand, Internet services, and other forms of digital and analog communications.

The invention uses a network of base stations that are interconnected via wireless and wired links. Wireless links are used to carry signals between base stations and between base stations and User locations. Connections to Users via cabling within buildings is also to be used where cost effective.

The network of base stations is connected to external telecommunications systems typically at multiple points. This is done to support multiple types of services and redundancy for specific connections. The base stations route User signals through the network of base stations using redundant optical and/or radio links. That is, each User's signal are carried over two or more links within the network for signal routing redundancy. This redundancy ensures blockage of any one path does not result in loss of signal.

The system contains a network operation center (NOC) which performs various control and switching functions. The NOC monitors and manage system components, signal routing, and connections external to the network. External connections includes connections to systems such as the Internet and dedicated links to other systems including other telecommunications networks based on the present invention.

Communications between Users within the same local network of base stations are achieved without passing the signals through external system connections. When using optical signals, the signals are passed between Users over the local network of base stations without demodulating the signals en route where feasible. This provides high speed broadband signaling capability cost efficiently.

It should be noted that the invention envisages several alternative types of antenna configurations, base station interconnections, optical wavelengths, and User equipment configurations. The interconnections between base stations, and between base stations and external system connection points, are achieved using means such as radio links, free space optical signal paths, fiber optic links and other cabling techniques. The selection of technique is made on a link by link basis and depends on the suitability and availability of resources. The system is equipped with various types of remote monitoring capabilities. Loopback capabilities are built in to the equipment to automate fault isolation and link evaluations. This is particularly useful for predicting signal performance through various alternative paths within the network. Such predictions are used to establish supportable levels of service on a User by User basis. The User equipment external interfaces have an "open" design ensuring ease of integration with industry standards based applications and equipment.

The novel features of the present invention are set forth with particularity in the appended claims. The invention is best understood from the following description when read in conjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a side view of an antenna and an object within its field of view.

Figure 2 shows a top view of the antenna and buildings within its field of view.

Figure 3 is a side view of an antenna showing receiver and transmitter elements located in the focal surface of the antenna.

Figure 4 is a top view showing multiple antennas of the present invention arranged to view the entire 360 degrees of the horizontal.

Figure 5 shows an enlarged view of an array of receiver and transmitter elements that is positioned at the focal surface of the antenna. Figure 6 shows the present invention using a parabolic lens instead of a parabolic

-5- reflector.

Figure 7 shows a portion of a parabolic reflector being used in conjunction with a flat reflective surface to extend the view of the antenna.

Figure 8 shows a parabolic reflector being used with a secondary reflector to provide an alternative line of sight to the object being viewed.

Figure 9 shows multiple flat surface reflectors used in connection with an optical lens to illuminate various objects.

Figure 10 shows a convex reflector used in conjunction with an optical lens to illuminate objects in a 360 degree range. Figure 11 shows a convex reflector having its center portion removed that is used in conjunction with a parabolic reflector.

Figure 12 shows a convex reflector having a center portion removed that is used in conjunction with a parabolic reflector and secondary lenses.

Figure 13 shows two convex reflectors an their associated parabolic reflectors. Figure 14 shows a mobile antenna having two hemispheric lenses.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The basic system of the present invention includes base stations that are capable of point- to-multi-point high bandwidth communication. User terminals share the same basic design as the base stations and are easily installed by the user.

Base stations consist of equipment and antennas. The antennas are mounted on building rooftops, sides of buildings or within buildings positioned inside windows or other openings. The signal interfaces to the base station equipment are electrical or optical depending on the most suitable for a given application. The base stations require very low transmitter output power due to the very short paths involved. Use of much lower power is practical primarily due to the reduction in potential weather related signal attenuation, a reduction that results from using shorter links. Use of shorter links also results in smaller antennas and simpler installations, since tall towers and significant support structures are not required.

The base stations are physically small, self contained to the extent technically feasible, light weight, and designed for ease of attachment in a wide variety of mounting circumstances. This includes free standing mounts able to withstand anticipated physical abuse. Optional housings are available with weather proofing, single point gripping mount attachments, mounts for attaching to mechanical structural elements of all shapes and sizes and at all angles, and mechanical extensions to ensure the antennas are not likely to be obstructed. All mountings are provided so as to ensure that the antennas are held in place during all anticipated conditions of

-6- weather and physical abuse.

Base stations are supplied with uninterruptable power supplies to ensure reliability of service. The equipment is modular for ease of servicing and repair.

Base station antennas are multi-beam antennas with independent signals carried over each beam. Two forms of antenna are used. One is a parabolic reflector type antenna, the other uses optical lenses. At the focal surface of the antenna, an array of optical detectors is placed for receiving incoming signals. Adjacent to each detector is a light source for transmitting in the reverse direction. This placement of detector and transmitting element adjacent to each other at the focal surface ensures that the receive and transmit signals share overlapping spot beams. The links to Users are relatively short. Whereas radio links operating in the 18 to 40 gHz bands are typically 1 to 3 miles in length, the links in the present system are on the order of 400 meters or less. The objective is to shorten the links so signal attenuation due to rain and fog is not severe enough to obstruct useful transmission. The shorter distances also reduce the required power output of the transmitters. For example, by reducing the path length from 3 miles to 400 meters, the rain attenuation is significantly reduced and the unfaded power level requirements drop by more than 20 dB. This is reflected in lower complexity and cost of the equipment.

Longer paths are used where service availability requirements are not high. For example, some residential Users are supplied broadband digital service with 95% availability over optical links many times longer than can be achieved when 99.99% availability is required. This allows the service provider to reduce system infrastructure costs for a selected coverage area.

The present invention will now be further described in connection with the figures. Figure 1 shows a side view of the basic operation of an antenna. It includes a base station antenna 20 having a focal surface 24 and a vertical field of view, the upper and lower limits of which are shown by lines 26. Within the field of view is shown the representation of a building 22 in which a user of the system would be located. For convenience of presentation herein, the image of a building is used to represent the optical image that would be formed by a user's signal coming from that building. The actual image that is formed is a dot or small circle formed by the incoming narrow beam of optical signal energy. The user inside the building 22 sets up a directional antenna, similar to the base station antenna, to optically communicate with base station antenna 20. Located within the focal surface 24 of the antenna 20 is an array of receiver and transmitter elements that are used to transmit to and receive signals from the user's antenna.

Figure 2 shows a top view of a base station antenna in which parabolic antenna 30 has a horizontal field of view, shown by lines 32, which covers objects 34, 35, and 36 within the field of view of the antenna 30.

The size of an antenna affects the amount of signal energy that is captured by the antenna, assuming the signal source is a distance away. However, if the distance is short and the antenna is large enough to intercept all the photons being transmitted, changing the distant does not affect the received signal level. The width of the beam is therefore a significant factor.

When determining beam width, a performance tradeoff is made between coverage area and signal performance. The data rate that is achieved is a function of the receive signal strength. This is affected by the base station antenna's beam width, distance to the User, angle of view from the base station antenna, and size of the User antenna. These parameters are adjusted/considered in the design of the system to achieve a high level of performance for anticipated applications.

The field of view for a base station antenna is selected for each targeted coverage area. Lenses are used with views from those of a "fish eye" or hemispherical to a more narrowly confined view. The parabolic antennas are on the order of 120 degrees or less. An antenna's angle of view is one of the variable characteristics determined when selecting an antenna for the coverage requirements of a particular service area. The selection of the angle of view is determined as a function of User density, location, and distance to the Users. Higher densities of Users would suggest narrower beams in order to service individual Users separately. If the physical distribution of Users forms a widely dispersed pattern, wider beams are suggested to reduce the number of base stations required. The geometry of the lens or parabolic reflector is selected based on the focal surface image size desired. Smaller images are desired for close in buildings, whereas larger images are used for distant buildings. Both applications have the same effective density of objects such as building windows at the focal surface. This permits use of the same pattern of detectors and transmitter elements at the focal surface. The effective gain of an antenna is nominally lower toward the edges of its coverage pattern. Users located on the edge of a base station antenna's view may need to be closer to the base station to compensate for the lower gain at the edge. Thus, the distance to the Users can affect the selection of the antenna angle of view, that is, the orientation of the base station antenna with respect to the User community. The base station antennas are placed throughout an intended service coverage area so as to illuminate the roofs and/or sides of buildings containing potential Users. Antennas can also be mounted on other structure such as towers, billboards, bridges, and other vantage points to achieve the desired coverage. Wireless communications systems are commonly designed for radio signals to illuminate building rooftops only. However, use of this invention results in illumination of building sides as well to allow use of antennas behind windows and other

-8- openings where suitable. This can significantly reduce installation costs since the approach reduces requirements for in-building wiring.

The beam width of individual spot beams vary depending on User locations as noted above. When the configuration of Users in an area exceeds the capacity of a single base station antenna, the system is expanded using adjacent base stations (within yards of each other) for servicing additional Users. The independent reception and transmission by such adjacent base stations takes advantage of the ability to aim the User antennas at differentiate base stations and prevent interference between signals from adjacent base stations. This concept of being able to add base stations at will to increase system capacity allows the initial system to be deployed with lower capacity and lower cost. The approach also ensures that the initial base stations are not obsoleted as the system expands.

With the flexibility to adjust beam widths, the number of spot beams is optimized for each antenna. Thus, the same type of antenna is used in areas of low User density as well as high density. Figure 3 is a more detailed drawing of a base station antenna of the present invention.

This drawing shows a parabolic reflector 40 having focus surface 52. Receiver elements 46, also referred to herein as detectors, and transmitter elements 48 are located adjacent to each other at the focal surface 52. Line 50 indicates the axis of adjustment for the receiver elements 46 and the transmitter elements 48 within the area of the focal surface 52. The receiver elements 46 have a lens 47 located at the end of a fiber optic strand to receive optical data from an observed object such as building 42. The transmitter elements 48 have ends 49 that allow the transmitter elements 48 to project optical signals toward reflector 40, which in turn focuses that energy into a narrow beam aimed at building 42 along the free space path 44. The reflecting surface of antenna 40 is coated with highly reflective material to facilitate the reflection efficiency of the antenna surface.

Base station antennas can have their beam widths adjusted by setting detectors and transmitter elements forward or backward from the nominal focal surface 52 of the antenna. Movement in the direction 50 is preferred as this results in minimum blockage of signals associated with adjacent elements 46 and 48. A second utility of being able to move the elements at the focal surface is to be able to account for variations in distance between a base station and users. The more distant users form images in focus closer to the parabolic reflector or lens. Users closer to the antenna form images further away. In essence the point of focus varies slightly depending on the distance of the object. This can be compensated for by moving the elements as noted. A single base station spot beam may be wide enough to service multiple User locations. To communicate with multiple users over a single spot beam, multiple frequencies can be used over each beam and assigned to different Users. To support this approach, User and base station antennas are equipped with detectors and signal sources for use a various frequencies. In fact, the selection of frequencies can be done to minimize interference from signal sources in the environment. Alternatively, other sharing techniques are used such as TDM, TDMA and CDMA.

User terminals consist of electronics and a user antenna. The electronics and antenna can be integrated into a single package. Uninterruptable power supplies can also be supplied for reliability of service. The user terminal's antenna is configured in several electrical/mechanical formats. In the simplest format, the user terminal includes an antenna consisting of a small parabolic reflector or lens and multiple receiver and transmitter elements mounted at the antenna's focal surface with electrical or optical connections to the elements, a housing, interface for connection to equipment, associated electronics, and a means of securing the antenna in position. The mechanical mounting and housing features of the User antenna is similar to the base station antennas as noted above.

A User antenna is installed by simply mounting it and aiming the antenna at a base station. This procedure would be similar to direct TV antenna installation procedures whereby the User mounts and aims the antenna at the satellite without requiring additional technical support from the service provider. A calibrated mechanical or optical sighting guide is used. A small visible pilot light of a specific color is equipped on the base station antenna for purposes of sighting. Since the antenna has a focal surface populated with multiple transmitter elements, some of them are reserved for these pilot lights. This ensures that the entire coverage area of the antenna is equipped with pilot light signals.

The visible light signals used to aid Users when aligning antennas manually is disabled when a base station is at capacity or otherwise unable to accommodate a new user.

If multiple base stations exist within view, the User would have a choice of selecting the one physically closest. This normally provides the greatest protection against rain and fog attenuation.

A User antenna can also be supplied with motorized or mechanized searching capability to scan the environment for available base station signals. This procedure would involve use of an intelligent device such as a PC computer to help direct and control the antenna positioning activity and record incoming signals during the scanning process. Alternatively, the User could remotely direct the scanning process by varying the antenna position through the use of control signals over electrical cables and monitor received signals without using automated signal processing as opposed to looking for visual indicators.

-10- Many customers are able to mount and aim antennas manually without assistance. Some mounting positions, however, may result in difficulties doing so manually. In some cases the base station may not be easily detected using a sighting device. Also, the mount may not be located where a person can conveniently reach the antenna to manipulate it. In such cases, the antenna is electronically directed to step through all possible angles of view to log the available signals from all base stations within line of sight.

To support this alignment process, spot beams from base stations broadcast special optical "flag" signals to indicate the beam is either unassigned, not available, idle, or busy. The "unassigned" signal indicates the beam is available for subscription as a shared or dedicated beam. A "not available" signals is carried on beams that are dedicated to a User. An "idle" signal is broadcast on beams that are shared, but not in use. Beams that are shared, but in use, carry a "busy" signal.

For beams carrying optical signals, the "busy" and "not available" statuses are derived from examination of the activity on the beam as noted above. For the "unassigned" state, either a coded or an unmodulated visible signal is carried by the beam. The visible signal approach would aid Users seeking to manually aim antennas.

Multiple User antennas can be installed near each other to achieve path redundancy. In many cases the two User terminals, each with its own antenna, is operated within the same base station beam. One of the two terminals would be in standby mode. Such a diversity technique is useful to overcome obstacles such as window cleaners as they go by and block the signal path. A signal switching device would be used to select the unblocked antenna based on signal performance at the User end of the link. For increased reliability the two antennas are directed to separate base stations, if an alternative base station is within view. If the User has multiple vantage points available from which to see a base station, it may be possible to use another beam associated with the same base station. For more robust redundancy, two such links could be operated in hot stand-by mode.

If the link with a base station has signal levels high enough, a lower cost beam splitter/combiner technique is used instead of a second antenna. In this technique a reflector is placed at the User location within sight of the User antenna. The User antenna is aimed through a beam splitter at the base station. The other aperture of the beam splitter is aimed at the reflector, which in turn is aimed at the base station. Signals arriving from the base station at the reflector are directed at the beam splitter/combiner and into the User antenna. The level of the reflected signal hitting the User antenna is adjusted to a level below the desired signal so it does not cause harmful interference during normal operation. User antennas are installed on rooftops using cabling from the antenna to customer

-11- premise equipment (CPE). From the CPE equipment, additional Users are connected to the system.

Another form of User antenna is a base station type antenna with both User and base station functionality. The one antenna is used to link other Users and/or base stations together. This approach could be suitable in the case where a User antenna is mounted on the rooftop of a building with other potential customers. Such a placement can result in cost savings when a particular building is well situated for locating base station antennas.

To initiate use of the system, a User acquires a User terminal which includes an antenna and associated hardware and software. The minimum complement of components allows the User to interface the User terminal with a PC computer for activation purposes. The antenna alignment process having been completed as noted above, the User is connected to the NOC via a relatively low data rate link over the selected beam. A relatively low data rate is to be used for the activation process, since the link is more likely to function at a lower data rate. Once the link has been evaluated by the NOC, as described in the next paragraph, and the User selects service options, higher rates should be possible.

When the system detects an attempt by a User to initiate service, the NOC automatically initiates testing of the User link. Knowing the base station beam being used by the User, the system knows the direction of the User's antenna. Using timing signals, the system determines the distance from the base station antenna to the User antenna. This allows the system to map the approximate location of the User. Using geo-coded location information, the system can automatically validate the location of the User during the registration process.

A series of transmission quality tests are then run by the NOC on the connection to the User. From these quality measurements and the distance measurements, it is possible to determine the quality of the link, information which is used to baseline the link performance for future reference. The information is also used to determine the optimum modulation technique to apply to the link and maximum allowable data rate that is supported by the link.

A prompt screen takes the User through the registration process, during which time service feature options is presented to the User for selection. The User has numerous choices as to service plans, data rates, quality of service, desired payment procedures, and other generic customer options. The User's selection may affect link parameters set by the NOC for that User's connection, such as modulation. Once the User has completed the registration process successfully, the User's account is activated and service is provided immediately.

The User has the ability to return to the log-in or registration process at will to modify services, access help menus, receive activity reports and other administrative functions. In addition to the registration processes, the User is presented web page style access to

-12- numerous forms of technical support, features, additional service offerings such as web site hosting, and advertising.

User terminals are all equipped with electronic identification numbers. This allows Users to move terminals and re-register without having necessarily to reestablish commercial relationships or require personnel assistance. The identification is also used to track equipment versions for modifications, recalls, service monitoring, technical support, and theft detection.

Figure 4 shows a top view of an antenna array in which six parabolic base station antennas 60 are combined to form an array of antennas to cover a 360 degree range. Each antenna has an angle of view shown by lines 62 that overlaps with adjacent antennas. Detection of the incoming optical signal is done using a signal energy gathering lens or parabolic reflector. The incoming optical energy is concentrated at a point on the focal surface of the lens or parabolic reflector. Located at this point is either an optical fiber leading from the antenna to signal processing equipment or an optical to electrical detector and an electrical connection to processing equipment. For this purpose, the end of the fiber is contoured to form that gathering lens, similar to what is done in fiber optical cameras used in exploratory medicine. In such devices a lens gathers light, creating an image at its focal surface. Located at the focal surface are the ends of a bundle of fibers. Each fiber receives a unique portion of the image and carries that information back to image processing devices viewable on devices such as CRTs. Figure 5 shows an array of transmitter elements 70 and receiver elements 72 located within the focal surface 52 (Figure 3) of an antenna 40. Superimposed on the array are the projected images 74 and 76 of buildings. This drawing illustrates that each window 75 of the buildings 74 and 76 are covered by the spot beams of at least one transmitter element 70 and one receiver element 72. The size of the transmitter and receiver element footprints (indicated by the size of the circles around "Ts" 70 and "Rs" 72) with respect to the size of the window will be discussed below along with the variables that define the size of the footprints. This illustrates that a user antenna can be placed in a window for connection to multiple links located on a base station.

The focal length of the lenses, parabolic reflector, and convex reflector are selected with a view to the optical signal concentration requirements of each implementation. The design objectives include sufficient signal gathering to ensure link performance, resolution adequate to differentiate objects at the focal surface, and image sizes small enough to be conveniently coupled into detectors.

Figure 6 shows that an optical lens 84 can be substituted for a parabolic reflector to communicate with user antennas. The optical energy from object 80 is transmitted along lines

-13- 86, through lens 84 to the focal surface 82.

A large optical lens can also be used in place of the parabolic reflector. When receiving, the lens forms an image at the lens' focal point of the constellation of Users within view. The resolution of the image does not necessarily have to be as high as the resolution of a photograph. Detection at this focal point is accomplished as noted above for the optical lens antenna using an array of detectors or signal gathering fiber ends. Likewise, transmitted energy from light sources placed at the focal point are directed at individual Users by the optical lens 84.

Figure 7 illustrates the use of a flat reflective surface 94 to view building 92 of a potential user that is not in the normal field of view of the antenna 90. An object 96 in the field of view of the antenna 90 is shown as object 98 in the focal surface of the antenna 90. Building

92 is shown as object 100 in the focal surface of the antenna.

Some User locations are not visible from existing base stations. To service these Users, new base stations can be added to the system. Alternatively, signal repeaters can be used. A repeater consists of two antennas and appropriate signal repeating capabilities. In some cases, it is possible to use simple reflectors to redirect signals when direct line of sight is not available.

Likewise, the simple reflector can provide a redundant path between the object and the base station antenna. Figure 8 shows the use of a flat reflective surface 112 to form a line of sight between building 114 and the base station antenna 110. The front face of the building 114 is in the normal field of vision of the antenna 110 and is represented as object 116 in the focal surface of the antenna. The top of the building 114 is represented as object 118 in the focal surface of the antenna.

Figure 9 is another embodiment of the present invention in which flat reflective surfaces

120 are used to transmit signals to and receive signals from objects 122, 124, 126 and 128.

These signals are sent through a parabolic lens 130 to and from the elements at the focal surface. The received signals are represented at the focal surface as images 132, 134, 136 and 138. Each of the reflective surfaces 120 can be used to illuminate multiple objects to the extent they appear in the view of the lens 130 via the reflector.

Figure 10 illustrates an embodiment of the invention in which a convex reflective surface

142 is used to reflect signals from objects 140 through parabolic lens 144 to an array of receiver and transmitter elements at the focal surface 146 of the lens 144. The image of objects 140 are represented as images 148 in the focal surface of lens 144.

Another type of reflector is a convex reflector which provides an antenna with a much wider field of view. A convex reflector is positioned above an antenna gathering element which is facing upwards. The reflector reflects signals from any point on the horizon downward into the gathering element. This provides 360 degrees of vision for the antenna to the horizon in all

-14- directions. The reflector can be shaped for optimum view in a slightly downward direction. This is appropriate for base stations on tops of buildings overlooking lower buildings. The reflector and gathering element positions can be reversed vertically if the base station is generally looking upwards at customer locations. Likewise, the arrangement can be tilted in various directions for coverage patterns that are not symmetric. The convex reflector directs signal energy to a lens or parabolic reflector as the gathering element. If a parabolic reflector is used, the focal surface of the parabola can be positioned within the confines of the convex reflector. To achieve this, the central portion of the convex reflector is removed to allow positioning of the array of receiver and transmitter elements. The removed portion of the convex reflector is not significant to operation of the antenna since it reflects energy from directions not normally associate with customers.

Figure 11 shows another arrangement in which a signal from an object 150 is directed to a modified convex reflector 152 that has a center section 156 removed. This removal allows the signal from the object 150 to be reflected from the modified convex reflector 152 to a parabolic reflector 154 and then to a receiver/transmitter array at the parabolic reflector's focal surface 158. This arrangement ensures that imaging from objects in all horizontal directions are reflected and focused with the same effectiveness. In Figure 1, the parabolic antenna is shown with the array of receiver and transmitter elements offset from the desires direction of view for the antenna. This was done so as not to obstruct optical energy from the object. In Figure 11 the desire is for the antenna to have equal vision in all horizontal directions. The depth of the parabolic shape of reflector 154 is shallower than may be the case for the parabola 20 in Figure 1. The greater shallowness of 154 ensures a substantial vertical view for the antenna arrangement of Figure 11 since a shallower parabola has a wider field of view. The shallower parabola, however, has a greater distance to its own focal surface. Thus, a hole in the convex reflector is used to allow useful placement of the focal surface of receiver and transmitter elements at a suitable distance.

It is desirable that the image formed by an incoming signal be approximately size of the detector element. To determine the size of an image, the signal source's antenna size is taken into account. More specifically, the size of the transmitting antenna that is illuminated directly affects the size of the object being imaged. The size of the resulting image on the focal surface is further determined by the physical shape of the reflectors and the focal lengths of the optical elements. Additional lenses can be added to the antenna's optical signal path to reduce or enlarge the size of the image without losing appreciable signal power. This technique is used to adjust the image size to match the selected density of detectors and transmitter elements, matching the size of signal antenna source images with the size of the detectors.

-15- Figure 12 is a variation of the arrangement shown in Figure 11 in which lenses 166 and 168 are used to direct the signal to and from object 160. The signal is reflected off the surface of convex reflector 162 to the surface of parabolic antenna 164, through lens 166, through the hole 167, through lens 168 to receiver/transmitter array 170. The advantages of this embodiment are the ability to change the size of images at the focal surface and the ability to design the antenna for different distances between the parabolic reflector 164 and the location of the elements on the focal surface 170. Lens 166 represents a compound lens that is configured using established art in the formation of images to achieve precisely the desired image sizes at the focal surface. Mobile Users use omnidirectional antennas, one version of which is exemplified in

Figure 12, with the modification in the slope of the convex reflector to expand the vertical view of the antenna. This ensures vision of greater expanse by the mobile's antenna than is required for most base station installations.

A second version of the mobile antenna uses an additional convex reflector to view base stations in an upward direction. Figure 13 shows the two convex reflectors 192 and their associated parabolic reflectors 194, which function as described with reference to convex reflector 162 and parabolic antenna 164 shown respectively above in Figure 12. Both the upper and lower sets of reflectors 192 and 194 direct the optical signal energy through lenses 166 and 184 and flat reflectors 186 whereby a common focal surface 170 can be used by both parts of the antenna. Objects viewed by the upper half of the antenna such as object 188 are not viewed by the lower half. Likewise, object 180 is viewed only by the lower half.

Figure 14 shows a second type of mobile antenna comprising two hemispheric lenses 200 configured back to back. Each lens has a view of approximately half a sphere or 6 steradian degrees of view. The optical paths of optical signals through both lenses pass through lenses 184 and 166 and are reflected at flat reflectors 186 and processed via the elements on the common focal surface 170. Although similar in operation to the antenna in Figure 13, the hemispherical antenna is provides improved coverage in the upward direction as there is no cutout of the convex lens as shown in Figures 11, 12, and 13.

The effective gain or signal collection capacity of a mobile antenna is lower than and less reliable than a fixed User antenna. This is compensated for by using transmitting and receiving at a lower bandwidth which does not require as much signal energy for the unit to perform adequately.

Base stations transmit pilot signals on the spot beams as described herein. The mobile unit continuously monitors its environment for spot beam pilot signals in all viewable directions. This information is used to select which base stations are to be used for communications. The

-16- mobile transmits on more than one beam at a time, if more than one base station is viewable. The mobile can communicate with multiple base stations simultaneously. Each transmission is packetized and contains a time stamp, sender and receiver IDs, and error detection and correction codes to enhance the reliability of the system. The time stamp plus the sender's ID uniquely identifies the packet. The receiving electronics at the end user receiver rejects redundant packets.

When a mobile passes into view of a base station's beam, the pilot signal carried over that beam is read to determine if that beam is occupied. If it is occupied, the pilot signal contains information as to whether or not it is available for shared use. If not, the mobile does not transmit within the direction of that base station. If sharing is supported, the sharing protocols described herein are exercised by the mobile and the base station to establish a connection.

The potential for conflict between fixed Users and mobile Users in minimal. Most fixed Users place fixed antennas in positions where line of sight to base stations is not likely to experience blockage. The mobiles Users typically move at ground level and do not use the same spot beams as the fixed location Users.

The size of the mobile antenna is smaller than the fixed User antenna. In order to still maintain sufficient energy capture on the mobile links, the spot beams of the base stations are more narrowly formed. This is done using the beam sizing techniques discussed herein to produce smaller spot beams in the direction where mobile units operate. The intensity of signal energy per area is thereby increased, reducing the antenna size requirement for the mobile. The shrinking of the beam size increases the density of beams which enhances the ability of the system to differentiate mobiles in close proximity. The pencil like discrete beams allow the system to map the user's location and to track the movement of the users while providing high bandwidth communications.

This invention facilitates growth of broadband services by providing simple procedures for accessing those services. Users purchase communication equipment through distributors or through retail outlets and are able to register on-line, using industry standard automated e- commerce procedures. Signals between base stations and Users, as well as within the network of local base stations and external interfaces, may be operated via cables or wirelessly at various frequencies, or combination of frequencies from microwave to optical, infrared, or ultraviolet frequencies. The radio frequencies currently being used for related broad-band telecommunications applications are in the millimeter wave bands. Multiple frequencies are used over the same links using industry standard signal separation and combining techniques such as dense wave

-17- division multiplexing and split band operation.

Broadband communications commonly refers to transmission of signals greater than 2 megabits per second. The current invention is used for data rates up to multiple terabits per second depending on the link distance. Furthermore, any forms of digital modulation are considered for use within the system as the choice of modulation technique is not related to the architecture of the system. Therefore, the system can be used to carry signals using modulation schemes such as phase, amplitude, and frequency modulation and various pulse position and amplitude modulation schemes.

The form of modulation selected for communicating with a specific User depends on numerous parameters including reliability requirements, link performance predictions based on NOC link performance testing, signal strength, data rate requirements, and cost.

The system supports a variety of transmission protocols including IP, TCP/IP, ATM, frame relay, SDH, pSDH and other industry standard protocols suitable for services such as LANs, WAN, MANs, VPNs, extranets, intranets, and other types of digital networks. Billing for services, operation of a network control center(s), and other customer care facilities and functions are intrinsic adjuncts to the implementation of the invention.

The access methods that are suitable include time division multiple access, frequency division multiple access, code division multiple access, time division duplexing, and frequency division duplexing. Signals to and from Users are routed over multiple links for redundancy under normal operation of the system. To achieve this, the network of base stations is pre-configured to route signals through the network. For example, an "unassigned" beam of a base station is connected through other beams within the network, or other forms of links available, to a central control point. This is done using various multiplexing and signal combining techniques to reduce the number of links required. For example, DWDM technology is be used to manage multiple independent signals within one spot beam. In particular, the system supports internal routing of signals from one User to another within the system without necessarily having to demodulate the signal en route. Intra-system routing supports efficient low cost communications for services with the coverage area of the network such as LANs, WANs, VPNs, and other forms of data networks.

The invention supports broadband telecommunications connectivity. The detailed provisioning of User services is done through the use of additional components such as data modems and multiplexers.

The primary characteristics of the signals carried by the system are response times, bandwidth or data rate, and availability. Data services are typically categorized in terms of

-18-

Claims

services internal to a local network and services that connect the User to, or through, external systems such as the Internet.In the near future, the typical User will not require the full bandwidth of a base station- to-User optical link. Therefore, a beam from a base station may be used on a shared basis. Insomuch as each beam is no more than a few degrees wide, it is anticipated that very few Users are visible within a single beam. Most Users are therefore expected to be willing to subscribe to shared service with little expectation of congestion. Industry standard contention protocols are used to manage the sharing.Some Users may want instant access without a need for continuous use. If immediate access is required, the User may want to consider a small but guaranteed maximum latency. Options are presented at the time of User registration to select a guaranteed access latency instead of full time use of a beam. Latency performance guarantees are achieved by using a token protocol. For example, Users can be allocated 5 milliseconds per use, or time slot, including guard time per use. Assuming a high number of existing Users on a beam such as 5, the new User may be satisfied with a guaranteed maximum of 30 milliseconds in latency (a total of 6 Users, 5 milliseconds each).While the communication system and antennas of the present invention are shown with reference to Figures 1 through 14, the instant invention is not limited to the exact system and devices, for obvious modifications can be made by a person skilled in the art.■19- What is claimed is:

1. A wireless optical communication system transmitting through free space using multi- beam antennas comprising: an optical base station antenna wherein an array of transmit and receive elements are mounted at the focal surface of the antenna to transmit and receive multiple discrete optical signals over a defined area, and a user antenna for receiving optical signals from and transmitting optical signals to said base station.

2. The communication system of claim 1 including, means for moving the transmit and receive elements of said base station within a range located on the focal surface of the antenna to increase or decrease the angular size of the spot beam associated with each of the transmitter and receiver elements and to change the size of the images of signal sources projected on the focal surface from said user antenna.

3. The communication system of claim 2 wherein, said transmitter and receiver elements of said base station are located adjacent each other so multiple receive and transmit beams are formed that overlap for bi-directional or uni- directional communication with user antennas or other base stations.

4. A multi-beam antenna comprising: an optical base station antenna wherein an array of transmit and receive elements are mounted at the focal surface of the antenna to transmit and receive multiple discrete optical signals over a defined area, a user antenna for receiving from and transmitting to said base station optical signals, means for determining when a user antenna has moved form the field of view of one of said base station receiver elements to another of said base station receiver elements, means for maintaining communicatiin of transmitted information from said base station to said user antenna based upon the altered positional information of the user antenna, and reflector in optical communication with said base station antenna that direct optical signals to and from a distant point.

5. The multi -beam antenna of claim 4 wherein: said detectors of said base station distinguish distant signal sources that are physically

-20- separated by determining which base station detector is receiving a signal from a particular user antenna, means for detecting that a signal from a user antenna that is moving from one base station detector to an adjacent base station detector by monitoring identification information being transmitted to said base station as part of the signal, and wherein the transmit signal to a user is associated with a base station detector for the time that said user transmit signal is in the field of view of said base station detector, and means for continuing said process of associating transmit and receive elements as said transmit signal is shifted.

6. The multi -beam antenna of claim 5 wherein: transmission of visible light from transmit elements of said base station anywhere within the transmit array for targeting the antenna.

7. The multi -beam antenna of claim 6 wherein: said light being one of steady state or varied and control logic to turn said light on or off or move it to another transmit element of said array as required to provide a visible indication of the status of the antenna and associated base station.

8. The multi-beam antenna of claim 1 wherein: said detectors of said base station distinguish distant signal sources that are physically separated by determining which base station detector is receiving a signal from a particular user antenna, means for detecting that a signal from a user antenna that is moving from one base station detector to an adjacent base station detector by monitoring identification information being transmitted to said base station as part of the signal, and wherein the transmit signal to a user is associated with a base station detector for the time that said user transmit signal is in the field of view of said base station detector, and means for continuing said process of associating transmit and receive elements as said transmit signal is shifted.

9. A wireless optical communication system of claim 1 having: multiple base station antennas adapted to be in communication with each other for communication with multiple user antennas.

-21-

10. A wireless optical communication system transmitting through free space using multi-beam antennas comprising: an optical base station antenna wherein an array of transmit and receive elements are mounted at the focal surface of the antenna to transmit and receive multiple discrete optical signals over a defined area, a user antenna for receiving optical signals from and transmitting optical signals to said base station, means for determining when a user antenna has moved from the field of view of one of said base station receiver elements to another of said base station receiver elements, and means for maintaining communication of transmitted information from said base station to said user antenna based upon the altered positional information of the user antenna.

-22- AMENDED CLAIMS

[received by the International Bureau on 5 December 2000 (05.12.00); original claimsl-10 replaced by new claims 1-10 (3 pages)]

What is claimed is:

1. A wireless optical communication system for transmitting through free space using multi-beam antennas comprising: an optical base station antenna, an array of optical transmit and receive elements mounted at a focal surface of the antenna for transmitting and receiving multiple discrete optical signals over a defined area, and a user antenna for receiving optical signals from and transmitting optical signals to said base station.

2. The communication system of claim 1 including, means for moving the transmit and receive elements of said base station within a range, located on the focal surface of the antenna for changing the angular size of a spot beam associated with each of the transmitter and receiver elements and for changing the size of images of optical signals projected on the focal surface from said user antenna.

3. The communication system of claim 2 wherein, said transmitter and receiver elements of said base station are adjacent each other for forming multiple overlapping receive and transmit beams for bi-directional or uni-directional communication with user antennas or other base stations.

4. A multi-beam antenna comprising: an optical base station antenna, an array of optical transmit and receive elements mounted at a focal surface of the antenna for transmitting and receiving multiple discrete optical signals over a defined area, a user antenna for receiving from and transmitting to said base station optical signals, means for determining when a user antenna has moved from a field of view of one of said base station receiver elements to a field of view of another of said base station receiver elements, means for maintaining communication of transmitted information from said base station to said user antenna based upon altered positional information of the user antenna, and reflector in optical communication with said base station antenna for directing optical signals to and from a distant point.

- 23 -

5. The multi-beam antenna of claim 4 wherein: said means for determining being arranged for distinguishing distant signal sources that are physically separated by determining which base station detector is receiving a signal from a particular user antenna, means for detecting that a signal from a user antenna is moving from one base station detector to another base station detector by monitoring identification information being transmitted to said base station as part of the signal, and wherein the transmit signal to a user is associated with a base station detector for an interval while said user transmit signal is in the field of view of said base station detector, and means for continuing to associate transmit and receive elements as said transmit signal is shifted.

6. The multi-beam antenna of claim 5 further including transmit elements for. transmitting visible light from said base station to anywhere within a transmit array for targeting the antenna.

7. The multi-beam antenna of claim 6 wherein: said visible light continuously has the same or variable amplitude, further including control logic for turning said visible light on or off or for moving it to another transmit element of said array as required to provide a visible indication of status of the antenna and associated base station.

8. The multi-beam antenna of claim 1 wherein: said means for determining being arranged for distinguishing distant signal sources that are physically separated by determining which base station detector is receiving a signal from a particular user antenna, means for detecting that a signal from a user antenna is moving from one base station detector to another base station detector by monitoring identification information being transmitted to said base station as part of the signal, and wherein the transmit signal to a user is associated with a base station detector for an interval while said user transmit signal is in the field of view of said base station detector, and means for continuing to associate transmit and receive elements as said transmit signal is shifted.

9. The wireless optical communication system of claim 1 including:

- 24 -