Abstract:
Free-space, line-of-sight, electro-magnetic communication (i.e., via light or microwaves) is employed to provide a wide range of communication services to geographically scattered users. A relay point or end point is typically associated with each user. Each relay point receives and retransmits information via line-of-sight communication. The end points are also receivers and transmitters of information via line-of-sight communication. Although spaced from one another, the relay and end points are close enough to one another to communicate via line-of-sight links. Hard-wired connections to the users are therefore unnecessary. Broadcast radio frequency communication capability may be provided as a backup for maintaining at least some service in the event of line-of-sight communication failure or interruption. This radio capability may additionally be used to provide cellular communication service to small cells associated with the relay and end points.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to telecommunications systems, and more particularly to telecommunications systems which can provide a wide range of services without the need for hard-wired connections to the end users of the system. 
     Traditional telecommunications systems rely heavily on hard-wired connections all the way to the end points of the system. For example, traditional telephone systems employ twisted pair wiring to each home, office, or other location served by the system. Traditional cable television systems similarly employ coaxial cable or optical fiber to each end user of the system. Such extensive hard-wired networks are extremely costly to install and maintain. A new service provider who is restricted to such technologies must therefore make an enormous capital investment in hard-wired plant before that provider can even begin to extend service to a new area. Existing technologies such as twisted pair wire or coaxial cable also have limited service capabilities. Upgrading such hard-wired connections (e.g., to optical fiber) to offer more services is very expensive even for the owner of the network. 
     In view of the foregoing, a need exists for new ways for telecommunications services providers to gain access to end users of such services. Such new access should be of lower cost than traditional hard-wired connections, and should also have greater capacity than such traditional technologies as twisted pair wire and even coaxial cable. 
     It is therefore an object of this invention to provide telecommunications systems which allow access to end users of the system without the need for hard-wired connections to those users. 
     SUMMARY OF THE INVENTION 
     This and other objects of the invention are accomplished in accordance with the principles of the invention by providing telecommunications systems which employ substantially unguided, point-to-point, free-space, electro-magnetic (i.e., optical or microwave) communication between area access points and end users in that area. For example, an area may be served from one or more area access points, each having a transceiver for bi-directional, free-space, line-of-sight, electro-magnetic communication with one or more nearby relay points. Each of these relay points has at least two transceivers, one of which is for the above-mentioned communication with the associated area access point, and the other of which is for similar bi-directional, free-space, line-of-sight, electro-magnetic communication with another nearby relay point or end point. An end point is similar to a relay point except that an end point has only one transceiver. Relay point and end point transceivers may be located on the roofs of houses in the neighborhood served from the above-mentioned area access point(s). Users of the system may be located at any relay point or end point. 
     Preferably at least a fraction of the relay points are reachable via more than one path through the network of relay points. In this way, if line-of-sight communication between two relay points is temporarily broken, service can still be provided through other relay points. 
     In addition to the above-described line-of-sight communication between the area access points, relay points, and end points, broadcast radio frequency communication is preferably provided between these points for such purposes as (1) helping to initially set up the system for line-of-sight communication and (2) backup communication for at least some services in the event of failure of the line-of-sight communication. It is contemplated that radio frequency communication will be needed for these purposes only infrequently. However, some of the radio frequency communication apparatus provided for the above purposes can also be used to provide wireless (e.g., mobile, cullular, and/or cordless) communication service in the area served by the system. For example, each relay point and end point can be the antenna in the center of a small cellular communictations cell. 
     The capacity of the line-of-sight communications network described above can be very high, thereby enabling the system to provide a wide range of services. Such services may include basic telephone service, high density mobile telephone service (e.g., as described at the end of the preceding paragraph), video service (analogous to CATV service), high-speed bi-directional digital data service, digital television service, etc. 
     Although it is anticipated that most of the line-of-sight communications links in networks constructed in accordance with this invention will be provided by light, point-to-point microwave links can be used either in place of or as backup for some optical links. For example, microwave links may be used for connections that are longer than can conveniently be made optically. Or particularly important optical links may be backed up with microwave in case extremely bad weather interferes with optical communication. 
     At least some of the transceivers used for the bi-directional, free-space, line-of-sight, electro-magnetic communication may be repositionable, e.g., to correct for misalignments and/or to completely redirect the transceiver for communication with any one of a plurality of other area access points, relay points, and/or end points. Such repositioning may be at least partly controlled using data about the locations of the various points in the system. This location data may be at least partly determined using a global positioning system. 
     Further features of the invention, its nature and various advantages, will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified plan view of an illustrative installation of a system constructed in accordance with this invention. 
     FIG. 2 is a simplified elevational view of an illustrative embodiment of a representative portion of the apparatus shown in FIG.  1 . 
     FIG. 3 is a view similar to FIG. 1 showing illustrative modifications of the FIG. 1 system in accordance with this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An illustrative area  10  served by a communications system constructed in accordance with this invention is shown in FIG.  1 . In the network shown in FIG. 1 all of the communications links  50  in area  10  are assumed to be optical links. In a later portion of this specification examples will be given as to how microwave links may be used in place of or in addition to optical links. 
     Area  10  is accessed from two gateway locations or area access points  20   a  and  20   b  in or near area  10 . Each of area access points  20  is connected to other external communications equipment (e.g., the global telephone network, one or more sources of television programming, etc.) via conventional connections  22 . For example, these connections  22  may be optical fibers extending to access points  20 . Access points  20   a  and  20   b  are preferably substantially redundant of one another, offering substantially redundant communication with area  10 . Therefore connections  22  are also preferably substantially redundant connections to the above-mentioned external communications equipment. 
     Each of access points  20  preferably includes one or more (two in the depicted embodiment) free-space optical transceivers mounted relatively far from the ground to facilitate unobstructed, line-of-sight communication  50  between the access point transceivers and similar transceivers on nearby relay points (e.g., relay points  30   a  and  30   f  in the case of access point  20   a , and relay points  30   e  and  30   j  in the case of access point  20   b ). For example, the access point transceivers may be mounted on relatively tall structures such as high-rise apartment or office buildings, communications or electric utility towers, utility poles, or the like. The transceivers of relay points  30  (and end points  40 , discussed below) may be mounted, for example, on the roofs of houses within area  10 . Although longer distances may be used if desired, the typical distance between communicating points  20  and  30  is less than about 500 to about 1000 meters. 
     Each relay point  30  has at least two, and in some cases more than two, free-space optical transceivers for line-of-sight optical communication  50  with an area access point  20 , one or more other relay points  30 , and/or one or more end points  40 . For example, relay point  30   c  is a typical relay point with two transceivers for optical communication  50  with relay points  30   b  and  30   d , respectively. Relay point  30   k  is typical of a relay point with two transceivers for communicating with relay point  30   g  and end point  40   a , respectively. And relay point  30   i  is typical of a relay point with three transceivers for communicating with relay points  30   d ,  30   h , and  30   j , respectively. 
     End points like  40   a  and  40   b  are similar to relay points  30 , except that an end point has only one optical transceiver for free-space optical communication  50  with a relay point  30 . 
     In general, each user of communications services in area  10  is associated with one of relay points  30  or end points  40 . Conversely, each relay point  30  or end point  40  generally has one or more users associated with it, although some relay points  30  without users may be needed to reach users at more distant relay or end points. 
     Area  10  could be served from only one area access point  20 , but it is preferred to have at least two area access points  20  for each area for such reasons as to provide backup in the event of failure or obstruction of one of the area access points or the optical communications links  50  between that area access point and the relay and/or end points in the area. More than two area access points  20  could be provided for area  10  to provide even more backup capability. Similarly, multiple links  50  from each access point  20  into area  10  are desirable for backup in the event of failure or obstruction of some links. At least some relay points  30  with three or more optical transceivers for communication  50  with three or more other relay points are also desirable to provide multiple communications paths through area  10  in the event of failure or obstruction of some links  50 . As an example of the foregoing, relay point  30   c  can communicate via any of several paths such as  20   a - 30   a - 30   b - 30   c ,  20   a - 30   f - 30   g - 30   h - 30   i - 30   d - 30   c ,  20   b - 30   e - 30   d - 30   c , and  20   b - 30   j - 30   i - 30   d - 30   c . If the link  50  between relay points  30   b  and  30   c  were to fail or become obstructed, there would still be several paths via which full service could be maintained to relay point  30   c.    
     In the illustrative embodiment of representative relay point  30  shown in FIG. 2, two free-space optical transceivers  120   a  and  120   b  and a radio antenna  130  are mounted on the roof of the house  110  of a user of the communications services provided by the system. At least one of transceivers  120  communicates bi-directionally via a free-space optical communication link  50  to an area access point  20  or another relay point  30 . One of transceivers  120  may communicate with an end point  40 . If the apparatus shown in FIG. 2 were for an end point  40 , only one transceiver  120  would be required. In all other respects, the construction and operation of an end point  40  can be generally similar to what is shown in FIG.  2  and described below (with modifications appropriate to the presence of only one transceiver  120 ). Each transceiver  120  detects light it receives via the associated communication link  50  and produces a corresponding output signal applied to associated circuitry  150 . Each transceiver  120  also responds to an input signal from circuitry  150  by transmitting corresponding light (e.g., from light emitting elements such as laser diodes) via the associated communication link  50 . 
     Radio antenna  130  may be part of a conventional IS136 radio port for cellular communication with other similar cellular communications equipment (e.g., at one or more of area access points  20  or other conventional cellular base stations). Any conventional cellular communication may be used such as CDMA, TDMA, IS95, or GSM. Radio antenna  130  may additionally be used for cellular communication with nearby wireless telephones such as the mobile cellular telephone shown at  140  in FIG.  2 . In this context radio antenna  130  and associated circuitry  150  functions as a small base station. 
     As has already been indicated, elements  120  and  130  are connected to relay point control circuitry  150 . The user&#39;s communications equipment such as telephone  160 , computer  170 , and television  180  are also appropriately wired to control circuitry  150 . 
     Control circuitry  150  typically performs and/or controls several functions. One function of control circuitry  150  is to process signals from photodetectors in each of transceivers  120  and to cause the light emitting elements in the other of transceivers  120  to transmit corresponding light, possibly with some modifications. An example of such modifications is the addition to the light transmitted by transceivers  120  of information originating at relay point  30  (e.g., voice information from telephones  140  and/or  160 , digital data information from computer  170 , entertainment service request information from television equipment  180 , etc.). It will be understood that the telephone voice information referred to in the preceding sentence includes other conventional telephone control information such on-hook, off-hook, dialing, cellular telephone identification and control information, etc. 
     Another function of circuitry  150  is to retrieve from the signals received via either of transceivers  120  information needed by the user at relay point  30 . For example, circuitry  150  may extract from the received light voice information for use by telephones  140  and/or  160 , digital data for use by computer  170 , video information for use by television  180 , etc. Again, it will be understood that the above-mentioned telephone voice information includes other conventional telephone control information such as ringing, cellular telephone control information, etc. Similarly, it will be understood that the above-mentioned video information may include television control information such as cable television “set top box” control information (e.g., viewer authorization codes, on-screen program guide data, etc.). 
     Still another function of circuitry  150  is to control reception and/or transmission of information via radio communications antenna  130 . For example, when optical communication via transceivers  120  is first being set up, or when it is being re-established after an interruption, radio communication via antenna  130  may be used for such purposes as to turn on transceivers  120 , to cause mechanisms associated with transceivers  120  to move those transceivers to look for the optical signal from other remote transceivers with which the first transceivers should establish links  50 , etc. This type of radio communication may be cellular-type communication with a central location such as an area access point  20 . Another example of the radio communications via antenna  130  that circuitry  150  may control is cellular communication with mobile cellular telephone  140  as described earlier. Still another example of antenna  130  radio communication that circuitry  150  may control is cellular communication between relay point  30  and a central location such as an area access point  20  for the purpose of providing some basic backup service (such as basic telephone service) in the event all communication with relay point  30  via optical links  50  fails or is interrupted. 
     Yet another function of circuitry  150  may be to control normal automatic adjustments of the positions of transceivers  120  to maintain optimal optical communication  50  with other transceivers. For example, temperature or other environmental changes may cause a transceiver  120  to become misaligned with its intended optical communication path. This may be detected (e.g., by a quad sensor which is part of the transceiver) and the outputs of the detection applied to circuitry  150  for processing. The result of this processing may be output signals of circuitry  150  applied to mechanisms  122  that are capable of moving the misaligned transceiver. For example, mechanisms  122  may be capable of rotating the transceiver about vertical and horizontal axes, as well as shifting the transceiver left or right, or up or down. Thus in this capacity circuitry  150  forms part of servo controls for positioning or repositioning transceivers  120 . This function of circuitry  150  is related to its possible use (described above) to initially position or reposition transceivers  120  during initial start-up, or during restarting or reconfiguring of the system after a failure or interruption. 
     Another function that circuitry  150  may perform is to select from among two or more received signals the better or best signal for use at relay point  30  and/or for retransmission to other points in the network (e.g., other relay points  30 , end points  40 , and/or area access points  20 ). For example, circuitry  150  may compare the strengths of the signals received via transceiver  120   a  and  120   b . If circuitry  150  determines that the transceiver  120   a  signal is stronger and contains all the information needed by the user at relay point  30 , circuitry  150  selects the transceiver  120   a  signal as the signal from which it derives the signals applied to devices  140 ,  160 ,  170 , and/or  180 . Alternatively, if circuitry  150  determines that the transceiver  120   b  signal is stronger and contains all necessary information, circuitry  150  derives the signals for devices  140 ,  160 ,  170 , and/or  180  from the transceiver  120   b  signal. If relay point  30  has three or more transducers  120 , circuitry  150  may compare the strength and information content of all of the incoming signals and select the strongest and/or most complete signal for local use and retransmission via the other transceivers that were not the source of the selected signal. 
     In connection with references to information content in the preceding paragraph, it will be appreciated that some of the communications links  50  in area  10  may carry the same or nearly the same information, while other links  50  may carry quite different information. For example, the link  50  between relay points  30   g  and  30   k  will carry, in the direction from  30   k  to  30   g , substantially only information originated by the users at relay point  30   k  and end point  40   a . In the opposite direction this link  50  will tend to carry much more information. The links  50  between relay point  30   g  and relay points  30   f  and  30   h  will tend to carry, in both directions, the relatively large amounts of information launched from area access points  20   a  and  20   b , as well as information added by users at relay point  30   g  and other points connected to point  30   g  by various routings through the network of links  50 . 
     Still another function of circuitry  150  is to monitor the condition of the network at relay point  30  and to report that condition to overall network control circuitry  60  (see FIG.  1 ). Circuitry  150  transmits such reports using links  50  if possible; but if not, then via radio frequency antenna  130 . For example, circuitry  150  may report that it is receiving signals via all of its transceivers  120 , or it may report that one or more of its transceivers  120  is not receiving signals. As another example, circuitry  150  may report on the relative strengths of the transceiver  120  signals it is receiving. 
     Overall network control circuitry  60  controls the flow of information throughout the network in area  10 . To some extent circuitry  60  performs this function in cooperation with the circuitry  150  in each of the relay and end points  30  and  40  in area  10 . For example, if one or more of circuits  150  reports to circuit  60  that a link  50  is not operating, circuit  60  attempts to find an alternate route for all information that would otherwise be carried by the inoperative link, and circuit  60  commands appropriate circuits  150  in a manner appropriate to establishing that alternate route. As a specific illustration of this, if the link  50  between relay points  30   b  and  30   c  is reported to circuit  60  as inoperative, circuit  60  may instruct the circuit  150  at relay point  30   b  to direct all information originating at that relay point out via the link  50  to relay point  30   a , and may similarly instruct the circuit  150  at relay point  30   c  to direct all information originating at that relay point out via the link  50  to relay point  30   d . In addition, circuit  60  may instruct the circuitry  150  at relay point  30   a  to send information received from relay point  30   b  back to area access point  20   a , and circuit  60  may instruct the circuitry  150  at relay point  30   d  to send information received from relay point  30   c  back to access point  20   a  or  20   b  via the best route (i.e.,  30   d - 30   i - 30   h - 30   g - 30   f - 20   a ,  30   d - 30   i - 30   j - 20   b , or  30   d - 30   e - 20   b ). As another example of the role played by circuit  60 , if both optical links  50  to relay point  30   b  were reported as interrupted, circuit  60  would attempt to establish radio frequency communication with relay point  30   b  via the radio frequency antenna  130  of that relay point as described above. 
     Network control point circuit  60  may contain a database of the exact location of each transceiver  120 . Such location information can be obtained at the time of installation using a global positioning system (“GPS”) or differential GPS. Based on this information, circuit  60  can determine the pointing direction to instruct each transceiver  120  to use. For example, circuit  60  may direct the control circuitry  150  at relay point  30   b  to use the appropriate mechanism  122  to reposition its transceiver  120  that was previously pointed toward relay point  30   c  to point toward relay point  30   i . Circuit  60  may do this by computing the exact angles both in the horizontal plane and elevation based on the locations of the transceivers. These locations are stored in a database and possibly are determined based on using GPS or a similar positioning system at the time of installation. Similarly, circuit  60  may also direct the control circuit  150  at relay point  30   i  to use the appropriate mechanism  122  to reposition the transceiver  120  that was previously pointed toward relay point  30   j  to point toward relay point  30   b . Once both transceivers are pointed in the correct direction, they may refine the alignment (again using mechanism  122 ) by going through a search pattern. Circuit  60  may also play a role in coordinating such a search process. 
     Thus control circuitry  60  cooperates with relay and end point control circuits  150  to control the routing of signals throughout area  10 , both during normal operation of the system and when special measures must be taken to compensate for various kinds of failures or interruptions in the system. The manner in which responsibility for this control of the network is allocated between central control  60  and distributed controls  150  can be varied as desired. For example, virtually all of the signal routing control for the network can be allocated to central control  60 , with distributed controls  150  primarily reporting local conditions and acting on instructions from the central control. Or more decision-making responsibility can be allocated to distributed controls  150  (e.g., decisions regarding which of two or more signals received via associated transceivers  120  should be retransmitted via the other transceivers associated with those controls). 
     Although other frequencies of light can be used for optical communications links  50 , in the presently preferred embodiments infrared light is used. One or several light frequencies may be used in each link  50 . Information may be transmitted by analog or digital modulation of the light. 
     From the foregoing it will be appreciated that the systems of this invention may employ many relatively short but interconnected free-space optical communications links  50  to reach users throughout potentially large areas. The optical signals are  30  regenerated at each relay point  30  so that free-space optical communication can be used to enable information to travel relatively long distances. The network of free-space optical communications links  50  preferably has sufficient interconnectivity so that even if some links  50  fail or are interrupted, alternate routes can be found through the network to compensate for the failed or interrupted links. If all else fails, radio communication is available to maintain at least some service to any user. Alternatively, the radio frequency equipment at each relay and end point  30  and  40  doubles as base stations for local wireless telephone communication. 
     If desired, point-to-point, free-space, line-of-sight, microwave communication may be used either in place of or as backup for some of the optical links in the networks of this invention. For example, FIG. 3 shows an alternative embodiment of the network of FIG. 1 in which bi-directional, line-of-sight, microwave communication links  70  are used as follows: (1) in place of the optical communication link  50  between nodes  20   a  and  30   f , (2) as backup for the optical link  50  between nodes  30   d  and  30   i , and (3) as another backup route into and out of area  10  between nodes  20   a  and  30   i . These are just some examples of how microwave links  70  may be used as supplements or additions to optical links  50  or as replacements for optical links  50  in some instances. For example, microwave links  70  may be useful for making longer connections than can conveniently be made optically. Or microwave links  70  may be useful for backing up particularly important optical links  50  in the event that bad weather interrupts those optical links. 
     Except for using a different transmission medium (i.e., point-to-point, line-of-sight, free-space microwaves rather than light), microwave links  70  may be generally similar to optical links  50 . Thus either of the transceivers  120  shown on representative relay point  30  in FIG. 2 can be converted to a microwave transceiver. Or one or more microwave transceivers can be added to the depicted optical transceivers  120 . In other respects the relay point  30  apparatus can be constructed and operated as described above. “Electro-magnetic communication” is sometime used herein as a generic term for the above-described optical and microwave communication. 
     It will be understood that the foregoing is only illustrative of the principles of the invention, and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. For example, the number of area access points  20  serving an area  10  can be more or less than the two shown in FIG. 1, the numbers of relay and end points  30  and  40  can be varied, the number of free-space, line-of-sight, electro-magnetic communication transceivers  120  at each relay point can be varied, etc. The use of end points  40  is entirely optional, and it may be possible to construct certain networks with only relay points  30  and no end points at all.