Patent Publication Number: US-2015063815-A1

Title: Fiber-to-the-antenna systems and fiber optic  demarcation units

Description:
BACKGROUND 
     1. Field 
     The present invention relates to fiber optic demarcation units and, more particularly, to fiber optic demarcation units for use in fiber-to-the-antenna (FTTA) systems. 
     2. Background 
     Radio networks use radio transceivers elevated by radio towers to broadcast or receive radio signals. Conventionally, coaxial cable operatively couples the radio transceiver to communication equipment on the ground. Coaxial cable has a large diameter, for example, about ½ inch to ¾ inch, and is heavy, which makes installation difficult. Coaxial cable also has high power consumption. Accordingly, there is need for radio networks that are easier to install and have improved power consumption. 
     SUMMARY 
     In some embodiments, a FTTA system comprises a multi-fiber cable configured to be operatively coupled to fiber optic equipment on the ground. The FTTA system also comprises a fiber optic demarcation unit optically coupled to the multi-fiber cable, and a multi-fiber jumper cable comprising a push-pull connector at one end configured to be optically coupled to the fiber optic demarcation unit. Additionally, the FTTA system comprises a remote radio head optically coupled to the adapter of the fiber optic demarcation unit. 
     In some embodiments, a FTTA system comprises a multi-fiber cable operatively coupled to fiber optic equipment on the ground. The fiber optic demarcation unit is optically coupled to the multi-fiber cable and to a remote radio head. The fiber optic demarcation unit comprises a housing and a strain relief device attached to the housing and to the multi-fiber cable such that a load of the multi-fiber cable is transferred from an interface between the multi-fiber cable and the housing of the fiber optic demarcation unit. 
     In some embodiments, a housing for a fiber optic demarcation unit in a fiber-to-the-antenna system comprises a first housing portion comprising a first wall, a side wall extending from an edge of the first wall, and a mounting flange extending outward from the side wall. The side wall defines a port for holding an adapter. The housing also comprises a second housing portion comprising a second wall. The first housing portion and the second housing portion are configured to be coupled to create an environmental seal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts. 
         FIG. 1  schematically illustrates an embodiment of a FTTA system comprising a demarcation unit. 
         FIG. 2  is a perspective view of a first housing portion of the demarcation unit in  FIG. 1 . 
         FIG. 3  is a perspective view of the demarcation unit in  FIG. 1 . 
         FIG. 4A  is a cross-sectional view of the demarcation unit in  FIG. 1  taken along line  4 - 4  in  FIG. 1 . 
         FIG. 4B  is an enlarged view of a portion of the demarcation unit in  FIG. 4A . 
     
    
    
     DETAILED DESCRIPTION 
     While the invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those skilled in the art with access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the invention would be of significant utility. 
       FIG. 1  depicts an embodiment of a FTTA system  100 . FTTA system  100  comprises a multi-fiber fiber optic cable  107 , a fiber optic demarcation unit  101  optically coupled to cable  107 , and one or more remote radio heads  114  optically coupled to demarcation unit  101  and, in turn, fibers of cable  107 . Demarcation unit  101  can be mounted on top of a radio tower in proximity to radio heads  114 . Demarcation unit  101  optically couples one or more radio heads  114  to fiber optic equipment on the ground, for example, an access terminal or electronic equipment in a ground enclosure. 
     Demarcation unit  101  comprises a housing  102  that encloses optical components. In some embodiments, housing  102  defines an environmentally sealed cavity for housing the optical components. Housing  102  may comprise two or more separate housing portions. For example, as shown in  FIGS. 1-3 ,  4 A, and  4 B, housing  102  comprises a first housing portion  104  and a separate, second housing portion  106 . First housing portion  104  and second housing portion  106  can be configured to be fixedly or selectively coupled together such that an environmental seal is created at the interface between first housing portion  104  and second housing portion  106 . 
     Demarcation unit  101  is optically coupled to a multi-fiber cable  107 . Cable  107  can comprise two or more fibers. For example, cable  107  can comprise twelve fibers. Cable  107  may comprise less than twelve fibers or more than twelve fibers. Cable  107  is optically coupled to fiber optic equipment on the ground, for example, an access terminal or electronic equipment in a ground enclosure proximate to the radio tower. 
     In some embodiments, cable  107  is fixedly coupled to demarcation unit  101 . For example, cable  107  is fixedly coupled to demarcation unit  101  using a packing (PG) gland. In some embodiments, cable  107  is selectively coupled to demarcation unit  101 . For example, demarcation unit  101  can comprise an adapter configured to optically couple with a connectorized end of cable  107 . Cable  107  runs from the ground and vertically up a radio tower to the location of demarcation unit  101 . In some embodiments, cable  107  has a diameter that ranges between about 3 mm to about 6 mm. 
     Demarcation unit  101  comprises one or more ports  108 . As shown in  FIG. 1 , demarcation unit  101  comprises six ports  108 . For example, as shown in  FIG. 1 , demarcation unit  101  comprises three ports  108  in a cascading configuration on one side of demarcation unit  101  and three ports  108  in a cascading configuration on an opposing side of demarcation unit  101 . Demarcation unit  101  may comprise less than six ports  108  or more than six ports  108 . 
     At each port  108 , demarcation unit  101  can comprise an adapter  110 . Each adapter  110  is optically coupled to two or more fibers of cable  107 . Adapters  110  are configured to couple to a connectorized end of a jumper cable  112 . Adapters  110  can be configured to create an environmental seal with the connectorized ends of jumper cables  112 . For example, in some embodiments, adapters  110  can be configured to create a water-tight seal with a push-pull connector at one end of jumper cables  112 . Each jumper cable  112  is optically coupled to one radio head  114 . Jumper cables  112  run from demarcation unit  101  to radio head  114 . The ends of jumper cables  112  opposite demarcation unit  101  can be spliced with remote radio heads  114  or can have connectors configured to optically couple to an adapter  115  of the remote radio heads  114 . In some embodiments, jumper cables  112  are multi-fiber cables that each comprise two or more fibers. 
     In some embodiments, housing  102  defines an opening  116  configured to allow a user to handle or secure demarcation unit  101 . In some embodiments, second housing portion  106  defines a rectangular opening  116  as shown in  FIG. 1 . In some embodiments (not shown), first housing portion  104  defines opening  116 . For example, a user may clip demarcation unit  101  to the user&#39;s belt using opening  116 . 
     In some embodiments, housing  102  defines one or more openings  118  configured to allow a fastening device to pass through. The fastening device(s) couple demarcation unit  101  to a radio tower or other desired location. As shown in  FIG. 1 , second housing portion  106  can define four rectangular openings  118  at the corners of second housing portion  106 . Openings  118  can be configured to allow a cable tie, screw, bolt, clamp, or any other suitable fastening device to pass through. 
     In some embodiments, demarcation unit  101  includes a strain relief device  120 . Strain relief device  120  may be a cord, cable, rope, thread, or any other suitable strain relief device. Strain relief device  120  is coupled to housing  102  of demarcation unit  101  and to a point  121  of cable  107  such that the load of cable  107  is transferred away from the interface between housing  102  and cable  107 . In some embodiments, location  121  may be about two feet away from housing  102 . 
       FIG. 2  depicts a perspective view of an interior of first housing portion  104 . First housing portion  104  defines a cavity  222  for housing components of demarcation unit  101 . As shown in  FIG. 2 , demarcation unit  101  can comprises an optical component  224 . In some embodiments, optical component  224  can be a fanout device configured to split the fibers of cable  107  into separate fibers or smaller bundles of two or more fibers. The separated fibers or bundles of fibers can be optically coupled to adapters  110  (not shown in  FIG. 2 ). 
     In some embodiments, optical component  224  can be a wavelength division multiplexer configured to split the fibers of cable  107  into separate fibers or smaller bundles of two or more fibers, each transmitting an optical signal of a different wavelength. In some embodiments, in which optical component  224  is a wavelength division multiplexer, cable  107  can include only two fibers. 
     First housing portion  104  comprises an outer wall  223  and side wall  225  extending from the outer wall  223 . Side wall  225  defines one or more ports  108 . For example, as seen in  FIG. 2 , side wall  225  defines six ports  108  in a cascading fashion. First housing portion  104  also comprises a mounting flange  226  extending outwardly from side wall  225 . Mounting flange  226  is configured to closely correspond to a mounting surface of second housing portion  106 . 
       FIG. 3  illustrates another perspective view of demarcation unit  101  with first housing portion  104  coupled to second housing portion  106 . Demarcation unit  101  can include one or more mounting brackets  328 . Mounting brackets  328  can be configured for a wall mount or coupling to a frame of a radio tower. As shown in  FIG. 3 , demarcation unit  101  comprises two mounting brackets  328 . Demarcation unit  101  may comprise one mounting bracket  328  or more than two mourning brackets  328 . Each mounting bracket  328  defines one or more slots  330 , for example, two slots, for receiving a fastening device that couple demarcation unit  101  to a wall or frame. Each mounting bracket  328  can define one opening  332  for coupling directly to strain relief device  120 . 
       FIG. 4A  is a cross-sectional view of demarcation unit  101  taken along line  4 - 4  in  FIG. 1 , and  FIG. 4B  is an enlarged view of portion  440  in  FIG. 4A . First housing portion  104  and second housing portion  106  can be configured to couple together to form an environmental seal. In some embodiments, demarcation unit  101  comprises a gasket  438 . Gasket  438  is spaced between first housing portion  104  and second housing portion  106  to substantially prevent fluid flow between the interface of first housing portion  104  and second housing portion  106 . Gasket  438  is adjacent mounting flange  226  of first housing portion  104 , and a surface  442  of second housing portion  106 . As best seen in  FIG. 4A , mounting flange  226  is substantially parallel to surface  442  of second housing portion  106 . First housing portion  104  can also comprise a lip  434  that extends from a distal edge of mounting flange  226  in a direction away from surface  442  of second housing portion  106 . Second housing portion  106  can also comprise a lip  436  that extends from a distal edge of surface  442  of second housing portion  106  in a direction generally parallel to lip  434  of first housing portion  104 . In some embodiments, lip  436  of second housing portion  106  helps create the environmental seal between first housing portion  104  and second housing portion  106 . 
     While an illustrative embodiment of the invention has been described above, it is, of course, understood that various modifications will be apparent to those of ordinary skill in the art. Such modifications are within the spirit and scope of the invention, which is limited and defined only by the appended claims.