Patent Publication Number: US-8992099-B2

Title: Optical interface cards, assemblies, and related methods, suited for installation and use in antenna system equipment

Description:
RELATED APPLICATIONS 
     This application is related to U.S. Provisional Patent Application Ser. No. 61/301,495 filed Feb. 4, 2010 entitled “Modular Distributed Antenna System Equipment Housings, Assemblies, And Related Alignment Feature,” which is incorporated herein by reference in its entirety. 
     This application is also related to U.S. Provisional Patent Application Ser. No. 61/301,488 filed Feb. 4, 2010 entitled “Modular Distributed Antenna System Equipment Housings, Assemblies, And Related Alignment Feature,” which is incorporated herein by reference in its entirety. 
     This application is also related to U.S. Provisional Patent Application Ser. No. 61/316,584 filed Mar. 23, 2010 entitled “Modular Distributed Antenna System Equipment Housings, Assemblies, And Related Alignment Feature,” which is incorporated herein by reference in its entirety. 
     This application is also related to U.S. patent application Ser. No. 12/751,884 filed Aug. 4, 2011 entitled “Communications Equipment Housings, Assemblies, and Related Alignment Features and Methods,” which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field of the Disclosure 
     The technology of the disclosure relates generally to enclosures for housing distributed antenna system equipment provided in a distributed antenna system. The distributed antenna system equipment can include optical fiber-based distributed antenna equipment for distributing radio frequency (RF) signals over optical fiber to remote antenna units. 
     2. Technical Background 
     Wireless communication is rapidly growing, with ever-increasing demands for high-speed mobile data communication. As an example, so-called “wireless fidelity” or “WiFi” systems and wireless local area networks (WLANs) are being deployed in many different types of areas (e.g., coffee shops, airports, libraries, etc.). Wireless communication systems communicate with wireless devices called “clients,” which must reside within the wireless range or “cell coverage area” in order to communicate with an access point device. 
     One approach to deploying a wireless communication system involves the use of “picocells.” Picocells are radio frequency (RF) coverage areas. Picocells can have a radius in the range from a few meters up to twenty meters as an example. Combining a number of access point devices creates an array of picocells that cover an area called a “picocellular coverage area.” Because the picocell covers a small area, there are typically only a few users (clients) per picocell. This allows for minimizing the amount of RF bandwidth shared among the wireless system users. In this regard, head-end communication equipment can be provided to receive incoming RF signals from a wired or wireless network. The head-end communication equipment distributes the RF signals on a communication downlink to remote antenna units distributed throughout a building or facility. Client devices within range of the picocells can receive the RF signals and can communicate RF signals back to an antenna in the remote antenna unit, which are communicated back on a communication uplink to the head-end communication equipment and onto the network. The head-end communication equipment may be configured to convert RF signals into optical fiber signals to be communicated over optical fiber to the remote antenna units. 
     It may be desirable to provide a housing or enclosure for communication equipment for a distributed antenna system that is easily assembled. Thus, the housing or enclosure can be easily assembled in the field. Further, it may be desirable to provide communication equipment for a distributed antenna system that is compatible with expansion of picocells. Thus, it may be desirable to provide communication equipment for a distributed antenna system that can be easily upgraded or enhanced to support an increased number or type of remote antenna units, as an example. It may be further desired to allow technicians or other users to provide this increased support in the field, thus making it desirable to allow equipment changes and upgrades to easily be made in the communication equipment with ease and proper function. 
     SUMMARY OF THE DETAILED DESCRIPTION 
     Optical interface cards, assemblies, and related methods, which may be suited for installation and use in antenna system equipment, are disclosed. In one embodiment, optical interface cards are disclosed. Optical interface cards can provide an interface between optical and electrical signals in a communication system, including a distributed antenna communication system, as an example. In certain embodiments, the optical interface card comprises a printed circuit board (PCB) having a first end and a second end opposite the first end. At least one opening is disposed in the PCB between the first end and the second end of the PCB and having at least one first opening end and at least one second opening end opposite the at least one first opening end. At least one optical sub-assembly (OSA) is mounted to the at least one first opening end and extends into the at least one opening. In this manner, the OSA can be mounted on an end of a PCB to limit the length of exposed, unshielded wire extensions and printed traces on the PCB. This can provide for signal integrity of the signals after conversion to electrical signals. 
     In another embodiment, an optical interface assembly is provided. The optical interface assembly includes a first optical interface card (OIC) that comprises at least one first opening between a first end and a second end of the first OIC having at least one first opening end, and at least one first optical sub-assembly (OSA) mounted to the at least one first opening end and extending into the at least one first opening. A second OIC is provided that comprises at least one second opening between a first end and a second end of the second OIC having at least one second opening end, and at least one second OSA mounted to the at least one second opening end and extending into the at least one second opening. The optical interface assembly also includes at least one standoff disposed between the first OIC and second OIC. 
     In another embodiment, a method of assembling an optical interface card is provided. The method comprises providing a printed circuit board (PCB) having a first end and a second end opposite the first end. The method also comprises mounting at least one optical sub-assembly (OSA) to at least one first opening end of at least one opening disposed in the PCB between the first end and the second end of the PCB. 
     In another embodiment, a communications equipment enclosure is provided. The communications equipment enclosure comprises at least one compartment configured to house a plurality of communications components between a lower plenum and an upper plenum. The communications equipment enclosure also comprises at least one fan configured to draw in air from a first side of the communications equipment enclosure into the lower plenum and across the plurality of communications components into the upper plenum. The communications equipment enclosure also comprises an air outlet disposed on a second side of the communications equipment enclosure and coupled to the upper plenum to direct air drawn by the at least one fan into the upper plenum through the air outlet. 
     In another embodiment, a method of providing air cooling of communications components installed in a communications equipment enclosure is provided. The method includes drawing in air from a first side of the communications equipment enclosure into a lower plenum using at least one fan installed in the communications equipment enclosure. The method also includes drawing the air from the lower plenum across a plurality of communications components installed in the communications equipment enclosure between the lower plenum and an upper plenum. The method also includes drawing the air outside of the communications equipment enclosure through an air outlet disposed on a second side of the communications equipment enclosure and coupled to the upper plenum. 
     In another embodiment, a modular distributed antenna system assembly is provided. The assembly includes at least one first plate including at least one first locating alignment slot. The assembly also includes at least one second plate including at least one locating tab. The at least one locating tab engages with the at least one first locating alignment slot to align the at least one first plate in at least two dimensions to the at least one second plate to form an enclosure configured to support at least one distributed antenna system component. 
     Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description that follows, the claims, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description present embodiments, and are intended to provide an overview or framework for understanding the nature and character of the disclosure. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments, and together with the description serve to explain the principles and operation of the concepts disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a partially schematic cut-away diagram of an exemplary building and building infrastructure in which a distributed antenna system is employed; 
         FIG. 2  is an exemplary schematic diagram of an exemplary head-end communications unit (“HEU”) deployed in the distributed antenna system in  FIG. 1 ; 
         FIG. 3  is an exemplary distributed antenna system equipment housing assembly (“assembly”) and enclosure configured to support the HEU of  FIG. 2 ; 
         FIG. 4  is an exemplary optical interface module (OIM) comprised of a pair of optical interface cards (OIC) configured to be installed in the distributed antenna system equipment housing assembly of  FIG. 3  as part of the HEU; 
         FIG. 5  is a front view of the enclosure of  FIG. 3  with a midplane interface card of the HEU of  FIG. 2  installed therein; 
         FIG. 6  is a rear side perspective view of the enclosure of  FIG. 3  with the midplane interface card of  FIG. 5  installed on a midplane support installed therein; 
         FIG. 7  is a close-up front, right side perspective view of the midplane interface card of  FIG. 5  installed on a midplane support installed in the enclosure of  FIG. 3 ; 
         FIG. 8  illustrates a front side of the midplane interface card of  FIG. 5  without connectors attached to the midplane interface card; 
         FIG. 9  illustrates a rear view of the enclosure of  FIG. 3  with a downlink base transceiver interface (BTS) card (BIC) being inserted into the enclosure and an uplink BIC fully inserted into the enclosure and connected to the midplane interface card disposed in the enclosure; 
         FIGS. 10A and 10B  illustrate front and rear perspective views, respectively, of BIC assemblies that can be inserted in the enclosure of  FIG. 3  with the BIC disposed in the assemblies connected to the midplane interface card disposed in the enclosure of  FIG. 3 ; 
         FIG. 11  illustrates a bottom view of the BIC assembly of  FIGS. 10A and 10B ; 
         FIG. 12  illustrates a top view of the BIC assembly of  FIGS. 10 and 10B  installed in the enclosure of  FIG. 3 ; 
         FIG. 13  is a side perspective view of the assembly of  FIG. 3  with downlink BIC connectors for the downlink BIC and uplink BIC connectors for the uplink BIC disposed in downlink and uplink BIC connector plates, respectively, which are attached to the front of the enclosure; 
         FIG. 14  is a front perspective view of the BIC connector plate illustrated in  FIG. 13  with BIC connectors disposed therethrough; 
         FIG. 15  is a rear perspective view of the BIC connector plate with BIC connectors disposed therethrough illustrated in  FIG. 14 ; 
         FIG. 16  is a rear side perspective view of the enclosure of  FIG. 13  illustrating cables connected to the BIC connectors disposed through the BIC connector plates routed through openings in the midplane support to the downlink BIC and uplink BIC disposed in the enclosure; 
         FIG. 17  is a top view of the enclosure of  FIG. 13  illustrating cables connected to the BIC connectors disposed through the BIC connector plates routed through openings in the midplane support to the downlink BIC and uplink BIC disposed in the enclosure; 
         FIG. 18  is a front exploded perspective view of plates of the enclosure of  FIG. 3  that are assembled together in a modular fashion to form the enclosure; 
         FIGS. 19A and 19B  illustrate top and bottom perspective views of the enclosure of  FIG. 3 ; 
         FIG. 20  illustrates a close-up view of the engagement of the top plate of the enclosure in  FIG. 3  with a side plate and midplane support of the enclosure of  FIG. 3 ; 
         FIG. 21  illustrates a close-up view of locating tabs disposed in the top plate of the enclosure of  FIG. 3  engaged with alignment slots disposed in the side plate of the enclosure of  FIG. 3 ; 
         FIG. 22  is a side view of the OIM that can be disposed in the enclosure of  FIG. 3 ; 
         FIG. 23  is another perspective side view of the OIM that can be disposed in the enclosure of  FIG. 3 ; 
         FIG. 24  is a rear perspective view of the OIM that can be disposed in the enclosure of  FIG. 3 ; 
         FIG. 25  is a perspective view of an alignment block that secures the OIC to an OIM plate of the OIM of  FIGS. 23 and 24 ; 
         FIG. 26A  is a rear perspective view the OIM of  FIGS. 23 and 24  without shields installed; 
         FIG. 26B  is a rear perspective view the OIM of  FIGS. 23 and 24  with shield plates installed; 
         FIG. 27  is a close-up rear view of the OIM of  FIGS. 23 and 24  showing standoffs disposed between two printed circuit boards (PCBs) of the OICs, wherein one of the PCBs is a floating PCB; 
         FIG. 28  is a cross-sectional side view of the PCBs of the OICs secured to each other via the standoffs of  FIG. 27  to provide one of the OIC PCBs as a floating PCB and the other of the OIC PCBs as a fixed PCB; 
         FIGS. 29A and 29B  are perspective views of the floating standoffs in  FIG. 27 ; 
         FIGS. 29C and 29D  are side and top views, respectively, of the standoffs of  FIG. 31 ; 
         FIG. 30  is a side cross-sectional view of the standoff of  FIG. 27 ; 
         FIG. 31  is a side cross-sectional view of an alternative standoff that can be employed to secure the OIC PCBs and provide one of the OIC PCBs as a floating PCB; 
         FIGS. 32A and 32B  are side cross-sectional views of an alternative standoff that can be employed to secure the OIC PCBs and shield plates and provide one of the OIC PCBs as a floating PCB; 
         FIG. 33  is a side view of the assembly of  FIG. 3  showing an OIC digital connector being connected to a complementary connector disposed in the midplane interface card to align the OIC RF connector to be connected to the complementary RF connector disposed in the midplane interface card; 
         FIG. 34  is a top perspective view of an OIC disposed in the OIM of  FIGS. 26A and 26B  illustrating the extension of the OIC PCB of beyond transmitter optical sub-assemblies (TOSAs) and receiver optical sub-assemblies (ROSAs) disposed in the OIC PCB; 
         FIG. 35  is a front perspective view of the assembly and enclosure of  FIG. 3  with a cooling fan protector plate installed to protect a cooling fan installed in the enclosure; 
         FIG. 36  is a side cross-sectional view of the enclosure of  FIG. 35  illustrating a cooling fan duct disposed behind the cooling fan in the enclosure to direct air drawn into the enclosure by the cooling fan into a lower plenum of the enclosure; 
         FIG. 37  is an exemplary schematic diagram of air flow drawn into the enclosure by the cooling fan through the enclosure of  FIG. 35 ; 
         FIG. 38  is another side cross-sectional view of the enclosure of  FIG. 35  illustrating the directing of air through openings in a lower plenum plate through OICs installed in the enclosure and through openings disposed in an upper plenum plate in the enclosure; 
         FIG. 39  is a rear perspective view of the enclosure of  FIG. 35  illustrating an air outlet from the upper plenum of the enclosure; 
         FIG. 40  is a rear perspective view of the enclosure of  FIG. 35  illustrating the air outlet from the upper plenum of the enclosure with the top plate of the enclosure removed and illustrating openings in the upper plenum plate into the uplink BIC compartment of the enclosure; and 
         FIG. 41  is a top view of the uplink BIC with openings disposed therein to allow air to flow from the downlink BIC to the uplink BIC disposed above the downlink BIC in the enclosure of  FIG. 35 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings, in which some, but not all embodiments are shown. Indeed, the concepts may be embodied in many different forms and should not be construed as limiting herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Whenever possible, like reference numbers will be used to refer to like components or parts. 
     Optical interface cards, assemblies, and related methods, which may be suited for installation and use in antenna system equipment, are disclosed. In one embodiment, optical interface cards are disclosed. Before discussing the exemplary distributed antenna system equipment, assemblies and enclosures and their alignment features, which start at  FIG. 3 , an exemplary distributed antenna system is first described with regard to  FIGS. 1 and 2 . In this regard,  FIG. 1  is a schematic diagram of a partially schematic cut-away diagram of a building  10  that generally represents any type of building in which a distributed antenna system  12  might be deployed. The distributed antenna system  12  incorporates a head-end communications unit or head-end unit (HEU)  14  to provide various types of communication services to coverage areas within an infrastructure  16  of the building  10 . The HEU  14  is simply an enclosure that includes at least one communication component for the distributed antenna system  12 . For example, as discussed in more detail below, the distributed antenna system  12  in this embodiment is an optical fiber-based wireless communication system that is configured to receive wireless radio frequency (RF) signals and provide the RF signals as Radio-over-Fiber (RoF) signals to be communicated over optical fiber  18  to remote antenna units (RAUs)  20  distributed throughout the building  10 . The distributed antenna system  12  in this embodiment can be, for example, an indoor distributed antenna system (IDAS) to provide wireless service inside the building infrastructure  10 . These wireless services can include cellular service, wireless services such as radio frequency identification (RFID) tracking, wireless fidelity (WiFi), local area network (LAN), and combinations thereof, as examples. 
     The terms “fiber optic cables” and/or “optical fibers” include all types of single mode and multi-mode light waveguides, including one or more optical fibers that may be upcoated, colored, buffered, ribbonized and/or have other organizing or protective structure in a cable such as one or more tubes, strength members, jackets or the like. Likewise, other types of suitable optical fibers include bend-insensitive optical fibers, or any other expedient of a medium for transmitting light signals. An example of a bend-insensitive optical fiber is ClearCurve® Multimode fiber commercially available from Corning Incorporated. 
     With continuing reference to  FIG. 1 , the infrastructure  16  includes a first (ground) floor  22 , a second floor  24 , and a third floor  26 . The floors  22 ,  24 ,  26  are serviced by the HEU  14  through a main distribution frame  28  to provide a coverage area  30  in the infrastructure  16 . Only the ceilings of the floors  22 ,  24 ,  26  are shown in  FIG. 1  for simplicity of illustration. In this example embodiment, a main cable  32  has a number of different sections that facilitate the placement of a large number of RAUs  20  in the infrastructure  16 . Each RAU  20  in turn services its own coverage area in the coverage area  30 . The main cable  32  can include, for example, a riser section  34  that carries all of the uplink and downlink optical fiber cables to and from the HEU  14 . The main cable  32  can include one or more multi-cable (MC) connectors adapted to connect select downlink and uplink optical fiber cables, along with an electrical power line, to a number of optical fiber cables  36 . 
     In this example embodiment, an interconnect unit  38  is provided for each floor  22 ,  24 , and  26 . The interconnect units  38  include an individual passive fiber interconnection of optical fiber cable ports. The optical fiber cables  36  include matching connectors. In this example embodiment, the riser section  34  includes a total of thirty-six (36) downlink and thirty-six (36) uplink optical fibers, while each of the six (6) optical fiber cables  36  carries six (6) downlink and six (6) uplink optical fibers to service six (6) RAUs  20 . The number of optical fiber cables  36  can be varied to accommodate different applications, including the addition of second, third, etc. HEUs  14 . 
     According to one aspect, each interconnect unit  38  can provide a low voltage DC current to the electrical conductors in the optical fiber cables  36  for powering the RAUs  20 . For example, the interconnect units  38  can include an AC/DC transformer to transform 110V AC power that is readily available in the infrastructure  16 . In one embodiment, the transformers supply a relatively low voltage DC current of 48V or less to the optical fiber cables  36 . An uninterrupted power supply could be located at the interconnect units  38  and at the HEU  14  to provide operational durability to the distributed antenna system  12 . The optical fibers utilized in the optical fiber cables  36  can be selected based upon the type of service required for the system, and single mode and/or multi-mode fibers may be used. 
     The main cable  32  enables multiple optical fiber cables  36  to be distributed throughout the infrastructure  16  (e.g., fixed to the ceilings or other support surfaces of each floor  22 ,  24  and  26 ) to provide the coverage area  30  for the first, second and third floors  22 ,  24  and  26 . In this example embodiment, the HEU  14  is located within the infrastructure  16  (e.g., in a closet or control room), while in another example embodiment, the HEU  14  may be located outside of the building at a remote location. A base transceiver station (BTS)  40 , which may be provided by a second party such as cellular service provider, is connected to the HEU  14 , and can be co-located or located remotely from the HEU  14 . A BTS is any station or source that provides an input signal to the HEU  14  and can receive a return signal from the HEU  14 . In a typical cellular system, for example, a plurality of BTSs are deployed at a plurality of remote locations to provide wireless telephone coverage. Each BTS serves a corresponding cell and when a mobile station enters the cell, the BTS communicates with the mobile station. Each BTS can include at least one radio transceiver for enabling communication with one or more subscriber units operating within the associated cell. 
     The HEUs  14  are host neutral systems in this embodiment which can provide services for one or more BTSs  40  with the same infrastructure that is not tied to any particular service provider. The HEU  14  is connected to six (6) optical fiber cables  36  in this embodiment. 
       FIG. 2  is a schematic diagram of the exemplary HEU  14  provided in the distributed antenna system  12  of  FIG. 1  to provide further detail. As illustrated therein, the HEU  14  includes a number of exemplary distributed antenna system components. A distributed antenna system component can be any component that supports communication for the distributed antenna system, such as the distributed antenna system  12  of  FIG. 1 . For example, a head-end controller (HEC)  42  is included that manages the functions of the HEU  14  components and communicates with external devices via interfaces, such as a RS-232 port  44 , a Universal Serial Bus (USB) port  46 , and an Ethernet port  48 , as examples. The HEU  14  can be connected to a plurality of BTSs, transceivers, etc. at BIC connectors  50 ,  52 . BIC connectors  50  are downlink connectors and BIC connectors  52  are uplink connectors. Each downlink BIC connector  50  is connected to a downlink BTS interface card (BIC)  54  located in the HEU  14 , and each uplink BIC connector  52  is connected to an uplink BIC  56  also located in the HEU  14 . The downlink BIC  54  is configured to receive incoming or downlink RF signals from the BTS inputs, as illustrated in  FIG. 2 , to be communicated to the RAUs  20 . The uplink BIC  56  is configured to provide outgoing or uplink RF signals from the RAUs  20  to the BTSs as a return communication path. 
     The downlink BIC  54  is connected to a midplane interface card  58 . The uplink BIC  56  is also connected to the midplane interface card  58 . The downlink BIC  54  and uplink BIC  56  can be provided in printed circuit boards (PCBs) that include connectors that can plug directly into the midplane interface card  58 . The midplane interface card  58  is also in direct electrical communication with a plurality of optical interface cards (OICs)  60 , which are in optical and electrical communication with the RAUs  20  via the optical fiber cables  36 . The OICs  60  convert electrical RF signals from the downlink BIC  54  to optical signals, which are then communicated over the optical fiber cable  36  to the RAUs  20 . The OICs  60  in this embodiment support up to three (3) RAUs  20  each. 
     The OICs  60  can also be provided in a PCB that includes a connector that can plug directly into the midplane interface card  58  to couple the links in the OICs  60  to the midplane interface card  58 . In this manner, the exemplary embodiment of the HEU  14  is scalable to support up to thirty-six (36) RAUs  20  since the HEU  14  can support up to twelve (12) OICs  60 . If less than thirty-four (34) RAUs  20  are to be supported by the HEU  14 , less than twelve OICs  60  can be included in the HEU  14  and connected into the midplane interface card  58 . An OIC  60  is needed for every three (3) RAUs  20  supported by the HEU  14  in this embodiment. OICs  60  can also be added to the HEU  14  and connected to the midplane interface card  58  if additional RAUs  20  are desired to be supported beyond an initial configuration. In this manner, the number of supported RAUs  20  by the HEU  14  is scalable and can be increased or decreased, as needed and in the field, by simply connecting more or less OICs  60  to the midplane interface card  58 . 
       FIG. 3  illustrates an exemplary distributed antenna system housing assembly  70  (referred to as “assembly  70 ”) that may be employed to provide an HEU, such as the HEU  14  in  FIG. 2 . An HEU is simply at least one communications component provided in an enclosure or housing. As will be described in more detail below, the assembly  70  is modular. The assembly  70  is configured to be easily assembled in a factory or in the field by a technician. Further, the assembly  70  supports a number of features that allow interface cards to be easily inserted and aligned with respect to the midplane interface card  58  to ensure that proper connections are made with other components of the HEU  14  that form part of the distributed antenna system, such as the distributed antenna system  12  in  FIG. 1 , for example. As illustrated in  FIG. 3 , the assembly  70  includes an enclosure  72 . The enclosure  72  is comprised of a bottom plate  74  (see also,  FIG. 14B ) and side plates  76 A,  76 B. An internal cavity  80  is formed in the space formed inside the bottom plate  74  and the side plates  76 A,  76 B when assembled together for locating components of the HEU  14 , such as the components illustrated in  FIG. 2 , for example. A top plate  82  can also be provided and secured to the side plates  76 A,  76 B, as illustrated in  FIG. 6 , to protect the internal cavity  80  and protect components of the HEU  14  disposed therein. Note that only two plates can be provided for the enclosure  72 , if desired. For example, one plate could be a first plate wherein a second plate is attached to the first plate. The first plate could be any of the bottom plate  74 , the side plates  76 A,  76 B, and top plate  82 . Also, the second plate could be any of the bottom plate  74 , the side plates  76 A,  76 B, and top plate  82 . 
     With continuing reference to  FIG. 3 , the enclosure  72  is configured to support the OICs  60  illustrated in  FIG. 2 . In this embodiment as illustrated  FIG. 4 , the OICs  60  are grouped together in pairs to form an optical interface module (OIM)  84 . Thus, an OIM  84  is comprised of two (2) OICs  60  that each support up to three (3) RAUs  20  and thus the OIM  84  supports up to six (6) RAUs  20  in this embodiment. As illustrated in  FIG. 4 , each OIC  60  is provided as a PCB  86  with integrated circuits provided therein to provide electrical signal to optical signal conversions for communication downlinks and vice versa for communication uplinks. An OIM plate  88  is provided to assist in coupling a pair of OICs  60  together to form the OIM  84 . As will be discussed in more detail below in this disclosure, the pair of OICs  60  are secured to the OIM plate  88  to form the OIM  84 . The OIM plate  88  serves to support the OIC  60  and contribute to the alignment the OICs  60  for proper insertion into and attachment to the enclosure  72 , which in turn assists in providing for a proper and aligned connection of the OICs  60  to the midplane interface card  58 , as shown in  FIG. 3 . In this embodiment, the PCBs  86  are attached to shield plates  95 A,  95 B that are attached to the OIM plate  88  to provide mechanical, RF, and other electromagnetic interference shielding. 
     The OICs  60  are also secured together via standoff connectors  89  that contain alignment features to allow self-alignment between the OICs  60  when connected to the midplane interface card  58 , as illustrated in  FIG. 4  and as will be described in more detail in this disclosure. Connector adapters  90  are disposed in the OIM plate  88  and provide for optical connections of OIC PCBs  86  of the OICs  60 . The connector adapters  90  are disposed through openings  92  in the OIM plate  88  to provide external access when the OIM  84  is installed in the enclosure  72 . RAUs  20  can be connected to the connector adapters  90  to establish connections to the OICs  60  of the HEU  14 , and thus provided as part of the distributed antenna system  12 , via the optical fiber cables  36  in  FIG. 1  being connected to the connector adapters  90 . These connector adapters  90  may receive any type of fiber optic connector, including but not limited to FC, LC, SC, ST, MTP, and MPO. The OIM  84  is secured to the enclosure  72  via spring-loaded connector screws  85  disposed in the OIM plate  88  that are configured to be inserted into apertures  87  (see  FIG. 5 ) to secure the OIM plate  88  to the enclosure  72 , as illustrated in  FIG. 3 . 
     To provide flexibility in providing OIMs  84 , the HEC  42 , and the downlink BIC  54  and uplink BIC  56  in the HEU  14 , the enclosure  72  provides for the midplane interface card  58  to be disposed inside the internal cavity  80  extending between the side plates  76 A,  76 B in a datum plane  81 , as illustrated in  FIG. 3 . As will be discussed in more detail below, alignment features are provided in the midplane interface card  58  and the enclosure  72  such that proper alignment of the midplane interface card  58  with the enclosure  72  is effected when the midplane interface card  58  is inserted in the enclosure  72 . Thus, when the OIMs  84 , the HEC  42 , and the downlink BIC  54  and uplink BIC  56  are properly and fully inserted into the enclosure  72 , the alignment between these components and the enclosure  72  effect proper aligned connections between connectors on these components (e.g., connectors  94 ) and the midplane interface card  58 . Proper connection to the midplane interface card  58  is essential to ensure proper connection to the proper components in the HEU  14  to support communications as part of a distributed antenna system supported by the HEU  14 . Aligning these connections is important for proper connection, especially given that the enclosure  72  is modular and tolerances of the enclosure components in the enclosure  72  can vary. 
     To illustrate the alignment features to properly align the midplane interface card  58  with the enclosure  72 ,  FIG. 5  is provided to illustrate a front view of the enclosure  72  with the midplane interface card  58  installed therein.  FIG. 5  illustrates a front side  93  of the midplane interface card  58 .  FIG. 6  illustrates a rear perspective view of the enclosure  72  with the midplane interface card  58  installed. No HEU  14  components are yet installed in the enclosure  72  in  FIG. 5 .  FIG. 6  illustrates channels  91 A that are disposed in the bottom plate  74  of the enclosure  72  to receive bottom portions of the HEC  42  and OIMs  84  to align these components in the X and Y directions of the enclosure  72 . Channels  91 B ( FIG. 14B ) are also disposed on the top plate  82  and are aligned with the channels  91 A disposed in the bottom plate  74  to receive top portions of the HEC  42  and OIMs  84  to align these components in the X and Y directions. It is important that the midplane interface card  58  be properly aligned with regard to the enclosure  72  in each of the X, Y, and Z directions, as illustrated in  FIG. 5 , because the midplane interface card  58  includes connectors  94 A,  94 B,  94 C that receive complementary connectors (described in more detail below) from components of the HEU  14  installed in the enclosure  72 . 
     The connectors  94 A are disposed in the midplane interface card  58  and designed to accept connections from the HEC  42  and other like cards with a compatible complementary connector, as illustrated in  FIG. 3 . The connectors  94 B are disposed in the midplane interface card  58  and designed accept digital connections from the OICs  60 . The RF connectors  94 C are disposed in the midplane interface card  58  and designed to accept RF connections from the OIC  60  (see element  195 ,  FIGS. 21 and 22 ). The enclosure  72  is designed such that alignment of the HEU  14  components is effected with respect to the enclosure  72  when installed in the enclosure  72 . Thus, if the connectors  94 A,  94 B,  94 C are not properly aligned with respect to the enclosure  72 , components of the HEU  14 , by their alignment with the enclosure  72 , may not be able to establish proper connections with the midplane interface card  58  and thus will not be connected to the distributed antenna system provided by the HEU  14 . 
     In this regard, as illustrated in  FIGS. 5 and 6 , a midplane support  100  is installed in the datum plane  81  of the enclosure  72  to align the midplane interface card  58  in the X, Y, and Z directions with regard to the enclosure  72 . The midplane support  100  may be a plate formed from the same material as the bottom plate  74 , the side plates  76 A,  76 B, and/or the top plate  82 . The midplane support  100  provides a surface to mount the midplane interface card  58  in the enclosure  72 . A divider plate  101  is also provided and attached to the midplane support  100 , as illustrated in  FIG. 6 , to separate compartments for the downlink and uplink BICs  54 ,  56  and a power supply  59  ( FIG. 6 ) to provide power for the HEC  42  and other components of the HEU  14 . As will also be described in more detail below, the modular design of the enclosure  72  is provided such that the midplane support  100  is properly aligned in the datum plane  81  in the X, Y, and Z directions when installed in the enclosure  72 . Thus, if alignment features are disposed in the midplane support  100  to allow the midplane interface card  58  to be properly aligned with the midplane support  100 , the midplane interface card  58  can be properly aligned with the enclosure  72 , and as a result, the connectors of the components of the HEU  14  installed in the enclosure  72  will be properly aligned to the connectors  94 A,  94 B,  94 C disposed in the midplane interface card  58 . 
     As illustrated in  FIG. 5 , two alignment features  102  are disposed in the midplane support  100  and the midplane interface card  58  to align the midplane interface card  58  in the X, Y, and Z directions with respect to the midplane support  100 , and thus the enclosure  72 .  FIG. 7  illustrates a close-up view of the right-hand side of the midplane interface card  58  installed on the midplane support  100  that also shows one of the alignment features  102 . The alignment features  102  in this embodiment are comprised of PCB support guide pins  104  that are configured to be disposed in alignment openings  106 ,  108  disposed in the midplane interface card  58  and midplane support  100 , respectively.  FIG. 8  illustrates a front side  109  of the midplane interface card  58  without connectors. The PCB support guide pins  104  are installed and configured to be disposed through the alignment openings  106 ,  108 . Before the PCB support guide pins  104  can be inserted through both alignment openings  106 ,  108  disposed in the midplane interface card  58  and midplane support  100 , the alignment openings  106 ,  108  are aligned with the PCB support guide pins  104 . Thus, by this alignment, the midplane interface card  58  is aligned in the X and Y directions with the midplate support  100 . For example, the inner diameter of the openings  106 ,  108  may be 0.003 inches or less larger that the outer diameter of the PCB support guide pin  104 . Also, the tolerances between the center lines in the X direction of the alignment openings  106 ,  108  may be less than 0.01 inches or 0.005 inches, as examples, to provide an alignment between the alignment openings  106 ,  108  before the PCB support guide pins  104  can be disposed through both alignment openings  106 ,  108 . Any other tolerances desired can be provided. 
     Once the PCB support guide pins  104  are inserted into the openings  106 ,  108 , the midplane interface card  58  can be screwed in place to the midplane support  100 . In this regard, additional openings  110  are disposed in the midplane interface card  58 , as illustrated in  FIG. 5 . These openings  110  are configured to align with openings  112  disposed in the midplane support  100  when the alignment openings  106 ,  108  are aligned or substantially aligned. A total of twenty (20) or other number of openings  110 ,  112  are disposed in the midplane interface card  58  and midplane support  100 , as illustrated in  FIG. 5 . Fasteners  114 , such as screws for example, can be disposed through the openings  110 ,  112  to secure the midplane interface card  58  to the midplane support  100  and to, in turn, align the midplane interface card  58  to the midplane support  100  in the Z direction. 
       FIG. 8  illustrates the midplane interface card  58  without the fasteners  114  disposed in the openings  110  to further illustrate the openings  110 . The fasteners  114  are screwed into self-clinching standoff. For example, the self-clinching standoff may be disposed in the midplane support  100 . The height tolerances of the self-clinching standoffs may be between +0.002 and −0.005 inches, as an example. The inner diameter of the openings  110  may be 0.030 inches greater than the outer diameter of the fasteners  114 , for example, since openings  110  are not used to provide the alignment provided by PCB support guide pins  104  and openings  106 ,  108 . Further, as illustrated in  FIG. 5 , openings  115  are disposed in the midplane support  100  to allow cabling to be extended on each side of the midplane interface card  58 . The nominal distance in one embodiment between the midplane support  100  and the midplane interface card  58  when installed is 0.121 inches, although any other distances could be provided. 
     The midplane interface card  58  is also configured to receive direct connections from the downlink BIC  54  and the uplink BIC  56  when installed in the enclosure  72 . As illustrated in the rear view of the enclosure  72  in  FIG. 9 , the downlink BIC  54  and uplink BIC  56  are designed to be inserted through a rear side  116  of the enclosure  72 . Referring back to  FIG. 8 , connector holes  116 A,  116 B are disposed on the midplane interface card  58  in  FIG. 8  show where connectors are provided that are connected to connectors  118  (see  FIGS. 10A and 10B ) of the downlink BIC  54  and uplink BIC  56  when the downlink BIC  54  and uplink BIC  56  are received are fully inserted into the enclosure  72 . The alignment features  102 , by being provided between the midplane interface card  58  and the midplane support  100  as previously discussed, also provide proper alignment of the connector holes  116 A,  116 B to be properly aligned with the connectors  118  in the downlink BIC  54  and uplink BIC  56  when inserted in the enclosure  72 . 
       FIGS. 10A and 10B  illustrate a BIC assembly  120  that supports the downlink BIC  54  or the uplink BIC  56  and is configured to be received in the enclosure  72  to connect the downlink BIC  54  or the uplink BIC  56  to the midplane interface card  58 . The BIC assembly  120  is the same whether supporting the downlink BIC  54  or the uplink BIC  56 ; thus, the BIC supported by the BIC assembly  120  in  FIGS. 10A and 10B  could be either the downlink BIC  54  or the uplink BIC  56 . The BIC assembly  120  includes a BIC support plate  122  that is configured to secure the downlink and uplink BICs  54 ,  56 . Standoffs  124  are provided to support a BIC PCB  126  of the downlink and uplink BICs  54 ,  56  above the BIC support plate  122 . A BIC face plate  128  is coupled generally orthogonal to the BIC support plate  122  to secure the downlink and uplink BICs  54 ,  56  to the enclosure, as illustrated in  FIG. 9 . Alignment features  130  are provided between the BIC support plate  122  and the BIC face plate  128  to ensure that the BIC PCB  126 , and thus its connector  118 , are properly aligned in the X and Y directions, as illustrated in  FIG. 9 , when the downlink and uplink BICs  54 ,  56  are inserted in the enclosure  72 . Thus, the connector  118  will be properly aligned with the enclosure  72  and thus the connector holes  116 A,  116 B on the midplane interface card  58  to allow a proper connection between the downlink and uplink BICs  54 ,  56  and the midplane interface card  58 . The alignment features  130  will ensure alignment of the BIC PCB  126  as long as the BIC PCB  126  is properly installed on the BIC support plate  122 , which will be described in more detail below. As illustrated on the bottom side  127  of the BIC assembly  120  in  FIG. 11 , the alignment features  130  in this embodiment are protrusions  132  attached to the BIC support plate  122  that are configured to be disposed through openings  134  disposed through the BIC face plate  128 , as illustrated in  FIG. 10A . The downlink or uplink BIC connectors  50 ,  52  (see also,  FIG. 2 ), as the case may be, are disposed through the BIC face plate  128  to allow BTS inputs and outputs to be connected to the downlink and uplink BICs  54 ,  56 , external to the enclosure  72  when the downlink and uplink BICs  54 ,  56  are fully inserted in the enclosure  72 . 
     To provide alignment of the BIC PCB  126  to the BIC support plate  122 , alignment features  140  are also disposed in the BIC PCB  126  and the BIC support plate  122 , as illustrated in  FIGS. 10A ,  10 B,  11  and  12 . As illustrated therein, PCB support guide pins  142  are disposed through alignment openings  144 ,  146  disposed in the BIC PCB  126  and BIC support plate  122 , respectively, when aligned. The alignment openings  144  and  146  are designed to only be aligned to allow the PCB support guide pin  142  to be disposed therein when the alignment openings  144 ,  146  are in alignment. For example, the tolerances between the alignment openings  144 ,  146  may be less than 0.01 inches or less than 0.005 inches, as examples, to ensure an alignment between the alignment openings  144 ,  146  before the PCB support guide pins  142  can be disposed through both alignment openings  144 ,  146 . Any other tolerances desired can be provided. 
       FIGS. 9-12  described above provide the BIC connectors  50 ,  52  disposed through the rear side  116  of the enclosure  70 . To establish connections with the BIC connectors  50 ,  52 , connections are established to the BIC connectors  50 ,  52  in the rear side  116  of the enclosure  72 . Alternatively, the enclosure  72  could be designed to allow connections to be established to the downlink BIC  54  and the uplink BIC  76  from the front side of the enclosure  72 . In this regard,  FIG. 13  is a side perspective view of the assembly  70  of  FIG. 3  with the downlink BIC connectors  50  for the downlink BIC and the uplink BIC connectors  52  for the uplink BIC  56  disposed through a front side  147  of the enclosure  72 . As illustrated therein, a downlink BIC connector plate  149  containing downlink BIC connectors  50  disposed therein is disposed in the front side  147  of the assembly  70 . Similarly, an uplink BIC connector plate  151  containing uplink BIC connectors  52  disposed therein is also disposed in the front side  147  of the assembly  70 . 
       FIGS. 14 and 15  illustrate front and rear perspective views of an exemplary BIC connector plate, which can be BIC connector plate  149  or  151 . As illustrated therein, the BIC connectors  50  or  52  are disposed through the BIC connector plate  149  or  151  so that the BIC connectors  50  or  52  can be accessed externally through the front side  147  of the assembly  70 . Fasteners  153  can be disposed through openings  155  in the BIC connector plates  149  or  151  to fasten the BIC connector plates  149  or  151  to the assembly  70 . Channel guides  173  are attached to the BIC connector plates  149  or  151  that are configured to be received in the channels  91 A,  91 B in the assembly  70  to assist in aligning the BIC connector plates  149  or  151  with the assembly  70  when disposing the BIC connector plates  149  or  151  in the assembly  70 . Because the downlink BIC  54  and uplink BIC  56  are disposed in the rear of the assembly  70 , as illustrated in  FIGS. 9-12 , the BIC connectors  50  or  52  are provided in the BIC connector plates  149  or  151  to connect the BIC connectors  50  or  52  to the downlink BIC  54  or uplink BIC  56 , as illustrated in  FIG. 15  and as will be described below with regard to  FIGS. 16 and 17 . Further, a BIC ribbon connector  157  is disposed in the BIC connector plates  149  or  151  to connect to the downlink BIC  54  or uplink BIC  56  to carry status signals regarding the downlink BIC  54  or uplink BIC  56  to be displayed on visual indicators  161  disposed on the BIC connector plates  149  or  151 . 
       FIG. 16  is a rear side perspective view of the enclosure  72  illustrating cables  165 ,  167  connected to the BIC connectors  50 ,  52  being disposed through an opening  169  in the midplane support  100  and an opening  171  in the divider plate  101 . The cables  165 ,  167  provide connections between the BIC connectors  50 ,  52  and the BIC ribbon connector  157  so that the BIC connectors  50 ,  52  can be disposed in the front side  147  of the assembly  70  with the downlink BIC  54  and the uplink BIC  56  disposed in the rear of the assembly  70 .  FIG. 17  is a top view of the assembly  70  further illustrating the routing of the cables  165 ,  167  connecting the BIC connectors  50 ,  52  and BIC ribbon connector  157  through the openings  169 ,  171  to the downlink BIC  54  and uplink BIC  56 . 
     The enclosure  72  is also provided as a modular design to allow the enclosure to be easily assembled and to effect proper alignment between the various plates and components that form the enclosure  72 . For example,  FIG. 18  illustrates a front exploded perspective view of the enclosure  72 . As illustrated therein, the enclosure  72  is formed from the side plates  76 A,  76 B being connected to and between the bottom plate  74  and the top plate  82 . The midplane support  100  is configured to be disposed in the datum plane  81  (see  FIG. 5 ) of the enclosure  72  when assembled. The divider plate  101  is configured to be attached to the midplane support  100  generally orthogonal to the datum plane  81  to divide compartments for the downlink and uplink BICs  54 ,  56  and a power module disposed in the HEU  14  on the rear side of the midplane support  100 . 
     To further illustrate the modularity and ease in assembly of the enclosure  72 ,  FIGS. 19A and 19B  illustrate top and bottom perspective view, respectively, of the enclosure  72  to further illustrate how the side plates  76 A,  76 B are attached to the top plate  82  and bottom plate  74 . In this regard, the top and bottom plates  82 ,  74  include an alignment feature in the form of locating tabs  150 ,  152 . The locating tabs  150 ,  152  are integrally formed in the top and bottom plates  74 ,  82  and are configured to engage with complementary alignment openings or alignment slots  154 ,  156  integrally disposed in the side plates  76 A,  76 B.  FIGS. 19A and 19B  also illustrates a close-up view of the top plate  82  attached to the side plate  76 B and the locating tabs  150  engaged with the alignment slots  154 . This allows the top and bottom plates  74 ,  82  to be attached in proper alignment quickly and easily with the side plates  76 A,  76 B when assembling the enclosure  72 . In the enclosure  72 , there are four (4) locating tabs  150 ,  152  on each side of the top and bottom plates  82 ,  74 , and four (4) complementary alignment slots  154 ,  156  disposed on each side of the side plates  76 A,  76 B, although any number of locating tabs and slots desired can be employed. Fasteners can then be employed, if desired to secure the locating tabs  150 ,  152  within the alignment slots  154 ,  156  to prevent the enclosure  72  from disassembling, as illustrated in  FIG. 20 .  FIG. 20  also illustrates a close-up view of the top plate  82  attached to the side plate  76 B in this regard. 
     As illustrated in  FIG. 20 , the top plate  82  contains rolled or bent up sides  180  that are configured to abut tightly against and a top inside side  182  of the side plate  76 B. The same design is provided between the top plate  82  and the side plate  76 A, and the bottom plate  74  and the side plates  76 A,  76 B. An outer width W 1  of the top and bottom plates  82 ,  74  is designed such that the fit inside an inner width W 2  of the side plates  76 A,  76 B, as illustrated in  FIG. 19A . Fasteners  184  disposed in openings  186  in the side plates  76 A,  76 B and openings  188  in the top and bottom plates  82 ,  74  pull the side plates  76 A,  76 B and the top and bottom plates  82 ,  74  close together tightly to provide a tight seal therebetween. Further, as illustrated in  FIG. 20 , an alignment tab  181  extending from the midplane support  100  is shown and extends into a slot  183  disposed in the top plate  82  to further align the midplane support  100  with the enclosure  72 . 
       FIG. 21  also illustrates alignment features provided in the midplane support  100  that are configured to align the midplane support  100  with the enclosure  72 . As illustrated in  FIG. 21 , the top plate  82  includes integral alignment slots  160  in the datum plane  81  when the top plate  82  is secured to the side plate  76 B. The side plate  76 B also includes alignment slots  162  integrally disposed along the datum plane  81  when the side plate  76 B is secured to the top plate  82 . The midplane support  100  includes locating tabs  164  that are disposed through the alignment slots  160 ,  162  when the midplane support  100  is properly aligned with the enclosure  72  and the top plate  82  and side plate  76 B (see also,  FIG. 7 ). In this manner, as previously described, when the midplane interface card  58  is properly aligned with the installed midplane support  100 , the midplane interface card  58  is properly aligned with the enclosure  72  and thus any HEU  14  components installed in the enclosure  72 . Alignment slots  166  similar to alignment slots  160  are also integrally disposed in the bottom plate  74 , as illustrated in  FIG. 19B . These alignment slots  166  are also configured to receive locating tabs  168  in the midplane support  100 , as illustrated in  FIG. 19B , to align the midplane support  100 . 
     Further, as illustrated in  FIGS. 19A and 19B , the enclosure  72  is also configured to receive and support removable mounting brackets  170 A,  170 B to secure the enclosure  72  to an equipment rack. As illustrated therein, the mounting brackets  170 A,  170 B include folded down components that form tabs  172 A,  172 B. The side plate  76 A,  76 B include integral alignment slots  174 ,  176 , respectively, that are configured to receive the tabs  172 A,  172 B. To secure the tabs  172 A,  172 B to the enclosure  72 , fasteners  178 A,  178 B are disposed through openings  179 A,  179 B in the tabs  172 A,  172 B, respectively, and secure to the top plate  82  and bottom plate  74 . 
     Other features are provided to support alignment of components of the HEU  14  and to support proper connection of these components to the midplane interface card  58 . For example, one of these components is the OIM  84 , as previously discussed. The OIM  84  is illustrated in  FIG. 22 , wherein fiber routing guides  190  can be disposed on the outside of the PCB  86  of the OIC  60  to assist in routing optical fibers  192  from connector adapters  90  that are configured to connect to optical fibers connected to the RAUs  20  (see  FIG. 2 ). The optical fibers  192  are connected to the electronic components of the OIC  60  to convert the received optical signals from the RAUs  20  into electrical signals to be communicated to the uplink BIC  56  via connector  194  and RF connectors  195  that are connected to the midplane interface card  58  when the OIM  84  is inserted into the enclosure  72 , as previously discussed. 
     As previously discussed, the OIM  84  includes two OICs  60  connected to the OIM plate  88  to be disposed in channels  91 A,  91 B in the enclosure  72 . Also, by providing two OICs  60  per OIM  84 , it is important that the connectors  194  are properly aligned and spaced to be compatible with the alignment and spacing of the complementary connectors  94 B in the midplane interface card  58  (see  FIG. 5 ). Otherwise, the OICs  60  may not be able to be properly connected to the midplane interface card  58 . For example, if the PCBs  86  of the OICs  60  are not both secured in proper alignment to the OIM plate  88 , as illustrated in  FIG. 23 , one or both OICs  60  may not be aligned properly in the Z direction. 
     In this regard,  FIG. 24  illustrates an alignment feature  200  to ensure that the PCBs  86  of the OICs  60  are properly secured and aligned with regard to the OIM plate  88  in the Z direction. As illustrated in  FIG. 24  and more particularly in  FIG. 25 , an alignment block  202  is provided. As illustrated in  FIG. 25 , the alignment block  202  includes two alignment surfaces  204 A,  204 B. As illustrated in  FIGS. 24 and 25 , alignment surface  204 A is configured to be disposed against the surface of the PCB  86 . Alignment surface  204 B is configured to be disposed against a rear surface  206  of the OIM plate  88 , as also illustrated in  FIG. 24 . As illustrated in  FIG. 25 , guide pin  208  extends from the alignment surface  204 A that is configured to be disposed in an opening in the PCB  86  of the OICs  60 . An opening  210  disposed in the alignment surface  204 A is configured to align with an opening disposed in the PCB  86  wherein a fastener can be disposed therein and engaged with the opening  210  to secure the PCB  86  to the alignment block  202 . To align the alignment block  202  to the PCB  86 , the guide pin  208  is aligned with an opening in the PCB  86  and inserted therein when aligned. 
     The alignment surface  204 B also contains an opening  212  that is configured to receive a fastener  214  ( FIG. 23 ) disposed through the OIM plate  88  and engage with the opening  212 . Some of the fasteners  214  may be configured to also be disposed through openings in the connector adapters  90 , as illustrated in  FIG. 23 , to secure both the connector adapters  90  to the OIM plate  88  and the OIM plate  88  to the OICs  60 . In this manner, the OIM plate  88  is secured to the alignment block  202 , and the alignment block  202  is aligned and secured to the PCB  86 . Thus, the OIM plate  88  is aligned with the PCB  86  of the OIC  60  in the Z direction. 
     Further, when tolerances are tight, it may be difficult to ensure proper mating of all connectors  194 ,  94 B between the OICs  60  and the midplane interface card  58 . For example, as illustrated in  FIG. 23 , if the spacing between standoffs  196  securing and spacing apart the PCBs  86  of the OICs  60  is not the same as the spacing between connectors  94 B in the midplane interface card  58 , alignment of the OICs  60  in the X, Y, or Z directions may not be proper, and thus only one or neither OIC  60  may be able to be connected to the midplane interface card  58  and/or without damaging the midplane interface card  58  and/or its connectors  94 B. 
     In this regard,  FIG. 26A  illustrates a rear perspective view of the OIM  84  of  FIGS. 23 and 24  with standoffs  196  provided between the two PCBs  86  of the OICs  60  that allow one PCB  86  to float with regard to the other PCB  86 .  FIG. 26B  illustrates a rear perspective view of the OIM  84  of  FIG. 26A  within optional shield plates  95 A,  95 B installed to the PCBs  86  and to the OIM plate  88  to provide mechanical, RF, and other electromagnetic interference shielding. In this regard, tolerances are eased when the OICs  60  are secured to the OIM plate  88  to allow one connector  194  of an OIC  60  to move or float slightly in the X, Y, or Z directions with regard to the other OIC  60 , as illustrated in  FIGS. 26A and 26B .  FIG. 27  illustrates a close-up view of one standoff  196  between two PCBs  86 A,  86 B of the OICs  60 . As will be described in more detail below, the standoff  196  is allowed to float about the top PCB  86 A to allow the positioning or orientation of the top PCB  86 A to move slightly in the X, Y, or Z directions with regard to the bottom PCB  86 B. 
       FIG. 28  is a side cross-sectional view of the top and bottom PCBs  86 A,  86 B of the OIM  84  mounted to each other with the standoff  196 , as illustrated in  FIGS. 26A and 26B  and  28 , to further illustrate the floating top PCB  86 A. In this regard, the standoff  196  is comprised of a body  199 . The body  199  of the standoff  196  is also illustrated in the perspective, side and top view of the standoff in  FIGS. 29A-29C , respectively. The body  199  includes a first collar  220  at a first end  222  of the body  199  of an outer diameter OD 1  than is smaller than an outer diameter OD 2  of a second collar  224  located at a second end  226  of the body  199 , as illustrated in  FIG. 28-30 . The first and second collars  220 ,  224  are configured to be received within openings  228 ,  230  of the top and bottom PCBs  86 A,  86 B, as illustrated in  FIG. 28 . The first end  222  and second end  226  of the body  199  contains shoulders  232 ,  234  that limit the amount of disposition of the first and second collars  220 ,  224  through the openings  228 ,  230  in the top and bottom PCBs  86 A,  86 B. 
     As illustrated in  FIG. 28 , the second collar  224  is designed so that the outer diameter OD 2  includes a tight tolerance with the inner diameter of the opening  230 . In this manner, the second collar  224  will not float within the opening  230 . Further, a height H 2  of the second collar  224  (see  FIG. 29C ) is less than a width W 3  of the PCB  86 A and opening  230  disposed therein, as illustrated in  FIG. 28 . This allows a head  236  of a fastener  238  to be secured directly onto the outer surface  239  of the bottom PCB  86 B when disposed through a threaded shaft  240  of the body  199  to firmly secure the standoff  196  to the bottom PCB  86 B. Because of the outer diameter OD 2  and height H 2  provided for the second collar  224  of the standoff  196 , the bottom PCB  86 B does not float. 
     However, to allow the top PCB  86 A to float, the outer diameter OD 1  and height H 1  of the first collar  220  is different from that of the second collar  224 . In this regard, as illustrated in  FIGS. 28-29C  and  30 , the outer diameter OD 1  of the first collar  220  is smaller than the inner diameter of the opening  228 . A gap G is formed therebetween to allow the first collar  220  to move slightly with respect to the opening  228  when disposed therein. Further, the height H 1  of the first collar  220  is taller than the width W 1  of the top PCB  86 A, as illustrated in  FIG. 28 . Thus when a fastener  242  is disposed within the threaded shaft  240  and tightened, a head  244  of the fastener  242  will rest against a top surface  246  of the first collar  220 . Because the first collar  220  extends in a plane about a top surface  248  of the top PCB  86 A, the head  244  of the fastener  242  does not contact the top surface  248  of the PCB  86 A. Thus, when the fastener  242  is tightened, a friction fit is not provided between the head  244  and the top surface  248  of the PCB  86 A, allowing the top PCB  86 A to float with respect to the standoff  196  and the bottom PCB  86 B. 
       FIG. 31  illustrates an alternative standoff  196 ′ that is the same as the standoff  196 , but the thread shaft does not extend all the way through the body  199 ′ like the standoff  196  in  FIG. 30 . Instead, the thread shafts  240 A′,  240 B′ are separated. The standoff  196 ′ can still be employed to provide the floating PCB  86  features discussed above. Also note that the standoffs  196 ,  196 ′ configured to allow a PCB to float can also be provided for the standoffs  196 ,  196 ′ provided to install any other components of the HEU  14 , including but not limited to the downlink BIC  54  and the uplink BIC  56 . Further, the design of the bodies  199 ,  199 ′ may include a hexagonal outer surface over the entire length of the bodies  199 ,  199 ′. 
       FIGS. 32A and 32B  are side cross-sectional views of an alternative standoff  250  that can be employed to secure the OIC PCBs  86  and provide one of the OIC PCBs  86  as a floating PCB. The alternative standoff  250  may be employed to secure the OIC PCBs  86  when the shield plates  95 A,  95 B are installed, as illustrated in  FIG. 26B . In this regard, one standoff  252  is configured to be disposed within another standoff  254 . The first standoff  252  contains a thread shaft  256  that is configured to receive a fastener to secure a shield plate  95  to the standoff  252  and the OIM  84 . The standoff  252  contains a threaded member  255  that is configured to be secured to a threaded shaft  257  disposed in the standoff  254 . The standoff  254  contains a collar  258  similar to the collar  220 , as described above in  FIGS. 28-29B , that surrounds the threaded shaft  257  and is configured to be received inside an opening of an OIC PCB  86  having a greater inner diameter than the outer diameter OD 3  of the collar  258 . This allows an OIC PCB  86  disposed on the collar  258  to float with respect to another OIC PCB  86  secured to a thread shaft  260  of the standoff  254 . The standoff  254  has a collar  262  having an outer diameter OD 4  that is configured to be received in an opening in an OIC PCB  86  that does not allow float. 
     Another alignment feature provided by the embodiments disclosed herein is alignment assistance provided by the digital connectors disposed in the midplane interface card  58  that accept digital connections from the OICs  60 , the downlink BIC  54 , and the uplink BIC  56 . As previously discussed and illustrated, digital connectors, including connectors  94 B, disposed in the midplane interface card  58  receive complementary digital connectors  194  from the OICs  60 , the downlink BIC  54 , and the uplink BIC  56  when inserted into the enclosure  72 . The OICs  60 , the downlink BIC  54 , and the uplink BIC  56  are designed such that their digital connections are first made to corresponding digital connectors disposed in the midplane interface card  58  when inserted into the enclosure  72  before their RF connections are made to RF connectors disposed on the midplane interface card  58 . In this manner, these digital connections assist in aligning the OICs  60 , the downlink BIC  54 , and the uplink BIC  56  in the X and Y directions with regard to the midplane interface card  58 . 
     In this regard,  FIG. 33  illustrates a side view of the assembly  70  showing a digital connector  194  from an OIC  60  being connected to a complementary connector  94 B disposed in the midplane interface card  58 . As illustrated therein, the digital connector  194  disposed in the OIC  60  is designed such that the digital connector  194  makes a connection with the complementary connector  94 B in the midplane interface card  58  before an RF connector  195  disposed in the OIC  60  makes a connection with the complementary RF connector  94 C disposed in the midplane interface card  58 . In this regard, when the digital connector  194  begins to connect with the complementary connector  94 B, the digital connector  194  aligns with the complementary connector  94 B. The end of the RF connector  195  in the OIC  60  is still a distance D away from the complementary RF connector  94 C. In one non-limiting embodiment, the distance D may be 0.084 inches. Because the digital connectors  194  on the OICs  60  are in a fixed relationship to the RF connectors  195  provided therein in this embodiment, alignment of the digital connectors  194  also provides alignment of the RF connectors  195  of the OICs  60  to the complementary RF connectors  94 C disposed in the midplane interface card  58  as well. Thus, as the digital connector  194  is fully inserted in the complementary connector  94 B, the RF connector  195  will be aligned with the complementary RF connector  94 C when disposed therein. Alignment of the RF connector  195  may be important to ensure efficient transfer of RF signals. This feature may also be beneficial if the RF connections require greater precision in alignment than the digital connections. The same alignment feature can be provided for the downlink BIC  54  and uplink BIC  56 . 
     As previously discussed and illustrated in  FIG. 4 , the OIM plate  88  provides support for the connectors  90  and for attaching the OICs  60  to the OIM plate  88  to provide alignment of the OICs  60  when inserted into the enclosure  72 . An OIM plate  88  is provided to assist in coupling a pair of OICs  60  together to form the OIM  84 . The OIM plate  88  serves to support the OICs  60  and contributes to the alignment the OICs  60  for proper insertion into and attachment to the enclosure  72 , which in turn assists in providing a proper and aligned connection of the OICs  60  to the midplane interface card  58 . In this regard, as illustrated in  FIG. 34 , one feature that can be provided in the OIM  84  to allow the OIM plate  88  to be provided in embodiments disclosed herein is to provide an OIC PCB  86  that extends beyond receiver optical sub-assemblies (ROSAs) and transmitter optical sub-assemblies (TOSAs) provided in the OIC  60 . 
     As illustrated in  FIG. 34 , a top perspective view of the OIM  84  is provided illustrating the extension of OIC PCBs  86  beyond transmitter optical sub-assemblies (TOSAs)  262  and receiver optical sub-assemblies (ROSAs)  260 . The TOSAs  262  and ROSAs  260  are connected via optical fibers  263 ,  265  to the connectors  90  that extend through the OIM plate  88  to allow connections to be made thereto. By extending the OIC PCBs beyond the TOSAs  262  and ROSAs  260 , the OIM plate  88  can be secured to the OIC PCBs  86  without interfering with the TOSAs  262  and ROSAs  260 . In this embodiment, the TOSAs  262  and ROSAs  260  are mounted or positioned on an end of a PCB to transmit and/or receive optical signals interfaced with electrical signal components disposed in the OIC PCB  86 . Mounting or positioning of TOSAs  262  and ROSAs  260  on the end of a PCB may limit the length of exposed, unshielded wire extensions between the TOSAs  262  and ROSAs  260  and printed traces on the PCB. This provides for signal integrity of the signals after conversion to electrical signals. 
     Thus, a sufficient space is provided to allow for the TOSAs  262  and ROSAs  260  to extend beyond an end of a PCB. In this regard, openings  264 ,  266  are disposed in the OIC PCB  86  in this embodiment. The openings  264 ,  266  allow the TOSAs  262  and ROSAs  260  to be disposed in the OIC PCB  86  without the TOSAs  262  and ROSAs  260  extending beyond an end  268  of the OIC PCB  86  where the OIM plate  84  is disposed. Thus, the openings  264 ,  266  allow the TOSAs  262  and ROSAs  260  to be disposed at an end  270  of the PCB where the openings  264 ,  266  start, but not at the end  268  of the OIC PCB  86  where the OIM plate  88  is located. In this manner, space is provided for the TOSAs  262  and ROSAs  260  such that they do not interfere with or prevent the OIM plate  88  from being disposed at the end  268  of the OIC PCB  86 . 
     It may also be desired to provide a cooling system for the assembly  70 . The components installed in the assembly  70 , including the downlink BIC  54 , the uplink BIC  56 , the HEC  42 , and the OICs  60  generate heat. Performance of these components may be affected if the temperature due to the generated heat from the components is not kept below a threshold temperature. In this regard,  FIGS. 35 and 36  illustrate the assembly  70  and enclosure  72  of  FIG. 3  with an optional cooling fan  280  installed therein to provide cooling of components installed in the enclosure  72 . View of the cooling fan  280  is obscured by a cooling fan protector plate  282  in front perspective view of the assembly  70  in  FIG. 35 ; however,  FIG. 36  illustrates a side cross-sectional view of the assembly  70  and enclosure  72  showing the cooling fan  280  installed in the enclosure  72  behind the cooling fan protector plate  282  attached to the enclosure  72 . In this embodiment, cooling is provided by the cooling fan  280  taking air into the enclosure  72  through openings  284  disposed in the cooling fan protector plate  282  and drawing the air across the components in the enclosure  72 , as will be described in more detail below. The air may be pushed through the rear of the enclosure  72  through an air outlet, as illustrated in  FIG. 36 . For example, the cooling fan  280  may be rated to direct air at a flow rate of sixty (60) cubic feet per minute (CFM) or any other rating desired. 
     With continuing reference to  FIG. 36 , a lower plenum  286  and an upper plenum  288  is provided in the enclosure  72 . The lower plenum  286  is provided to direct air pulled in the enclosure  72  by the cooling fan  280  initially to the bottom of the enclosure  72  to allow the air to then be directed upward through OICs  60  installed in the enclosure  72  and to the upper plenum  288  to be directed to the rear and outside of the enclosure  72 . Passing air across the OICs  60  cools the OICs  60 . This air flow design is further illustrated in the air flow diagram of  FIG. 37 . In this regard, with reference to  FIG. 36 , a fan duct  290  is provided behind the cooling fan  280  to direct air drawn into the enclosure  72  by the cooling fan  280 . A plate  292  is installed in the fan duct  290  to direct air flow down from the fan duct  290  into the lower plenum  286 . The air from the lower plenum  286  passes through openings disposed in a lower plenum plate  294  and then passes through the openings disposed between OICs  60  wherein the air then passes through openings  296  disposed in an upper plenum plate  298 , as illustrated in  FIG. 38 . In this manner, air is directed across the OICs  60  to provide cooling of the OICs  60 . Air then entering into the upper plenum  288  is free to exit from the enclosure  72 , as illustrated in  FIG. 36 . The upper plenum  288  is open to the outside of the enclosure  72  through the rear of the enclosure  72 , as illustrated in  FIGS. 36 and 37  and in  FIG. 39 . 
     Further, as illustrated in  FIGS. 40 and 41 , openings  300  and  302  can also be disposed in the upper plenum plate  298  above the uplink BIC  56  and in the downlink BIC  54  to provide further movement of air for cooling purposes. These openings  300 ,  302  allow some of the air flowing into the enclosure  72  from the cooling fan  280  to be drawn from the lower plenum  286  into the downlink BIC  54  and then into the uplink BIC  56  via openings  302 . Air can then be directed from the uplink BIC  56  through openings  300  and into the upper plenum  288  outside of the enclosure  72 . 
     Further, as illustrated in  FIGS. 36 ,  39 , and  41  an optional second cooling fan  301  is provided below the upper plenum plate  298 . In this manner, some of the air from the enclosure  72  is drawn through the power supply  59  by the second cooling fan  301  to provide cooling of the power supply  59 . For example, the second cooling fan  301  may be rated to direct air at a flow rate of thirteen (13) cubic feet per minute (CFM) or any other rating desired. 
     Many modifications and other embodiments set forth herein will come to mind to one skilled in the art to which the embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the description and claims are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. For example, the embodiments disclosed herein can be employed for any type of distributed antenna system, whether such includes optical fiber or not. 
     It is intended that the embodiments cover the modifications and variations of the embodiments provided they come within the scope of the appended claims and their equivalents. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation