Abstract:
A Femto Base Station (FBS) includes a communication functionality and a reliability functionality. A control entity within the reliability functionality detects an FBS reliability compromising event (for example, an unscheduled loss of external power to the FBS). As a result of detecting the FBS reliability compromising event, the control entity sends a message (an “FBS Reliability Compromising Event Compensation Message” or “FBSRCECM”) to the communication functionality. The FBSRCECM initiates an action that compensates for the FBS reliability compromising event. In many examples, the action is the initiating of a handover from the FBS to another base station. The reliability functionality typically includes a rechargeable battery that powers the FBS for a time until the handover is completed gracefully. By performing a graceful handover, cellular network reliability is improved as compared to situations in which a conventional FBS simply stops working and connections handled by the conventional FBS are broken.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority under 35 U.S.C. §119 from U.S. Provisional Application No. 61/139,656, entitled “Reliable Femtocell System for Wireless Communication Networks,” filed on Dec. 22, 2009, the subject matter of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates Femto Base Stations (FBSs), and more particularly to FBSs that communicate using a WiMAX, IEEE 802.16, 3GPP UMTS or 3GPP LTE communication protocol. 
       BACKGROUND 
       [0003]      FIG. 1  (Prior Art) is a diagram that shows a part of a cellular network  1  sometimes referred to as a cell  2 . Cell  2  is the coverage area of a Macro Base Station (MBS)  3 . There are many such MBSs that make up the overall cellular network. A Mobile Station (MS) can move from one cell to another. As a MS passes out of one cell and into another cell, the wireless communication link between the MS and the cellular network is handed off from one MBS of one cell, to the next MBS of the next cell. In the diagram of  FIG. 1 , the block  4  labeled “cellular network” represents a networked set of such BS. Cellular network  4  is connected to the internet  5  via a broadband link or links  6 . The user of an MS can use the MS to access the internet via the cellular network. In the illustrated example, an MS  7  is located out of doors. The Radio Frequency (RF) cellular communication signal link  8  between MBS  3  and MS  7  is relatively strong and the link is a relatively high bandwidth link. The link provides a relatively high Quality of Service (QoS). MS  7  is usable to consume services that require relatively high bandwidth communication between the MS and the internet. 
         [0004]    In the illustrated example of  FIG. 1 , however, another MS  9  is located inside a building  10 . Due to the building, the RF cellular communication link  11  between MS  9  and MBS  3  is weak. This link does not provide a high QoS. The weak link makes accessing services that require high bandwidth communication between the mobile station and the internet unpleasant and slow. In such situations, users often decline to use the cellular network to access internet services and often opt to use a separate access point  12  to access the internet. In a typical example, access point  12  is a WiFi access point that communicates in accordance with mobile stations using an IEEE 802.11 standard. The link between access point  12  and MS  9  is a strong high-bandwidth link  13  offering good QoS. Access point  12  is also connected to the Internet via a wired broadband link  14  referred to as the backhaul link. Backhaul link  14  is provided by an Internet Service Provider (ISP) that is a different entity than the entity operating the cellular network. As a result, the cellar network operator entity loses potential revenue that otherwise might be derived if the cellular operator could have provided the bandwidth-intensive internet content to the user through the cellular network. 
         [0005]      FIG. 2  (Prior Art) illustrates a possible solution to the problem discussed above in connection with  FIG. 1 . In  FIG. 2 , a small base station  15  of limited communication range, referred to here as a “Femto Base Station” (FBS), is used to provide access to cellular network  4 . FBS  15  is typically installed inside the building  10  as illustrated. An FBS typically provides very small cell coverage (e.g. &lt;35 meters) but provides extreme high-speed transmission for indoor communication devices. The FBS uses the same air-interface cellular communication protocol and may use the same licensed spectrum as another MBS in the cellular network. By using the same air-interface cellular communication protocol in the same licensed spectrum as MBS  3 , the cellular network operator can derive increased revenue from providing the user high bandwidth indoor wireless services. Unlike access point  12  of  FIG. 1 , FBS  15  of  FIG. 2  is part of the cellular telephone network and communicates using the same cellular telecommunications protocol used by the base station and the mobile stations. Because of the proximity of FBS  15  and MS  9  inside the building, however, the reliability and bandwidth of communication link  16  between MS  9  and the cellular network is improved as compared to the example of  FIG. 1 . The user need not resort to using an access point that is not part of the cellular network. The FBS  15  is typically connected to the internet by a broadband “backhaul” connection  17 . 
         [0006]    If, for example, the user of MS  9  were to want to access a bandwidth-intensive internet service, then the user may elect to use MS  9  to communicate with a server on the internet via FBS  15 , backhaul link  17 , an ISP-provided link  18 , link  19 , cellular network  14 , and link  6  back to the internet  5 . The overall communication link therefore passes through the cellular network, and the cellular network operator may derive revenue from providing the internet-based services to the user. 
         [0007]    Problems, however, may present themselves where FBSs are utilized, especially where numerous inexpensive FBSs are utilized in the same cellular network by nonprofessionals. Unlike the large macro base stations of the cellular network that are maintained and operated in a reliable manner by the cellular network operator, the FBSs are typically inexpensive equipment that are operated in a less reliable fashion by individual users. Such an individual user may not realize, or even care, that actions taken by the user with the user&#39;s local FBS may adversely impact operation of the remainder of the cellular network. Impacts on operation of such a cellular network may be complex and varied, depending on the particular situation and the actions of the user. Solutions to such undesirable impact on the cellular network are desired. 
       SUMMARY 
       [0008]    A Femto Base Station (FBS) includes communication functionality and novel reliability functionality. The communication functionality includes an air-interface and a backhaul modem. The air-interface may, for example, be an air-interface for communicating in accordance with a WiMAX, an IEEE 802.16, a 3GPP UMTS or a 3GPP LTE communication protocol. In one example, the communication functionality includes an air-interface integrated circuit, a network processor, and a backhaul modem. 
         [0009]    The novel reliability functionality, in one example, includes an External Power and Power Backup Source (EPPBS) and a control entity. The EPPBS includes a rechargeable battery and a power supply/battery charger circuit. The power supply/battery charger circuit receives external AC power from external power terminals, and generates a DC supply voltage usable by the remainder of the FBS circuitry, and keeps the rechargeable battery charged under normal operating conditions. If for some reason the EPPBS will not be able to continue to supply power to the FBS, then the EPPBS outputs “power status information” to the control entity. This power status information alerts the control entity of an upcoming future interruption of operating power. 
         [0010]    In one method, the FBS experiences and detects what is referred to here as an “FBS Reliability Compromising Event.” An example of the FBS reliability compromising event is an unscheduled unplugging of the FBS from AC wall power (110 Volts AC or 220 Volts AC) by the user. The EPPBS within the FBS detects this event and in response outputs the “power status information” to the control entity as described above. The power status information alerts the control entity of the event. In response, the control entity sends an “FBS Reliability Compromising Event Compensation Message” (FBSRCECM) to the communication functionality, thereby initiating the sending of a message from the FBS. In one example, the message sent from the FBS initiates a handover of a Mobile Station (MS) served by the FBS to a macro BS of the cellular network of which the FBS is a part. The message may be a handover request sent via the backhaul modem of the communication functionality to the macro BS via a wired network connection. Alternatively, the message is a handover command sent via the air-interface of the communication functionality to the MS. Regardless of the type of message that initiates the handover, it is assured that the FBS will be powered during the transmission of the message due to the battery within EPPBS. Typically the FBS interacts and communicates with the MS and/or cellular network to facilitate complete handover of the MS while the EPPBS is powering the FBS. 
         [0011]    In the example above, the “FBS reliability compromising event” is an unscheduled unplugging of the FBS by the user. There are, however, other examples of FBS reliability compromising events. Other examples of FBS reliability compromising events include: a disconnection of a backhaul network connection to the FBS, an occurrence of congestion in a backhaul network connection to the FBS, an occurrence of congestion in an air-interface connection to the FBS, a receipt onto the FBS of a message to reconfigure the FBS from a backhaul controller, and a receipt onto the FBS of a message to shut down the FBS from a backhaul controller. Rather than the FBS responding to the FBS reliability compromising event by sending a message to initiate a handover of a mobile station served by the FBS, the FBS may in other examples send one of the following messages: a command sent to a mobile station to enter an idle mode, a message indicative of the FBS reliability compromising event, an error message, a message that includes a recommendation for fixing an error. The message sent out from the FBS in response to the FBS reliability compromising event need not be a message to initiate a handover in all examples. The message may, for example, be a message that causes the cellular network to reconfigure itself to increase bandwidth (throughput) of the link between the FBS and the remainder of the cellular network. The message may be an error message that indicates a potential error or problem and proposes a solution to the error of problem. The message may be sent to a mobile station, to a macro base station, or to another entity such as the backhaul controller entity. Regardless of the type of message sent out from the FBS and regardless of the recipient(s) of the message, the message serves to increase reliability of the overall cellular network of which the FBS is a part. 
         [0012]    Other embodiments and advantages are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention. 
           [0014]      FIG. 1  (Prior Art) is a diagram of a cellular network that includes a Macro Base Station (MBS) and two Mobile Stations (MSs). One of the MSs can also access the internet using a WiFi access point. 
           [0015]      FIG. 2  (Prior Art) is a diagram of a cellular network that includes an MBS and two MSs. One of the MSs can access the internet using a Femto Base Station (FBS). 
           [0016]      FIG. 3  is a diagram of a system  50  in accordance with one novel aspect. The system includes a cellular network involving a plurality of MBSs, a backhaul network, and a novel FBS. 
           [0017]      FIG. 4  is a more detailed diagram of one example of the broadband access connection in  FIG. 3  between FBS  65  and the internet  81 . 
           [0018]      FIG. 5  is a simplified block diagram of the novel FBS  65  of  FIG. 3 . 
           [0019]      FIG. 6  is a flowchart of a first novel method  200 . 
           [0020]      FIG. 7  is a flowchart of a second novel method  300 . 
           [0021]      FIG. 8  is a flowchart of a third novel method  400 . 
           [0022]      FIG. 9  is a flowchart of a fourth novel method  500 . 
           [0023]      FIG. 10  is a flowchart of a fifth novel method  600 . 
           [0024]      FIG. 11  is a flowchart of a generalized novel method  700 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
         [0026]      FIG. 3  is a diagram of a system  50  in accordance with one novel aspect. System  50  includes a cellular communication network involving a plurality of cells  51 - 57 . A Macro Base Station (MBS) serves each of the cells. The MBSs illustrated are identified by reference numerals  58 - 64 . The cellular telephone network further includes many Femto Base Stations (FBSs), one of which is illustrated as FBS  65 . FBS  65  has its own smaller coverage area or cell  66 . MBSs  51 - 57  and FBS  65  are networked together by communication links and associated network equipment. These communication links are represented by lines  67 - 78  and the network equipment is represented by blocks  79  and  80 . The lines and blocks  67 - 80  are provided for illustrative purposes. The actual cellular network and backhaul structure that interconnects the MBSs and FBSs may take various other forms and may involve wireless links and other hardware and software functionality as is known in the art. 
         [0027]    Like the MBSs, FBS  65  has a backhaul link that connects it to the remainder of the cellular network. In the example of  FIG. 3 , this backhaul link includes link  75  between FBS  65  and the internet  81 , link  76  through the internet that is typically provided at least in part by an Internet Service Provider (ISP), and a link  77  to the networking equipment  80  of the cellular network. Networking equipment  80  is a control server (also referred to as an Access Service Network Gateway: “ASN-GW” or a Radio Network Controller: “RNC”) for the FBSs of the system. Networking equipment  79  is a control server for the MBSs of the system. The overall backhaul communication link  75 - 77  from FBS  65  to control server  80  in the illustration is a simplification provided to illustrate that the backhaul link for FBS  65  is provided at least in part by an ISP. The cellular network operator&#39;s networking equipment  79  and  80  includes a distributed backhaul controller entity  82  and  83  that manages the backhaul links to the various base stations. The backhaul controller entity  82 ,  83  can, depending on the circumstance, control the base stations such that more traffic flows through selected base stations and selected backhaul links and such that less traffic flows through other selected base stations and selected backhaul links. The backhaul controller entity  82 ,  83  can reconfigure base stations and other network equipment, and can instruct selected base stations to shut down and stop operating. 
         [0028]    In the example of  FIG. 3 , a user uses MS 1   96  to interact with the cellular network. In conventional cellular network fashion, MS 1   96  typically remains in wireless communication with at least one MBS as MS 1   96  moves throughout the coverage areas served by the MBSs  51 - 57 . Moreover, if MS 1   96  is located in cell  66  then MS 1   96  can also communicate with FBS  65 . FBS  65  may, for example, be a FBS located in a building and the user may be using MS 1   96  within the building. 
         [0029]    When located in cell  66 , the user of MS 1   96  can access the internet via FBS  65 , backhaul link  75 - 77  to networking equipment  80 , and from the cellular network back to the internet via link  78 . The bandwidth of the short relatively unobstructed RF link between MS 1   96  and FBS  65  is greater than the bandwidth of the longer relatively obstructed RF link between MS 1   96  and MBS  64 . By providing the user with a high bandwidth communication link  75 - 77  through the cellular network to the internet using such an FBS, the user may tend to use the cellular network to consume bandwidth intensive internet-based services. 
         [0030]      FIG. 4  is a more detailed diagram that shows one example of the backhaul link  75  of  FIG. 4  between FBS  65  and internet  81 . DSL modems and FBSs of multiple users located in many different buildings  84 - 88  are coupled to the “Local Telecom Operator Office”  89  via ordinary copper telephone lines  90 . The information being communicated to and from these many users is aggregated at the “Local Telecom Operator Office”  89  by a “Digital Subscriber Line Access Multiplexer” (DSLAM) onto a single line  91  such as a T1 line. The T1 line  91  is an Asynchronous Transfer Mode (ATM) trunk that extends to an ATM switch  92 . The amount of bandwidth available to MS 1   96  to the internet therefore depends on the loading by neighborhood devices that are aggregated onto line  91 . The next link  93  to ISP 2  may, for example, be a link to a router  94  operated by a cable television network operator. The internet traffic that the cellular network operator wants to provide to the user of mobile station  96  is rerouted from the router  94  (operated by the cable television network operator ISP 2 ) to a router  95  (operated by the cellular telephone network operator). Router  95  in this case is part of the cellular network. The link from router  94  to router  95  may be somewhat unreliable. The QoS provided by the backhaul link to FBS  65  is variable due to numerous factors such as the sharing of bandwidth with other aggregated traffic. Service outages of the air-interface of an FBS may result in unpredictable changes in backhaul traffic if the system is operated in a conventional manner. Moreover, backhaul link QoS limitations due to other uses of the backhaul network may limit the level of QoS that a particular user may enjoy using a particular FBS. 
         [0031]    In addition to service reliability issues related to the structure and operation of the backhaul link, there are also service reliability issues due to FBS hardware reliability problems. From the perspective of the cellular network, an FBS is generally not as robust as the hardware of an MBS. For example, a user may attempt to move an FBS physically, thereby impacting the effective coverage area of the FBS. The change in coverage area of the FBS may change traffic flows elsewhere in the cellular network. The user may also accidentally power off the FBS and this may result in a disconnection between the FBS and a mobile stations being served by the FBS. The accidental power off may also result in a backhaul link disconnection and surges in backhaul link traffic. When the backhaul links are broken, an existing TCP/IP connection to the mobile station is generally not gracefully transferred, but rather is broken. Packets may be lost. The lost packets must generally be resent across another connection after the other connection to the destination is setup and established. 
         [0032]    In addition to the reliability issues mentioned above due to actions by the user of the FBS, there are reliability issues due to structure and operation of the FBS itself. For example, an FBS may interfere with a cellular telephone or other device and as a result the FBS may need to be shut down or idled. Shutting down the FBS may change operation and interference distribution of the cellular network. There may be unacceptable interference if multiple FBSs are densely deployed. To prevent unwanted interference for these reasons and other reasons, the backhaul controller entity  82 , 83  may instruct a particular FBS to shut down or to go into a low duty mode. As mentioned above, shutting down the FBS may change operation of the cellular network and interference distribution. In addition, relatively unreliable FBSs may cause the MBSs that serve the unreliable FBSs to suffer high levels of unreliability. 
         [0033]      FIG. 5  is a more detailed diagram of FBS  65 . FBS  65  has features usable to counter the reliability concerns set forth above. FBS  65  includes a communication functionality  100 , an antenna  101 , a plug  102  for coupling to a backhaul connection cable  103 , and a reliability functionality  104 . Cable  103  may be a twisted pair for DSL communication as illustrated, or may be a coaxial cable for coupling with a cable modem, or may be another type of cable used for backhaul communication. 
         [0034]    Communication functionality  100  includes an air-interface integrated circuit  105  adapted to send and to receive WiMAX/802.16, UMTS or LTE wireless communications. Air-interface integrated circuit  105  includes an RF transceiver  106 , a PHY layer protocol processing functionality  107  and a MAC layer protocol processing functionality  108 . Communication functionality  100  further includes a network layer processing functionality  109 , and a backhaul modem  110 . In the illustrated example, air-interface integrated circuit  105  communicates with the reliability functionality  104  across one or more conductors  111 . These conductors  111  are typically conductors on a printed circuit board upon which integrated circuit  105  is disposed. Similarly, in the illustrated example, backhaul modem  110  communicates with the reliability functionality  104  across one or more conductors  112 . Communication between network processor  109  and the reliability functionality  104  may pass across similar conductors  113  on the printed circuit board as illustrated in  FIG. 5  in situations in which network processor  109  and control entity  114  are disposed on different integrated circuits. Alternatively, the network processor  109  and a control entity  114  of the reliability functionality  104  are realized using hardware and/or software disposed on the same integrated circuit. Communication between the network processor  109  and the control entity  114  in such cases may occur using registers or memory locations or other mechanisms usable to pass information from one subroutine or dedicated hardware circuit to another subroutine or dedicated hardware circuit within a larger overall processor circuit. Communication between the various parts of the communication functionality  100  and the reliability functionality  104  can occur across multiple separate dedicated conductors as illustrated, or in other examples can occur across a single bus. In the event a single bus is used, interface  126  may be a bus interface for a standard serial bus commonly used to communicate between integrated circuits. Of importance, the communication functionality  100  is powered by internal power (internal to FBS  65 ) received from the reliability functionality  104  across power PWR and ground GNS conductors  115  and  116 . 
         [0035]    Reliability functionality  104  includes external power terminals  116  and  117  for receiving 110 volt AC power from an external source such as a wall plug, an External Power And Power Backup Source (EPPBS)  119 , and the control entity  114 . EPPBS  119  includes an AC-to-DC power supply and battery charging circuit  120  and a rechargeable battery  121 . The AC-to-DC power supply and battery charging circuit  120  receives 110 or 220 Volt AC power from terminals  117  and  118 , generates therefrom a regulated DC voltage on conductors  115  and  116 , and maintains rechargeable battery  121  in a charged state. As long as FBS  65  is connected to a suitable external power source, EPPBS  119  performs its AC-to-DC power supply function and supplies a DC supply voltage to communications functionality  100  via PWR and GND conductors  115  and  116 . If, however, FBS  65  were to become unplugged from the external power source as represented by the power disconnect event star symbol  122 , then EPPBS  119  continues to supply the DC supply voltage to communications circuitry  100  via PWR and GND conductors  115  and  116  but the energy for this supply originates from battery  121 . In response to the power disconnect event  122 , EPPBS  119  also outputs power status information  123 . In the present example, power status information  123  is a multi-bit digital value communicated across conductors  124 . Power status information  123  alerts control entity  114  of the power disconnect event. In response to receiving power status information  123  from EPPBS  119 , control entity  114  sends an “FBS Reliability Compromising Event Compensation Message” (FBSRCECM)  125  to communication functionality  100 . As explained in further detail below, FBSRCECM  125  may cause communication functionality  100  to initiate a handover of a connection between FBS  65  and MS 1   96  to MBS  64  such that the connection then exists between MS 1   96  and MBS  64 . The connection is gracefully transferred from the FBS to the MBS. 
         [0036]    In one example, reliability functionality  104  is a separately encased module that is manufactured separately from the remainder of FBS  65 . The module has a hardware interface  126  involving a plurality of terminals. The FBSRCECM  125  is output by control entity  114  such that the FBSRCECM  125  passes out of the module through the terminals of the interface  116 . The module may removably plug into the remainder of FBS  65  such that control entity  114  can communicate across interface  126  with communication functionality  100 . In this example, control entity  114  is realized on one integrated circuit of the module, whereas the communication functionality  100  is realized on multiple other integrated circuits outside of the module. 
         [0037]    In another example, reliability functionality  104  is not a separately encased module, but rather control entity  114  is a set of processor-executable instructions executing on a suitable processor. This processor also executes other sets of processor-executable instructions in carrying out an operation of the communication functionality  100 . The processor may, for example, be a Digital Signal Processor (DSP) integrated circuit that executes a control entity sub-routine of processor-executable instructions and that also executes a network processor sub-routine of processor-executable instructions. 
         [0038]      FIG. 6  is a flowchart of a first method  200  involving a scheduled FBS shut down. In  FIG. 6 , the label MS 1  denotes MS 1   96  of  FIG. 3 . Label MS 2  denotes another mobile station (not shown) within cell  66  served by FBS  65 . The “FEMTO BS” notation denotes FBS  65  of  FIG. 3 . The “MACRO BS” notation denotes MBS  64  of  FIG. 3 . In the diagram of  FIG. 6 , time extends downward. In method  200 , a shut down notice  201  occurs and in response FBS  65  sends a handover request message  127  to MBS  64 . Shut down notice  201  may, for example, be a notice received from the backhaul controller entity  82 ,  83  via the backhaul network. The notice may be an instruction to FBS  65  to shut down due to interference problems. The shut down notice is passed to the control entity  114  in the form of backhaul connection status information  128  (see  FIG. 5 ). Control entity  114  receives information  128  and in response sends an appropriate FBSRCECM  125  to communication functionality  100 . FBSRCECM  125  instructs communication functionality  100  to generate and send the handover request  127  to MBS  64 . 
         [0039]    Next, as illustrated in  FIG. 6 , MBS  64  responds by sending a handover response  202  back to FBS  65  via the backhaul network. Handover response  202  is received by backhaul modem  109  of FBS  65 . In response, FBS  65  sends a confirmation  203  back to MBS  64  via the backhaul network. This handover request, response, and confirm mechanism may be a conventional mechanism employed in the cellular network. 
         [0040]    Next, FBS  65  sends a handover command message to each of the mobile stations FBS  65  is serving. In the example of  FIG. 6 , handover command  204  goes to MS 1   96  denoted MS 1  and handover command  205  goes to another MS denoted MS 2  (not illustrated). The mobile stations MS 1  and MS 2  and the base stations FBS  65  and MBS  64  then communicate with one other in order to carry out and complete the handover process in standard fashion. During the entire time this handover process is occurring, the FBS  65  is certain to be powered due to energy stored in battery  121 . Typically the circuitry of the FBS  65  is powered at least to some extent during this time by energy previously stored in battery  121 . After the handover process is complete, for example as determined by expiration of a timer in FBS  65  as indicated by symbol  206 , the FBS  65  stops operating and shuts down. In one example, this shutting down involves the reliability functionality  104  no longer providing internal power via conductors  115  and  116  to communication functionality  100  and control entity  114 . Accordingly, rather than FBS  65  causing reliability issues in the cellular network due to broken connections between the FBS and mobile stations and/or due to broken connections between the FBS and the backhaul network when FBS  65  shuts down, the FBS  65  remains operational and initiates an orderly handover and then after the handover has been completed shuts down gracefully thereby reducing adverse impact on the cellular network. 
         [0041]    In one example, when the high bandwidth link between a mobile station and FBS  65  is lost and the traffic is to be transferred to a lower bandwidth link between the mobile station and a macro base station, QoS for the mobile stations may be maintained by handing over some of the mobile stations to one macro base station and handing over other of the mobile stations to another macro base station. How the handover is to be performed as indicated by the backhaul controller entity  82 ,  83  in the handover response  202 , and this information is passed on as appropriate by FBS  65  to mobile stations MS 1  and MS 2  as part of the handover commands  204  and  205 . In response, each mobile station attempts to handover to a different specified macro base station if multiple macro base stations are within range. 
         [0042]      FIG. 7  is a flowchart of a second method  300  involving an unexpected power off of FBS  65 . In response to a power failure or unexpected power disconnect event  122 , EPPBS  119  (see  FIG. 5 ) sends power status information  123  to control entity  114  informing control entity  114  of the power failure. EPPBS  119  supplies the communication functionality  100  and control entity  114  with backup power from battery  121  via conductors  115  and  116 . The supplying of power by EPPBS  119  in  FIG. 7  is illustrated by the cross-hatched shaded area  301 . 
         [0043]    Control entity  114  receives the power status information  123  and in response sends an appropriate FBSRCECM  125  to the communication functionality  100 . FBSRCECM  125  instructs the communication functionality  100  to initiate a handover. Communication functionality  200  responds by sending a handover request message  302  via the backhaul network. The handover request message  302  initiates a handover operation involving message  302 , a handover response message  303 , and a handover confirm message  304  as illustrated in  FIG. 7 . This handover process is not a conventional one, but rather FBS  65  informs MBS  64  of the number of handover users to expect as a result of event  122 . MBS  64  uses this burst alert to make preparations to prevent a potential ranging flash crowd. In one example, MBS  64  provides a contention-free ranging region by designating particular ranging slots for the flash crowd and by reserving other ranging slots for other traffic. Communication of the contention-free ranging region is illustrated in  FIG. 7  by arrow  306 . In another example, MBS  64  allocates additional ranging slots in response to the handover request directed from the FBS and to accommodate the many handover users. This “additional ranging slots” example is illustrated below in  FIG. 8 . 
         [0044]    In response to unexpected power disconnect event  122 , communication functionality  100  also broadcasts a broadcast and handover command  305  from its air-interface to the mobile stations MS 1  and MS 2  that FBS  65  is serving. In the example of  FIG. 7 , the FBS  65  is powered down before the handover is completed, but the handover process is nonetheless conducted gracefully in the fashion as illustrated. FBS  65  handshakes with its neighboring MBS  64  to initiate the handover and also commands the mobile stations MS 1  and MS 2  in a handover command to handover before EPPBS  119  stops powering the FBS. The mobile stations, having received broadcast handover comment  305 , complete the handover from FBS  65  to MBS  64  using the quarantine ranging region even though FBS  64  has stopped operating. 
         [0045]      FIG. 8  is a flowchart of a third method  400  involving an unexpected power off of FBS  65 . In the example of  FIG. 8 , the unexpected power disconnect event  122  occurs, but the FBS  65  stops operating even before handover handshaking with MBS  64  can be completed. EPPBS  119  (see  FIG. 5 ) detects power disconnect event  122 , and in response sends power status information  123  to control entity  114 . As in the example of  FIG. 7 , the power status information  123  informs control entity  114  of the power failure. Control entity  114  in turn sends FBSRCECM  125  to the communication functionality  100 , thereby causing a handover request message  401  and a broadcast and handover command to be sent out of FBS  65 . FBS  65  stops operating before standard handshaking with MBS  64  can be completed. MBS  64  sends a handover response  403 , but it is not received by FBS  65  nor is it acknowledged. The mobile stations and the macro base station are configured to complete the handover by themselves without the FBS as illustrated. The mobile stations MS 1  and MS 2  send communications  404  and  405  to MBS  64  and interact MBS  64  to complete the handover. In some examples, this may be triggered by timers in MS 1  and MS 2 . Such a timer starts from the broadcast command from the FBS, where the timer may be preconfigured or may be configured according to the value indicated in the broadcast command from the FBS. MBS  64  provides for the handover crowd by providing additional ranging slots. In some examples, both techniques of providing additional ranging slots for the handover crowd and of providing quarantine ranging regions for the handover crowd are used together. 
         [0046]      FIG. 9  is a flowchart of a fourth method  500  involving unexpected backhaul congestion from and/or to FBS  65 . Unexpected backhaul congestion occurs as indicted by the star symbol  501 . FBS  65  may determine that its backhaul link is not working properly by itself without being informed, or alternatively FBS  65  may receive a message from the backhaul network itself informing the FBS  65  of the backhaul congestion problem. The backhaul link between FBS  65  and MBS  64  may be totally unusable, or may suffer and undesirably large amount of congestion. 
         [0047]    In one example, the backhaul controller entity  82 ,  83  (see  FIG. 3 ) informs FBS  65  of backhaul congestion by sending FBS  65  a message via the backhaul network. The message is received by backhaul modem  110  (see  FIG. 5 ), and the information is forwarded to control entity  114  in the form of backhaul connection status information  128  (see  FIG. 5 ). Control entity  114  responds by sending a FBSRCECM  125  back to communication functionality  100 . The FBSRCECM  125  causes a broadcast and handover command  502  to be sent from the air-interface to all mobile stations MS 1  and MS 2 . Any data destined for mobile stations that had been buffered in FBS  65  is also forwarded to the appropriate mobile stations MS 1  and MS 2  as indicated by arrows  503  and  504 . The mobile stations MS 1  and MS 2  seek to establish communication with MBS  64  as illustrated without using the backhaul link between FBS  64  and the backhaul network. In the case of MS 1   96  being used to receive streaming video from the backhaul network via FBS  65 , the handover from FBS  65  to MBS  64  is completed before the buffered video data  503  has been consumed and viewed, and as a result service disruption in the viewing of the video on MS 1   96  is avoided. 
         [0048]      FIG. 10  is a flowchart of a fifth method  600  involving an unexpected breakdown of the FBS  65 . In this scenario, FBS  65  breaks down without informing either the MBS  64  or the mobile stations MS 1  and MS 2  that it will no longer be operating. In this scenario, unfortunately, the reliability functionality  104  of FBS  65  does not provide for enhanced cellular network reliability. The MBSs that fail to receive communications from FBS  65 , however, are configured to attempt to establish communication with MBS  64  using a timer and backoff mechanism that prevents ranging flash crowding and prevents loss of TCP/IP connections. In the example of  FIG. 10 , mobile stations MS 1  and MS 2  have timers  604  to detect breakdown of the FBS. After timers  604  expire and FBS  65  detects breakdown  601 , and before any connections extending to the mobile stations MS 1  and MS 2  are broken or are declared “out of service”, MS 1  uses backoff period  602  to send a ranging code to MBS  64  whereas MS 2  uses backoff period  603  to send a ranging code of MBS  64 . Reception of the ranging codes by MBS  64  is spread out over time. Throughout the handover process of  FIG. 10 , mobile stations MS 1  and MS 2  remain authenticated and registered with the network, so the mobile stations MS 1  and MS 2  perform the handover operations to MBS  64  without loss of their respective connections. 
         [0049]    Although not pictured in a diagram, control entity  114  of  FIG. 5  can also be prompted to send FBSRCECM  125  as a result of air-interface status information  129  received from communication functionality  100 . An example of air-interface status information  129  is a message indicating a level of air-interface congestion. In response to receiving this information  129 , control entity  114  sends an appropriate FBSRCECM  125  thereby initiating a handover of a link to a mobile station served by FBS  65  to MBS  64 . The method of messaging appears much as method  600  of  FIG. 10  in that FBS  65  does not communicate with the mobile stations to be handed over. Unlike the method  600  of  FIG. 10 , however, FBS  65  may inform MBS  64  via the backhaul network that it will be receiving handover users. MBS  64  may therefore employ the contention-free ranging region technique of  FIG. 7  and/or the additional ranging slots technique of  FIG. 8  to prevent a handover crowd problem. Although examples are set forth above where FRCECM  125  results in a handover, in other examples the communication function is made to send other messages. For example, a message may be sent from FBS  65  to the backhaul controller entity  82 ,  83  to increase FBS backhaul connection throughput. A message may be sent from FBS  65  to the backhaul controller entity  82 ,  83  that both indicates an error condition and also includes a recommendation for fixing the error condition. 
         [0050]      FIG. 11  is a flowchart of a generalized novel method  700  involving FBS  65  of  FIG. 5 . In a first step (step  701 ), an “FBS Reliability Compromising Event” is detected on the FBS. Examples of an FBS Reliability Compromising Event include, but are not limited to: 1) a disconnection of external power supplied to the FBS, 2) an FBS low battery charge condition, 3) a disconnection of a backhaul network connection to the FBS, 4) an occurrence of congestion in a backhaul network connection to the FBS, 5) an occurrence of congestion in an air-interface connection to the FBS, 6) a receipt onto the FBS of a message to reconfigure the FBS, and 7) a receipt onto the FBS of a message to shut down the air-interface of the FBS. In a second step (step  702 ), FBS  65  sends a message from the FBS to compensate for the “FBS Reliability Compromising Event” detected in step  701 . Examples of the message include, but are not limited to: 1) a command sent to a mobile station served by the FBS for triggering handover, 2) a message sent to a mobile station to put the mobile station into an idle mode, 3) a handover request sent to a macro base station to which the handover is to occur, and 4) a command sent to the backhaul modem to request reconfiguration of the backhaul connection bandwidth or QoS level. 
         [0051]    In one example of the generalized method  700 , the “FBS Reliability Compromising Event” is an unscheduled disconnection of external power supplied to FBS  65 . The control entity  114  detects this event as a result of receiving power status information  123  from EPPBS  119 . The power status information  123  indicates that external power has been lost and/or indicates the amount of charge on battery  121 . As a result of receiving information  123 , control entity detects the “FBS Reliability Compromising Event.” Control entity  114  then sends FRCECM  125  to communication functionality  100 , thereby initiating a handover as illustrated in either  FIG. 7  or  FIG. 8 . Power to FBS  65  is ensured during steps  701  and  702  due to EPPBS  119  and battery  121 . 
         [0052]    Although the present invention is described above in connection with certain specific embodiments for instructional purposes, the present invention is not limited thereto. The generalized method of  FIG. 11  is applicable to femto base stations utilizing various different air-interface communication protocols other than WiMAX including LTE, GSM, UMTS, CDMA200, and TD-SCDMA. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.