Abstract:
There is disclosed for use in a wireless network comprising a plurality of base transceiver substations capable of communicating with a plurality of mobile stations, an apparatus for preventing the dropping of an emergency call associated with a first one of the plurality mobile stations. The apparatus comprises a call drop controller for receiving from the wireless network a maintenance command directed to a first base transceiver substation handling the emergency call, determining whether the maintenance command may cause the first base transceiver substation to drop the emergency call and, in response to such a determination, preventing the maintenance command from being executed by the first base transceiver substation. The call drop controller also is capable of: 1) receiving a failure notification from a failed base transceiver substation, 2) determining whether the failed base transceiver substation is handling the emergency call and, 3) in response to such a determination, at least one of: a) increasing transmission power of at least one base transceiver substation proximate to the failed base transceiver substation; b) increasing a TDROP value of the failed base transceiver substation; and 3) decreasing a TADD value of at least one base transceiver substation proximate to the failed base transceiver substation.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention is directed, in general, to wireless networks and, more specifically, to a system for preventing 911 emergency calls from being dropped due to sector wilting in a base station. 
     BACKGROUND OF THE INVENTION 
     Wireless networks, and cellular telephone networks in particular, have become ubiquitous in society. Within the United States, cellular service is offered by cellular service providers, by the regional Bell companies, and by the national long distance operators. The enhanced competition has driven the price of cellular service down to the point where it is affordable to a large segment of the population. 
     One of the most important features of a wireless (or cellular) phone is its use in emergency situations. A wireless phone allows a subscriber to call for help nearly instantaneously from practically any location. Enhanced services in cellular phones may also allow a wireless network to remotely determine the location of a cellular telephone, thereby allowing police, firefighters and other emergency personnel to be sent to the location of the cellular phone. 
     However, certain maintenance procedures and emergency fault procedures may unintentionally cause an emergency call to be dropped as a result of “wilting” a sector or even an entire base station. It is frequently necessary, for the purposes of routine maintenance and/or recovering from a critical fault, to reduce (i.e., to wilt) the power of one or more RF transmitters in a base station in a wireless network. The wilting may be done to a single sector in a multi-sector base station or it may be done to all sectors of the base station. Wilting a base station (or a sector) causes mobile stations that are in communication with the base station (or sector) to search for other base stations and eventually causes the mobile stations to be handed off to new base stations. If a new base station cannot be found in time, a call may be dropped due to the wilting. While this may be annoying for routine wireless telephone calls, dropping an emergency call may result in loss of life. 
     There is therefore a need in the art for improved wireless networks that are less susceptible to dropping emergency calls. In particular, there is a need for wireless networks that are less likely to drop emergency calls during routine maintenance or during critical failures in one or more sectors of a base station. 
     SUMMARY OF THE INVENTION 
     To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide, for use in a wireless network comprising a plurality of base transceiver substations capable of communicating with a plurality of mobile stations, an apparatus for preventing the dropping of an emergency call associated with a first one of the plurality mobile stations. According to an advantageous embodiment of the present invention, the apparatus comprises a call drop controller capable of 1) receiving from the wireless network a maintenance command directed to a first base transceiver substation handling the emergency call, 2) determining whether the maintenance command is capable of causing the first base transceiver substation to drop the emergency call and, 3) in response to a determination that the maintenance command may cause the first base transceiver substation to drop the emergency call, preventing the maintenance command from being executed by the first base transceiver substation. 
     According to one embodiment of the present invention, the call drop controller, in response to a determination that the maintenance command will not cause the first base transceiver substation to drop the emergency call, allows the maintenance command to be executed by the first base transceiver substation. 
     According to another embodiment of the present invention, the call drop controller is further capable of determining whether a second base transceiver substation proximate to the first base transceiver substation is handling a second emergency call, and, in response to a determination that the second base transceiver is handling the second emergency call, preventing the maintenance command from being executed. 
     According to still another embodiment of the present invention, the call drop controller, in response to a determination that the second base transceiver is not handling the second emergency call, allows the maintenance command to be executed by the first base transceiver substation. 
     It is also a primary object of the present invention to provide, for use in a wireless network comprising a plurality of base transceiver substations capable of communicating with a plurality of mobile stations, an apparatus for preventing the dropping of an emergency call associated with a first one of the plurality mobile stations, wherein the apparatus comprises a call drop controller capable of receiving from the wireless network a maintenance command directed to a first base station controller, determining whether the maintenance command is capable of causing a first base transceiver substation controlled by the first base station controller to drop the emergency call, and, in response to a determination that the maintenance command may cause the first base transceiver substation to drop the emergency call, preventing the maintenance command from being executed by the first base station controller. 
     According to a further embodiment of the present invention, the call drop controller, in response to a determination that the maintenance command will not cause the first base transceiver substation to drop the emergency call, allows the maintenance command to be executed by the first base station controller. 
     According to a still further embodiment of the present invention, the call drop controller is further capable of determining whether a second base transceiver substation proximate to the first base transceiver substation is handling a second emergency call, and, in response to a determination that the second base transceiver is handling the second emergency call, preventing the maintenance command from being executed by the first base station controller. 
     According to a yet further embodiment of the present invention, the call drop controller, in response to a determination that the second base transceiver is not handling the second emergency call, allows the maintenance command to be executed by the first base transceiver substation. 
     Another object of the present invention to provide an apparatus that prevents emergency calls from being dropped when a base station resource fails in the wireless network. Accordingly, in an advantageous embodiment of the present invention, there is provided, for use in a wireless network comprising a plurality of base transceiver substations capable of communicating with a plurality of mobile stations, an apparatus for preventing the dropping of an emergency call associated with a first one of the plurality mobile stations, wherein the apparatus comprises a call drop controller capable of: 1) receiving a failure notification from a failed base transceiver substation, 2) determining whether the failed base transceiver substation is handling the emergency call and, 3) in response to a determination that the failed base transceiver substation is handling the emergency call, at least one of: a) increasing transmission power of at least one base transceiver substation proximate to the failed base transceiver substation; b) increasing a TDROP value of the failed base transceiver substation; and 3) decreasing a TADD value of at least one base transceiver substation proximate to the failed base transceiver substation. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form. 
     Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,”as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like numbers designate like objects, and in which: 
     FIG. 1 illustrates an exemplary wireless network according to one embodiment of the present invention; 
     FIG. 2 illustrates an emergency call monitor system in the exemplary base station manager according to one embodiment of the present invention; 
     FIG. 3 is a flow chart illustrating the operation of an emergency call monitor system in response to actions taken by maintenance personnel according to one embodiment of the present invention; and 
     FIG. 4 is a flow chart illustrating the operation of an emergency call monitor system in response to automatic failure notifications generated by devices in the wireless network according to one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 through 4, discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged wireless network. 
     FIG. 1 illustrates exemplary wireless network  100  according to one embodiment of the present invention. Wireless network  100  comprises a plurality of cell sites  121 - 127 , each containing one of the base transceiver substations (BTS), BTS  101 , BTS  102 , BTS  103 , BTS  104 , BTS  105 , BTS  106 , or BTS  107 . Base transceiver substations  101 - 107  are operable to communicate with a plurality of mobile stations (MS)  111 - 114 . Mobile stations  111 - 114  may be any suitable cellular devices, including conventional cellular telephones, PCS handset devices, portable computers, metering devices, and the like. 
     Dotted lines show the approximate boundaries of exemplary cell sites  121 - 127  in which base transceiver substations  101 - 107  are located. The cell sites are shown approximately circular for the purposes of illustration and explanation only. It should be clearly understood that the cell sites may have other irregular shapes, depending on the cell configuration selected and natural and man-made obstructions. 
     In a typical wireless network, a base transceiver subsystem is at the center of each cell site. Frequently, multiple base transceiver subsystems may be connected to a single base station controller (BSC) and multiple base station controllers may be connected to a single mobile switching center (MSC), such as MSC  140 . Base station controllers, base transceiver subsystems, and mobile switching centers are well known to those skilled in the art. A base station controller is a device that manages wireless communications resources, including the base transceiver subsystem, for specified cells within a wireless communications network. A base transceiver subsystem comprises the RF transceivers, antennas, and other electrical equipment located in each cell site. This equipment may include air conditioning units, heating units, electrical supplies, telephone line interfaces, and RF transmitters and RF receivers. A mobile switching center is a switching device that provides services and coordination between the subscribers in a wireless network and external networks, such as the public switched telephone network (PSTN) (not shown). 
     BTS  101 , BTS  102  and BTS  103  transfer voice and data signals between each other and the public switched telephone network via communications line  131 , base station controller  160 , and mobile switching center  140 . BTS  104 , BTS  105 , BTS  106 , and BTS  107  transfer voice and data signals between each other and the public switched telephone network via communications line  132 , base station controller  165 , and mobile switching center  140 . Communications lines  131  and  132  may be any suitable connection means, including a T 1  line, a T 3  line, a fiber optic link, a network backbone connection (such as an Internet protocol (IP) network), and the like. In some embodiments of the present invention, communications lines  131  and  132  may be several different data links, where each data link couples one of BTS  101 , BTS  102 , and BTS  103  to BSC  160  and one of BTS  104 , BTS  105 , BTS  106 , and BTS  107  to BSC  165 . 
     In the exemplary wireless network  100 , MS  111  is located in cell site  121  and is in communication with BTS  101 ; MS  113  is located in cell site  122  and is in communication with BTS  102 ; and MS  114  is located in cell site  123  and is in communication with BTS  103 . The MS  112  is also located in cell site  121 , close to the edge of cell site  124 . The direction arrow proximate MS  112  indicates the movement of MS  112  towards cell site  124 . At some point, as MS  112  moves into cell site  124  and out of cell site  121 , a “handoff” will occur. 
     As is well known, the “handoff” procedure transfers control of a call from a first cell to a second cell. For example, if MS  112  is in communication with BTS  101  and senses that the signal from BTS  101  is becoming unacceptably weak, MS  112  may then switch to a BTS that has a stronger signal, such as the signal transmitted by BTS  104 . MS  112  and BTS  104  establish a new communication link and a signal is sent through BSC  165 , MSC  140 , and BSC  160  to BTS  101  and the public switched telephone network to transfer the on-going voice, data, or control signals through BTS  104 . The call is thereby seamlessly transferred from BTS  101  to BTS  104 . An “idle”handoff is a handoff between cells of a mobile device that is communicating in the control or paging channel, rather than transmitting voice and/or data signals in the regular traffic channels. 
     Wireless network  100  also comprises base station manager (BSM)  150 , which is a central monitoring facility operated by the wireless service provider that operates wireless network  100 . Maintenance personnel (sometimes referred to herein as “the craft”) use BSM  150  to monitor the operation of the various base station controllers, base transceiver subsystems, and the mobile switching center that form wireless network  100 . In addition to its monitoring capabilities, BSM  150  also may control the operations of each of the base station controllers, base transceiver subsystems, and the mobile switching center. This allows the maintenance personnel to reduce or to increase the transmitter power of the base station transmitters, to completely shut down base transceiver substations, to download new operating parameters or new software to base transceiver substations, among other things. Furthermore, BSM  150  may receive automatic failure notifications and status messages from one or more of the base station controllers, the base transceiver subsystems, and the mobile switching center. 
     FIG. 2 illustrates emergency call monitor system  200 , which is associated with, or located in, exemplary base station manager  150 , according to one embodiment of the present invention. Emergency call monitor system  200  comprises call drop controller  205  and memory  210 . Memory  210  comprises call drop application program  215 , maintenance command look-up table (LUT)  220 , and up to “N” call lists, one for each of the base transceiver subsystems in wireless network  100 . The N call lists include exemplary call lists  231 - 234 , which are labeled BTS  101  Call List, BTS  102  Call List, BTS  103  Call List, and BTS N Call List, respectively. 
     The term “controller” as used with respect to call drop controller  205  is broadly defined and may mean any device, system or part thereof that controls at least one operation. Those skilled in the art will recognize that such a device may be implemented in hardware, firmware, or software, or some combination of at least two of the same. Furthermore, the functionality associated with call drop controller  205  may be centralized or distributed, whether locally or remotely. Call drop controller  205  may comprise one or more data processors and associated input/output devices and memory that execute one or more application programs and an operating system program. In particular, call drop controller  205  may be a data processor that executes call drop application program  215 . 
     According to the principles of the present invention, emergency call monitoring system  200  may be located in many different locations in wireless network  100 , such as in BSC  160 , BSC  165 , MSC  140 , or any one of BTS  101 - 107 . Those skilled in the art will understand that the particular implementation of the present invention described hereafter in which emergency call monitor system  200  is associated with exemplary base station manager  150  is illustrative only. 
     Call drop application program  215  is a software program which directs the manner in which call drop controller  205  handles active 911 calls during times of scheduled or failure induced service restriction, such as for scheduled maintenance or in the event of a power amplifier failure, for example. Maintenance command look-up table (LUT)  220  stores various maintenance commands that may be received from maintenance personnel and which may affect communications with mobile stations. Maintenance command LUT  220  also store corrective actions which may be taken in the event that an emergency 911 call is in progress when the maintenance command is received. Each of exemplary call lists  231 - 234  stores a list of calls that are presently in progress for each network base transceiver substation, including information indicating whether or not a particular call is an emergency 911 call. The operation of emergency call monitor system  200  and its various components is described below in greater detail in connection with FIGS. 3 and 4. 
     FIG. 3 depicts flow chart  300 , which illustrates the operation of an emergency call monitor system in response to actions taken by maintenance personnel according to one embodiment of the present invention. During routine maintenance, craft or maintenance personnel at base station manager (BSM)  150  may enter a maintenance command which is transferred to emergency call monitor system  200  (process step  305 ). Call drop controller  205 , under the direction of call drop application program  215 , examines maintenance command look up table (LUT)  220  to determine whether the entered maintenance command is a command which affects call service (process step  310 ). If data in LUT  220  indicates that the entered maintenance command is not a service affecting command, emergency call monitor system  200  forwards the command to the appropriate BTS and/or BSC (process step  315 ). 
     If the entered command does affect service, call drop controller  205  determines whether the command affects service at the base transceiver system (BTS) level or the base system controller (BSC) level (process step  320 ). If the entered command affects service at the BTS level, emergency call monitor system  200  examines call lists associated with the identified BTS for the presence of 911 calls on the cell site served by the BTS, as well as its neighboring cell sites. For example, if BTS  101  is the identified BTS, the service affected cell site is cell site  121 , the neighboring cell sites are cell sites  122  and  124 , and call lists  231 ,  232 , and  234  are examined for the presence of 911 calls (process step  325 ). If no 911 calls are in progress, emergency call monitor system  200  forwards the command to the appropriate BTS and/or BSC (process step  315 ). If one or more 911 calls are in progress for the identified cell sites, emergency call monitor system  200  prevents the maintenance command from being forwarded to the appropriate BTS and/or BSC and sends a 911 resource risk notification to the maintenance personnel as an explanation for why the maintenance command was aborted (process step  330 ). 
     If the entered maintenance command is determined to affect service at the BSC level, emergency call monitor system  200  examines call lists associated with the affected BSC for the presence of 911 calls on cell sites served by the affected and by its neighboring cells. For example, if BSC  160  is the affected BSC, emergency call monitor system  200  checks call lists associated with BTS  101 , BTS  102  and BTS  103 , as well as the call lists for neighboring cell sites, such as BTS  104  and BTS  105 , which are served by BSC  165  (process step  335 ). If no 911 calls are in progress, emergency call monitor system  200  forwards the command to the appropriate BTS and/or BSC (process step  340 ). If one or more 911 calls are in progress, emergency call monitor system  200  prevents the maintenance command from being forwarded to the appropriate BTS and/or BSC and sends a 911 resource risk notification to maintenance personnel as an explanation for why the maintenance command was aborted (process step  330 ). 
     FIG. 4 depicts flow chart  400  which illustrates the operation of an emergency call monitor system in response to automatic failure notifications generated by devices in wireless network  100  according to one embodiment of the present invention. During normal operation, emergency call monitor system  200  may receive from a failing RF resource (for example BTS  101 ) a failure notification, such as a power amplifier failure notice, a base transceiver system failure notice, or the like (process step  405 ). Under the control of call drop application program  215 , emergency call monitor system  200  determines if there are any 911 calls in progress in the cell associated with the failure, i.e. cell site  121  (process step  410 ). 
     If emergency call monitor system  200  determines that a 911 call is in BTS  101  Call List, emergency call monitor system  200  causes base transceiver substations (i.e., BTS  102  in cell site  122  and BTS  104  in cell site  124 ) adjacent to the failed BTS (i.e, BTS  101  in cell site  121 ) to increases transmit power levels. Increasing the power levels in adjacent cells increases the likelihood that the mobile station originating the 911 call (i.e., MS  112 ) will switch to an adjacent BTS with a stronger signal, such as BTS  104  (process step  415 ). Emergency call monitor system  200  also causes BTS  101  to increase its transmission threshold drop (TDROP) value, which is, in turn, transmitted to mobile stations in cell site  121 . Increasing the TDROP value causes a mobile station, such as MS  112 , to drop BTS  101  and move to another BTS sooner (process step  420 ). Emergency call monitor system  200  also causes neighboring base stations (i.e., BTS  102  and BTS  104 ) to decrease their transmission threshold addition (TADD) values. Decreasing TADDs for neighboring cells increases the likelihood that the mobile station with the 911 call, MS  112 , will switch to a neighboring cell site, such as cell site  124  (process step  425 ). As it well known to those skilled in the art, TDROP and TADD are parameter used in code division multiple access (CDMA) wireless networks to set the boundaries (conditions) for performing a handoff. 
     If no 911 calls are indicated by BTS  101  call list  231 , emergency call monitor system  200  examines BTS  102  Call List and BTS  104  Call List to determine if BTS  102  and BTS  104 , which are adjacent to failed cell site  121 , are processing 911 calls (process step  450 ). If emergency call monitor system  200  detects that no 911 calls are in progress in adjacent cell sites  122  and  124 , emergency call monitor system allows the automated recovery procedures to proceed (process step  455 ). 
     If one or more 911 calls are found to be in progress in adjacent cells sites  122  or  124 , emergency call monitor system  200  causes BSC  160  to increase the TDROP values of the failed BTS (i.e., BTS  101  in cell site  121 ) (process step  460 ) and to decrease the TADD values of BTS  102  and BTS  104  in neighboring cell sites  122  and  124  (process step  465 ). Increasing the TDROP value of BTS  121  and decreasing the TADD values of BTS  102  and BTS  104  makes it less likely that the mobile station(s) originating the 911 call(s) will attempt to handoff to BTS  101 . Emergency call monitor system  200  also causes BTS  102  and BTS  104  to increase their transmit power. This further increases the likelihood that the 911 call will be maintained by adjacent cell sites  122  or  124  during the failure period (process step  470 ). 
     In another embodiment, emergency call monitor system  200  may delay selected fault recovery processes in order to maintain call service during periods of peak usage. For example, call drop application program  215 , working in conjunction with LUT  220  and call lists  231 - 234 , may be configured to detect the number of total calls which are in progress in one or more cell sites. Emergency call monitor system  200  may then warn the maintenance personnel when a large number of calls may be dropped if a specific maintenance command is activated for identified cell site(s). IN such an embodiment, maintenance personnel or the system administrator may determine the call traffic conditions under which maintenance action may be made. 
     In another embodiment of the present invention, emergency call monitor system  200  may enhance service for cell sites which have equipment failures during intervals of high traffic. In a further embodiment, emergency call monitor system  200  may allow maintenance personnel to override 911 or peak-traffic maintenance bypasses so that the maintenance process can proceed with alternative craft provided direction. 
     Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.