Abstract:
In a mobile station capable of accessing a wireless network, an apparatus for reporting call drop (or service loss) location information associated with the mobile station to a server accessible via a communication network coupled to the wireless network. The apparatus comprises: 1) a memory capable of storing mobile station current position information; and 2) a controller, coupled to the memory, capable of determining a geographic location of the mobile station at the time an ongoing call is dropped by the mobile station (or a service loss occurs) and storing the geographic location in the memory, wherein the controller is further capable of establishing a connection with the server at a later point in time and transmitting the geographic location over the wireless network to the server.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    The present invention is directed, in general, to wireless networks and, more specifically, to a system for identifying coverage holes in a wireless network.  
         BACKGROUND OF THE INVENTION  
         [0002]    Wireless communication systems, including cellular phones, paging devices, personal communication services (PCS) devices, and wireless data networks, have become ubiquitous in society. The prices of end-user wireless devices, such as cell phones, pagers, PCS systems, and wireless modems, have been driven down to the point where these devices are affordable to nearly everyone and the price of a wireless device is only a small part of the total cost to the end-user. To continue to attract new customers, wireless service providers concentrate on reducing infrastructure costs and operating costs, while improving quality of service in order to make wireless services cheaper and better.  
           [0003]    One of the key service quality issues of any wireless network is providing complete and reliable radio frequency (RF) coverage. This is accomplished by eliminating (or at least minimizing) the number of RF “holes” in the geographical area of the wireless network. A hole is an area in which the RF signals from the base station or from the mobile station are blocked by terrain, buildings, vegetation, or any other object. When a wireless device (or mobile station) that is idle, but turned ON, moves into a RF hole, service may be lost (i.e., the mobile station is dropped) because the mobile station cannot receive the pilot channel signal, the paging channel signal, the synchronization channel signal, or other control channel signal. The mobile station must reacquire the wireless network when the mobile station moves out of the RF hole. If the mobile station is ON and active (i.e., handling a voice call or an Internet protocol (IP) data call), the mobile station may drop the call because the forward or reverse traffic channel signal is blocked.  
           [0004]    Wireless services providers routinely monitor their wireless networks in order to detect RF holes. Wireless service providers have primarily relied on drive-testing, which uses specialized vehicles to determine coverage holes in the wireless network. Drive-testing is first performed during network launch and is then periodically repeated, depending on the operational plan of the service provider. The periodic tests are necessary to ensure no coverage holes have developed due to change in the terrain (new buildings) and changes in RF parameters in the system. Obviously, the more comprehensive and frequent such tests are, the quicker and more accurate will be the corrective actions of the service provider. However, such specialized tests are expensive to service providers.  
           [0005]    During the past few years, pushed by the mobile E-911 effort, advanced location services have been defined to accurately determine the location of mobiles in times of emergency. The solutions for these location services can be mainly categorized into handset-based or network-based. Service providers can try to make use of these location services to determine coverage holes instead of drive tests. Network-based location determination requires that the mobile station location determination circuitry be positioned on network elements (e.g., base stations) in order to correlate power and round-trip delay information from various base stations. Unless the wireless service provider continuously monitors the location of all mobile stations, it is difficult to use that information to determine coverage holes. Also, continually monitoring the positions of all mobile stations consumes an excessive amount of RF bandwidth and processing power in the base stations. Furthermore, network-based location devices determine mobile station location using principles of extrapolation that often prove inaccurate.  
           [0006]    Therefore, there is a need in the art for improved systems and methods for determining RF coverage holes in a wireless network. In particular, there is a need for an improved apparatus for determining the location of RF coverage holes in a wireless network that does not require the wireless network to continually monitor the positions of all mobile stations and does not required all mobile stations to continually transmit their position information to the wireless network.  
         SUMMARY OF THE INVENTION  
         [0007]    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 mobile station capable of accessing a wireless network, an apparatus for reporting call drop location information associated with the mobile station to a server accessible via a communication network coupled to the wireless network. According to an advantageous embodiment of the present invention, the apparatus comprises: 1) a memory capable of storing mobile station current position information; and 2) a controller, coupled to the memory, capable of determining a geographic location of the mobile station at the time an ongoing call is dropped by the mobile station and storing the geographic location in the memory, wherein the controller is further capable of establishing a connection with the server at a later point in time and transmitting the geographic location over the wireless network to the server.  
           [0008]    According to one embodiment of the present invention, the controller is further capable of determining a drop time at which the ongoing call is dropped by the mobile station and storing the drop time in the memory, wherein the controller is further capable of transmitting the drop time over the wireless network to the server.  
           [0009]    According to another embodiment of the present invention, the apparatus further comprises a Global Positioning System (GPS) device coupled to the controller, wherein the controller determines the geographic location and the drop time using the GPS device.  
           [0010]    According to still another embodiment of the present invention, the controller is further capable of encrypting the geographic location and the drop time prior to transmission to the server.  
           [0011]    It is another primary object of the present invention to provide, for use in a mobile station capable of accessing a wireless network, an apparatus for reporting service loss location information associated with the mobile station to a server accessible via a communication network coupled to the wireless network. According to an advantageous embodiment of the present invention, the apparatus comprises: 1) a memory capable of storing mobile station current position information; and 2) a controller, coupled to the memory, capable of determining a geographic location of the mobile station at the time a control channel is lost by the mobile station and storing the geographic location in the memory, wherein the controller is further capable of establishing a connection with the server at a later point in time and transmitting the geographic location over the wireless network to the server.  
           [0012]    In one embodiment of the present invention, the controller is further capable of determining a service loss time at which the ongoing call is dropped by the mobile station and storing the service loss time in the memory, wherein the controller is further capable of transmitting the service loss time over the wireless network to the server.  
           [0013]    In another embodiment of the present invention, the apparatus further comprises a Global Positioning System (GPS) device coupled to the controller, wherein the controller determines the geographic location and the service loss time using the GPS device.  
           [0014]    In still another embodiment of the present invention, the controller is further capable of encrypting the geographic location and the service loss time prior to transmission to the server.  
           [0015]    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.  
           [0016]    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  
       [0017]    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:  
         [0018]    [0018]FIG. 1 illustrates an exemplary wireless network according to one embodiment of the present invention;  
         [0019]    [0019]FIG. 2 illustrates an exemplary wireless mobile station in greater detail according to one embodiment of the present invention;  
         [0020]    [0020]FIG. 3 illustrates an exemplary radio frequency (RF) coverage server in greater detail according to one embodiment of the present invention;  
         [0021]    [0021]FIG. 4 is a message flow diagram illustrating the operation of a mobile station and a base station during a call drop according to an exemplary embodiment of the present invention; and  
         [0022]    [0022]FIG. 5 is a message flow diagram illustrating the operation of a mobile station and a base station during a service loss according to an exemplary embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    [0023]FIGS. 1 through 5, 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.  
         [0024]    [0024]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 - 123 , each containing one of the base stations, BS  101 , BS  102 , or BS  103 . Base stations  101 - 103  communicate with a plurality of mobile stations (MS)  111 - 114  over, for example, code division multiple access (CDMA) channels. Mobile stations  111 - 114  may be any suitable wireless devices, including conventional cellular radiotelephones, PCS handset devices, personal digital assistants, portable computers, or metering devices. The present invention is not limited to mobile devices. Other types of access terminals may be used. However, for the sake of simplicity, only mobile stations are shown and discussed hereafter.  
         [0025]    Dotted lines show the approximate boundaries of the cell sites  121 - 123  in which base stations  101 - 103  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.  
         [0026]    As is well known in the art, cell sites  121 - 123  are comprised of a plurality of sectors (not shown), each sector being illuminated by a directional antenna coupled to the base station. The embodiment of FIG. 1 illustrates the base station in the center of the cell. Alternate embodiments position the directional antennas in corners of the sectors. The system of the present invention is not limited to any one cell site configuration.  
         [0027]    In one embodiment of the present invention, BS  101 , BS  102 , and BS  103  comprise a base station controller (ESC) and one or more base transceiver subsystem(s) (BTS). Base station controllers and base transceiver subsystems 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 stations, 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. For the purpose of simplicity and clarity in explaining the operation of the present invention, the base transceiver subsystem in each of cells  121 ,  122 , and  123  and the base station controller associated with each base transceiver subsystem are collectively represented by BS  101 , BS  102  and BS  103 , respectively.  
         [0028]    BS  101 , BS  102  and BS  103  transfer voice and data signals between each other and the public switched telephone network (PSTN) (not shown) via communications line  131  and mobile switching center MSC)  140 . Line  131  also provides the connection path to transfers control signals between MSC  140  and BS  101 , BS  102  and BS  103  used to establish connections for voice and data circuits between MSC  140  and BS  101 , BS  102  and BS  103 .  
         [0029]    Communications line  131  may be any suitable connection means, including a T1 line, a T3 line, a fiber optic link, a network packet data backbone connection, or any other type of data connection. Line  131  links each vocoder in the BSC with switch elements in MSC  140 . Those skilled in the art will recognize that the connections on line  131  may provide a transmission path for transmission of analog voice band signals, a digital path for transmission of voice signals in the pulse code modulated (PCM) format, a digital path for transmission of voice signals in an Internet Protocol (IP) format, a digital path for transmission of voice signals in an asynchronous transfer mode (ATM) format, or other suitable connection transmission protocol. Those skilled in the art will recognize that the connections on line  131  may a provide a transmission path for transmission of analog or digital control signals in a suitable signaling protocol.  
         [0030]    MSC  140  is a switching device that provides services and coordination between the subscribers in a wireless network and external networks, such as the PSTN or Internet  190 . MSC  140  is well known to those skilled in the art. In some embodiments of the present invention, communications line  131  may be several different data links where each data link couples one of BS  101 , BS  102 , or BS  103  to MSC  140 . Alternatively, BS  101 , BS  102  and BS  103  may transfer voice and data signals directly with Internet  190  via network communications line  132 , thereby bypassing mobile switching center MSC)  140 .  
         [0031]    In the exemplary wireless network  100 , MS  111  is located in cell site  121  and is in communication with BS  101 . MS  113  is located in cell site  122  and is in communication with BS  102 . MS  114  is located in cell site  123  and is in communication with BS  103 . MS  112  is also located close to the edge of cell site  123  and is moving in the direction of cell site  123 , as indicated by the direction arrow proximate MS  112 . At some point, as MS  112  moves into cell site  123  and out of cell site  121 , a hand-off will occur.  
         [0032]    As is well known, the hand-off procedure transfers control of a call from a first cell site to a second cell site. As MS  112  moves from cell  121  to cell  123 , MS  112  detects the pilot signal from BS  103  and sends a Pilot Strength Measurement Message to BS  101 . When the strength of the pilot transmitted by BS  103  and received and reported by MS  112  exceeds a threshold, BS  101  initiates a soft hand-off process by signaling the target BS  103  that a handoff is required as described in TIA/EIA IS-95 or TIA/EIA IS-2000.  
         [0033]    BS  103  and MS  112  proceed to negotiate establishment of a communications link in the CDMA channel. Following establishment of the communications link between BS  103  and MS  112 , MS  112  communicates with both BS  101  and BS  103  in a soft handoff mode. Those acquainted with the art will recognize that soft hand-off improves the performance on both forward (BS to MS) channel and reverse (MS to BS) channel links. When the signal from BS  101  falls below a predetermined signal strength threshold, MS  112  may then drop the link with BS  101  and only receive signals from BS  103 . The call is thereby seamlessly transferred from BS  101  to BS  103 .  
         [0034]    Wireless network  100  further comprises radio frequency (RF) coverage server  195 , which is used to detect RF holes in the RF coverage area of wireless network  100 , including cell sites  121 - 123 . According to the principles of the present invention, the wireless service provider that operates wireless network  100  distributes to some (and perhaps all) of its subscribers specially-equipped mobile stations (e.g., cell phones). Each of the specially-equipped mobile stations is equipped with a Global Positioning System (GPS) device that enables the mobile station to rapidly determine its position in the event that a call is dropped or service is dropped. This GPS information is the geographical position of the mobile station at the time the call was dropped or service was lost.  
         [0035]    When service is restored, the mobile station establishes a session with RF coverage server  195  and relays the GPS position and/or time information to RF coverage server  195 . Over time, RF coverage server  195  builds up a database of service drop/call drop position information only from those phones that actually experience a call or service drop. This information is used to establish a map of the coverage area of wireless network  100  that illustrates the location of RF coverage holes.  
         [0036]    [0036]FIG. 2 illustrates exemplary wireless mobile station  111  in greater detail according to one embodiment of the present invention. Wireless mobile station  111  comprises antenna  205 , radio frequency (RF) transceiver  210 , transmitter (TX) processing circuitry  215 , microphone  220 , receiver (RX) processor circuitry  225 , speaker  230 , main processor  240 , input/output (I/O) interface (IF)  245 , keypad  250 , display  255 , and position locator  260 , which may be, for example, a global positioning system (GPS) receiver. Wireless mobile station  111  further comprises memory  270 , that stores basic operating system (OS) program  271 , drop location data file  281 , encryption-decryption key(s) file  282 , encryption-decryption application program  283 , and MS location server access application program  284 . Drop location data file  281  comprises drop type field  291  and GPS position/time field  292 .  
         [0037]    Wireless mobile station  111  may be a cell phone, a personal digital assistant (PDA) device equipped with a wireless modem, a two-way pager, a personal communication system (PCS) device, or any other type of wireless mobile station.  
         [0038]    RF transceiver  210  receives, from antenna  205 , an incoming RF signal transmitted by a base station of a wireless communication network. RF transceiver  210  down-converts the incoming RF signal to produce an intermediate frequency (IF) or a baseband signal. The IF or baseband signal is sent to RX processing circuitry  225  that produces a processed baseband signal by filtering, decoding, and/or digitizing the baseband or IF signal to produce a processed baseband signal. RX processing circuitry  225  transmits the processed baseband signal to speaker  230  (i.e., voice data) or to main processor  240  for further processing (i.e., web browsing).  
         [0039]    TX processing circuitry  215  receives analog or digital voice data from microphone  220  or other outgoing baseband data (i.e., web data, e-mail, interactive video game data) from main processor  240 . TX processing circuitry  215  encodes, multiplexes, and/or digitizes the outgoing baseband data to produce a processed baseband or IF signal.  
         [0040]    RF transceiver  210  receives the outgoing processed baseband or IF signal from TX processing circuitry  215 . RF transceiver  210  up-converts the baseband or IF signal to an RF signal that is transmitted via antenna  205 .  
         [0041]    Main processor  240  may be implemented as a microprocessor or microcontroller. Main processor  240  executes basic OS program  271  in order to control the overall operation of wireless mobile station  111 . In one such operation, main processor  240  controls the reception of forward channel signals and the transmission of reverse channel signals by RF transceiver  210 , RX processing circuitry  225 , and TX processing circuitry  215 , in accordance with well known principles. Main processor  240  is also capable of controlling and/or interfacing with position locator  260  in order to transfer the location of MS  111  to memory  270 .  
         [0042]    Main processor  240  is capable of executing other processes and programs that are resident in memory  270 . Main processor  240  can move data into or out of memory  270 , as required by an executing process. Main processor  240  is also coupled to I/O interface  245 . I/O interface  245  provides the mobile station with the ability to connect to other devices such as laptop computers and handheld computers. I/O interface  245  is the communication path between these accessories and main controller  240 .  
         [0043]    Main processor  240  is also coupled to keypad  250  and display unit  255 . Keypad  250  is used by the end-user of the mobile station to enter data into the mobile station. Display  255 , in the preferred embodiment, is a liquid crystal display capable of rendering text and/or at least limited graphics from Web sites. Alternate embodiments use other types of displays.  
         [0044]    Memory  270  is coupled to main processor  240 . Memory  270  may be comprised of solid-state memory such as random access memory (RAM), various types of read only memory (ROM), or Flash RAM. Memory  270  may also include other types of memory such as micro-hard drives or removable storage media that stores data. Memory  270  stores basic operating system  271  that provides the basic operational control of mobile station  111 . Drop location data file  281  indicates the location and time of mobile station  111  at the time that service and/or a call was dropped.  
         [0045]    Memory  270  also stores encryption-decryption key(s)  282  that are used to transfer position location information in drop location data file  281  to BS  101  and RF coverage server  195 . The use of encryption-decryption keys enables the mobile station to transmit its location securely over-the-air and through public data networks.  
         [0046]    Memory  270  also stores RF coverage server access application program  284 , which enables MS  111  to transfer position data to RF coverage server  195  in FIG. 1. RF coverage server access application program  284  may be an e-mail program, a Transmission Control Protocol/Internet Protocol (TCP/IP) program, a User Datagram Protocol (UDP) program, a short messaging service (SMS) program, a CDMA data burst program, or any combination of these programs. These various types of communication programs are for illustration purposes only. The present invention is not limited to any one type or combination of server access programs.  
         [0047]    [0047]FIG. 3 illustrates exemplary radio frequency (RF) coverage server  195  in greater detail according to one embodiment of the present invention. RF coverage server  195  comprises data processor  305  and memory  310 . Data processor  305 , in one embodiment, is a microprocessor or microcontroller. Other embodiments use other types of controllers, such as parallel processors, for greater processing power. Data processors are well known in the art and are not discussed further.  
         [0048]    Memory  310  may be comprised of solid-state memory such as random access memory (RAM), various types of read only memory (ROM), or Flash RAM. Memory  310  may also include other types of memory such as micro-hard drives or removable storage media that stores data.  
         [0049]    Memory  310  is coupled to data processor  305  and stores basic operating system  320 , RF coverage server application program  330 , mobile station interface (IF) application program  340 , mobile station database  350 , and RF coverage map  380 . Mobile station database  350  contains N mobile station records, including exemplary mobile station records  360 ,  370  and  380 , which are arbitrarily labeled MS1 Record, MS2 Record, and MSn Record, respectively. Exemplary mobile station record  360  contains MS1 drop data field  361 , and encryption-decryption key(s)  363 . MS drop data field  361  contains the geographic location and time information for a particular mobile station (e.g., MS  111 ). Exemplary mobile station records  370  and  380  contain similar data fields.  
         [0050]    Basic operating system  320  is run by data processor  305  in order to control the overall operation of the location server. RF coverage server application program  330  is responsible for securely gathering location information from mobile stations that have dropped calls or lost service and generating therefrom RF coverage map  380 , which identifies RF coverage holes in wireless network  100 . According to one embodiment of the present invention, RF coverage map  380  may be a simple two dimensional map showing dots, squares, or other icons that represent the locations of mobile stations at the time of a service loss or call drop. The map may illustrate drop location data gathered over an entire extended time period, such as a month, a week, or a day.  
         [0051]    Alternatively, RF coverage map  380  may comprise multiple two dimensional maps for certain times of day, such as a first map that shows drop location data for the time period between 12 AM and 1 AM on a particular day, a second map that shows drop location data for the time period between 1 AM and 2 AM on the same day, a third map that shows drop location data for the time period between 2 AM and 3 AM on the same data, and so forth. Also, the maps may cover multiple days. For example, the first map may show drop location data for the time period between 12 AM and 1 AM for every day for an entire month.  
         [0052]    Mobile station IF application program  340  communicates with RF coverage server access application program  284  in MS  111  in order to receive drop location data from MS  111 . Mobile station IF application program  340  may comprise an e-mail program (e.g., EUDORA), a Transmission Control Protocol/Internet Protocol (TCP/IP) program, a User Datagram Protocol (UDP) program, a short messaging service (SMS) program, a CDMA data burst program, or any combination of these programs. These various types of communication programs are for illustration purposes only. The present invention is not limited to any one type or combination of server access programs.  
         [0053]    According to an advantageous embodiment of the present invention, MS  111  and BS  101  may utilize new parameters in the Extended System Parameters message (Base Station-to-Mobile Station Paging Channel message) and in the Registration message in order to relay exact location and time information of MS  111  in the event of a call drop or a service loss. The present invention thus provides an efficient mechanism to report the call drop location and time information to RF coverage server  195  via the appropriate messaging, in the event of a call drop or service failure due to a coverage hole in wireless network  100 . This enables the network operator to pinpoint the exact location of a call drop or service failure, thereby facilitating collection of valuable data to determine RF holes in wireless network  100 .  
         [0054]    The present invention greatly reduces the required efforts of wireless service providers to improve service coverage and to reduce dropped calls. Advantageously, the base station is not required to continually request location information from all mobiles, which is highly inefficient. The present invention discloses an efficient mechanism for identifying coverage holes with minimum additional impact on air-interface.  
         [0055]    The invention may utilize intelligent triggers in the air-interface:  
         [0056]    1. Two new trigger bits, REPORT SERVICE LOSS and REPORT CALL DROP are defined in the Extended System Parameters message and in-traffic system parameters message,  
         [0057]    2. When REPORT SERVICE LOSS is set to True (e.g., Logic 1) for the current cell, if the mobile is idle and it loses service (pilot channel/sync channel/paging channel/access trouble), the mobile station stores the service loss location and time. This information should not be overwritten until it is reported to the base station.  
         [0058]    3. When REPORT CALL DROP is set to True for the current cell, if the mobile is in a call and a call drops due to RF signal failure, the mobile station stores the call failure location and time. This information should not be overwritten until it is reported to the base station.  
         [0059]    4. Usually, a mobile station loses service or a call, the mobile station tries to re-acquire the system. In doing so, the mobile station can send a registration message with additional information: which event (call drop/pilot signal/sync signal/paging signal/access failure) occurred, event location, and event time.  
         [0060]    5. Field registration type (REG TYPE) in registration message is modified to include SERVICE RECONNECT as a new reason. Every time after the mobile station acquires the system, the mobile station should complete its regular registration processing, then send another registration message with the SERVICE RECONNECT reason, if it has stored an unreported call drop event or service loss event. For example, the following fields may be used in the registration message: integer event type (0=call drop, 1=pilot lost, 2=sync error, 3=paging error, 4=access failure, etc.), appropriate type to specify the event time, and an appropriate type to report the GPS location where the event happened.  
         [0061]    [0061]FIG. 4 depicts message flow diagram  400 , which illustrates the operation of mobile station  111  and base station  101  during a call drop according to an exemplary embodiment of the present invention. Initially, MS  111  has already accessed BS  101 . BS  101  transmits control message  405  with REPORT CALL DROP set to Logic 1 (True). This alerts MS  111  to report call drop events. At time T1, MS  111  establishes a call (i.e., Call origination) with BS  101 . At time T2, MS  111  enters an RF coverage hole and MS  111  drops the call (i.e., Call Drop) with BS  101 . At time T3, MS  101  leaves the RF coverage hole and MS  111  reacquires (Reacq.) BS  101  (or some other base station). MS  111  then transmits special registration message  410  that reports the call drop event, location, and time.  
         [0062]    [0062]FIG. 5 depicts message flow diagram  500 , which illustrates the operation of mobile station  111  and base station  101  during a service loss according to an exemplary embodiment of the present invention. Initially, MS  111  has already accessed BS  101 . BS  101  transmits control message  505  with REPORT SERVICE LOSS set to Logic 1 (True). This alerts MS  111  to report service loss events. At time T1, MS  111  enters an RF coverage hole and MS  111  loses service with BS  101  by losing one of the control channels (e.g., pilot, page, sync). At time T2, MS  101  leaves the RF coverage hole and MS  111  reacquires (Reacq.) BS  101  (or some other base station) MS  111  then transmits special registration message  510  that reports the service loss event, location, and time.  
         [0063]    Advantageously, a service provider is not required to implement GPS position locator  260 , drop location data file  281 , and RF coverage server access application program  284  in every mobile station distributed to subscribers of wireless network  100 . The present invention may adequately identify coverage holes in wireless network  100  even if only a subset of subscribers use mobile stations (i.e., cell phones) that are equipped according to the principles of the present invention. The wireless service provider need only ensure that an adequate number of phones are so equipped in order to obtain a good sampling of the RF coverage holes in wireless network  100 . For example, if a wireless service provider has 200,000 subscribers in a certain metropolitan area (e.g., Dallas, Tex.), the wireless service provider may distribute, for example, 1,000, 5,000, or 10,000 mobile stations that are equipped as shown in FIG. 2 and according to the principles of the present invention. These mobile stations would then be used to identify holes in the RF coverage of wireless network  100 .  
         [0064]    Moreover, out of the subset of mobile stations that are equipped according to the principles of the present invention, the wireless service provider may further reduce the number of mobile stations that are reporting RF coverage holes by selectively enabling the present invention in only some of the equipped mobile stations. As explained in FIGS. 4 and 5, the equipped mobile stations only report a service loss event or a call drop event if the trigger bits REPORT SERVICE LOSS and REPORT CALL DROP, respectively, are enabled. If the service provider does not set these trigger bits as described with respect to FIGS. 4 and 5, then the mobile stations do not report service loss events or call drop events.  
         [0065]    It should also be noted that the present invention may operate in the reverse manner by disabling the trigger bits REPORT SERVICE LOSS and REPORT CALL DROP. In other words, when a mobile station is powered ON, it may be enabled, by default, to report service loss events and call drop events. The trigger bits REPORT SERVICE LOSS and REPORT CALL DROP may then be used to disable (i.e., turn OFF) the reporting of service loss events or call drop events.  
         [0066]    Although the present invention has been described in detail, those skilled in the art should understand that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.