Abstract:
A method that rapidly and precisely determines the geographical location of areas of high concentration of usage (hot spots) and areas of poor RF frequency reception (dead spots) by measuring the number of failed call attempts, dropped calls and the like and comparing them to the identification of a mobile station and its location are recorded as record at selected points during a call. If a high number of uncompleted calls or dropped calls are recorded, then the base station can use the last known location of the wireless units involved to circumscribe an area in which the hot spot or dead spot occurs.

Description:
FIELD OF THE INVENTION 
     This invention relates to the area of wireless telecommunications networks and, more specifically, to a tool for determining radio frequency coverage trouble spots in cells in a wireless network. 
     BACKGROUND OF THE INVENTION 
     All wireless telecommunications service providers attempt to maximize usage of their networks, provide uninterrupted service for all network users and keep the cost of providing these services to a minimum. There are many tradeoffs involved between the first two goals when compared to the third. One aspect of wireless communications where the tension between these goals may be seen is in radio frequency coverage trouble spots within cells in the wireless network. 
     The geographic region served by a wireless network is divided into a plurality of areas known as “cells”. Each cell includes a base station to provide a radio frequency (RF) connection between the public switched telephone network (PSTN) and wireless stations in the cell. When the geographic region is first divided into cells, the cells are engineered to provide coverage for the anticipated wireless station usage. Further, the cell is engineered to take into account topological aspects of its sub-region, such as tall buildings, highway traffic and geological formations such as mountains. 
     Only when the wireless network is placed into service is the accuracy of the engineering assumptions tested. There may be areas of high usage in the cell that were not anticipated at the time the cell was engineered. Further, there may be dead spots that were unanticipated. The service provider receives complaints regarding inability to place calls (in congested areas) and cutoffs or no response from the wireless system (in the dead spots). The service provider then must send out a specially equipped truck (or several trucks) to determine the location and extent of the problems. In most cases, the service provider adds repeaters or supplemental “micro” or “pico” cells to provide coverage in the hot and dead spots. In many cases, however, additional micro cells to alleviate congestion are frequently over engineered and one (or more) of the micro cells end up lightly loaded. The service provider has thus unnecessarily increased cost while providing modestly improved service. 
     Therefore, a problem in the art is that RF coverage problems within a cell are determined through expensive effort and still may be insufficient or overly sufficient. 
     SUMMARY OF THE INVENTION 
     This problem is solved in technical advances achieved in the art by a system and method that rapidly and precisely determines the geographical area of high concentration of usage (hot spots), areas of poor RF frequency reception (dead spots), and areas of handoff thrashing. The number of failed call attempts, dropped calls land the like, are measured. The identification of a wireless station and its location are recorded at selected points during a call. If a high number of uncompleted, dropped or handed off calls are recorded, then the base station uses the last known location of the wireless stations that report trouble to circumscribe an area in which the hot spot or dead spot occurs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the invention may be obtained from consideration of the following description in conjunction with the drawings in which: 
     FIG. 1 is a block diagram of a wireless communication network, illustrating geographical areas of high usage and low RF reception; 
     FIG. 2 is a block diagram of a wireless communications network illustrating the operation of an exemplary embodiment of this invention; and 
     FIG. 3 is a flowchart of operation according to an exemplary embodiment of this invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a wireless communications network shown generally at  10 , in which an exemplary embodiment of a tool according to this invention may locate radio frequency coverage trouble areas. Wireless network  10  supplies wireless communications within a defined geographical region  12 . Geographical region  12  is subdivided into cells  14 ,  15 ,  16 ,  17 ,  18  and  19 , each of which define a subregion in which radio frequency communication is supported by a single base station  24 ,  25 ,  26 ,  27 ,  28  and  29  (respectively), which provides the RF connection between wireless stations in cells  14 - 19  and wireless network  10 . Speech and/or data received via the RF link is delivered from base stations  24 - 29  through trunks  34 ,  35 ,  36 ,  37 ,  38  and  39  (respectively) to mobile switching center (MSC)  40 . MSC  40  controls and coordinates communications between base stations  24 - 29  in their respective cells  14 - 19  and wireless stations within those cells. MSC  40  also is connected via trunks  42  to the public switched telephone network  44 . Of course, wireless network  10  in practice includes many more cells, base stations and may include multiple MSCs. Further, there may be intermediate nodes between base stations  24 - 29  and MSC  40 . 
     For purposes of describing this exemplary embodiment of this invention, area  46  in cell  18  has a very high call volume represented by wireless stations  48 ,  49 ,  50 ,  51 ,  52  and  53 . Area  46  may include, for example, a busy intersection or airport where wireless telephone use is high. 
     Conversely, area  60  in cell  15  is a “hole” or an area of poor RF reception. In this case, when a wireless station is in or near hole  60 , such as wireless stations  62 ,  63 ,  64  and  65 , they have very poor RF communication or lose the RF connection with base station  35  entirely. A hole such as hole  60  may form in a geographical depression, an area where there are many tall buildings or similar known instances of RF interference. 
     MSC  40  maintains a record of performance characteristics of each of the cell sites  24 - 29 . Such performance characteristics include number of dropped cails, number of call attempts, number of originations, etc. Further, MSC  40  associates the identification of wireless stations with the performance characteristics (i.e., originating idle dropped terminating). Thus, MSC  40  can coordinate the origination drop etc. statistics with individual wireless terminals. 
     One emerging technology is determining the location of a wireless station (in fact the Federal Communications Commission has mandated that by October, 2001, cellular and PCS carriers must be able to locate a mobile phone that is calling for emergency assistance within 125 meters). Such location information may be determined by combining a global positioning system in the wireless station, by triangulation among base stations or by using the information in the signals themselves to determine the location of the wireless station. This location information, when available, is currently associated with the identification of the wireless station, so that, in the case of an emergency, the wireless station may be located quickly. 
     According to this invention, by combining the performance; characteristics of wireless stations with their respective locations, a determination as to the need for supplemental base stations may be readily and rapidly determined. For example, in an area of congestion such as  46 , cell site  28  reports all originations and, in addition, all blockage due to lack of resources. Additionally, MSC has information regarding the call attempts including identification of the wireless station and its location. Therefore, MSC can determine an area within cell  18  where the “hot spot” is located. The hot spot mapped out or a perimeter drawn around a statistical center of the high usage area. In this manner, statistical abnormalities may be eliminated and excess equipment will not be deployed where it is not needed. 
     Likewise, hole  60  may be determined by the last known locations of wireless stations  62 ,  63 ,  64 , and  65  if they move into the hole, the MSC will have a location of the dropped call that can be connected with the dropped call. Taken over time, these statistics will show where the “hole” is located and thus a micro or pico cell may be deployed. 
     Area  70  is on the approximate borders of three cells,  14 ,  16  and  17 . If, for example, wireless stations  72 ,  74  and  76  are moving through the area, or conversely, objects such as trucks which reflect or disrupt wireless communication RF signals pass by, the wireless stations  72 ,  74  and  76  will be handed off among base stations  24 ,  26  and  27  quite rapidly. By tracking such handoffs, a location of handoff churning such as described above in area  70  may be detected and a repeater or micro cell added that prevents such churning and thus save system resources. 
     FIG. 2 illustrates wireless network  10  after corrective action is taken. Hot spot  46  is now served by a satellite basestation  200 . Satellite basestation  200  may serve part or all of hot spot  46 , depending on traffic patterns. The relative coverage areas of basestation  28  and satellite basestation  200  may be fine tuned using traffic patterns derived according to the teachings of this invention. In this manner, wireless stations  48 - 53  now all receive service, while the operating company could pinpoint the trouble spot without large expenditures of time and money. 
     Likewise, satellite basestation  202  serves deadspot  60 . All wireless stations  62 - 65  receive service from either basestation  25  or  202 . Satellite basestation  204  may relieve handoff thrashing. When a wireless station such as  72 - 74  enters the service area  70  of satellite basestation  204 , it is handed over once, and then not handed over again until the wireless station  72 - 74  is clearly in one of the surrounding cells  14 ,  16  or  47 . 
     Turning now to FIG. 3, a flowchart of processing according to one aspect of this invention is shown. Processing starts in box  300  where a cell is selected for measurement and moves to box  302 , where a determination is made on the number of calls that have been dropped (or attempted or handed off) by the base station within a predetermined time. By determining the number of calls dropped over a time period, prevents statistical abnormalities from triggering corrective action. Processing moves to decision diamond  304  where the number is compared to a threshold. If the number is below the threshold, processing proceeds to box  306  where the next cell is selected. In decision diamond  304 , if the number is above the threshold, then it is possible a hole has been identified in the area. Processing moves to box  308 , where an approximate location of each wireless station is determined when the call was dropped and is interpolated into a boundary of a region of a dead zone (or hot spot) within a cell. The system can then forward this information to a maintenance center or conversely a program according to this invention may be run manually or automatically from the MSC when trouble reports have been made in box  310 . Processing continues to box  306  where the next cell is selected. 
     It is to be understood that the above-described embodiment is merely an illustrative principle of the invention, and that many variations may be devised by those skilled in the art without departing from the scope of this invention. It is, therefore, intended that such variations be included within the scope of the claims.