Abstract:
Method and apparatus for creating and using a database containing automated measurements to pin point cell sites and sectors with antenna-related problems are disclosed. Each base station in a wireless communications network is equipped with a site test mobile (“STM”) connected to the antenna(s) for the cell site. A database contains information regarding the location (latitude and longitude) of every cell site, or base station, and the design type, orientation, patterns (vertical and horizontal), and gain for every antenna in the network by sector. Automated measurements of various transmission parameters are periodically taken using the respective STMs and compared with calibration data stored in the database to determine the location and type of antenna problems that exist in the network.

Description:
TECHNICAL FIELD 
     The invention relates generally to wireless communications networks and, more particularly, to a method for locating antenna problems in a wireless communications network. 
     BACKGROUND OF THE INVENTION 
     The performance of various radio frequency (“RF”) links in a wireless communications network is a critical differentiator in providing a competitive advantage; therefore, it is very important to be able quickly and efficiently to identify factors that contribute to poor RF link performance. 
     Certain performance problems can be identified using operational and maintenance statistics taken from measurements that the network takes periodically to isolate equipment-related problems. Once a problem is isolated to a particular location, a network engineer or technician is sent out to manually collect additional data in the identified area using, for example, a test vehicle equipped with the necessary equipment. Subsequently, the collected data must be analyzed to isolate specific problems. In most cases, this involves physically doing measurements to identify the antenna problem. 
     In terms of optimizing both analog and digital wireless communications networks, it is well known that antenna-related issues are a significant contributor to performance degradation. Two major antenna problems, i.e., bad antennas and incorrectly-oriented antennas, are not generally identifiable by visual inspection. Bad receive (“Rx”) antennas are especially difficult to locate. Given the cost and resource involvement in optimization, significant cost and resource savings could be realized if antenna-related network performance problems could be easily identified. Clearly, at present it is difficult and costly to identify and isolate antenna-related problems in a wireless communications network. 
     In view of the foregoing, what is needed are a method and apparatus for locating antenna-related problems in a wireless communications network in a timely, efficient and cost-effective manner so that the problems can be corrected before they are too serious. 
     SUMMARY OF THE INVENTION 
     One embodiment of the invention, accordingly, is a method and apparatus for pinpointing cell sites and sectors with antenna-related problems are disclosed. Each base station in a wireless communications network is equipped with a site test mobile (“STM”) connected to the antenna(s) for the cell site. A database contains information regarding the location (latitude and longitude) of every cell site, or base station, and the design type, orientation, patterns (vertical and horizontal), and gain for every antenna in the network by sector. Automated measurements of various transmission parameters are periodically taken using the respective STMs and compared with calibration data stored in the database to determine the location and type of antenna problems that exist in the network. 
     A technical advantage achieved with the invention is that it is much more cost- and resource-effective than current methods of locating antenna-related problems in a wireless communications network. 
     Another technical advantage achieved with the invention is that it is capable of tracking trends, which information is useful in preventing future problems. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a system block diagram of a cellular wireless communications network embodying features of the present invention. 
     FIGS. 2A and 2B, respectively, are a plan view and an elevational view of a typical pair of cell sites of the network of FIG.  1 . 
     FIG. 3 is a flowchart of the operation of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a system block diagram of a cellular wireless communications network  10  embodying features of the present invention. As shown in FIG. 1, the network  10  comprises a plurality of cell sites, represented in FIG. 1 by cell sites C 1  and C 2 , each of which may be subdivided into a plurality of sectors S 1 , S 2 , and S 3 , and S 4 , S 5 , and S 6 , respectively. Each cell site C 1 , C 2 , comprises a base station BS 1 , BS 2 , respectively, the primary function of which is to provide over-the-air RF communication with mobile units, such as a mobile unit  12 . The base stations BS 1 , BS 2 , are further connected via a link to a base station controller (“BSC”)  18 , which is in turn connected to a mobile switching center (“MSC”)  20 . As will be described in greater detail with reference to FIGS. 2A and 2B, antennas for communicating with the mobile unit  12  are provided at each of the cell sites C 1 , C 2 . In particular, each sector S 1 -S 6  has associated therewith at least two antennas, including one Tx/Rx duplexed antenna and one Rx only. Alternatively, there may be three antennas, including two Rx and one Tx. The antennas for each sector are represented in FIGS. 2A and 2B as a single antenna. 
     Additionally, in accordance with a feature of the present invention, each base station BS 1 , BS 2 , is equipped with a site test mobile STM 1 , STM 2 , respectively, for communicating with other base stations, as will be described. Each site test mobile STM 1 , STM 2 , is connected to the antennas located at the respective base station BS 1 , BS 2 , so that it is capable of measuring the signal transmitted at the antenna. The site test mobile at each cell site is common to all of the sectors of that cell site and can be switched between sectors. A database  26  is provided at the BSC  18  for purposes that will also be described in greater detail below. 
     The MSC  20  connects the entire network  10  to a public switched telephone network (“PSTN”)  24  via a land line  27 . As the individual components of the network  10 , as well as the PSTN  24 , are well known in the art, the details thereof will not be further described, except as necessary to impart a complete understanding of the present invention. 
     FIGS. 2A and 2B are a plan view and an elevation view, respectively, of the pair of adjacent cell sites C 1  and C 2 . It will be recognized that for each of the cell sites C 1 , C 2 , the arrows designated S 1 -S 6  represent the optimal or desired direction of the antenna for the respective cell site/sector, as described below. As shown in FIG. 2A, the cell site C 1  is centered at coordinates (x C1 , y C1 ) with a sector S 1  antenna Ant 1   C1  (FIG. 2B) directed toward the cell site C 2  and having an orientation of angle α1 C1  from true north N and a gain G 1   C1 . Similarly, cell site C 2  is centered at coordinates (x C2 , y C2 ) with a sector S 6  antenna Ant 6   C2  (FIG. 2B) directed toward the cell site C 1  and having an orientation of angle α6 C2  and a gain G 6   C2 . It will be assumed, for the sake of example, that the antennas Ant 1   C1  and Ant 6   C2  have respective heights of H 1   C1  and H 6   C2 , respectively, as best shown in FIG.  2 B. Angles θ1 and θ2 (FIG. 2A) will be discussed in greater detail below. 
     An initial measurement is taken for a pair of sites, such as the sites C 1  and C 2 , at the time of commissioning of the network, for new networks, or during a routine maintenance period for calibration purposes, for existing networks. Thereafter, measurements are automated and carried out during the network&#39;s least busy time, which is usually at night, for each pair of “neighbor” sectors, as determined by the database  26  entries for each site. Simultaneous measurements, with both cell sites transmitting and receiving at the same time, are taken from both sectors under consideration, to minimize variations due to unequal propagation conditions. Given below are the format of the cell site database  26  entries and the flowchart for the decision-making algorithm. There will be two tables maintained in the database  26  for every cell site. Table 1 will contain the calibration (i.e., fixed) information from the time of calibration and Table 2 will contain information updated real time, from automated measurements. The format of Table 2 is identical to that of Table 1, except that the information contained in Table 2 is changing real time. For example, the value M 1   C1,Nn , gives the site test mobile STM 1  measurement of cell site C 1 , sector S 1 , taken with a neighbor cell Nn transmit/receive (Tx/Rx) antenna. This involves one Rx antenna of cell site C 1 , sector S 1 , and a Tx/Rx (duplexed) antenna of a neighbor cell Nn, e.g., cell site C 2 , sector S 6 . As used herein, a “neighbor” is a cell site/sector combination that has an antenna that is optimally directed toward the antenna of the cell site/sector combination under consideration. 
     The aforementioned simultaneous measurement from the site test mobile STM 2  of cell site C 2 , sector S 6 , will test the other Rx antenna of the cell site C 2 , sector S 6 , and the Tx/Rx (duplexed) antenna of cell site C 1 , sector S 1 . The azimuth and elevation antenna patterns will reference to a lookup table such as that shown in Table 1 below: 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 EXAMPLE 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Cell Site No.: 
                 C1 
                   
                   
               
               
                 Location: 
                 (x C1 , y C1 ) 
               
               
                   
                 Sector S1 
                 Sector S2 
                 Sector S3 
               
               
                 Antenna Type: 
                 Ant1 C1   
                 Ant2 C1   
                 Ant3 C1   
               
               
                 Pattern Elevation: 
                 Table E1 C1   
                 Table E2 C1   
                 Table E3 C1   
               
               
                 Pattern Azimuth: 
                 TableA1 C1   
                 TableA2 C1   
                 TableA3 C1   
               
               
                 Antenna Orientation: 
                 α1 C1   
                 α2 C1   
                 α3 C1   
               
               
                 Antenna Height: 
                 H1 C1   
                 H2 C1   
                 H3 C1   
               
               
                 Receive Antenna Gain: 
                 G1 C1, Rx   
                 G2 C1, Rx   
                 G3 C1, Rx   
               
               
                 Effective Isotropic 
                 P1 C1, Tx   
                 P2 C1, Tx   
                 P3 C1, Tx   
               
               
                 Radiated Power 
               
               
                 (“EIRP”) 
               
               
                 (Transmit Antenna) 
               
               
                 (dB): 
               
               
                 Rx Antenna Path Loss 
                 L1 C1   
                 L2 C1   
                 L3 C1   
               
               
                 (dB): 
               
               
                 N1: 
                 M1 C1, N1   
                 M2 C1, N1   
                 M3 C1, N1   
               
               
                 N2: 
                 M1 C1, N2   
                 M2 C1, N2   
                 M3 C1, N2   
               
               
                 . 
                 . 
                 . 
                 . 
               
               
                 . 
                 . 
                 . 
                 . 
               
               
                 . 
                 . 
                 . 
                 . 
               
               
                 Nn 
                 M1 C1, Nn   
                 M2 C1, Nn   
                 M3 C1, Nn   
               
               
                   
               
             
          
         
       
     
     Using the angle (θ1-α1 C1 ) and the lookup value from the antenna Ant 1   C1  azimuth table, the gain of the antenna Ant 1   C1  azimuth pattern in the direction of the cell site C 2  is determined. Similarly, the gain of the antenna Ant 1   C1  elevation pattern in the direction of the cell site C 2  is determined using θ2 and the lookup value from the antenna Ant 1   C1  elevation table. θ1 and α2 for the pair cell site C 1 , sector S 1 , and cell site C 2 , sector S 6 , are given by: 
     
       
         θ1=tan −1 [( X   C2   -X   C1 )/( Y   C2   -Y   C1 )] 
       
     
     
       
         θ2=tan −1 [( H   6   C2   -H   1   C1 )/[{( Y   C2   -Y   C1 ) 2 +( X   C2   -X   C1 ) 2 } ½ ] 
       
     
     The azimuth and elevation pattern gains for antenna Ant 6   C2  can be determined in a similar manner. The lookup table gain values for both azimuth and elevation antenna patterns are normalized and the lookup table will provide the reduction from maximum gain for a specific angle. 
     Assuming for the sake of example that the azimuth and elevation gain reductions for the antenna Ant 1   C1  are given by GA 1   C1,Rx , GE 1   C1,Rx , for the receive antenna and GA 1   C1,Tx , GE 1   C1,Tx , for the transmit antenna, that the azimuth and elevation gain reductions for the antenna Ant 6   C2  are given by GA 6   C2,Rx , GE 6   C2,Rx , for the receive antenna and GA 6   C2,Tx , GE 6   C2,Tx , for the transmit antenna, and that the propagation conditions are the same during the simultaneous measurements between cell site C 1 , sector S 1 , and cell site C 2 , sector S 6 , and that the over-the-air path loss is L OA  and that N 1  for cell site C 1 , sector S 1 , is cell site C 2 , sector S 6 , and vice versa: 
     
       
           M   1   C1,N1   ={P   6   C2,Tx −( GA   6   C2,Tx   +GE   6   C2,Tx )} −L   OA   +{G   1   C1,Rx −( GA   1   C1,Rx   +GE   1   C1,Rx )}− L   1   C1,Rx   
       
     
     
       
           M   6   C2,N1   ={P   1   C1,Tx −( GA   1   C1,Tx   +GE   1   C1,Tx )}− L   OA   +{G   6   C2,Rx −( GA   6   C2,Rx   +GE   6   C2,Rx )}− L   6   C2,Rx   
       
     
     The above equations for real time measurements can be compared with calibration measurements to identify any antenna-related issues. The Pi Cj,Tx  terms include the transmission (Tx) antenna gain (Gi Cj,Tx ) for that sector. Bad antennas will have bad gains (Gi Cj,Tx , or Pi Cj,Tx , for Tx antennas and Gi Cj,Rx  for Rx antennas). Problems related to incorrect orientation will be associated with gain reduction terms for the respective antennas (i.e., GAi Cj,Tx  and GEi Cj,Tx  for Tx antennas and GAi Cj,Tx  and GEi Cj,Tx  for Receive antennas). For a given sector and its associated neighbors, gain reduction terms will be different due to different angles θ1 i  and θ2 i  for every sector. However, the gain term of sector i (Gi Cj,Tx , Gi Cj,Rx ) will be the same for measurements associated with its neighbors. 
     By comparing measurements for a single sector (i.e., same base station Tx antenna) with multiple neighbors (i.e., multiple STMs), bad antenna, and orientation-related issues could be isolated. A flowchart of an algorithm for implementing the present invention is set forth in FIG.  3 . 
     As shown in FIG. 3, execution begins at step  300 . In step  302 , a cell site and sector are to be tested are selected. In step  304 , a neighbor cell site and sector for the cell site/sector selected in step  302  are selected. For example, referring to FIG. 2, if the cell site/sector selected in step  302  was cell site C 1 , sector S 1 , the neighbor cell site/sector selected in step  304  could be cell site C 2 , sector S 6 . Referring again to FIG. 3, in step  306 , a determination is made whether the network has been calibrated. If not, execution proceeds to step  308  in which calibration measurements are taken. As previously indicated, this calibration will occur at the time of commissioning of the network, for new networks, or during a routine maintenance period for calibration purposes, for existing networks; otherwise, execution proceeds to step  310  in which automated measurements, as described above, are made. 
     Upon completion of step  308  or  310  execution proceeds to step  312 , in which a determination is made whether all of the neighbors have been done. If not, execution returns to step  306 . If in step  312  it is determined that all of the neighbors have been done, execution proceeds to step  314 , in which, for each sector, the measurements are compared with its calibrated pair and all neighbor measurements. In step  315 , a determination is made whether there are orientation problems or gain problems associated with the sector, in the manner described below. If not, execution proceeds to step  316 ; otherwise, execution proceeds to step  317 , in which a determination as to the type of problems associated with the sector, in the manner described below. If in step  317  it is determined that there are orientation problems associated with the sector, execution proceeds to step  318 . In contrast, if in step  317  it is determined that there are bad antenna (i.e., gain) problems associated with the sector, execution proceeds to step  320 . 
     The determination as to whether there are orientation or bad antenna problems associated with the sector (step  315 ) is made as follows. First, for a given pair of sectors p and q, if (Mp Ci,Nk −Mq Ci,Nk ) auto , where “auto” refers to the automatic measurements periodically made by the network and stored in Table 2 and Nk is a neighbor sector, is approximately equal to (Mp Ci,Nk −Mq Ci,Nk ) calib , where “calib” refers to the calibration measurements stored in Table 1, then both sectors p and q have good antennas and no orientation problems. 
     Referring now to step  317 , assuming cell site C 2 , sector S 6 , and another neighboring cell site/sector to cell site C 1 , sector S 1 , designated cell site C 3 , sector S 8 , have been determined to have neither antenna nor orientation problems, and cell site C 2 , sector S 6 , and cell site C 3 , sector S 8  are first and second neighbors, respectively, of cell site C 1 , sector S 1 , designated “N1” and “N2”, respectively, if: 
     
       
           V   1 =|( M   1   C1,N1   −M   6   C2,N2 ) calib −( M   1   C1,N1   −M   6   C2,N2 ) auto | 
       
     
     then if V 1  is not approximately equal to zero, then cell site C 1 , sector S 1 , has either a bad antenna or orientation problems. A large value for V 1  is an indication of a bad antenna (i.e., gain) problem. 
     Therefore, if: 
     
       
           V   2 =|( M   1   C1,N2   −M   8   C3,N2 ) calib −( M   1   C1,N2   −M   8   C3,N2 ) auto|   
       
     
     then if V 1  is approximately equal to V 2 , the problem is one of a bad antenna (i.e., a gain problem) with respect to cell site C 1 , sector S 1 . Conversely, if V 1  and V 2  are very different, the problem is one of orientation with respect to cell site C 1 , sector S 1 . 
     As a result, the present invention presents a cost- and resource-effective method of identifying cell sites with bad and/or incorrectly oriented antennas. A major benefit will be realized by wireless network providers with inferior maintenance schedules that could lead to a substantial amount of antenna-related performance issues and associated costs. 
     Although an illustrative embodiment of the invention has been shown and described, other modifications, changes, and substitutions are intended in the foregoing disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.