Abstract:
A method of calculating position data for an airborne aircraft using a GPS-based airborne navigation system includes the processing of a position component of a relative state function by fusing a plurality of different types of measurement data available in the GPS-based system into a weighted least squares algorithm to determine an appropriate covariance matrix for the plurality of different types of measurement data.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This applications claims the benefit under 35 U.S.C. Section 119(e), of co-pending Provisional Application No. 60/822,195, filed Aug. 11, 1006, the disclosure of which is incorporated herein by reference in its entirety. 
     
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to Global Positioning System (GPS)-based Relative Navigation Systems, and more particularly to a method for processing the relative state of the position component of an airborne navigation system. 
         [0005]    2. Background of the Invention 
         [0006]    A need has been found for providing a rapidly deployable, adverse weather, adverse terrain, day-night, survivable, and mobile precision approach and landing capability that supports the principles of forward presence, crisis response and mobility. The capability should enable military forces to land on any suitable surface world wide (land and sea), under both peace time and hostile conditions, with ceiling and/or visibility the limiting factor. 
         [0007]    The Joint Precision Approach and Landing System (JPALS) is an integral part of such a strategic system. JPALS is a differential GPS that provides a rapidly deployable, mobile, adverse weather, adverse terrain, day-night, and survivable precision approach and landing capability. The JPALS allows an aircraft to land on any suitable land or sea-based surface worldwide, while minimizing the impact to airfield operations, because of low ceiling or poor visibility. This approach and landing system provides the capability of performing conventional and special operations from a fixed-base, shipboard, and austere environments under a wide range of meteorological and terrain conditions. 
         [0008]    One of the primary functions of sea-based JPALS is to determine the relative state (position, velocity and acceleration) of an airborne vehicle with respect to its assigned ship. This function is called “Relative State Function” or “Relative Navigation” (“RelNav”). Existing civil and military systems do not satisfy JPALS requirements because they have a number of shortcomings that limit joint operations. The multiplicity of systems, in and of itself, hinders inter-Service, civil, and allied operations. 
         [0009]    Among the limitations of conventional systems, especially as applied to calculating position data of an aircraft closing in on a target, is that in order to calculate an aircraft&#39;s position, numerous measurements must taken. Certain measurement types have better accuracy but require more processing time to achieve results. Traditionally, four measurements of the same type are needed to be used in a solution; otherwise optimal solutions can not be made available. Conventional methods that use a weighted least squares position solution use only a single measurement type. Furthermore, conventional methods have been less than satisfactory when relative position estimation is needed between two moving vehicles (e.g., between an aircraft and a ship). 
       SUMMARY OF THE INVENTION 
       [0010]    As used herein, the terms “invention” and “present invention” are to be understood as encompassing the invention described herein in its various embodiments and aspects, as well as any equivalents that may suggest themselves to those skilled in the pertinent arts. 
         [0011]    The present invention provides a novel and effective system and method for a GPS-based airborne navigation system to process the position component of the Relative State Function by fusing different types measurement data, i.e., data representing several different measured parameters. More specifically, the present invention provides an improved method of calculating the position data of aircraft closing in on target locations. 
         [0012]    The present invention enhances the speed and accuracy of such position calculations. This is accomplished by the fusing some or all of the different types of measurement data available in a GPS-based system into a weighted least squares algorithm to determine the appropriate covariance matrix, given the different measurement types. This method allows optimal accuracy in the position solution by including all satellites, and their best available measurements. Moreover, the invention can operate and provide satisfactory results whenever relative position estimation is needed between two vehicles (e.g., an aircraft and a ship). 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is an illustration of the overall set up of a relative navigation system, of the type in which the system and method of the present invention may be employed; 
           [0014]      FIG. 2  is an architectural block diagram of an airborne relative state system that includes an airborne RelNav computer system and interfaces; 
           [0015]      FIG. 3  is a flow diagram showing major functional/processing blocks of an airborne RelNav system including the RelNav computer system and interfaces; and 
           [0016]      FIG. 4  is a flow chart identifying process steps to calculate position data in accordance with present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    The following definitions are provided as they are typically (but not exclusively) used in GPS-based navigation systems implementing the various adaptive aspects of the present invention. 
         [0018]    The GPS is a satellite-based navigation system having a constellation of 24 Earth orbiting satellites. These satellites are approximately uniformly dispersed around six circular orbits having four satellites in each orbit. Each GPS satellite transmits at two frequencies: L1 (1575.42 MHz) and L2 (1227.60 MHz). The L1 frequency has two different spread-spectrum codes modulated on it: a coarse acquisition (CA) code, and a Y code. The Y code is also modulated onto the L2 carrier. 
         [0019]    Earth centered, Earth fixed (ECEF) is a Cartesian coordinate system used for GPS. It represents positions as X. Y. and Z coordinates in meters. The point (0.0.0) denotes the center of the earth, hence the name Earth-Centered. 
         [0020]    World Geodetic System of 1984 (WGS 84) a geodetic reference systems used by GPS and developed by the U.S. Defense Mapping Agency. 
         [0021]    Double Difference (technique) is a measurement method using two receivers. Differences are formed at each measurement epoch between two satellites on each receiver and then between the same two receivers. 
         [0022]    To better understand the invention, an overall system description is given, and the function and operation of the present invention will be described in specific detail. 
         [0023]      FIG. 1  shows an overall set up for a relative navigation system  100  between an aircraft  102  and a ship  106 . Both the aircraft  102  and the ship  106  receive L1 and L2 GPS measurements from a GPS satellite constellation  104 . The ship  106  processes its measurement data to generate its state (position, velocity) and estimated wide lane phase ambiguities. Ship measurement data are generated from as many as 4 GPS antennas. The computed ship state (position, velocity) and estimated wide lane phase ambiguities are broadcast, using radio frequencies, for use by all aircraft within broadcast range of the ship. 
         [0024]    The aircraft  102  combines its own measurements with the ship measurements, state, and ambiguities received over the broadcast, to produce a relative vector solution between its own GPS antenna and the ship&#39;s reference point. It also determines the quality of the relative vector solution. 
         [0025]    Referring to  FIG. 2 , an Airborne Relative State System  110  includes an Airborne RelNav computer system  116  that computes the relative position and velocity vector between the ship  106  and the aircraft  102 . It also computes the uncertainty of the computed position and velocity vectors. The computed relative state and its uncertainty are inputted to a guidance and control (G&amp;C) system  118  for guidance and control of the aircraft  102 . 
         [0026]    To assure system modularity, the interfaces in the airborne relative state system  110  are well defined. Five such interfaces are shown in  FIGS. 2 and 3 : 
         [0027]    Aircraft Avionic System  117  and its associated avionics interface (AI)  117 A; 
         [0028]    Airborne GPS receiver  119  and its associated GPS receiver interface (AGRI)  119 A; 
         [0029]    Airborne Data Link  112  and its associated data link interface (DLI)  112 A; 
         [0030]    Configuration data  114  and its associated configuration date interface (CDI)  114 A; and 
         [0031]    Airborne Guidance and Control system  118  and its associated guidance and control interface (GCI)  118 A. 
         [0032]    The Relative State Function has been partitioned into several sub-functions, as illustrated in  FIG. 3 . The algorithms to implement each sub-function are not described; only the sub-functions performed are identified. A detailed description of functionality and algorithmiic implementation is provided only for the Precision Relative State module (PRS)  137 , since its architecture and operation embody the present invention. 
         [0033]    The functional representation of the RelNav computer system  116  in  FIG. 3  identifies nine functional blocks along with three sub-blocks. A Measurement Management and Validation (MMV) function  129  receives data from Airborne GPS receivers  119  via the AGRI  119 A, Configuration Data  114  via the CDI  114 A, and Ship Data Uncompressed (DU)  125  via the DLI  112 A. The DU  125  converts ship position and velocity data to WGS-84 ECEF coordinates. The MMV function  129  validates Pseudo Range (PR) and Carrier Phase (CP) data (“Measurement Validation”  127 ), synchronizes the use of ephemeral data between ship and aircraft (“Sync. of Ephemeral Data”  127   a ), propagates ship position and velocity data to aircraft time (“Propagation of Ship Data . . . ”  126 ), synchronizes aircraft measurements to ship time (“Sync. of Aircraft Data . . . ”  128 ), and computes the sigma value of each aircraft GPS measurement (“Compute Sigma”  128   a ). 
         [0034]    A Ship Troposphere Correction (STC) function  131  applies tropospheric corrections to ship GPS measurements. An Aircraft Troposphere Correction function (ATC)  132  applies tropospheric corrections to aircraft GPS measurements. An Absolute Position and Velocity (APV) function  130  computes the aircraft s absolute position, the positions of satellites from the ephemeral data, and the aircraft&#39;s absolute velocity solution. A Relative Measurements (PM) function  133  calculates Double-Difference (DD) measurements (L1 PR, L2 PR, L1 CP, L2 CP. WL CP, NL PR) at ship time, and calculates variance components (multipath and noise, ionosphere corrections, troposphere corrections) of DD measurements from Single-Difference (SD) measurements (L1 PR, L2 PR, L1 CP, L2 CP, WL CP, NL PR) and variances at ship time. The satellite highest in elevation is chosen as a reference, and the PM function  133  calculates covariance matrices components (multipath and noise, ionosphere corrections, troposphere corrections) of the DD measurements. Since ship measurements may come from four separate antennas, four separate solutions may be required. 
         [0035]    A Wide Lane Ambiguities (WLA) function  134  determines WL float ambiguities and covariance (Ship UD, Aircraft UD, SD, and DD). It determines the probability of correctly fixing WL ambiguities, and it also determines the Discrimination Ratio of integer ambiguities, validates integer ambiguities, and fixes WL ambiguities. An L1/L2 Ambiguities (L1L2A) function  135  is performed assuming WL fixed ambiguities have been resolved successfully. It determines L1 and L2 float ambiguities and covariance, determines the probability of correctly fixing L1 and L2 ambiguities, determines the Discrimination Ratio (DR) of resolved L1 and L2 integer ambiguities, validates integer ambiguities, and fixes L1 and L2 ambiguities. A Basic Relative State (BRS) function  136  computes a Basic Relative State (position and velocity) at aircraft time and computes a Covariance of Basic Relative State (position and velocity). 
         [0036]    The G &amp; C Interface (GCI)  118 A provides precision relative state outputs to Guidance and Control functions, and it receives input from the Precision Relative State module (PRS)  137 . The Avionics Interface (AI)  117 A provides Basic Relative State outputs to the aircraft avionics system. The PRS module  137  determines a Precision Relative State only if an aircraft&#39;s distance to the ship is less than 10 nautical miles A satellite should only be considered in a particular solution if its measurements have been consecutively available for a configurable amount of time. The initial interval is set at 30 seconds or 60 samples. 
         [0037]    A functional block diagram for the Precision Relative State (PRS) module  137  is shown in  FIG. 4 , illustrating the different calculations performed to arrive at a Precision Relative State solution. A first computing module  138  computes code range and phase range values from Measurements and Covariance. DD NL Code Range Observables are calculated by Equations (1), (2) and (3): 
         [0000]    
       
         
           
             
               
                 
                   
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         [0038]    where R 1  and R 2  are DD code ranges 
       DD Phase Range Observables are calculated by Equations (4) to (9): 
     L1 Float:— 
       [0039]      Φ 1     ≦     flo =Φ 1 −λ 1   N   1     —     flo    (4) 
         [0000]    
       
      
       C 
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         [0000]        C   Φ     1 flo     =C   Φ     1   +λ 1   2   C   N     1—     flo    
       L2 Float:— 
       [0040]      Φ 2     —     flo =Φ 2 −λ 2   N   2     —     flo    
         [0000]        C   101      1     =C   DD     ≦     L     2—     m,e   +C   DD     —     L     2—     iono   +C   DD     —     L     2—     tropo    (5) 
         [0000]        C   Φ     2—     flo   =C   Φ     2   +λ 2   2   C   N     2—     flo    
       L1 Fixed:— 
       [0041]      Φ 1     —     fix =Φ 1 −λ 1   N   1     —     fix    (6) 
         [0000]      C Φ     1—       fix   =C Φ     1      
       L2 Fixed:— 
       [0042]      Φ 2     —     fix =Φ 2 −λ 2   N   2     —     fix    (7) 
         [0000]      C Φ     2—       fix   =C Φ   2    
         [0000]    
       
         
           
             
               
                 
                   
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       WL Fixed :— 
       [0043]      Φ w1     —     fix =Φ w1 −λ w1   N   w1     —     fix    (9) 
         [0000]      C Φ   w1     —     fix =C Φ     w1      
         [0044]    After the calculations are performed by the first computing module  138 , first and second functional modules  139  and  140  select measurement data for further processing. The best data are selected based on measurement variance from each of the double difference pair, using the above-defined methods. The orders are: L1 fixed, L2 fixed, L1 float. L2 float, Wide Lane Fixed. Wide Lane Float, and Narrow Lane Code. This way every visible satellite is used in the solution, weighted only by its own relative uncertainty. 
         [0045]    A third functional module  141  assembles data for a covariance matrix element calculation. The covariance matrix to be used in the solution is more difficult to generate than the other solutions and is done element by element. Diagonal elements for this solution are simply taken from the diagonal elements of the double difference covariance matrix and the measurement type is determined using the equations above. For examples if measurement two were a wide land fixed measurement, the M(2, 2) element would be taken from the WL fixed covariance matrix and placed in the hybrid covariance matrix in the same spot. 
         [0046]    A fourth functional module  142  performs the covariance matrix element calculation. Off diagonal elements are determined by the relationships between each measurement type. The simplest way to provide the information is to show a complete example and provide the algorithms. For this example the hybrid solution includes each type of measurement in descending order as follows, and each of these measurements is the first measurement in its respective solution type. 
         [0047]    L1_fixed 
         [0048]    L2_fixed 
         [0049]    L1_float 
         [0050]    L2_float 
         [0051]    WL_fixed 
         [0052]    WL_float 
         [0053]    NL_Code 
         [0054]    The covariance matrix is shown by Equation (10): 
         [0000]    
       
         
           
             
               
                 
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         [0055]    where the elements of matrix calculated by Equations (11) to (32: 
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                       2 
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
             
               
                 
                   c 
                   = 
                   
                     
                       
                         ( 
                         
                           1 
                           - 
                           
                             
                               λ 
                               1 
                             
                             
                               
                                 λ 
                                 2 
                               
                               - 
                               
                                 λ 
                                 1 
                               
                             
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             1 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     + 
                     
                       
                         ( 
                         
                           
                             
                               λ 
                               2 
                             
                             + 
                             
                               2 
                                
                               
                                 λ 
                                 1 
                               
                             
                           
                           
                             λ 
                             1 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
             
               
                 
                   d 
                   = 
                   
                     
                       
                         - 
                         
                           ( 
                           
                             
                               λ 
                               2 
                             
                             
                               
                                 λ 
                                 2 
                               
                               - 
                               
                                 λ 
                                 1 
                               
                             
                           
                           ) 
                         
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             1 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     + 
                     
                       
                         ( 
                         
                           
                             
                               2 
                                
                               
                                 λ 
                                 2 
                                 2 
                               
                             
                             + 
                             
                               
                                 λ 
                                 2 
                               
                                
                               
                                 λ 
                                 1 
                               
                             
                           
                           
                             λ 
                             1 
                             2 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
             
               
                 
                   e 
                   = 
                   
                     
                       
                         ( 
                         
                           
                             λ 
                             WL 
                           
                           
                             λ 
                             1 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             1 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     - 
                     
                       
                         ( 
                         
                           
                             λ 
                             2 
                           
                           
                             λ 
                             1 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   15 
                   ) 
                 
               
             
             
               
                 
                   f 
                   = 
                   
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     - 
                     
                       
                         ( 
                         
                           
                             λ 
                             2 
                           
                           
                             λ 
                             1 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   16 
                   ) 
                 
               
             
             
               
                 
                   g 
                   = 
                   
                     
                       σ 
                       
                         
                           AB_L 
                            
                           
                               
                           
                            
                           2 
                            
                           _m 
                         
                         , 
                         
                           e_key 
                            
                           _SV 
                         
                       
                       2 
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     + 
                     
                       
                         ( 
                         
                           
                             λ 
                             2 
                             4 
                           
                           
                             λ 
                             1 
                             4 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   17 
                   ) 
                 
               
             
             
               
                 
                   h 
                   = 
                   
                     
                       
                         ( 
                         
                           
                             λ 
                             1 
                           
                           
                             
                               λ 
                               2 
                             
                             - 
                             
                               λ 
                               1 
                             
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             2 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     + 
                     
                       
                         ( 
                         
                           
                             
                               λ 
                               2 
                               3 
                             
                             + 
                             
                               2 
                                
                               
                                 λ 
                                 1 
                               
                                
                               
                                 λ 
                                 2 
                                 2 
                               
                             
                           
                           
                             λ 
                             1 
                             3 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   18 
                   ) 
                 
               
             
             
               
                 
                   i 
                   = 
                   
                     
                       
                         ( 
                         
                           1 
                           + 
                           
                             
                               λ 
                               2 
                             
                             
                               
                                 λ 
                                 2 
                               
                               - 
                               
                                 λ 
                                 1 
                               
                             
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             2 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     + 
                     
                       
                         ( 
                         
                           
                             
                               2 
                                
                               
                                 λ 
                                 2 
                                 4 
                               
                             
                             + 
                             
                               2 
                                
                               
                                 λ 
                                 2 
                                 3 
                               
                                
                               
                                 λ 
                                 1 
                               
                             
                           
                           
                             λ 
                             1 
                             4 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   19 
                   ) 
                 
               
             
             
               
                 
                   j 
                   = 
                   
                     
                       
                         - 
                         
                           ( 
                           
                             
                               λ 
                               WL 
                             
                             
                               λ 
                               2 
                             
                           
                           ) 
                         
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             2 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     - 
                     
                       
                         ( 
                         
                           
                             λ 
                             2 
                             3 
                           
                           
                             λ 
                             1 
                             3 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   20 
                   ) 
                 
               
             
             
               
                 
                   k 
                   = 
                   
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     - 
                     
                       
                         ( 
                         
                           
                             λ 
                             2 
                             3 
                           
                           
                             λ 
                             1 
                             3 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   21 
                   ) 
                 
               
             
             
               
                 
                   l 
                   = 
                   
                     
                       
                         
                           ( 
                           
                             1 
                             - 
                             
                               
                                 λ 
                                 1 
                               
                               
                                 
                                   λ 
                                   2 
                                 
                                 - 
                                 
                                   λ 
                                   1 
                                 
                               
                             
                           
                           ) 
                         
                         2 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             1 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       
                         
                           ( 
                           
                             
                               λ 
                               1 
                             
                             
                               
                                 λ 
                                 2 
                               
                               - 
                               
                                 λ 
                                 1 
                               
                             
                           
                           ) 
                         
                         2 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             2 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     + 
                     
                       
                         
                           ( 
                           
                             
                               
                                 2 
                                  
                                 
                                   λ 
                                   1 
                                 
                               
                               + 
                               
                                 λ 
                                 2 
                               
                             
                             
                               λ 
                               1 
                             
                           
                           ) 
                         
                         2 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   22 
                   ) 
                 
               
             
             
               
                 
                   m 
                   = 
                   
                     
                       
                         - 
                         
                           ( 
                           
                             1 
                             - 
                             
                               
                                 λ 
                                 1 
                               
                               
                                 
                                   λ 
                                   2 
                                 
                                 - 
                                 
                                   λ 
                                   1 
                                 
                               
                             
                           
                           ) 
                         
                       
                        
                       
                         ( 
                         
                           
                             λ 
                             2 
                           
                           
                             
                               λ 
                               2 
                             
                             - 
                             
                               λ 
                               1 
                             
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             1 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     + 
                     
                       
                         ( 
                         
                           1 
                           + 
                           
                             
                               λ 
                               2 
                             
                             
                               
                                 λ 
                                 2 
                               
                               - 
                               
                                 λ 
                                 1 
                               
                             
                           
                         
                         ) 
                       
                        
                       
                         ( 
                         
                           
                             λ 
                             1 
                           
                           
                             
                               λ 
                               2 
                             
                             - 
                             
                               λ 
                               1 
                             
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             2 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       
                         ( 
                         
                           
                             
                               2 
                                
                               
                                 λ 
                                 2 
                                 3 
                               
                             
                             + 
                             
                               5 
                                
                               
                                 λ 
                                 2 
                                 2 
                               
                                
                               
                                 λ 
                                 1 
                               
                             
                             + 
                             
                               2 
                                
                               
                                 λ 
                                 1 
                                 2 
                               
                                
                               
                                 λ 
                                 2 
                               
                             
                           
                           
                             λ 
                             1 
                             3 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   23 
                   ) 
                 
               
             
             
               
                 
                   n 
                   = 
                   
                     
                       
                         - 
                         
                           ( 
                           
                             
                               λ 
                               WL 
                             
                             
                               λ 
                               2 
                             
                           
                           ) 
                         
                       
                       * 
                       
                         ( 
                         
                           
                             λ 
                             1 
                           
                           
                             
                               λ 
                               2 
                             
                             - 
                             
                               λ 
                               1 
                             
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             2 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       
                         ( 
                         
                           
                             λ 
                             WL 
                           
                           
                             λ 
                             2 
                           
                         
                         ) 
                       
                       * 
                       
                         ( 
                         
                           1 
                           - 
                           
                             
                               λ 
                               1 
                             
                             
                               
                                 λ 
                                 2 
                               
                               - 
                               
                                 λ 
                                 1 
                               
                             
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             1 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     - 
                     
                       
                         ( 
                         
                           
                             
                               2 
                                
                               
                                 λ 
                                 1 
                               
                                
                               
                                 λ 
                                 2 
                               
                             
                             + 
                             
                               λ 
                               2 
                               2 
                             
                           
                           
                             λ 
                             1 
                             2 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   24 
                   ) 
                 
               
             
             
               
                 
                   o 
                   = 
                   
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     - 
                     
                       
                         ( 
                         
                           
                             
                               2 
                                
                               
                                 λ 
                                 1 
                               
                                
                               
                                 λ 
                                 2 
                               
                             
                             + 
                             
                               λ 
                               2 
                               2 
                             
                           
                           
                             λ 
                             1 
                             2 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   25 
                   ) 
                 
               
             
             
               
                 
                   p 
                   = 
                   
                     
                       
                         
                           ( 
                           
                             
                               λ 
                               2 
                             
                             
                               
                                 λ 
                                 2 
                               
                               - 
                               
                                 λ 
                                 1 
                               
                             
                           
                           ) 
                         
                         2 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             1 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       
                         
                           ( 
                           
                             1 
                             + 
                             
                               
                                 λ 
                                 2 
                               
                               
                                 
                                   λ 
                                   2 
                                 
                                 - 
                                 
                                   λ 
                                   1 
                                 
                               
                             
                           
                           ) 
                         
                         2 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             2 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     + 
                     
                       
                         ( 
                         
                           
                             
                               2 
                                
                               
                                 λ 
                                 2 
                                 2 
                               
                             
                             + 
                             
                               
                                 λ 
                                 2 
                               
                                
                               
                                 λ 
                                 1 
                               
                             
                           
                           
                             λ 
                             1 
                             2 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   26 
                   ) 
                 
               
             
             
               
                 
                   q 
                   = 
                   
                     
                       
                         - 
                         
                           ( 
                           
                             
                               λ 
                               WL 
                             
                             
                               λ 
                               1 
                             
                           
                           ) 
                         
                       
                       * 
                       
                         ( 
                         
                           
                             λ 
                             2 
                           
                           
                             
                               λ 
                               2 
                             
                             - 
                             
                               λ 
                               1 
                             
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             1 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     - 
                     
                       
                         ( 
                         
                           
                             λ 
                             WL 
                           
                           
                             λ 
                             2 
                           
                         
                         ) 
                       
                       * 
                       
                         ( 
                         
                           1 
                           + 
                           
                             
                               λ 
                               2 
                             
                             
                               
                                 λ 
                                 2 
                               
                               - 
                               
                                 λ 
                                 1 
                               
                             
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             2 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     - 
                     
                       
                         ( 
                         
                           
                             
                               2 
                                
                               
                                 λ 
                                 2 
                                 3 
                               
                             
                             + 
                             
                               
                                 λ 
                                 2 
                                 2 
                               
                                
                               
                                 λ 
                                 1 
                               
                             
                           
                           
                             λ 
                             1 
                             3 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   27 
                   ) 
                 
               
             
             
               
                 
                   r 
                   = 
                   
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     - 
                     
                       
                         ( 
                         
                           
                             
                               2 
                                
                               
                                 λ 
                                 2 
                                 3 
                               
                             
                             + 
                             
                               
                                 λ 
                                 2 
                                 2 
                               
                                
                               
                                 λ 
                                 1 
                               
                             
                           
                           
                             λ 
                             1 
                             3 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   28 
                   ) 
                 
               
             
             
               
                 
                   s 
                   = 
                   
                     
                       
                         
                           ( 
                           
                             
                               λ 
                               WL 
                             
                             
                               λ 
                               2 
                             
                           
                           ) 
                         
                         2 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             2 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       
                         
                           ( 
                           
                             
                               λ 
                               WL 
                             
                             
                               λ 
                               1 
                             
                           
                           ) 
                         
                         2 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             1 
                              
                             _m 
                           
                           , 
                           
                             e_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     + 
                     
                       
                         ( 
                         
                           
                             λ 
                             2 
                             2 
                           
                           
                             λ 
                             1 
                             2 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   29 
                   ) 
                 
               
             
             
               
                 
                   t 
                   = 
                   
                     
                       
                         ( 
                         
                           
                             λ 
                             2 
                             2 
                           
                           
                             λ 
                             1 
                             2 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   30 
                   ) 
                 
               
             
             
               
                 
                   u 
                   = 
                   
                     s 
                     + 
                     
                       
                         λ 
                         WL 
                         2 
                       
                       * 
                       
                         C 
                         
                           mw_SD 
                            
                           _fl 
                            
                           _key 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   31 
                   ) 
                 
               
             
             
               
                 
                   v 
                   = 
                   
                     
                       
                         
                           ( 
                           
                             
                               λ 
                               NL 
                             
                             
                               λ 
                               1 
                             
                           
                           ) 
                         
                         2 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             1 
                              
                             _M 
                           
                           , 
                           
                             E_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       
                         
                           ( 
                           
                             
                               λ 
                               NL 
                             
                             
                               λ 
                               2 
                             
                           
                           ) 
                         
                         2 
                       
                       * 
                       
                         σ 
                         
                           
                             AB_L 
                              
                             
                                 
                             
                              
                             2 
                              
                             _M 
                           
                           , 
                           
                             E_key 
                              
                             _SV 
                           
                         
                         2 
                       
                     
                     + 
                     
                       σ 
                       
                         AB_tropo 
                          
                         _key 
                          
                         _sv 
                       
                       2 
                     
                     + 
                     
                       
                         ( 
                         
                           
                             λ 
                             2 
                             2 
                           
                           
                             λ 
                             1 
                             2 
                           
                         
                         ) 
                       
                       * 
                       
                         σ 
                         
                           AB_L 
                            
                           
                               
                           
                            
                           1 
                            
                           _iono 
                            
                           _key 
                            
                           _sv 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   32 
                   ) 
                 
               
             
           
         
       
     
         [0056]    The cases not covered in the example are the relationships between common solutions. In these cases the following applies: 
         [0057]    L1_fixed to L1_fixed is equivalent to b; 
         [0058]    L2_fixed to L2_fixed is equivalent to g; 
         [0059]    L1_float to L1_float is equivalent to l; 
         [0060]    L2 float to L2_float is equivalent top; 
         [0061]    WL_fixed to WL fixed is equivalent to s; 
         [0062]    WL_float to WL_float is equivalent to u; and 
         [0063]    NL code to NL code is equivalent to v: 
         [0064]    A fifth functional module  143  calculates a Relative Position Solution using the Weighted Least Squares Method. The measurements should include every satellite, using the most accurate (smallest variance) measurement available for that satellite. The calculations executed by different steps of the WLS algorithm are shown below. The initialization is performed once at the start of a filter. All other steps are iterated (2 or 3 times) until a solution converges. 
         [0065]    Step  1  initializes the baseline vector b (at start of the filter) by Equation (33) 
         [0000]      x k   − =0   (33) 
         [0066]    Step  2  calculates Measurements and Covariance by Equations (34), (35) and (36): 
         [0000]      Z=Z Hybrid    (34) 
         [0000]      C z =Σ Hybrid    (35) 
         [0000]      W=C z   −1    (36) 
         [0067]    Step  3  calculates LOS (Line of Sight) vectors from Ship and Aircraft to Satellite j by Equations (37)-(42): 
       In the equations, satellite position {x s ,y s ,z s } is from ephemeris and ship position {x A ,y A ,z A } is from an absolute position solution. 
     LOS Vectors: 
       [0068]    
       
         
           
             
               
                 
                   
                     
                       
                         Ship 
                          
                         
                             
                         
                          
                         
                           ( 
                           A 
                           ) 
                         
                          
                         
                             
                         
                          
                         to 
                          
                         
                             
                         
                          
                         satellite 
                          
                         
                             
                         
                          
                         j 
                       
                     
                     
                       
                         
                           as 
                            
                           
                             ( 
                             j 
                             ) 
                           
                         
                         = 
                         
                           [ 
                           
                             
                               
                                 
                                   
                                     
                                       x 
                                       s 
                                     
                                      
                                     
                                       ( 
                                       j 
                                       ) 
                                     
                                   
                                   - 
                                   
                                     x 
                                     A 
                                   
                                 
                               
                             
                             
                               
                                 
                                   
                                     
                                       y 
                                       s 
                                     
                                      
                                     
                                       ( 
                                       j 
                                       ) 
                                     
                                   
                                   - 
                                   
                                     y 
                                     A 
                                   
                                 
                               
                             
                             
                               
                                 
                                   
                                     
                                       z 
                                       s 
                                     
                                      
                                     
                                       ( 
                                       j 
                                       ) 
                                     
                                   
                                   - 
                                   
                                     z 
                                     A 
                                   
                                 
                               
                             
                           
                           ] 
                         
                       
                     
                   
                   
                     
                       
                         Aircraft 
                          
                         
                             
                         
                          
                         
                           ( 
                           B 
                           ) 
                         
                          
                         
                             
                         
                          
                         to 
                          
                         
                             
                         
                          
                         satellite 
                          
                         
                             
                         
                          
                         j 
                       
                     
                     
                       
                         
                           
                             
                               
                                 bs 
                                  
                                 
                                   ( 
                                   j 
                                   ) 
                                 
                               
                               = 
                               
                                 [ 
                                 
                                   
                                     
                                       
                                         
                                           
                                             x 
                                             s 
                                           
                                            
                                           
                                             ( 
                                             j 
                                             ) 
                                           
                                         
                                         - 
                                         
                                           x 
                                           B 
                                         
                                       
                                     
                                   
                                   
                                     
                                       
                                         
                                           
                                             y 
                                             s 
                                           
                                            
                                           
                                             ( 
                                             j 
                                             ) 
                                           
                                         
                                         - 
                                         
                                           y 
                                           B 
                                         
                                       
                                     
                                   
                                   
                                     
                                       
                                         
                                           
                                             z 
                                             s 
                                           
                                            
                                           
                                             ( 
                                             j 
                                             ) 
                                           
                                         
                                         - 
                                         
                                           z 
                                           B 
                                         
                                       
                                     
                                   
                                 
                                 ] 
                               
                             
                           
                         
                         
                           
                             
                               = 
                               
                                 [ 
                                 
                                   
                                     
                                       
                                         
                                           
                                             x 
                                             s 
                                           
                                            
                                           
                                             ( 
                                             j 
                                             ) 
                                           
                                         
                                         - 
                                         
                                           ( 
                                           
                                             
                                               x 
                                               A 
                                             
                                             + 
                                             
                                               
                                                 b 
                                                 ^ 
                                               
                                               x 
                                             
                                           
                                           ) 
                                         
                                       
                                     
                                   
                                   
                                     
                                       
                                         
                                           
                                             y 
                                             s 
                                           
                                            
                                           
                                             ( 
                                             j 
                                             ) 
                                           
                                         
                                         - 
                                         
                                           ( 
                                           
                                             
                                               y 
                                               A 
                                             
                                             + 
                                             
                                               
                                                 b 
                                                 ^ 
                                               
                                               y 
                                             
                                           
                                           ) 
                                         
                                       
                                     
                                   
                                   
                                     
                                       
                                         
                                           
                                             z 
                                             s 
                                           
                                            
                                           
                                             ( 
                                             j 
                                             ) 
                                           
                                         
                                         - 
                                         
                                           ( 
                                           
                                             
                                               z 
                                               A 
                                             
                                             + 
                                             
                                               
                                                 b 
                                                 ^ 
                                               
                                               z 
                                             
                                           
                                           ) 
                                         
                                       
                                     
                                   
                                 
                                 ] 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   
                     
                       
                         ( 
                         37 
                         ) 
                       
                     
                   
                   
                     
                       
                           
                       
                     
                   
                   
                     
                       
                           
                       
                     
                   
                   
                     
                       
                           
                       
                     
                   
                   
                     
                       
                         ( 
                         38 
                         ) 
                       
                     
                   
                 
               
             
           
         
       
     
         [0069]    Magnitudes of LOS vectors: 
         [0000]        as _mag( j )=∥ as ( j )∥;and   (39) 
         [0000]        bs _mag( j )=∥ bs ( j )∥  (40) 
       Predicted SD Measurement (as-bs) 
       [0070]        dab ( j )= as _mag( j )− bs _mag( j );   (41) 
       Predicted DD Measurements 
       [0071]    
       
         
           
             
               
                 
                   
                     Z 
                     k 
                     - 
                   
                   = 
                   
                     [ 
                     
                       
                         
                           
                             
                               dab 
                                
                               
                                 ( 
                                 1 
                                 ) 
                               
                             
                             - 
                             
                               dab 
                                
                               
                                 ( 
                                 2 
                                 ) 
                               
                             
                           
                         
                       
                       
                         
                           
                             
                               dab 
                                
                               
                                 ( 
                                 1 
                                 ) 
                               
                             
                             - 
                             
                               dab 
                                
                               
                                 ( 
                                 3 
                                 ) 
                               
                             
                           
                         
                       
                       
                         
                           … 
                         
                       
                       
                         
                           
                             
                               dab 
                                
                               
                                 ( 
                                 1 
                                 ) 
                               
                             
                             - 
                             
                               dab 
                                
                               
                                 ( 
                                 K 
                                 ) 
                               
                             
                           
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   ( 
                   42 
                   ) 
                 
               
             
           
         
       
     
         [0000]    using satellite 1 (highest) as reference 
         [0072]    Step  4  performs Linearization by evaluating Equations (43)-(45): 
         [0000]    Unit LOS Vectors from Aircraft to Satellite j: 
         [0000]    
       
         
           
             
               
                 
                   
                     [ 
                     
                       
                         
                           
                             
                               1 
                               x 
                             
                              
                             
                               ( 
                               j 
                               ) 
                             
                           
                         
                       
                       
                         
                           
                             
                               1 
                               y 
                             
                              
                             
                               ( 
                               j 
                               ) 
                             
                           
                         
                       
                       
                         
                           
                             
                               1 
                               z 
                             
                              
                             
                               ( 
                               j 
                               ) 
                             
                           
                         
                       
                     
                     ] 
                   
                   = 
                   
                     
                       
                         bs 
                          
                         
                           ( 
                           j 
                           ) 
                         
                       
                       / 
                       bs_mag 
                     
                      
                     
                       ( 
                       j 
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   43 
                   ) 
                 
               
             
           
         
       
     
       Differences of Unit Vectors 
       [0073]        e   x (1 ,j )=1 x (1)−1 x ( j ) 
         [0000]        e   y (1 ,j )=1 y (1)−1 y ( j )   (44) 
         [0000]        e   z (1 ,j )=1 z (1)−1 z ( j ) 
       H Matrix (Matrix Formed by Differenced Unit Vectors) 
       [0074]    
       
         
           
             
               
                 
                   H 
                   = 
                   
                     [ 
                     
                       
                         
                           
                             
                               e 
                               x 
                             
                              
                             
                               ( 
                               
                                 1 
                                 , 
                                 2 
                               
                               ) 
                             
                           
                         
                         
                           
                             
                               e 
                               y 
                             
                              
                             
                               ( 
                               
                                 1 
                                 , 
                                 2 
                               
                               ) 
                             
                           
                         
                         
                           
                             
                               e 
                               z 
                             
                              
                             
                               ( 
                               
                                 1 
                                 , 
                                 2 
                               
                               ) 
                             
                           
                         
                       
                       
                         
                           
                             
                               e 
                               x 
                             
                              
                             
                               ( 
                               
                                 1 
                                 , 
                                 3 
                               
                               ) 
                             
                           
                         
                         
                           
                             
                               e 
                               y 
                             
                              
                             
                               ( 
                               
                                 1 
                                 , 
                                 3 
                               
                               ) 
                             
                           
                         
                         
                           
                             
                               e 
                               z 
                             
                              
                             
                               ( 
                               
                                 1 
                                 , 
                                 3 
                               
                               ) 
                             
                           
                         
                       
                       
                         
                           ⋯ 
                         
                         
                           ⋯ 
                         
                         
                           ⋯ 
                         
                       
                       
                         
                           ⋯ 
                         
                         
                           ⋯ 
                         
                         
                           ⋯ 
                         
                       
                       
                         
                           ⋯ 
                         
                         
                           ⋯ 
                         
                         
                           ⋯ 
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   ( 
                   45 
                   ) 
                 
               
             
           
         
       
     
         [0075]    Steps  5  computes the Weighted Least Square Relative Position solution by Equations (46)-(49): 
       Filter Observable: 
       [0076]      Δ Z=[Z   k   −Z   k   − ]  (46) 
       WLS Solution and Solution Covariance: 
       [0077]      Δ{circumflex over (x)}=[H T WH] −1 H T W ΔZ   (47) 
         [0000]        {circumflex over (x)}   k   +   ={circumflex over (x)}   k   −   +Δ{circumflex over (x)}   (48) 
         [0000]      Σ {circumflex over (x)} =[H T W H] −1    (49) 
         [0078]    The solution is arrived at by transforming each Relative Position Solution and its Covariance from WGS-84 to NED coordinates (north-east-down coordinates at ship reference point). 
         [0079]    The final output from the process includes the following data: 
         [0080]    Hybrid Relative Position NED 
         [0081]    Covariance of Hybrid Relative Position