Patent Publication Number: US-10760911-B2

Title: Integrity monitoring method for navigation systems with heterogeneous measurements

Description:
BACKGROUND 
     As the navigation technology evolves, there is an effort to hybridize navigation information provided from different navigation information producing sources into a single navigation solution (typically covering position, velocity, and altitude/heading). Example navigation information producing sources may include an inertial measurement unit (IMU), a global navigation satellite system (GNSS), a magnetometer, air-data, distance measuring equipment (DME), eLoran, odometers, radar-altimeter, maps, vision sensors, etc. The hybridizing of the different navigational information sources introduces the need for a technique which assures the integrity of this complex single navigation solution. Current integrity monitoring algorithms focus mainly on particular navigation parameters (mostly position) of the snap-shot GNSS or hybridized GNSS/INS systems without any regard to other navigation parameters. This however, is an approach not suitable for aiding sources with heterogeneous measurements. 
     For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an integrity monitoring technique of the navigation information provided by a navigation algorithm solution integrating complex and heterogeneous aiding sources. 
     SUMMARY OF INVENTION 
     The above-mentioned problems of current systems are addressed by embodiments of the present invention and will be understood by reading and studying the following specification. The following summary is made by way of example and not by way of limitation. It is merely provided to aid the reader in understanding some of the aspects of the invention. In embodiments, an integrity monitoring algorithm is applied to measurement clusters instead of the measurements themselves. 
     In one embodiment, an integrity monitoring method for navigation systems with heterogeneous measurements is provided. The method includes defining integrity monitoring classes specifying quantities of a navigation information to be protected. Measurements from a plurality of different type navigation aiding sources are received. The measurements are categorized by an information domain, an aiding class and an aiding section. The information domain is a category of at least one of estimated states and measurements that represent a same physical category. The aiding class is a category that uses a same physical method to acquire measurements. The aiding section is a category of measurements from the same aiding source. The measurements are organized into a plurality of measurement clusters based at least in part on measurement fault modes to be detected, measurement fault modes to be excluded, available computer resources and required performance. An integrity monitoring algorithm is applied to the measurement clusters to determine an integrity solution for all defined integrity monitoring classes. 
     In another embodiment, a program product for implementing an integrity monitoring for navigation systems with heterogeneous measurements is provided. The program product comprising a processor-readable medium on which program instructions are embodied, wherein the program instructions are operable, when executed by at least one processor in a navigation system, to cause the navigation system to; categorize received measurements from a plurality of different type navigation aiding sources by an information domain, an aiding class and an aiding section, wherein the information domain is a category of at least one of estimated states and measurements that represent a same physical category, wherein the aiding class is a category that uses a same physical method to acquire measurements, wherein the aiding section is a category of measurements from the same aiding source; organize the measurements into a plurality of measurement clusters based at least in part on measurement fault modes to be detected, measurement fault modes to be excluded, available computer resources and required performance; and apply an integrity monitoring algorithm to the measurement clusters to determine an integrity solution for all defined integrity monitoring classes. 
     In yet another embodiment, a system having an integrity monitoring function for heterogeneous measurements is provided. The system includes at least one input, at least one memory and at least one controller. The at least one input receives navigation related measurement information from a plurality of different sources. The at least one memory is used to store at least one filter and at least one integrity function. The at least one controller is in communication with the at least one input and the at least one memory. The at least one controller is configured to execute the at least one filter and at least one integrity function in processing the received navigation related measurement information from the plurality of different sources to determine the integrity of the received related measurement navigation information. The controller, based on the execution of the at least one filter, is configured to categorize measurements from the navigation related measurement information by an information domain, an aiding class and an aiding section. The information domain is a category of at least one of estimated states and measurements that represent a same physical category. The aiding class is a category that uses a same physical method to acquire measurements. The aiding section is a category of measurements from the same aiding source. The at least one controller is further, based on the execution of the at least one filter, configured to organize the measurements into a plurality of measurement clusters based at least in part on measurement fault modes to be detected, measurement fault modes to be excluded, available computer resources and required performance. The at least one controller, based on the execution of the at least one integrity function, is configured to apply an integrity monitoring algorithm to the measurement clusters to determine an integrity solution for all defined integrity monitoring classes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more easily understood and further advantages and uses thereof will be more readily apparent, when considered in view of the detailed description and the following figures in which: 
         FIG. 1  illustrates a vehicle of an embodiment having an integrity monitoring navigation system; 
         FIG. 2  illustrates a general process flow diagram of an embodiment; 
         FIG. 3A  illustrates a formation of first layer solutions of an embodiment; 
         FIG. 3B  illustrates a formation of layer solutions of an embodiment; 
         FIG. 3C  illustrates the use of a virtual clusters of an embodiment; 
         FIG. 4  illustrates an integrity monitoring flow diagram of an embodiment; and 
         FIG. 5  illustrates an example solution formation of an embodiment. 
     
    
    
     In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize specific features relevant to the present invention. Reference characters denote like elements throughout Figures and text. 
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the inventions may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the claims and equivalents thereof. 
     Embodiments of the present invention provide a system and methodology of integrity monitoring of navigation information estimated by a statistical filter on the basis of a mathematical model and heterogeneous measurements. The method provides a general framework for the integrity monitoring of any navigation system where the computational complexity and achievable performance of the results can be adjusted according to the user requirements. In embodiments using a centralized hybridization architecture (all sensors/units/systems from the set of aiding measurements fused in a single statistical filter), all the aiding measurements are distributed among multiple clusters as discussed below in detail. In embodiments, the design of the clusters are used to account for different fault modes that should be detected (i.e. single GPS satellite failure, Galileo constellation failure, single wheel odometer failure) taking into consideration requirements on the fault detection ability, exclusion availability and computational demands. As a core algorithm, a solution separation methodology is used that forms sub-solution, sub-sub-solution, etc. based on the measurement clusters, instead of satellite measurements like in “classical” solution separation. The centralized filter hybridization also assures the integrity for all domain constraints only by the states estimated within the statistical filter. This approach enables fairly straightforward approach to gain an optimal performance from the multiple navigation sensors/unit/systems (centralized) hybridization, while maintaining required safety/integrity and reasonable computational demands. 
     An example of a vehicle  100  implementing embodiments is illustrated in the  FIG. 1 . The vehicle includes a navigation and information integrity monitoring system  102 , a plurality of navigation related measurement information sources  110 - 1  through  110 - n  and a vehicle system  112 . The plurality of navigation related measurement information sources  110 - 1  through  110 - n  may include, but are not limited to, an inertial measurement unit (IMU), a global navigation satellite system (GNSS), a magnetometer, air-data, distance measurement equipment (DME), eLoran, odometers, a radar-altimeter, maps, vision sensors, etc. The navigation related measurement information sources  110 - 1  through  110 - n  are generally designated as  110  here forth. Navigation related measurement information of the navigation related measurement information sources  110  are provided to at least one input  105  of the navigation and information integrity monitoring system  102  in this example embodiment. The navigation and information integrity monitoring system  102  includes a controller  104  and a memory  106 . In embodiments the navigation system with assured integrity  102  further includes a statistical filter  108  and an integrity monitoring function  107 . In an embodiment, the filter  108  is a statistical filter that is stored in the memory  106  that is executed on the navigation related measurements information of the navigation related measurement information sources  110  by the controller  104  to organize information outputs into clusters as discussed in detail below. Further in an embodiment, the integrity monitoring function  107  is stored in memory  106  and implemented by the controller  104 . The integrity monitoring function  107  includes an integrity monitoring algorithm used to determine a set of solutions such as a full solution and sub-solutions as discussed below in detail. In an embodiment, the controller  104  after processing the navigation related measurement information of the navigation related measurement information sources  110  with the statistical filter  108  and integrity monitoring function  107  provides navigation information to the vehicle system  112 . The vehicle system  112 , in an embodiment, is a vehicle control that in turn uses the navigation information from the navigation and information integrity monitoring system  102  to at least in part control directional operations of the vehicle  100 . Moreover, in other embodiments, the vehicle system  112  may include at least one of a surveillance system, a display system, a management system and like systems. 
     In general, the controller  104  may include any one or more of a processor, microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field program gate array (FPGA), or equivalent discrete or integrated logic circuitry. In some example embodiments, controller  104  may include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, one or more FPGAs, as well as other discrete or integrated logic circuitry. The functions attributed to the controller  104  (such as the statistical filter and integrity monitoring functions) herein may be embodied as software, firmware, hardware or any combination thereof. The controller  104  may be part of a system controller or a component controller. The memory  106  may include computer-readable operating instructions that, when executed by the controller  104  provides functions of the navigation and information integrity monitoring system  102 . Such functions may include the functions of statistical filter  108  and integrity monitoring function  107  described below. The computer readable instructions may be encoded within the memory  106 . Memory  106  may comprise computer readable storage media including any volatile, nonvolatile, magnetic, optical, or electrical media, such as, but not limited to, a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other single or multiple storage medium. 
     A general process flow diagram  200  of an embodiment is illustrated in  FIG. 2 . As illustrated, the process starts by taking the navigation related measurement information from the navigation related measurement information sources  110  and categorizing  202  the received navigation related measurement information based on three characteristics in this example embodiment. The categories in this example include an information domain  204 , an aiding class  206  and an aiding section  208 . The characteristics associated with the information domain  204  includes states and/or measurements which represent the same physical quantity. For example, the information domain  204  may include position, velocity, attitude/heading, etc. The information in the information domain may be represented by a vector of primary states having many different measurements defined for it. The characteristics associated with the aiding class  206  relate to measurements for which the same physical method was used to acquire the information. An example of the characteristics of the aiding class include RF satellite ranging and RF terrestrial ranging. The characteristics associated with the aiding section  208  relate to measurements taken from the same aiding source. An example of the characteristics of the aiding section  208  are GPS PR measurements or Galileo PR measurements. 
     Once the measurements are sorted by characteristics, the measurements are further organized into measurement clusters  210 . In an example embodiment, the clusters are organized according to requirements  219  of an embodiment that includes the fault modes that are to be detected  212 , fault modes that are to be excluded  214 , the available computer resources  216  that are included, and required performance  218  in terms of integrity, accuracy, availability, and continuity for each integrity monitoring class. In embodiments, an integrity monitoring algorithm  220  is applied to the measurement clusters instead of the measurements themselves. Cluster formation may follow the following rules; all measurements in one cluster are typically from the same information domain and a cluster can include measurements from different aiding sections and from different aiding classes. If exclusion capability is required (another layer of solutions is to be added) but the set of fault modes to be excluded is smaller than the ones to be detected, selection exclusion (lowest) layer solution(s) can form virtual clusters(s), too. This extends the set of fault modes to be detected (but not excluded). 
     Referring to  FIG. 3A , an example of a solution formation of first layer  300  is provided. In this example embodiment, there are 17 measurements  301  through  317  provided by navigation information sources  110  that are categorized and clustered into 7 clusters  321  through  327 . The first cluster  321  includes measurement  301  that was categorized in information domain  1 , aiding class A and aiding section a. The second cluster  322  includes measurements  302  and  303  that were categorized in information domain  1 , aiding class B and aiding section b. The third cluster  323  includes measurements  304  and  305  that were also categorized in information domain  1 , aiding class B and aiding section b. The fourth cluster  324  includes measurements  306 ,  307  and  308  that were categorized in information domain  2 , aiding class C and aiding section c. The fifth cluster  325  includes measurements  309 ,  310  and  311  that were categorized in information domain  2 , aiding class D and aiding section d. The sixth cluster  326  includes measurements  312 ,  313  and  314 . Measurements  312  and  313  were also categorized in information domain  2 , aiding class D and aiding section d while measurement  314  is categorized in information domain  2 , aiding class D and aiding section e. The seventh cluster  327  includes measurements  314 ,  315 ,  316  and  317 . Measurements  314 ,  315 ,  316  and  317  are all categorized in information domain  2 , aiding class D and aiding section e. Hence, as illustrated in this example, cluster groups may share a measurement (i.e. measurement  314  of cluster groups  326  and  327 ). 
     The solution formation of first layer  300  example of  FIG. 3A  includes a full solution  330 . The full solution  330  processes all of the measurement clusters  321  through  327 . The solution formation of first layer  300  example also includes seven sub-solutions  331  through  337 . The sub-solution process each measurement cluster minus one cluster. A lowest layer solution formation  340  in an example embodiment is illustrated in  FIG. 3B . In this example, six sub-sub-solutions  341  through  346  off of sub-solution  331  is illustrated. Further  FIG. 3C  illustrates a solution  350  with the use of virtual cluster  360 . The virtual cluster  360  in this example includes measurements  302 ,  303 ,  304  and  305 . As discussed above, if exclusion capability is required (another layer of solutions is to be added) but the set of fault modes to be excluded is smaller than the ones to be detected, selection exclusion (lowest) layer solution(s) can form virtual clusters(s). This extends the set of fault modes to be detected (but not excluded). The solution  350  further illustrates sub-sub-solutions  351  through  356  of sub-solution  335 . Also illustrated in the example of  FIG. 3C  is that sub-sub-solution  355  represents the virtual cluster related sub-sub-solution, where an additional statistic with respect to full solution  330  to be processed by the fault detection is constructed. 
     An integrity monitoring flow diagram  400  is illustrated in  FIG. 4 . The integrity monitoring flow diagram  400  shows a series of steps ( 402 ) through ( 430 ). The steps are shown in a particular order, one or more steps may be in a different order in other embodiments. The process starts be defining failures to be detected ( 402 ), failures to be excluded ( 404 ) and defining the required probabilities ( 406 ) of hazardously misleading information (HMI) and false alert (FA) (p(HMI) and P(FA)). These definitions along with, gathered available measurements ( 408 ) and computational resources ( 410 ) are used to categorize and create measurement clusters ( 412 ) into information domains, integrity monitoring classes, aiding classes and sections (including specification of the measurement devices properties—noise prop., failure prob.). The M C  measurement clusters are then created C 1 , . . . , C M  with properties:
         a. C i ≠C j , i≠j, i,j=1, . . . , M C      b. C i ∩C j  (may or may not be an empty set)   c. S=C 1  ∪C 2 ∪C j ∪ . . . ∪C M          

     M V  virtual clusters (if applied) may also be created. The simplest possibility is to design the clusters according to failures to be detected. A statistical filter estimating the navigation information (i.e. state) at time k, further denoted x k , based on the mathematical model and all available measurements in S up to time k, further denoted as Z k   S  ( 414 ). The filter, further denoted as the full-solution, provides a conditional state estimate in form of the probability density function (PDF) at time k denoted as:
 
 x   k   S     x   k   ˜p ( x   k   |Z   k   S )
 
     An example of the statistical filters that may be used is an extended Kalman filter or a particle filter. Navigation information may be for example composed of 3 position, 3 velocity, and 3 attitude/heading elements. 
     A set of statistical filters estimating the navigation information based on the mathematical model and measurements from all but one clusters denoted is applied at step ( 416 ) to determined sub-solutions. This is further denoted as Z k   Sm , where:
 
 S   m   =C   1   ∪ . . . ∪C   m−1   ∪C   M+1   ∪ . . . ∪C   M   ,m= 1, . . . , M,M=M   c   +M   V  
 
     A filter, further denoted as the sub-solution, provides state estimate of the form:
 
 x   k   Sm     x   k   ˜p ( x   k   |Z   k   Sm )
 
     Note that the sub-solutions are created for both measurement and virtual clusters, i.e. M=M C +M V  sub-solutions is defined. 
     In addition to the full-solution and sub-solutions, a joint PDF is determined ( 418 ). The joint PDF is represented by:
 
 p ( x   k   S   ,x   k   S     1     , . . . ,x   k   S     M   )
 
     For the estimated state, the joint PDF characterizes also the correlation between the full-solution and all sub-solutions and sub-sub-solutions related to the measurement and virtual clusters (if any). The joint PDF can be computed either by a stand-alone algorithm or from the conditional PDFs of the full-solution and sub-solutions. The former approach is represented, for example, by the idea of cross-covariance propagator introduced in Brenner, M.: “Integrated GPS/Inertial Fault Detection Availability,” NAVIGATION: Journal of The Institute of Navigation, vol. 43, no. 2, 1996 and the latter by the approach proposed in Young, S. Y. R. and McGraw, G. A.: “Fault Detection and Exclusion Using Normalized Solution Separation and Residual Monitoring Methods,” NAVIGATION: Journal of the Institute of Navigation, vol. 50, no. 3, pp 151-169, 2003, where the cross-covariance matrices are computed on the basis of covariance matrices of the full-solution and sub-solutions. 
     The state estimate of the full-solution and all sub-solutions is transformed from the information domains (in which the statistical filters are working) to integrity monitoring classes (in which the integrity monitoring is working) ( 420 ). Transformation is, generally a nonlinear transformation of the estimated PDF according to:
 
 Y   k   S   =f ( x   k   S )
 
 y   k   Sm   =f ( x   k   Sm ), m= 1, . . . , M  
 
where f(.) is the known vector function, which results in:
 
 y   k   S     y   k   ˜p ( y   k   |Z   k   S )
 
 y   k   Sm     y   k   ˜p ( y   k   |Z   k   Sm )
 
As an example, transformation of the horizontal position described by two coordinates p x  and p y , which are part of the state and thus estimated by the statistical filter, into the horizontal range ‘r=f(p x , p y )=sqrt(p x   2 +p y   2 )’, which is further assessed by the integrity monitoring algorithm.
 
     The joint PDF is nonlinearly transformed as well, i.e. the PDF as represented as:
 
 p ( y   k   S   ,y   k   S     1     , . . . ,y   k   S     M   )  (1)
 
is computed. As mentioned above, the statistical filter state is defined in the information domain (e.g., 3 position, 3 velocity, and 3 attitude/heading elements, 9 elements in total), but for the integrity monitoring algorithm different variables (e.g., the horizontal and vertical position, horizontal and vertical velocity, and attitude/heading) are considered. These quantities define the integrity monitoring classes.
 
     The steps continue with defining test statistics for sub-solution ( 422 ). The defined statistics for a sub-solution is defined as:
 
 d   m,k   =y   k   Sm   −y   k   S   ,m= 1, . . . , M  
 
of which PDF p(d m, k ) can be computed using a convolution of known PDFs of:
 
 y   k   Sm  and  y   k   S  
 
on the basis of the PDF (1). Thus, the PDF
 
 p ( d   k )= p ( d   1,k   ,d   2,k   , . . . ,d   M,k )  (2)
 
is known.
 
     The mean value of the test statistics is determined as in step ( 424 ):
 
 {circumflex over (d)}   m,k   =ŷ   k   Sm   −ŷ   k   S   ,m= 1, . . . , M  
 
where ŷ k   Sm  stands for the mean of ŷ k|k   Sm , i.e., for ŷ k   Sm =E[y k   Sm ].
 
     Detection thresholds D m,k  are determined ( 426 ) for each statistics fulfilling the equality:
 
   p   (FA)=(1− p (FA))= P (| d   1,k   |&lt;D   1,{grave over (k)}   |d   2,k   |&lt;D   2,k   , . . . ,|d   M,k   |&lt;D   M,k )  (3)
 
where |d| stands for the absolute value of each element of vector d. If d is a vector then the notation d&lt;D means that each element of the vector d fulfils the inequality.
 
     The thresholds can be computed by the solution to the following integral relation in step ( 428 ): 
                         p   _     ⁡     (   FA   )       =       ∫   hyperrectangle             ⁢       p   ⁡     (     d   k     )       ⁢     dd   k           ⁢                   (   4   )               
meaning integration of the PDF of variable:
 
 d   k   =[d   1,k   T   ,d   2,k   T   , . . . ,d   M,k   T ] T  
 
over hyperrectangle with edge lengths defined by the thresholds:
 
 D   k   =[D   1,k   T   ,D   2,k   T   , . . . ,D   M,k   T ] T  
 
     Integration is based on the joint PDF p(d k ) (2). There exist indefinitely many hyperrectagles which fulfil the equation (3) and the integral equation (4) for:
 
   p   (FA)
 
     In different embodiments, from all these, thresholds D k  can be selected based on:
         (1) Distributing p(FA) budget among the integrity monitoring classes in predefined ratio (e.g., 15% allocated for vertical/horizontal position, vertical/horizontal velocity, roll, and pitch and 10% for heading), and   (2) Optimizing user-defined criterion(s), for example: (a) Minimum vertical position protection level and (b) Minimum volume of the hyperrectangle or a hyperrectangle defined by a subset of D k .       

     Except very special cases, the solution to the definite integral relation (3) is numerical. A straightforward solution to (3) can be based on numerical solution to the relation 
                 p   _     ⁡     (   FA   )       =         ∑     m   =   1     M     ⁢         p   _     m     ⁡     (   FA   )         -   corr           
where corr stands for the terms considering mutual correlation between particular terms d m . The correlation term is a function of union probabilities, i.e., of
 
 P (− D   m   &lt;d   m   &lt;D   m   ∪ . . . ∪−D   n   &lt;d   n   &lt;D   n ),∀ m,n,m≠n  
 
which are, however, unknown. Evaluation of the correlation term may require a too computationally demanding numerical solution. In the following, therefore, two numerically efficient algorithms for computation of the hyperrectangle edges D k  to fulfil (3) under assumption of the Gaussian joint PDF (2) are proposed (for the sake of simplicity, the time index k is omitted).
 
     Algorithm 1:
         1) The given probability  p (FA) is to be distributed among the test statistics d m , where m=1, . . . , M, and the probability related to d m  is denoted as  p   m (FA). The partial probability p m (FA) can be further written as
 
   p     m (FA)= P (| d   m   |&lt;D   m )= P (− D   m   &lt;d   m   &lt;D   m )
   Considering correlated statistics d m  and unknown correlation term corr, the total budget is initially distributed (according to user preferences) so that       

     
       
         
           
             
               
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             The probability is, thus, distributed under assumption of uncorrelated test statistics and the neglected and unknown correlation corn is compensated by the following steps. 
             2) Based on the set of partial probabilities and Gaussianity assumption, upper bound thresholds D m   up  are computed so that
 
   p     m   req (FA)= P (− D   m   up   &lt;d   m   &lt;D   m   up )∀ m  
 
             The computation can be performed using cumulative distribution function (CDF) of the Gaussian PDF given the moments of the PDF p(d m ) computed on the basis of full-solution and sub-solutions. 
             3) The upper bound thresholds D m   up  defines a region where the thresholds respecting the correlation, i.e, D m  should be searched. Using an optimization approach, the thresholds D m  are computed to fulfil
 
   p   (FA)=(1− p (FA))= P (| d   1,k   |&lt;D   1,k   |d   2,k   |&lt;D   2,k   , . . . ,|d   M,k   |&lt;D   M,k )  (5)
 
             subject to 
           
         
       
    
     
       
         
           
             
               
                 
                   
                     
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             where  p   m (FA)=P(−D m &lt;d m &lt;D m ), ∀m 
           
         
       
    
     A simple numerical solution to the optimization is based on specification of several candidate thresholds D m,(i) , ∀m, where i=1,2, . . . , and evaluation of (5) with respect to (6) and given  p (FA). Eq. (5) can be evaluated on the basis of a technique given in Genz, A.: “Numerical Computation of Multivariate Normal Probabilities,” J. Comp. Graph Stat 1, pp. 141-149, 1992, and standard results of CDF properties. The candidate thresholds D m,(i)  are selected on the basis of computed upper bound thresholds D m   up . 
     Algorithm 2:
         1) The joint probability (5) can be using the Bayes&#39; rule written as follows       

     
       
         
           
             
               
                 
                   
                     
                       
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             where the notation P(δ m |δ n ) stands for the conditional probability of δ m  conditioned by δ n . 
             Having given the total budget  p (FA), a set of particular values of the conditional probabilities, denoted as  ρ   m  (FA), can be constructed according to the user preferences so that
 
   p   (FA)= ρ   1 (FA) ρ   2 (FA)× . . . × ρ   M (FA)
 
             2) Having the probability  ρ (FA) and assuming Gaussian distribution of p(d M ), detection threshold D M  can be computed to fulfill
 
   p     M (FA)= P (| d   M   |&lt;D   M )= P (− D   M   &lt;d   M   &lt;D   M )
 
             using CDF of a Gaussian distribution. 
             3) Having the probabilities  ρ   M−1 (FA),  ρ   M (FA), the joint probability 
           
         
       
    
     
       
         
           
               
             
               
                 
                   
                     
                       
                         
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             can be computed. As the threshold D M  is already computed, the only unknown variable is D M−1  which can be numerically computed using results given in Genz, 1992 as the joint PDF p(d M−1 , d M ) can be computed from (2). 
             4) The algorithm analogously continues for all remaining conditional probabilities in (7). 
           
         
       
    
     Both algorithms represent a tool for computing detection thresholds while the test statistics are correlated. Note that Algorithm 1 performs one optimization over M-dimensional space, whereas Algorithm 2 performs M optimizations over one dimensional space. 
     Computed detection thresholds D m , ∀m, are to be used for detection of a failure. A failure is detected and an alarm is raised if there exist at least one m that
 
 d   m   ∉     −D   m   ,D   m   .
 
     The probability of missed detection p(MD) for each measurement cluster and the respective error bounds a m,k  is determined at step ( 428 ) for each sub-solution or sub-sub-solution (in case of virtual clusters). The computation requires solution to the following relations
         a. Total budget of p(HMI) can be written as:       

               p   ⁡     (   HMI   )       =         ∑     m   =   1     M     ⁢         p   m     ⁡     (   CF   )       ⁢       p   m     ⁡     (   MD   )           +       p   rem     ⁡     (   HMI   )               
where p m (CF) is a priori probability of m th  (measurement or virtual) cluster failure given by the probability of singe failure—p(SF) or probability of wide failure p(WF) related to measurement devices in the cluster, p m (MD) is required allowed probability of missed detection of the m th  cluster, and p rem (HMI) is the allocation of the HMI budget which cannot be detected by the method (e.g., simultaneous failure of all clusters).
 
     Error bounds a m,k  are computed to fulfil the equality:
 
   p   (MD)=(1− p (MD))= P (( y   k   −ŷ   k   S     1   )&lt; a   1,k ,( y   k   −ŷ   k   S     2   )&lt; a   2,k , . . . ,( y   k   −ŷ   k   S     M   )&lt; a   M,k )  (8)
 
where p(MD) is computed on the basis of partial probabilities p m (MD).
 
     The solution to error bounds is, analogously to thresholds computation, typically numerical and versions of Algorithms 1 and 2 can be straightforwardly used. Contrary to threshold computation, where definite integral relation (2), the solution to the error bounds in (8) requires solution to an improper integral (lower limit is infinite). 
     The required protection levels for the whole navigation information (for all integrity monitoring classes) is determined at step ( 430 ) as: 
               PL   k     =       max       m   =   1     ,           ⁢   …   ⁢           ,   M       ⁢     {       D     m   ,   k       +     α     m   ,   k         }             
where the function max select maximum value for each element of the vector. Note a different function for PL computation can be selected.
 
     The steps set out above describe detection of the failures in the clusters in an embodiment. If detection and exclusion is required, an additional layer needs to be created for each sub-solution. Mechanization of the additional level is analogous to the introduced steps, just the virtual clusters are not considered. In one embodiment, the concept of the fault detection and exclusion in the presented is analogous to the fault detection and exclusion in the solution separation. 
     An example, is herein provided to aid in the understanding of an embodiment. The example probability failures from the different navigation aiding sources  110  are summarized to include:
         1. Measurement: Information domain; aiding class; aiding section; probability of single failure (p(SF)); probability of wide failure (p(WF))   2. True air speed: velocity; air data speed; true air speed; p(SF)=1e−4/hr; p(WF)=n/a —just a single measurement   3. Odometer speed: velocity; odometer speeds; one-wheel odometer speed; p(SF)=1e −5/hr; p(WF)=1e−9/hr   4. DME range: position; RF terrestrial ranging; DME range; p(SF)=1e−4/hr; p(WF)=1 e−7/hr   5. GPS pseudo-range: position; RF satellite ranging; GPS pseudo-range; p(SF)=1e−5/hr; p(WF)=1e−8/hr   6. Galileo pseudo-range: position; RF satellite ranging; Galileo pseudo-range; p(SF)=1e−4/hr; p(WF)=1e−6/hr       

     The state of the full solution and the sub-solutions (i.e., the navigation information) include: 3-D position, 3-D velocity, attitude/heading. Integrity monitoring classes include: horizontal position, vertical position, horizontal velocity, vertical velocity, roll, pitch, &amp; heading. 
     Integrated monitoring (IM) requirements in this example include: 
     1. p(HMI)=1e−7/hr, and 
     2. p(FA)=1e−5/hr 
     Given the IM requirements and single and wide failure probabilities for each measurements, a following set of failures to be detected and excluded can be formed: 
     A. Failures to be excluded:
         1. Single true air speed failure   2. Single odometer speed failures   3. Single DME range and wide DME failures   4. Single GPS and Galileo satellites failures   5. Wide Galileo failure       

     B. Failures to be detected:
         6. All failure to be excluded   7. Wide odometer system failure   8. Wide GPS failure       

     Referring to  FIG. 5  the example provided above is illustrated in diagram  500 . As illustrated, the example include seven different clusters formed from 17 different measurements  301  through  317  from the navigation aiding sources  110 . A first cluster  521  is formed in an information domain; velocity, aiding class; air data speed and aiding section; true air speed. It includes one measurement  501 . The second cluster  522  includes two measurements  502  and  503 . The second cluster is in the information domain; velocity, aiding class; odometer speed, and aiding section, one-wheel odometer speed. The third cluster  523  includes measurements  504  and  505  and is also in the information domain; velocity, aiding class; odometer speed, and aiding section; one-wheel odometer speed. In this example, the second and third clusters  522  and  523  are further part of a first virtual cluster  531 . In this embodiment, the first virtual cluster  531  enables detection of wide failure (failure of all measurements in this aiding section) of the odometer aiding. The fourth cluster  524  includes measurement  506 ,  507  and  508 . They are in the information domain; position, aiding class; RF terrestrial ranging, and aiding section; DME range. The fifth cluster  525  includes measurement  509 ,  510  and  511 . They are in the information domain; position, aiding class; RF satellite ranging, and aiding section; GPS pseudo-range. The sixth cluster  526  includes measurements  512  and  513 . They are also in the information domain; position, aiding class; RF satellite ranging, and aiding section; GPS pseudo-range. Clusters  525  and  526  are further part of a second virtual cluster  532 . The seventh cluster  527  includes measurements  514 ,  515 ,  516  and  517 . They are in the information domain; position, aiding class; RF satellite ranging, and aiding section; Galileo pseudo-range. In this example, the second virtual cluster  532  also includes measurement  514  of the seventh cluster  527 . The example formation  500  of  FIG. 5 , further illustrates a full-solution  550 , seven sub-solutions  551  through  557  and  16  sub-sub-solutions  561  through  576 . Sub-sub-solutions  564  and  571  are related to virtual cluster #1 and #2 as well. 
     EXAMPLE EMBODIMENTS 
     Example 1, includes an integrity monitoring method for navigation systems with heterogeneous measurements, the method includes defining integrity monitoring classes specifying quantities of a navigation information to be protected. Measurements from a plurality of different type navigation aiding sources are received. The measurements are categorized by an information domain, an aiding class and an aiding section. The information domain is a category of at least one of estimated states and measurements that represent a same physical category. The aiding class is a category that uses a same physical method to acquire measurements. The aiding section is a category of measurements from the same aiding source. The measurements are organized into a plurality of measurement clusters based at least in part on measurement fault modes to be detected, measurement fault modes to be excluded, available computer resources and required performance. An integrity monitoring algorithm is applied to the measurement clusters to determine an integrity solution for all defined integrity monitoring classes. 
     Example 2 includes the method of Example 1, further wherein all measurements formed into a cluster are from the same information domain, further wherein all clusters include measurements from at least one aiding class, further wherein at least one cluster includes measurements from at least a first aiding section and a second aiding section. 
     Example 3 includes any aspects of the Examples 1-2, wherein applying an integrity monitoring algorithm to the measurement clusters to determine an integrity solution for all defined integrity monitoring classes further includes, processing all measurements to determine a full navigation solution. A subset of all measurements is processed to determine a set of navigation sub-solutions. The subset has a selected structure within the measurement clusters. Mutual dependence of the full navigation solution and the set of sub navigation solutions is assessed. Faults detection and possibly exclusion functionality and computing protection levels of quantities of a navigation information specified in integrity monitoring classes is provided based at least in part on the basis of a full solution estimate, sub-solutions estimates, dependence among the solutions, and required probabilities of missed detection and false alert. 
     Example 4 includes any aspects of the Examples 1-3, further including estimating a joint probability function to characterizes a correlation between the full navigation solution and the navigation sub-solutions. The probability functions of the full solution estimate, the sub-solution and the joint probability function are transformed from an information domain into the integrity monitoring classes. 
     Example 5 includes any aspects of the Examples 1-4, further including defining test statistics for each sub-solution, determining a mean value of the test statistics and determining detection thresholds of the test statistics and performing detection of the faults. 
     Example 6 includes any aspects of the Examples 1-5, wherein the determination of the detected thresholds of the test statistics further includes distributing budget among the integrity monitoring classes in a predefined ratio and optimizing user-defined criteria. 
     Example 7 includes any aspects of the Examples 1-6, further including determining the probability of missed detection for each measurement cluster and determining respective error bounds for each sub-solution. 
     Example 8 includes any aspects of the Examples 1-8, further including creating an additional layer of solutions for each lowest layer solution when detection and exclusion is required. 
     Example 9, includes any aspects of the Examples 1-8, further including forming at least one virtual cluster to include exclusion capability, the at least one virtual cluster including at least two of the plurality of measurement clusters. 
     Example 10 includes a program product for implementing an integrity monitoring for navigation systems with heterogeneous measurements, the program product comprising a processor-readable medium on which program instructions are embodied, wherein the program instructions are operable, when executed by at least one processor in a navigation system, to cause the navigation system to; categorize received measurements from a plurality of different type navigation aiding sources by an information domain, an aiding class and an aiding section, wherein the information domain is a category of at least one of estimated states and measurements that represent a same physical category, wherein the aiding class is a category that uses a same physical method to acquire measurements, wherein the aiding section is a category of measurements from the same aiding source; organize the measurements into a plurality of measurement clusters based at least in part on measurement fault modes to be detected, measurement fault modes to be excluded, available computer resources and required performance; and apply an integrity monitoring algorithm to the measurement clusters to determine an integrity solution for all defined integrity monitoring classes. 
     Example 11 includes the aspects of the program product of Example 10, wherein all measurements formed into a cluster are from the same information domain, further wherein all clusters include measurements from at least one aiding class, further wherein at least one cluster includes measurements from at least a first aiding section and a second aiding section. 
     Example 12 includes any of the aspects of Examples 11-12, wherein the program instructions operable, when executed by the at least one processor, cause the navigation system to; process all measurements to determine a full navigation solution; process a subset of all measurements to determine a set of navigation sub-solutions, the subset having a selected structure within the measurement clusters; assess mutual dependence of the full navigation solution and the set of sub navigation solutions; and provide faults detection and possibly exclusion functionality and computing protection levels of quantities of a navigation information specified in integrity monitoring classes based at least in part on the basis of a full solution estimate, sub-solutions estimates, dependence among the solutions, and required probabilities of missed detection and false alert. 
     Example 13 includes a system having an integrity monitoring function for heterogeneous measurements, the system including at least one input, at least one memory and at least one controller. The at least one input receives navigation related measurement information from a plurality of different sources. The at least one memory is used to store at least one filter and at least one integrity function. The at least one controller is in communication with the at least one input and the at least one memory. The at least one controller is configured to execute the at least one filter and at least one integrity function in processing the received navigation related measurement information from the plurality of different sources to determine the integrity of the received navigation related measurement information. The controller, based on the execution of the at least one filter, is configured to categorize measurements from the navigation related measurement information by an information domain, an aiding class and an aiding section. The information domain is a category of at least one of estimated states and measurements that represent a same physical category. The aiding class is a category that uses a same physical method to acquire measurements. The aiding section is a category of measurements from the same aiding source. The at least one controller is further, based on the execution of the at least one filter, configured to organize the measurements into a plurality of measurement clusters based at least in part on measurement fault modes to be detected, measurement fault modes to be excluded, available computer resources and required performance. The at least one controller, based on the execution of the at least one integrity function, is configured to apply an integrity monitoring algorithm to the measurement clusters to determine an integrity solution for all defined integrity monitoring classes. 
     Example 14 is a system including the aspects of Example 13, wherein all measurements formed into a cluster are from the same information domain, further wherein all clusters include measurements from at least one aiding class, further wherein at least one cluster includes measurements from at least a first aiding section and a second aiding section. 
     Example 15 is a system including any of the aspects of Examples 13-14, wherein the at least one filter is configured to process all measurements to determine a full navigation solution, the at least one filter is further configured to process a subset of all measurements to determine a set of navigation sub-solutions, the subset having a selected structure within the measurement clusters, the at least one controller is further configured implement an algorithm to assess mutual dependence of the full navigation solution and the set of sub navigation solutions and provide faults detection and possibly exclusion functionality and computing protection levels of quantities of a navigation information specified in integrity monitoring classes based at least in part on the basis of a full solution estimate, sub-solutions estimates, dependence among the solutions, and required probabilities of missed detection and false alert. 
     Example 16 is a system including any of the aspects of Examples 13-15, further including a plurality of navigation related measurement sources to provide the navigation related measurement information. 
     Example 17 is a system including any of the aspects of Example 16, wherein the plurality of navigation related measurement sources includes at least two of an inertial measurement unit, a global navigation satellite receiver, a magnetometer, air-data, distance measurement equipment, eLoran, odometer, a radar-altimeter, a map and vision sensor. 
     Example 18 is a system including any of the aspects of Examples 13-17, further including a vehicle system in communication with the controller to receive the determined integrity solution. 
     Example 19 is a system including any of the aspects of Examples 13-18, wherein the vehicle system is a control system to control operations of vehicle based at least in part on the determined integrity solution. 
     Example 20 is a system including any of the aspects of Examples 13-18, wherein the vehicle system is at least one of a control system, a surveillance system, a display system and a management system. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.