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6.2 SELECTION OF SBAS SATELLITE,CORRECTION DATA OF WHICH IS USED

 

The Receiver has been so designed that three SBAS satellites may be tracked simultaneously. Therefore, we have to decide which correction data among those three SBAS satellites is to be used for position-fixing. The technique we adopted is that position-fixing calculation is performed internally applying correction data of each SBAS satellite independently and then we have three position fixes at maximum. Among those three fixes, each calculated HPLWAAS is compared each other and the fix having the least HPLWAAS is adopted. The reason why we adopted this technique is that we can provide the position fix with the highest accuracy by comparing the protection levels. The Receiver, as it is the prototype, is so designed that it may give each result of position-fixing and the result of position- fixing calculation using GPS only in order to give better understanding on comparison of results of position-fixing using multiple SBAS satellites.

 

6.3 USE OF PSEUDO-RANGE OF SBAS SATELLITE

 

The pseudo-range of SBAS satellite is used without paying particular attention to the mixed use. For example, if the satellite, the correction amount of which is used, broadcasts that it is in WAAS HEALTHY state to the other SBAS satellite, the pseudo-range measured with such other SBAS satellite is also used for position-fixing. Definitely speaking, if the fast correction for the said SBAS satellite is broadcast and UDREI indicating the pseudo-range error satisfies the requirements of position-fixing mode, such pseudo-range can be used.

 

7. FD/FDE PROCESSING

 

FD/FDE processing is a module where the Receiver alone monitors integrity and it is carried out once a second. The requirements of the MOPS for FD/FDE are different depending on the PA mode and on the other modes. First of all, for the PA mode, while the integrity has naturally been obtained from WAAS, it is also required to detect the existence of abnormality in satellite in order to cope with local abnormality. Secondly, for the other modes, it is required to detect the existence of abnormality in satellite and if possible, the abnormal satellite is requested to be identified and excluded. The requirements described in the MOPS are shown in Table 3. Where there exist excluded satellites (excluded in the processes of step error detection or FDE), it is requested that they are monitored and made return for position-fixing soon after abnormality in them is removed. This function (monitoring of excluded satellites for restoration) is also achieved by FD/FDE processing. Finally, in order to utilize the baro-altimeter for position-fixing computation, it is required to memorize the difference in altitude between GPS position-fixing and baro-altimeter and use it corrected.

 

Table 3. Requirements for FD/FDE Process

179-1.gif

 

The following four functions are provided for the FD/FDE processing to realize the above requirements:

 

1) Failure detection

2) Exclusion of failed satellite

3) Monitoring of excluded-satellites for restoration

4) Calibration of baro-altimeter

 

In our Receiver, the functions corresponding to the seven methods of position-fixing described in subclause 5.2 are determined to be performed.

The relationship is shown in Table 4.

 

 

 

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