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WSEAS TRANSACTIONS on ELECTRONICS

{ } m a x U r r n m n w x =

Step 2: Calculate the center of the weighting interval zrn .

Zr = {zr1, zr 2 ,K, zrt }

( ) / 2 L U r n r n r n z w w = +

Step 3: Calculate the extension distance.

EDG =

t n=I

( ) / 2 ( ) / 2 P U L m n r n r n r n U L r n r n x z w w w w

I +

Step 4: Define the extension distance of the atom clock oscillation frequency EDS . Determine whether

the extension distance of the controlled receiver EDG is equal to EDS or not. If EDS = EDG , then

maintain the original output. If it is not the same then go to Step 5.

Step 5: Readjust the center of the weighting interval.

(1)

z

new pn

=z

old pn

+η(x

p ( old ) mn

) o l d p n z

z

new pn

=z

old pn

η(x

p ( old ) mn

) o l d p n z

(2) Adjust the weighting factor interval.

p n p n L(new) w w U (new)

p n L(old ) w =

p n U (old ) w =

+η(x

p ( old ) mn

( m n x p ( old ) η +

) ) o l d p n o l d p n z z

p n p n w L(new) w U (new)

p n p n L(old ) w w U (old ) = =

η(x ( m n x p (old ) mn p ( old ) η

) ) o l d p n o l d p n z z

(3) Let EDS = EDG , Oms is the result of the last output.

Oms = z

new pn

+η(x

p ( old ) mn

z

new pn

)

5 Experimental Results

Accurate single point positioning is generally performed using a pair of dual-frequency GPS receivers. The ionospheric and tropospheric delay

ISSN: 1109-9445

154

Guo-Shing Huang

transmission errors can be dispelled via the GPS carrier phase observation and pair of GPS receivers to improve the position precision. However, if there is no oscillation frequency syntonization between the GPS receiver and satellite clock, the position precision will be reduced. Therefore, the extension controller and extension neural network are used to adjust the receiver oscillation frequency to synchronize the satellite oscillation frequency.

Figure 3 shows the structure of the experimental system. The oscillation frequency of the atomic clock is used to reduce the bias between the receiver and the atom clock frequency. The proposed approach can more accurately resolve the integer ambiguity, clock bias and wide lane carrier phase. Enhancing the accuracy of these parameters allows the vehicle position to be estimated more precisely.

Figure 3. System Functional Block Diagram

Figure 4 shows the navigator’s position error using GPS receiver observation. Using GPS ephemeredes and carrier phase measurements, the time errors between the GPS receiver and satellite can be estimated, as shown in Figure 5. Position precision is analyzed about 3.5 meters before using the extension controller. The time error is about

4.85×107 seconds.

Issue 7, Volume 4, July 2007

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