Specifications

VP ONCORE COMMAND REFERENCE

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xDOP HYSTERESIS (@@Ak)

Setting this parameter allows the user to change the criteria by which the

Motorola VP GPS receiver selects satellites. The VP evaluates the

geometry for all satellites in view every few seconds. In doing so, it

evaluates every combination of the visible satellites (based on the

Position Fix Algorithm Type selection), computes an xDOP parameter for

each combination (xDOP type as selected with the

@@Aj command)

and sorts them into ascending order. If only three or four satellites are

visible, the receiver tracks the visible satellites and computes position

without regard to geometry (xDOP) since these satellites represent the

only choice at that time. However, if five satellites are visible, then five

combinations of four satellites are possible for navigation (with the

Position Fix Algorithm Type set for "Best-4"). The VP computes an xDOP

for each combination and determines position from the set of four

satellites corresponding to the best xDOP, leaving any remaining

satellites that are tracked in reserve for use if one or more of the primary

four satellites are lost momentarily. With the Position Fix Algorithm Type

set for "N-in-View"

(@@Ar command) the GPS receiver compares the

closeness of xDOP for all combinations of visible satellites greater than

the number of receiver channels.

There are periods where the relative difference in xDOP among the

many satellite combinations is small, and the GPS receiver would switch

satellites needlessly if it were not for this parameter. To combat this, the

xDOP hysteresis command can be used. When set to a non-zero

number, a threshold on the change in xDOP is added to the satellite

selection criteria. If the parameter is set to zero, then the GPS receiver

will select the best satellites after every satellite alert computation without

regard to the "closeness" of xDOP. If the parameter is set relatively high,

then the receiver will switch satellites only if the geometry on the tracked

satellites becomes very poor, or if one of the tracked satellites goes

below the satellite elevation mask angle.

Range: 0.0 to 99.9 Default value: 1.0

Resolution: 0.1

37 Synergy Systems, LLC 05OCT01