u-blox ANTARIS 4, Руководство по системной интеграции

Страница: 29 / 187

1.7 High Sensitivity GPS (SuperSense
®
GPS)
GPS signals are already very weak when they arrive at the Earth’s surface. By the time the GPS signals arrive at
the receiver they are typically as weak as –130dBm (–160dBW). This is well below the thermal noise level.
Standard GPS receivers (e. TIM-4A) integrate the received GPS signals for up to 20ms. This results in the ability
to track signals down to about –150dBm (–180dBW). High Sensitivity GPS receivers are able to integrate the
incoming signals much longer than this and can therefore track down to levels approaching -160dBm. High
Sensitivity GPS can provide positioning in many but not all indoor locations. Signals are either heavily attenuated
by the building materials or reflected in as multipath. High Sensitivity GPS Receivers can also compensate the
performance deficits of smaller antennas.
For Standard GPS Receivers, signal reflections and multipath effects are undesirable phenomena. Indoor GPS
reception, however, must - besides the direct line-of-sight signal - rely on reflected GPS signals in order to
receive a sufficient number of satellites to calculate positions. Since reflections increase the propagation delays,
the positioning accuracy will obviously decrease. Good High Sensitivity GPS Receivers like SuperSense
®
will tune
their multipath suppression in such a way that multipath is suppressed on channels with strong signals in order
in case of poor reception in order to provide an
optimal GPS coverage.
e at a price. Customers must accept some tradeoffs while the signal
mance (acquisition sensitivity, increased acquisition times), positioning
g.
to achieve an excellent accuracy whereas it accepts all signals
The benefits of weak signal tracking com
level is low: Reduced acquisition perfor
accuracy and dynamic responsiveness.
Strong Signals Weak Signals
Acquisition
Positioning Accuracy Very good
Depends on signal quality
and Environment
Fast Limited
Dynamic Responsiveness High Limited
Figure 23: Trade-off in Weak Signal GPS
High Sensitivity GPS Receivers open new applications and market opportunities such as navigation in building
interiors or the covert use of GPS receivers in vehicles and they help to drive down the costs by allowing the use
of smaller GPS antennas.
Antenna: Located under seat
+
3D Fix
+
2D Fix
+
Degraded Mode
+
Invalid Fixes
TIM-LL (ANTARIS) TIM-LH (SuperSense)
Patch antenna in upright position
Antenna
underneath
driver's
seat
Antenna: Located under seat
+
3D Fix
+
2D Fix
+
Degraded Mode
+
Invalid Fixes
+
3D Fix
+
2D Fix
+
Degraded Mode
+
Invalid Fixes
TIM-LL (ANTARIS) TIM-LH (SuperSense)
Patch antenna in upright position
driver's seat
Figure 24: Improved GPS Coverage with High Sensitivity GPS Receivers
Antenna
underneath
GPS Modules - System Integration Manual (SIM) (incl. Reference Design) GPS Fundamentals
GPS.G4-MS4-05007-A1 Page 29