SE868Kx-Ax Family Product User Guide
1VV0301201 Rev. 5
Page 55 of 83
2021-07-15
Not Subject to NDA
4.
Extraneous path loss (e.g. rain)
5.
Partial or total path blockage (such as foliage or buildings)
6.
Multipath interference (caused by signal reflection)
7.
GNSS antenna characteristics
8.
Signal path after the GNSS antenna
The GNSS signal is relatively immune to attenuation from rainfall. However, it is heavily
influenced by attenuation due to foliage (such as tree canopies, etc.) as well as outright
blockage caused by buildings, terrain or other objects near the line of sight to each
specific GNSS satellite. This variable attenuation is highly dependent upon satellite
location. If enough satellites are blocked, say at a lower elevation, or all in one general
direction, the geometry of the remaining satellites will be
worse (higher DOP) and will
result in a lower position accuracy. The receiver reports this geometry effect in the form
of PDOP, HDOP and VDOP numbers.
For example, in a vehicular application, the GNSS antenna may be placed on the
dashboard or rear package tray of an automobile. The metal roof of the vehicle will cause
significant blockage, plus any thermal coating applied to the vehicle glass can attenuate
the GNSS signal by as much as 15 dB. Again, both of these factors will affect the
performance of the receiver.
Multipath interference results when the signal from a particular satellite is
reflected from
a surface (e.g. a building or the roof of a car)
and is received by the GNSS antenna either
in addition to or in place of the line of sight signal. The reflected signal has a path length
that is longer than the line of sight path and can either attenuate the original signal, or, if
received in place of the original signal, can add error in determining a solution because
the distance to the particular satellite is actually shorter than measured. It is this
phenomenon (as well as the partial sky obscuration) that makes GNSS navigation in
urban canyons (narrow roads surrounded by high rise buildings) so challenging. In
general, the reflection of a GNSS signal causes its polarization to reverse. The
implications of this are covered in the next section.
GNSS Antenna (included in the module)
The SE868xx-Ax modules include a SMT 9 x 9 mm ceramic patch antenna shown in the
following table:
Module
Antenna
Constellations supported
SE868K3-A
9 x 9 x 4 mm
GPS, Galileo, GLONASS
SE868K3-AL
9 x 9 x2 mm
GPS, Galileo, GLONASS
