Appendix A: BRM Support for Steered Antennas
A.1: Steered Antenna Control
In conjunction with the BRM’s RESTful and web-socket interface the BRM can support a wide range
of automatic steered antenna types.
The process for the antenna to seek the satellite is initiated by the BRM whenever the BRM enters (or
re-enters) pointing mode. The BRM provides to the FEM/antenna via the I2C interface aids to aid
antenna alignment including:
>
Current satellite azimuth and elevation
>
Current receive frequency
>
Current received signal strength (C/No) and bearer type
>
GNSS derived heading
>
GNSS derived speed
Methods the FEM/antenna may use for determining how well aligned the antenna is to the satellite
include:
>
Dead reckoning
>
Using a receiver incorporated in the FEM/antenna tuned to the current BRM receive frequency
to measure signal strength
>
Using the BRM’s receiver to provide received signal strength and bearer type
The FEM/antenna is responsible for deciding if the antenna has successfully ‘seeked’ the satellite and
can start to track the satellite maintaining antenna alignment as the antenna moves. The decision to
move from seeking to tracking is typically through receiving a predefined signal strength threshold
and/or detection of a peak in received signal strength.
The FEM/antenna is responsible for providing antenna status messages to the BRM which are then
passed onto the user of the antenna status via a web-socket.
The user, or possibly automation built into the terminal application or web UI, knowing both the BRM
received signal strength and antenna status is responsible for making the decision on when the
terminal exits pointing mode and starts the registration process.
A.1.1: Example With Receiver Incorporated into the Antenna
A message sequence chart for a steered antenna using a custom receiver built into the antenna to
determine received signal strength is shown in
.
Note:
Heading and speed may be continually requested at intervals of up to once per second.
80:
BGAN Radio Module Terminal Development Kit User Guide
Confidential and Proprietary – Inmarsat Global Limited
