Page 24
J-Series Data Radio – User Manual
Issue 09-10
SmartPath™ and Roaming Remotes
SmartPath™ allows the user to design networks that permit Remote radios to roam. In a roaming network, a remote is typically installed on a
moving vehicle or object, such as a truck or a train. Access Point radios are installed at key locations where good RF coverage can be provided.
The desired outcome is for connectivity to any available Access Point. In this scenario, there is no requirement to configure a preferred or
alternative list of Access Points. The trusted Access Point list remains empty, and the roaming remote radio will associated with any Access Point it
can find that has the appropriate network name.
RSSI Threshold and Roaming Remotes
SmartPath™ has a feature that allows the user to prevent excessive Access Point hand-overs due to inadequate RF signal strength. Refer to the
diagram shown above. In this scenario, several Access Points have been positioned or located together to provide over-lapping coverage. The
outer circle represents the range of usable signal strength from that Access Point. To prevent Remote radios from synchronising to Access Points
that do not currently provide adequate levels of received signal strength, RSSI Threshold filter facility can be enabled.
The RSSI Threshold defines the minimum acceptable received RSSI level before a radio will synchronise to an Access Point. When a Remote
finds an acceptable Access Point in the network, it first checks to ensure that the received RSSI is above the RSSI Threshold. If the received RSSI
is below the threshold, the Remote radio will continue to search for other Access Points. Once synchronised to an Access Point, the Remote will
remain synchronised until the RSSI level is 10dB below the threshold (ie: a 10dB hysteresis is applied). When the RSSI drops below this value, the
remote searches for new acceptable Access Points with a received signal strength above the RSSI Threshold.
For example, if the RSSI threshold is configured to be -80dBm, then when a remote detects the current Access Point is being received at -90dBm,
the remote will drop synchronisation with that Access Point and start searching for another Access Point with a signal strength of -80dBm or better.
This ensures that Remotes which are in the range of other Access Points with more usable signal strength do not remain associated with their
existing Access Point at very low or inadequate signal strengths.
