CableFree FSO ATPC

ATPC is a standard feature of Carrier-class CableFree FSO products.

A CableFree FSO Link comprises two FSO units, each transmitting user data and telemetry signals to each other. Each FSO head unit decodes the incoming remote RSSI levels and a sophisticated software algorithm uses these to vary the local transmit laser power. In automatic mode, this is adjusted to maintain a optimum received power level at the remote FSO terminal.

In automatic mode, the local transmit power is regularly updated to avoid either low signal or saturation of the remote optical receiver, which would cause data errors and ultimately link outage. ATPC acts to decrease output power from the nominal ‘full power’ output of a CableFree FSO system. This ensures that optical eye safety is not compromised, compliant with Class 1M standards at all power levels; and that the laser device(s) experience lower stress, therefore extending the operational lifetime.

As ATPC does not increase power beyond ‘nominal full power’, it does not extend the maximum range of each system type; however, it does allow the system to be installed at much shorter distances than without ATPC. Reducing the output power eliminates the requirement for defocusing or attenuation of the link to achieve the optimum RSSI levels.

ATPC gives a CableFree link a 12dB advantage over non-ATPC systems in poor weather, such as fog; increased atmospheric attenuation is overcome by increasing the optical output power up to the maximum available.

ATPC can also help if the link suffers from interference by the sun; in rare cases where solar energy is incident on the receiver, the laser output power of the opposite unit is reduced to ensure that the combined solar plus FSO power received does not saturate the optical receiver.

ATPC can be controlled by an installer using the CableFree Alignment Module, and remotely from a workstation or laptop using FSO LinkManager™.

The alignment module incorporates a menu system where the mode of operation can be selected between ATPC mode “off” (maximum power), “manual” (enabling manual control of the local Tx power) or “auto” where the local unit adjusts it’s output power to maintain the pre-set RSSI value of the remote end.

LinkManager™ provides the same control as the alignment module with the added options of being able to control both the local and remote settings and being able to adjust the pre-set RSSI targets stored in the heads. By this means, ATPC features can be enabled or disabled remotely without need to visit a rooftop location.