1.696 Uplink-Power-Control

The Uplink-Power-Control logical device adjusts the level of a transmit signal in order to compensate the atmospheric attenuation in the signal uplink. To achieve this, the Uplink-Power-Control logical device reads the level of the satellite's beacon from a beacon receiver. The decrease of the beacon level with respect to it's 'clear sky' value describes the degree of downlink atmospheric attenuation which is used to estimate the atmospheric attenuation in the uplink.

The Uplink-Power-Control logical device must not use the level indication of the signal received back from the satellite instead of the beacon level. This would create a 'closed loop' level control which tends to oscillate or at least overshoot in an impermissible way.

Device window pages

The following table shows which device window pages are available with this individual device type. Tool-bar functions not mentioned here are described at the general description of device windows .

• --- This page shows the operational parameters.
• --- The device info page.
• --- The maintenance page. The configuration parameters described below are set at this page.

Configuration parameters

At the maintenance page of the device window there are a couple of configuration parameters which must be set to interconnect the Level-Set device to the devices it monitors and controls.

Clear Sky Settings

Before the uplink power control can work, it must know the nominal values for the transmit power and the beacon level under clear sky conditions. You may enter these values to the appropriate fields at the primary device window page of the device. However, the more comfortable way is to press the 'CLEAR SKY' button once the transmit level has been setup properly. The this function also may be used to re-adjust the nominal values from time to time in order to compensate for some gain drift.

Control Ratio

The device has to estimate the atmospheric attenuation in the uplink from a lowering of the beacon (downlink) level. As transmission usually is done at higher frequencies than the downlink, the uplink atmospheric attenuation will be higher than the measured beacon level degradation.

The 'ratio' parameter found at the 'Advanced Parameters' page defines the uplink/downlink atmospheric attenuation ratio to be applied. You may set this value manually or let the device calculate it from the transmit / receive frequencies (ratio mode = 'AUTO'). E.g. for the Ku-band a ratio of 1.2 may be used which means that the transmit power gets increased by 1.2 dB if the beacon level falls by 1 dB.

When using the automatic mode, the device calculates the ratio from the frequency values shown at the same page. If you did set the 'txFrequencyId' and 'rxFrequencyId' configuration parameters, the frequency value are read automatically from the real settings. If you didn't configure this, you have to enter the frequency values manually.

Filtering And Hysteresis

The device provides some parameters to adjust the behaviour of the control that it does not react on every glitch in the beacon level. These parameter are:

• clear sky hysteresis: The control will only increase the transmit level if the beacon level is at least this value below it's nominal reading. A typical value for this setting is 0.3 dB. The uplink power control ignores the natural jitter of the beacon level and starts to work if the beacon level falls to 0.3 dB below the clear sky value.
• output hysteresis: Once the uplink power control starts to work, it adjusts the transmit level with every tenth of a dB the beacon level changes. If you want that the transmit level is only adjusted when the value changes significantly, set this hysteresis parameter to a non-zero value.
• filter: The device also includes a low pass filter which may be applied to the beacon level readings. Please note, that activating the filter always will introduce an additional delay to the processing in the device.

Output Power Slope Limit

The device is capable to limit the slope of the commanded output power to user defined values. This means, a leap of the input power does not lead to an output power leap, the output power is commanded step by step to reach its target value with the given slope.

Power increment / decrement slopes are defined in dB/sec, the device internally interprets this as dB / driver cycle. Please ensure, that the IDLE time of the interface containing the Uplink-Power-Control device is set to 1000 msecs to match 'dB/sec' and 'dB / driver cycle'.

To enable the slope limits, set the parameter 'speed limit' to 'YES' and the slope values as desired.

Limits And Fault Detection

The device provides two parameters to limit the amount of transmit power adjustment:

• max power increase: The value defines the maximum increase the uplink power control applies to the transmit level. If the beacon level falls in a way that would lead to a higher transmit power, the latter is commanded to the highest possible value and a 'High limit' fault is raised. The fault is cleared as soon as the limit condition disappears.
• max power decrease: This limit value works the same way, but for transmit level decreases . Usually you will set this to zero in order to prevent the device from decreasing the transmit power below the nominal value.

Additionally, the device reports a 'long term power increase' fault which becomes active, when the 'power increase fault' is constantly active for a given time. This fault is latching am mut be reset by the 'RST FLT' button to be cleared. The duration how long the 'power increase fault' must be active to trigger this fault is tunable as a configuration parameter.

Beside the limit values discussed above, the device provides a parameter called drop threshold . If this parameter is set to a non zero value, the device permanently monitors the change of the beacon level from one reading to the next. If the beacon level suddenly falls by an amount larger than the threshold set, the uplink power control gets stopped before this dubitable value is processed. The device raises a 'Drop detected' fault and stops working until the RESET button ist pressed to clear the fault. This behaviour shall prevent the device from setting the transmit power to it's maximum in case of a failure or maloperation of the beacon receiver.

Inhibiting the UPC

The device is capable to watch an external parameter value and inhibit the UPC processing if this parameter turns to a certain value. This way for example a LNB fault can be watched and used to to inhibit the control loop in case of an error.

The inhibit state is latching, it must be cleared manually by pressing 'RST INH'. Depending on the 'resetOnDisable' mode, the control loop freezes when inhibited (resetOnDisable=NO) or reverts to the nominal output power (resetOnDisable=YES) when inhibited.

Variables defined by this device driver