Uplink power control – Comtech EF Data MIDAS 4 System and Design User Manual
Page 50
System and Design Manual, Revision 2
3–8
Theory of Operation
These three steps are performed as follows:
1. The LinkSync™ Modem measures the receive frequency of the outbound
control channel and provides this information to the MIDAS Controller
periodically, the period being user-configurable.
a. The MIDAS Controller then calculates the offset from the
nominal, which is used to correct the Network Control Modem’s
TX frequency.
2. The Node Control Modem determines the receive offset by measuring the
receive frequency of the outbound control channel.
a. This offset is used to calibrate the RX frequency of the Node Control
Modem and all the traffic modems (during call setup) at the node.
b. The traffic modems that have active calls are not adjusted.
Calibrations are periodically performed where the period is user –
configurable.
3. MIDAS Controller periodically polls a Node Control Modem to transmit
exclusively, and measures the receive frequency for the incoming bursts
from the Node Control Modem on the inbound control channel.
a. It then estimates the offset and provides this information to the Node
Control Modem.
b. The Node Control Modem then applies this offset to correct its TX
frequency and that of all the traffic modems (during call setup).
c. The traffic modems that have active calls are not adjusted. This
process is repeated periodically, the period being user-configurable.
U
U
p
p
l
l
i
i
n
n
k
k
P
P
o
o
w
w
e
e
r
r
C
C
o
o
n
n
t
t
r
r
o
o
l
l
Uplink Power Control at the MIDAS Controller site compensates for
outbound control channel uplink degradation so that it always downlinks at a
constant power at the satellite.
A reference E
b
/N
o
is calculated for the received outbound control channel at
the MIDAS Controller site for clear sky conditions. The LinkSync™ Modem,
at the MIDAS Controller site, measures the received outbound control channel
E
b
/N
o
on a continuous basis.
• If the measured E
b
/N
o
differs from the calculated reference, the MIDAS
Controller calculates the offset to be applied to the transmit power level
of the outbound control channel to achieve the desired reference E
b
/N
o
.
• The transmit power is adjusted only when the difference exceeds a
threshold, which is configurable.