Full modulation range: 256QAM, 128QAM, 64QAM, 32QAM, 16QAM, 4QAM
Traffic can be mapped into different priorities, which define the level of service for each
application.
Figure 4.3
illustrates how different services – such as rich voice and video – are mapped
into different classes of availability (CoA) such as 99.995% or 99.687%.
The implementation of multiple priorities increases the available capacity up to 10 times that of
standard links. When conditions are clear, the wireless link operates at maximum capacity and
provides all services with the full data rate. When link conditions are poor – during harsh rain, for
example – predefined high-availability services such as voice are not affected. However, the capacity
of low-priority services is adapted dynamically to the changing link conditions. This is done by
provisioning bandwidth according to the link conditions and traffic priority.
An ACM profile defines the link parameters (modulation) for a given range of the Radial MSE. The
Radial MSE range of each profile defines the threshold for switching from one ACM profile to another.
Each ACM profile has a different spectral efficiency, derived from its modulation.
The receiver continuously monitors the link condition based on Radial MSE value.
Once the estimators at the receiver side show that the link performance is not suitable for the
current ACM profile, an ACM switching process will be initiated. In case of degradation in the link
performance, the new ACM profile will include lower modulation, decreasing the link bitrate. The
ACM switching rate is measured in dB/s and is a key feature of ACM systems.
In general, the higher the switching rate, the better the system’s immunity to rapid Radial MSE
changes. When the switching is being executed, the payload rate is being modified to fit the
aggregated data rate to the new available link data rate.
Alternatively, ACM can also be used to increase the link distance, resulting in added link spectral
efficiency. The same concept is implemented as previously, with the margins that were kept for
99.995-percent bandwidth availability now used to increase the link distance. Whenever the link
conditions are degraded, the system will switch to an ACM profile with lower spectral efficiency to
enable maintaining the link.
The following real-world example illustrates the benefits of ACM. Consider a CFIP link operating
at 23 GHz with 56 MHz channel spacing and 45.9 dBi (120 cm) antenna gain. The link is operating in a
moderate rain region similar to central Europe with a distance of 15 kilometers.
The system operation is set to a minimal payload of 69 Mbps Ethernet for 99.995% availability.
Most of the time system would support a 366Mbps Ethernet connection instead of 69 Mbps
connection. The system automatically monitors the link conditions and changes the capacity without
interrupting the data transmission (hitless changes), as shown in
Figure 4.3
.
The CFIP Lumina Series Full Outdoor Unit Technical Description and Configuration Guide • Rev. 1.10 •
© SAF Tehnika JSC 2013
