SAF Integra-X, Руководство пользователя

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INTEGRA-X User Manual FUNCTIONAL DESCRIPTION
SAF Tehnika JSC 100
: FUNCTIONAL DESCRIPTION
ACM - Adaptive Coding and Modulation
ACM technology allows operators to achieve high-capacity data transmission over microwave
links and improve link utilization. This reduces both operational and capital expenditures for
maintaining high-capacity links. ACM can maintain the highest link spectral efficiency possible at
any given time in any link condition.
In traditional voice-dominated wireless backhaul transmission networks, service availability levels
of 99.995% are the norm. However, newer services such as Internet browsing, video streaming,
video conferencing and file moving (download/upload) can operate at more relaxed availability
levels. Knowing traffic parameters and weather conditions in link location it is possible to build a
very reliable system. There could be temporary link congestion situations, which could be even
unnoticeable for a customer if the link has not completely lost its synchronization. Switching
between modulation schemas is hitless - this means that during modulation change there is no
data loss. This is one more advantage for moving from TDM to IP traffic. For this ACM technology
maintains the best possible capacity in given conditions. The link will reduce capacity, but still
stay up, synchronization is not lost. In case of very harsh weather conditions, if the link lost sync,
it will become synchronized faster if ACM is enabled.
Figure 5-1 Modulation switching scheme
Let’s look at hard weather scenario for the 15km long link in N climatic zone, 11GHz frequency,
see
Figure 5-1
.
When weather conditions are clear, the wireless link operates at maximum capacity and maximum
modulation 2048QAM providing services with the full data rate. If link conditions become poor –
during heavy rain, severe atmospheric refraction changes for very long links, for example –
services is adapted dynamically to the changing link conditions. This is done by switching
between modulation schemes according to the radio conditions. If we look at availability values
in
Figure 5-1
, we see that link is available practically all the time, if properly installed.
An ACM profile defines the modulation for a given range of the MSE (Mean Square Error) alone,
which is inverse of SNR (Signal to Noise Ratio). The 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. MSE is visible all the time in default System summary and
also in the main page, see
Main page
on page
24
.
There is a maximal Tx power difference between higher modulation and lower modulation
scheme. Tx power is decreased for higher modulations because input and output radio frequency