User manual

Chapter 2 - Managing a Single Device/Cell Performance Parameters Page
AlvariCRAFT Device Manager 146 User Manual
the AU/BU and is also included in the Adaptive Modulation Algorithm information
messages transmitted by the AU/BU and the SU/RB. The higher the value of this
parameter, the higher is the weight of history in the formula.
Available values: -1 to 32. -1 is for no weight for history, meaning that average
SNR equals the last measured SNR.
2.23.5 Maximum Modulation Level
When the Adaptive Modulation Algorithm is enabled, it changes the modulation
level dynamically according to link conditions. The purpose is to increase the
probability of using the maximum possible modulation level at any given moment.
Although the algorithm will avoid using modulation levels that are too high for the
prevailing link conditions, it might be better under certain conditions to limit the
use of higher modulation levels. If the link quality is not sufficient, it is
recommended that the maximum modulation level be decreased, as higher
modulation levels increase the error rate. In such conditions, a higher Maximum
Modulation Level increases the number or retransmissions before the modulation
level is being reduced by the Adaptive Modulation Algorithm. A high number of
retransmissions reduces the overall throughput.
The link quality can be estimated based on the SNR measurement:
For an SU, the uplink SNR can be viewed in the Details section for the applicable
SU in the SUs Information page of the AU (“SUs Information Page (AU only)” on
page 73). If the measured SNR is less than a certain threshold, it is recommended
that the maximum modulation level of the SU/RB be decreased in accordance
with the recommendations provided in Section 2.23.12 below, using the values of
typical sensitivity. It is recommended to add a 2 dB safety margin to compensate
for possible measurement inaccuracy or variance in the link quality. Note that the
SNR measurement at the AU is accurate only when receiving transmissions from
the applicable SU.
For the AU, the Maximum Modulation Level should be set to a value that is proper
for all the SUs it serves. This means a value that is at least the same as the
highest Maximum Modulation Level in configured in the SUs.
For a BreezeNET B link, the SNR can be viewed in the “Site Survey Per Modulation
Level Counters Page (SU and RB Only)” on page 94
When the Adaptive Modulation Algorithm is disabled, this parameter defines the
fixed Modulation Level used for transmissions.
The minimum and maximum values for the Maximum Modulation Level are
defined by the Sub-Band in use. Currently, all Sub Bands support the entire
range of modulation levels, from 1 to 8, except to BreezeNET B units using a 40