User manual

Chapter 2 - Managing a Single Device/Cell Performance Parameters Page
AlvariCRAFT Device Manager 151 User Manual
The decisions made by the Adaptive Modulation Algorithm for the modulation
level to be used are based on multiple parameters, including information on
received signal quality (SNR) that is received periodically from the destination
unit, the time that has passed since last transmission to the relevant unit, and
the recent history of successful and unsuccessful transmissions/retransmissions.
In the AU the decision algorithm is performed separately for each SU.
The transmission/retransmission mechanism operates as follows:
1 Each new frame (first transmission attempt) will be transmitted at a
modulation level selected by the Adaptive Modulation algorithm.
2 If first transmission trial has failed, the frame will be retransmitted at the
same modulation level up to the maximum number of retransmission
attempts defined by the Number of HW Retries parameter.
Adaptive Modulation
Option
The Adaptive Modulation Option enables or disables the Adaptive
Modulation decision algorithm. When enabled, the algorithm supports
decrease/increase of transmission's modulation levels between the
lowest possible level to the value configured for the Maximum
Modulation Level parameter. If the Maximum Modulation Level is set
at the lowest possible level, the Adaptive Modulation algorithm has no
effect.
Minimum Interval
Between Adaptive
Modulation Algorithm
Messages (sec)
The Minimum Interval Between Adaptive Modulation Messages sets
the minimum interval between two consecutive adaptive modulation
messages, carrying information on the SNR of received signals. The
messages in the AU include SNR information on all the SUs
associated with it.
The available range is from 1 to 3600 seconds.
Adaptive Modulation
Decision Threshold
This parameter enables selection between Normal and High decision
thresholds for the Adaptive Modulation algorithm. Typically “Normal”
threshold should be used. In links with a low SNR (below 13), the
Adaptive Modulation algorithm may not stabilize on the correct
modulation level when using the standard decision thresholds. In this
case the algorithm may try to use a modulation level that is too high,
resulting in a relatively large number of dropped frames. The "High"
option solves this limitation and ensures good performance also in
links with a low SNR.