User's Manual

Menus and Parameters
Manual Revision 1.0
4-79
Maximum Modulation Level
When the Adaptive Modulation Algorithm (see Adaptive Modulation
Algorithm on page 4-81) 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
desired 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, since 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 of the applicable SU as well as all other SUs associated with
the same AU.
The link quality can be estimated based on the SNR measurement of the
SU at the AU, which can be viewed in the MAC Address Database option
in the Site Survey menu. If the measured SNR is less than a certain
threshold, it is recommended that the maximum modulation level of the
SU be decreased in accordance with Table 4-9, 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
The SNR measurement at the AU is accurate only when receiving transmissions from
the applicable SU. If necessary, use the Ping Test utility in the Site Survey menu to
verify data transmission.
When the Adaptive Modulation Algorithm is disabled, this parameter
will serve to determine Fixed Modulation Level used for transmissions.
The minimum value for the Maximum Modulation Level is defined by
the Sub Band in use.
The maximum value for the Maximum Modulation Level is defined by
the Sub Band in use and the HW revision of the unit. Units with HW
revision A support a maximum value of 7, while units with HW revision
B and higher support a maximum value of 8.
For information on how to view the Sub Bands supported by the unit
and the supported parameters’ values and options, refer to Show
Country Dependent Parameters on page 4-9.
The default is the highest supported Modulation Level.