Specifications

Chapter 4 - Operation and Administration Menus and Parameters
BreezeACCESS 4900 166 System Manual
4.2.6.5.5 Maximum Modulation Level
When the Adaptive Modulation algorithm (see “Adaptive Modulation” on page 169)
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 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 4-16, 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.
When the Adaptive Modulation algorithm is disabled, this parameter will serve to
determine Fixed Modulation Level used for transmissions.
The minimum and maximum values for the Maximum Modulation Level are
defined by the Sub-Band in use. For information on how to view the Sub-Bands
supported by the unit and the supported parameters' values and options, refer to
section “Show Country Dependent Parameters” on page 72. Currently, all Sub
Bands support the entire range of modulation levels, from 1 to 8. However, the
highest modulation level supported by units with HW revision A is modulation
level 7.
The default is the highest supported modulation level (8 for all units with HW
revision B or higher, 7 for units with HW revision A).
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.