Alvarion BreezeACCESS VL System Manual page 217

4.2.6.5.3 Multicast Modulation Level (AU only)
The Multicast Modulation Level parameter defines the modulation level used for
transmitting multicast and broadcast data frames. Multicast and broadcast
transmissions are not acknowledged; therefore if a multicast or broadcast
transmission is not properly received there is no possibility of retransmitting. It is
recommended that you set a lower modulation level for broadcast and multicast
frame transmissions to increase the probability that they are received without
errors.
The Multicast Modulation Level parameter is applicable only to data frames.
Beacons and other wireless management and control frames are always
transmitted at the lowest modulation level according to the Sub-Band.
The minimum and maximum values for the Multicast 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 4.2.2.4. 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 value is the lowest supported modulation level (modulation level 1).
4.2.6.5.4 Maximum Modulation Level
When the Adaptive Modulation Algorithm (see section 4.2.6.5.8) 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 of
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 4-12, 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.
Operation and Administration
Menus and Parameters
185