Alvarion SW VERSION 5.1 system manual Multicast Modulation Level AU only, Maximum Modulation Level

Menus and Parameters

4.2.6.5.3Multicast 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).

4.2.6.5.4Maximum 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

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