Alvarion BreezeACCESS EZ AU-EZ, System Manual

Page: 131 / 175

Chapter 4 - Operation and Administration Menus and Parameters
BreezeACCESS EZ AU-EZ 112 System Manual
When the above mentioned retransmission percentages are reached, the
Statistics-Based Rate Control algorithm will lower the modulation.
If the connection is stable on a particular modulation, the unit will periodically
check whether it can further increase the modulation (except on modulation 8), by
sending a number of test packets using this higher modulation and checking the
retransmission rate.
The user can configure a Packet Threshold to Test Up Rate parameter to define
the number of successfully transmitted frames after which the unit will test the
higher modulation. The number of frames used for this test can also be configured
by the user via the Packet No On Upper Rate parameter.
When a frame needs to be retransmitted, the Statistics-Based Rate Control
algorithm may gradually decrease the modulation used for retransmitting that
particular frame. Based on the Number of HW retries parameter (see
“Number of
HW Retries” on page 109 for more details), the unit will try to perform the three
final retransmission attempts at progressively lower modulations.
The retransmission mechanism described above does not apply for test frames
sent for evaluating link quality on higher modulations. If the number of HW
retries is lower than 3 or if the initial modulation is lower than 4, the number of
modulations used for retransmission will be limited as shown in
Table 4-14 .
Table 4-13: Retransmission Percentage Equivalence
Modulation
Level PHY Rate
(Mbps) PHY Rate Difference Compared
to Previous Modulation (Mbps) Retransmission Percentage
Equivalent to PHY Rate Difference
8 54 54-48=6 6/54=11%
7 48 48-36=12 12/48=25%
6 36 36-24=12 12/36=33%
5 24 24-18=6 6/24=25%
4 18 18-12=6 6/18=33%
3 12 12-9=3 3/12=25%
2 9 9-6=3 3/9=33%
1 6