Table 4-15: Retransmission Percentage Equivalence - Alvarion BreezeNET B System Manual

Chapter 4 - Operation
evaluates the achievable throughput for a particular modulation by counting the
number of packets that are successfully transmitted and the packets that are not
received and that need to be retransmitted. Based on these statistics, and on each
modulation's specific data rate, it will calculate the real throughput that the unit
can support in the current conditions for a particular modulation.
When choosing between modulations, up to a limit, a small number of
retransmissions on a higher modulation is compensated by the overall better
performance ensured by that modulation. When a critical retransmissions
percentage is reached however, it is necessary to decrease the modulation to
achieve better throughputs as shown in
Modulation PHY Rate
Level (Mbps)
8 54
7 48
6 36
5 24
4 18
3 12
2 9
1 6
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
BreezeNET B

Table 4-15: Retransmission Percentage Equivalence

PHY Rate Difference Compared
to Previous Modulation (Mbps)
54-48=6
48-36=12
36-24=12
24-18=6
18-12=6
12-9=3
9-6=3
Table 4-15.
Retransmission Percentage
Equivalent to PHY Rate Difference
6/54=11%
12/48=25%
12/36=33%
6/24=25%
6/18=33%
3/12=25%
3/9=33%
159
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