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Chapter 4 - Operation and Administration
BreezeACCESS VL System Manual
188
The default is Enable.
4.2.6.5.7.2 Burst Mode Time Interval
The Burst Mode Time Interval defines the burst size, which is the time in which
data frames are sent immediately without contending for the wireless medium.
The range is 1 to the value of the Maximum Burst Duration defined for the Sub-
Band.
The default is 5 milliseconds or the value of Maximum Burst Duration defined for
the Sub-Band (the lower of the two values).
4.2.6.5.8 Adaptive Modulation
The Adaptive Modulation algorithm enables adapting the modulation level of
transmitted data to the prevailing conditions of the applicable radio link. The
algorithm provides Access Units with simultaneous, adaptive support for multiple
Subscriber Units at different modulation levels, as transmission’s modulation
level decisions are made separately for each associated SU.
Link quality fluctuates due to various environmental conditions. Dynamically
switching between the possible modulation levels increases the probability of
using the maximum modulation level suitable for the current radio link quality at
any given moment.
When enabled, the Adaptive Modulation algorithm, constantly evaluates the
acievable 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 Table 4-13.
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