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Chapter 4 - Operation and Administration
from the served SUs. Optimal values are calculated separately for the uplink and
downlink for each SU, taking into account also the applicable QoS requirements.
MAP messages transmitted to the SUs include information on the uplink rate that
should be used by each SU for its next transmission.
The Basic Rate is the minimum rate to be used by the Multirate algorithm. This is
also the rate to be used for downlink broadcasts and multicasts. Broadcasts and
multicasts messages are not acknowledged, so that the ARQ mechanism cannot
be used and there is no way to guarantee that all intended recipients will receive
them properly. In addition, multicasts and broadcasts are sent to multiple
recipients with different link qualities. Therefore, it is preferable to use a relatively
low rate for these transmissions, thus reducing the probability of errors and
increasing the likelihood that all intended recipients will receive them properly.
In the uplink, this is the rate to be used by SUs for non-scheduled transmissions,
such as during the contention period.
The Basic Rate is also the initial rate to be used by the algorithm for each new SU
that joins the cell when the Multirate algorithm is enabled.
When the Multirate algorithm is disabled, communication with connected SUs will
continue using the last uplink and downlink rates selected by the Multirate
algorithm. The Set Rates option in the SU (see
becomes available only when the Multirate algorithm is disabled in the AU,
enables setting the Uplink Current Rate and the Downlink Current Rate to any of
the values listed in
The multirate algorithm chooses dynamically between 8 rates. These are also the
rates that can be configured for the Basic Rate parameters.
The Multirate menu enables viewing/updating the following parameters:
116
Figure
4-5.
Table 4-5: Rates (Modulation Schemes and Coding)
No.
1
2
3
4
5
6
7
8
Section
4.9.6.3.4.2), which
Rate
BPSK 1/2
BPSK 3/4
QPSK 1/2
QPSK 3/4
QAM16 1/2
QAM16 3/4
QAM64 2/3
QAM64 3/4
Operation
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