User's Manual

Chapter 4 - Operation and Administration
BreezeACCESS VL System Manual
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is transmitted in the beacon messages to all SUs served by the AU, and is used
by all units to calculate the size of the time slot, that must be the same for all
units in the same sector. When the Per SU Distance Learning option is enabled,
the AU uses the re-association message to send to each SU its estimated distance
from the AU. The per-SU distance is used to calculate the ACK timeout to be used
by the SU. When the Per SU Distance Learning option is disabled (or if it cannot
be used because the SU uses a previous SW version that does not support this
feature), the SU will use the maximum cell distance to calculate the ACK timeout.
The AU always uses the maximum cell distance to calculate the ACK timeout.
It should be noted that if the size of the time slot used by all units is adapted to
the distance of the farthest unit, then no unit will have an advantage when
competing for services. However, this reduces the overall achievable throughput
of the cell. In certain situations, the operator may decide to improve the overall
throughput by reducing the slot size below the value required for full fairness.
This means that when there is competition for bandwidth, the back-off algorithm
will give an advantage to SUs that are located closer to the AU.
The Cell Distance Parameters menu includes the following parameters:
4.2.6.2.10.1 Cell Distance Mode
The Cell Distance Mode option defines whether the maximum distance of the AU
from any of the SUs it serves will be determined manually (using the Maximum
Cell Distance parameter) or automatically. In addition, the Per SU Distance
Learning feature is supported only when the Cell Distance Mode is set to
Automatic.
The Options are Automatic or Manual.
The default is Automatic.
4.2.6.2.10.2 Maximum Cell Distance
The Maximum Cell Distance parameter allows configuring the maximum distance
when the Cell Distance Mode option is Manual.
The range is 0 to 54 (Km). The value of 0 has a special meaning for No
Compensation: Acknowledge Time Out is set to a value representing the
maximum distance of 54 km. The time slot size is set to its minimal value of 9
microseconds.
The default is 0 (No Compensation).
4.2.6.2.10.3 Fairness Factor
The Fairness Factor enables to define the level of fairness in providing services to
different SUs. When set to 100%, all SUs have the same probability of getting
services when competing for bandwidth. If set to X%, then SUs located up to X%
of the maximum distance from the AU will have an advantage in getting services
over SUs located farther than this distance.