User's Manual

Menus and Parameters
Manual Revision 1.0
4-55
! To ensure fairness in the contention back-off algorithm between SUs
located at different distances from the AU, the size of the time slot
should also take into account the one-way propagation delay. The
size of the time slot of all units in the cell should be proportional to
the distance from the AU of the farthest SU served by it.
The distance from the AU of the farthest SU served by it can be
determined either manually or automatically. In manual mode, this
distance is configured manually. In automatic mode, the AU uses a
special algorithm to estimate its distance from each of the SUs it serves,
determine which SU is located the farthest and use the estimated
distance of the farthest SU as the maximum distance.
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, than 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 advantage to SUs that are located closer to the AU.
The Cell Distance Parameters menu includes the following parameters:
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.
The Options are Automatic or Manual.
The default is Automatic.
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).