User's Manual

Chapter 4 - Operation and Administration BS Menu
BreezeMAX Extreme 194 System Manual
The default is Enable.
4.8.2.2.4 Multi Rate
The system employs a multirate algorithm to dynamically adapt the modulation
scheme and Forward Error Correction (FEC) coding to actual link conditions. The
algorithm is managed by the BS taking into account also information received
from the served MSs. Optimal values are calculated separately for the uplink and
downlink for each MS. MAP messages transmitted to the MSs include information
on the uplink rate that should be used by each MS for its next transmission.
The multirate algorithm optimizes the trade-off between capacity and error rate:
In most deployments, most of the links use high order modulation most of the
time, maximizing capacity. “Bad” links use lower order modulation, maximizing
availability. The algorithm provides independent adaptation per MS, and it is
performed independently for UL and DL, based on link quality information. The
algorithm provides dynamic adaptation - modulation can be changed on a per
burst basis.
The Multi Rate submenu enables viewing/updating the following parameters:
 Uplink Multi Rate Support
 Uplink Basic Rate
 Uplink Fade Margin
 Downlink Multi Rate Support
 DL Multi Rate Type
 Downlink Basic Rate
 Downlink Fade Margin
4.8.2.2.4.1 Uplink Minimum Sub-Channels
The minimum number of sub-channels to be used by the uplink rate adaptation
mechanism. At each rate, the mechanism will move from the highest supported
number of sub-channels (35 for 10 MHz BS bandwidth, 17 for 5 MHz BS
bandwidth) down to the value of this parameter before reaching a decision to
switch to a lower rate. In the other direction, the mechanism will start at this
value and move up to the highest supported number of sub-channels before
reaching a decision to switch to a higher rate.