Multi Rate Parameters

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 AU/Micro Base Station taking into account also information received 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 Basic Rates becomes available for configuration in each SU only when the Multirate algorithm is disabled in the AU/Micro Base Station.

The Multirate Parameters include: