BreezeMAX 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. 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 lower the rate used by any SU, the higher is the number of symbols that should be allocated to it for transmitting/receiving a certain amount of data, resulting in reduced overall capacity of the sector. To minimize such a degrading effect on the performance of the entire sector, a Minimum Data Rate per SU can be configured. If the SU operates at a rate lower than the defined minimum, the QoS parameters of the services allocated to it will be decreased to reduce the effect on overall sector capacity. The Minimum Data Rate can be configured separately for the Downlink and Uplink, and the effect on QoS parameters ia as follows:
For a Continuous Grant (CG) connection: The service will be denied as long as the SU operates in a rate that is lower than the Minimum Data Rate.
For BE, NRT and RT connections, the MIR and or CIR values will be reduced according to the formula: Corrected Value=Configured Value * (Current Rate Bytes per Symbol)/(Minimum Data Rate Bytes per Symbol), where the Bytes per Symbol for each rate are defined in the following table:
Rate |
Modulation and Coding |
Bytes per Symbol |
|
BW=1.75 MHz |
BW=3 .5 MHz |
||
1 |
BPSK 1/2 |
6 |
12 |
2 |
BPSK 3/4 |
9 |
18 |
3 |
QPSK 1/2 |
12 |
24 |
4 |
QPSK 3/4 |
18 |
36 |
5 |
QAM16 1/2 |
24 |
48 |
6 |
QAM16 3/4 |
36 |
72 |
7 |
QAM64 2/3 |
48 |
96 |
8 |
QAM64 3/4 |
54 |
108 |
The Multi Rate Parameters include:
Parameter |
Description |
Multirate Support |
A read-only display of the Multirate Support option as configured in the AU/Micro Base Station. |
Uplink Current Rate |
The current uplink rate. Configurable in the SU only when the Multirate Support is disabled in the AU/Micro Base Station. |
Minimum Uplink Data Rate |
The minimum uplink rate for data transmissions. |
Uplink Rate Below Minimum |
Indicates whether the current uplink rate is below the Minimum Uplink Data Rate or not. When it is below the minimum, quality of service parameters will be reduced as described above. |
Uplink SNR (dB) |
The current Signal to Noise Ratio of the SU's signal as received at the Base Station's ODU. |
Uplink RSSI (dBm) |
The current Signal Strength of the SU's signal as received at the Base Station's ODU. |
Tx Power (dBm) |
The current Tx Power of the SU (at the antenna's port) |
Distance (m) |
The estimated distance from the Base Station. The accuracy is from several hundreds of meters for line-of-sight links to 1500 meters for non-line-of-sight links. |
Downlink Current Rate |
The current downlink rate. Configurable in the SU only when the Multirate Support is disabled in the AU/Micro Base Station. |
Minimum Downlink Data Rate |
The minimum downlink rate for data transmissions. |
Downlink Rate Below Minimum |
Indicates whether the current downlink rate is below the Minimum Downlink Data Rate or not. When it is below the minimum, quality of service parameters will be reduced as described above. |
Downlink SNR (dB) |
The current Signal to Noise Ratio of the signal received by the SU. |
Downlink RSSI (dBm) |
The current Signal Strength of the signal received by the SU. |
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