How is the PHY bit rate or modulation and coding scheme (MCS) selected in 802.11 and can I vary the frame aggregation count of 802.11? I am working on NetSim and would like to know the correct operation per standards and also implementation in NetSim (if someone knows).
MCS selection is based on Min receive sensitivity tables available in the 802.11 standards. The received power is computed, and this is checked against the tables. The highest MCS for which the Rx sensitivity is lower than Rx power is chosen.
In NetSim, Packet aggregation is a UI variable which you can set.
One should be careful, and understand received signal strength (RSS) and Signal to interference plus noise radtio (SINR) affect performance.
If the rate adaptation algorithm is off, then the transmitter chooses MCS by comparing the RSSI against the Receiver-Sensitivity for different MCS (per the tables in the standards). The highest possible MCS is then chosen. This means the MCS is not fixed but adapts to the received signal strength, even with rate adaption turned off in the MAC layer.
Received SINR is not used in rate determination at the transmitter, but is rather used for error computation based on the SINR-BER curves.
Thus, RSS is used to determine rate (MCS) while SINR is used to determine packet error probabilities.
I had two further questions and was hoping someone may know the answers (i) What is max aggregation count that can be set in 802.11n and 802.11 ac in NetSim and where is this available? (ii) I understand MCS can be “indirectly” set. That is we “directly” vary transmit power and pathloss. This then changes received power which is used internally in NetSim for MCS selection. Is this correct?
Harshita Sharma
Max aggregation count is 64 for 802.11n and 1024 for 802.11 ac. It is available in the MAC layer properties of the access points (APs) or the wireless nodes (STAs) Yes, the received power is compared against the MCS tables to determine the PHY rate.
Nihal Sanil
Rate adaptation based on the MAC ACKs received. NetSim has two options. a. Generic - The MCS goes up one step for every 20 successful packets and is done one step for 3 consecutive packet failures. b. Minstrel - This is per the minstrel algorithm running in Linux
Ananya Hegde One more question: Please tell me how the received power is calculated.
The received power in WiFi is the power of the received signal at the receiver. It is typically measured in dBm and is an important parameter as it determines the quality and performance of the wireless connection.
To calculate the received power in WiFi, the following formula can be used:
Received Power (dBm) = Transmitted Power (dBm) - Path Loss (dB)
where the transmitted power is the power of the transmitted signal at the transmitter, and the path loss is the loss of the signal due to various factors, such as distance, obstacles, and fading. The path loss can be calculated using a propagation model, such as the free space model or the log-distance model.
For example, if the transmitted power is 20 dBm and the path loss is 30 dB, the received power would be -10 dBm.
- Badges
- Science topic
- Similar topics
- Computer Science and Engineering
- Programming Languages
- Python