Rate Adaptation in 802.11b

NetSim rate adaptation is explained in section 3.1.19 of this document.

Open NetSim, Select Examples > Internetworks > Wi-Fi > 802.11 Rate Adaptation then click on the tile in the middle panel to load the example as shown in below Figure.


The following network diagram illustrates what the NetSim UI displays when you open the example configuration file for Rate Adaptation.


Network Settings

  1. Environment Grid length: 500m * 500m
  2. Distance between AP and Wireless Node is 65.5m
  3. Enabled Packet Trace and plot option
  4. Set rate adaptation as Generic in datalink properties of access_point and wireless node
  5. Set DCF as the medium access layer protocol under datalink layer properties of access_point and wireless node.
  6. Click on the Application icon present in the top ribbon/toolbar and set Transport Protocol to UDP
  7. Set WLAN Standard $\rightarrow$ 802.11b
  8. Channel Characteristics $\rightarrow$ Path Loss only, Path Loss Model $\rightarrow$ Log Distance and Path loss Exponent $\rightarrow$ 3.25. (Wireless Link Properties)
  9. CBR application with 10Mbps generation rate (Set Packet Size: 1460 Bytes, Inter Arrival Time: 1168 micro sec)
  10. Simulate for 10 sec.

Results and Discussion#

Open Packet Trace and filter Packet Type to CBR, Transmitter_ID to Access Point 3 and then calculate Phy rate. Phy rate can be calculated using packet trace by using the formula shown below: $$Phy \ rate (802.11b) = \frac{Phy\ layer\ payload * 8}{(phy \ end \ time - phy \ arrival \ time - 192)}$$

192$\mu s$ is the approximate preamble time for 802.11b

Calculate PHY rate for all the data packets coming from Access Point to Wireless Node. For doing this please refer NetSim User Manual > Section 8.4.2 How to set filters to NetSim Trace file


The ‘Generic’ rate adaptation algorithm is similar to the Auto Rate Fall Back (ARF) algorithm. In this algorithm:

  • Rate goes up one step for 20 consecutive packet successes.
  • Rate goes down one step for 4 continuous packet failures

In the above screenshot, the Phy rate reduces from 11Mbps to 5.5Mbps, since there are 4 consecutive data error packets. Then the rate increases from 5.5Mbps to 11Mbps one there is 20 consecutive successful data packet transmissions.