802.11n MAC layer simulation

1. 802.11n MAC layer simulation Submitted by: Niv Tokman Aya Mire Oren Gur-Arie

2. Standard protocol transaction 1. Data arrives at Tx FIFO of STA A from VoIP data generator. IAC is sent. 2. AP receives IAC, wait SIFS and respond with RAC. 3. RAC received. STA A sends non-aggregated VoIP data 4. After DIFS, the operation is repeated by STA B 5. Aggregation size is reached. AP send IAC followed by the aggregated data 6. Data is received by STA C

3. Simulation structure and flow

4. Simulation assumptions • There is no random noise in the simulation and error rate is zero. • All stations are 802.11n (no legacy devices) • Each station can be involved in one conversation at a time • All conversations are between a local station and remote network (Through the AP) • Only AP uses aggregated packages • The destinations of conversations are distributed equally. • The length of conversations is distributed exponentially. • No Ack packages in MAC layer - the simulated network layer

5. Network capacity calculation • The idea: to create a standard reference point to network capacity, regardless of aggregation size used. • The network capacity is the percentage of bandwidth actually used. Due to different timing scheme, the percentage differs between regular station and AP. • Thus we calculate them independently and perform a weighted sum. • This is a static calculation. A dynamic calculation taking actual collisions and transmissions into account provide different capacity per aggregation, which makes comparison impossible. • The equations are in the next slide:

6. Network capacity equations • The AP has priority on the channel, thus STA can transmit only when AP is accumulating the aggregation. The weight is based on the AP portion of time: • Efficiency of STA/AP is the amount of actual data transmission out of the total transmission period (including handshake and wait times). Note that transmission of control messages is negligible: • Thus the total network efficiency is the weight sum:

10. Simulation analysis • We can see that at lower network capacity, we get better results for the higher aggregation sizes, while at higher network capacities we get better performance for middle range of aggregation size • In the current simulation configuration, the aggregated AP has priority over the regular stations. When network capacity is low, it takes time to accumulate an aggregation, which gives equal opportunity to the stations to transmit their messages. • When the network capacity is high, aggregations are accumulated in no time, and the AP starves the other stations, thus their messages expire and the success rate is falling.

11. Simulation analysis (cont.) • Aggregation of 100 is like almost no aggregation at all. Success rate is poor at lower network capacities, while at higher rates the success rate is similar to higher aggregation sizes. • It can be seen that the trends are kept as margin is raised.

12. Network capacity (MB/s)

13. Success rate analysis • It can be seen that for low-mid range network capacity, the largest aggregation is the best. • At higher network capacities, the larger aggregations causes regular stations starvation, thus success rates are slightly lower than at smaller aggregation sizes.

14. Conclusions • At all simulated network capacities, the larger aggregations provide better results than smaller aggregation sizes. The only exception is at the highest network capacities, at which a slight degradation can be observed. • Higher aggregation size is better for almost all network capacities, even at a network were not all devices aggregate. • The degradation at higher network capacities is probably simulation dependent. In networks with better balance between AP and stations priorities (such as QoS), one can assume that there will be no degradation.

15. Thank you Niv, Oren & Aya