Wi-Fi performance Issues

1. Wi-Fi performance Issues • Throughput subject to packet size • High latency: 11 – 32 ms • Not flexible • Choose high throughput or low latency

2. Atheros Throughput Example Wi-Fi is extremely sensitive to packet size Max throughput can only be achieved when big packet sizes are transmitted.

3. Concatenation • The small packet problem can be solved in Wi-Fi through concatenation. • Small packets are received in the radio and grouped into larger packets. • The end result is similar data throughput as with large packets. PROBLEM: Concatenation adds 10 – 14 ms Delay!

4. Fragmentation • The latency problem in Wi-Fi can be resolved by fragmenting packets so that smaller packets are sent on a fixed time interval. • This means that all packet sizes are fixed and at a smaller size. • As seen on the previous slides, Wi-Fi performance suffers when packet-sizes are small. PROBLEM: Fixed frames lower data throughput!

5. Wi-Fi performance Issues • Throughput subject to packet size • Concatenation solves problem • Adds significant delay (+10 – 14ms) • High latency: 11 – 18 ms (21 – 32ms w/concatenation) • Fixed frame sizes (fragmentation) solves latency • Turn-off concatenation • Choose latency or throughput • Wi-Fi based product can offer: • High Throughput with high latency • Low latency with low throughput at fixed frame rate