Partially Overlapping Channels Not Considered Harmful Trevor Reid ECE 256

Single Channel Spatial Reuse a b d c

What else can we do? Utilize the frequency domain We have all of this space…

Split the spectrum into Channels Frequency Power

But it’s not perfect Can’t get full channel capacity without an ideal band-pass filter Instead the channels look more like… Frequency Power

Aside: Band-pass Filters Only accepts frequencies within a certain range. Everything else is rejected.

Partially Overlapping Channels Frequency

802.11(b) Specifications Operates at 2.4 GHz Split into 11 Channels 22 Mhz Wide 5 Mhz Separation

Looks Like This… (kind of)

Why use them? Reduce Contention 11 partially overlapping channels reduce contention by a factor of 3.05 compared to using 3 overlapping channels.

How to Model Interference I factor: I(i,j) = Amount of overlap between i and j

Which looks like this

Transmission Range

BER

Take Away Partially overlapping channels can reduce contention We can model interference between two channels with an I factor Interference falls off rapidly with channel separation Bit Error Rate falls of rapidly with channel separation

How Can We Utilize this? AP Eric Stephanie Jason Jimmy Not Going To Help.

But with many APs AP3 Stephanie Trevor AP1 Eric Jimmy AP2 Valentin Jason Prof Choudhury

Channel Assignment Algorithm OBJ(T,θ) = Total interference experienced for each client. Steps: – Evaluate OBJ(T,θ) – For each AP Assign to channel that minimizes interference – Evaluate OBJ(T,θ) again Stop if nothing changed, otherwise repeat.

Modify For Multiple Channels Instead of calculating interference on only the same channel find channels that interfere (using I-factor). Add up interference at client from all interfering channels. It just works.

So does it work? Yes. By a factor of ~ 2.57

Wireless Mesh Networks Use similar approach to modify existing channel assignments algorithms. Using partially overlapped channels shows significant improvements.

So What’s the Catch? Me Neighbor Starbucks Free Wifi Noisy people below you linksys Cute Girl Upstairs Who Coordinates Channel Assignment?

Does this actually perform well? We don’t know Never actually implemented Don’t know how effective the I-Factor model is in real world conditions.

Resources df df Fi_channels_% b,g_WLAN%29.svg 2.svg 2.svg