Bending the Laws of Physics! Or, How Wi-Fi Keeps Getting Faster.

Shannon's Law tells you how fast you can transmit information over a channel with a given bandwidth and noise level. You just can't beat the limit — until we start talking about ways you can.

Learn how adding more antennas lets you squeeze more information out of the air! (Note: this is actually the coolest!) Along the way, we'll discuss what the silly numbers and letters on your router mean, and the fantastic bag of signal processing and programming tricks that lets you carry the internet around in your pocket!

Transcript

1. spoiler: it’s a grab bag of magic tricks! Getting WiFi to go Faster! Kiran Bhattaram @kiranb
2. An Overview! data estimated data ????
3. An Overview! NOISY CHANNELS Modulation! Demodulation! Decoding Decompression data estimated data Compress Huffman, LZW, etc Channel Coding Viterbi, Turbo codes, LPDC, etc.
4. Shannon-Hartley Theorem C = B log2 (1+S/N) Channel capacity in bits/s bandwidth of the channel signal-to-noise ratio
5. Getting More out of your Bandwidth if you have more space, you can encode more information!
6. Phase-Amplitude Modulation 4 phases, 2 amplitudes = 8 symbols Carrier Wave Modulated Wave 000 110 001 111 0º, 1x 180º, 0.5x 90º, 1x 270º, 0.5x
7. Phase-Amplitude Modulation 4 phases, 2 amplitudes = 8 symbols 000 110 001 111 010 011 100 101 in phase (I) 90º phase (Q)
8. Optimizing Bandwidth 0000 0001 0010 0011 0100 0110 0101 0111 1100 1101 1111 1110 1001 1000 1011 1010 Q I
9. Tradeoff: Yelling over Noisy Channels 0000 0001 0100 0110 1100 1101 1111 1110 1001 1000 1011 1010 Q I
10. Optimizing Bandwidth: more! 52 independent streams in 20 MHz. … n0: 0001001010… n1: 00010100…. n2: 101010111…. n50: 101010111…. n51: 101010111…. 20MHz
11. Tradeoff: Interference
12. Getting more out of your SNR if you speak louder, you can speak faster!
13. Improving SNR: Beamforming send out the same signal twice at 1/2 the power
14. Improving SNR: Beamforming double the intensity at points! "Single slit and double slit2" by Jordgette - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons
15. Improving SNR: Beamforming
16. Improving SNR: spatial multiplexing Licensed under Public Domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/ File:Kanalmatrix_MIMO.png#/media/File:Kanalmatrix_MIMO.png
17. THE FUTURE ❖ MU-MIMO ❖ more bandwidth at 60GHz: 2 GHz!! ❖ ???
18. LINKS ❖ http://apenwarr.ca/ ❖ wikipedia! ❖ whitepapers!