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

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spoiler: it’s a grab bag of magic tricks! Getting WiFi to go Faster! Kiran Bhattaram @kiranb

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An Overview! data estimated data ????

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An Overview! NOISY CHANNELS Modulation! Demodulation! Decoding Decompression data estimated data Compress Huffman, LZW, etc Channel Coding Viterbi, Turbo codes, LPDC, etc.

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Shannon-Hartley Theorem C = B log2 (1+S/N) Channel capacity in bits/s bandwidth of the channel signal-to-noise ratio

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Getting More out of your Bandwidth if you have more space, you can encode more information!

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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

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Phase-Amplitude Modulation 4 phases, 2 amplitudes = 8 symbols 000 110 001 111 010 011 100 101 in phase (I) 90º phase (Q)

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Optimizing Bandwidth 0000 0001 0010 0011 0100 0110 0101 0111 1100 1101 1111 1110 1001 1000 1011 1010 Q I

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Tradeoff: Yelling over Noisy Channels 0000 0001 0100 0110 1100 1101 1111 1110 1001 1000 1011 1010 Q I

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Optimizing Bandwidth: more! 52 independent streams in 20 MHz. … n0: 0001001010… n1: 00010100…. n2: 101010111…. n50: 101010111…. n51: 101010111…. 20MHz

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Tradeoff: Interference

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Getting more out of your SNR if you speak louder, you can speak faster!

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Improving SNR: Beamforming send out the same signal twice at 1/2 the power

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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

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Improving SNR: Beamforming

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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