Analog Network Coding. Sachin Katti. Shyamnath Gollakota and Dina Katabi. Current Wireless. Router C

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1 Analog Network oding Sachin Katti Shyamnath Gollakota and Dina Katabi urrent Wireless Router

2 urrent Wireless Router Traditional Routing requires 4 time slots urrent Wireless Router Traditional Routing requires 4 time slots

3 Last Year Network oding OPE Router XOR = Traditional Routing requires 4 time slots Last Year Network oding OPE Router Traditional Routing requires 4 time slots

4 Last Year Network oding OPE Router XOR = XOR = Traditional Routing requires 4 time slots OPE requires 3 time slots an we Higher do it in throughput 2 time slots? Instead of router mixing packets Exploit that the wireless channel naturally mixes signals Analog Network oding (AN)

5 Analog Network oding Router Analog Network oding Router Interference 1) Dina and Jon transmit simultaneously

6 Analog Network oding Router 1) Dina and Jon transmit simultaneously 2) Router amplifies and broadcasts interfered signal Analog Network oding Router 1) Dina and Jon transmit simultaneously 2) Router amplifies and broadcasts interfered signal 3) Dina subtracts known signal from interfered signal

7 Analog Network oding Router Analog 1) Dina Network and Robert oding transmit requires simultaneously 2 time slots 2) Router amplifies Higher and broadcasts throughput interfered signal 3) Dina subtracts known signal from interfered signal It Is More Than Going From 3 To 2! Philosophical shift in dealing with interference Strategically exploit interference instead of avoiding it Promises new ways of dealing with hidden terminals

8 Hidden Terminal Scenario Src R1 R2 Dst Hidden Terminal Scenario Src R1 R2 Dst P1

9 Hidden Terminal Scenario Src R1 R2 Dst P2 P1 1) Src and R2 transmit simultaneously Hidden Terminal Scenario Src R1 R2 Dst P1 P2 1) Src and R2 transmit simultaneously 2) R1 subtracts P1, which he relayed earlier to recover P2 that he wants

10 Hidden Terminal Scenario Src R1 R2 Dst P1 P2 R2 and Src are hidden terminals Today : Simultaneous transmission AN : Simultaneous transmission ollision Success! Hidden Terminal Scenario Src R1 R2 Dst Other Benefits of AN: First step toward addressing hidden terminals AN extends network coding to new scenarios

11 How do we make it work? Practical hallenges Interfered signal is not exactly the sum hannel distorts signals Two signals are never synchronized It is not s D (t) + s J (t) but f1(s D (t)) + f2(s J (t-t)) Prior work assumes full synchronization and ignores channel distortion Not Practical!

12 Key Idea: Exploit Asynchrony! Key Idea: Exploit Asynchrony! Signal No Interference No Interference Time Dina uses interference-free parts to estimate channel and timing Dina compensates for her interfering signal Jon runs the same algorithm backwards! Exploit asynchrony to make it practical

13 ross layer realization of our idea Protocol Router senses idle medium and broadcasts a trigger to Dina and Jon Dina and Jon jitter their start times randomly and transmit Router amplifies and forwards interfered signal Dina and Jon receive and decode How do they decode?

14 Primer on Modulation Nodes transmit vectors on channel Focus on MSK (Minimum Shift Keying) modulation leads by 90 degrees Bit 1 lags by 90 degrees Bit 0 Primer on hannel Effects Attenuation hannel and are attenuated by the same amount

15 Primer on hannel Effects Attenuation Rotation hannel Primer on hannel Effects Attenuation Rotation hannel To decode, receiver computes angle between received vectors Angle (, Angle ) between = 90 degrees vectors is Bit preserved 1 was transmitted

16 So, How Does Dina Decode? Signal No Interference No Interference Time Dina s Signal Jon s Signal So, How Does Dina Decode? Signal No Interference No Interference Time Interference Small uninterfered part at the start Decodes uninterfered part via standard MSK demodulation Once interference starts, Dina changes decoding algorithm

17 What did Dina send? What did Dina send? What did Jon send? J1 J2

18 What is Interference Vector addition X1 J1 X2 J2 What does Dina know? X1 J1 X2 J2

19 What does Dina know? X1 No Interference Amplitude of her Vectors α X2 Amplitude of Jon s Vectors β What does Dina know? J1 X1 J1 X2 Dina finds solutions for X1 and X2

20 What does Dina know? J1 X1 J2 J1 X2 J2 Dina Two finds solutions for for each X1interfered and X2 vector! What does Dina know? J1 X1 J2 J1 X2 J2 Dina finds solutions Four possible for X1 and angles! X2

21 What does Dina know? J2 X1 J1 J2 X2 J1 Dina finds solutions Four possible for X1 and angles! X2 What does Dina know? X1 J1 J2 J1 X2 Dina finds solutions Four possible for X1 and angles! X2 J2

22 What does Dina know? J1 X1 J2 J1 X2 J2 Dina finds solutions Four possible for X1 and angles! X2 What does Dina know? J1 X1 J2 J1 X2 Dina finds solutions Four possible for X1 and angles! X2 J2

23 What does Dina know? J1 X1 J2 J1 X2 J2 Dina Pick finds the solutions correct for angle X1 and 90 X2degrees What does Dina know? X1 J1 J2 J1 X2 J2 Dina Pick finds the solutions correct for angle X1 and +90 X2 degrees

24 What does Dina know? J2 X2 X1 J1 J2 J1 Dina finds Dictates solutions solution for X1 for and Jon s X2 vectors! What does Dina know? X1 X2 J2 J1 Dina finds angle between J1 and J2 and decodes

25 Decoding Algorithm Decoding interference Signal Interference Time Decode rest of the interfered part using this algorithm Decode final uninterfered part from Jon via standard MSK demodulation Performance

26 AN Implementation Software GNURadio codebase Hardware USRP frontend GHz frequency range SNR of db anonical topologies in mesh networks Dina and Jon Router AN throughput gain over current 4/2 = 2 AN throughput gain over OPE 3/2 = 1.5

27 Throughput gain for Dina-Jon scenario DF Gain over Routing Throughput gain Median Gain over Routing 70% Throughput gain for Dina-Jon scenario DF Gain over OPE Gain over Routing Throughput gain Median Gain over Routing 70% Median Gain over Routing 70% Median Gain over OPE 30%

28 X topology Router Interference apture! apture! X topology Router Interference apture! apture!

29 X topology Router AN throughput gain over current 4/2 = 2 AN decodes interference using overheard signals AN throughput gain over OPE 3/2 = 1.5 Throughput gain X topology DF Gain over Routing Throughput gain Median Gain over Routing 65%

30 Throughput gain X topology DF Gain over OPE Gain over Routing Throughput gain Median Gain over Routing 65% Median Gain over OPE 28% hain topology Src R1 R2 Dst AN throughput gain over current 3/2 = 1.5

31 Throughput gain hain topology DF Throughput gain Median Gain over Routing 37% onclusion Shifts in the design of wireless networks to recognize wireless for what it is Embrace Broadcast Embrace Interference Implementation that yields large throughput gains