Machine Learning for Body Sensor Networks
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Slides from the tutorial on "Machine Learning for Body Sensor Networks" at the BSN Conference in Zürich, Switzerland, June 2014. It covers mainly reinforcement learning, neural networks and decision trees and their applications in body sensor networking.
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Machine Learning for Body Sensor Networks
- 1. Machine Learning for BSN Dr. Anna Förster, Alessandro Puia4 BSN Tutorial, June 17th 2014 Zürich, Switzerland Copyright A.Förster, A.Puia4 2014 1
- 2. Presenters Dr. Anna Förster Researcher at SUPSI anna.foerster@ieee.org Alessandro Puia< Senior researcher at SUPSI alessandro.puia<@supsi.ch 2 Copyright A.Förster, A.Puia4 2014
- 3. Schedule and outlook • Data in Body Sensor Networks • What is Machine Learning? • Decision Trees and their applicaNons • Discussion • Break • Neural networks and their applicaNons • Reinforcement Learning and its applicaNons • Other Machine Learning techniques • Comparison of ML for BSNs • Open discussion! 3 Copyright A.Förster, A.Puia4 2014
- 4. BSN: The Challenges Dr. Anna Förster, Alessandro Puia4 BSN Tutorial, June 17th 2014 Zürich, Switzerland Copyright A.Förster, A.Puia4 2014 4
- 5. BSN vs WSN DC-DC Sensors ADC MCU Memory Wireless Battery Node Architecture Network Architecture DC-DC Sensors ADC MCU Memory Wireless Battery DC-DC Sensors ADC MCU Memory Wireless Battery DC-DC Sensors ADC MCU Memory Wireless Battery SINK 5 Copyright A.Förster, A.Puia4 2014
- 6. BSN vs WSN: Number of Nodes WSN BSN 6 Copyright A.Förster, A.Puia4 2014
- 7. BSN vs WSN: Parameters WSN BSN Almost homogeneous: same sensors in every node Extremely heterogeneous: different sensor for each node Temperature Humidity Light Body Temperature EEG EMG SPO2 7 Copyright A.Förster, A.Puia4 2014
- 8. BSN vs WSN: Other requirements 8 Requirements WSN BSN Babery life Years App. dependent Network topology Mostly Mesh Star Mobility StaNc Mobile ComputaNon Low Low, Medium, High Frequency Low High Form factor Almost indifferent Hidden, Invisible “Wearability” -‐-‐ Mandatory Copyright A.Förster, A.Puia4 2014
- 9. BSN Form Factor 9 hbp://cnbi.epfl.ch/page-‐39979-‐en.html hbp://blog.broadcom.com/wireless-‐technology/ Copyright A.Förster, A.Puia4 2014
- 10. BSN Form Factor 10 hbp://cnbi.epfl.ch/page-‐39979-‐en.html hbp://blog.broadcom.com/wireless-‐technology/ Copyright A.Förster, A.Puia4 2014
- 11. BSN Form Factor 11 hbp://cnbi.epfl.ch/page-‐39979-‐en.html hbp://blog.broadcom.com/wireless-‐technology/ Copyright A.Förster, A.Puia4 2014
- 12. BSN Devices 12 Copyright A.Förster, A.Puia4 2014
- 13. BSN Applications 13 INTERNETT1 T1T1 T1 T1 hbp://si.epfl.ch/page-‐34870-‐en.html Patel at al, 2012 hbp://technabob.com/blog/2013/09/04/priovr-‐full-‐body-‐sensor/ Copyright A.Förster, A.Puia4 2014
- 14. BSN Applications 14 INTERNETT1 T1T1 T1 T1 hbp://si.epfl.ch/page-‐34870-‐en.html Patel at al, 2012 hbp://technabob.com/blog/2013/09/04/priovr-‐full-‐body-‐sensor/ Copyright A.Förster, A.Puia4 2014
- 15. BSN Applications 15 INTERNETT1 T1T1 T1 T1 hbp://si.epfl.ch/page-‐34870-‐en.html Patel at al, 2012 hbp://technabob.com/blog/2013/09/04/priovr-‐full-‐body-‐sensor/ Copyright A.Förster, A.Puia4 2014
- 16. BSN Applications 16 INTERNETT1 T1T1 T1 T1 hbp://si.epfl.ch/page-‐34870-‐en.html Patel at al, 2012 hbp://technabob.com/blog/2013/09/04/priovr-‐full-‐body-‐sensor/ Copyright A.Förster, A.Puia4 2014
- 17. BSN: In Summary • High heterogeneous data • High sampling/sending frequency • Small number of nodes (even only one) • Many applicaNons: not only e-‐health Copyright A.Förster, A.Puia4 2014 17
- 18. Introduction to Machine Learning Dr. Anna Förster, Alessandro Puia4 BSN Tutorial, June 17th 2014 Zürich, Switzerland Copyright A.Förster, A.Puia4 2014 18
- 19. Major goal Produce models (rules, paberns) from data ProperGes Robust and flexible Global models from local data No environmental model Machine Learning … Neural Networks Reinforcement Learning GeneNc Algorithms Decision Trees Swarm Intelligence Copyright A.Förster, A.Puia4 2014 Clustering 19
- 20. Classes of Machine Learning Algorithms Copyright A.Förster, A.Puia4 2014 Pre-‐labeled Training Dataset TesNng Dataset (Usage) Supervised learning Model Unsupervised learning Model Non-‐labeled data item Reinforcement learning Agent / Model Environment 20
- 21. Online against Batch Learning Training dataset Use the model Batch Learning Model Use the model Online learning Model Next data item Copyright A.Förster, A.Puia4 2014 21
- 22. Introduction to Decision Trees Dr. Anna Förster, Alessandro Puia4 BSN Tutorial, June 17th 2014 Zürich, Switzerland Copyright A.Förster, A.Puia4 2014 22
- 23. Decision Based Learning • Classifying objects into groups based on abribute pairs form = round color = orange taste = sour form = round color = red, orange, green taste = sweet apple orange ? 23 Copyright A.Förster, A.Puia4 2014
- 24. Decision Based Learning • Classifying objects into groups based on abribute pairs form = round color = orange taste = sour form = round color = red, orange, green taste = sweet apple orange form = ? color = ? taste = ? 24 Copyright A.Förster, A.Puia4 2014
- 25. Decision Based Learning • Classifying objects into groups based on abribute pairs form = round color = orange taste = sour form = round color = red, orange, green taste = sweet apple orange form = round color = ? taste = ? ??? 25 Copyright A.Förster, A.Puia4 2014
- 26. Decision Based Learning • Classifying objects into groups based on abribute pairs form = round color = orange taste = sour apple orange form = round color = orange taste = ? ??? form = round color = red, orange, green taste = sweet 26 Copyright A.Förster, A.Puia4 2014
- 27. Decision Based Learning • Classifying objects into groups based on abribute pairs form = round color = orange taste = sour apple orange form = round color = orange taste = sweet apple! form = round color = red, orange, green taste = sweet 27 Copyright A.Förster, A.Puia4 2014
- 28. Decision Based Learning • Classifying objects into groups based on abribute pairs form = round color = orange taste = sour apple orange form = round color = orange taste = sweet apple! form = round color = red, orange, green taste = sweet 3 quesNons! 28 Copyright A.Förster, A.Puia4 2014
- 29. Decision Based Learning • Classifying objects into groups based on abribute pairs form = round color = orange taste = sour apple orange taste = sweet color = ? form = ? apple! form = round color = red, orange, green taste = sweet 29 Copyright A.Förster, A.Puia4 2014
- 30. Decision Based Learning • Classifying objects into groups based on abribute pairs form = round color = orange taste = sour apple orange taste = sweet color = ? form = ? apple! form = round color = red, orange, green taste = sweet 1 quesNon! 30 Copyright A.Förster, A.Puia4 2014
- 31. Decision Tree Learning • Supervised learning approach (use pre-‐labeled dataset) • Maps observaNons (features, abributes) into classes (decisions) • Very powerful and efficient technique to analyze large and fuzzy datasets Is male? Is age < 9.5? Family on board > 2.5? survived survived died died 0.73 : 36% 0.89 : 2% 0.05 : 2% 0.17 : 61% Probability of survival on the Titanic : %observa@ons 31 Copyright A.Förster, A.Puia4 2014
- 32. Decision Based Learning • Classifying objects into groups based on abribute pairs • Which quesNons to ask first, which next? • Compute informaNon gain of abributes • How well does an abribute separates the tesNng set? 32 Copyright A.Förster, A.Puia4 2014
- 33. C4.5 algorithm Goal: construct a decision tree with aVribute at each node 1. Start at root 2. Find the abribute with maximal informaNon gain, which is not an ancestor of the node 3. Put a child node for each value of this abribute 4. Add all examples from the training set to the corresponding child 5. If all examples of a child belong to the same class, put the class there and go back up in the tree 6. If not, conNnue with step 2 while abributes are let 7. When no more abributes are let, put the classificaNon of the majority of the examples to this node 33 Copyright A.Förster, A.Puia4 2014
- 34. C4.5 algorithm: Example example form color class 1 round red apple 2 round orange apple 3 round orange orange 4 round green apple 5 round yellow apple 6 round orange orange ¡ InformaNon gain of FORM: zero ¡ InformaNon gain of COLOR: more 34 Copyright A.Förster, A.Puia4 2014
- 35. C4.5 algorithm: Example example form color class 1 round red apple 2 round orange apple 3 round orange orange 4 round green apple 5 round yellow apple 6 round orange orange ¡ InformaNon gain of FORM: zero ¡ InformaNon gain of COLOR: more color red green orange yellow 35 Copyright A.Förster, A.Puia4 2014
- 36. C4.5 algorithm: Example example form color class 1 round red apple 2 round orange apple 3 round orange orange 4 round green apple 5 round yellow apple 6 round orange orange ¡ InformaNon gain of FORM: zero ¡ InformaNon gain of COLOR: more color red green orange yellow 1 4 2,3,6 5 36 Copyright A.Förster, A.Puia4 2014
- 37. C4.5 algorithm: Example example form color class 1 round red apple 2 round orange apple 3 round orange orange 4 round green apple 5 round yellow apple 6 round orange orange ¡ InformaNon gain of FORM: zero ¡ InformaNon gain of COLOR: more color red green orange yellow 1 4 2,3,6 5 apple apple apple ? 37 Copyright A.Förster, A.Puia4 2014
- 38. C4.5 algorithm: Example example form color class 1 round red apple 2 round orange apple 3 round orange orange 4 round green apple 5 round yellow apple 6 round orange orange ¡ InformaNon gain of FORM: zero ¡ InformaNon gain of COLOR: more ¡ Only let abribute: FORM color red green orange yellow 1 4 2,3,6 5 apple apple apple form round 2,3,6 orange 38 Copyright A.Förster, A.Puia4 2014
- 39. C4.5 algorithm: Problems example form color class 1 round red apple 2 round orange apple 3 round orange orange 4 round green apple 5 round yellow apple 6 round orange orange ¡ All orange apples will be classified as oranges ¡ Leaf node FORM unnecessary ¡ DECISION TREE DEPENDS ON TRAINING SET color red green orange yellow 1 4 2,3,6 5 apple apple apple form round 2,3,6 orange 39 Copyright A.Förster, A.Puia4 2014
- 40. Information Gain • Input are T tuples (classified samples with K features): • The informaNon gain of feature a is defined in terms of the entropy as follows: x,Y( )= x1, x2, x3,..., xk,Y( ) xa ∈ vals a( ),Y = class IG T,a( )= H T( )− x ∈ T xa = v{ } T ⋅ H x ∈ T xa = v{ }( )∑ H(T) = − pi log2 i=1 Y ∑ (pi ) Entropy of the full dataset Entropies of the sub-‐ datasets “MALE” and “FEMALE” 40 Copyright A.Förster, A.Puia4 2014
- 41. Properties of Decision Based Learning • Good for fast classificaNon of fuzzy, overlapping groups • Tree generated only once • Well-‐suited for staNc, but error-‐prone environments • Needs a good large training set • Moderate processing and large memory requirements (to hold the training set) 41 Copyright A.Förster, A.Puia4 2014
- 42. Incremental Decision Trees • Hoeffding tree algorithm • Hoeffding bound guarantees that if Xa is indeed the best feature with some small probability Copyright A.Förster, A.Puia4 2014 Pre DT +/-‐ WSN IDT Disc Classify the new sample Save the sample at the leaf Compute IG for each feature X All samples belong to same class? IG(Xa )− IG(Xb ) < ε Split the node according to feature Xa true false IG(Xa )− IG(Xb ) < ε [Domingos:2000] P. Domingos and G. Hulten: Mining High-‐speed Data Streams, in Proceedings of the 6th ACM Interna@onal Conference on Knowledge Discovery and Data Mining (SIGKDD) 42
- 43. Neural Networks – Introduction and Applications Dr. Anna Förster, Alessandro Puia4 BSN Tutorial, June 17th 2014 Zürich, Switzerland Copyright A.Förster, A.Puia4 2014 43
- 44. Background • Simplified (extremely!) model of the human brain and its neurons 44 Copyright A.Förster, A.Puia4 2014
- 45. Fundamentals 45 Copyright A.Förster, A.Puia4 2014
- 46. Perceptron • Simplest form of neural network • Computes linear funcNons only • AcNvaNon funcNon is simple threshold • Where do the weights come from? 46 Copyright A.Förster, A.Puia4 2014
- 47. Perceptron Learning 1. Present the network with an input 2. Calculate its current output 3. Compare with real output (supervised learning!) 4. Correct the weights to minimize the error between the computer output and the desired one wnew = wold – α*(desired-‐output)*input, α – learning constant 47 Copyright A.Förster, A.Puia4 2014
- 48. Multi-‐Layer Networks 48 • Generalizes all possible funcNons • Uses the logisNc funcNon (sigmoid) for acNvaNon • Back propagaNon is the most oten used weight learning method Copyright A.Förster, A.Puia4 2014
- 49. Applications • Very well suited for • Pabern recogniNon, image recogniNon • Noise cancelling • PredicNon (based on extrapolated data) • ProperNes: • Supervised learning, requires a large training set • Memory and processing intensive training • TesNng is also processing intensive • Examples from BSN: • Paberns recogniNon based on mulN-‐modal data • Cardio-‐vascular problems, heart abacks • Falls • AcNviNes 49 Zhanpeng Jin, Yuwen Sun, and Allen C. Cheng: PredicNng Cardiovascular Disease from Real-‐Time Electrocardiographic Monitoring: An AdapNve Machine Learning Approach on a Cell Phone, IEEE EMBS 2009. Copyright A.Förster, A.Puia4 2014
- 50. Introduction to Reinforcement Learning Dr. Anna Förster, Alessandro Puia4 BSN Tutorial, June 17th 2014 Zürich, Switzerland Copyright A.Förster, A.Puia4 2014 50
- 51. Reinforcement Learning • A learning agent • A pool of possible acNons • Goodness of acNons • A reward funcNon • Select one acNon • Execute the acNon • Observe the reward • Correct the goodness of the executed acNon 51 Copyright A.Förster, A.Puia4 2014
- 52. Introduction to Q-‐Learning 52 Copyright A.Förster, A.Puia4 2014
- 53. Introduction to Q-‐Learning ¤ Learning agent 53 Copyright A.Förster, A.Puia4 2014
- 54. D B A E F C START Introduction to Q-‐Learning ¤ Learning agent ¤ Internal current state st 54 Copyright A.Förster, A.Puia4 2014
- 55. D B A E F C START Introduction to Q-‐Learning ¤ Learning agent ¤ Internal current state st ¤ Pool of possible acNons At(st) 55 Copyright A.Förster, A.Puia4 2014
- 56. Introduction to Q-‐Learning D B A E F C START ¤ Learning agent ¤ Internal current state st ¤ Pool of possible acNons At(st) ¤ Associated Q-‐value to each acNon in each state 56 Copyright A.Förster, A.Puia4 2014
- 57. D B A E F C START 0 0 0 0 100 0 0 0 100 0 0 action with immediate reward 0 and cost -1 action with immediate reward 100 and cost -2 0 100 100 Introduction to Q-‐Learning ¤ Learning agent ¤ Internal current state st ¤ Pool of possible acNons At(st) ¤ Associated Q-‐value to each acNon in each state ¤ Immediate reward ater each acNon 1. select an ac+on 57 Copyright A.Förster, A.Puia4 2014
- 58. D B A E F C START 0 0 0 0 100 0 0 0 100 0 0 action with immediate reward 0 and cost -1 action with immediate reward 100 and cost -2 0 100 100 Introduction to Q-‐Learning ¤ Learning agent ¤ Internal current state st ¤ Pool of possible acNons At(st) ¤ Associated Q-‐value to each acNon in each state ¤ Immediate reward ater each acNon ¤ Learning procedure: ¤ select an acNon 1. select an ac+on 58 Copyright A.Förster, A.Puia4 2014
- 59. D B A E F C START 0 0 0 0 100 0 0 0 100 0 0 action with immediate reward 0 and cost -1 action with immediate reward 100 and cost -2 0 100 100 Introduction to Q-‐Learning ¤ Learning agent ¤ Internal current state st ¤ Pool of possible acNons At(st) ¤ Associated Q-‐value to each acNon in each state ¤ Immediate reward ater each acNon ¤ Learning procedure: ¤ select an acNon ¤ execute the acNon 1. select an ac+on 2. execute the ac+on 59 Copyright A.Förster, A.Puia4 2014
- 60. D B A E F C START 0 0 0 0 100 0 0 0 100 0 0 action with immediate reward 0 and cost -1 action with immediate reward 100 and cost -2 0 100 100 Introduction to Q-‐Learning ¤ Learning agent ¤ Internal current state st ¤ Pool of possible acNons At(st) ¤ Associated Q-‐value to each acNon in each state ¤ Immediate reward ater each acNon ¤ Learning procedure: ¤ select an acNon ¤ execute the acNon ¤ observe reward 1. select an ac+on 2. execute the ac+on 3. receive reward 60 Copyright A.Förster, A.Puia4 2014
- 61. D B A E F C START 0 0 0 0 100 0 0 0 100 0 0 action with immediate reward 0 and cost -1 action with immediate reward 100 and cost -2 0 100 100 Introduction to Q-‐Learning ¤ Learning agent ¤ Internal current state st ¤ Pool of possible acNons At(st) ¤ Associated Q-‐value to each acNon in each state ¤ Immediate reward ater each acNon ¤ Learning procedure: ¤ select an acNon ¤ execute the acNon ¤ observe reward ¤ update state and Q-‐ values 1. select an ac+on 2. execute the ac+on 3. receive reward 4. st = D, Q(aD, C) 61 Copyright A.Förster, A.Puia4 2014
- 62. D B A E F C START 0 0 0 0 100 0 0 0 100 0 0 action with immediate reward 0 and cost -1 action with immediate reward 100 and cost -2 0 100 100 Introduction to Q-‐Learning ¤ Learning agent ¤ Internal current state st ¤ Pool of possible acNons At(st) ¤ Associated Q-‐value to each acNon in each state ¤ Immediate reward ater each acNon ¤ Learning procedure: ¤ select an acNon ¤ execute the acNon ¤ observe reward ¤ update state and Q-‐ values 1. select an ac+on 2. execute the ac+on 3. receive reward 4. st = D, Q(aD, C) 62 Copyright A.Förster, A.Puia4 2014
- 63. How to recompute the Q-‐values? € Q st +1,at( ) = Q st,at( )+ γ R st,at( )− Q st,at( )( ) new Q-‐Value old Q-‐Value immediate reward received a`er execuGng acGon a in state s at Gme t old Q-‐Value learning constant ¡ Learning constant: avoid oscillaNons of Q values at the beginning of the learning process (smooth the Q-‐Values) ¡ γ ≈ 1 : new Q-‐Value is exchanged with the reward ¡ γ ≈ 0 : new Q-‐Value is the same as the old one 63 Copyright A.Förster, A.Puia4 2014
- 64. How to deTine the reward function? • Two main types: • Pre-‐defined • Computed ater each acNon • Oten used : • zero awards for acNons leading directly to the goal • negaNve for all others (e.g. -‐1) • Also used: • Manhaban distance to the goal • Geographic distance to the goal • Currently best available Q value at the state (!!) 64 Copyright A.Förster, A.Puia4 2014
- 65. How to decide which action to take? • ExploraGon strategy (acGon selecGon policy) • Cannot be random, need to use accumulated knowledge • Cannot be greedy, need to explore all possibiliNes • Oten used: ε-‐greedy • select a random acNon with probability ε • select the best available one (best Q-‐value) with probability (1-‐ε) 65 Copyright A.Förster, A.Puia4 2014
- 66. Properties of Reinforcement Learning • Simple, flexible model • Adapts to changing environments, re-‐learns quickly • Copes successfully with mobile or unreliable environments • Simple to design and implement • Small to moderate processing and memory needs • Can be implemented fully distributed 66 Copyright A.Förster, A.Puia4 2014
- 67. Reinforcement Learning for BSNs? • All distributed problems: • RouNng protocols • Clustering protocols • Neighborhood management protocols • Medium Access protocols • Further • Parameter opNmizaNon and learning • ApplicaNon-‐level cooperaNon among nodes 67 Copyright A.Förster, A.Puia4 2014
- 68. Applications of Reinforcement Learning Dr. Anna Förster, Alessandro Puia4 BSN Tutorial, June 17th 2014 Zürich, Switzerland Copyright A.Förster, A.Puia4 2014 68
- 69. Q-‐Learning in WSN Routing • Agents: the packets • States: the nodes • AcGons: next hops • q-‐values: esNmaNons of rouNng costs • IniGal q-‐values: some first guess about rouNng costs • Reward funcNon: the best cost esNmaNon of the next hop • ExploraGon strategy: simple, e.g. ε-‐greedy 69 Copyright A.Förster, A.Puia4 2014
- 70. Unicast routing with RL Sending a packet from A to D Init all q values to 10 (guess) A B C D Rewards:" "r = qbest, if not sink" "r = 0, if sink" Send rewards to all neighbors (broadcast)" 70 Copyright A.Förster, A.Puia4 2014
- 71. Sending a packet from A to D Init all q values to 10 (guess) A B C D QB = 10 (initial)" QC = 10 (initial)" Action selection policy" (Exploration strategy)" "ε-greedy" Balance exploration/exploitation" Unicast routing with RL state Q B 10 C 10 state Q A 10 C 10 D 10 state Q B 10 A 10 D 10 71 Copyright A.Förster, A.Puia4 2014
- 72. A B C D QB = 10 (initial)" Sending a packet from A to D Select next hop (state) B Unicast routing with RL state Q B 10 C 10 72 Copyright A.Förster, A.Puia4 2014
- 73. A B C D QA = 10 (initial)" Sending a packet from A to D B has 3 possible next hops, with qbest = 10 QC = 10 (initial)" QD = 10 (initial)" Unicast routing with RL state Q A 10 C 10 D 10 73 Copyright A.Förster, A.Puia4 2014
- 74. A B C D Sending a packet from A to D B selects D as next hop, packet" Unicast routing with RL state Q A 10 C 10 D 10 74 Copyright A.Förster, A.Puia4 2014
- 75. A B C D Sending a packet from A to D B selects D as next hop, reward = qbest = 10 packet" reward" reward" Unicast routing with RL state Q A 10 C 10 D 10 75 Copyright A.Förster, A.Puia4 2014
- 76. A B C D Sending a packet from A to D B selects D as next hop, reward = qbest = 10 packet" reward" QB = cB + rB = 11" QC = 10" reward" QA = 10" QB = cB + rB = 11" QD = 10" Unicast routing with RL state Q A 10 C 10 D 10 76 Copyright A.Förster, A.Puia4 2014
- 77. A B C D Sending a packet from A to D B selects D as next hop, reward = qbest = 10 packet" reward" QB = cB + rB = 11" reward" QB = cB + rB = 11" Unicast routing with RL state Q A 10 C 10 D 10 state Q B 11 C 10 state Q B 11 A 10 D 10 77 Copyright A.Förster, A.Puia4 2014
- 78. A B C D Sending a packet from A to D D is the sink, goal reached Unicast routing with RL 78 Copyright A.Förster, A.Puia4 2014
- 79. A B C D Sending a packet from A to D D is the sink, goal reached reward = 0 (real costs) reward" reward" Unicast routing with RL 79 Copyright A.Förster, A.Puia4 2014
- 80. A B C D Sending a packet from A to D D is the sink, goal reached reward = 0 (real costs) reward" QD = cB + rB = 1" QD = cB + rB = 1" reward" Unicast routing with RL state Q A 10 C 10 D 1 state Q B 11 A 10 D 1 80 Copyright A.Förster, A.Puia4 2014
- 81. A B C D Sending a packet from A to D State of the network ater first packet Unicast routing with RL state Q B 11 C 10 state Q A 10 C 10 D 1 state Q B 11 A 10 D 1 81 Copyright A.Förster, A.Puia4 2014
- 82. A B C D Sending a packet from A to D State of the network ater many packets Unicast routing with RL state Q B 2 C 2 state Q A 3 C 2 D 1 state Q B 2 A 3 D 1 How to go faster?! Make better guesses!! 82 Copyright A.Förster, A.Puia4 2014
- 83. Unicast routing with RL Bene3its • Simple and powerful • Reacts immediately to changes: • New rewards propagate quickly • New routes are learnt • Only necessary changes in the immediate neighborhood of failure • Route iniNalizaNon is sink/source driven • Low memory and processing overhead 83 Copyright A.Förster, A.Puia4 2014
- 84. Unicast Routing with RL • Hops: too trivial to deserve a publicaNon… • Maximum aggregaNon rate: P. Beyens, M. Peeters, K. Steenhaut, and A. Nowe. RouGng with compression in wireless sensor networks: A Q-‐learning approach. In Proceedings of the 5th European Workshop on AdapNve Agents and MulN-‐Agent Systems (AAMAS), page 12pp., Paris, France, 2005. • Combined with geographic rouNng: R. Arroyo-‐Valles, R. Alaiz-‐Rodrigues, A. Guerrero-‐Curieses, and J. Cid-‐ Suiero. Q-‐probabilisGc rouGng in wireless sensor networks. In Proceedings of the 3rd InternaNonal Conference on Intelligent Sensors, Sensor Networks and InformaNon Processing (ISSNIP), pages 1–6, Melbourne, Australia, 2007. • Minimum delay: J. A. Boyan and M. L. Libman. Packet rouGng in dynamically changing networks: A reinforcement learning approach. Advances in Neural InformaNon Processing Systems, 6:671–678, 1994. 84 Copyright A.Förster, A.Puia4 2014
- 85. • Challenges: • AcNons need to reflect not the next hop, but HOPS • Reward funcNon is distributed among several neighbors • Set of acNons very large – needs a lot of exploraNon! • SoluNon steps: • Separate acNons into sub-‐acNons • Smart iniNal Q values Multicast Routing with RL A B C D A. Förster and A. L. Murphy. FROMS: A Failure Tolerant and Mobility Enabled MulGcast RouGng Paradigm with Reinforcement Learning. Elsevier Ad Hoc Networks, 2011 85 Copyright A.Förster, A.Puia4 2014
- 86. FROMS: Multicast routing with Q-‐Learning § Localized view ater sink announcement § The minimum esNmated is not the opNmal: § best esNmate for (A,B): 3 + 3 -‐ 1 = 5 hops § opNmal for (A,B): 4 hops A -‐ 5 hops B -‐ 3 hops A -‐ 3 hops B -‐ 5 hops 2 1 3 A B A -‐ 4 hops B -‐ 4 hops st+1, Qt+1 environmentagent rt(st,at) at st, At, Qt 86 Copyright A.Förster, A.Puia4 2014
- 87. FROMS: Multicast routing with Q-‐Learning agent st+1, Qt+1 environmentagent rt(st,at) at st, At, Qt § Agent: each node in the network 87 Copyright A.Förster, A.Puia4 2014
- 88. FROMS: Multicast routing with Q-‐Learning agent st+1, Qt+1 environmentagent rt(st,at) at st, At, Qt § Agent: each node in the network § State: agent’s neighbors 88 Copyright A.Förster, A.Puia4 2014
- 89. FROMS: Multicast routing with Q-‐Learning 2 1 3 agent for sink A for sink B ai = {n1 for A}, {n3 for B} ! Actions:! aj = {n2 for A,B} ! for sinks A, B sub-actions st+1, Qt+1 environmentagent rt(st,at) at st, At, Qt § Agent: each node in the network § State: agent’s neighbors § Possible acNons: combinaNon of neighbors to reach all sinks 89 Copyright A.Förster, A.Puia4 2014
- 90. FROMS: Multicast routing with Q-‐Learning 2 1 3 for sink A for sink B for sinks A, B Q(n2, {A,B}) Q(n3, {B}) Q(n1, {A}) st+1, Qt+1 environmentagent rt(st,at) at st, At, Qt § Agent: each node in the network § State: agent’s neighbors § Possible acNons: combinaNon of neighbors § Q Values: associate with § each sub-‐acNon § computable for each (full) acNon 90 Copyright A.Förster, A.Puia4 2014
- 91. FROMS: Multicast routing with Q-‐Learning 2 1 3 for sinks A (4 hops) B (4 hops) Q(n2, {A,B}) = 4+4-‐1 st+1, Qt+1 environmentagent rt(st,at) at st, At, Qt § Agent: each node in the network § State: agent’s neighbors § Possible acNons: combinaNon of neighbors § Q Values: associate with sub-‐acNons, compute for acNons § IniNalize Q Values with number of esNmated hops 91 Copyright A.Förster, A.Puia4 2014
- 92. FROMS: Multicast routing with Q-‐Learning 2 1 3 st+1, Qt+1 environmentagent rt(st,at) at st, At, Qt § Agent: each node in the network § State: agent’s neighbors § Possible acNons: combinaNon of neighbors § Q Values: associate with sub-‐acNons, compute for acNons § IniNalize Q Values with number of esNmated hops § Environment: all other nodes 92 Copyright A.Förster, A.Puia4 2014
- 93. FROMS: Multicast routing with Q-‐Learning 2 1 3 for sinks A,B st+1, Qt+1 environmentagent rt(st,at) at st, At, Qt § Agent: each node in the network § State: agent’s neighbors § Possible acNons: combinaNon of § Q Values: associate with sub-‐acNons, compute for acNons § IniNalize Q Values with number of esNmated hops § Environment: all other nodes 93 Copyright A.Förster, A.Puia4 2014
- 94. FROMS: Multicast routing with Q-‐Learning 2 1 3 § Agent: each node in the network § State: agent’s neighbors § Possible acNons: combinaNon of § Q Values: associate with sub-‐acNons, compute for acNons § IniNalize Q Values with number of esNmated hops § Environment: all other nodes § Reward: the best available Q value + 1 hop for sinks A,B i st+1, Qt+1 environmentagent rt(st,at) at st, At, Qt 94 Copyright A.Förster, A.Puia4 2014
- 95. environmentagent FROMS: Multicast routing with Q-‐Learning 2 1 3 § Agent: each node in the network § State: agent’s neighbors § Possible acNons: combinaNon of § Q Values: associate with sub-‐acNons, compute for acNons § IniNalize Q Values with number of esNmated hops § Environment: all other nodes § Reward: the best available Q value + 1 hop § Update at neighboring nodes (learn) for sinks A,B i st+1, Qt+1 rt(st,at) at st, At, Qt exploraNon strategy update rules reward computaNon 95 Copyright A.Förster, A.Puia4 2014
- 96. Parameters of FROMS • Possible cost funcNons: • Any cost funcNon defined over the edges or nodes of the communicaNon graph • Here: minimum hops to desGnaGons • Further: minimum delay to the sinks; minimum geographic progress; minimum transmission power; maximum remaining energy on the nodes; combinaNons; … • ExploraNon strategy • Balance exploraNon against exploitaNon • Depend on the used cost funcNon • Memory management • HeurisNcs for pruning the available acNons and sub-‐acNons st+1, Qt+1 environmentagent rt(st,at) at st, At, Qt 96 Copyright A.Förster, A.Puia4 2014
- 97. Further Applications of RL to WSNs • Clustering for WSNs: Anna Förster and Amy L. Murphy, Clique: Role-‐free Clustering with Q-‐ Learning for Wireless Sensor Networks, in Proceedings of the 29th InternaNonal Conference on Distributed CompuNng Systems (ICDCS) 2009, 9pp., Canada, June 2009 • MAC protocols: Z. Liu and I. Elahanany. RL-‐MAC: A reinforcement learning based MAC protocol for wireless sensor networks. InternaNonal Journal on Sensor Networks, 1(3/4):117–124, 2006. • Best coverage: M.W.M. Seah, C.K. Tham, K. Srinivasan, and A. Xin. Achieving coverage through distributed reinforcement learning in wireless sensor networks. In Proceedings of the 3rd InternaNonal Conference on Intelligent Sensors, Sensor Networks and InformaNon Processing (ISSNIP), 2007. 97 Copyright A.Förster, A.Puia4 2014
- 98. Discussion Dr. Anna Förster, Alessandro Puia4 BSN Tutorial, June 17th 2014 Zürich, Switzerland Copyright A.Förster, A.Puia4 2014 98
- 99. ML Techniques! Memory! ComputaGon! Tolerance to topology changes! OpGmality! Init.costs! Add. costs! Reinforcement Learning! low" low" high" high" medium" low" Swarm Intelligence! medium" low" high" high" high" medium" HeurisGcs! low" low" low/medium" medium" high" low" Mobile Agents! low" low" medium" low" low" medium /high" Neural networks! medium" medium" low" high" high" low" GeneGc algorithms! high" medium" low" high" high" low" Comparison of properties required memory for on-‐node storage required processing on the node or base staNon flexibility of the found soluNon to environmental changes opNmality of derived soluNon compared to a centrally computed opNmal soluNon required communicaNon or processing costs before starNng normal work addiNonal communicaNon or processing costs during runNme 99 Copyright A.Förster, A.Puia4 2014
- 100. ML Techniques! Memory! ComputaGon! Tolerance to topology changes! OpGmality! Init.costs! Add. costs! Reinforcement Learning! low" low" high" high" medium" low" Swarm Intelligence! medium" low" high" high" high" medium" HeurisGcs! low" low" low/medium" medium" high" low" Mobile Agents! low" low" medium" low" low" medium /high" Neural networks! medium" medium" low" high" high" low" GeneGc algorithms! high" medium" low" high" high" low" Comparison of properties 100 Copyright A.Förster, A.Puia4 2014
- 101. ML Techniques! Memory! ComputaGon! Tolerance to topology changes! OpGmality! Init.costs! Add. costs! Reinforcement Learning! low" low" high" high" medium" low" Swarm Intelligence! medium" low" high" high" high" medium" HeurisGcs! low" low" low/medium" medium" high" low" Mobile Agents! low" low" medium" low" low" medium /high" Neural networks! medium" medium" low" high" high" low" GeneGc algorithms! high" medium" low" high" high" low" Comparison of properties 101 Copyright A.Förster, A.Puia4 2014
- 102. ML Techniques! Memory! ComputaGon! Tolerance to topology changes! OpGmality! Init.costs! Add. costs! Reinforcement Learning! low" low" high" high" medium" low" Swarm Intelligence! medium" low" high" high" high" medium" HeurisGcs! low" low" low/medium" medium" high" low" Mobile Agents! low" low" medium" low" low" medium /high" Neural networks! medium" medium" low" high" high" low" GeneGc algorithms! high" medium" low" high" high" low" Comparison of properties 102 Copyright A.Förster, A.Puia4 2014
- 103. ML Techniques! Memory! ComputaGon! Tolerance to topology changes! OpGmality! Init.costs! Add. costs! Reinforcement Learning! low" low" high" high" medium" low" Swarm Intelligence! medium" low" high" high" high" medium" HeurisGcs! low" low" low/medium" medium" high" low" Mobile Agents! low" low" medium" low" low" medium /high" Neural networks! medium" medium" low" high" high" low" GeneGc algorithms! high" medium" low" high" high" low" Comparison of properties 103 Copyright A.Förster, A.Puia4 2014
- 104. ML Techniques! Memory! ComputaGon! Tolerance to topology changes! OpGmality! Init.costs! Add. costs! Reinforcement Learning! low" low" high" high" medium" low" Swarm Intelligence! medium" low" high" high" high" medium" HeurisGcs! low" low" low/medium" medium" high" low" Mobile Agents! low" low" medium" low" low" medium /high" Neural networks! medium" medium" low" high" high" low" GeneGc algorithms! high" medium" low" high" high" low" Comparison of properties 104 Copyright A.Förster, A.Puia4 2014
- 105. ML Techniques! Memory! ComputaGon! Tolerance to topology changes! OpGmality! Init.costs! Add. costs! Reinforcement Learning! low" low" high" high" medium" low" Swarm Intelligence! medium" low" high" high" high" medium" HeurisGcs! low" low" low/medium" medium" high" low" Mobile Agents! low" low" medium" low" low" medium /high" Neural networks! medium" medium" low" high" high" low" GeneGc algorithms! high" medium" low" high" high" low" Comparison of properties 105 Copyright A.Förster, A.Puia4 2014
- 106. Comparison of properties ML Techniques! Memory! ComputaGon! Tolerance to topology changes! OpGmality! Init.costs! Add. costs! Reinforcement Learning! low" low" high" high" medium" low" Swarm Intelligence! medium" low" high" high" high" medium" HeurisGcs! low" low" low/medium" medium" high" low" Mobile Agents! low" low" medium" low" low" medium /high" Neural networks! medium" medium" low" high" high" low" GeneGc algorithms! high" medium" low" high" high" low" 106 Copyright A.Förster, A.Puia4 2014
- 107. Comparison of properties ML Techniques! Memory! ComputaGon! Tolerance to topology changes! OpGmality! Init.costs! Add. costs! Reinforcement Learning! low" low" high" high" medium" low" Swarm Intelligence! medium" low" high" high" high" medium" HeurisGcs! low" low" low/medium" medium" high" low" Mobile Agents! low" low" medium" low" low" medium /high" Neural networks! medium" medium" low" high" high" low" GeneGc algorithms! high" medium" low" high" high" Low " Decision Trees medium medium low high high low 107 Copyright A.Förster, A.Puia4 2014
- 108. Comparison of properties ML Techniques! Memory! ComputaGon! Tolerance to topology changes! OpGmality! Init.costs! Add. costs! Reinforcement Learning! low" low" high" high" medium" low" Swarm Intelligence! medium" low" high" high" high" medium" HeurisGcs! low" low" low/medium" medium" high" low" Mobile Agents! low" low" medium" low" low" medium /high" Neural networks! medium" medium" low" high" high" low" GeneGc algorithms! high" medium" low" high" high" low" Decision Trees! high" medium" low" high" high" low" Distributed problems Centralized and localized problems Optimization 108 Copyright A.Förster, A.Puia4 2014
- 109. Further readings M. Dorigo and T. Stuetzle. Ant Colony OpGmizaGon. MIT Press, 2004. J. Kennedy and R.C. Eberhart. Swarm Intelligence. Morgan Kaufmann, 2001. T.M. Mitchell. Machine Learning. McGraw-‐Hill, 1997. A. Förster. Teaching Networks How to Learn SVH Verlag, 2009 S.J. Russell and P. Norvig. ArGficial Intelligence: A Modern Approach. PrenNce Hall InternaNonal, 2003. R. S. Subon and A. G. Barto. Reinforcement Learning: An IntroducGon. The MIT Press, March 1998. 109 Copyright A.Förster, A.Puia4 2014
- 110. Copyright A.Förster, A.Puia4 2014 110
- 111. OPEN DISCUSSION 111 Copyright A.Förster, A.Puia4 2014