Optimal Anti-Jamming Strategy in Sensor Networks

1. Optimal Anti-Jamming Strategy in Sensor Networks Presenter: Yu Wen Chiou Advisor: Yeong Sung Lin Communications (ICC), 2012 IEEE International Conference

2. Agenda • Introduction • Model and Problem Formulation • Optimal Anti-jamming Strategy • Performance Evaluation • Conclusion

3. I. Introduction

4. Introduction • Wireless Sensor Network的特性 • Low-cost • Easy to deploy • Unattended operation • Ability of withstanding harsh environmental conditions • Wireless Sensor Network的應用 • Environment monitoring • Event detection • Wireless Sensor Network的關鍵問題 • Sensor nodesare typically powered by batteries and hence limited in powersupply.

5. Introduction(Cont’d) • Radio Jamming Attacks • Sensor networks transmit wireless signals over the open shared media. This leaves a sensor network vulnerable to radio jamming attacks. • Ex, Corrupt control packets, the jammer just keeps sending packets like RTS to prevent transmission of legitimate packets. • Cause severe damage to the sensor network with only modest overhead. • Anti-JammingMethods • Energy-efficient • Ex, channel surfing, error correction codes, transmission power adjustment

6. Introduction(Cont’d) • 研究動機 • These existing countermeasuresof jamming attacks are usually suitable for a limitedrange of jamming conditions with varying operation cost. Inthe real world scenario, jamming attacks may be very differentin nature and may change over time. • Different nodes suffer different degrees of radiojamming. Thus, it is inefficient for a whole sensor networksimply to apply a single anti-jamming technique. This mayresult in poor performance of anti-jamming and/or still sufferserious performance degradation of energy consumption.

7. Introduction(Cont’d) • 研究目的 • This paper focuses on proposing an adaptive approach toanti-jamming for sensor networks, by combining the strengthof different anti-jamming techniques. • We are formulating the anti-jamming problem of the sensor network as a Markov decision process and propose an algorithm for computing the best anti-jamming strategy.

8. II. Model and Problem Formulation Problem Description Anti-jamming Techniques

9. Model and Problem Formulation A. Problem Description Based on , the nodechooses the proper anti-jamming technique to deal with differentjamming signal.

10. Model and Problem Formulation(Cont’d) • For the node, each anti-jamming technique has different cost, .We evaluate this cost as a function of the energy that the node will consume in the next period. 能耗函數 Node 定期評估 channelcondition的週期 時間點 t 時，所選用的anti-jamming技術 k

11. Model and Problem Formulation(Cont’d) • The performance reward of thenode using specific anti-technique is the improvement of thecommunication between the nodes. 時間點t時，所選用的anti-jamming技術 k，所帶來的 performancereward 時間點t 過了一個週期的時間點 時間點t時的communication quality

12. Model and Problem Formulation(Cont’d) • 本文的目的是要為每個node選用一個合適的anti-jamming技術，選用的準則必須同時考量上述第(1),(2)式的 cost 及 reward。 • We makethe objective by minimizing the product of cost and reward. • We focus on a relatively long time period, denoted as T, sothe nodes totally make [T/τ] decisions. The set of anti-jamming techniques

13. Model and Problem Formulation(Cont’d) B. Anti-jamming Techniques • Without loss of generality, this paper assumes that each sensor node is capable of applying three representative anti-jamming techniques. • Transmission Power Adjustment:With this technique, asender node increases its transmission power, and thus increasesthe SNR at the receiver node. This technique issuitable under a slight jamming condition. This technique introduces modest energy cost. • Error-Correcting Code(ECC): An error-correcting code isused for correcting some error bits that occurred duringtransmission.

14. Model and Problem Formulation(Cont’d) • Channel Hopping(Channel Surfing):With this technique, a sensor node will change the working channel when it detects strong jamming signals in the current channel.

15. Model and Problem Formulation(Cont’d) • 每一個節點都會有一組anti-jamming技術可供應用，表示成： :Nulltechnique :Transmission power adjustment :Error-correctingcode :Channel hopping(Channel surfing)

16. III. Optimal Anti-jamming Strategy System State Transition Probability Cost of Anti-jamming Techniques Policy Determination Algorithm Framework

17. Optimal Anti-jamming Strategy • 在此章節中，將仔細描述，如何為每個node選用最佳的anti-jamming技術。 • We formulate the problem as a 4-tuple: :the set of all the node states that describe the channel conditions (3-A) :the set of anti-jamming techniques (2-B) :the probability that the node state becomes s’ after technique δ is performed at state s. (3-B) :the cost of the anti-jamming technique (3-C)

18. Optimal Anti-jamming Strategy(Cont’d) • System States (S) • 考量到sensornodes的有限運算能力，因此降低演算法的複雜度是非常重要的。故本文僅使用四種狀態，表示成 S = {0, 1, 2, 3}。這四種狀態表示四種不同的 jamming conditions，及其所對應的 anti-jamming strategies (前述之Δ={δ0, δ1, δ2, δ3})。 • 根據過往的文獻，使用PDR及RSSI來表示jammingsignals，本文亦使用PDR及RSSI作為判斷 S 的依據。 • 當S值越大時，表示jammer出現；S值越小時，表示jammer未出現。

19. Optimal Anti-jamming Strategy(Cont’d) • PDRand RSSI

20. Optimal Anti-jamming Strategy(Cont’d) PDR值大時，表示jammer未出現，prefer a light anti-jamming strategy These two functions output the system state depending on the current countermeasure RSSI值小時，表示jammer未出現，normal state (PDR<Φor RSSI > K) Jammer出現，使state值為大

21. Optimal Anti-jamming Strategy(Cont’d) • Transition Probability (P) • Since the state of nodes changes due to the varying jamming conditions, the transition probability of the states also describes the variation of jamming signals. • The transition probability is acquired by analyzing historicaldata.

22. Optimal Anti-jamming Strategy(Cont’d) • When S( t - τ) = iand S(t) = j. Then, the transition probability can be calculated as: j i 運用δ技術時，state 為 i的node中，有多少比例會由statei 變為 statej The total number of nodes that reach the state i

23. Optimal Anti-jamming Strategy(Cont’d) • Cost of Anti-jamming Techniques (C) • Adjusting Transmission power It is the raised power multiplied the packet transmission time. 在週期 τ 內的封包數 The time of transmitting every packet. The cost of the increasing power action. The bits transmission rate. The packet length. 傳送每個封包所消耗的能量

24. Optimal Anti-jamming Strategy(Cont’d) • Error-Correcting Codes(ECC) • The energy consumed by this technique is the power that used for the encoding and decoding process and transmitting the redundant bits. • For the error-correcting codes has to be undertaken by both of the communicating nodes, the notification process also consume extra energy. The energy expended for the notification process The length of the encoded packets. 傳送每個封包所消耗的能量 The energy that spendfor decoding the packets or correcting the errors of the receivedsignal.

25. Optimal Anti-jamming Strategy(Cont’d) • Channel Hopping(Channel Surfing) • As the error-correcting code strategy, the nodes have to notify the neighbors that it will change to another channel, for the neighbors undertaking the same strategy to keep the connectivity of the network. • When the nodes take this strategy, the intermediate nodes also need to send some packets when it switches to each channel. The node has to inform the neighbors when it goes to a new channel. This is the energy expended to send those packets The energy expended for the notification process The total channel switches

26. Optimal Anti-jamming Strategy(Cont’d) • Policy Determination • In the following, we use PDR to describe performance reward, • And we define: 同前述第(2)式， performancereward γ 是 cost 的係數。這個係數設計的目的是為了調整使用這個科技的成本，調整時會參考使用這個科技對於質量的好壞影響。 the cost of technique δat state i. Ex. More effective technique → R 大 → γ 小 → λ 小

27. Optimal Anti-jamming Strategy(Cont’d) • Based on the definitions above, we devise the policy improvement algorithm to solve the MDP problem. • 我們令 為 node 從 statei開始，演化 n 週期後的預期總成本。Then we have: The cost of the next n period policy period state The cost introduced in the first period. (10)

28. Optimal Anti-jamming Strategy(Cont’d) • The long run expected averagecost per unit time could be expressed as: There are M states in total The steady distribution of the states

29. Optimal Anti-jamming Strategy(Cont’d) • We can have an approximate relationship when n is large: node 從 statei 開始，演化 n 週期後的預期總成本，同第(11)式 The effect on the total expectedcost due to beginning in state i The long run expected averagecost per unit time(12)

30. Optimal Anti-jamming Strategy(Cont’d) • After substituting (13) into(11), we get: 代入 The long run expected averagecost per unit time

31. Optimal Anti-jamming Strategy(Cont’d) • The policy improvement algorithm starts by choosing an arbitrary policy and set . Then, it solves (14) to We use to find another policy such that for each state i: Where . When and are identical, this iteration process will stop. Otherwise, it sets n= n + 1 and this process continues.

32. Optimal Anti-jamming Strategy(Cont’d) • Algorithm Framework • The framework of the optimal anti-jamming algorithm is shown in Algorithm 2. the nodes begin to communicate with each other Algorithm 1. It updates the transition probabilities, which is for later policy determination. The nodes choose a proper anti-jamming strategy based on the current policy It will send a notification to make sure the nodes are using the same anti-jamming strategy

33. IV. Performance Evaluation Metrics and Setting Performance Results

34. Performance Evaluation • Metrics and Setting • The nodes are uniformly distributed in an square area of 40m by 40m. • The distance between nodes are 5 meters. • The jammer placed in the middle of the network so that it jams as many nodes as possible. • The packet length is 25 Bytes, and is 50 Bytes. • These values comply with the IEEE 802.15.4 Standard.

35. Performance Evaluation(Cont’d) • Performance Results Packet Delivery Ratio • Figure 2 shows the effectiveness of the computed anti-jamming strategies. • Channel Surfing 及 Optimal Strategy在不同的jammingconditions下，都有很好的表現。 Distance from the jammer

36. Performance Evaluation(Cont’d) • Figure 3 shows the energy consumption of the nodes. • Optimal Strategy的能量消耗較Channel Surfing為低。 • With Figure 2 and Figure 3, we conclude that our design iseffective and efficient at the same time.

37. V. Conclusion

38. Conclusion • We propose an approach for combining the strength of several jamming countermeasures and allow a sensor node to adopt the best anti-jamming technique. • Sensor nodes in the sensor network can adaptively change their anti-jamming methods as the jamming condition changes over time. • Thecomprehensive simulation experiments have demonstratedthat our algorithm achieves good performance in terms ofsuccessful delivery rate and at the meanwhile consumesslightly more energy.