International Conference on Communication and Signal Processing, April 3-5, 2014, India

A Novel Anti Jamming Technique for Wireless Sensor Networks

E.Achuthan, R.Kishore

Abstract- Wireless Sensor Network (WSN) is formed by deploying several sensor nodes in a region of interest for gathering information. The measured events are broadcasted via many sensor nodes to reach the sink node. In this scenario, there is a possibility for the presence of one or many jamming nodes which can introduce jamming attack into the network, which is a typical Denial of Service (DoS) attack. To escape from jamming Frequency Hopping Spread Spectrum technique is used where in the information will be transmitted with different carrier frequencies at different intervals of time. Therefore the intruder node might not be able to detect the data carrier frequency at an instant. In order to get synchronized, all nodes in sensor network should have same hopping pattern. The objective is to generate an indefinite length of uncorrelated frequency hopping pattern, to ensure secured communication between sensor nodes with low memory. The idea is to build security architecture within all wireless sensor nodes present in the network to provide secured radio channel selection for data transmission from source to sink nodes.

Index Terms- Frequency hopping, security, hopping pattern, sensor networks, anti jamming.

I. INTRODUCTION Wireless sensor network is an important technology in pervasive computing, remote area monitoring and for

other pro active and reactive applications. Design of wireless sensor network is based on IEEE 802.15.4 Standard. Securing such wireless nodes is very important for data confidentiality, access control and data non-repudiation. There are several types of attacks in WSN, but major attacks focus on physical layer because data transmission is done across the physical radio channel. Attacks at different layers can be rectified by available error correcting algorithms whereas attacks at physical layer cannot be corrected by error correcting algorithms.

Radio channel for communication across the network is decided by Physical (PHY) layer and Medium Access Control (MAC) sublayer. PHY layer contains all the operating frequencies enabled for WSN, it has the capability to turn ON

E.Achuthan is with the Department of Electronics and Communication Engineering, Sri Sivasubramaniya Nadar college of Engineering, Kalavakkam, Chennai, lndia.(e-mail: njoyachu@gmail.com).

R.Kishore is with the Department of Electronics and Communication Engineering, Sri Sivasubramaniya Nadar college of Engineering, Kalavakkam, Chennai, India.(e-mail: kishorer@ssn.edu.in).

978-1-4799-3358-7114/$31.00 2014 IEEE

and turn OFF the transceiver and also have the feature of channel selection.

The Service provided by Physical layer are PHY data service and PHY management service. MAC sublayer act as an intermediate between Physical layer and upper layers. MAC sublayer is responsible for establishing a standard link for MAC entities, Network synchronization, surety for communication between nodes. Jamming is one of the Denial Of Service (DOS) attack that takes place in the physical layer, which prevents the network from doing its basic functionality. There are several types of jammers available such as spot jammers, sweep jammers, barrage jammers, base jammers, repeater jammers etc, these jammers can be either proactive or reactive. To provide secured and reliable data transmission across sensor nodes spread spectrum technique is used. The most popular spread spectrum techniques are Direct Sequence Spread Spectrum (DSSS), Frequency Hopping Spread Spectrum (FHSS) and Hybrid FHSSIDSSS.

In FHSS the data is subdivided into symbols and these symbols are continuously transmitted by switching the radio channel. Depending on number of symbols transmitted in a hop, they are classified into Fast Frequency Hopping Spread Spectrum (FFHSS) and slow Frequency Hopping Spread Spectrum (SFHSS) [I], [2]. The scope of the spread spectrum technique is to avoid jamming and also multi path interference. It poses some limitation such as limited bandwidth and extra power used for its computation [3].

II. RELATED WORKS

Peng Du and Dr. George Roussos (2012) modeled a technique based on adaptive time synchronous channel hopping (A-TSCH) [4]. TSCH is divided into infinite successive slots which are grouped as super frames. TSCH uses three kinds of slots such as Advertisement (ADV), Transmit (Tx) Receive (Rx). Each time slot have a fixed variable, the value in the elapsed time slot is stored in Absolute slot number (ASN). ASN information is broadcasted as ADV. By using modulo arithmetic the channels are selected. A Blacklist is used to exclude some channels from hopping sequence. Link mask computation is performed for Tx and Rx only if the channel is not blacklisted. The analysis is done between packet delivery ratio and the number of attempts. This conveys that blacklisting provides better performance from interference. The advantage is that, the channel with low Packet delivery ratio is not used for

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communication. The limitation is that, frequency hopping takes place only after the channel gets jammed.

Weile Zhang et al. (2010) proposed a model for frequency hopping pattern based on Time Difference Of Arrival (TDOA) [5]. First the distance between nodes is calculated, which is directly propotional to the time the signal takes to propogate from one node to another. A super resolution time of arrival estimator is used to estimate the time of arrival. TDOA is calculated by using a hyperbolic algorithm. From the estimated TDOA, frequency hopping patterns are derived for Ultra Wide Band WSN. Performance is measured for TDOA for different bandwidth and range of error for estimation with and without diversity. The limitation is that, the algorithm followed is quite complex.

Aasha Nandhini Sukumaran et al. (2013) designed a novel frequency hopping spread spectrum technique which contains 20 hopping patterns with 6 channels in each pattern. The channels are arranged based on two criteria [1]. 20 seed values are arranged with 10 hopping patterns for each seed value. These seed values are arranged randomly and stored. These seed values routes for synchronized channel selection. The illustration is done for probability of matching symbols against number of trials, seed values of SFHSS and FFHSS. It is inferred that as number of trials and seed values increases probability of matching also increases. The advantage is that the computation energy for hopping sequence generation is low. The limitation is that, it requires lot of seed values to be stored to attain lengthy non repetitive hopping sequence.

III. SPECTRUM ALLOCA nON

IEEE 802.15.4 standard defines three frequency bands at 868MHz, 915MHz and 2450MHz. 868MHz band has 1 channel with center frequency 868.3MHz that occupies the channel number O. In 915MHz band there are 10 channels numbered from 1 to 10. For 2450MHz band there are 16 channels with 3MHz bandwidth and 5MHz channel spacing [6].

TABLE I CHANNEL NUMBER, CENTER FREQUENCY AND FREQUENCY SPECTRUM

Channel number Center frequency Frequency (GHz) spectrum(GHz)

11 2.405 2.4035-2.4065 12 2.410 2.4085-2.4115 13 2.415 2.4135-2.4165 14 2.420 2.4185-2.4215 15 2.425 2.4235-2.4265 16 2.430 2.4285-2.4315 17 2.435 2.4335-2.4365 18 2.440 2.4385-2.4415 19 2.445 2.4435-2.4465 20 2.450 2.4485-2.4515 21 2.455 2.4535-2.4565 22 2.460 2.4585-2.4615 23 2.465 2.4635-2.4665 24 2.470 2.4685-2.4 715 25 2.475 2.4735-2.4765 26 2.480 2.4 785-2.4815

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The center frequency for the channel is given by the equation [6].

Ie = 2405 + 5(Z -11)

where Z is the channel number, Z E [11,26]

(1)

Table I gives the center frequency, frequency spectrum with its channel number for 2450MHz band as per IEEE802.15.4 standard [1].

IV. NETWORK MODEL

Considering two deployments (random and grid) of 100 sensor nodes in 100 x 100m2 area, it can be observed that in random deployment the nodes may cluster at some area and may not be present in some area which results in poor coverage. In grid deployment the nodes are equally distributed, so that good coverage is achieved by all the sensor nodes. Consider a jammer 'x' with jamming range of 10m. Fig.l shows the coverage of single jammer in random deployment and Fig.2 shows the coverage of single jammer in grid deployment.

100

90

80

70

60

50 a

40

30

20 ... 10

0

random deployment

..

,0 o

o . ..

..

0 10 20 30 40 50 60 70 80 90 100 meters

Fig. 1 Random deployment

Grid deployment 100

90

80

70

60

:l 50 a

0, 0

40 o

30

20

10

0 0 10 20 30 40 50 60 70 80 90 100

meters

Fig. 2 Grid Deployment

V. PROPOSED TECHNIQUE

To ensure high security in frequency hopping spread spectrum, a novel idea for generating hopping pattern in wireless sensor network is proposed which takes countermeasure against jamming. As per IEEE 802.15.4 standard there are 16 channels numbered at 2450MHz frequency band [6]. The steps involved for the proposed technique is as follows.

A. Formation o/Generator matrix

The generator matrix is designed such that it Should provide high security. Should occupy very less memory. Should be less complex. Should be less biased to specific channel. Should lie within the channel number.

Based on the above observation, the Generator Matrix is

where,

G = [gobLn (4)

l'::;;a,b'::;;n,a*b

n is the number of rows and columns in a square matrix.

a is the row selected by the source.

b is the column selected by sink node.

X and Y are variables.

N is the total number of channels, N = 16 [6]. Z is the resultant channel number

In order to achieve synchronization, this generator matrix is built in all sensor nodes in the network, so that they can generate same hopping pattern in all sensor nodes. By using this generator matrix model different hopping patters can be generated for [en x n) - n] times. In case, If a=b, the results are not good enough because the results get biased towards some selected channels.

When a sensor node gathers information, in order to send the information with high security FHSS technique is followed. The generator matrix is used to generate the hopping sequence for FHSS using the following steps.

Step I: The source node broadcasts a random integer 'a' (1 ::; a ::; n) to its neighboring nodes which is further broad casted to the sink node. This integer is taken as the row number.

Step 2: In turn the sink node broadcasts a random integer 'b' (1::::; b::::; n,a =;t:. b) to source node which is taken as column number.

where n should be stored in all sensor nodes. Now all nodes present in the network knows the Row and Column number. Fig.3 shows the basic block diagram of the proposed technique.

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source sink

Random integer(l,n) (row)

Random integer (l,n) (column)

I G .... '" I I G .... '" I matnx matrIX Hopping pattern

Fig. 3 Basic block diagram

The generator matrix requires two variables X and Y. The variable is the heart of the hopping pattern generation.

Choose two four digit numbers m I and m2 such that m2 should not be in powers of 2, powers of 5 and multiples of both. The decimal part of m 11m2 equals to a sequence of non repeated numbers of length 'k' , k> lOOO.

ml -- = aOa1aZa3a4a'" m2 Assign all ai'S to X.

(2)

Choose two four digit numbers m3 and m4 such that m4 should not be in powers of 2, powers of 5 and multiples of both, The decimal part of m3/m4 equals to a sequence of non repeated numbers of length '1', I

> lOOO. m3 - = bo.bJbZb3b4 ...... boo (3) m4

Assign all bi's to Y. Consider an example

ml 5878 m2 2767

= 2.l243 ......... 568 where X = 2,1,2,4, .. . . 5,6,8, ...

This produces a non repeated sequence up to 2767th position and then it starts repeating.

m3 7876 m4 3769

= 2.0896 ......... 798 where Y = 2,0,8,9, .... 7,9,8, ... This produces a non repeated sequence up to 1885th

position and then it starts repeating.

B. Hopping Sequence Generation For generating hopping sequence continuously in all sensor

nodes, substitute the values of a, b, n, N, X and Y in the generator matrix. Fig.4 shows the steps involved in generating hopping sequence.

START

For Pattern

1:=

m1 = (m1%m 2)x10

m3 = (m3%m4)x 10

Fig. 4 Algorithm for frequency hopping sequence generation

For the above considered example the hopping sequence will repeat at 2,lcm(2766,1884) + 2,(2 x Icm(2766, 1884)) + 2, ...

C. Attack Model Jamming can be either intentional or unintentional. There is

possibility for an intruder to attack the network by jamming it and also there is a possibility that appliances operating in same frequency can create jamming. Two types of attacks are considered, Constant jammer tries to jam the network continuously at a particular frequency with energy more than the energy of the transmitted signal. In case of Random jammer, jamming occurs when jammer's high energy is shifted from one frequency to another in a random manner.

VI. SIMULATION RESULTS AND DISCUSSION

A. Performance GfSlow Frequency Hopping

Slow frequency hopping is the process of sending more than one symbol per hop. Fig.S shows the performance in terms of probability of matching symbols in slow frequency hopping. Comparison is made between traditional method and proposed technique for 2000 trials which shows that the probability of

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matching symbols increases as the number of trials increases. The probability of matching symbols for proposed technique is less when compared with traditional method.

0.9

-a 0.8

.Q E 0.7 i;;' .5' 0.6 .c

0.5 '8 .q0.4 20.3 c :;. 0.2

0.1

Traditional method --+-- proposed tedlllique

200 400 600 800 1000 1200 1400 1600 1800 2000 nwnber of trials

Fig. 5 Probability of matching symbols vs number of trials in slow FHSS

B. Frequency hopping sequence In existing technique [1] each time when the radio module is

switched ON, the hopping pattern is selected from the beginning. By continuously monitoring, the jammer can easily identify the hopping pattern in existing technique. In case of proposed technique, the row and column is selected by the source and sink respectively, so that whenever the radio module is switched ON the hopping pattern will change.

TABLE II

COMPARISION TABLE FOR EXISTING TECHNIQUE AND PROPOSED TECHNIQUE

Existing Technique[ll

17 14 23 13 22 18 19 16 25 17

a,b Proposed Technique

1,2 19 14 25 24 26 16 25 21 13 12

1,3 23 14 25 26 22 14 25 23 23 14

1,4 19 14 25 16 26 24 25 13 21 20

2,1 19 20 21 26 24 18 21 17 25 22

2,3 19 20 21 18 24 26 21 25 17 14

2,4 15 20 21 24 12 20 21 15 15 20

3,1 23 22 25 18 14 22 25 23 23 22

3,2 19 22 25 24 18 16 25 13 21 12

3,4 19 22 25 16 18 24 25 21 13 20

4,1 19 12 21 26 16 18 21 25 17 22

4,2 15 12 21 16 20 12 21 15 15 12

4,3 19 12 21 18 16 26 21 17 25 14

Table II gives the comparison of frrst 10 frequency hopping pattern in existing technique [1] with the proposed technique for different row (a) and column (b) combination by considering the above example with square matrix of size n=4.

The proposed technique has hopping sequence repeated only at 2,868526. In order to achieve such non repeating hopping sequence, the existing technique [1] should have 14476 seed values to be stored in all sensor nodes.

By adding more variables in the Generator matrix, the length of non repetitive hopping sequence can be increased further.

C. FFHSS Permutation Fast Frequency Hopping Spread Spectrum (FFHSS) is the

process of sending one symbol in many hops (r). While using r hop for transmitting a symbol, the existing technique [1] follows the frrst law of permutation, "Permutation with Repetition of Indistinguishable Objects". Since the hopping channel number does not repeat in 'r' hop FFHSS. The total number of permutation available is NPr

For 6 hop FFHSS (e.g. 17 14 23 15 24 20), the probability of jamming a symbol is given as

1 prob= ----5765760

The proposed technique follows the second law of permutation, "permutation when objects can repeat". Since the channel number can repeat in r hop FFHSS. The total number of permutation available is Nr .

For 6 hop FFHSS (e.g. 15 12 21 16 20 12), the probability of jamming a symbol is given as

1 prob

= 16777216

D. Memory Comparision Memory is one of the major issues in wireless sensor

nodes. Sensor nodes are provided with very limited memory and limited processing capability. By limiting the memory for frequency hopping pattern, memory space can be saved and used for other purpose. TELOSB TPR 2400CA nodes use program flash memory of 10 KB and 1 MB external memory. Integer occupies 2 bytes of memory and float occupies 4 bytes of memory for storing and processing of data by the microcontroller in the sensor node.

Memory comparison is done between the proposed technique and existing technique. Existing technique [1] uses 20 seeds, each seed contains 10 hopping pattern. Each hopping pattern contains 6 channel numbers. 100 seed values are stored at random. So the Execution memory for existing technique [1] IS

(20 x 6 x2) + (20 x 10 x2) + ( 1 x 100 x 2) = 840bytes Program memory for existing technique (20x6x 2) +(20x lOx 6x 2) +(100x lOx 6x 2) = 14.29KB

In case of proposed technique, 11 integers and 2 floats are used so the Execution memory for proposed technique

( 1 1 x 2) + (2 x 4) = 30bytes Program memory for proposed technique

346 + 8 = 354bytes This conveys that the proposed technique requires only

minimum memory.

VII. CONCLUSIONS

This paper presents a novel anti jamming technique with minimum memory requirement, high security feature with infmite hopping sequence for Frequency hopping spread spectrum which is compatible for both slow and fast Frequency Hopping spread spectrum in Wireless Sensor Network. Comparison is done between the proposed technique and existing schema, which concludes that the proposed technique is highly secured. In future this technique can be extended for Hybrid FHSS/DSSS. This technique can not only be used in Wireless Sensor Network but by doing slight modification and changing the total number of radio channels N it can be used for several applications which support frequency hopping.

REFERENCES

[I] Aasha Nandhini Sukumaran, R. Kishore and S. Radha "A Novel Frequency Hopping Spread Spectrum Technique using Random Pattern Table for WSN", in Ad Hoc & Sensor Wireless Networks, to be published. Old City Publishing, inc, Vol. 0, pp. 1-21,2013.

[2] Aristides Mpitziopoulos, Damianos Gavalas, Charalampos Konstantopoulos, Grammati Pantziou, "A Survey on Jamming Attacks and Countermeasures in WSNs", iEEE Communications Surveys & Tutorials, Vol. II, no. 4, pp.I-14, fourth quarter 2009.

[3] Rajani Muraleedharan, Lisa Ann Osadciw, "Jamming Attack Detection and Countermeasures In Wireless Sensor Network Using Ant System", SPIE - The international society for optics and photonics, Vol. 6248 DOL: 10.1117/12.666330, may 2006.

[4] Peng Du, Dr. George Roussos, "Adaptive Time Slotted Channel Hopping for Wireless Sensor Networks" 4th Computer Science and Electronic Engineering Conference (CEEC), 2012.

[5] Weile Zhang, Qinye Yin, Xue Feng, Wenjie Wang, "Distributed TDoA Estimation for Wireless Sensor Networks Based on Frequency-Hopping in Multipath Environment ", in iEEE ,2010.

[6] IEEE Standard for Local and metropolitan area networks Part 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs), 5 september 2011.

[7] Ismail Mansour, G'erard Chalhoub, Alain Quilliot, "Security architecture for wireless sensor networks using frequency hopping and public key management"- international Conference on Networking, Sensing and Control, Delft, the Netherlands, pp.II-13, Apr 2011.

[8] Wassim ltania, Ayman Khalilb, Diana Sidanic, Lina Aghad ,"A Novel Frequency Hopping Scheme for Secure and Reliable Communication Systems" American Academic & Scholarly Research Journal Vol. 4, pp. 5, Sep 2012.

[9] S.Aasha Nandhini, R.Kishore, S.Radha, "An Efficient Anti Jamming Technique for Wireless Sensor Networks", international Conference on Recent Trends in information Technology, pp.361-366, 20i 2.

[10] Aristides Mpitziopoulos, Damianos Gavala, "An effective defensive node against jamming attacks in sensor networks", Security Comm. Networks. Published online in Wiley interScience, DOl: 10.1 002/sec.81, pp.l-19,2008.

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