1. Electronics - IJECIERD - ECG Key Gen Using - Mohana - Boopathi.pdf

8/10/2019 1. Electronics - IJECIERD - ECG Key Gen Using - Mohana - Boopathi.pdf

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www.tjprc.org [email protected]

ECG KEY GEN USING RSA ENCRYPTION TECHNIQUE AND TRANSMISSION BY

OFDM SYSTEM OVER RAYLEIGH FADING CHANNEL

J. MOHANA1& V. THULASIBAI2

1Department of ECE, Saveetha School of Engineering, Saveetha University,Thiruvallur, Tamil Nadu, India

2Dean/R&D, Prathyusha Institute of Technology and Management,Thiruvallur, Tamil Nadu, India

ABSTRACT

In this paper, present an efficient technique by ECG signal to generate 128 bit key from the peak value of QSR

ECG value by the RSA Encryption algorithm. The 128-bit key generator using electrocardiogram (ECG) signals comprises

two independent stages, namely, enrollment and verification-generation. This work is based on the uniqueness andquasi- stationary behavior of ECG signals with respect to an individual. The performance degradation over Rayleigh

Fading channels is determined by the deep fades of the received signal power. RSA implements a public-key cryptosystem,

as well as digital signatures. The Encrypted data will be transmitting over Rayleigh fading channel by OFDM system. Then

the original data decrypted by the same technique with low SNR margin and Bit Error Rate (BER) rate. The BER

performance of OFDM systems communicating over Rayleigh fading channels has been extensively studied and slow loss.

KEYWORDS:Electrocardiogram (ECG), OFDM System, Rayleigh Fading

INTRODUCTION

Electrocardiogram (ECG) is produced through a nerve impulse stimulus to a heart. Due to this impulse current is

generated on the surface of the body which later develops a potential drop. A single impulse may cause a potential of

nearly V to mV. The produced potential amplitude is very low which has to be amplified many times. Orthogonal

Frequency Division Multiplexing (OFDM) is considered in most of the works for communicating messages over frequency

selective fading channels.The primary benefit of the OFDM technique compared to a single carrier modulation is that it

facilitates the use of high data rates with a relatively low complexity receiver, which requires only a Fast Fourier

Transform (FFT) processor. Hence Fourier series can be used for representing ECG signal.

Interest in the application of Wireless Body Area Network (WBAN) is increasing rapidly. A WBAN includes a

patient observing structure that delivers flexibility and freedom of movement to patients. However, there are serious

performance and reliability issues in WBANs that must be addressed. The commonly used network topology in WBAN for

such flexible trainings is the star configuration as shown in Figure This is because nodes usually are sensor nodes and do

not need to communicate with each other. Therefore, the star topology is used and each sensor node communicates with

the central node using a hub. This raises reliability questions as the hub or the central node may fail leading to total system

failure. Even the communication links may perform poorly or fail. Since data fusion is used in almost all applications, even

the failure of any of the sensors or the communication links would result in system failure. Ylisaukko-oja et al. (2004)

presented the implementation and practical use of a bland five-point acceleration sensing WBAN with portable device data

sorting abilities shown in Figure 5. They used TDMA based MAC protocol and RS232 for serial communications with

external devices. They reported good communications performance in laboratory conditions but weaker field test

International Journal of Electronics,

Communication & Instrumentation Engineering

Research and Development (IJECIERD)

ISSN(P): 2249-684X; ISSN(E): 2249-7951

Vol. 4, Issue 4, Aug 2014, 1-12

TJPRC Pvt. Ltd.


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2 J. Mohana & V. Thulasibai

Impact Factor (JCC): 4.9467 Index Copernicus Value (ICV): 3.0

performance. Their tests indicated significant losses in communication. Under laboratory conditions, they lost the remote

slots from 0.31% to3.09% in various parts of the test while in the field tests; they lost central data up to 3.84% and lost

remote slots from 13.66% to 52.51%. This indicates a high degree of reliability problems especially in communications.

Figure 1: Shows the Main Block Diagram of the System ECG Signal

ECG SIGNAL

ECG is used for the demonstration of the electrical motion of the heart muscle as it varies with time. It is

reproduced on broadsheet for comfortable study. Similar to other muscles, cardiac muscle contracts in reaction to electrical

depolarization of the muscle cells. All the electrical activity is summed, amplified and documented for producing the

information known as ECG. Here the ECG signal converts as a text format for clear data representation. To read the text

data into matlab from a file the modest however easy procedure is to read the entire contents of the file in a single step by

using the load command. The file containing the data is to be ordered into a rectangular array which is the requirement of

the load command. Column titles are not allowed. One valuable method of the load command is load name.ext,

MATLAB statements will load this data into the matrix ``data (:, 1) and then copy it into two vectors, x and y.

x=data (:, 1); y=data (:, 2); [r c]=size(y); plot(x, y)

There is no need to copy the data into x and y. When the ''x'' data is required it is referred as my_xy (:, 1).

Duplication the data into ''x'' and ''y'' creates the code easier to read and is more likeably interesting. This process of

duplicating the data will not affect MATLAB's memory for most uncertain data sets.

Figure 2: Normal Intervals


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ECG Key Gen Using RSA Encryption Technique and Transmission by OFDM System Over Rayleigh Fading Channel 3


The time taken several phases of electrical depolarization can be calculated by recording an ECG on normal

paper. There isa standard usual range for such intervals: Due to greater muscle mass in the ventricles the depolarization

of the ventricles is responsible for the largest part of the ECG signal and this largest part is well-known as the QRS

complex.

The Q wave is the first primary down or negative deflection. The R wave is the subsequent upward deflection if

it crosses the isoelectric line and develops positive The S wave is formerly the following deflection downwards, provided

it crosses the isoelectric line to convert into negative before returning to the isoelectric baseline

PR Interval:Recorded as of the start of the P wave to the initial deflection of the QRS complex. Usual range

120 200 ms.

QRS Duration: Recorded after initial deflection of QRS complex to the completion of QRS complex at

isoelectric line. Usual range up to 120 ms.

QT Interval:Recorded after initial deflection of QRS complex to end of T wave at isoelectric line Usual range

up to 440 ms yet differs with heart rate and it is to some extent lengthier in females.

QRS DETECTION METHOD

Pan-Tompkins algorithm is the mostly used for QRS wave detection. Three graphical deflections perceived on a

usual electrocardiogram (ECG) is combined and given the term QRS wave. The QRS wave is the dominant and apparent

portion of the deflections traced. It is the depolarization of the right and left ventricles of the human heart. In adults, it

usually persists 0.06 - 0.10 s, in children and during physical activity it is short. To reduce the noise, the wave is send

through a band pass filter poised of cascaded high-pass and low-pass integer filters. Following processes are DerivativeFilter differentiation, squaring, and moving integration of the signal.

PAN TOMPKINS ALGORITHM

Band Pass Filter

The band pass filter is designed by connecting low pass filter and high pass filter in cascade. The low pass filter is

used in the circuit to suppress the high frequency noise [9]. A digital filter with integer coefficients is utilized for design

purpose which permits real time processing speeds. Speed is high since floating point processing is not required. The

merits of designed band pass filter for the QRS detection algorithm is that it diminishes the ECG signal noise by matching

the spectrum of average QRS complex, eliminates the noise owing to muscle artifacts. It also includes wandering of

baseline and elimination of T wave interference. The pass band range includes around 5 to 15 Hz range due to which the

energy of QRS is maximized. The filter is an integer filter

Figure 3: Block Diagram Showing QRS Detection Using Pan Tompkins Algorithm Process

The second order low pass filter has the transfer function of as shown in equation (1).

H (z) = (1- z-6)2/ (1- z-1)2 (1)


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The cut- off frequency of the filter is 11 Hz, delay is 5 samples and the gain is 36 [9]. The difference equation of

the filter is as shown in equation (2).

y(nT)=2y(nT-T)-y(nT-2T)+x(nT)2x(nT6T)+x(nT12T) (2)

The high pass filter is implemented by subtracting a first order low pass filter from an all pass filter with delay [9].

The transfer function of the low pass filter is as shown in equation (3).

H(low)(z)=Y(z)/X(z)=(1z-32)/(1z-1) (3)

The transfer function of the high pass filter is as shown in equation (4).

H(hp)(z)=P(z)/X(z)=z^-16-[(1-z^-32)/(1-z^-1)] (4)

The low cut off frequency of the filter is about 5 Hz and delay is 80 ms.

Figure 4: Shows the Low Pass Filter

Figure 5: Shows the High Pass Filter

Derivative Filter

The signal received from the band pass filter is differentiated to get the data about the slope of the QRS wave.

A five point derivative is applied with the transfer function. the signal established the differentiation operation in frequency


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domain. We also have derived the expression in the frequency domain for the operation of integration. This is because if

we accomplish the derivative operation by multiplying by i2f, then to undo the derivative (integrate) all we have to do is

divide by i2f. That is, the frequency domain expression for the indefinite integral s(t) dt is simply 1/(i2f) x S(f). The

transfer function for integration in the frequency domain is 1/(i2f).

Figure 6: Shows the Derivative Wave Form

Squaring

Now, the signal is to be squared. This is the non linear processing of the signal. It is done to get all positive

values so that later these values can be processed to get the corresponding squared waves. Also this processing emphasizes

the higher frequencies of the ECG signal which are due to the presence of the QRS complexes [9]. Point by point squaring

of the signal obtained from the differentiator is implemented by equation (9).

y (nT)= [x(nT)]2 (9)

Figure 7: Shows the Squaring

Moving Integrator

The R wave slope alone is not enough to identify QRS complexes in an ECG. There are numerous lengthy period

and huge amplitude QRS waves in the ECG which is irregular. Single slope of R wave cannot identify these waves [9].Hence a moving window integrator is used to identify these waves. The difference equation for this moving window.


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Figure 8: Shows the Integrated

Figure 9: Shows the QRS Detection WaveHAMMING DISTANCE

The analysis performed using the wavelet symlet8 allows to obtain the best complement Hamming distance value

at the selected security factor. To compute the complement Hamming distance of the sample. To compare the computed

complement Hamming distance of the previous step with the complement Hamming distance of each ECG sample stored

into the centralized database. To maintain the matched sample from the centralized database whether a match took place.

The minimum complement Hamming distance that considers a match must be between 28 and 34 when the ECG sample is

77 samples length. The values for a 120 samples length must be between 46 and 52.

Figure 10: Shows the Hamming Distance


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The minimum complement Hamming distance for other input vectors length can be computed by extrapolation.

The sample used in the verification stage can be discarded as well. To extract the coefficients that match (complement

Hamming distance coefficients) from both samples to create the basis vector for the next step.

To compute and release the 128-bit key, Hamming distance is an easy-to-define metric; it is used to search the

state space for design flaws. In digital communication Hamming distance was at first designed for recognition and

rectification of errors. Hamming distance is used to calculate the number of bits that are different between two bit vectors.

Now 128 bit key generated 128-bit K -DE2EA259FF3FF8D37ECFA1DFBCC6A3B1

RSA ALGORITHM

To avoid the reputed complexity of factoring large integers the factoring problem, RSA an algorithm for

public-key cryptography was described. RSA is for Ron Rivest, Adi Shamir and Leonard Adleman, who took the initiation

to describe the algorithm in 1977. Also an English mathematician, Clifford Cocks have described a corresponding structure

in 1973, however it wasn't declassified until 1997.

In RSA the product of two large prime numbers is created and then published with a supplementary value, as

their public key. The secrecy of prime factors is maintained. The public key can be used to encrypt a message. However

with presently available structure, if the public key is very huge, only somebody aware of the prime factors can possibly

decode the information.

RSA comprises of public keyand a private key.The public key is well-known by everybody and is utilised for

encrypting information. By means of the private key, the information encrypted with the public key can be decrypted in a

sensible quantity of time. The subsequent ways are followed for generating the keys for the RSA algorithm.

Encryption

Aabha communicates the public key (m, f) to Ali and maintains the private key secret. Later Ali desires to mail

message M to Aabha. Ali initially converts M into an integer m, such that 0 m < n by by means of an agreed-upon

reversible protocol recognized as a padding scheme. Ali next calculates the cipher text cequivalent to

The above process is made rapidly by the technique of exponentiation by squaring. Ali then transmits cto Aabha.

The encryption process run by separate function as rsaen.m file. The equation is in the matlab form of

c=m. ^e* (mod (3, n));

Decryption

Aabha can recuperate m from c by by means of the private key exponent d via computing

Given m, the original message M can be recovered by reversing the padding scheme. The encryption presses run

by separate function as rsade.m file the equation is in the matlab form of

Msg= [c1'.^key(2) /(mod (3, key1)];


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OFDM COMMUNICATION METHOD

Orthogonal Frequency Division Multiplexing (OFDM) is a recent digital modulation technique where

transmission of data stream takes place on numerous carriers instead of using only one carrier. The common idea was

introduced in 1971, but it is only in the previous decade, with the growth of Digital Signal Processors (DSP) that

applications become visible.

OFDM is mainly used on wideband transmissions. Well see that OFDM is well suited for transmissions in

frequency selective channels. Such a situation is met for example in multipath environments.

Figure 11: OFDM Transmission System

Inverse Fourier Transform

The avalable Spectrum is utilised efficiently in OFDM by spacing the channels much closer together. The carriers

are made orthogonal to one another, It avoids the interference between the closely spaced carriers. The orthogonality of the

carriers should be maintained to perform OFDM successfully. This is done by selecting the spectrum needed and

converting it back to its time domain signal using an Inverse Fourier Transform. Inverse Fast Fourier Transform is used in

many applications, since it performs the transformation efficiently. It also delivers a easy way of assuring that the carrier

signals produced are orthogonal. So, it is written as:

[ ] [ ]

=

=

1

0

2exp1 N

k

nnN

kljkX

Nlx

For l = 0, 1, , N-1

Channel and Receiver Parts

Let us consider the problem of transmitting the signal [ ]mxn~

over the time-varying linear channel ( ),tc

without additional noise. If we call [ ]mc the sampling version of the Channel, then the output obtained by the channel is:

[ ] [ ] [ ]+

=

=

1

0

~~LN

l

nn lmclxmy

m = 0, 1, , N+L-1


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Figure 12: Shows the OFDM QAM Transmission with Raleigh Channel Model

The receiver basically does the reverse operation to the transmitter. The signal got is [ ]myn~

that containss

N+L-1 samples, before the demodulation, The L last samples of the received signal is lost and then the guard period is

removed to utilise correctly the Fourier Transform properties. The demodulation process is a fundamental FFT according

to the IFFT used for modulation. Hence, there is a need to find out N samples (one per carrier) at the modulator input. An

FFT to the signal [ ]myn~

isapplied.

[ ] [ ]

=

=

1

0

2exp~~ N

l

nnN

ljklykY

[ ] [ ] [ ]

=

+

=

=

1

0

1

0

2exp~~ N

l

LN

m

nnN

ljkmlcmxkY

[ ] [ ] [ ]

=

+

=

=

1

0

1

0

2exp~~ N

l

LN

m

nnN

ljkmlcmxkY

[ ] [ ] [ ]( )kcN

mjkmxkY

LN

m

nn

=

+

=

2exp~~ 1

0

The initial term of the multiplication above appeares like a Fourier Transform expression. If summation index is

restricted from m = 0 to m = N-1. It is equivalent to drop the L last samples of the signal [ ]myn~

. So the signal produced

by the demodulator is:

[ ] [ ] [ ]( )kcN

mjkmxkY

N

m

nn

=

=

2exp~~ 1

0

[ ] [ ]( ) [ ]( )kckxkY nn =~

[ ] [ ] [ ]kCkXkY nn =~

To receive the transmitted signal a simple division by the Channel frequency response is done. The modulation

does not require any equalization. The data samples are later combined back to the same size as the original data.


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[ ]1nX

[ ]0nX

[ ]1NXn

[ ]1nx

[ ]0nx

[ ]1Nxn

IFFT

Bit-Rate

The modulation system used on all the carriers is QPSK. The carriers are separated by a gap of around 1/Ts,

where Tsis symbol period. The maximum bit rate available is 2bit/s/Hz of the bandwidth. This figure is decreased by the

inefficiency (signal redundancy) of the guard interval, the null symbol and the error coding. The same decryption processes

will be done at the next step in which the process explained previously. Finally the transmitted 128 bit key data received by

the decryption process.

Figure 13: Shows the BER-Rate

CONCLUSIONS

In this paper, we have presented the 128 bit key generator based on ECG signal by the RSA encryption algorithm.

The values are encrypted and decrypted over Rayleigh fading channel by OFDM and bit error rate is reduced and the

simulation is obtained.

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1. Electronics - IJECIERD - ECG Key Gen Using - Mohana - Boopathi.pdf

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