8/3/2019 01_7225-IJWCS__pp 1-6

1/6

International Journal of Wireless Communication and SimulationVolume 3 Number 1 (2011), pp. 1-6 Research India Publicationshttp://www.ripublication.com/ijwcs.htm

Simulation and Analysis of Chaotic Sequence based

Encryption Method for Different Wireless

Communication Systems

1Swapnil Shrivastava and

2Sumit Sharma

1M.Tech., SRIT, Jabalpur, M.P., India

E-mail: swapnilmtech@yahoo.in2H.O.D., EC Deptt., SRIT Jabalpur, M.P., India

Abstract

Security is an important issue in all communications systems for the users andproviders of such systems. Although mobile application have specialrequirements because it is accessible for every one within the range of

transmitter and are therefore of special concern. Encryption of the data bysome way is one of the simplest solutions for stated problem but for the properoperation of the system the method must be fast enough and should be simpleso that it can implemented on the low resources mobile devices, also it shouldnot increase the power requirements of the systems. In this paper we proposedand analyzed the chaotic sequence based encryption technique for differenttypes of communication systems like OFDM, CDMA, QPSK and GMSK, andwe also simulated the BER of each system with respect to SNR. Thesimulation of all techniques is done on MATLAB.

Keywords: Wireless Communication, Encryption, Chaotic Sequence.

IntroductionMobile devices are designed to be portable, i.e., light and small. Until a more suitablealternative is found, mobile devices will more than likely be battery powered withinthe foreseeable future. In order to conserve energy, processing speeds need to beslower and processor cycles reduced. Data transmissions also consume energytherefore it must be reduced. The former imposes limits on the computationalcomplexity of encryption algorithms and the number of messages involved in security

protocols. Even though using special purpose circuitry or encryption chips can

8/3/2019 01_7225-IJWCS__pp 1-6

2/6

2 Swapnil Shrivastava and Sumit Sharma

alleviate this problem. Faxed business letters can be intercepted at will through tappedphone lines or intercepted microwave transmissions without the knowledge of thesender or receiver. To increase the security of this and other data communications,including digitized telephone conversations, the binary codes representing data maybe scrambled in such a way that unauthorized interception will produce anindecipherable sequence of characters. Authorized receive stations will be equippedwith a decoder that enables the message to be restored. The process of scrambling,transmitting, and descrambling is known as encryption. This paper presents thechaotic sequence based encryption technique which can be easily programmed inmain processor or can be implemented on integrated circuits at low cost. In somecases, it can be incorporated into the main circuitry of a data communications deviceand function without operator knowledge. In other cases, an external circuit can also

be used so that the device, and its encrypting/decrypting technique, may betransported easily.

Chaotic SequencesChaos is a deterministic, random-like process found in non-linear, dynamical system,which is non-period, non-converging and bounded. Moreover, it has a very sensitivedependence upon its initial condition and parameter. Chaotic signals can be used incommunication.

A chaotic map is a discrete-time dynamical systemx f x x k

k k k+ = < < =1 0 1 0 1 2( ), , , , ,

running in chaotic state. The chaotic sequence

{ }x kk

: , , ,= 0 1 2

can be used as spread-spectrum sequence in place of PN sequence in conventionalCDMA DS/SS communication systems or as encrypting sequence in any digitalcommunication system. Chaotic sequences are uncorrelated when their initial values

are different, so in chaotic spread-spectrum systems, a user corresponds to an initialvalue.In addition, it is possible to synchronize two copies of a discrete-time chaotic

system, in the sense that their state trajectories tend asymptotically to be identicalwhen one system is suitably driven by the other. If the driving signal is selectedappropriately, the discrete-time synchronization will be immediate.

OFDMOrthogonal frequency division multiplexing, (OFDM), essentially identical to codedOFDM (COFDM) and discrete multi-tone modulation (DMT), is a frequency-division

8/3/2019 01_7225-IJWCS__pp 1-6

3/6

Simulation and Analysis of Chaotic Sequence 3

multiplexing (FDM) scheme used as a digital multi-carrier modulation method. Alarge number of closely-spaced orthogonal sub-carriers are used to carry data. Thedata is divided into several parallel data streams or channels, one for each sub-carrier.Each sub-carrier is modulated with a conventional modulation scheme (suchas quadrature amplitude modulation or phase-shift keying) at a low symbol rate,maintaining total data rates similar to conventional single carrier modulation schemesin the same bandwidth.

OFDM has developed into a popular scheme for wideband digital communication,whether wireless or over copper wires, used in applications such as digital televisionand audio broadcasting, wireless networking and broad band internet access.

The primary advantage of OFDM over single-carrier schemes is its ability to copewith severe channel conditions (for example attenuation of high frequencies in a long

copper wire, narrowband interference and frequency-selective fading dueto multipath) without complex equalization filters. Channel equalization is simplifiedbecause OFDM may be viewed as using many slowly-modulated narrowband signalsrather than one rapidly-modulated wideband signal. The low symbol rate makes theuse of a guard interval between symbols affordable, making it possible to eliminateintersymbol interference (ISI) and utilize echoes and time-spreading (that shows upas ghosting on analogue TV) to achieve a diversity gain, i.e. a signal-to-noiseratio improvement. This mechanism also facilitates the design of single frequencynetworks (SFNs), where several adjacent transmitters send the same signalsimultaneously at the same frequency, as the signals from multiple distant transmitters

may be combined constructively, rather than interfering as would typically occur in atraditional single-carrier system.

CDMAIn telecommunications, direct-sequence spread spectrum (DSSS) isa modulation technique. As with other spread spectrum technologies, the transmittedsignal takes up more bandwidth than the information signal that is being modulated.The name 'spread spectrum' comes from the fact that the carrier signals occur over thefull bandwidth (spectrum) of a device's transmitting frequency. 802.11b use DSSS

signaling.DSSS phase-modulates a sine wave pseudo randomly with acontinuous string of pseudo noise (PN) code symbols called "chips", each of whichhas a much shorter duration than an information bit. That is, each information bit ismodulated by a sequence of much faster chips. Therefore, the chip rate is much higherthan the information signal bit rate.

DSSS uses a signal structure in which the sequence of chips produced by thetransmitter is known a priori by the receiver. The receiver can then use the same PNsequence to counteract the effect of the PN sequence on the received signal in order toreconstruct the information signal.

8/3/2019 01_7225-IJWCS__pp 1-6

4/6

4 Swapnil Shrivastava and Sumit Sharma

GMSKIn digital modulation, minimum-shift keying (MSK) is a type of continuous-phase frequency-shift keying that was developed in the late 1950s and 1960s.Similarto OQPSK, MSK is encoded with bits alternating between quadature components,with the Q component delayed by half the symbol period. However, instead of squarepulses as OQPSK uses, MSK encodes each bit as a half sinusoid. This results in aconstant-modulus signal, which reduces problems caused by non-linear distortion. Inaddition to being viewed as related to OQPSK, MSK can also be viewed as acontinuous phase frequency shift keyed (CPFSK) signal with a frequency separationof one-half the bit rate.

QPSKSometimes this is known as quaternary PSK, quadriphase PSK, 4-PSK, or 4-QAM.(Although the root concepts of QPSK and 4-QAM are different, the resultingmodulated radio waves are exactly the same.) QPSK uses four points on theconstellation diagram, equispaced around a circle. With four phases, QPSK canencode two bits per symbol, shown in the diagram with gray coding to minimizethe bit error rate (BER) sometimes misperceived as twice the BER of BPSK.

The mathematical analysis shows that QPSK can be used either to double the datarate compared with a BPSK system while maintaining the same bandwidth of the

signal, or to maintain the data-rate of BPSKbut halving the bandwidth needed. In thislatter case, the BER of QPSK is exactly the same as the BER of BPSK - and decidingdifferently is a common confusion when considering or describing QPSK.

Given that radio communication channels are allocated by agencies such asthe Federal Communication Commission giving a prescribed (maximum) bandwidth,the advantage of QPSK over BPSK becomes evident: QPSK transmits twice the datarate in a given bandwidth compared to BPSK - at the same BER. The engineeringpenalty that is paid is that QPSK transmitters and receivers are more complicated thanthe ones for BPSK. However, with modern electronics technology, the penalty in costis very moderate.

As with BPSK, there are phase ambiguity problems at the receiving end,and differentially encoded QPSK is often used in practice.

Simulation ResultsEach of the above mentioned method are implemented and simulated on matlab thesimulation are performed for 104 bits, and for different AWGN values, in allsimulation the main data stream is firstly encrypted by using chaotic encryptiontechnique and then at receiver side decrypted using same technique.

8/3/2019 01_7225-IJWCS__pp 1-6

5/6

Simulation and Analysis of Chaotic Sequence 5

Figure 1: Performance of OFDM System with Chaotic sequence based encryptiontechnique.

Figure 2: Performance of CDMA System with Chaotic sequence based encryptiontechnique.

Figure 3: Performance of QPSK System with Chaotic sequence based encryption

technique.

8/3/2019 01_7225-IJWCS__pp 1-6

6/6

6 Swapnil Shrivastava and Sumit Sharma

Figure 4: Performance of GMSK System with Chaotic sequence based encryptiontechnique.

ConclusionThe results shows that the encryption scheme does not affects the basic characteristicsof the modulation techniques and hence it can be adopted as a fast and efficientencryption method in either in built system or with external devices.

References

[1] O. Edfors, M. Sandell, J.-J. de Beek, D. Landstrom, F.Sjoberg, \Anintroduction to orthogonal frequency-divisionmultiplexing,"

[2] E. Lawrey, \The suitability of ofdm as a modulation tech-nique for wirelesstelecommunications, with a cdma com-parison," MSc. thesis, James CookUniversity, Australia,October 1997.

[3] A. Engelhart, H. Gryska, C. Sgraja, W.G. Teich, J. Lind-ner, \The discrete-timechannel matrix model for general bfdm packet transmission schemes,"Proceedings of 1 st In- ternational POFDM-Workshop Hamburg, 21-22September 1999.

[4] J. Proakis, Digital Communications. New York: McGraw-Hill, 3 ed., 1995.[5] N. Yee, J.P.M.G. Linnartz, \Multi-carrier CDMA in an in-door wirless radio

channel," UCB/ERL, 1994. U.C. Berke-ley, UCB/ERL M94/6, ElectronicsResearch Lab.

[6] R. van Nee, R. Pasad, OFDM for Wireless Multimedia Communication. BostonLondon: Artech House Publishers,2000.

[7] T. Keller, L. Hanzo, \Adaptive multicarrier modulation:A convencientframework for time-frequency processing in wireless communications,"Procideengs of the IEEE, vol. 88,May 2000.