Journal of Signal and Information Processing, 2011, 2, 175-177

doi:10.4236/jsip.2011.23023 Published Online August 2011 (http://www.SciRP.org/journal/jsip)

Copyright © 2011 SciRes. JSIP

175

Performance Evaluation of FM-COOK Chaotic

Communication System

Hikmat N. Abdullah1, Alejandro A. Valenzuela2

1Department of Electrical Engineering, Al-Mustansiryah University, Baghdad, Iraq; 2Department of Electrical Engineering, Mecha-

nical Engineering and Technical Journalism, University of Applied Sciences Bonn-Rhein-Sieg, Bonn, Germany.

Email: {hikmat.abdullah, alejandro.valenzuela}@h-brs.de

Received May 3rd, 2011; revised May 30th, 2011; accepted June 7th, 2011.

ABSTRACT

In this paper, the performance evaluation of Frequency Modulated Chaotic On-Off Keying (FM-COOK) in AWGN,

Rayleigh and Rician fading channels is given. The simulation results show that an improvement in BER can be gained

by incorporating the FM modulation with COOK for SNR values less than 10 dB in AWGN case and less than 6 dB for

Rayleigh and Rician fading channels.

Keywords: Chaotic Transceiver, On-Off Keying, FM Modulation

1. Introduction

Chaotic signals are a relatively new field of interest in

communication systems. Motivations of this method de-

rived from the advantages offered by chaotic signals,

such as robustness in multipath environments and resis-

tance to jamming. Chaotic signals are non-periodic, broa-

dband, and difficult to predict and reconstruct. These are

properties which match with requirements for signals

used in communication systems [1].

Various types of modulation can be used in direct

chaotic communication systems like chaotic on-off key-

ing (COOK), differential chaotic shift keying (DCSK)

and additive chaos modulation (ACM), etc. Among all

chaotic modulation types, DCSK with orthonormal basis

functions of fers th e be st robustn ess ag ainst multip ath an d

channel imperfections [2]. Due to the length and non-

-periodicity of chaotic sample functions, the energy per

bit is not constant and varies from one sample function to

another. As a result, this varied energy per bit limits the

noise performance of modulation system.

In 1998, Kolumbán et al. [3] show that FM-DCSK

scheme generates an inherently wideband signal with

constant energy per bit, which enhances the noise per-

formance of DCSK. In 2001, Z. Galias and G. Maggio [4]

proposed QCSK (Quadrature Chaos Shift Keying) sche-

me which can transmit 2 bits in a sample function to im-

prove the speed of chaos shift keying. Then in 2006, Y.

Zhang [5] devised FM-QCSK which enhanced the noise

performance of QCSK by using frequency modulation,

because it can generate constant energy per bit and its

frequency spectrum. In 2009, J. Pan and H. Zhang [6]

proposed an advanced version of the previous scheme

named FM-QACSK (Frequency Modulated Quadrature

Amplitude chaos shift keying) where 256QAM modula-

tion is used to increase data rate also combined with the

use of FM modulation.

Although the performance of COOK chaotic modula-

tion lags behind the DCSK, the COOK have an advan-

tage of that it consumes less pow er since it sends chaotic

signal only in case of sending the data bit “1” while no

power is sent for case of data bit “0”. However, we don’t

find in the literature the performance evaluation of the

use of FM modulation with COOK to get constant en-

ergy per bit. So, this paper is an attempt to evaluate the

performance of FM-COOK modulation scheme.

2. FM-COOK Modulation

Figure 1 shows the block diagram of FM-COOK system.

Since the chaotic signal is nonperiodic and never re-

peated, the energy in each bit (for symbol “1”) would

vary from one bit to another. The variance of estimation

can be reduced by increasing the statistical bandwidth of

the transmitted chaotic signal or by increasing the bit

duration [7]. Alternatively, one may solve the problem

directly by modifying the generation of the basis func-

tions such that th e transmitted energy for each symbol is

kept constant by applying the chaotic signal to an FM