Improved Non-coherent Communication Systems Using Noise Reduction Chaotic ON–OFF Keying (NR-COOK) Techniques

Abstract

The major drawback of the conventional chaotic ON–OFF keying (COOK) scheme is that the transmitted signal energy is not constant due to the non-periodic nature of the chaotic sequences. These chaotic sequences increase the amount of noise present in the received signal and degrade the system performance under multipath fading channel conditions. Moreover, in COOK scheme, the optimum threshold for symbol detection depends on the Signal to Noise Ratio (SNR) available at the detector input. In this paper, a noise reduction COOK scheme is proposed for improved performance. In this scheme, for transmitting binary bit ‘1’ $\frac{\beta }{R}$ distinct chaotic samples are generated and each sample is repeated R times to get a required spreading sequence length of β and no signal is being transmitted during binary bit ‘0’. For demodulation of the transmitted data, each of the R identical samples are averaged, correlated with itself and summed over the bit duration $T_{b}$ where $T_{b} = \frac{\beta }{R}T_{c}$ to recover the transmitted data. The averaging operation over R identical samples reduces the effect of noise present in the received signal and improves the performance of the system over noisy channels. Closed form expression for bit error rate (BER) of the proposed NR-COOK system is derived and analyzed under multipath fading channel and are validated through simulation results to demonstrate performance improvement over conventional non coherent schemes.