Метод підвищення скритності систем передачі інформації на основі модуляції з ортогональним частотним розділенням і мультиплексуванням хаотичних піднесучих

The subject of the research is the processes of formation and processing of signals with orthogonal frequency divisionand multiplexing (OFDM) of chaotic sequences to ensure the stealthiness of data transmission. The research synthesizes the method for increasing the stealthiness of information transmission systems based on signals with OFDM-modulation on the basis of forming an analytical signal and chaotic mapping of Chebyshev polynomial. It would enable ensuring reliable information protection in radio transmission systems that use signals with OFDM-modulation, at the cost of the high level of structural and independent and Identically distributed (IID) (the degree of signal masking under noise) stealthiness of the signals. The tasks are to investigate the effectiveness of the developed method for increasing the stealthiness of information transmission systems by numerical assessment of the level of structural and IID-stealthiness and the quality of recovery of the masked information on the receiving side. The methods used are for the formation and processing of chaotic subcarriers in the signal with OFDM-modulation – methods of nonlinear dynamics, approaches to the formation of analytical chaotic signal and methods of the statistical theory of observation processing; to assess the level of structural and IID-stealthiness – steganography theory, a method of nonlinear time series analysis based on the use of BDS-statistics. The following results are obtained: the method for increasing the stealthiness of information transmission systems based on the use of signals with OFDM-modulation and chaotic subcarriers has been synthesized, has also evaluated the level of structural and IID-stealthiness of signals, that generated using the proposed method. It is established that compared with systems that use harmonic signals with OFDM-modulation, chaotic signals with OFDM-modulation can provide a higher level of IID-stealthiness. It was confirmed by the obtained results of visual, frequency, statistical and dynamic analysis. To assess the level of structural stealthiness, the expenditure of detecting the generated signals with a given probability has been estimated. The obtained results showed that the level of structural stealthiness increased by 2…2.5 times. It has shown that to ensure the required level of recovery of the generated signal, the signal-to-noise ratio at the input of the receiver must be greater than 4 dB. Conclusions. The scientific novelty of the obtained results lies in the following: for the first time, the method of subcarrier formation for signals with OFDM-modulation based on the use of analytical signal and Chebyshev polynomial of the first kind of tertiary is obtained. The proposed method provides the required level of structural and IID-stealthiness of information transmission systems, compared with conventional methods of signal generation with OFDM-modulation, due to the similarity of the generated signals with “white” noise.

Performance analysis of symmetrical and bidirectional 40 Gbps TWDM-PON employing m-QAM-OFDM modulation with multi-color LDs based VLC system

In this work, a full-duplex time and wavelength division multiplexing-passive optical network (TWDM-PON) system is analysed. Orthogonal frequency division multiplexing (OFDM) with m-quadrature amplitude modulation (m-QAM) is employed to improve the performance of TWDM-PON for downstream and upstream transmission. Simultaneously, multi-color (390–750 nm) laser diodes (LDs) are employed for visible light communication (VLC) using various VLC links to encourage the information rate of fiber/VLC optical network. A TWDM-PON utilizing 16-, 32- and 64-QAM OFDM with ten LDs based VLC system has been analysed for full-duplex multi-color VLC signals of the system. The impact of the LDs input current and high transmission rate in the proposed PON/VLC link has been investigated for m-QAM OFDM modulation. The results show that the 40/40 Gbps 16-, 32- and 64-QAM signals over ten 8000 m VLC links and a 50 km fiber link are successfully transmitted at the modulation input current of 9 mA under bit error rate (BER) of 3.8×10− 3. Also, the proposed system employing 16-, 32- and 64-QAM signals over a 10 km fiber and ten 10 m VLC links provide the maximum transmission rate of 120, 100 and 80 Gbps respectively. Moreover, the measured error vector magnitudes (EVMs) and calculated BER values for 16-QAM downstream and upstream signals, are well below the required FEC limit than high-order modulation formats. Further, the numerical analysis of the proposed system reveals the superiority of the proposed fiber/VLC links.

A Performance Analysis of Wavelet based LTE-OFDM with Multi-equalizers

A rapid change in usage of mobile data and mobile based applications such as online gaming, mobile TV etc. motivates the mobile wireless communication system to work on new emerging trends Long Term Evolution (LTE). LTE-4G architecture provides an optimized packet based radio access technology. The basic signal format of LTE is Orthogonal Frequency Division Multiplexing (OFDM) Modulation. This modulation scheme satisfies the spectrum flexibility requirement in LTE. LTE-MIMO-OFDM with IFFT and FFT transform introduced to provide the cost-effective solution for very wide carriers with high PAPR. Inter-symbol Interference (ISI) and inter carrier interference (ICI) are predominant factors which exist in the wireless communication channel. Existing methods of ISI and ICI reduction to improve signal quality have been achieved using conventional OFDM techniques. However, a better modulation scheme is required to achieve high data rate, low latency and flexible bandwidth deployment. This paper has proposed a Wavelet based LTE-MIMO-OFDM modulation scheme with multi equalizer that improves the performance of system by reducing PAPR and BER in MCM. Experimental results show the performance of this scheme and the results is compared with existing MMSE and Multi equalizer MMSE and achieves a flexible spectral efficiency with reduction of PAPR and BER.

Mitigation of Phase Noise and Nonlinearities for High Capacity Radio-over-Fiber Links

Radio-over-fiber (RoF) links successfully provide high data rates and bandwidth capacity with a low complexity system architecture, as compared to its counterpart digital-RoF. In addition, the compound of quadrature amplitude modulation (QAM) and orthogonal frequency division multiplexed (OFDM) modulation schemes further enhance the process of these achievements. However, high data rates and bandwidth-capacity-supported RoF links face nonlinearities (NLs), linear distortions (LDs), and phase noise challenges that degrade the reliability of communication networks (CNs). Therefore, in this paper, to suppress NLs, LDs, and phase noise, next generation cloud radio access networks (CRANs) are investigated using RoF links and wavelength division multiplexing (WDM) methodology based on 16, 32, and 64 QAM-OFDM modulation schemes. The receiver of the proposed framework is designed, applying an improved digital signal processing (DSP) system that includes overlap frequency domain equalization (OFDE), a synchronization process, and time domain equalization (TDE). Theoretical and simulation models are organized for estimating the proposed RoF link with the aid of different values of transmission ranges, input power, output power, bit rate, bits per symbol, channel spacing, and the number of users. The fitness of the model matches that of existing approaches.