Use of Chaotic Oscillations for Precoding and Synchronization in OFDM

This paper proposes a novel linear precoding method for Orthogonal Frequency Division Multiplex- ing (OFDM) based on the employment of the chaotic waveforms generated by the fourth-order chaotic os- cillator and orthonormalized by the Gram-Schmidt process. The proposed linear precoding method is aimed to increase resilience to the multipath propagation issues and reduce the Peak-to-Average Power Ratio (PAPR) of the transmitted signal. Moreover, the chaotic waveform enables novel timing synchronization methods to be implemented in the re- ceiver. The modeling of baseband Linear Precoded OFDM (LP-OFDM) data transmission system with Rayleigh channel has been performed in Simulink en- vironment to validate the proposed method and to com- pare the performance to the classic precoding meth- ods, such as Walsh-Hadamard Transform (WHT). Experiments have shown that in a high Signal-to-Noise Ratio (SNR) scenario, the employment of the novel precoding scheme allows reducing Bit Error Ratio (BER) by several dB compared to non-precoded OFDM. The proposed precoding method leads to the reduction of PAPR; however, it is not as efficient as classi- cal precoding schemes, such as WHT. Experimental evidence of synchronization of the chaotic oscillators within 50 samples long time interval is presented

Computationally efficient chaotic spreading sequence selection for asynchronous DS-CDMA

Choice of the spreading sequence for asynchronous in direct-sequence code-division multiple access (DS-CDMA) systems plays a crucial role for mitigation of multiple access interference. Considering rich dynamics of chaotic sequences, use of them for spreading allows to overcome limitations of the classical spreading sequences. However, to ensure low cross-correlation between the sequences, careful selection must be performed. This paper presents a novel exhaustive search algorithm, which allows to find sets of chaotic spreading sequences of required length with particularly low mutual cross-correlation. Efficiency of the search is verified by simulations, which show significant advantage compared to non-selected chaotic sequences. Moreover, impact of sequence length on the efficiency of the selection studied

Performance comparison of SVD- and GMD-assisted MIMO systems

Singular-value decomposition (SVD)-based multiple-input multiple-output (MIMO) systems have attracted a lot of attention in the wireless community where the whole MIMO channel is decomposed into a number of unequally weighted independent single-input single-output (SISO) channels. The unequal weighting of the SISO channels has led to intensive research on bit- and power allocation even in MIMO channel situations with poor scattering conditions identified as the antenna correlation effect. In this situation, the unequal weighting of the SISO channels becomes even much stronger. In comparison to the SVD-assisted MIMO transmission, geometric mean decomposition (GMD)-based MIMO systems are able to compensate for the drawback of weighted SISO channels when using SVD at the cost of remaining interferences which can be easily removed by using dirty paper precoding. Together with different QAM constellation sizes per layer, bit loading and power allocation can be helpful to balance the bit-error probabilities in the activated number of MIMO layers. The novel contribution of this paper is that optimal and suboptimal power allocation solutions are investigated under the assumption of unequal SISO channels as well as different QAM constellation sizes per MIMO layer. Our results show that GMD-based MIMO transmission has the potential to significantly simplify the process of bit and power loading and outperforms the SVD-based MIMO transmission as long as the same QAM-constellation size is used on all equally-weighted SISO channels

Waveform Impact on RF Wireless Power Transfer Efficiency of Low Power Harvesting Devices

The paper is dedicated to the study of the impact waveform parameters: peak-to-average power ratio (PAPR) and spectral characteristics, on the performance of low power harvesting device during wireless power transfer (WPT) under real life scenario. In the current study a low power RF harvesting device, consisting of a classic voltage doubler circuit for RF-DC conversion and a DC-DC converter based on Texas Instruments manufactured chip BQ25504, is chosen. Moreover, as harvesting device consists of RF-DC converter and DC-DC converter, the study of the impact of load resistance on conversion efficiency for RF-DC rectifier and the whole harvesting device is performed. For the study of conversion efficiency and harvesting device performance three types of waveforms are used: single tone, multicarrier signals with low PAPR and multicarrier signal with high PAPR level; the number of subcarriers is varied from 4 to 16. To generate high PAPR signals all subcarriers with the same amplitude are summed in-phase, while to generate low PAPR signals, subcarriers with the same amplitude but specially selected phases are summed together. All signals are transmitted in an unlicensed sub-gigahertz ISM band with the same bandwidth of 5 MHz, while single tone frequency corresponds to the carrier frequency of multi-carrier signals. For baseband signal generation MATLAB/Simulink software is used, and for transferring on carrier frequency a software defined radio (SDR) USRP B210 is employed. During WPT directional antennas are used and the distance between them is varied up to 1.8 m. To evaluate performance of harvesting device and efficiency of conversions the average voltages at the input and output of the RF-DC converter as well as at the output of the DC-DC converter are measured

Waveform Impact on Wireless Power Transfer Efficiency using Low-Power Harvesting Devices

The paper addresses the impact of peak-to-average power ratio (PAPR) and spectrum of the waveform, as well as load resistance on the performance of low-power harvesting device in a real-life wireless power transfer (WPT) scenario. In the current study, a combination of the classic voltage doubler circuit for RFDC conversion and premanufactured device for DC-DC conversion is used. For the investigation of conversion efficiency and harvesting device performance, three types of waveforms are used: single tone, multicarrier signals with low PAPR and multicarrier signal with high PAPR. In order to generate high-PAPR signal, subcarriers with the same amplitude and phase are summed, whereas for generation of low PAPR signal the phases of the subcarriers are chosen pseudo-randomly. Over-the-air transmission in 865 MHz ISM band is made using directional antennas and all multicarrier waveforms have equal 5 MHz bandwidth. To evaluate the performance of harvesting device and conversion efficiency, the average voltages at the input and output of the RF-DC converter as well as at the output of the DC-DC converter with corresponding input and load impedance are measured. The experiments have shown that the employed multicarrier signals can greatly improve the performance of harvesting device during WPT under certain conditions, which are discussed in the paper

Design of Acoustic Signals for a Seal Deterrent Device

During the past decade, attacks by grey seals on fishing nets in the Baltic Sea have caused considerable loss of fish catch and damage to fishing gears. One of the approaches to reduce the number of seal attacks on fishing nets is to use acoustic deterrent devices (ADDs). Unfortunately, most of the commercially available ADDs are not well suited to the deployment in the sea and require considerable additional investments. The objective of the present research is to develop a compact and cost-efficient ADD for deployment in the sea environment. This paper is devoted to the design of acoustic signals for a prototype ADD. Signals from other experimental and commercially available ADDs are studied and compared. Moreover, limitations imposed by the underwater environment, transducers, battery power, and fish hearing are analysed and considered during the development of signal patterns. The results of tests conducted in an artificial reservoir and in the sea are presented

On the Development of Long-Range Water Quality Monitoring System for Outdoor Aquaculture Objects

The paper is dedicated to the development of hardware and software components for the autonomous water quality monitoring system (WQMS) for fishing farms. The system can measure main water quality parameters, storing and processing data on the remote server. The LoRaWAN technological solutions and infrastructure are utilized, providing the optimal tradeoff between data transmission range and adaptive power consumption. The main implementation and exploitation issues are described, and the proposed solutions are provided

Impact of the Chaotic Synchronization’s Stability on the Performance of QCPSK Communication System

The current work presents a study of the implementation of a quadrature chaos phase-shift keying communication system (QCPSK) based on the employment of different chaos oscillators. The research takes two directions, with one being the study of the chaos synchronization’s noise immunity for several chaos oscillators that are the potential core blocks of the QCPSK system. The correlation coefficient over time is used to estimate the synchronization noise immunity. The second direction is the estimation of the QCPSK system’s baseband model performance in the AWGN propagation channel using the bit error ratio (BER) as the estimation method for several chaos oscillators employed as the core of the QCPSK system’s model

Passive Electrical and Optical Methods of Ultra-Short Pulse Expansion for Event Timer-Based TDC in PPM Receiver

The energy efficiency of a communication system using pulse position modulation (PPM) can be increased by reducing the duration of the pulses transmitted over the communication channel to several tens of picoseconds. The employment of an event timer device as a time-to-digital converter (TDC) for demodulation allows the use of PPM with many pulse positions and achieves competitive data transfer speeds. However, along with several-picosecond accuracy of modern event timers, they require a pulse duration of several hundred picoseconds for precise detection. This research is devoted to developing passive techniques for precise pulse expansion from tens of picoseconds to hundreds of picoseconds. We propose two methods: the electrical method, which employs a microstrip low-pass filter (LPF), and the optical method, which uses fiber Bragg grating (FBG). This research offers a detailed analysis of distortion-free pulse expansion requirements, the design of prototypes meeting these requirements, and experimental design verification. Theoretical background, mathematical models, and results of experimental validation of the proposed pulse expansion methods within the laboratory transmitted reference pulse-position modulation (TR-PPM) communication system are provided