Spatially periodic temperature modulation of a compressible fluid

Nonlinear frequency down-conversion of acoustic wave beams in the atmosphere and ionosphere under different types of modulation (regular item)

Linear stability analysis is performed for the onset of thermosolutal convection in a horizontal fluid layer with rigid-rigid boundaries. The temperature field between the walls of the fluid layer consists of two parts: a steady part and a time-dependent periodic part that oscillates with time. Only infinitesimal disturbances are considered. The effect of temperature modulation on the onset of thermosolutal convection has been studied using the Galerkin method and Floquet theory. The critical Rayleigh number is calculated as a function of frequency and amplitude of modulation, Prandtl number, diffusivity ratio and solute Rayleigh number. Stabilizing and destabilizing effects of modulation on the onset of double diffusive convection have been obtained. The effects of the diffusivity ratio and solute Rayleigh number on the stability of the system are also discussed.

There are two main types of optical signals propagating in wired or wireless communication links: time continuously varied or analog, which corresponds to narrowband channels, and time discrete varied or pulse-shaped, which corresponds to wideband channels. Therefore, there are different types of modulation that are usually used for such types of signals. This chapter defines the process of modulation and demodulation. It describes the main principle of both kinds of modulation, analog and digital, and provides some examples of the most useful types of modulation adapted for both kinds of channels, narrowband and wideband. There are three types of modulation, depending on what characteristic is time varied in the modulating signal – amplitude modulation, phase modulation, and frequency modulation. There are three kinds of digital modulation: amplitude shift keying, frequency shift keying, and phase shift keying.

The present study is related to the analytical investigation of the magnetohydrodynamic flow of Ag − MgO/ water hybrid nanoliquid with slip conditions via an extending surface. The thermal radiation and Joule heating effects are incorporated within the existing hybrid nanofluid model. The system of higher-order partial differential equations is converted to the nonlinear system of ordinary differential equations by interpreting the similarity transformations. With the implementation of a strong analytical method called HAM, the solution of resulting higher-order ordinary differential equations is obtained. The results of the skin friction coefficient, Nusselt number, velocity profile, and temperature profile of the hybrid nanofluid for varying different flow parameters are attained in the form of graphs and tables. Some important outcomes showed that the Nusselt number and skin friction are increased with the enhancement in Eckert number, stretching parameter, heat generation parameter and radiation parameter for both slip and no-slip conditions. The thermal profile of the hybrid nanofluid is higher for suction effect but lower for Eckert number, stretching parameter, magnetic field, heat generation and radiation parameter. For both slip and no-slip conditions, the hybrid nanofluid velocity shows an upward trend for both the stretching and mixed convection parameters.

This chapter is concerned with different types of modulations: Pulse Amplitude Modulation, Pulse Width Modulation, Pulse Position Modulation, Pulse Code Modulation, Line Codes, Delta Modulation, \(\Sigma -\Delta \) Modulation, Differential Pulse Code Modulation and Adaptive Differential Pulse Code Modulation. In this chapter, Time Division Multiplexing is also explained.

Automatic Modulation Recognition (AMR) is a critical component of smart communication and it contributed to the development of many applications such as Cognitive Radio (CR). Therefore, many researchers have been interested in this field. In this paper, a brief review of AMR. More specifically, classification methods using Deep Learning (DL), especially those that give high accuracies, Such as Convolutional Neural Networks (CNN), take into account the database, the method of extracting features, and the number of modulation types for each (SNR). Accordingly, this paper demonstrates that the best classification accuracy results are obtained using (DL) when using CNN. In recent research, the accuracy has been obtained reaching more than 90% when the classification is for 24 different types of modulation and the size of the signal is 2.5 million.

This paper discusses the design on the front-end that is compatible with analog modulation signal (compliance with PAL) and digital modulation signal (compliance with DVB-C). Although the PAL signal and the DVB-C signal are two signals with different types of modulation, they can use one RF tuner together to save the cost. These two signals have different spectrum characteristics, so they need different in-band response of the channel filter to satisfy the receiving requirement. Meanwhile, we choose two appropriate intermediate frequencies to make them in the same range. We design a programmable intermediate frequency (IF) and a switching circuit for the IF signal.

Arising modulations of surface gravity waves in a shallow-water resonator under harmonic forcing is discovered in laboratory experiments. Different types of modulations are found. When certain conditions are satisfied (appropriate frequency and sufficient force of excitation), the standing waves become modulated, and the envelopes of standing waves propagate in the channel. Strongly nonlinear numerical simulations of the Euler equations are performed reproducing the modulational regimes observed in the laboratory experiments. The physical mechanism responsible for the occurrence of modulated waves is determined on the basis of the simulations; quantitative estimates are made with the help of a simplified weakly nonlinear theory. This work was initiated by and performed under the guidance of Prof. A. Ezersky. We dedicate this text to the memory of him.

In this work, we describe an effective video communication for wireless transmission of H.264/AVC medical ultrasound video over mobile WiMAX networks. Medical ultrasound is encoded using error resilient encoding in which, the quantization levels are varied according to the function of the diagnostic significance of image region. We explain how our proposed system allows for the transmission of high-resolution clinical video which is being encoded at the clinical acquisition resolution and then decoded with low delay. We perform this functional concept by using OPNET simulations of the mobile WiMAX medium and also considering some of the physical layer characteristics also such as service prioritization classes, different types of modulation being performed, fading channel's conditions, coding schemes and their types and mobility. We are encoding the ultrasound videos at 4CIF (704×576) resolution to provide high level of clarity. The video quality assessment is being done based on both of their evaluations in objective and subjective manner.

Digital video broadcasting - handheld (DVB-H) is the technology driving mobile TV, which uses orthogonal frequency division multiplexing (OFDM) systems with multiple-input multiple-output technology (MIMO). These mobile communication systems have a promising future of supporting high data rate transmissions for both video and data. However, since the OFDM systems are sensitive to the peak-to-average power ratio (PAPR) problem, this work proposes a new technique (novel technique to reduce the PAPR based on turbo coding (NTRPT)), based on the turbo encoding technology, to reduce the PAPR effects for MIMO-OFDM-based DVB-H systems. This technique has been implemented and validated in hardware. It can support different types of modulation and coding techniques, and offers better results in reducing the PAPR than the conventional techniques currently proposed for this purpose, such as the clipping technique and the partial transmit sequence (PTS) technique, presented here using computer simulations.

This paper proposes a new method for classifying Digital Modulations, including the typical PSK (Phase Shift Keying), FSK (Frequency Shift Keying), ASK (Amplitude Shift Keying) as well as the present OFDM (Orthogonal Frequency Division Multiplex) modulation. The method is based on the analysis of the time frequency representation of the digitally modulated signals. At first, some experiments have been done to monitor the time frequency representation for different types of modulations. Then a statistical method has been applied and finally a peak detection technique has been employed to classify the modulation types. The method is capable to classify PSK, ASK, FSK 2, FSK 4, FSK 8, FSK16 and OFDM signals. Finally many simulations have been conducted and it is shown that, our method is capable to classify the right modulation against an SNR (Signal to Noise Ratio) of less than 5 dB. The classification rate is 100% for PSK and ASK signals, and 96.5% for OFDM signals. No explicit prior information is required for this method. ©2010 IEEE.

This chapter deals with parameters estimation of satellite channels based on IEEE 802.11a standard. Dependencies of a signal to noise ratio on free space path loss for different types of modulation (BPSK, QPSK, 16QAM, 64QAM), noise temperatures, number of OFDM symbols, Doppler frequency offsets, satellite amplifier gain, and aircraft antenna diameter were received using model “OFDM_FSPL_Sat_FSPL_802.11a.” A method for parameters estimation of satellite OFDM communication channel was proposed. The spectrums and signals constellations of received signals were compared for different types of the amplifier nonlinearity. The developed model allows predicting spectral regrowth of digitally modulated OFDM signals due to the amplifier nonlinearity. Channel parameters were received for the Rayleigh and Rician fading, different types of Doppler spectrum, the gain of multipath channels, the delay time of message flow using models “OFDM_Multipath_Sat_Multipath_802.11a,” “OFDM_AWGN_Sat_Multipath_802.11a,” and “OFDM_FSPL_Sat_Rician_802.11a.”

The basic atmospheric phenomena (mainly fog) influencing the optical beams, which are generated by laser diodes at wavelengths of 650 and 850 nm, will be introduced in this article. Also the possibilities of the Software Defined Radio utilization, which can create different types of modulation (M-QAM, M-PSK) and can be used for evaluation of the influences of artificial atmospheric effect on the modulated optical beam in the acrylate box, will be presented. The results from the real measurements compared with ANSYS software models will be shown as well.

The paper presents an overview of the need address the spectrum crunch to deliver higher data rates for future wireless networks. Two techniques which are currently being investigated are the use of dynamic spectrum access and new frequency bands in the mm wave. Both techniques require thorough propagation studies. In the case of dynamic spectrum access it is necessary to ensure that the technique used to identify the primary user is sufficiently robust to reduce the possibility of interference. Two possible approaches are sensing the spectrum to identify unused frequency bands and the second approach involves the setting up of a large data base identifying the availability of frequency bands in space i.e. geographic location and time. To evaluate the feasibility of sensing, it is necessary to identify a minimum detection threshold level to detect the primary user. To evaluate the sensing approach a number of sensing devices have been evaluated under the EU funded project, CREW at Durham University with respect to a number of transmissions ranging from simple CW transmissions to more demanding WiFi transmissions, frequency hopping and frequency sweeps. Low cost and high cost sensing engines were evaluated including commercial off the shelf equipment and custom designed devices such as the receiver of the frequency swept channel sounder at Durham University. The test which was performed in the large anechoic chamber at Durham University with devices tested simultaneously to ensure uniformity identified high end devices as the only ones that are capable of detecting the primary user for the different types of modulation. This is an important result since for the sensing approach to be successful it would need the capability to detect the primary user with a high level of confidence at a low cost. The second approach which involves setting up a data base requires extensive radio propagation measurements and accurate modelling and is the subject of current research. At Durham University a high end channel sounder based on the digital chirp technique has been designed and implemented to study both approaches. The sounder is capable of both radio propagation measurements in various frequency bands and of sensing since it uses a high rate frequency sweep which covers 750 MHz bandwidth in 204.8 microseconds. This enables the detection of the signal at the packet level for accurate modelling of occupancy and the feasibility of using the idle time. To investigate the use of the mm wave band for future radio networks, it is necessary to characterise the radio channel in the expected bands. Candidate bands include the 60 GHz and the 28 GHz band. To enable such studies, a wideband channel sounder which is capable of measuring the 60 GHz band with 6 GHz bandwidth has been developed at Durham with measurements performed in different scenarios including on body networks, indoor and outdoor environments to estimate both the path loss and delay spread. Currently the sounder architecture is being upgraded to the 28 GHz band. The upgraded sounder will then be used for comparative studies between different bands as it enables multi-band channel characterisation which is of importance for multi-tier multi-frequency cellular networks where the mm wave band provides high data rates and the lower frequency bands provide coverage.

Different types of laser source modulation techniques have been used in various applications depending on the objective. As optical systems extract the laws and the best solutions from experiments and simulations, the present study uses simulation software with different modulation types so the output signals can be compared. The modulators used are Mach-Zehnder, which is an external modulator, and electro-absorption modulator and laser rate equation modulator, which are direct modulators. All these types have an optical link multimode (MM) fiber with a photodiode in the receiver end that can be modeled. The input and output signals are analyzed using different types of modulations.