Adaptive Digital Satellite Transmission Ground Terminal Design Considerations

The key technical elements in designing digital mobile satellite communication systems are identified, and tradeoff studies on the transmission parameters of the satellite link, which were based on experience with an experimental system and the results of field trials, on digital maritime and aeronautical satellite communication systems, are described. The future evolution of the various new communication services to be offered in the digital mobile communication systems are discussed. In the digital mobile satellite communication systems which will be operated under the condition of low C/N and with a signal-level fluctuation due to multipath fading etc., it has been found that the most important requirement is to establish the frame synchronization quickly and maintain it stably in addition to the stable carrier/clock tracking, under this severe link condition. >

Pi 2 pulsations are often used to indicate the start of the substorm expansion phase. In this report the relationship between the Pi 2 polarization pattern observed at a mid‐latitude longitudinal chain of stations and synchronous orbit magnetic activity is explored. Eighteen single‐ and multiple‐substorm‐onset intervals, consisting of 55 Pi 2's, are examined using data from the Air Force Geophysics Laboratory Magnetometer Network and the synchronous orbit satellites GOES 2 and 3. Magnetic fluctuations at synchronous orbit are found to be enhanced when the satellite is near the Pi 2 pattern center, defined as the longitude where the major axis of the polarization ellipse is along the H axis. The pattern center is also observed to separate regions of dipolarization and more taillike magnetic signatures. East of the pattern center the field inclination becomes larger, i.e., more dipolelike, while west of the center the field inclination becomes smaller, i.e., more taillike. Although regions of substorm activation, as determined by the Pi 2 pattern, move between onsets during multiple‐onset events, no consistent azimuthal motion was found.

Speed control of three phase and single phase induction motors represents a very important issue in residential and industrial applications. This paper presents a voltage to frequency speed control of both single phase and three phase induction motors derived by multi-level inverters (MLIs). 15-level and 31-level multi-level inverters are considered. Both MLIs are operated by applying two proposed simplified and efficient modulation techniques in addition to the application of conventional multicarrier sinusoidal pulse width modulation technique MC-SPWM. The proposed modulation techniques overcome several difficulties related to MC-SPWM. The scaler voltage to frequency control method operates very well during starting along with step changes in motor speeds. Simulation results verify the high performance of the proposed modulation techniques when controlling both induction motors based on 15-level and 31-level MLIs.

This thesis presents modulation and control strategies for neutral-point-clamped (NPC) converters. These converters produce ac voltages with lower harmonic distortion and the switches operate with less switching frequencies than traditional two-level voltage-source converters. NPC converters are widely employed in grid integration of renewable energy sources like solar and wind energy, high-power motor drives, shunt active power filters, etc. The NPC converters suffer from challenges such as, the subsequent increase in switching losses while controlling the capacitor voltage (CV) ripples, neutral-point (NP) voltage instability arising in the presence of nonlinear loads enriched in even-order harmonics, and the divergence of CVs in the presence of nonzero average NP current. The focus of this thesis is to address these challenges and develop more efficient modulation and control techniques for the NPC converters. In order to find a trade-off solution between the CV ripple magnitude and the switching power losses, a new feedforward compensated modulation technique for the three-phase NPC converter is proposed in this thesis. With this technique, the CVs are limited within a predefined voltage band. An innovative feedforward compensation is introduced to avoid low-frequency distortion on the output voltages of the converter arising due to oscillations in the CVs. Limiting the CV ripples helps in the design of the NPC converter, since the maximum voltage that the dc-link capacitors and the power semiconductors have to withstand is predefined. Though the proposed feedforward compensated modulation strategy offers a trade-off between the CV ripples and switching losses, its performance deteriorates in the presence of extreme nonlinear loads due to the tendency of the CVs to frequently bounce out of the voltage band leading to higher switching losses. In order to address this drawback, a band-limited three-level (BL-3L) modulation technique is proposed which aims to balance the average CVs without any substantial increase in the switching losses, thereby concentrating mainly on enhancing the steady state performance of the system. In addition to the predefined voltage band (applied to the CVs), a variable current band is applied to the phase currents. The size of the current band is varied based on the tendency of the operational condition to unbalance the NP. Therefore, the BL-3L modulation is another approach to have a trade-off between the CV ripples and the switching power losses, which ensures the average CVs are balanced even in the presence of nonlinear loads enriched in even-order harmonics. For bipolar dc-bus applications of NPC converters like feeding multiterminal dc-loads, back-to-back systems and grid-connected photovoltaic (PV) systems, the main challenge is to generate the required nonzero average NP current which, if not compensated, causes the CVs to diverge and hence destabilizes the converter. In order to address this issue, a dual-mode modulation technique is proposed which utilizes the inherent capability of the NPC converter to generate the required average NP current and does not employ any additional hardware. This technique is developed analytically using ac-side voltages and currents, and is applicable for all bipolar dc-bus applications of the NPC converter with balanced CVs. The analytical solution also provides the maximum average NP current injection capacity of the NPC converter, which defines the stable operating region of the converter. The applications of dual-mode modulation technique are limited to systems with balanced CVs. In order to extend this analysis to applications of the NPC converter with unbalanced CVs, a dual-input NPC inverter-based grid-connected PV system is considered. A control strategy is proposed for this system to asymmetrically control the PV arrays without incorporating any additional external circuit. This is achieved by employing an analytically developed linearization block, similar to the dual-mode modulation technique, which helps in generating the required NP current to counter for the difference in the PV currents. Experimental results are obtained on a laboratory developed prototype to validate all the proposed modulation techniques under different operating conditions. Finally, this thesis summarizes the work that has been done and presents some directions for future research.

Within the last few months satellite communication systems have moved from the experimental phase of the Telstar and Relay satellites to the beginnings of commercial operation with the HS 303 (Early Bird) synchronous orbit satellite. When one considers the leap forward in technology, which the art of using satellites for world-wide communication itself entails, it is remarkable that this development has taken place in a period of less than five years. And this has occurred at a time when another means for long-distance world-wide communication—the submarine repeatered coaxial cable—has also achieved considerable success in spanning the oceans with hundreds of telephone circuits.

The use of optical spatial modulation (OSM), which has been recently emerged as a power and bandwidth efficient pulsed modulation technique for indoor optical wireless communication, is proposed as a simple, low-complexity means of achieving spatial diversity in coherent free space optical (FSO) communication systems. In doing so, this paper makes several novel contributions as follows. It presents a generic analytical framework for obtaining the Average Bit Error Probability (ABEP) of uncoded OSM with coherent detection in the presence of turbulence-induced fading. Although the framework is general enough to accommodate any type of models based on turbulence scattering, the focus in this paper is the H-K distribution. Although this distribution represents a very general scattering model valid over a wide range of atmospheric conditions, it is has not been considered in the past in conjunction with FSO systems possibly because of its mathematical complexity. The proposed analytical framework yields exact performance evaluation results for MIMO systems with two transmit- and an arbitrary number of receive apertures. In addition, tight upper bounds are derived for the error probability for OSM systems with an arbitrary number of transmit apertures as well as for convolutionally encoded signals. The performance of OSM is compared to that of well established coherent FSO schemes, employing spatial diversity at the transmitter or the receiver only. Specifically, it is shown that OSM can offer comparable performance with conventional coherent FSO schemes while outperforming the latter in terms of spectral efficiency and hardware complexity. Various numerical performance evaluation results are also presented and compared with equivalent results obtained by Monte Carlo simulations which verify the accuracy of the derived analytical expressions.

The institute of medical and veterinary science clinical laboratory computing system

The multicarrier code division multiple access (MC-CDMA) technique has received considerable interest for its potential application to future wireless communication systems due to its high data rate. A common problem regarding the blind multiuser detectors used in MC-CDMA systems is that they are extremely sensitive to the complex channel environment. Besides, the perturbation of colored noise may negatively affect the performance of the system. In this paper, a new coherent detection method will be proposed, which utilizes the modified fast independent component analysis (FastICA) algorithm, based on approximate negentropy maximization that is subject to the second-order cone programming (SOCP) constraint. The aim of the proposed coherent detection is to provide robustness against small-to-medium channel estimation mismatch (CEM) that may arise from channel frequency response estimation error in the MC-CDMA system, which is modulated by downlink binary phase-shift keying (BPSK) under colored noise. Noncoherent demodulation schemes are preferable to coherent demodulation schemes, as the latter are difficult to implement over time-varying fading channels. Differential phase-shift keying (DPSK) is therefore the natural choice for an alternative modulation scheme. Furthermore, the new blind differential SOCP-based ICA (SOCP-ICA) detection without channel estimation and compensation will be proposed to combat Doppler spread caused by time-varying fading channels in the DPSK-modulated MC-CDMA system under colored noise. In this paper, numerical simulations are used to illustrate the robustness of the proposed blind coherent SOCP-ICA detector against small-to-medium CEM and to emphasize the advantage of the blind differential SOCP-ICA detector in overcoming Doppler spread.

Some electronic modules perform the monitoring and recording of electrical events in power plants. Such equipment is based on signals provided by transducers that measure the process parameters. For example, PC-08/104 Process Control is an equipment which performs monitoring and recording of specific parameters when transient electrical events occur, for the post-failure analysis and diagnosis. This programmable digital equipment is versatile and can be connected to an IBM compatible PC or process server. The results obtained in hydropower plants in Romania - where PC-08/104 equipment runs for more years - confirm its utility and robustness. The paper is focused on the results obtained in monitoring and recording more specific parameters of transient electrical events using PC-08/104 digital equipment in several hydropower plants. The analyzed results are based on the processing of analog and digital signal samples acquired at successive moments. Eight analog inputs and sixteen digital inputs are acquired. The analog inputs are the voltages of phases R, S and T, currents of phases R, S and T, homopolar voltage and the homopolar current. The main specific parameters to be monitored are the root mean square value and phase shift of each analog input, status of each digital input or logical functions associated, active and reactive powers, monitored electrical line impedances. The waveforms of all analog input signals, the status of each digital input signal and the phase diagram of the currents and voltages for the R, S, T phases are also displayed.

Orthogonal frequency division multiplexing (OFDM) is a type of multicarrier modulation (MCM) technique in which larger bandwidth is divided into parallel narrow bands each of which is modulated by different subcarriers. All the subcarriers are orthogonal to each other and hence it reduces the interference among various subcarriers. OFDM technique is an efficient modulation technique used in certain wired and wireless application.In a wireless communication channel, the transmitted signal can travel from transmitter to receiver over multiple reflective paths. This results to multipath fading which causes fluctuations in amplitude, phase and angle of arrival of the received signal. For example, the signal which is transmitted from BTS (base transceiver station) may suffer multiple reflections from the buildings nearby, before reaching the mobile station. Such multipath fading channels are classified into slow fading/fast fading and frequency-selective/flat fading channels. This paper discusses the performance of OFDM system using various fading channels and channel coding. The parameter which is known as Bit error rate (BER) is calculated under different fading channels (AWGN, Rayleigh and Rician) for different digital modulation (BPSK, QPSK and QAM) and Channel coding (linear/Cyclic coding). Matlab Simulink tool is used to calculate the BER parameter.

This paper describes a design technique and its implementation for OLN (Optimized Low-cost Node) a wireless sensory network node. The basic design considerations include low cost, small foot print factor with a flexibility to modularize the sensory inputs and supports for dual mode wireless communications. The uniqueness of this work include: (1) high level programming language C support for the low cost miniaturized 8-bit CPU development environment; (2) modular RF unit to support ZigBee, and other ASK/FSK RF band, and (3) dual mode sensor input support, e.g., analog and digital sensor input. Detailed steps of the design are given in this paper. Experiments are conducted to verify the design, and they confirmed the design objectives.

A pulsed plasma microthruster system was designed, built, flight qualified, and delivered to the Massachusetts Institute of Technology (MIT) Lincoln Laboratory for installation in the LES-6 satellite. The system was designed to meet the requirements for east-west stationkeeping of the spin stabilized, synchronous orbit satellite. Four valveless pulsed plasma microthrusters using solid Teflon as the propellant are spaced on the satellite periphery. The flight qualification and acceptance program was successful in meeting environmental constraints and indicated that RFI was not a serious problem in the application of the thruster to the communication satellite. East-west stationkeeping was functionally performed in more than 16 months of space operation.

Aiding gastrointestinal diagnostic laboratory by designing a device for the non invasive detection of peptic ulcer.

In this paper, orthogonal frequency division multiplexing (OFDM) systems with coherent, incoherent and quasi-coherent demodulation schemes will be considered respectively. Resulting system performance figures will be compared in terms of bit error rate (BER) and hardware complexity. It is well known that non-differential modulation and coherent demodulation techniques have optimum BER performance but lead to a significantly increased system overhead due to pilot signals and system complexity due to channel estimation procedure. This paper describes differential modulation schemes, which do not require any radio channel estimation, and two related incoherent and quasi-coherent demodulation techniques. The resulting BER performance is nearly identical compared with coherent demodulation, but the computation complexity is drastically reduced. A field programmable gate array (FPGA) based experimental system has been developed, which is used for BER performance measurements and system complexity considerations

The paper deals with the use of a digitally controlled voltage source (d.c.v.s.) as a general-purpose interface element. This concept has been successfully applied to bidirectional analogue-digital (a.d.) and radix conversions. The element may also be controlled from a digital computer to synthetise ‘analogue’ functions. A further application involves the use of a series of d.c.v.s. elements to generate a power series of terms from which sine, exponential, logarithmic and other functions may be constructed using a binary counter to provide the digital input. Methods of generating repetitive or nonrepetitive functions are outlined which can be given precisely controlled frequencies and/or amplitude. The D.C.V.S. element may be given to independent digital inputs as well as an analogue input, and this allows the generation of very complex waveforms. Relatively unsophisticated linear- and logic-circuit packages will achieve accuracies within 0.1% in the applications described.