Distributed Transmit Beamforming without Phase Feedback

Today a growing number of applications in design engineering, production and environmental testing, and system service require specific analog waveforms and digital patterns. Such requirements are neither satisfactorily nor easily met by the use of standard function or single purpose, custom generators. Traditional methods of waveform generation suffer from undesirable complexity or mediocre performance and are otherwise limited. For the majority of arbitrary waveform generation applications, including medical engineering, modal analysis and electronic engineering, direct digital synthesis techniques are satisfactory. Direct digital synthesis, based generally on periodic retrieval of predetermined amplitude values, may be used to 2 generate such waveforms. Within the limits imposed by the system's maximum sample rate and the Nyquist criteria, any waveform may be produced using these techniques. The objective of this inquiry, within a particular set of constraints, is to extend the cost/performance envelope of direct digital synthesis techniques for the generation of arbitrary waveforms. Performance is enhanced, particularly in the areas of output bandwidth and signal purity.

The technique of direct waveform synthesis (DWS) is analyzed based on the technique of direct digital synthesis (DDS). The digital modulated waveforms are created by lookup tables (LUT) which contain waveform samples precomputed using the DWS technique. A novel DWS technique is proposed whose carrier frequency is programmable compared to the current one. Furthermore, the effect of memory versus computation is performed. The simulation results show that it is an efficient scheme to implement the software radio modulation for the DWS technique especially the novel technique of DWS with carrier frequency programmability.

In this paper, we propose a low-cost arbitrary waveform generator to simulate battery voltage transients specified by ISO 16750–2 voltage profiles. The proposed methodology is based on the technique of direct digital synthesis (DDS) implemented in a microcontroller. The proposed approach allows reducing the amount of Flash memory used by the lookup table. The device generates several types of waveforms and uses a sequencer to combine them into the desired voltage profile. For testing purposes, emulations of the variations on the cranking voltage and the superimposed A.C. voltage are used to validate the proposed solution.

In-phase and quadrature-phase (IQ) sinusoidal signals are used as bases functions in many phase modulation schemes in communication systems. Generating such signals in engineering education laboratories without higher-end signal generators is quite challenging. Most of the time, the IQ signals used in undergraduate engineering education laboratories are in audio frequency range that is used to demonstrate or experiment with various phase modulation schemes. This paper presents a method to generate IQ sinusoids in the audio frequency range using direct digital synthesis technique. The system developed is simulated using MathWorks® Simulink and implemented on commonly available Xilinx’s® Spartan 6 FPGA. The system designed is capable of producing phase correct sine and cosine waves having frequencies between 1 Hz and 20 kHz.

Long Range(LoRa) Backscattering Communication (BC) not only has the advantages of low cost and low power consumption, but also has a long communication distance. However, the existing LoRa BC scheme is complex and can not be applied to actual engineering. For this purpose, a new LoRa BC method is proposed. A Direct Digital frequency Synthesis (DDS) technique is used to generate a square wave with a linear frequency variation as a LoRa scattering modulation signal. For the first time, the prototype of LoRa BC system based on MCU is demonstrated. Experimental results show that design can successfully realize backscatter communication at any position between the station and the receiver which are 208 meters apart, while being compatible with commodity LoRa chipset. In addition, the method is also applicable to an Application Specific Integrated Circuit (ASIC) design, which enables the LoRa backscattering IC to have higher robustness, lower cost, and lower power consumption.

Phase to amplitude conversion is an essential part in the technique of direct digital frequency synthesis. A novel theory of phase to amplitude conversion named curve approximation is proposed in this paper to solve the existing problems of present digital frequency synthesizers. It has more advantages over traditional phase to amplitude conversion methods, such as simple hardware circuit, fast conversion speed, low loss and high precision. A mathematical function approximating normalized waveforms is presented in the paper and then is corrected by a small ROM lookup table containing the difference between normalized waveform and curve approximation. It can be seen from MATLAB simulation that the given curve is essentially coincident with the normalized waveform. Frequency synthesizer based on DSP and MCU verifies the feasibility of curve approximation in direct digital frequency synthesis. Experimental result shows that this method has excellent performance.

Standing-wave ultrasonic motors (usm) have the advantages of small volume, light weight, fast response, high-precision position, power-off self-locking, no electromagnetic interference and vacuum adaptability etc. It has broad application prospects in the field of space laser communication. Because the driving force and power of single motor are limited, and in order to meet the requirement of torque margin in engineering applications, ultrasonic motors are usually used in pairs in laser tracking and pointing system. However, due to the preload of the motor, the inconsistency between production and manufacturing, and the matching between the driving circuit and the motor and so on, the resonance frequency among motors varies from hundreds of Hz to several kHz, which makes it difficult to realize synchronous control. In addition, the inherent nonlinear characteristics of piezoelectric ceramic also affect the high-precision control of the ultrasonic motor. In order to further improve the synchronous driving control performance of parallel motor, an ultrasonic motor driving control system based on high-performance Digital Signal Processor(DSP) and Direct Digital Synthesis(DDS) technique is designed in the paper. The frequency, amplitude and phase of the motor driving signal can be tuned independently and precisely in this design, and the open-loop characteristics of the ultrasonic motor are measured.

The authors describe a phase-locked loop architecture for the locking of nonsinusoidal waveforms. It is based on the generation of the locking signal by means of a proper waveform synthesizer. The free-running frequency of the synthesizer is dynamically adjusted to ensure a suitable lock range. The system has been functionally analyzed and simulated, and its feasibility has been demonstrated. The lock range can extend over more than one decade. The system is suited to implementation using an oversampling approach. The reference waveform is generated with the direct-digital synthesis technique, which obtains the digital representation of the required locking signal by means of a proper ROM. This is converted into a sigma-delta flow by a digital sigma-delta modulator, and is then multiplied by the sigma-delta flow which represents the input signal. The filters and the processing circuits included in the system were realized with digital techniques.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This paper presents a detailed study on the design of a miniature, ultra-broadband, high-resolution, low-power consumption frequency synthesizer which employs both the direct and indirect frequency synthesis techniques. A high-resolution, fast frequency-switching DDS (direct digital synthesis) acts as the reference of a broad-band phase locked loop which is the key component of the frequency synthesizer. The theoretical resolution of the design is 128μHz and the bandwidth ranges from 137.5MHz to 4.4GHz. The supply voltage is 5V, corresponding to a total power consumption of 2W. The frequency synthesizer is described in detail and some analyses are made based on the experimental results.

High silica zeolite Y nanocrystals by dealumination and direct synthesis

Perovskite quantum dots (PQDs) photoresists are promising building blocks for photolithographically patterned devices. However, their complex synthesis and combination processes limit their optical properties and potential patterning applications. Here, we present an exceptionally simple strategy for the synthesis of PQDs photoresist. Unlike traditional approaches that involve centrifugation, separation, and combination processes, our direct synthesis technique using polymerizable acrylic monomer as solvent to fabricate PQDs photoresists without complex post-synthesis process. We demonstrate that the change in solubility of the precursors is the main reason for the formation of PQDs in the polymerizable monomer. By direct photolithography, colorful PQD patterns with high photoluminescence quantum yields and high thickness are successfully demonstrated. This work opens a new avenue for the direct synthesis of PQDs photoresist, expanding their applications in various integrated applications, such as photonic, energy harvesting, and optoelectronic devices.

PurposeThis paper aims to analyze the pressure behavior in dual porosity reservoirs using different techniques in an attempt to correctly characterize reservoir properties. Pressure transient tests in naturally fractured reservoirs often exhibit non-uniform responses.Design/methodology/approachThe pressure transient tests in naturally fractured reservoirs were analyzed using conventional semi-log analysis, type curve matching (using commercial software) and Tiab’s direct synthesis (TDS) technique. In addition, the TDS method was applied in case of a naturally fractured formation with a vertical hydraulic fracture. These techniques were applied to a single-layer, naturally fractured reservoir under pseudosteady state matrix flow. By studying the unique characteristics of the different flow regimes appear on the pressure and pressure derivative curves, various reservoir characteristics can be obtained such as permeability, skin factor and fracture properties.FindingsFor naturally fractured reservoirs, a comparison between the results semi-log analysis, software matching and TDS method is presented. In case of wellbore storage, early time flow regime can be obscured that lead to incomplete semi-log analysis. Furthermore, the type curve matching usually gives a non-uniqueness solution, as it needs all the flow regimes to be observed. However, the direct synthesis method used analytical equation to calculate reservoir and well parameters without type curve matching. For naturally fractured reservoirs with a vertical fracture, the pressure behavior of wells crossed by a uniform flux and infinite conductivity fracture is analyzed using TDS technique. The different flow regimes on the pressure derivative curve were used to calculate the fracture half-length in addition to other reservoir properties.Originality/valueThe results of different field cases showed that TDS technique offers several advantages compared to semi-log analysis and type curve matching. It can be used even if some flow regimes are not observed. Direct synthesis results are accurate compared to the available core data and the software matching results. It can be used to confirm the software matching results and to give reliable reservoir characteristics when there is lack of data.

Nearly all commercial hydraulic fracture design models are based on the assumption that a single fracture is initiated and propagated identically and symmetrically about the wellbore, i.e., the fracture growth and proppant transport occurs symmetrically with respect to the well. However, asymmetrical fractures have been observed in hundreds of hydraulic fracturing treatments and reported to be a more realistic outcome of hydraulic fracturing. The asymmetry ratio (length of short fracture wing divided by length of long wing) influenced the production rate adversely. In the worst case, the production rate could be reduced to that of an unfractured well. Several authors observed asymmetrically propagated hydraulic fractures in which one wing could be ten times longer than the other. Most pressure transient analysis techniques of hydraulically fractured wells assume the fracture is symmetric about the well axis for the sake of simplicity in developing mathematical solution. This study extends the work by Rodriguez to evaluate fracture asymmetry of finite-conductivity fracture wells producing at a constant-rate. The analysis presented by Rodriguez only involves the slopes of the straight lines that characterize the bilinear, linear and radial flow from the conventional Cartesian and semilog plots of pressure drop versus time. This study also uses the Tiab’s direct synthesis (TDS) technique to analyze the linear and bilinear flow regimes in order to find the asymmetry factor of the fractured well. With the fracture conductivity estimated from the bilinear flow region, dimensionless fracture conductivity and the asymmetry ratio are calculated. A technique for estimating the fracture asymmetry ratio from a graph is presented. An equation relating the asymmetry ratio and dimensionless fracture conductivity is also presented. This equation assumes that the linear and/or bilinear flow regime is observed. However, using the TDS technique, the asymmetry ratio can be estimated even in the absence of bilinear or linear flow period. It is concluded that the relative position of the well in the fracture, i.e., the asymmetry condition, is an important consideration for the fracture characterization. A log-log plot of pressure derivative can be used to estimate the fracture asymmetry in a well intersected with a finite-conductivity asymmetric fracture. The analysis using pressure derivative plot does not necessarily require the radial flow period data to calculate the asymmetric factor.

Naturally fractured reservoirs are prolific producers since fractures provide the main path for fluid flow towards the wellbore. Conventional drawdown and buildup tests are not always practical due to various technical difficulties to maintain a constant flow rate during a drawdown test or the loss of production during the shut-in period of a buildup test. In this case multirate tests represent a practical and effective alternative. This paper presents a complete multi-rate test analysis methodology in naturally fractured reservoirs. The convolution theorem was used to accommodate the change in the rate if the test is multirate. The integral method is used if the rate is continuously changing. It was found that the pressure derivative provides a powerful tool for analyzing multirate pressure transient tests. The Tiab's Direct Synthesis (TDS) technique, which uses exact analytical solutions to obtain reservoir parameters, was applied to different possible cases and the results were compared to those obtained from the other conventional techniques. In the case of long series of constant flow rate, the log-log plot of pressure and pressure derivative using equivalent radial time or equivalent linear time give approximately similar results. If the wellbore storage effect is large, the error in the permeability (especially during the early radial flow) is greater mainly if the late radial flow is not observed. When the early radial flow is missing, the dimensionless storage capacity ratio ? and the interporosity flow parameter ? cannot be estimated using conventional methods. In such case, they can be determined only from the pressure derivative plot using the TDS technique. During a multirate test, the changing flow rate must be systematically recorded since it is an integral part of all the analysis equations. Several examples were solved to illustrate the use of the techniques developed. The results show that the multiple rate tests and the TDS technique can be successfully used to characterize naturally fractured reservoirs.

it has been long recognized that in some reservoirs the flow does not follow the expected radial cylindrical pattern. Spherical flow may take place in systems with wells completed in thick reservoirs where a short completion interval is open to flow yielding a unique and more complex early-time pressure behavior. Some of the main reasons for partial penetration are to avoid coning of water and minimize sand production. A similar early-time pressure behavior may be due to the presence of plugged perforations. Such well completions are referred to as limited-entry, restricted-entry or partially penetrating wells. A typical case of spherical propagation of pressure transients occurs during the repeat formation tester measurements. Such a test measures spot formation pressures and recovers formation fluid samples for gaining an insight into the reservoir flow mechanics. The purpose of this study is to identify on the pressure and pressure derivative curves the unique characteristics for different flow regimes resulting from these type of completions and to determine various reservoir parameters, such as vertical, horizontal permeability, and various skin factors. The interpretation is performed using Tiab’s Direct Synthesis (TDS) Technique, introduced by Tiab (1993), which uses analytical equations obtained from characteristic lines and points found on the log-log plot of pressure and pressure derivative to determine permeability, skin and wellbore storage without using type-curve matching. The extension of this methodology for the case under study includes wellbore storage and skin effects. It is applied to both drawdown and buildup tests. We found that a spherical or hemispherical flow regime occurs prior to the radial flow regime whenever the penetration ratio of about 20%. A half-slope line on the pressure derivative is the unique characteristic identifying the presence of the spherical/hemispherical flow. The typical half-slope line of theses flow regimes is used to estimate spherical permeability and spherical skin values. These parameters are then used to estimate vertical permeability, anisotropy index and skin. Results of TDS technique where successufully compared to those of conventional technique for field and simulated examples.