Mixed microwave-digital and multi-rate approach for wideband beamforming applications using 2-D IIR beam filters and nested uniform linear arrays

The presented work explores novel methods for synthesizing approximately frequency independent array factors at lower hardware complexity for wideband beamforming applications. The proposed approach employs 2-D infinite impulse response (IIR) digital beam filters together with nested uniform linear arrays (ULAs). The array is designed to have multiple levels of nesting. Each level of nesting consists of a ULA covering a temporal subband of the incident wideband signal. The use of nested arrays provides the required aperture size using a smaller number of elements compared to using a single ULA to capture the entire wideband signal. The use of different levels of nesting allows the operation of the digital processor for each sub-band at different clock rates. This is a hierarchical approach that saves both digital VLSI hardware and power consumption. The 2-D IIR digital beam filters that process each subband signal from each of the nested subarray achieves wideband beamforming. Simulations illustrate approximately frequency independent passbands as required in wideband beamforming.     

A weighted least-squares method for the design of stable 1-D and2-D IIR digital filters

We present a new approach to the least-squares design of stable infinite impulse response (IIR) digital filters. The design is accomplished by using an iterative scheme in which the denominator polynomial obtained from the preceding iteration is treated as a part of the weighting function, and each iteration is carried out by solving a standard quadratic programming problem that yields a stable rational function. When the iteration converges, a stable and truly least-squares solution is obtained. The method is then extended to address the least-squares design of stable IIR two-dimensional (2-D) filters. Examples are included to illustrate the proposed design techniques     

Broadband beamforming of dense aperture array (DAA) and focal plane array (FPA) signals using 3D spatio-temporal filters for applications in aperture synthesis radio astronomy

It is shown that 3D spatio-temporal filters have potential applications in aperture synthesis radio astronomy for the broadband-beamforming of the array of signals that is received from dense aperture arrays (DAAs) and also from focal plane arrays (FPAs). In particular, we consider possible applications for the planned Square Kilometer Array (SKA) project where broadband beamforming is required at the front-end of the signal processing system for some experiments such as pulsar timing. In the case of a synthesized aperture that is composed of DAAs, the required 3D magnitude frequency response has a non-separable narrow-cone-shaped (or narrow-frustum-shaped) passband whereas, for FPAs, the required 3D magnitude frequency response has a non-separable wide-cone-shaped (or wide-frustum-shaped) passband. The corresponding 3D passbands are designed to faithfully transmit the celestial signals of interest (SOIs), whereas the 3D stopbands are designed to significantly attenuate such undesired signal components such as natural and artificial sources of radio frequency interference (RFI) and the dominant part of the 3D electronic broadband noise that is contributed by millions of low noise amplifiers (LNAs), each of which amplifies the signal received in each elemental antenna of the DAAs or FPAs. The criteria for designing both narrow- and wide-cone/frustal filters, in order to achieve optimal sensitivity, are presented in terms of the power of the recovered signal and the power of the contaminating noise.     

S-transformation based integrated approach for spectrum estimation,storage, and sensing in cognitive radio

Cognitive Radio (CR) uses the principle of dynamic spectrum allocation to improve the utilization of spectrum bands. The estimation of missing data is essential for maintaining an uninterrupted quality of service in the CR. However, the existing methods are not suitable for interpolating missing data in high frequency signals. The storage of spectrum occupancy information is crucial for learning the spectrum usage and prediction. The existing techniques for wideband spectrum sensing suffer from poor edge detection capabilities. This paper proposes an S-Transformation (ST) based approach to solve these problems. For missing samples, the proposed method improves the accuracy of estimation. The ST can also be used to store the spectrum occupancy information. The simulation results show that the proposed scheme outperforms others by improving the accuracy of edge detection. Further, the simple implementation of the ST in the frequency domain is an advantage for the real time application.     

Separate/joint optimization of error feedback and realization for roundoff noise minimization in a class of 2-D state-space digital filters

Techniques for the separate/joint optimization of error-feedback and realization are developed to minimize the roundoff noise subject to l ₂-norm dynamic-range scaling constraints for a class of 2-D state-space digital filters. In the joint optimization, the problem at hand is converted into an unconstrained optimization problem by using linear-algebraic techniques. The unconstrained problem obtained is then solved by applying an efficient quasi-Newton algorithm. A numerical example is presented to illustrate the utility of the proposed techniques.     

New results in 2-D systems theory, part II: 2-D state-space models—Realization and the notions of controllability, observability, and minimality

In this part, a comparison between the different state-space models is presented. We discuss proper definitions of state, controllability and observability and their relations to minimality of 2-D systems. We also present new circuit realizations and 2-D digital filter hardware implementation of 2-D transfer functions.     

Parallel, Pipelined and Folded Architectures for Computation of 1-D and 2-D DCT in Image and Video Codec

Several parallel, pipelined and folded architectures with different throughput rates are presented for computation of DCT, one of the fundamental operations in image/video coding. This paper begins with a new decomposition algorithm for the 1-D DCT coefficient matrix. Then the 2-D DCT problem is converted into the corresponding 1-D counterpart through a regular index mapping technique. Afterward, depending on the trade-off between hardware complexity and speed performance, the derived decomposition algorithm is transformed into different parallel-pipelined and folded architectures that realize the butterfly operations and the post-processing operations. Compared to other DCT processor, our proposed parallel-pipelined architectures, without any intermediate transpose memory, have the features of modularity, regularity, locality, scalability, and pipelinability, with arithmetic hardware cost proportional to the logarithm of the transform length.     

Energy consumption minimization and throughput improvement in cognitive radio networks by joint optimization of detection threshold,sensing time and user selection

Wireless Networks - Cooperative spectrum sensing schemes proposed to solve the hidden terminal problem and mitigate multipath fading and shadowing effects, which enhance the sensing performance and...     

RF, DC, and Reliability Performance of MIM Capacitors Embedded in Organic Substrates by Wafer-Transfer Technology (WTT) for System-on-Package Applications

In this paper, radio frequency (RF), dc, and reliability performance have been studied on metal-insulator-metal (MIM) capacitors embedded in organic substrates. The MIM structure including ~74-nm SiN dielectric was prefabricated on Si and then transferred onto organic substrates (FR-4) by wafer-transfer technology (WTT). The RF characteristics up to 30 GHz were investigated by equivalent lumped circuit modeling, showing that the parameters associated with the MIM layers including the main capacitance, parasitic inductance, and resistance were only slightly changed by the WTT process. The substrate-related parasitics were reduced as a result of the replacement of lossy Si with insulating FR-4 substrates. Excellent capacitance linearity, low voltage coefficient (~2.2 ppm/V²), and temperature coefficient (~38 ppm/degC) were obtained for capacitors on FR-4 substrates. Current-voltage and time-dependent dielectric breakdown tests verified that, after the harsh processes of WTT, the MIM structures maintained the intrinsic reliability as those originally fabricated on Si. This paper, along with earlier reports, proved that WTT presented a new dimension to realize embedded capacitors for high-density circuit board and system-on-package applications     

平板式大面积放电射频激励CO2激光器小信号增益分布测试及分析

此研究结果表明这类激光器的小信号增益分布与气体流速;有关。在静止气体或非常慢速流动下,小信号增益分布取决于气体温度的分布,而当气体流速增加到一定数值后,小信号增益分布则取决于气体速度在放电管内的分布。     

The effects of delay spread on 2-PSK, 4-PSK, 8-PSK and 16-QAM in aportable radio environment

Computer simulation results are presented of a study of delay spread on digital modulations with different constellations in a quasi-static multipath radio channel. Unfiltered 2-, 4-, and 8-PSK and 16-QAM with a rectangular signaling pulse are compared first, followed by 4- and 16-QAM with a raised-cosine Nyquist pulse. The bit error rate performances averaged over fading samples under the influence of the intersymbol interference caused by delay spread are compared for modulations of different levels. It is found that 4-level modulation is the most desired method for both performance and implementation in a quasistatic, frequency-selective fading radio channel. Both the spectral and the power efficiencies can be enhanced using Nyquist signaling pulses     

Bi-directional 2-D mesh representation for video object rendering,editing and superresolution in the presence of occlusion

In this paper, we propose a new bi-directional 2-D mesh representation of video objects, which utilizes forward and backward reference frames (keyframes). This framework extends the previous uni-directional mesh representation to enable efficient rendering, editing, and superresolution of video objects in the presence of occlusion by allowing bi-directional texture mapping as in MPEG B-frames. The video object of interest is tracked between two successive keyframes (which can be automatically or interactively selected) both in forward and backward directions. Keyframes provide the texture of the video object, whereas its motion is modeled by forward and backward 2-D meshes. In addition, we employ “validity maps”, associated with each 2-D mesh, which allow selective texture mapping from the keyframes. Experimental results for efficient video object editing and object-based video resolution enhancement in the presence of self-occlusion are presented to demonstrate the effectiveness of the proposed representation.