Fast-polarization-hopping transmission diversity to mitigate prolonged deep fades in indoor wireless communications

Fast-polarization-hopping (FPH) transmission diversity is herein proposed to mitigate prolonged deep fades at the mobile receiver in, for example, the indoor propagation environment. Even if the individual multipaths are each sufficiently strong for detection, deep fades may occur due to the multipath signals' destructive summation at the receiver. The relative immobility of the transmitter, the propagation environment, and the receiver in the indoor environment means that a deep fade may last for a very long duration, dropping calls or severing links. By rapidly hopping the transmission polarization (say, alternating transmission between a vertically-polarized-dipole antenna and a horizontally-polarized-dipole antenna - or between two "X"-oriented dipoles), the effective propagation channel experiences consecutive polarization modes (each involving a different multipath summation), all within the duration allowed by the channel-coder's interleaving depth. This scheme is usable for either frequency-shift keying (with incoherent demodulation), or for channel-coded phase-shift keying (with differential coding, or with pilot-symbol phase synchronization). This scheme requires no change in the mobile receiver (which does not need to be dual polarized). The base station also needs no spatially separated antenna array, nor any other additional hardware, no mechanical movement of the transmitting antenna(s), and no sophisticated signal processing (such as channel estimation or closed-loop feedback) nor any additional software. The proposed scheme's cost - relative to using antenna arrays at the base station and/or the mobile - is a potentially doubling of the transmission bandwidth. The proposed scheme's potential is illustrated by limited computer simulations using CINDOOR, a polarization-sensitive indoor wireless-propagation ray-tracing simulation software package based on geometrical optics and the uniform theory of diffraction (GO/UTD).     

Color demosaicing using variance of color differences.

This paper presents an adaptive demosaicing algorithm. Missing green samples are first estimated based on the variances of the color differences along different edge directions. The missing red and blue components are then estimated based on the interpolated green plane. This algorithm can effectively preserve the details in texture regions and, at the same time, it can significantly reduce the color artifacts. As compared with the latest demosaicing algorithms, the proposed algorithm produces the best average demosaicing performance both objectively and subjectively.     

An efficient search strategy for block motion estimation usingimage features

Block motion estimation using the exhaustive full search is computationally intensive. Fast search algorithms offered in the past tend to reduce the amount of computation by limiting the number of locations to be searched. Nearly all of these algorithms rely on this assumption: the mean absolute difference (MAD) distortion function increases monotonically as the search location moves away from the global minimum. Essentially, this assumption requires that the MAD error surface be unimodal over the search window. Unfortunately, this is usually not true in real-world video signals. However, we can reasonably assume that it is monotonic in a small neighborhood around the global minimum. Consequently, one simple strategy, but perhaps the most efficient and reliable, is to place the checking point as close as possible to the global minimum. In this paper, some image features are suggested to locate the initial search points. Such a guided scheme is based on the location of certain feature points. After applying a feature detecting process to each frame to extract a set of feature points as matching primitives, we have extensively studied the statistical behavior of these matching primitives, and found that they are highly correlated with the MAD error surface of real-world motion vectors. These correlation characteristics are extremely useful for fast search algorithms. The results are robust and the implementation could be very efficient. A beautiful point of our approach is that the proposed search algorithm can work together with other block motion estimation algorithms. Results of our experiment on applying the present approach to the block-based gradient descent search algorithm (BBGDS), the diamond search algorithm (DS) and our previously proposed edge-oriented block motion estimation show that the proposed search strategy is able to strengthen these searching algorithms. As compared to the conventional approach, the new algorithm, through the extraction of image features, is more robust, produces smaller motion compensation errors, and has a simple computational complexity.     

A self-timed divider using a new fast and robust pipeline scheme

This paper investigates the potential of self-timed property of differential cascode voltage switch logic (DCVSL) circuits, and examines architectural techniques for achieving self-timing in DCVSL circuits. As a result, a fast and robust handshake scheme for dynamic asynchronous circuit design is proposed. It is novel and more general than other similar schemes. The proposed self-timed datapath scheme is verified by an 8-bit divider which is implemented using AMS 0.6-μm CMOS technology, and the chip size is about 1.66 mm×1.70 mm. The chip testing results show that the divider functions correctly and the latency for 8-bit quotient-digit generation is 17 ns (about 58.8 MHz)     

Modeling and Simulation of New Encoding Schemes for High‐Speed UHF RFID Communication

In this paper, we present novel high‐speed transmission schemes for high‐speed ultra‐high frequency (UHF) radio‐frequency identification communication. For high‐speed communication, tags communicate with a reader using a high‐speed Miller (HS‐Miller) encoding and multiple antennas, and a reader communicates with tags using extended pulse‐interval encoding (E‐PIE). E‐PIE can provide up to a two‐fold faster data rate than conventional pulse‐interval encoding. Using HS‐Miller encoding and orthogonal multiplexing techniques, tags can achieve a two‐ to three‐fold faster data rate than Miller encoding without degrading the demodulation performance at a reader. To verify the proposed transmission scheme, the MATLAB/Simulink model for high‐speed backscatter based on an HS‐Miller modulated subcarrier has been designed and simulated. The simulation results show that the proposed transmission scheme can achieve more than a 3 dB higher BER performance in comparison to a Miller modulated subcarrier.     

Performance of large-size superconducting coil in 0.21T MRI system

A high-temperature superconductor (HTS) was used on magnetic resonance imaging (MRI) receiver coils to improve image quality because of its intrinsic low electrical resistivity. Typical HTS coils are surface coils made of HTS thin-film wafers. Their applications are severely limited by the field of view (FOV) of the surface coil configuration, and the improvement in image quality by HTS coil is also reduced as the ratio of sample noise to coil noise increases. Therefore, previous HTS coils are usually used to image small in vitro samples, small animals, or peripheral human anatomies. We used large-size HTS coils (2.5-, 3.5-, and 5.5-in mean diameter) to enhance the FOV and we evaluated their performance through phantom and human MR images. Comparisons were made among HTS surface coils, copper surface coils, and cool copper surface coils in terms of the signal-to-noise ratio (SNR) and sensitivity profile of the images. A theoretical model prediction was also used to compare against the experimental result. We then selected several human body parts, including the wrist, feet, and head, to illustrate the advantage of HTS coil over copper coil when used in human imaging. The results show an SNR gain of 200% for 5.5-in HTS coil versus same size copper coils, while for 2.5- and 3.5-in coils it is 250%. We also address the various factors that affect the performance of large size HTS coils, including the coil-to-sample spacing due to cryogenic probe and the coil-loading effect.     

Personalized Healthcare System for Chronic Disease Care in Cloud Environment

The rapid increase in the number of patients with chronic diseases is an important public healthcare issue in many countries, which accelerates many studies on a healthcare system that can, whenever and wherever, extract and process patient data. A patient with a chronic disease conducts self‐management in an out‐of‐hospital environment, particularly in an at‐home environment, so it is important to provide integrated and personalized healthcare services for effective care. To help provide effective care for chronic disease patients, we propose a service flow and a new cloud‐based personalized healthcare system architecture supporting both at‐home and at‐hospital environments. The system considers the different characteristics of at‐hospital and at‐home environments, and it provides various chronic disease care services. A prototype implementation and a predicted cost model are provided to show the effectiveness of the system. The proposed personalized healthcare system can support cost‐effective disease care in an at‐hospital environment and personalized self‐management of chronic disease in an at‐home environment.     

A detection statistic for random-valued impulse noise.

This paper proposes an image statistic for detecting random-valued impulse noise. By this statistic, we can identify most of the noisy pixels in the corrupted images. Combining it with an edge-preserving regularization, we obtain a powerful two-stage method for denoising random-valued impulse noise, even for noise levels as high as 60%. Simulation results show that our method is significantly better than a number of existing techniques in terms of image restoration and noise detection.     

Mobility degradation effects in CMOS differential pair transconductors

The influence of the mobility reduction factor on the dominant third-harmonic distortion and effective transconductance in CMOS differential pair transconductors is examined. Analytical expressions are developed which are suitable for hand calculation and generate realistic estimates for distortion and transconductance. The results produced have been tested against SPICE simulations over a wide range of parameter values and show excellent agreement. The analysis highlights the importance of mobility degradation and reveals that the linearity of the source-coupled differential pair is actually improved as the mobility reduction factor increases. This surprising finding suggests that where 0.15, for example, acceptably low distortion levels (<60 dB for V _i =1 V _pp ) should be achievable with the basic long-tailed pair and that complex linearization schemes may be unnecessary.This work is supported by a grant of the Science and Engineering Research Council.     

红外激光的光学参量及它们的关系

本文用微机控制使反射镜扫描激光束,给出了CO_2激光的光强分布;用绕着光轴旋转的ZuSe布氏窗的反射和透射光强,给出了激光的偏振度。着重研究了内腔CO_2激光器的输出强度,增益,模式,能量分布,以及偏振度等光学参量间的相互关系。