IEEE 802.16m technology is expected to provide high speed packet data service over wireless. Due to the large amount of data to be processed over a short period of time, an efficient MAC processing in the modem is crucial. Since the MAC processing algorithm has optimization limitations, we focus on a data flow optimization in the system level design, so that the number of external memory accesses is minimized. Experimental results show that our approach results in an up to sixteen times faster IEEE 802.16m modem system.

View full abstract

With the development of wireless networks and the use of mobile devices, mobile user's privacy issue is becoming more and more important. In order to protect mobile user's privacy, the previous works in the literature mainly considered anonymous authentication of mobile users. Unfortunately anonymity only is not sufficient to guarantee the intended privacy if messages are identified to belong to one specific user. In this paper, we propose an anonymous authentication scheme with unlinkability for wireless environments. The analysis results show that all the previous anonymous schemes are linkable while our scheme is anonymous and unlinkable. The scheme is still efficient when compared with the previous schemes providing anonymity only.

View full abstract

In this paper, we propose a three-threshold decision based cooperative spectrum sensing algorithm (TTDCSS) with two rounds cooperation. Specifically, after the failure of the first cooperation, cognitive users begin to report the second local decision bit to the fusion center (FC) to perform a second cooperation, thus sensing failure is eliminated. Furthermore, by integrating uncertainty of noise variance, we propose a simple method to set local decision thresholds. Numerical results show that the TTDCSS algorithm is superior to the conventional double-threshold decision based sensing methods in the performance with a little increase of sensing bits.

View full abstract

This paper presents a nonlinear control strategy using robust nonlinear dynamic inversion (RNDI) for an electric throttle which is a dc-motor driven valve for automotive engines. Controlling of the electric throttle is a great challenge due to strong nonlinearities, such as “limp-home” nonlinearity, friction and backlash. In this paper, a novel robust nonlinear dynamic inversion technique is proposed in order to achieve a fast and accurate reference tracking performance even in the presence of highly nonlinear characteristics. The effectiveness of the proposed method is analyzed through computer simulations.

View full abstract

A novel multi-channel LED driver is presented, consisting of an active current regulator and a switch-mode voltage regulator for each channel. This driver is implemented using a 0.35µm 40V high voltage process. The active current regulator directly controls an LED-current without any current-sensing resistor and its operating voltage is self-optimized by the switch-mode voltage regulator. This self-optimization is successfully achieved and the active current regulators have channel-current deviations of a maximum of ±2%. Its power-conversion efficiency is up to 91% at the load power of 7W.

View full abstract

Asymptotic solution with higher-order approximation has been derived for the transient whispering gallery (WG) mode radiation field excited by a Gaussian-type modulated ultra-wideband pulse source. Time-domain asymptotic solution is obtained by applying the saddle point technique to evaluate the inverse Fourier transform for the transient WG mode radiation field. Asymptotic solution with higher-order approximation provides the new physical phenomena that the instantaneous angular frequency changes as the function of a time and the shape of the Gaussian beam is expanded in terms of a time. The validity of the asymptotic solution has been confirmed by comparing with the reference solution.

View full abstract

With mature development of wired and wireless communications technologies, a variety of applications based on systems with the technologies have emerged. The industry in which time-to-market has become a significant factor requires conditions under which network applications are able to be developed as rapidly as possible. As the network applications are executed in wired and wireless communications system environment where multiple nodes are distributedly arranged, it takes enormous amounts of time and efforts to verify such applications in a real environment. Therefore, to address such an issue, this paper proposes a simulator that makes it possible to execute and verify network applications in a virtual environment. With repect to performance, the proposed integration simulator shows high process performance, because the integration of simulators led to the additional operation cost of 10% only. With regard to functions, it makes real network appliations executed easily, because it provides an interface highly similar to one in common operating systems.

View full abstract

This paper proposes an adaptive block-based compressed sensing (ABCS) technique to build a new progressive image coding scheme, in which both image acquisition and reconstruction are carried out in two layers. At the base layer, an original image is sampled and restored by the block-based compressed sensing (BCS) method with a low and fixed measurement rate. Second, all blocks in the enhancement layer are re-sampled with different rates according to a block classification. The final reconstruction of a block at the enhancement layer is performed in multiple stages where each stage only knows a part of sampled coefficients. We present some experimental results to show that our proposed ABCS method outperforms the BCS method; in particular, it produces a better visual quality in regions that contain edges, patterns, and textures.

View full abstract

In this paper, we propose a new energy-efficient and QoS-aware geographic routing (EQGR) protocol for wireless sensor networks. EQGR maximizes the network lifetime and uses optimum cost function to select the best neighbor node. For minimizing inter-node and intra-node timeliness, we use two neighbor information routing tables for reliability and real-time domains. To minimize the queue waiting time for time-sensitive packets, scheduling policy considers different priorities for different types of data according to their criticality. Simulation results show that EQGR can achieve reliable data forwarding with energy-efficiency, low missed-deadline data delivery, low end-to-end latency, and extremely low control signal overhead.

View full abstract

In this paper, an ultra low power 15-bit digitally controlled oscillator (DCO) is proposed. The proposed DCO is designed based on a segmental coarse-tuning stage which employs novel Schmitt-trigger based hysteresis delay cells (HDC) as well as digitally controlled varactor (DCV) in the fine-tuning stage. Simulation of the proposed DCO using TSMC 180nm model achieves controllable frequency range of 191MHz ∼ 850MHz with a wide linearity. Monte Carlo simulation demonstrates that the time-period jitter due to random power supply fluctuation is under 124.8ps and the power consumption is 137µW at 215MHz with 1.8V power supply.

View full abstract

We propose two novel III-V/Si hybrid laser structures with patterned window arrays in metal thin film wafer-bonding layers. The metal-mediated bonded III-V/Si heterointerface exhibits high electrical and thermal conductivity while allowing optical coupling between the III-V gain layer and the underneath Si waveguide through the openings in the metal bonding layer. We numerically examine the validity of the proposed hybrid laser structures through calculations of their modal propagation loss by metal's absorption and threshold current densities. We also propose another hybrid laser structure utilizing conductive direct semiconductor/semiconductor wafer bonding exploiting a spatial gain profile well overlapped with the waveguide mode and no metal-induced loss relative to those metal-mediated-bonded. All of these three structures have advantages such as spontaneous lateral current confinement and simpler fabrication over conventional oxide-mediated-bonded hybrid lasers.

View full abstract

This paper presents a novel approach for removing noise from multi-echo knee magnetic resonance images using global intensity normalization and the averaging operation along the echo-time. Firstly, the global mean and standard deviation at the zero echo-time are estimated by applying the mono-exponential spin echo model to the means and standard deviations of multi-echo images. Secondly, the signal and noise levels at multi-echo images are normalized to the estimated mean and standard deviation at the zero echo-time. Then, the normalized multi-echo images are averaged along the echo-time into a noise-removed zero echo-time image. Finally, the multi-echo MR images are reconstructed from the noise-removed zero echo-time image by the inverse normalization. The experiments demonstrate that the proposed method effectively removes not only the noises of each multi-echo image but also noises of the Quantitative T2 image.

View full abstract

We demonstrate 20-Gb/s W-band wireless transmission in free space with a distance of 30mm using optical signal generation. Optically synthesized QPSK signal and direct optical upconversion technique ease generation of W-band RoF signals for dual purpose of wireline and wireless transmission link. A W-band radio receiver with W-band frequency downconversion and digital signal processing will be applicable for any W-band radio detection.

View full abstract

When a carrier aggregation communication system suffers from receiving power imbalance (RPI) in its antenna array due to design flaw, operator's negligence etc. the system performance may be degraded to an unacceptable level. Specifically in this paper a carrier aggregation communication system with two carrier links while one link suffers RPI is considered, various modulation techniques, such as QPSK, 16 QAM and 64 QAM and/or coding schemes, Convolution Code (CC) and Low Density Parity Check Code (LDPC) are implemented in the system performance simulation to investigate the system behavior when it has the design request to maintain the same system performance in each link when the RPI has values of 7 or 10dB.

View full abstract