Adaptive blind receivers for MC‐CDMA communication systems

In this paper, we propose three adaptive blind algorithms for multiuser multicarrier code division multiple‐access systems in multipath fading channels. The proposed adaptive blind receivers are based on the property of the discreteness of the input data symbol and are updated in every symbol interval. We also use the concept that the variance of the output signal approaches to the variance of the desired signal to get the cost function. The three proposed receiver structures are the traditional finite impulse response (FIR) structure, the despreading (DES) filter structure and the generalized sidelobe canceller (GSC) structure. The advantage of the FIR filter is that the length of the filter weights does not have to be the same length as the spreading code. For the DES filter, the combination of the adaptive weight and the despreading code has the simplest structure than the other two proposed receiver structures. The constrained GSC filter is superior to the other two proposed receiver structures in the environments dominated by multiple‐access interference. By this constraint, the blind GSC filter can guarantee to converge to the desired solution. Simulation results are given to show the effectiveness and comparison of the proposed adaptive blind receivers. Copyright © 2012 John Wiley & Sons, Ltd.     

A New Digital Sense Multiple Access (DSMA) Protocol for High-Speed Wireless Networks

In this paper, we propose a new digital sensemultiple access with delayed transmission (DSMA/DT)protocol for reverse channel in high-speed wirelessnetworks. The new protocol is motivated by theobservation that the existing DSMA protocol does not yieldsatisfactory throughput for long round-trip propagationand processing delay, which occurs in outdoor high-speedenvironments or when the receiver hardware requires long signal processing time. The newDSMA/DT protocol is intended to reduce the performanceimpacts of the round-trip delay. Look-ahead busy/idleflag, seizure queueing, and reserved time slots are also devised for the new protocol. Whilerequiring at most two additional status bits on theforward channel and no additional hardware capability,these features further enhance the protocol performance and enable constant-bit-rate service withlittle added complexity in control. The channelthroughput of the DSMA/DT protocol and the optionalfeatures are analyzed. Closed-form expressions for thethroughput are obtained. For non-negligible round-tripdelay relative to packet transmission time, ournumerical results show that the new protocol improvesthe throughput by as much as 60% when compared to theexisting DSMA protocol. For superior performance andsimplicity, the DSMA/DT protocol will be appropriate foruse in high-speed wireless networks.     

A novel search method to reduce PAPR of an OFDM signal using partial transmit sequences

One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) is the high peak‐to‐average power ratio (PAPR) of the transmitted OFDM signal. Partial transmit sequence (PTS) technique can improve the PAPR statistics of an OFDM signal. As ordinary PTS technique requires an exhaustive search over all combinations of allowed phase factors, the search complexity increases exponentially with the number of sub‐blocks. In this paper, we propose a novel PTS technique with reduced complexity that each level inverts twice of phase factor bits from previous level. Then we also use initial random phase sequence to find the better search way of PAPR reduction. Numerical results show that the proposed method can achieve significant reduction in search complexity with little performance degradation. Copyright © 2006 John Wiley & Sons, Ltd.     

Plasma-induced charging damage in ultrathin (3-nm) gate oxides

Plasma-induced damage in various 3-nm-thick gate oxides (i.e., pure oxides and N₂O-nitrided oxides) was investigated by subjecting both nMOS and pMOS antenna devices to a photoresist ashing step after metal pad definition. Both charge-to-breakdown and gate leakage current measurements indicated that large leakage current occurs at the wafer center as well as the wafer edge for pMOS devices, while only at the wafer center for nMOS devices. These interesting observations could be explained by the strong polarity dependence of ultra thin oxides in charge-to-breakdown measurements of nMOS devices. In addition, pMOS devices were found to be more susceptible to charging damage, which can be attributed to the intrinsic polarity dependence in tunneling current between nand p-MOSFETs. More importantly, our experimental results demonstrated that stress-induced leakage current (SILC) caused by plasma damage can be significantly suppressed in N₂O-nitrided oxides, compared to pure oxides, especially for pMOS devices. Finally, nitrided oxides were also found to be more robust when subjected to high temperature stressing. Therefore, nitrided oxides appear to be very promising for reducing plasma charging damage in future ULSI technologies employing ultrathin gate oxides     

Ideal duobinary generating filter for optically amplified systems

We develop a simple analytical model of an ideal duobinary generating low-pass filter. The model provides important physical insight into the design of optically amplified duobinary systems. We verify the theory with experimental data at 10 Gb/s.     

Electrophosphorescent Polyfluorenes Containing Osmium Complexes in the Conjugated Backbone

Electrophosphorescent copolymers have been synthesized by covalent bonding of a red‐emitting osmium complex Os(bpftz), which contains two 3‐trifluoromethyl‐5‐(4‐tert‐butyl‐2‐pyridyl)triazolate (bpftz) cyclometalated ligands, into the backbone of a bipolar polyfluorene (PF) copolymer. Employing these copolymers, a highly efficient red polymer light‐emitting diode has been realised that has an external quantum efficiency of 18.0%, a maximum brightness of 38 000 cd m^?2, and an emission centered at 618 nm. In addition, after incorporating appropriate amounts of green‐emitting benzothiadiazole (BT) and the aforementioned Os(bpftz) into the bipolar PF, an efficient white‐light electroluminescent polymer is obtained that displays simultaneous blue, green, and red emissions.     

Cross-layer QoS Analysis of Opportunistic OFDM-TDMA and OFDMA Networks

Performance analysis of multiuser orthogonal frequency division multiplexing (OFDM-TDMA) and orthogonal frequency division multiple access (OFDMA) networks in support of multimedia transmission is conducted in this work. We take a cross-layer approach and analyze several quality-of-service (QoS) measures that incilude the bit rate and the bit error rate (BER) in the physical layer, and packet average throughput/delay and packet maximum delay in the link layer. The authors adopt a cross-layer QoS framework similar to that in IEEE 802.16, where service classification, flow control and opportunistic scheduling with different subcarrier/bit allocation schemes are implemented. In the analysis, the Rayleigh fading channel in the link layer is modeled by a finite-state Markov chain, and the channel state information (CSI) is assumed to be available at the base station. With the M/G/1 queueing model and flow control results, the analysis provides important insights into the performance difference of these two multiaccess systems. The derived analytical results are verified by extensive computer simulation. It is demonstrated by analysis and simulation that OFDMA outperforms OFDM-TDMA in QoS metrics of interest. Thus, OFDMA has higher potential than OFDM-TDMA in supporting multimedia services.     

Fabrication and testing of surface micromachined polycrystallineSiC micromotors

The authors present the fabrication and testing of surface micromachined polycrystalline silicon carbide micromotors. A new multilayer fabrication process utilizing low temperature deposition and micromolding techniques was developed to create the desired SiC structural components. Typical operating voltages of salient-pole and wobble micromotors in room air were 100 and 80 V, respectively. Wobble micromotors were tested at room temperature in atmospheres of argon, nitrogen, oxygen, and room air (25% humidity). The gear ratio as a function of applied voltage was higher for operation in room air as compared with the other gases, suggesting a relationship between gear ratio and relative humidity. In addition, micromotors were tested at elevated temperatures and exhibited stable operation up to 500°C     

Design of robust envelope-constrained filter with orthonormal bases

In the continuous-time envelope-constrained (EC) filtering problem using an orthonormal filter structure, the aim is to synthesize an orthonormal filter such that the noise enhancement is minimized while the noiseless output response of the filter with respect to a specified input signal stays within the upper and lower bounds of the envelope. The noiseless output response of the optimum filter to the prescribed input signal touches the output boundaries at some points. Consequently, any disturbance in the prescribed input signal or error in the implementation of the optimal filter will result in the output constraints being violated. In this paper, we review a semi-infinite envelope-constrained filtering problem in which the constraint robustness margin of the filter is maximized, subject to a specified allowable increase in the optimal noisy power gain. Using a smoothing technique, it is shown that the solution of the optimization problem can be obtained by solving a sequence of strictly convex optimization problems with integral cost. An efficient optimization algorithm is developed based on a combination of the golden section search method and the quasi-Newton method     

Improvement of color temperature using independent control of red, green, blue luminance in AC plasma display panel

This paper presents a new driving scheme for the improvement and flexibility of a color temperature without sacrificing a peak white luminance using an independent control of the red (R), green (G), and blue (B) luminance in an alternating current plasma display panel (AC-PDP). The independent control for the R, G, and B emissions can be achieved by selective application of the various narrow auxiliary pulses to the R, G, and B address electrodes during a sustain-period. The auxiliary pulses can control the luminance levels independently from the R, G, and B cells by forming the fast and efficient plasma or by slight disturbing of the wall charge accumulation. By the application of various auxiliary pulses leading to the simultaneous control of each color's luminance, it is observed that the new driving scheme can improve the color temperature from 5396 K to 10 980 K in a 4-in test panel with almost the same peak white luminance as that of the conventional driving scheme.