The Earth will require sustainable electricity sources equivalent to 3 to 5 times the commercial power presently produced by 2050. Solar Power Satellite (SPS) is one option for meeting the huge future energy demand. SPS can send enormous amounts of power to the Earth as the form of microwave (MW). A highly efficient microwave power transmission (MPT) system is needed for SPS. A critical goal of SPS is to maintain highest Beam Efficiency (BE) because the microwaves from SPS will be converted to utility power unlike the MW from communication satellites. Another critical goal of SPS is to maintain Side Lobe Levels (SLL) as small as possible to reduce interference to other communication systems. One way to decrease SLL and increase BE is the edge tapering of a phased array antenna. However, tapering the excitation requires a technically complicated system. Another way of achieving minimum SLL is with randomly spaced element position but it does not guarantee higher BE and the determination of random element position is also a difficult task. Isosceles Trapezoidal Distribution (ITD) edge tapered antenna was studied for SPS as an optimization between full edge tapering and uniform amplitude distribution. The highest Beam Collection Efficiency (BCE) and lowest SLL (except maximum SLL) are possible to achieve in ITD edge tapering and ITD edge tapered antenna is technically better. The performance of ITD is further improved from the perspective of both Maximum Side Lobe Level (MSLL) and BE by using unequal spacing of the antenna elements. A remarkable reduction in MSLL is achieved with ITD edge tapering with Unequal element spacing (ITDU). BE was also highest in ITDU. Determination of unequal element position for ITDU is very easy. ITDU is a newer concept that is experimented for the first time. The merits of ITDU over ITD and Gaussian edge tapering are discussed.

A single-pass rate control algorithm based on motion estimation error statistics is presented. The algorithm consists of two steps. The first step deals with the target bit allocation for each frame. The complexity measure which determines the target bit allocation is calculated by using the motion estimation error statistics. The second step is to compute the bit spending profile within a frame. A nonlinear profile based on motion estimation statistics is used to allocate bits for each macroblock more efficiently. Experimental results show that the performance in terms of PSNR is significantly improved over a conventional rate control algorithm. Compared to the conventional algorithm, the new algorithm has little added complexity because it uses existing information from motion estimation.

This paper proposes a new partial channel state information (CSI) reporting method for spatial scheduling in TDD/MIMO systems. In the proposed method, a terminal transmits pilot signals using transmit beams which have large channel gains between the base station (BS) and the terminal. Then, the BS can obtain partial CSI through responses of the pilot signals. Furthermore, adaptive allocation of pilot signals is proposed, in which pilot signals for CSI reporting are adaptively allocated to terminals depending on the number of terminals. We evaluate system throughput of spatial scheduling under the partial CSI reporting from multiple terminals. Numerical results show that the proposed method reduces uplink signalling for CSI reporting effectively, keeping high system throughput of spatial scheduling.

In this Letter, we investigate the correlation rate of a random sequence data set which is collected by RFID (Radio Frequency IDentification) readers in an indoor location. Using a passive RFID tag introduces reading error, which causes a loss of original data. From the question of how sensing errors of RFID readers affect the location prediction algorithm used for context awareness services at home, we analyze the correlation rate of a collected data set with respect to RFID reader-sensing error rate. Through our analysis, we conclude that the prediction accuracy can be better or worse than the one of the original data streams according to the error rate. We suggest that the reader specification has to be satisfied by the error boundary which is found in this work for the tolerant location prediction.

Energy-efficient transmission scheme is very essential for Wireless Personal Area Networks (WPNs) for maximizing the lifetime of energy-constrained wireless devices and assuring the required QoS in the actual physical transmission at each allocated TDMA time slot. We therefore propose the minimum energy (ME) criterion based adaptive transmission scheme which determines the optimum combination of transmit power, physical data rate and fragment size required to simultaneously minimize the energy consumption and satisfy the required QoS in each assigned time duration. The improved performances offered by the proposed algorithm are demonstrated via computer simulation in terms of throughput and energy consumption.

The cognitive radio system consists of multiple wireless access systems that cover overlapping areas and cognitive terminals that use one or more of the wireless accesses simultaneously. In this paper, we describe the architecture of the cognitive radio system and the inter-system handover protocols. In the architecture, each cognitive terminal, which can access multiple radio systems, operates with a single local IP address. The control sequence and packet format are designed to achieve fast handover among the radio systems. Based on the architecture, we have developed a testbed system. On this system, we demonstrate that data can be delivered continuously and radio systems can be switched correctly without any packet loss. In addition, we present the result of the evaluation of the end-to-end latency on the testbed system. These testbed results demonstrate the system architecture described in the paper can achieve a cognitive radio system.

Cognitive Radios (CRs) are expected to perform more significant role in the view of efficient utilization of the spectrum resources in the future wireless communication networks. In this paper, a cognitive radio coexisting with cellular systems is proposed. In the case that a cellular system adopts Frequency Division Duplex (FDD) as a multiplexing scheme, the proposed CR terminals communicate in local area on uplink channels of the cellular system with transmission powers that don't interfere with base stations of the cellular system. Alternatively, in the case that a cellular system adopts Time Division Duplex (TDD), the CR terminals communicate on uplink slots of the cellular system. However if mobile terminals in the cellular system are near the CR network, uplink signals from the mobile terminals may interfere with the CR communications. In order to avoid interference from the mobile terminals, the CR terminal performs carrier sense during a beginning part of uplink slot, and only when the level of detected signal is below a threshold, then the CR terminal transmits a signal during the remained period of the uplink slot. In this paper, both the single carrier CR network that uses one frequency channel of the cellular system and the multicarrier CR network that uses multiple frequency channels of the cellular system are considered. The probabilities of successful CR communications, the average throughputs of the CR communications according to the positions of the CR network, and the interference levels from cognitive radio network to base stations of the cellular system are evaluated in the computer simulation then the effectiveness of the proposed network is clarified.

In this paper, an architecture of MIMO mesh network which avoids co-channel interference and supplies link multiplexing simultaneously, namely MIMO spatial spectrum sharing, is proposed. As a MIMO transmission scheme, linear (such as zero-forcing) and nonlinear (such as dirty paper coding and successive interference cancellation) MIMO algorithm are developed for the proposed mesh network. It is found from numerical analysis that the proposed MIMO mesh network achieves significantly higher channel capacity than that of conventional mesh networks.

In this paper we analyze the characteristics of vehicle mobility and propose a novel Mobility Prediction Progressive Routing (MP2R) protocol for Inter-Vehicle Communication (IVC) that is based on cross-layer design. MP2R utilizes the additional gain provided by the directional antennas to improve link quality and connectivity; interference is reduced by the directional transmission. Each node learns its own position and speed and that of other nodes, and performs position prediction. (i) With the predicted progress and link quality, the forwarding decision of a packet is locally made, just before the packet is actually transmitted. In addition the load at the forwarder is considered in order to avoid congestion. (ii) The predicted geographic direction is used to control the beam of the directional antenna. The proposed MP2R protocol is especially suitable for forwarding burst traffic in highly mobile environments. Simulation results show that MP2R effectively reduces Packet Error Ratio (PER) compared with both topology-based routing (AODV [1], FSR [2]) and normal progressive routing (NADV [18]) in the IVC scenarios.

A novel Uniform Discrete Multitone (DMT) transceiver is proposed, utilizing a wavelet packet based filter bank transmultiplexer in conjunction with a DMT transceiver. The proposed transceiver decomposes the channel spectrum into subbands of equal bandwidth. The objective is to minimize the bit error rate (BER), which is increased by channel-noise amplification. This noise amplification is due to the Zero-Forcing equalization (ZFE) technique. Quantization of the channel-noise amplification is presented, based on post-equalization signal-to-noise ratio (SNR) and probability of error in all subbands of the Uniform DMT system. A modified power loading algorithm is applied to allocate variable power according to subband gains. A BER performance comparison of the Uniform DMT with variable and uniform power-loading and with a conventional DMT system in a Digital Subscriber Line (DSL) channel is presented.

A technique for suppressing the clipping noise of an analogue-to-digital converter (ADC) is proposed to realize a cognitive radio transceiver that offers high sensitivity carrier-sensing. When a large bandwidth cognitive radio transceiver performs carrier-sensing, it must receive a radio wave that includes many primary user transmissions. The radio wave may have high peak-to-average power ratio (PAPR) and clipping noise may be generated. Clipping noise becomes an obstacle to the achievement of high-sensitivity carrier-sensing. In the proposed technique, the original values of the samples clipped by an ADC are estimated by interpolation. Polynomial spline interpolation to the clipped signal is performed in the first step, and then SINC function interpolation is applied to the spline interpolated signal. The performance was evaluated using the signals with various PAPR. It has been found that suppression performance has a dependency on the number of samples clipped at once rather than on PAPR. Although there is an upper limit for the number of samples clipped at once that can be compensated with high accuracy, about 20 dB suppression of clipping noise was achieved with the medium degree of clipping.

We propose a neurodynamical approach to a large-scale optimization problem in Cognitive Wireless Clouds, in which a huge number of mobile terminals with multiple different air interfaces autonomously utilize the most appropriate infrastructure wireless networks, by sensing available wireless networks, selecting the most appropriate one, and reconfiguring themselves with seamless handover to the target networks. To deal with such a cognitive radio network, game theory has been applied in order to analyze the stability of the dynamical systems consisting of the mobile terminals' distributed behaviors, but it is not a tool for globally optimizing the state of the network. As a natural optimization dynamical system model suitable for large-scale complex systems, we introduce the neural network dynamics which converges to an optimal state since its property is to continually decrease its energy function. In this paper, we apply such neurodynamics to the optimization problem of radio access technology selection. We compose a neural network that solves the problem, and we show that it is possible to improve total average throughput simply by using distributed and autonomous neuron updates on the terminal side.

In this paper, we propose a soft decision based cooperative sensing method for cognitive radio (CR) networks for opportunistic frequency usage. To identify unused frequency, CR should exploit sensing technique to detect presence or absence of primary user and use this information to opportunistically provide communication among secondary users while performance of primary user should not be deteriorated by the secondary users. Because of multipath fading or shadowing, the detection of primary users may be significantly difficult. For this problem, cooperative sensing (CS), where gathered observations obtained by multiple secondary users is utilized to achieve higher performance of detection, has been investigated. We design a soft decision based CS analytically and analyze the detector in several situations, i.e., signal model where single-carrier case and multi-carrier case are assumed and two scenarios; in the first scenario, SNR values of secondary users are totally equal and in the second scenario, a certain SNR difference between secondary users is assumed. We present numerical results as follows. The first scenario shows that there is little difference between the signal models in terms of detection performance. The second scenario shows that CS is superior to non-cooperative sensing. In addition, we presents that detection performance of soft decision based CS outperform detection performance of hard decision based CS.

In one-cell-frequency-reuse Orthogonal Frequency Division Multiple Access based Time Division Multiple Access (OF/TDMA) systems, communication is blocked by interference from adjacent cells. The most promising solution would be an adaptive modulation and coding scheme that is controlled by estimating the signal-to-interference ratio (SIR). However, there has so far been no way to accurately estimate the SIR using the spreading codes for OF/TDMA systems, because of the asynchronous fast Fourier transform (FFT). In this paper, we propose a novel SIR estimation method that uses a spread pulse-wave symbol and carrier interferometry. Moreover, to introduce multi- input multi-output systems, we modify the proposed method by allocating a different spreading code to each cell. Computer simulation confirmed that the SIR is estimated accurately even if the FFT is asynchronous. On cell boundaries, the average estimation errors that are a ratio between accurate and estimated propagation characteristics are less than 2 dB.

Transmission line metamaterials on coplanar waveguide with series-capacitive and shunt-inductive distributed loading in periodical intervals are characterized using our developed fullwave self-calibrated method of moments. Firstly, the two effective per-unit-length transmission parameters, i.e., complex propagation constant and characteristic impedance, are numerically extracted. The results provide a straightforward insight into the forward- and backward-wave propagation characteristics in several distinctive bands, including the left- and right-handed stopbands and passbands. In particular, it is demonstrated that in the whole left-handed passband, the propagation constant has purely negative phase constant while the characteristic impedance has only positive real quantity. Next, varied left- and right-handed passbands are studied in terms of lower/higher cut-off frequencies based on ideal equivalent circuit model and practical distributed CPW elements, respectively. Of particular importance, the left-handed and right-handed passbands find to be able to be directly connected with a seamless bandgap under the condition that normalized inductance and capacitance of loaded CPW inductive and capacitive elements become exactly the same with each other. Finally, the 9-cell metamaterial circuits on CPW with actual 50 Ω feed lines are designed and implemented for experimental validation on the derived per-unit-length parameters.

The Project Authorization Request (PAR) for the IEEE P1900.4 Working Group (WG), under the IEEE Standards Coordinating Committee 41 (SCC41) was approved in December 2006, leading to this WG being officially launched in February 2007 [1]. The scope of this standard is to devise a functional architecture comprising building blocks to enable coordinated network-device distributed decision making, with the goal of aiding the optimization of radio resource usage, including spectrum access control, in heterogeneous wireless access networks. This paper introduces the activities and work under progress in IEEE P1900.4, including its scope and purpose in Sects. 1 and 2, the reference usage scenarios where the standard would be applicable in Sect. 4, and its current system architecture in Sect. 5.

Recently Tate pairing and its variations are attracted in cryptography. Their operations consist of a main iteration loop and a final exponentiation. The final exponentiation is necessary for generating a unique value of the bilinear pairing in the extension fields. The speed of the main loop has become fast by the recent improvements, e.g., the Duursma-Lee algorithm and ηT pairing. In this paper we discuss how to enhance the speed of the final exponentiation of the ηT pairing in the extension field F36n. Indeed, we propose some efficient algorithms using the torus T2(F33n) that can efficiently compute an inversion and a powering by 3n + 1. Consequently, the total processing cost of computing the ηT pairing can be reduced by 16% for n=97.

In recent years, certain countermeasures against differential power analysis (DPA) at the logic level have been proposed. Recently, Popp and Mangard proposed a new countermeasure-masked dual-rail pre-charge logic (MDPL); this countermeasure combines dual-rail circuits with random masking to improve the wave dynamic differential logic (WDDL). They claimed that it could implement secure circuits using a standard CMOS cell library without special constraints for the place-and-route method because the difference between the loading capacitances of all the pairs of complementary logic gates in MDPL can be compensated for by the random masking. In this paper, we particularly focus on the signal transition of MDPL gates and evaluate the DPA-resistance of MDPL in detail. Our evaluation results reveal that when the input signals have different delay times, leakage occurs in the MDPL as well as WDDL gates, even if MDPL is effective in reducing the leakage caused by the difference in loading capacitances. Furthermore, in order to validate our evaluation, we demonstrate a problem with different input signal delays by conducting measurements for an FPGA.

In this paper, an evolutionary approach is proposed to obtain a discrete-time state-space interval model for uncertain continuous-time systems having interval uncertainties. Based on a worst-case analysis, the problem to derive the discrete interval model is first formulated as multiple mono-objective optimization problems for matrix-value functions associated with the discrete system matrices, and subsequently optimized via a proposed genetic algorithm (GA) to obtain the lower and upper bounds of the entries in the system matrices. To show the effectiveness of the proposed approach, roots clustering of the characteristic equation of the obtained discrete interval model is illustrated for comparison with those obtained via existing methods.

This paper deals with the scattering of a transverse magnetic (TM) plane wave from a perfectly conductive sinusoidal surface with finite extent. By use of the undersampling approximation and a rectangular pulse approximation, an asymptotic formula for the total scattering cross section at a low grazing limit of incident angle is obtained explicitly under conditions such that the surface is small in roughness and slope, and the corrugation width is sufficiently large. The formula shows that the total scattering cross section is proportional to the square root of the corrugation width but does not depend on the surface period and surface roughness. When the corrugation width is not large, however, the scattered wave can be obtained by a single scattering approximation, which gives the total scattering cross section proportional to the corrugation width and the Rayleigh slope parameter. From the asymptotic formula and the single scattering solution, a transition point is defined explicitly. By comparison with numerical results, it is concluded that the asymptotic formula is fairly accurate when the corrugation width is much larger than the transition point.