This letter presents the field uniformity characteristics of a triangular prism reverberation chamber. A reverberation chamber that generally uses a stirrer to create a uniform electric field inside is an alternative to the semi-anechoic chamber for an electromagnetic compatibility test. To overcome the size and maintenance problems of a stirrer, we propose to replace it with a Quadratic Residue Diffuser which is commonly used in acoustics. To confirm that the diffuser is a valid alternative to the stirrer, a diffuser and an equilateral triangular prism reverberation chamber are designed and fabricated for 2.3-3.0 GHz operation. To investigate the field uniformity characteristics by varying the location of the transmitting antenna, both simulation and measurement in the triangular prism reverberation chamber were also done at its two positions, respectively. A commercial program XFDTD 6.2, engaging the finite difference time domain (FDTD), is used for simulation and a cumulative probability distribution, which the IEC 61000-4-21 recommends, is used to evaluate the field uniformity. Both simulation and measurement results show that the field uniformity in the chamber satisfies the international standard requirement of 6 dB tolerance and 3dB standard deviation, which means that a diffuser can be substituted for a stirrer.

The logic mapping problem and the problem of finding a largest sub-crossbar with no defects in a nano-crossbar with nonprogrammable-crosspoint defects and disconnected-wire defects are known to be NP-hard. This paper shows that for nano-crossbars with only disconnected-wire defects, the former remains NP-hard, while the latter can be solved in polynomial time.

In order to reduce the convergence time in an iterative procedure, some gradient based preliminary processes are employed to eliminate outliers. The adaptive variable block size is also introduced to balance the accuracy and computational complexity. Moreover, the use of Canberra distance instead of Euclidean distance illustrates higher performance in measuring motion similarity.

This paper evaluates the performance of a pilot-assisted fine carrier frequency offset (CFO) estimation scheme for orthogonal frequency division multiplexing (OFDM) in time-varying channels. An analytical closed-form expression of the mean square error (MSE), of the post-FFT based CFO synchronization scheme, is presented in terms of time-variant fading channels. To verify our analysis in this paper, simulations are carried out within the framework of mobile WiMAX systems.

An asymptotic expansion of the amplitude of the scattered wave by an imperfection core in a waveguide system is derived and it is shown that the scattered wave is partially canceled by the direct wave at large distance and a shadow takes place. For z→ ∞ where z is the distance along the waveguide axis the amplitudes of the direct and scattered waves decrease in proportion to z- and in the shadow region the amplitude of the sum of both waves decreases in proportion to z-. To supplement the analytical results some numerical examples are shown.

We obtained flat optical frequency combs by using the FM laser operation of a fiber ring laser and external intensity modulation. Extremely wide FM spectra can be easily obtained by the moderate internal phase modulation of an FM laser. We used an external intensity modulator to extract a linearly chirped part from the FM light in order to obtain flat spectra. In our experiments, we obtained a flat optical frequency comb with a spectral bandwidth of about 0.5 THz and a power deviation of less than 1.5 dB.

It is necessary to perform arithmetic in Fp12 to use an Ate pairing on a Barreto-Naehrig (BN) curve, where p is a prime given by p(z)=36z4+36z3+24z2+6z+1 for some integer z. In many implementations of Ate pairings, Fp12 has been regarded as a 6th degree extension of Fp2, and it has been constructed by Fp12=Fp2[v]/(v6-ξ) for an element ξ ∈ Fp2 such that v6-ξ is irreducible in Fp2[v]. Such a ξ depends on the value of p, and we may use a mathematical software package to find ξ. In this paper it is shown that when z ≡ 7,11 (mod 12), we can universally construct Fp12 as Fp12=Fp2[v]/(v6-u-1), where Fp2=Fp[u]/(u2+1).

In OFDM systems, in-phase and quadrature (I/Q) imbalances generated in the analog front-end introduce inter-channel interference and, consequently, error performance degradation. This letter provides an exact expression involving the two-dimensional (2-D) Gaussian Q-function for the error probability of an arbitrary 2-D modulated OFDM signal with I/Q imbalances. The effects of I/Q imbalances on the distribution of an AWGN and the error performance are analyzed.

In UWB systems, data symbols are transmitted and received continuously. The Fast Fourier Transform (FFT) processor must be able to seamlessly process input/output data. This paper presents the design and implementation of a continuous data flow parallel memory-based FFT (CF-PMBFFT) processor without the use of input buffer for pre-loading the input data. The processor realizes a memory space of two N-words and multiple processing elements (PEs) to achieve the seamless data flow and meet the design requirement. The circuit has been fabricated in TSMC 0.18 µm 1P6M CMOS process with the supply voltage of 1.8 V. Measurement results of the test chip shows that the developed CF-PMBFFT processor takes a core area of 1.97 mm2 with a power consumption of 62.12 mW for a throughput rate of 528 MS/s.

Hybrid automatic repeat request (HARQ) is employed for the Evolved Universal Terrestrial Radio Access (E-UTRA) downlink. The base station not only decodes the ACK/NACK signals from the user equipment (UE), but also detects a termination of the transmission (DTX) of the ACK/NACK signals caused by the mis-detection of the downlink control information (DCI) at the UE side. Since ACK/NACK signals from UEs are multiplexed by CDMA, there are sometimes severe inter-code interference (ICI) effects, which significantly degrade the performance of ACK/NACK signals. In order to mitigate such ICI effects, in [1],[2], we proposed a novel phase rotation scheme on the constellations of the uplink ACK/NACK signals, and confirmed the effects on the ACK/NACK bit error rate performance; however, the previous paper did not analyze the effects of the phase rotation on the DTX detection performance. Hence, in this paper, we further analyze the effects of the phase rotation for the ACK/NACK signals in conjunction with a new DTX detection scheme which utilizes equalizer outputs, and investigate the performance of the proposed scheme by means of computer simulations.

Orthogonal frequency division multiplexing (OFDM) communication systems have great advantages, such as high spectrum efficiency and robustness against multipath fading. In order to enhance the advantages, this paper investigates an efficient utilization of both diversity combining and higher-level modulation (adaptive modulation) with a repetition code on the frequency domain in the OFDM systems. The repetition coded OFDM systems can achieve an improvement of performance with such a simple structure as one pair of transmit/receive antennas. In this paper, we derive simple closed-form equations for bit error probability (BEP) and throughput, and then improvements of those performances in the proposed OFDM systems are verified by both theoretical analysis and Monte Carlo simulation.

This paper presents flexible inner-outer Krylov subspace methods, which are implemented using the fast multipole method (FMM) for solving scattering problems with mixed dielectric and conducting object. The flexible Krylov subspace methods refer to a class of methods that accept variable preconditioning. To obtain the maximum efficiency of the inner-outer methods, it is desirable to compute the inner iterations with the least possible effort. Hence, generally, inaccurate matrix-vector multiplication (MVM) is performed in the inner solver within a short computation time. This is realized by using a particular feature of the multipole techniques. The accuracy and computational cost of the FMM can be controlled by appropriately selecting the truncation number, which indicates the number of multipoles used to express far-field interactions. On the basis of the abovementioned fact, we construct a less-accurate but much cheaper version of the FMM by intentionally setting the truncation number to a sufficiently low value, and then use it for the computation of inaccurate MVM in the inner solver. However, there exists no definite rule for determining the suitable level of accuracy for the FMM within the inner solver. The main focus of this study is to clarify the relationship between the overall efficiency of the flexible inner-outer Krylov solver and the accuracy of the FMM within the inner solver. Numerical experiments reveal that there exits an optimal accuracy level for the FMM within the inner solver, and that a moderately accurate FMM operator serves as the optimal preconditioner.

Recently, network coding (NC) has been popularly applied to wireless networks in order to improve scarce wireless capacity. In wireless LANs, NC can be applied to packet retransmission, and a base station can simultaneously retransmit multiple packets destined to different wireless stations by a single retransmission trial. On the other hand, NC creates additional packet delay at both base station and wireless stations, and hence, packet transfer delay may increase seriously. However, existing NC-based retransmission methods do not consider this additional delay explicitly. In addition, when the number of flows is small, NC exhibits less benefit because the chances of NC-based retransmission are highly reduced. Therefore, in this paper, we propose a novel NC-based retransmission method in order to improve packet transfer delay and jitter of received packets. Moreover, to achieve further improvement of delay, jitter and retransmission efficiency even when there exist a small number of traffic flows, we propose a retransmission method in which NC-based retransmission cooperates with the typical ARQ method. We overcome the disadvantage of NC-based retransmission by combining with ARQ cooperatively. Finally, we show the effectiveness of the proposed methods by extensive computer simulation.

Spectrum sensing is a fundamental function for cognitive radio network to protect transmission of primary system. Cooperative spectrum sensing, which can help increasing sensing performance, is regarded as one of the most promising methods in realizing a reliable cognitive network. In such cooperation system, however the communication resources such as sensing time delay, control channel bandwidth and consumption energy for reporting the cognitive radio node's sensing results to the fusion center may become extremely huge when the number of cognitive users is large. In this paper, we propose an ordered sequential cooperative spectrum sensing scheme in which the local sensing data will be sent according to its reliability order to the fusion center. In proposed scheme, the sequential fusion process is sequentially conducted based on Dempster Shafer theory of evidence's combination of the reported sensing results. Above all, the proposed scheme is highly feasible due to the proposed two ordered sequential reporting methods. From simulation results, it is shown that the proposed technique not only keeps the same sensing performance of non-sequential fusion scheme but also extremely reduces the reporting resource requirements.

An immense number of LAN switches are currently in use worldwide. Therefore, methods that can reduce the energy consumption of these devices are of great practical interest. A simple way to save power in LAN switches is to switch the interfaces to sleep mode when no packets are buffered and to keep the interfaces in active mode while there are packets to be transmitted. Although this would appear to be the most effective energy saving scheme, mode switching gives rise to in-rush current, which can cause electrical damage to devices. This problem arises from excessive mode switching, which should be avoided. Thus, the main objective is to develop a method by which to reduce the number of mode switchings that result in short-duration sleep modes because these switchings do not contribute greatly to energy efficiency but can damage the device. To this end, a method is adopted whereby the interface is kept in active mode for an "extra" period of time after all packets have been flushed from the buffer. This period is the "extra active period (EAP)" and this scheme protects the device at the expense of energy saving efficiency. In this paper, this scheme is evaluated analytically in terms of its power reduction ratio and frequency of mode changes by modifying the M/M/1 and IPP/M/1 queuing models. The numerical results show how the duration of the extra active period degrades the energy saving performance while reducing the number of mode changes. We analytically show an exact trade-off between the power reduction ratio and the average number of turn-ons in the EAP model with Poisson packet arrival. Furthermore, we extend the scheme to determine the EAP dynamically and adaptively depending on the short-term utilization of the interface and demonstrate the effectiveness of the extended scheme by simulation. The newly developed scheme will enable LAN switches to be designed with energy savings in mind without exceeding the constraints of the device.

Multimedia applications such as video and audio have recently come into much wider use. Because this heterogeneous traffic consumes most of the network's resources, call admission control (CAC) is required to maintain high-quality services. User satisfaction depends on CAC's success in accommodating application flows. Conventional CACs do not take into consideration user satisfaction because their main purpose is to improve the utilization of resources. Moreover, if we assume a service where an ISP provides a "flat-based charging," each user may receive same user satisfaction as a result of users being accommodated in a network, even if each has a different bandwidth. Therefore, we propose a novel CAC to maximize total user satisfaction based on a new philosophy where heterog eneous traffic is treated equally in networks. Theoretical analysis is used to derive optimal thresholds for various traffic configurations with a full search system. We also carried out theoretical numerical analysis to demonstrate the effectiveness of our new CAC. Moreover, we propose a sub-optimal threshold configuration obtained by using an approximation formula to develop practical CAC from these observations. We tested and confirmed that performance could be improved by using sub-optimal parameters.

This paper investigates the relationship between averaged SAR (Specific Absorption Rate) over 10 g mass and temperature elevation in Japanese numerical anatomical models when devices are mounted on the body. Simplifying the radiation source as a half-wavelength dipole, the generated electrical field and SAR are calculated using the FDTD (Finite-Difference Time-Domain) method. Then the bio-heat equation is solved to obtain the temperature elevation due to the SAR derived using the FDTD method as heat source. Frequencies used in the study are 900 MHz and 1950 MHz, which are used for mobile phones. In addition, 3500 MHz is considered because this frequency is reserved for IMT-Advanced (International Mobile Telecommunication-Advanced System). Computational results obtained herein show that the 10 g-average SAR and the temperature elevation are not proportional to frequency. In addition, it is clear that those at 3500 MHz are lower than that at 1950 MHz even though the frequency is higher. It is the point to be stressed here is that good correlation between the 10 g-average SAR and the temperature elevation is observed even for the body-worn device.

Base Station (BS) cooperation has been considered as a promising technology to mitigate co-channel interference (CCI), yielding great capacity improvement in cellular systems. In this paper, by combining frequency domain cooperation and space domain cooperation together, we design a new CCI mitigation scheme to maximize the total utility for a multi-cell OFDMA network. The scheme formulates the CCI mitigation problem as a mixture integer programming problem, which involves a joint user-set-oriented subcarrier assignment and power allocation. A computationally feasible algorithm based on Lagrange dual decomposition is derived to evaluate the optimal value of the problem. Moreover, a low-complexity suboptimal algorithm is also presented. Simulation results show that our scheme outperforms the counterparts incorporating BS cooperation in a single domain considerably, and the proposed low-complexity algorithm achieves near optimal performance.

This paper presents a novel regularity evaluation of placement structure and techniques for handling conditional design rules along with dynamic diffusion sharing and well island generation, which are developed based on Sequence-Pair. The regular structures such as topological rows, arrays and repetitive structures are characterized by the way of forming sub-sequences of a sequence-pair. A placement objective is formulated balancing the regularity and the area efficiency. Furthermore, diffusion sharing and well island can be also identified looking into forming of a sequence-pair. In experiments, we applied our regularity-oriented placement mixed with the constraint-driven technique to real analog designs, and attained the results comparable to manual designs even when imposing symmetry constraints. Besides, the results also revealed the regularity serves to increase row-structures applicable to the diffusion sharing for area saving and wire-length reduction.

We present an orthogonal frequency division multiple access (OFDMA) based multichannel slotted ALOHA for cognitive radio networks (OMSA-CR). The performance of an infinite population based OMSA-CR system is analyzed in terms of channel capacity, throughput, delay, and packet capture effect. We investigate the channel capacity for OMSA-CR with perfect or imperfect spectrum sensing. We introduce the proposed CR MAC based on two channel selection schemes: non-agile channel selection (NCS) and agile channel selection (ACS). Comparing them, we show the tradeoff between complexity and system performance. We verify the proposed CR system model using numerical analysis. In particular, using simulation with a finite populated linear feedback model, we observe the OMSA-CR MAC tradeoff between throughput and minimum delay whose results matched those of the analytical framework. Numerical results for the proposed system throughput are also compared to conventional MACs, including pure ALOHA based CR MAC.