This letter presents results showing improved field uniformity in a reverberation chamber using quadratic residue diffusers. The optimal occupying ratio of the diffusers on one side wall of the chamber is presented. A reverberation chamber is an alternative to the semi-anechoic chamber, which is widely used for the analysis and measurement of electromagnetic interference and immunity. To analyze the field characteristics, quadratic residue diffusers were designed for the 1-3 GHz frequency band, and the FDTD method was used. At 1-3 GHz, the standard deviation of the test volume in the reverberation chamber was investigated. The reverberation chamber had good field uniformity when quadratic residue diffusers occupy 37.5-50% of one side wall of the reverberation chamber; the field uniformity saturated at the diffuser occupancy rate of 75%.

In this letter, we consider a novel ultra-wideband (UWB) spatial multiplexing (SM) multiple input multiple output (MIMO) structure, which consists of prerake diversity combiners in the transmitter and a zero forcing (ZF) detector in the receiver. For a UWB SM MIMO system with N transmit antennas, M receive antennas, and L resolvable multipath components, it is shown that the proposed prerake combining-based MIMO detection scheme has the diversity order of (LN-M+1) and its BER performance is analytically presented in a log-normal fading channel and also compared with that of a rake combining-based ZF scheme.

A high efficient HBT MMIC power amplifier with a new on-chip bias control circuit was proposed for PCS applications. By adjusting the quiescent current in accordance with the output power levels, the average power usage efficiency of the power amplifier is improved by a factor of 1.4. The bias controlled power amplifier, depending on low (high) output power levels, shows 62(103) mA of quiescent current, 16(28) dBm output power with 7.5(35.4)% of power-added efficiency(PAE), -46(-45) dBc of adjacent-channel power ratio (ACPR), and 23.7(26.9) dB of gain

In loudspeaker-based 3D audio systems, there are some acoustic crosstalk cancellation methods to enlarge the 'sweet spot' around a fixed listener position. However, these methods have common defect that most of them can be applied only to the specific narrow frequency band. In this letter, we propose the more robust acoustic crosstalk cancellation method so that we can cancel the crosstalk signal in far wider frequency band and enlarge 'sweet spot. ' For this goal, we apply a sum and difference filter to the conventional three loudspeaker-based 3D audio system.

This paper presents a heuristic algorithm that minimizes the delay of the given circuit through a two-pass cell selection in cell-based design. First, we introduce a new graph, called candidate web, which conveniently represents all cell combinations available for the implementation of the given circuit. We, then, present an efficient method to obtain a tentative set of optimal cells, while estimating the delay of the longest path between each cell and the primary output on the candidate web. In this step, multiple cells are allowed to bind the same logic gate. Finally, we describe how the proposed approach actually selects the optimal cells from the tentative set, which would minimize the circuit delay. Experimental results on a set of benchmarks show that the proposed approach is effective and efficient in minimizing the delay of the given circuit.

This paper proposes a new codec design method based on JPEG for face images and presents its application to face recognition. Quantization table is designed using the R-D optimization for the Yale face database. In order to use in the embedded systems, fast codec design is also considered. The proposed codec achieves better compression rates than JPEG codec for face images. In face recognition experiments using the linear discriminant analysis (LDA), the proposed codec shows better performance than JPEG codec.

The non-individualized head related transfer function (HRTF) is known to have a few problems, which are referred to as the 'hole in the middle' phenomenon and 'front-back reversals.' To overcome these problems, an HRTF refinement technique was introduced, but unfortunately, this refinement technique causes sudden degradation in sound quality and difficulty in cross-talk cancellation because of notch frequency exaggeration. In this paper, an HRTF refinement using directional weighting function is proposed. This newly proposed technique weights ordinary HRTF according to its direction to amplify frontal sound intensity. Since the proposed technique does not exaggerate the notch frequency, spectral differences in the 'cone-of-confusion' region become more pronounced within overall audible frequencies, resulting in mitigating the sound degradation. In addition, the cross-talk cancellation can be done more easily. We verified the superiority of the proposed technique over the existing one by means of the sound localization and sound quality tests in headphone and loudspeakers.

The electrostatic characteristics of broadside-coupled striplines in a shield are investigated with the mode-matching method. The Fourier series is employed to describe electrostatic potential distributions. Numerical results are shown for coupled transmission line cell applications.

A low-power switching method using a bootstrapping circuit is proposed for a high-speed output driver of transmitter. Compared with a conventional output driver, the proposed scheme employs only nMOSFETs to transmit data. The bootstrapping circuit ensures the proper switching of nMOSFET. The proposed scheme is simulated and fabricated using a 0.18 µm CMOS technology, showing 10.2% lower power consumption than a conventional switching driver at 2.5 Gb/s data rate.

Recently much attention is being devoted to a femtocell's potential for improving indoor cellular coverage with the provision of high data rate services in a wireless environment. Femtocells are usually deployed in homes and buildings and overlay existing macrocells, or microcells which cover wider service areas. In such an overlaid network structure, one of the important issues in network planning is the analysis of system capacity achievable by femtocells, which could be significantly affected by indoor radio propagation properties. This paper addresses a typical environmental scenario where a detailed indoor radio propagation model can be adopted. Moreover, a performance evaluation of embedded femteocell networks reflecting various environmental scenarios and factors is provided by the metrics of outage probability, dynamic range of spectral efficiency, and required separation distances for various wall structures, distance, and the number of walls between the home femtocell and the user. Our computer simulation and numerical analysis indicate an outage probability of 1%∼58%, dynamic range of spectral varies from around 2.2 to 7, while the required separation from the macrocell station is 25 m ∼ 327 m. This information could be useful for femtocell network planning.

In this paper, an effective congestion control algorithm is proposed to increase the end-to-end delivery success ratio of upstream traffic by reduction of buffer drop probabilities and their deviation in wireless sensor networks. According to the queue length of parent and child nodes, each child node chooses one of the parents as the next hop to the sink and controls the delay before transmission begins. It balances traffics among parents and mitigates congestion based on congestion level of a node. Simulation results show that the proposed algorithm reduces buffer drop probabilities and their deviation and increases the end-to-end delivery success ratio in wireless sensor networks.

For V-band applications, this paper presents a fully embedded multi-layer dielectric waveguide filter (DWGF) with very low insertion loss and small size, which does not need any more assemblies such as flip-chip bonding and bond wires. The top and bottom plane are grounded, and therefore, although we make a metal housing, there will be no resonance occurrences. Especially, the proposed structure is very suitable for MMICs interconnection because the in/output pads consist of conductor backed co-planar waveguide (CBCPW). The filter is formed incorporating metallized through holes in low temperature co-fired ceramic (LTCC) substrates with relative dielectric constant of 7.05. The total volume of the filter including transitions is 4.5 mm2.65 mm0.4 mm. A fabricated DWGF with four transitions shows an insertion loss and a return loss of 2.95 dB and less than 15 dB at the center frequency of 62.17 GHz, respectively. According to the authors' knowledge, the proposed filter shows the lowest insertion loss among the embedded multi-layer millimeter-wave filters ever reported for 60 GHz applications.

In this paper, we propose a novel Web service composition framework which dynamically accommodates various failure recovery requirements. In the proposed framework called Adaptive Failure-handling Framework (AdaFF), failure-handling submodules are prepared during the design of a composite service, and some of them are systematically selected and automatically combined with the composite Web service at service instantiation in accordance with the requirement of individual users. In contrast, existing frameworks cannot adapt the failure-handling behaviors to user's requirements. AdaFF rapidly delivers a composite service supporting the requirement-matched failure handling without manual development, and contributes to a flexible composite Web service design in that service architects never care about failure handling or variable requirements of users. For proof of concept, we implement a prototype system of the AdaFF, which automatically generates a composite service instance with Web Services Business Process Execution Language (WS-BPEL) according to the users' requirement specified in XML format and executes the generated instance on the ActiveBPEL engine.

This paper reports on a fiber-optic system for in-building wireless communication/broadcast systems developed in Samsung Electronics. Our system delivers the third generation mobile system, satellite-digital multimedia broadcast, and wireless local access network services over a single strand of single-mode fiber or multi-mode fiber. We present the design issue and experimental results of the radio-over-fiber link.

The default server strategy is commonly used to manage the location and state of mobile hosts in cellular networks. With this strategy, connections can be established after the client obtains the location information of the mobile host by querying the default server. Unfortunately, the communication cost increases if the query requests are frequent and the distance between the default server and the client is long. Still more, no connection to a mobile host can be established when the default server of the destination mobile host fails. These problems can be solved by replicating the default servers and by letting the nearest replicated default server process the query request which is sent from a client [9]. It is important to allocate replicated default servers efficiently in networks and determine the number of replicated default servers. In this paper, we suggest and evaluate a default server replication strategy to reduce communication costs and to improve service availabilities. We consider optimal replication degree as well as location for replicating the default servers in n-grid and tree networks.

This paper presents a current-reused quadrature voltage-controlled oscillator (QVCO) which adopts a source-connection coupling structure. The QVCO simultaneously achieves low phase noise and low power consumption by newly combining current-reused VCOs and coupling transistors. The measured QVCO obtains good FoM of -188.2 dBc at a frequency of 2.2 GHz with 3.96 mW power consumption.

In this letter, a post-detection signal to noise ratio (SNR) is considered for transmit antenna selection, when a sorted QR decomposition (SQRD) algorithm is used for signal detection in spatial multiplexing (SM) ultra-wideband (UWB) multiple input multiple output systems. The post-detection SNR expression is obtained using a QR factorization algorithm based on a sorted Gram-Schmidt process. The employed antenna selection criterion is to utilize the largest minimum post-detection SNR value. It is shown via simulations that the antenna selection significantly enhances the BER performance of the SQRD-based SM UWB systems on a log-normal multipath fading channel.

Electrical capacitance tomography (ECT) is used to obtain information about the distribution of a mixture of dielectric materials inside a vessel or pipe. ECT has several advantages over other reconstruction algorithms and has found many applications in the industrial fields. However, there are some difficulties with image reconstruction in ECT: The relationship between the permittivity distribution and measured capacitance is nonlinear. And inverse problem is ill-posed so that the inverse solution is sensitive to measurement error. To cope with these difficulties iterative image reconstruction algorithms have been developed. In general, the iterative reconstruction algorithms in ECT have comparatively good-quality in reconstructed images but result in intensive computational burden. This paper presents the iterative image reconstruction algorithm for ECT that can enhance the speed of image reconstruction without degradation in the quality of reconstructed image. The main contribution of the proposed algorithm is new weighting matrices, which are obtained by the interpolation of the grouped electrical field centre lines (EFCLs). Extensive simulation results have demonstrated that proposed algorithm provides improved reconstruction performance in terms of computational time and image quality.

In order to exploit the benefits of soft handoff, finding good values of handoff control parameters is important. In cellular system specifications such as IS-95C and WCDMA, handoff decision algorithm includes signal strength averaging and drop timer in addition to hysteresis. This paper analyzes the effects of signal strength averaging and drop timer and their performance tradeoffs. Because averaging and drop timer are both based on time delay, one may expect that they have similar impact on soft handoff performance. The results show that the effects of averaging and drop timer are rather similar and closely connected in terms of reducing the signaling overhead. However, they have different impacts on resource usage and diversity gain of the system.

In the vehicular ad hoc network (VANET), broadcast is used to disseminate emergency warning messages (EWM) in public safety applications and delay is one of the most stringent requirements. Although flooding is the simplest broadcast scheme, it introduces a broadcast storm problem, and numerous broadcast protocols have been proposed for VANET in order to improve the performance of broadcast. In this letter, we analyze the tradeoff between two location-based broadcast protocols, i.e., distance-based relay selection (DBRS) and range-based relay selection (RBRS) schemes under various vehicular densities. Then, we propose a dynamic broadcast scheme, which selects an appropriate scheme from DBRS and RBRS, based on the estimation of vehicle density. The results of a performance analysis show that the proposed scheme dynamically selects the better scheme for varying vehicle density.