With the big success of 802.11 wireless networks, there have been many proposals addressing end-to-end QoS guarantees in 802.11 WLAN. However, we have found that current end-to-end QoS architectures lack of one or more important properties such as cross-layer interaction, end-to-end integration, reconfigurability and modularity. In this work, we present an end-to-end reference QoS architecture for 802.11 WLAN that encapsulates in an unifying fashion software-based QoS components (mechanisms, algorithms, services), proposed in the literature. To show the usefulness and correctness of the reference architecture, we present three case studies of end-to-end QoS architectures addressing different QoS requirements such as bandwidth and delay with different approaches such as differentiated services and integrated services. We will give an architectural comparison and performance evaluation of these architectures. We believe the reference QoS architectures can help QoS designers to understand the importance and the complexity of various QoS components during the design phase and thus choose these QoS components appropriately.

In this paper we present a study on the design optimization of voltage-controlled oscillators. The phase noise of LC-type oscillators is basically limited by the quality factor of inductors. It has been experimentally shown that higher-Q inductors can be achieved at higher frequencies while the oscillation frequency is limited by parasitic capacitances. In this paper, the minimum transistor size and the degradation of the quality factor caused by a switched-capacitor array are analytically estimated, and the maximum oscillation frequency of VCOs is also derived from an equivalent circuit by considering parasitic capacitances. According to the analytical evaluation, the phase noise of a VCO using a 65 nm CMOS is 2 dB better than that of a 180 nm CMOS.

A new signature scheme of MPKC is proposed. It is created by perturbing a traditional encryption scheme in two ways. The proposed perturbation polynomials successfully reinforce the Matsumoto-Imai cryptosystem This new signature scheme has a structure very difficult to cryptanalyze. Along with the security against algebraic attacks, its security against existing attacks is discussed. The experimental data imply that the scheme can create a both lightweight and secure signature system.

In differentiated services, packet classification is used to categorize incoming packets into multiple forwarding classes based on pre-defined filters and make information accessible for quality of service. Although numerous algorithms have presented novel data structures to improve the search performance of packet classification, the performance of these algorithms are usually limited by the characteristics of filter databases. In this paper, we use a different approach of filter preprocessing to enhance the search performance of packet classification. Before generating the searchable data structures, we cluster filters in a bottom-up manner. The procedure of the filter clustering merges filters with high degrees of similarity. The experimental results show that the technique of filter clustering could significantly improve the search performance of Pruned Tuple Space Search, a notable hash-based algorithm. As compared to the prominent existing algorithms, our enhanced Pruned Tuple Space Search also has superior performance in terms of speed and space.

For an arbitrary set B of Boolean functions satisfying a certain condition, we give a general method of constructing a class CB of read-once Boolean formulas over the basis B that has the following property: For any F in CB, F can be transformed to an optimal formula (i.e., a simplest formula over the standard basis {AND, OR, NOT}) by replacing each occurrence of a basis function h ∈ B in F with an optimal formula for h. For a particular set of basis functions B* = {AND,OR,NOT,XOR,MUX}, we give a canonical form representation for CB* so that the set of canonical form formulas consists of only NPN-representatives in CB*.

This paper presents a pilot-aided channel estimation method which is particularly suitable for mobile WiMAX 802.16e Downlink Partial Usage of Subchannel mode. Based on this mode, several commonly used channel estimation methods are studied and the method of least squares line fitting is proposed. As data of users are distributed onto permuted clusters of subcarriers in the transmitted OFDMA symbol, the proposed channel estimation method utilizes these advantages to provide better performance than conventional approaches while offering remarkably low complexity in practical implementation. Simulation results with different ITU-channels for mobile environments show that depending on situations, enhancement of 5 dB or more in term of SNR can be achieved.

This paper proposes a cross-layer packet scheduling scheme for QoS support in audio-video transmission with IEEE 802.11e HCCA and assesses application-level QoS and QoE of the scheduling scheme under lossy channel conditions. In the proposed scheme, the access point (AP) basically allocates transmission opportunity (TXOP) for each station in a service interval (SI) like the reference scheduler of the IEEE 802.11e standard, which is referred to as the TGe scheme in this paper. In the proposed scheme, however, the AP calculates the number of MAC service data units (MSDUs) arrived in an SI, considering the inter-arrival time of audio samples and that of video frames, which are referred to as media units (MUs), at the application layer. The AP then gives additional TXOP duration in the SI to stations which had audio or video MAC protocol data units (MPDUs) in their source buffers at the end of the previous TXOP. In addition, utilizing video frame information from the application layer, we propose video frame skipping at the MAC-level of a source station. If a station fails to transmit a video MPDU, it drops all the following video MPDUs in the source buffer until the next intra-coded frame comes to the head of the buffer. We compare the reference scheduler (TGe scheme), the proposed packet scheduling scheme with and without the video frame skipping at the source in terms of application-level QoS and QoE. We discuss the effectiveness of the proposed packet scheduling scheme from a viewpoint of QoE as well as QoS. Numerical results reveal that the proposed packet scheduling scheme can achieve higher quality than the TGe scheme under lossy channel conditions. We also show that the proposed scheduling scheme can improve the QoS and QoE by using the video frame skipping at the source. Furthermore, we also examine the effect of SI on the QoS and QoE of the proposed packet scheduling scheme and obtain that the appropriate value of SI is equal to the inter-arrival time of video frame.

In this paper, we discuss QoE (Quality of Experience) requirements for MVV (Multi-View Video) and audio transmission over IP networks and study the effect of the playout buffering time, contents and viewpoint change interfaces on the QoE and user's behavior. Unlike previous works, which mainly discuss MVV transmission from aspects of video codecs, we study MVV and audio transmission under various IP traffic and delay conditions by experiment. We compare two schemes: a scheme that the user watches from a single viewpoint and the one that he/she can choose one viewpoint from many ones. As a result, we show that the users prefer the scheme where they can choose one viewpoint from many ones. We have found that when using proper buffering time, the users feel faster viewpoint changes; it improves their satisfaction compared to that when they watch on a single viewpoint. We have also noticed that the user pays more attention to the degradation of the video when watching on a single viewpoint. We have observed that the users tend to change the viewpoint more frequently in light traffic and low delay.

In this paper, a novel orthogonal frequency-division multiplexing (OFDM) modulator/demodulator based on real-valued discrete Hartley transform (DHT) is presented and implemented for the IEEE 802.11a/g wireless local area network (LAN). Instead of the conventional complex-valued fast Fourier transform (FFT) for OFDM systems, the proposed architecture employs two real-valued fast DHT (FHT) kernels and one post processing unit. By taking advantage of the real-valued operation of FHT, this approach reduces the number of multiplications compared with the radix-2 FFT. The proposed DHT-based modulator/demodulator was designed and fabricated in 0.18-µm CMOS technology with a core area of 928935 µm2. The average power consumption is about 20.16 mW at 20 MHz and 1.8 V supply voltage. Measurement results of the integrated circuit illustrate its superior chip area and power consumption.

In the area of wireless sensor networks, the efficient spatial query processing based on the locations of sensor nodes is required. Especially, spatial queries on two sensor networks need a distributed spatial join processing among the sensor networks. Because the distributed spatial join processing causes lots of wireless transmissions in accessing sensor nodes of two sensor networks, our goal of this paper is to reduce the wireless transmissions for the energy efficiency of sensor nodes. In this paper, we propose an energy-efficient distributed spatial join algorithm on two heterogeneous sensor networks, which performs in-network spatial join processing. To optimize the in-network processing, we also propose a Grid-based Rectangle tree (GR-tree) and a grid-based approximation function. The GR-tree reduces the wireless transmissions by supporting a distributed spatial search for sensor nodes. The grid-based approximation function reduces the wireless transmissions by reducing the volume of spatial query objects which should be pushed down to sensor nodes. Finally, we compare naive and existing approaches through extensive experiments and clarify our approach's distinguished features.

VoIP service is expected as one of the key applications of Mobile WiMAX, but the speech quality of VoIP service often suffers deterioration due to the fluctuating transmission delay called jitter. This is commonly ameliorated by a de-jitter buffer, and we aim to find the optimal size of de-jitter buffer to achieve speech quality comparable to PSTN. We developed a new model of the packet drops at the de-jitter buffer and the end-to-end packet delay which takes account of the additional delay introduced by the WiMAX power-saving mode. Using our model, we analyzed the optimal size of the de-jitter buffer for various network parameters, and showed that the results obtained by analysis accord with simulation results.

In this paper, it is shown that our fabricated MTJ of 60180 nm2, which is connected to the MOSFET in series by 3 levels via and 3 levels metal line, can dynamically operate with the programming current driven by 0.14 µm CMOSFET. In our measurement of transient characteristic of fabricated MTJ, the pulse current, which is generated by the MOSFET with an applied pulse voltage of 1.5 V to its gate, injected to the fabricated MTJ connected to the MOSFET in series. By using the current measurement technique flowing in MTJ with sampling period of 10 nsec, for the first time, we succeeded in monitor that the transition speed of the resistance change of 60180 nm2 MTJ is less than 30 ns with its programming current of 500 µA and the resistance change of 1.2 kΩ.

We experimentally studied the polarization mode dispersion (PMD) tolerance of an feed-forward equalizer (FFE) electronic dispersion compensation (EDC) IC in the absence of adaptive control, in 43-Gbit/s RZ-DQPSK transmission. Using a 3-tap FFE IC composed of InP HBTs, differential group delay (DGD) tolerance at a 2-dB Q penalty is shown to be extended from 25 ps to up to 29 ps. When a polarization scrambler is used, the tolerance is further extended to 31 ps. This value is close to the tolerance obtained with adaptive control, without a polarization scrambler.

In this paper, we have succeeded in the fabrication of high performance Magnetic Tunnel Junction (MTJ) which is integrated in CMOS circuit with 4-Metal/ 1-poly Gate 0.14 µm CMOS process. We have measured the DC characteristics of the MTJ that is fabricated on via metal of 3rd layer metal line. This MTJ of 60180 nm2 achieves a large change in resistance of 3.52 kΩ (anti-parallel) with TMR ratio of 151% at room temperature, which is large enough for sensing scheme of standard CMOS logic. Furthermore, the write current is 320 µA that can be driven by a standard MOS transistor. As the results, it is shown that the DC performance of our fabricated MTJ integrated in CMOS circuits is very good for our novel spin logic (MTJ-based logic) device.

Due to the development and popularization of high-definition televisions, digital video cameras, Blu-ray discs, digital broadcasting, IP television and so on, it plays an important role to identify and quantify video quality degradations. In this paper, we propose SV-CIELAB which is an objective video quality assessment (VQA) method using a spatio-velocity contrast sensitivity function (SV-CSF). In SV-CIELAB, motion information in videos is effectively utilized for filtering unnecessary information in the spatial frequency domain. As the filter to apply videos, we used the SV-CSF. It is a modulation transfer function of the human visual system, and consists of the relationship among contrast sensitivities, spatial frequencies and velocities of perceived stimuli. In the filtering process, the SV-CSF cannot be directly applied in the spatial frequency domain because spatial coordinate information is required when using velocity information. For filtering by the SV-CSF, we obtain video frames separated in spatial frequency domain. By using velocity information, the separated frames with limited spatial frequencies are weighted by contrast sensitivities in the SV-CSF model. In SV-CIELAB, the criteria are obtained by calculating image differences between filtered original and distorted videos. For the validation of SV-CIELAB, subjective evaluation experiments were conducted. The subjective experimental results were compared with SV-CIELAB and the conventional VQA methods such as CIELAB color difference, Spatial-CIELAB, signal to noise ratio and so on. From the experimental results, it was shown that SV-CIELAB is a more efficient VQA method than the conventional methods.

We have revealed that the electronic states in the electrodes give a significant influence to the electron transport in nano-electronic devices. We have theoretically investigated the time-evolution of electron transport from a two-dimensional electron gas (2DEG) to a quantum dot (QD), where 2DEG represents the electrode in the nano-electronic devices. We clearly showed that the coherent electron transport is remarkably modified depending on the initial electronic state in the 2DEG. The electron transport from the 2DEG to the QD is strongly enhanced, when the initial state of the electron in the 2DEG is localized below the QD. We have proposed that controlling the electronic state in the electrodes could realize a new concept device function without modifying the electrode structures; that achieves a new controllable state in future nano-electronic devices.

Entanglement is expected to play a crucial role in the next-generation quantum communication systems. This paper reviews recent quantum communication experiments over optical fiber using 1.5-µm telecom-band entangled photon pairs. After describing the telecom-band entanglement sources based on spontaneous parametric processes, we review three quantum communication experiments using entangled photons: a long-distance entanglement distribution, an entanglement-based quantum key distribution, and an entanglement swapping.

We try to use a computer algebra system Mathematica as a test case generation system. In test case generation, we generally need to solve equations and inequalities. The main reason why we take Mathematica is because it has a built-in function to solve equations and inequalities. In this paper, we deal with both black-box testing and white-box testing. First, we show two black-box test case generation procedures described in Mathematica. The first one is based on equivalence partitioning. Mathematica explicitly shows a case that test cases do no exist. This is an advantage in using Mathematica. The second procedure is a modification of the first one adopting boundary value analysis. For implementation of boundary value analysis, we give a formalization for it. Next, we show a white-box test case generation procedure. For this purpose, we also give a model for source programs. It is like a control flow graph model. The proposed procedure analyzes a model description of a program.

Differential-phase-shift (DPS) quantum key distribution (QKD) is one scheme of quantum key distribution whose security is based on the quantum nature of lightwave. This protocol features simplicity, a high key creation rate, and robustness against photon-number-splitting attacks. We describe DPS-QKD in this paper, including its setup and operation, eavesdropping against DPS-QKD, system performance, and modified systems to improve the system performance.

Two novel frequency rotation techniques that suppress multipath interference and increase the frequency diversity gain are proposed for uplink IFDMA systems. These benefits are especially important as the performance of traditional IFDMA falls significantly when the number of simultaneous accessing users becomes large. Frequency rotation was originally proposed to suppress the multipath interference and enlarge the frequency diversity gain of downlink access. Unfortunately, it cannot be applied to the uplink due to the loss of orthogonality among users in the frequency domain. In the proposed frequency rotation techniques, users do not share the multiple frequency orthogonal channels and thus orthogonality among users is maintained. The proposed technique is verified by computer simulations.