To meet users' multi-service requests under dynamic and heterogenous environment with high-assurance, the Autonomous Network-Based Integration System based on Faded Information Field (FIF) has been proposed, which permits to actively integrate the correlated information services according to the current situation of the system. However, the increase in the total number of users' requests and changes in users' preferences cause the unbalancing load in the system and the overload in the locality. In this paper, based on the autonomous access distribution in the locality, a new approach of autonomous correlated services access is proposed to reduce the load of the system and achieve the adaptability and timeliness of correlated services utilization. We proved the effectiveness of the proposed technology through the simulation and the results show that the system can improve the average response time not only for joint requests of correlated services, but also for separate requests of each service under changing environments.

Wireless sensor networks are expected to play an essential role as a social infrastructure to realize our safe and secure living environment. In such a network, critical information must be transmitted faster and more reliably than other information. We propose a distributed transmission mechanism which enables emergency packets to be carried with high reliability and low latency along a preferential path, which is called an "assured corridor." In this self-organizing assured corridor mechanism (ACM), which works above the network layer and does not depend on any specific routing or MAC protocol, a corridor is gradually established as the first packet containing urgent information propagates to the base station. The nodes surrounding the corridor suppress the transmission of non-urgent information and nodes in the corridor are kept awake to forward emergency packets. ACM avoids packet loss and possible delay caused by collisions in the wireless transmission and normal sleep scheduling. An acknowledgment and retransmission scheme is incorporated into ACM in order to improve reliability of transmission of urgent information. Simulation experiments showed that, when only one node transmitted urgent information, the retransmission contributed to establish a corridor quickly and that ACM improved the delivery ratio and the delay of the urgent information transmission once a corridor is established. It was proved that ACM was effective to improve the reliability and the latency of urgent information as well in the cases where multiple nodes sent urgent information at once.

Many handover techniques in the Internet have been introduced with the development of mobile computing technologies. Although many proposed handover schemes utilize multiple wireless interfaces, having multiple wireless interfaces in a mobile device increases its power consumption, device installation space, and hardware costs. We have been studying handover schemes for mobile nodes with a single wireless interface. To achieve seamless and efficient handover, we focus on Stream Control Transmission Protocol (SCTP) that offers a message-oriented, reliable and connection-oriented delivery transport service. Unlike other transport protocols like TCP, SCTP can provide an end-to-end handover mechanism with multi-homing feature. However, the handover mechanism in the current SCTP causes large handover latency particularly when a mobile node has only one single wireless interface. This paper investigates the current issues of the SCTP handover mechanism, and proposes a new efficient handover scheme based on SCTP, which identifies a communication path as a pair of source and destination address. Additionally, we modified SCTP behavior when an SCTP endpoint received a SET PRIMARY message to change primary destination of peer endpoint. This paper shows that our scheme can reduce the handover latency by two to thirty seconds.

Orthogonal frequency division multiplexing (OFDM) systems for mobile applications suffer from inter-carrier-interference (ICI) due to frequency offset and to time-variation of the channels and from high peak-to-average-power ratio (PAPR). In this paper, we revisit symmetric cancellation coding (SCC) proposed by Sathananthan et al. and compare the effectiveness of SCC with a fixed subtraction combining and the well-known polynomial cancellation coding (PCC) over Rayleigh fading channels with Doppler spread in terms of the signal-to-interference plus noise power ratio (SINR) and bit-error-rate (BER). We also compare SCC with subtraction combining and SCC of Sathananthan et al. with maximum ratio combining (MRC). Our results show that SCC-OFDM with subtraction combining gives higher SINR than PCC-OFDM over the flat Rayleigh fading channel and that this superiority is not maintained under multi-path induced frequency-selective fading unless diversity combining is used. A simulation result shows, however, that SCC-OFDM with subtraction combining may perform better than PCC-OFDM for a certain range of Doppler spread when differential modulation is employed. Finally, we also demonstrate that the SCC-OFDM signal has less PAPR compared to the normal OFDM and PCC-OFDM and hence may be more practical.

In recent years, wireless communications systems such as wireless LAN, Bluetooth, etc. are being rapidly adopted. As the antennas used in wireless communications systems are usually installed in small mobile devices, it is demanded that the volume should be small. In our research, we focus our attention on flexible printed circuits (FPCs) to meet the miniaturization demand. In this paper, we introduce a planar inverted F antenna (PIFA) suitable for IEEE802.11b/g and Bluetooth. The antenna is made of FPC. We measured the radiation pattern of the antenna when the antenna is successively curved and folded, and it is clear that its radiation performance does not vary much when the antenna is deformed. We analyzed the antenna by using the moment method.

The electric fields inside and outside a car must be carefully determined when designing a wireless communication system to be employed in the car. This paper introduces an effective simulation method and a precise measurement method of electric field distributions in a cabin of a simplified scale car model. A 1/3 car model is employed for ease of measurement. The scaled frequency of 2859 MHz, 3 times 953 MHz, is employed. The use of a moment method simulator utilizing the multilevel fast multipole method allows calculations to be performed on a personal computer. In order to judge the accuracy of simulation results, convergence of simulation output in accordance with segment size (triangle edge length) changes is ensured. Simulation loads in the case of metallic body only and a metallic body with window glass are also shown. In the measurements, an optical electric field probe is employed so as to minimize the disturbances that would otherwise be caused by metallic feed cable; precise measurement results are obtained. Comparisons of measured and simulated results demonstrate very good agreement which confirms the accuracy of the calculated results. 3-dimensional electric field distributions in the car model are shown and 3-dimensional standing wave shapes are clarified. Moreover, calculated and measured radiation patterns of the car model are shown so the total electric field distributions around a car are clarified.

In the 300 MHz to 3 GHz range, probes used to measure specific absorption rate (SAR) of mobile communication devices are usually calibrated using a rectangular waveguide filled with tissue-equivalent liquid. Above 3 GHz, however, this conventional calibration can be inaccurate because the diameter of the probe is comparable to the cross-sectional dimension of the waveguide. Therefore, an alternative method of SAR probe calibration based on another principle was needed and has been developed by the authors. In the proposed calibration method, the gain of the reference antenna in the liquid is first evaluated using the two-antenna method based on the Friis transmission formula in the conducting medium. Then the electric field intensity radiated by the reference antenna is related to the output voltage of the SAR probe at a given point in the liquid. However, the fields are significantly reduced in the liquid, and the gain is impossible to calibrate in the far-field region. To overcome this difficulty, the Friis transmission formula in the conducting medium must be extended to the near-field region. Here, we report results of simulations and experiments on estimated gain based on the extended Friis transmission formula, which holds in the near-field region, and test the validity of the new formula.

In order to support driving safety, TPMS (Tire Pressure Monitoring System) has been introduced in U.S.A. and Europe. In Japan, the AIRwatch system has been developed and commercialized. Some studies were made to clarify the electric field environment of this system. However, no detailed calculation of the electric field between the transmitter in the tire and the receiving antenna has been published. This paper clarifies the electric field environment of the Japanese system through electromagnetic simulations by a high performance MoM simulator that utilizes the MLFMM scheme. First of all, electric wave emissions from an antenna mounted in a tire are shown to be larger than that of the same antenna in free space. The tire rubber effects are also investigated. Next, electric field distributions on the windshield holding the receiving antenna are calculated. By comparing calculated electric field levels with those in the free space condition, car body interruptions are clarified. Because car body interruptions are not so severe, it is shown that the free space electric field levels can be used as rough design parameters. Moreover, electric field changes due to tire rotation are also clarified. Calculation accuracy is confirmed by the good agreement with measured data collected from a 1/5 scale car model. To permit estimations to be made in actual situations, the effects of the ground are also investigated. This simulation study introduces a lot of important data useful in TPMS system design.

This paper proposes a new binary motion estimation algorithm that improves the motion vector accuracy by using a hybrid distortion measure. Unlike conventional binary motion estimation algorithms, the proposed algorithm considers the sum of absolute difference (SAD) as well as the sum of bit-wise difference (SBD) as a block-matching criterion. In order to reduce the computational complexity and remove additional memory accesses, a new scheme is used for SAD calculation. This scheme uses 8-bit data of the lowest layer already moved into the local buffer to calculate the SAD of other higher binary layer. Experimental results show that the proposed algorithm finds more accurate motion vectors and removes the blockishness of the reconstructed video effectively. We applied this algorithm to existing video encoder and obtained noticeable visual quality enhancement.

We introduce a novel configuration for a multi-user Multiple-Input Multiple-Output (MIMO) system in mobile communication over fast fading channels using space-time block coding (STBC) and adaptive array. The proposed scheme adopts the simultaneous transmission of data and pilot signals which reduces control errors caused by delay of obtaining channel state information (CSI). Data and pilot signals are then encoded using a space-time block code and are transmitted from two transmit antennas. In order to overcome the fast fading problem, implementation of adaptive array using recursive least squares (RLS) algorithms is considered at the base station. Through computer simulation, it is shown that the proposed scheme in this way can overcome Doppler spread in higher frequencies and suppress co-channel interference up to N-1 users for N receiving antennas.

Self-Clocked Fair Queueing (SCFQ) and Credit-Based Fair Queueing (CBFQ) are well-known fair scheduling schemes for packet-switched network. In this paper, it is shown that SCFQ and CBFQ are equivalent in selecting packets to transmit. For this, we modified the per-packet service tag based SCFQ algorithm to an equivalent per-session service tag based algorithm, SCFQ+, and showed that the service tags for SCFQ+ and CBFQ evolve identically.

This paper presents an approximation method of statistical distribution of the largest eigenvalue of i.i.d. (independent and identically distributed) MIMO (multiple input multiple output) channel correlation matrices under Nakagami-Rice fading environment. The equation is actually derived for MIMO Nakagami m fading channel which is known as a good approximation of Nakagami-Rice fading, hence it well approximates the curves of the largest eigenvalue distribution of noncentral Wishart matrices. In the proposed approximation method, MIMO MRC (maximal ratio combining) system is ascribed to SIMO space diversity theory with the same number of branches, and the statistical distribution becomes a monomial gamma distribution. As a result, the derived marginal density function does not contain any special functions, and has a simple monomial gamma form which is suitable for various calculations of performance indices. Through computer simulations, it is shown that the proposed approximation formula is effective and has a better precision than conventional method.

In order to realize a higher density version of the conventional optical disk, shorter wavelength laser and narrower track pitch have been put to practical use. However, using narrow track pitch can cause the increase of the crosstalk from the adjacent tracks. Moreover, the use of narrow pitch and short wavelength can also give rise to the increase of deterioration of the detected signal characteristics due to the microscopic roughness of disk surface. In this paper, in order to estimate the effect of surface roughness theoretically, we try to analyze the light-beam scattering and detected signal characteristics of a blue laser optical disk model with random rough surfaces by the Finite Difference Time Domain (FDTD) method.

Recently, space-time block codes (STBCs) obtained from coordinate interleaved orthogonal designs (CIODs) have attracted considerable attention, due to the advantages of full-diversity transmission and single-symbol decodability. In this letter, we design a novel STBC from CIOD for two transmit antennas. The proposed code guarantees full-diversity and full-rate along with low peak-to-minimum power ratio (PMPR). Furthermore, in contrast to the existing Alamouti code, the performance of the proposed code is not degraded even in severely time-selective fading channels.

This paper proposes probabilistic pruning techniques for a Bayesian video face recognition system. The system selects the most probable face model using model posterior distributions, which can be calculated using a Sequential Monte Carlo (SMC) method. A combination of two new pruning schemes at the resampling stage significantly boosts computational efficiency by comparison with the original online learning algorithm. Experimental results demonstrate that this approach achieves better performance in terms of both processing time and ID error rate than a contrasting approach with a temporal decay scheme.

In this paper, we discuss the relationship between the test generation complexity for path delay faults (PDFs) and that for stuck-at faults (SAFs) in combinational and sequential circuits using the recently introduced τk-notation. On the other hand, we also introduce a class of cyclic sequential circuits that are easily testable, namely two-column distributive state-shiftable finite state machine realizations (2CD-SSFSM). Then, we discuss the relevant conjectures and unsolved problems related to the test generation for sequential circuits with PDFs under different clock schemes and test generation models.

This paper reports an efficient Discrete Cosine Transform (DCT) processing method for images using a massive-parallel memory-embedded SIMD matrix processor. The matrix-processing engine has 2,048 2-bit processing elements, which are connected by a flexible switching network, and supports 2-bit 2,048-way bit-serial and word-parallel operations with a single command. For compatibility with this matrix-processing architecture, the conventional DCT algorithm has been improved in arithmetic order and the vertical/horizontal-space 1 Dimensional (1D)-DCT processing has been further developed. Evaluation results of the matrix-engine-based DCT processing show that the necessary clock cycles per image block can be reduced by 87% in comprison to a conventional DSP architecture. The determined performances in MOPS and MOPS/mm2 are factors 8 and 5.6 better than with a conventional DSP, respectively.

Bandwidth management over wired bottleneck links has been an effective way to utilize network resources. For the rapidly emerging IEEE 802.11b Wireless LAN (WLAN), the limited WLAN bandwidth becomes a new bottleneck and requires bandwidth management. Most possible existing solutions only exclusively focus on optimizing multimedia traffic, pure downlink or pure uplink fairness, or are incompatible with IEEE 802.11b. This study proposes a cooperative deficit round robin (co-DRR), an IEEE 802.11b-compatible host-based fair scheduling algorithm based on the deficit round robin (DRR) and distributed-DRR (DDRR) schemes, to make the uplink and downlink quantum calculations cooperate to simultaneously control uplink and downlink bandwidth. Co-DRR uses the standard PCF mode to utilize the contention-free period to compensate for the unfairness in the contention period. Numerical results demonstrate that: co-DRR can scale up to 100 mobile hosts even under high bit error rate (0.0001) while simultaneously achieving uplink/downlink long-term fairness (CoV<0.01) among competing mobile hosts.

Probability distribution of the node degree has long been regarded as one of the important metrics to characterize the wireless ad hoc networks. However, there is no exact formulation for this probability distribution when shadow fading effects are considered. In this letter, by deriving the conditional probability of the node degree and the joint distribution of the distances between nodes and a randomly selected reference node (RSRN), we show that the probability distribution of the node degree for the wireless ad hoc networks in the shadow fading environments is binomial.

A precise analysis of the capacity of a wireless downlink packet data system with a fair scheduler is presented. We assume the use of a transmit diversity scheme is operating at each link under the assumption of spatially correlated Rayleigh fading. Numerical results show that spatial fading correlation of the channel improves the capacity of multiuser diversity by reducing the space diversity gain of transmit diversity in each link.