This paper describes the Differential Pass Transistor Pulsed Latch (DPTPL) which enhances D-Q delay and reduce power consumption using NMOS pass transistors and feedback PMOS transistors. The proposed flip-flop uses the characteristic of stronger drivability of NMOS transistor than that of transmission gate if the sum of total transistor width is the same. Positive feedback PMOS transistors enhance the speed of the latch as well as guarantee the full-swing of internal nodes. Also, the power consumption of proposed pulsed latch is reduced significantly due to the reduced clock load and smaller total transistor width compared to conventional differential flip-flops. DPTPL reduces ED by 45.5% over ep-SFF. The simulations were performed in a 0.1 µm CMOS technology at 1.2 V supply voltage with 1.25 GHz clock frequency.

In wireless local area networks (WLANs), the necessity of quality-of-service (QoS) control for uplink flows is increasing because interactive applications are becoming more popular. Fairness between flows transmitted by stations with different physical transmission rates must be ensured in QoS control for link-adaptive WLANs, which are widely used nowadays. We propose a novel distributed access scheme called QC-DCA to satisfy these requirements. QC-DCA adaptively controls the parameters of carrier sense multiple access with collision avoidance (CSMA/CA). QC-DCA has two QoS control functions: guarantee and classification. QC-DCA guarantees target throughputs and packet delays by quickly adjusting CSMA/CA parameters. In QoS classification, the difference of throughputs and packet delays between different QoS classes is maintained. These two functions allow QC-DCA to suppress the unfairness caused by differences of transmission rates in the physical layer. We evaluated the throughput and delay performances of our scheme using computer simulations. The results show the viability of our scheme.

In this study, we achieved predictable control of a wheelchair by changing the existing mapping method of the joystick, which considers the consecutive operations of a motor of a wheelchair, to a new mapping method that corresponds to the internal model of a human being. Since the existing method uses the polar coordinate system, it is not easy at all to use this method to predict either the direction of motion or the operating order for changing the position of the wheelchair according to the requirements of an operator. In order to improve the embodiment, we divided the existing joystick mapping method into two degrees of freedom-one in the vertical axis that can control the velocity and the other, in the horizontal axis for direction control. Based on this division, we implemented a wheelchair model that can be controlled by the electromyography (EMG) signal from the neck and the arm muscles of an operator. This was achieved by mapping the divided degrees of freedom onto the degrees of freedom of the neck and arm of the operator. In this case, since the operator controls the direction of motion by the joint of his/her neck, he/she can move the wheelchair in the desired direction; thus, a more intuitive human interface is implemented.

The concept of M-convex functions has recently been generalized for functions defined on constant-parity jump systems. The b-matching problem and its generalization provide canonical examples of M-convex functions on jump systems. In this paper, we propose a steepest descent algorithm for minimizing an M-convex function on a constant-parity jump system.

Recently, voice over WLAN has become an attractive service, and it is expected to be the most popular application in the near future due to its low cost and easy deployment. It has been reported that there occurs unfairness between downlink and uplink in the 802.11 WLAN. This is mainly caused by CSMA/CA employed in DCF. All stations including an AP fairly compete for shared wireless medium. Thus, in particular, the unfairness has an adverse impact on bi-directional voice calls. Downlink voice connections become a primary factor to limit voice capacity. In this paper, we propose a novel medium access protocol, so called DCFmm, in order to improve QoS of downlink voice traffic as well as fairness between bi-directional voice connections. DCFmm is designed to enhance 802.11 DCF, and is fully compatible with the legacy DCF. In addition, it requires only protocol modifications of an AP. Thus, it can be easily implemented into existing 802.11 WLANs. DCFmm is compared with two conventional techniques through computer simulations. Extensive simulation results show that the proposed DCFmm can improve fairness between downlink and uplink, and consequently, support larger number of voice calls than DCF.

In this paper, we study the feedback vertex set problem for trivalent Cayley graphs, and construct a minimum feedback vertex set in trivalent Cayley graphs using the result on cube-connected cycles and the Cayley graph representation of trivalent Cayley graphs.

A linkage is a collection of line segments, called bars, possibly joined at their ends, called joints. We consider flattening a tree-like linkage, that is, a continuous motion of their bars from an initial configuration to a final configuration looking like a"straight line segment," preserving the length of each bar and not crossing any two bars. In this paper, we introduce a new class of linkages, called "radial trees," and show that there exists a radial tree which cannot be flattened.

Content-based image search has long been considered a difficult task. Making correct conjectures on the user intention (perception) based on the query images is a critical step in the content-based search. One key concept in this paper is how we find the user preferred low-level image characteristics from the multiple positive samples provided by the user. The second key concept is how we generate a set of consistent "pseudo images" when the user does not provide a sufficient number of samples. The notion of image feature stability is thus introduced. The third key concept is how we use negative images as pruning criterion. In realizing the preceding concepts, an image search scheme is developed using the weighted low-level image features. At the end, quantitative simulation results are used to show the effectiveness of these concepts.

In this paper, we propose a new localization scheme for wireless sensor networks consisting of a huge number of sensor nodes equipped with simple wireless communication devices such as wireless LAN and Bluetooth. The proposed scheme is based on the Point-In-Triangle (PIT) test proposed by He et al. The scheme is actually implemented by using Bluetooth devices of Class 2 standard, and the performance of the scheme is evaluated in an actual environment. The result of experiments indicates that the proposed scheme could realize a localization with an error of less than 2 m.

In this letter we consider topology control and routing problem in wireless networks where equipped with point-to-point wireless links such as directional antennas or free space optics. In point-to-point wireless networks, each node has a limited number of transceivers and hence can communicate with only a limited number of nodes within its transmission range. The selection of the limited number of neighbors is very critical for the network performance. In this letter, we propose a topology control algorithms which consider the topology control and routing of each demand is considered simultaneously. For this, we introduce the degree constraint shortest path problem for finding optimal (shortest) paths in wireless point-to-point networks. Also, we propose two topology control algorithms: minimum hop (MHA) and resource availability ratio (RAR) algorithm. The resource availability ratio algorithm considers not only the available link bandwidth but also the available interfaces between neighbors. By simulation experiments, we compare the performance of each algorithm.

The recent burst growth of the Internet use overloads networking systems and degrades the quality of communications, e.g., bandwidth loss, packet drops, delay of responses, etc. To overcome such degradation of communication quality, the notion of Quality of Service (QoS) has received attention in practice. In general, QoS switches have several queues and each queue has several slots to store arriving packets. Since network traffic changes frequently, QoS switches need to control arriving packets to maximize the total priorities of transmitted packets, where the priorities are given by nonnegative values and correspond to the quality of service required to each packet. In this paper, we first derive the upper bounds for the competitive ratio of multi-queue preemptive QoS problem with priority between 1/α and 1, i.e., for any α ≥ 1, the algorithm TLH is (3-1/α)-competitive. This is a generalization of known results--for the case that packets have only priority 1 (α =1), the algorithm GREEDY (or TLH) is 2-competitive; for the case that packets have priorities between 0 and 1 (α = ∞), the algorithm TLH is 3-competitive. Then we consider the lower bounds for the competitive ratio of multi-queue preemptive QoS problem with priority between 0 and 1, and show that the competitive ratio of any multi-queue preemptive QoS algorithm is at least 1.514.

In STS-based mapping, it is necessary to obtain the correct order of probes in a DNA sequence from a given set of fragments or an equivalently a hybridization matrix A. It is well-known that the problem is formulated as the combinatorial problem of obtaining a permutation of A's columns so that the resulting matrix has a consecutive-one property. If the data (the hybridization matrix) is error free and includes enough information, then the above column order uniquely determines the correct order of the probes. Unfortunately this does not hold if the data include errors, and this has been a popular research target in computational biology. Even if there is no error, ambiguities in the probe order may still remain. This in fact happens because of the lack of some information regarding the data, but almost no further investigation has previously been made. In this paper, we define a measure of such imperfectness of the data as the minimum amount of the additional fragments that are needed to uniquely fix the probe order. Polynomial-time algorithms to compute such additional fragments of the minimum cost are presented. A computer simulation using genes of human chromosome 20 is also noted.

This letter presents a simple but accurate analytical model to evaluate the throughput of IEEE 802.11 distributed coordination function in non-saturated conditions. The influence of offered load on the throughput of both basic and RTS/CTS access mechanisms are analyzed and compared. It's shown that basic access scheme can achieve the same maximal throughput as that of RTS/CTS mechanism in non-saturated conditions while the latter is robust to the number of contending stations compared to basic mechanism. The analytical results are validated by extensive simulations.

We theoretically analyze the performance of coherent ultrashort light pulse code-division multiple-access (CDMA) communication systems with a nonlinear optical thresholder. The coherent ultrashort light pulse CDMA is a promising system for an optical local area network (LAN) due to its advantages of asynchronous transmission, high information security, multiple access capability, and optical processing. The nonlinear optical thresholder is based on frequency chirping induced by self-phase modulation (SPM) in optical fiber, and discriminates an ultrashort pulse from multiple access interference (MAI) with picosecond duration. The numerical results show that the thermal noise caused in a photodetector dominates the bit error rate (BER). BER decreases as the fiber length in the nonlinear thresholder and the photocurrent difference in the photodetector increase. Using the nonlinear optical thresholder allows for the response time of the photodetector to be at least 100 times the duration of the ultrashort pulses. We also show that the optimum cut-off frequency at the nonlinear thresholder to achieve the minimum BER increases with fiber length, the total number of users, and the load resistance in the photodetector.

Genetic Algorithm (GA) and other Evolutionary Algorithms (EAs) have been successfully applied to solve constrained minimum spanning tree (MST) problems of the communication network design and also have been used extensively in a wide variety of communication network design problems. Choosing an appropriate representation of candidate solutions to the problem is the essential issue for applying GAs to solve real world network design problems, since the encoding and the interaction of the encoding with the crossover and mutation operators have strongly influence on the success of GAs. In this paper, we investigate a new encoding crossover and mutation operators on the performance of GAs to design of minimum spanning tree problem. Based on the performance analysis of these encoding methods in GAs, we improve predecessor-based encoding, in which initialization depends on an underlying random spanning-tree algorithm. The proposed crossover and mutation operators offer locality, heritability, and computational efficiency. We compare with the approach to others that encode candidate spanning trees via the Pr?fer number-based encoding, edge set-based encoding, and demonstrate better results on larger instances for the communication spanning tree design problems.

The Public Wireless Local Area Network (PWLAN) is an emerging service for wireless access to the Internet. However, the service coverage of the PWLAN is limited by the deployment of access points (APs) because only those who stay near the AP can access the PWLAN. A feasible way of extending the service coverage of a PWLAN is to deploy mobile ad hoc access networks (MAHANs) so that users who are not in an AP's radio coverage area can send their packets to the AP in a multihop manner. However, in a MAHAN, mobile nodes that intend to access the Internet have to discover routes to the AP first, which may result in considerable bandwidth cost. In this paper, we propose the Appointed BrOadcast (ABO) method to reduce the cost of route discovery in MAHANs. Using the ABO method can achieve this goal on the basis of packet overhearing. Functions that are necessary for network and data link layers to employ the ABO method are also discussed. Simulation results show that using the ABO method can significantly reduce the cost on route discoveries. Due to the widespread use of legacy IEEE 802.11 nodes, the problem of how ABO-enhanced and legacy IEEE 802.11 nodes can coexist in a MAHAN is also discussed.

An RF adaptive array antenna (RF-AAA) configured with variable capacitors is proposed. This antenna system can control the power combining ratio and phase value of received signals. In this paper, we focus on the diversity effects of RF-AAA. First, we show the design methodology of the combiner circuit to realize the effective combining. Second, the perturbation method and the steepest gradient method are compared for the optimization algorithms to provide fast convergence and suboptimum solutions among the variable circuit constants. Finally, in simulation, we show the RF-AAA can achieve diversity antenna gains of 7.7 dB, 10.9 dB and 12.6 dB for 2-branch, 3-branch and 4-branch configuration, respectively, which have higher performance than the selection combining.

The modeling of gate delays has always been one of the most difficult and market-sensitive works. In submicron designs, the second-order effects such as the input-to-output coupling capacitance have a significant influence on gate delay as shown in this paper. However, the accurate analysis of the input-to-output coupling capacitance effect has not been presented in previous research. In this paper, an analytical model for the influence of the input-to-output coupling capacitance on CMOS inverter delay is proposed, in which a novel algorithm for computing overshooting time is given. Experimental results show good agreement with Spice simulations.

This paper concerns the design, implementation and subsequent experimental validation of a low-voltage analog CMOS switch based on a gate-bootstrapped method. The main part of the proposed circuit is a new low-voltage and low-stress CMOS clock voltage doubler. Through the use of a dummy switch, the charge injection induced by the bootstrapped switch is greatly reduced resulting in improved sample-and-hold accuracy. An important attribute of the design is that the ON-resistance is nearly constant. A test chip has been designed and fabricated using a TSMC 0.18 µm CMOS process (single poly, n-well) to confirm the operation of the circuit for a supply voltage of down to 0.65 V.

IEEE 802.11 DCF is a contention-based channel access protocol, and medium access delay greatly increases as the number of contending stations in a service area increases. This severely affects on delay-sensitive video applications. In this paper, we focus on MAC-layer solutions for realizing high quality video transmission in 802.11 DCF networks. A new channel access protocol based on the timestamp (TS) of video packets is proposed for real-time video. The TS information is carried by RTP header from the video application to 802.11 MAC. For video packets with the same RTP TS, they are simultaneously transmitted in a single channel access. Additional contention and back-off processes can be avoided because the whole packets of a video frame are completely delivered. The proposed TS-based access protocol can be easily implemented by the DCF with packet bursting. In addition, it is backward compatible to the legacy DCF. Extensive simulations show that the TS-based channel access achieves lower cumulative distributions of application-level video frame delay when compared to the DCF protocol.