An efficient quality-of-service MAC protocol for infrastructure WLANs

In this paper, we propose a new efficient MAC protocol, named quality-of-service MAC (QMAC), which is an integrated solution for providing QoS guarantees to real-time multimedia applications in infrastructure WLANs. In addition, QMAC has the following attractive features: (i) its reservation scheme ensures that real-time stations enter the polling list in bounded time, (ii) it supports multiple priority levels and guarantees that high-priority stations always join the polling list earlier than low-priority stations, (iii) it employs the distributed pre-check technique such that the access point can admit as many newly flows as possible, while not violating admitted flows' guarantees, (iv) its dynamic bandwidth allocation scheme provides real-time traffic transmission with per-flow probabilistic bandwidth assurances, and (v) it uses a multipoll frame to poll all stations on the polling list at a time, therefore, the bandwidth can be utilized more efficient. Through simulations, we demonstrate the advantage of our QMAC.     

Nonparametric Identification of a Building Structure from Experimental Data Using Wavelet Neural Network

Abstract:   This study presents a wavelet neural network-based approach to dynamically identifying and modeling a building structure. By combining wavelet decomposition and artificial neural networks (ANN), wavelet neural networks (WNN) are used for solving chaotic signal processing. The basic operations and training method of wavelet neural networks are briefly introduced, since these networks can approximate universal functions. The feasibility of structural behavior modeling and the possibility of structural health monitoring using wavelet neural networks are investigated. The practical application of a wavelet neural network to the structural dynamic modeling of a building frame in shaking tests is considered in an example. Structural acceleration responses under various levels of the strength of the Kobe earthquake were used to train and then test the WNNs. The results reveal that the WNNs not only identify the structural dynamic model, but also can be applied to monitor the health condition of a building structure under strong external excitation.     

Location awareness in ad hoc wireless mobile networks

Networks composed of dynamically repositioning mobile hosts require location awareness to provide new geographic services and to maximize routing efficiency and quality of service. Because wireless networks can operate in a 3D physical environment, exploiting mobile hosts' location information is both natural and inevitable. Emerging geographic services based on mobile ad-hoc networks (manets) must confront several challenges, including how to increase positioning accuracy and how to establish a connection from location information to the vast body of Web data, as in a tour-guide system for example     

Application of m-CNTs/NaClO4/Ppy to a fast response, room working temperature ethanol sensor

A new blended material, m-CNTs/NaClO₄/Ppy, was developed as a gas sensor to detect ethanol concentrations at room temperature. The sensing material polypyrrole (Ppy) was synthesized in situ by UV-photo-polymerization. The multiwall carbon nanotubes (m-CNTs) added enhanced the short-term repeatability of the Ppy-sensing material. The relative resistance variation (R_ethanol/R_air) of m-CNTs/NaClO₄/Ppy was 1.193 when exposed to ethanol of 30,000 ppm. The sensor response and recovery times (both 20 s) were very short to this concentration. An unstable baseline of the sensor was explained by theoretical calculation of molecular dynamics made for ethanol adsorption on polypyrrole, which revealed formation of a new bond, N–HO. Adsorption energy decreased with increasing the number of ethanol molecules adsorbed and was 0.8 kcal/mol at eight adsorbed molecules. Sensor responses of three different Ppy samples were measured to ethanol concentrations of 18,000–40,000 ppm.     

Three-layer 1.3 µm In1-xGaxAsyP1-ylasers with quaternary confining layers

Improvements in the surface morphology of InGaAsP DH wafers were obtained with addition of small amounts of Ga and As in the confining layers. This method was used to improve interface flatness between active and confining layers, consequently improving wafer yield and reproducibility. Three-dimensional lattice-mismatch data of the confining layers were determined in detail using simultaneous multiple Bragg diffraction of X-rays. In all wafers tested, independent of the active layer thickness, the maximum threshold current density Jthwas at most 60 percent higher than Jthminimum. The minimum normalized threshold current density obtained by us-3.4 kA/cm²μmis to our knowledge the lowest reported to date. Low resistance contacts-differential series resistance of 1 to 2 Ω for 10 μm SiO2stripe-geometry contact-can consistently be directly applied to tile top confining layer, thus dispensing with file need of a cap layer. CW operation at room temperature has been achieved with these three-layer devices.     

Route Maintenance in a Wireless Mobile Ad Hoc Network

A mobile ad-hoc network (MANET) is formed by a cluster of mobile hosts, without the infrastructure of base stations. To deal with the dynamic changing topology of a MANET, many routing protocols have been proposed. In this paper, we consider the route maintenance problem, which includes two parts: route deterioration and route breakage. In a MANET, a route may suddenly become broken because only one host roams away. Even if a route remains connected, it may become worse due to host mobility or a better route newly being formed in the system. Existing protocols, however, will stick with a fixed route once it is discovered, until it is expired or broken. In this paper, we show how to enhance several existing protocols with route optimization and local route recovery capability. So the routing paths can be adjusted on-the-fly while they are still being used for delivering packets and can be patched in minimum wireless bandwidth and delay while route errors occur.     

Active Pulse Structural Control Using Artificial Neural Networks

Increasing interest has focused on applying active control systems to civil engineering structures subjected to dynamic loading. This study presents an active pulse control algorithm, termed the adaptive neural structural active pulse (ANSAP) controller, to control civil engineering structures under dynamic loading. The ANSAP controller minimizes structural cumulative responses during earthquakes by applying active pulse control forces. The effect of pulses is assumed to be delayed until just before the next sampling time so that the control force can be calculated in time and applied; the newly developed control strategy circumvents the effect of time delay due to the computation time. The ANSAP controller also circumvents the difficulty of obtaining system parameters of a real structure for the algorithm for active structural control. Illustrative examples reveal significant reductions in cumulative structural responses, which demonstrates the feasibility of using the adaptive artificial network for controlling civil engineering structures under dynamic loading.     

Cell-related location area planning for 4G PCS networks with variable-order Markov model

Location management is a critical issue in personal communication service (PCS) networks, tracking the location of user equipment (UE) with the goal of minimizing total signaling cost. Previous work can be classified into two categories: static and dynamic. Static schemes partition networks into fixed size LAs. However, these schemes are inefficient because they do not take UEs’ mobility and the call arrival rate into account. On the other hand, focusing on individual UEs, dynamic schemes have minimized the location management cost. However, they are difficult to implement because recording the individual information of numerous UEs and planning each of their LAs consume uncontrollable cost. Because of these reasons, we propose a cell-based scheme between static and dynamic schemes. Considering people usually stay in specific zones for long periods and the movement of UEs usually presents a strong moving direction in areas, this study presents a distributed algorithm by employing variable-order Markov models to find the mobility characteristic shared by UEs to plan better LAs with lower location management cost. When the order of Markov model is set to 1, our method is equal to a pure cell-centric LAP scheme; while the order of Markov model is high, it is more like a profile-based dynamic scheme. So, the setting of the order actually is a trade-off problem between the overall location management cost and the computing complexity. We present to retrieve a balance by using the expected location management cost and the number of total states of Markov models. In simulations, the origin–destination matrix (O–D matrix) from the Taipei Rapid Transit Corporation is used for representing the association between two cells. Simulation results demonstrate that the proposed scheme achieves good performance.     

A Priority MAC Protocol to Support Real-Time Traffic in Ad Hoc Networks

Carrier sense multiple access and its variants have been widely used in mobile ad hoc networks. However, most existing access mechanisms cannot guarantee quality for real-time traffic. This paper presents a distributed medium access control protocol that provides multiple priority levels for stations to compete for the wireless channel. One common channel is assumed to be shared by all stations. Stations are assumed to be able to hear each other (i.e., the network is fully connected). The channel is accessed by stations according to their priorities, and for stations with the same priority, they send frames in a round robin manner. The channel access procedure is divided into three stages: priorities classification period, ID initialization period, and transmission period. Simulation results indicate that our protocol provides high channel utilization and bounded delays for real-time frames.