1,721,138 research outputs found
A fast rerouting scheme using reservation in wireless ATM
No full textWith growing demand for higher bandwidth multimedia services in the wireless domain over the past few years, wireless asynchronous transfer mode (ATM) has emerged as a fine solution. Wireless ATM provides mobility support for mobile ATM users as they move among base stations. One of the key issues to support user mobility is the handoff. For a relatively smaller cell environment in wireless ATM, a handoff scheme should exhibit low handoff delay. Efficient usage of network resources is also required. In this paper, we propose a fast rerouting scheme for wireless ATM referred to as a path reservation scheme. For localized handoffs, we adopt a wireless cell clustering method. Cell grouping and a path reservation technique are proposed to achieve fast handoffs. This paper presents an analysis of the proposed scheme and simulation results of several handoff schemes compared with the proposed scheme. From the simulation results, our path reservation scheme achieves low handoff delay and efficient usage of network resources such as buffer and bandwidth requirements
A FAST NEWTON/LMS ALGORITHM
No full textA fast Newton/LMS algorithm is proposed which uses an efficient inversion technique of input autocorrelation matrix when the periodic pseudo random sequence is used as the reference signal. The number of operations is greatly reduced and the computational results show fast convergence rate and low misadjustment error. And the application of the algorithm to the case of nonperiodic reference signal is described
REVERSED ABSORBING MARKOV-CHAIN - A SAMPLE PATH APPROACH
No full textWe present a sample path based approach for analyzing the time-reversed discrete-time finite-state absorbing Markov chain
A highly sensitive bolometer structure with an electrostatic-actuated signal bridge
No full textA novel bolometer structure has been proposed to achieve high detectivity. The detectivity is inversely proportional to the thermal conductance, of a bolometer, and most of the thermal conductance is due to a metal wire, the placement of which is necessary for the reading of a signal. However, the thermal conductance of the proposed bolometer was unaffected by the thermal conductance of a metal wire. This is because a movable signal bridge was employed to lower the thermal conductance, thereby yielding a thermal conductance of 4.13 x 10(-8) W/K. A measured detectivity of up to 4.23 x 10(9) cm . Hz(1/2)/W was attained at room temperature
NEWTON/LMS ALGORITHM USING MODIFIED DCT
No full textA Newton/LMS algorithm using a modified DCT is proposed which uses an efficient technique of inverting the input autocorrelation matrix when the periodic pseudorandom sequence is used as the reference signal. The number of operations is greatly reduced and the computational results show fast convergence rate and low misadjustment error. The application of the algorithm to the case of nonperiodic reference signal is also described
Mobility and traffic analyses in three-dimensional PCS environments
No full textWe need to solve various mobility/traffic problems in one-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) micro or picocell environments to efficiently plan future personal communications services (PCS's), However, mobility/traffic problems have thus far primarily been studied in 1-D and 2-D cell structures. In this paper, we extend the previous mobility modeling from 1-D or 2-D space to 3-D unbounded indoor building environments having staircase regions by analytically modeling mobility to estimate the number of handoffs, We also characterize the blocking probability of each cell according to mobility by predicting the equivalent input traffic per cell. Based on the blocking probability model, we obtain the required number of channels per cell under the given blocking probability constraint, For example, 13 channels per cell are required to be assigned in order to meet the requirement that the blocking probability does not exceed 0.02 in the case where the number of radio ports (RP's) (cells) is four and 180 users are moving with the mean 2 km/h (horizontal motion) and 2/3 km/h (vertical motion) on each floor. The computer simulation results are also close to the analytical ones. These results can be utilized in the network planning of future PCS's
Bit-error probabilities of multicode direct-sequence spread-spectrum multiple-access systems
No full textMany techniques for calculating bit-error probabilities (BEPs) of direct-sequence spread-spectrum multiple-access systems (DS-SSMA) have been reported, Among them are the following three techniques: 1) the standard Gaussian approximation; 2) the improved Gaussian approximation; 3) and the simplified improved Gaussian approximation. We extend these techniques to derive the BEPs of multicode DS-SSMA systems. We assess the three techniques by comparing their results with the result of computer simulation
Mobility modeling and traffic analysis in three-dimensional high-rise building environments
No full textTo efficiently plan future personal communications services, we need to solve various mobility/traffic problems in one dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) micro- or pico-cell environments. Although many users exhibit vertical motion inside elevators in high-rise buildings, there have been no studies regarding cell planning which take into account vertical motion with elevators, In this paper, we extend the previous 3-D indoor mobility modeling by considering the proper boundary conditions on each floor and vertical motions through elevators and modeling mobility in high-rise buildings in order to estimate the number of handoffs, We then propose a blocking probability model with mobility as a traffic model in 3-D indoor environments, Using this model, we can obtain the required number of channels per cell under the given blocking probability constraint. These results can be used in planning the networks of future personal communications services
Moving elevator-cell system in indoor buildings
No full textTo plan efficient future PCS networks, indoor environments as well as outdoor environments must be considered. Users typically exhibit vertical motion through elevators and horizontal motion on building floors in indoor environments. A user on the way into or out of an elevator may experience difficulty in communicating with a base station (BS) due to large signal attenuation caused by the metal structure of the elevator, especially the door. The user also may suffer From handoffs as the user passes several floors during the course of a call as the elevator moves. It is necessary to overcome these problems related to elevators for indoor cell planning, In this paper, a nonmoving and two moving elevator-cell systems for a building are considered. The undesirable inter-floor handoffs while the user Is inside the elevator of the nonmoving elevator-cell system (N-system) are eliminated by introduction of two moving elevator-cell systems: a simple moving elevator-cell system (S-system) and a proposed moving elevator-cell system (P-system), The S-system does not seamlessly maintain calls between an elevator and adjacent floors due to insufficient time when the elevator is open to complete the handoff, while the P-system seamlessly maintains calls using a macro diversity with a distributed antenna scheme. The movements of an elevator and users are modeled and the P-system is compared with the S-system in terms of the required number of channels. The P-system reduces the total required number of channels compared with the S-system under heavy traffic conditions. The elevator-cell system and modeling results can be used in the design of future indoor wireless systems
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