Performance analysis of contention based bandwidth request mechanisms in WiMAX networks

This article is posted here with the permission of IEEE. The official version can be obtained from the DOI below - Copyright @ 2010 IEEEWiMAX networks have received wide attention as they support high data rate access and amazing ubiquitous connectivity with great quality-of-service (QoS) capabilities. In order to support QoS, bandwidth request (BW-REQ) mechanisms are suggested in the WiMAX standard for resource reservation, in which subscriber stations send BW-REQs to a base station which can grant or reject the requests according to the available radio resources. In this paper we propose a new analytical model for the performance analysis of various contention based bandwidth request mechanisms, including grouping and no-grouping schemes, as suggested in the WiMAX standard. Our analytical model covers both unsaturated and saturated traffic load conditions in both error-free and error-prone wireless channels. The accuracy of this model is verified by various simulation results. Our results show that the grouping mechanism outperforms the no-grouping mechanism when the system load is high, but it is not preferable when the system load is light. The channel noise degrades the performance of both throughput and delay.This work was supported by the U.K. Engineering and Physical Sciences Research Council (EPSRC) under Grant EP/G070350/1 and by the Brunel University’s BRIEF Award

Carrier-envelope phase dependence in single-cycle laser pulse propagation with the inclusion of counter-rotating terms

We focus on the propagation properties of a single-cycle laser pulse through a two-level medium by numerically solving the full-wave Maxwell-Bloch equations. The counter-rotating terms in the spontaneous emission damping are included such that the equations of motion are slightly different from the conventional Bloch equations. The counter-rotating terms can considerably suppress the broadening of the pulse envelope and the decrease of the group velocity rooted from dispersion. Furthermore, for incident single-cycle pulses with envelope area 4$\pi$, the time-delay of the generated soliton pulse from the main pulse depends crucially on the carrier-envelope phase of the incident pulse. This can be utilized to determine the carrier-envelope phase of the single-cycle laser pulse.Comment: 6 pages, 5 figure

Heat transport study of the spin liquid candidate 1T-TaS2

We present the ultra-low-temperature thermal conductivity measurements on single crystals of the prototypical charge-density-wave material 1$T$-TaS$_2$, which was recently argued to be a candidate for quantum spin liquid. Our experiments show that the residual linear term of thermal conductivity at zero field is essentially zero, within the experimental accuracy. Furthermore, the thermal conductivity is found to be insensitive to the magnetic field up to 9 T. These results clearly demonstrate the absence of itinerant magnetic excitations with fermionic statistics in bulk 1$T$-TaS$_2$ and, thus, put a strong constraint on the theories of the ground state of this material.Comment: 5 pages, 3 figure

Power quality disturbance detection based on mathematical morphology and fractal technique

Based on mathematical morphology and grille fractal, a novel approach on power quality disturbance detection and location is presented in this paper. At first a parallel composite morphological filter with multiple-structure elements is designed to filter the random noise and impulse noise in power quality disturbance signals. Then to the filtered curves, an easy implementation criterion for singularity detection based on the change regularity of grille fractal is proposed to locate the start and end time that disturbance occurs. The voltage sag, swell, harmonic and their combined disturbances are used to verify the validity of the proposed filter-location approach. Numerical results show that the proposed approach is valid and effective. © 2005 IEEE.published_or_final_versio

Market Allocation Between Bilateral Contracts and Spot Market without Financial Transmission Rights

In the electricity market, it is very important for Generation Companies (Gencos) to decide how to sell energy among different transaction markets in order to maximize profits with relatively low risk. In this paper, two energy transaction markets are considered: spot markets and bilateral contract markets. An energy selling allocation approach with network congestion consideration is established based on modern portfolio theory. Analytical solution for the optimal allocation is derived with given bilateral contract prices and statistical characteristics of the spot market prices. The numerical simulation for energy selling allocation is demonstrated based on the actual data of the USA California power market.published_or_final_versio

Available transfer capability evaluation by decomposition

A central issue of running a successful electric power market is the evaluation of the associated available transfer capability (ATC) representing the room available for trading. Due to the need to post and update ATC values at regular intervals, the underlying calculation method should be moderately fast with acceptable accuracy. This paper proposes the evaluation of ATC by using Benders decomposition. The problem is first broken up into a master problem expressing the steady state operating condition and subproblems for the contingent conditions. Each subproblem is solved independently and a linear constraint using Lagrange multipliers of the subproblem is generated and added to the master problem. The proposed decomposition scheme is applied to IEEE 30 bus system with satisfactory results as compared with the distribution factors method.published_or_final_versio

Kemampuan Berbahasa Anak Autis Tipe Pddnos di Slb Muhammadiyah Sidayu Gresik: Kajian Psikolinguistik

Communication will be successful if the speakers and the hearers are successfully producing and comprehending the speech. In this case, if someone have difficulties to produced or understand the speech, they cannot communicate like a normal person, that is autism with PDDNOS. Autism with PDDNOS have differents characteristics with other types of autism, that is autism children with PDDNOS can communicate on social behaviour. The goals of this research are to know characteristics of language production based onScovel theory about language production of human. On the basis of the research problem, this study is a descriptive qualitative research, and the data is taken through observation with recording on videos. The data of this research is transfered to computer and it is observed several times, and then it is transcribed in order to be easily analyzed. Scovel's theory (1998), is about language productionssuch as conceptialization, formulation, articulation, and self-monitoring. The result of this study is children with PDDNOS have difficulties to produced his language. He also repeated what the speaker says if he didnot understand the meaning of the communicaton