In indoor wireless communication networks, mobile computing devices need to be handed off to different base stations based on certain criteria. In this paper, a fuzzy logic based scheme for selection of base station a t the time of handoff is presented. The scheme considers three criteria, namely, received power levels, user population and used bandwidth of each base station to arrive at a fuzzy handoff decision regarding handoff t o any particular base station. For comparison, the conventional power level based handoff and user population based handoff schemes are also considered. It is shown through simulation that the fuzzy logic based scheme results in uniform user load for the base stations and optimizes the number of base station switchings. I IntroductionThe core of pervasive computing environments in homes and offices will be formed of wireless networks of mobile computing devices which interface t o wired backbone networks by means of access points or base stations (BSs). Commmuincation in these wireless networks will be based on emerging standards such as Bluetooth and IEEE 802.11 which define a packet-data macro-and picocellular paradigm of operation. In such networks, a major issue that needs efficient real-time solutions is the problem of handing off mobile units between base stations. It is required that the supporting system choose a target base station and perform handoff as fast as possible t o provide reasonable QoS levels to the end users.Situations wherein more than one base station can receive a mobile through handoff will be frequent in indoor wireless networks because close placement of base stations results in the received power levels from several candidate base stations to be more than the threshold required for hand off. The simplest scheme of choosing between these is to select that BS from which the received power level is the maximum. However, this can lead to overloading of the BS and cause degradation of QoS in overloaded cells or higher number of handoff failures if the number of users in a BS is restricted. Therefore it is desirable to distribute the mobile user load among the BSs in the cellular network. . 'This research work was carried out as a part of suinmcr training piogram for IIT Delhi students hf S Daiig and A Piakasli i n IBBI India Research Laborator7The handoff schemes presented in this paper are based on the criterion of not only the received power level, but also the user population and the bandwidth (where "bandwidth" refers to data transfer rate in Kbps) used in each of the candidate BSs to select the target BS. The processing of the various criteria can be carried out in various ways. In this paper it is done based on fuzzy logic. Generally fuzzy logic is useful in control and decision making situations where the system model and it's behavior are not clearly known. While it has been applied successfully in control situations where the transition between control states needs to be gradual, it is only recently that its application in mobile cellular communications...
In the next generation internet (NGI) featuring grid technology, as a foundation of grid Meta-Computing, grid node must have large capability of data storage and processing. In this paper, parallel processing and computing environment for Multi-Central processing unit (MCPU) and Multi-Memory Device(MMEM) is researched, the main part as follows.Coarse wavelength division multiplexing (CWDM) is adopted to realize interconncection with single optical fiber for parallel high capability computers whose parallel scale are less than 16. In order to make grid and Internet be compatible with each other and improve transmission efficiency, IP packet format is taken to be data transmission format. More emphases are put on researching Odd-Even merging network to build optical routing system. The optimizing analysis of the number of optical switches needed in different parallel systems has also been done in the paper. Routing control system is designed featuring centralized control and built-in. In the meanwhile, optical switching protocol used between MCPU and MMEM is contrived, which can control route switching for different wavelength signals effectively. Finally, simulation shows that under network load, this network structure and route switching protocol can decrease network congestion efficiently to meet requirement of data transmission.
As the Internet traffic exponentially growing, the next generation IP network is forced to scale far beyond its present performances. The more and more mature optical switching technology, such as optical burst switching, is expected to provide an ideal infrastructure for meeting the demands. However in optical switching, there is one critical issue, namely contention, which roots from multiple optical data requesting the same output port How to resolve contention in optical domain will have a significant effect on the performance (in terms of the burst-loss rate, average delay time and network throughput) of optical switching network. The paper proposes a contention resolution scheme based on FDL, AWG and TWC. Here FDL is used as two functions, i.e. forwarding and feedback for smaller or longer buffering time requirements respectively. In the paper we incorporate the scheme into the design of optical switch. We descript the optical data buffering strategy when contention occurs. We also study the performance of the scheme in a Markov process model under the assumption of uniform Bernoulli traffic, and validate the analysis through numerical simulation. The computer simulation results show that the scheme can efficiently use FDL buffering and AWG switching capacities, hence can obviously reduce the contentions.
Along with progresses in high-speed, wideband long-haul and full service transmission in optical fiber system, the polarization mode dispersion has become one of major limiting factors in term of the system bandwidth and the linearity, and leads to severe signal impairments, especially the second-order PMD for an analog system. Therefore the purpose of the paper is to present a detailed description of PMD effects (in term of composite second-order) on PAL-D 60 channels analog CATV signals and to show the numerical simulations about some important relations between the CSO and the PMD distortion factors. Based on the simulation results, we also discuss a second-order PMD compensation scheme for optical DWDM network, which can efficiently reduce second-order, or even higher-order nonlinear distortions.
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