Current Issue : April - June Volume : 2014 Issue Number : 2 Articles : 5 Articles
Visible light communication (VLC) is gaining increasing attention and is considered as a promising technology for\r\nfuture wireless indoor communications. Because movable users expect a seamless connectivity experience when\r\nswitching among transmitters (i.e., VLC access points) in the VLC system, fast link switching operations must be\r\nsupported by the networks. This paper presents a novel hard link switching scheme for VLC networks with the use\r\nof pre-scanning and received signal strength (RSS) prediction. Our proposed scheme achieves the advantages of\r\nboth conventional hard and soft link switching schemes without changing device hardware or the IEEE 802.15.7\r\nmedium access control (MAC) protocol. To help compare our proposed scheme with conventional hard and soft\r\nlink switching schemes, the signal-to-interference-plus-noise ratio (SINR), the outage probability regarding the link\r\nswitching situation, and the queuing models for link switching schemes are taken into account. Simulation and\r\nnumerical results validate that our proposed scheme outperforms conventional hard and soft link switching schemes....
Background: Wireless mesh networks (WMNs) are a very attractive new field of research. They are low cost, easily\r\ndeployed, and a high-performance solution to last-mile broadband Internet access. In WMNs, admission control (AC)\r\nis one of the key traffic management mechanisms that should be deployed to provide quality of service (QoS) support\r\nfor real-time traffic.\r\nResults: In this paper, we introduce a novel admission control model, based on bandwidth and delay parameters,\r\nwhich integrates a dynamic link scheduling scheme. The proposed model is built on two different methods to access\r\nthe medium: on a contention-based channel access method for control packets and on a dynamic time division\r\nmultiple access (DTDMA) for data packets. Each time a new flow is admitted in the network, the WMN�s link\r\nscheduling is modified according to the flows� requirement and network conditions while respecting the\r\nsignal-to-interference-plus-noise ratio (SINR); this allows establishing collision-free transmissions.\r\nConclusions: Using extensive simulations, we demonstrate that our model achieves high resource utilization by\r\nimproving throughput, establishing collision-free transmission, as well as respecting requirements of admitted flows\r\nin terms of delay and bandwidth....
We report here on the utilization of signal in-phase-quadrature (I-Q) diagrams in a novel modulation classification\r\n(MC) technique. This MC technique is able to classify linear digital single-carrier modulations as well as multi-carrier\r\nmodulations. The method uses the waveforms� I-Q diagrams and, by employing a combination of k-center and\r\nk-means algorithms, determines the type of modulation. Implementation and refinement of the novel single-carrier\r\nmodulation classification technique using the I-Q diagrams are discussed in detail. Further, a model for classification of\r\nmulti-carrier signals is presented, including Gaussianity, cyclostationarity, and autocorrelation tests for further\r\nextracting orthogonal frequency division multiplexing signal parameters. Finally, results of this method are presented\r\nand compared to other classification methods, and the considerations for implementing the method in hardware are\r\nbriefly discussed. As a future direction of this research, the performance of the algorithm in fading channels is an\r\ninteresting topic to pursue....
Indoor target localization is an essential and fundamental issue for wireless sensor networks (WSN). However, it\r\nis rather difficult for WSN to maintain the localization accuracy in line-of-sight (LOS) and non-line-of-sight (NLOS)\r\nmixed environment. NLOS propagation always leads to larger ranging error than LOS does. When the target\r\nmoves in the rooms and corridors, the signal transmission state will switch frequently between LOS and NLOS.\r\nIt is a challenging task to deal with this situation because the ranging error characteristics under LOS and NLOS\r\nconditions are quite different. In this paper, we propose an interacting multiple model-extended Kalman filter\r\n(IMM-EKF) algorithm to improve the localization accuracy for moving target in indoor environment. In the IMM\r\nstructure, two Kalman filters (KF) are adopted in parallel to accurately smoothen the distance measurement. The\r\nproposed algorithm can adapt to the dynamically changing condition between LOS and NLOS due to the two\r\nKFs'' interaction so that large NLOS ranging errors are further reduced. Once the estimated ranges are obtained,\r\nthe EKF is employed to estimate the target''s location. Empirical measurement results are obtained from typical\r\noffice environment to verify the effectiveness of the proposed algorithm. Experimental results illustrate that the\r\nIMM smoother can efficiently mitigate the NLOS effects on ranging errors and achieve high localization accuracy....
The aim of this paper is to propose and evaluate multi-user iterative block decision feedback equalization (IB-DFE)\r\nschemes for the uplink of single-carrier frequency-division multiple access (SC-FDMA)-based systems. It is assumed\r\nthat a set of single antenna users share the same physical channel to transmit its own information to the base\r\nstation, which is equipped with an antenna array. Two space-frequency multi-user IB-DFE-based processing are\r\nconsidered: iterative successive interference cancellation and parallel interference cancellation. In the first approach,\r\nthe equalizer vectors are computed by minimizing the mean square error (MSE) of each individual user, at each\r\nsubcarrier. In the second one, the equalizer matrices are obtained by minimizing the overall MSE of all users at each\r\nsubcarrier. For both cases, we propose a simple yet accurate analytical approach for obtaining the performance of\r\nthe discussed receivers. The proposed schemes allow an efficient user separation, with a performance close to the\r\none given by the matched filter bound for severely time-dispersive channels, with only a few iterations....
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