Current Issue : July - September Volume : 2012 Issue Number : 3 Articles : 4 Articles
Although relaying can be very beneficial for wireless systems, understanding which relaying schemes can achieve specific\r\nperformance objectives under realistic fading is crucial. In this paper we present a general framework for modeling and evaluating\r\nthe performance of dual-hop decode-and-forward (DF) relaying schemes over independent and not necessarily identically\r\ndistributed (INID) Nakagami-m fading channels.We obtain closed-form expressions for the statistics of the instantaneous output\r\nsignal-to-noise ratio of repetitive transmission with selection diversity. Furthermore, we present a unified statistical overview of\r\nother three significant relaying schemes with DF, one based on repetitive transmission with maximal-ratio diversity and the other\r\ntwo based on relay selection (RS). To compare the considered schemes, we present closed-form and analytical expressions for\r\nthe outage probability and the average symbol error probability under various modulation methods, respectively. Importantly,\r\nit is shown that when the channel state information for RS is perfect, RS-based schemes always outperform repetitive ones.\r\nFurthermore, when the direct link between the source and the destination nodes is sufficiently strong, relaying may not result\r\nin any gains, and it should be switched off....
Collection of rare but delay-critical messages from a group of sensor nodes is a key process in many wireless sensor network\r\napplications. This is particularly important for security-related applications like intrusion detection and fire alarm systems. An\r\nevent sensed by multiple sensor nodes in the network can trigger many messages to be sent simultaneously. We present Alert, a\r\nMAC protocol for collecting event-triggered urgent messages from a group of sensor nodes with minimum latency and without\r\nrequiring any cooperation or prescheduling among the senders or between senders and receiver during protocol execution. Alert\r\nis designed to handle multiple simultaneous messages from different nodes efficiently and reliably, minimizing the overall delay\r\nto collect all messages along with the delay to get the first message. Moreover, the ability of the network to handle a large number\r\nof simultaneous messages does not come at the cost of excessive delays when only a few messages need to be handled. We analyze\r\nAlert and evaluate its feasibility and performance with an implementation on commodity hardware. We further compare Alert\r\nwith existing approaches through simulations and show the performance improvement possible through Alert....
Focusing on the principles and the paradigm of OBS an overview addressing expectable performance and application issues\r\nis presented. Proposals on OBS were published over a decade and the presented techniques spread into many directions. The\r\npaper comprises discussions of several challenges that OBS meets, in order to compile the big picture. The OBS principle is\r\npresented unrestricted to individual proposals and trends. Merits are openly discussed, considering basic teletraffic theory and\r\ncommon traffic characterisation. A more generic OBS paradigmthan usual is impartially discussed and found capable to overcome\r\nshortcomings of recent proposals. In conclusion, an OBS that offers different connection types may support most client demands\r\nwithin a sole optical network layer....
Deployment of a large number of femtocells to jointly provide coverage in an enterprise environment raises critical challenges\r\nespecially in future self-organizing networks which rely on plug-and-play techniques for configuration. This paper proposes a\r\nmulti-objective heuristic based on a genetic algorithm for a centralized self-optimizing network containing a group of UMTS\r\nfemtocells. In order to optimize the network coverage in terms of handled load, coverage gaps, and overlaps, the algorithm\r\nprovides a dynamic update of the downlink pilot powers of the deployed femtocells. The results demonstrate that the algorithm\r\ncan effectively optimize the coverage based on the current statistics of the global traffic distribution and the levels of interference\r\nbetween neighboring femtocells. The algorithm was also compared with the fixed pilot power scheme. The results show over fifty\r\npercent reduction in pilot power pollution and a significant enhancement in network performance. Finally, for a given traffic\r\ndistribution, the solution quality and the efficiency of the described algorithm were evaluated by comparing the results generated\r\nby an exhaustive search with the same pilot power configuration....
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