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Search Results: 1 - 10 of 402441 matches for " M. Yeh "
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The Potential Use of Intrauterine Insemination as a Basic Option for Infertility: A Review for Technology-Limited Medical Settings
Abdelrahman M. Abdelkader,John Yeh
Obstetrics and Gynecology International , 2009, DOI: 10.1155/2009/584837
Abstract: Objective. There is an asymmetric allocation of technology and other resources for infertility services. Intrauterine insemination (IUI) is a process of placing washed spermatozoa transcervically into the uterine cavity for treatment of infertility. This is a review of literature for the potential use of IUI as a basic infertility treatment in technology-limited settings. Study design. Review of articles on treatment of infertility using IUI. Results. Aspects regarding the use of IUI are reviewed, including ovarian stimulation, semen parameters associated with good outcomes, methods of sperm preparation, timing of IUI, and number of inseminations. Implications of the finding in light of the needs of low-technology medical settings are summarized. Conclusion. The reviewed evidence suggests that IUI is less expensive, less invasive, and comparably effective for selected patients as a first-line treatment for couples with unexplained or male factor infertility. Those couples may be offered three to six IUI cycles in technology-limited settings.
Asymptotically Optimal Multiple-access Communication via Distributed Rate Splitting
Jian Cao,Edmund M. Yeh
Mathematics , 2006,
Abstract: We consider the multiple-access communication problem in a distributed setting for both the additive white Gaussian noise channel and the discrete memoryless channel. We propose a scheme called Distributed Rate Splitting to achieve the optimal rates allowed by information theory in a distributed manner. In this scheme, each real user creates a number of virtual users via a power/rate splitting mechanism in the M-user Gaussian channel or via a random switching mechanism in the M-user discrete memoryless channel. At the receiver, all virtual users are successively decoded. Compared with other multiple-access techniques, Distributed Rate Splitting can be implemented with lower complexity and less coordination. Furthermore, in a symmetric setting, we show that the rate tuple achieved by this scheme converges to the maximum equal rate point allowed by the information-theoretic bound as the number of virtual users per real user tends to infinity. When the capacity regions are asymmetric, we show that a point on the dominant face can be achieved asymptotically. Finally, when there is an unequal number of virtual users per real user, we show that differential user rate requirements can be accommodated in a distributed fashion.
Directed Percolation in Wireless Networks with Interference and Noise
Zhenning Kong,Edmund M. Yeh
Mathematics , 2007,
Abstract: Previous studies of connectivity in wireless networks have focused on undirected geometric graphs. More sophisticated models such as Signal-to-Interference-and-Noise-Ratio (SINR) model, however, usually leads to directed graphs. In this paper, we study percolation processes in wireless networks modelled by directed SINR graphs. We first investigate interference-free networks, where we define four types of phase transitions and show that they take place at the same time. By coupling the directed SINR graph with two other undirected SINR graphs, we further obtain analytical upper and lower bounds on the critical density. Then, we show that with interference, percolation in directed SINR graphs depends not only on the density but also on the inverse system processing gain. We also provide bounds on the critical value of the inverse system processing gain.
Connectivity, Percolation, and Information Dissemination in Large-Scale Wireless Networks with Dynamic Links
Zhenning Kong,Edmund M. Yeh
Mathematics , 2009,
Abstract: We investigate the problem of disseminating broadcast messages in wireless networks with time-varying links from a percolation-based perspective. Using a model of wireless networks based on random geometric graphs with dynamic on-off links, we show that the delay for disseminating broadcast information exhibits two behavioral regimes, corresponding to the phase transition of the underlying network connectivity. When the dynamic network is in the subcritical phase, ignoring propagation delays, the delay scales linearly with the Euclidean distance between the sender and the receiver. When the dynamic network is in the supercritical phase, the delay scales sub-linearly with the distance. Finally, we show that in the presence of a non-negligible propagation delay, the delay for information dissemination scales linearly with the Euclidean distance in both the subcritical and supercritical regimes, with the rates for the linear scaling being different in the two regimes.
Percolation Processes and Wireless Network Resilience to Degree-Dependent and Cascading Node Failures
Zhenning Kong,Edmund M. Yeh
Mathematics , 2009,
Abstract: We study the problem of wireless network resilience to node failures from a percolation-based perspective. In practical wireless networks, it is often the case that the failure probability of a node depends on its degree (number of neighbors). We model this phenomenon as a degree-dependent site percolation process on random geometric graphs. In particular, we obtain analytical conditions for the existence of phase transitions within this model. Furthermore, in networks carrying traffic load, the failure of one node can result in redistribution of the load onto other nearby nodes. If these nodes fail due to excessive load, then this process can result in a cascading failure. Using a simple but descriptive model, we show that the cascading failure problem for large-scale wireless networks is equivalent to a degree-dependent site percolation on random geometric graphs. We obtain analytical conditions for cascades in this model.
Analytical Lower Bounds on the Critical Density in Continuum Percolation
Zhenning Kong,Edmund M. Yeh
Mathematics , 2006,
Abstract: Percolation theory has become a useful tool for the analysis of large-scale wireless networks. We investigate the fundamental problem of characterizing the critical density $\lambda_c^{(d)}$ for $d$-dimensional Poisson random geometric graphs in continuum percolation theory. By using a probabilistic analysis which incorporates the clustering effect in random geometric graphs, we develop a new class of analytical lower bounds for the critical density $\lambda_c^{(d)}$ in $d$-dimensional Poisson random geometric graphs. The lower bounds are the tightest known to date. In particular, for the two-dimensional case, the analytical lower bound is improved to $\lambda^{(2)}_c \geq 0.7698...$. For the three-dimensional case, we obtain $\lambda^{(3)}_c \geq 0.4494...$
Node-Based Optimal Power Control, Routing, and Congestion Control in Wireless Networks
Yufang Xi,Edmund M. Yeh
Computer Science , 2006,
Abstract: We present a unified analytical framework within which power control, rate allocation, routing, and congestion control for wireless networks can be optimized in a coherent and integrated manner. We consider a multi-commodity flow model with an interference-limited physical-layer scheme in which power control and routing variables are chosen to minimize the sum of convex link costs reflecting, for instance, queuing delay. Distributed network algorithms where joint power control and routing are performed on a node-by-node basis are presented. We show that with appropriately chosen parameters, these algorithms iteratively converge to the global optimum from any initial point with finite cost. Next, we study refinements of the algorithms for more accurate link capacity models, and extend the results to wireless networks where the physical-layer achievable rate region is given by an arbitrary convex set, and the link costs are strictly quasiconvex. Finally, we demonstrate that congestion control can be seamlessly incorporated into our framework, so that algorithms developed for power control and routing can naturally be extended to optimize user input rates.
Throughput Optimal Distributed Control of Stochastic Wireless Networks
Yufang Xi,Edmund M. Yeh
Computer Science , 2006,
Abstract: The Maximum Differential Backlog (MDB) control policy of Tassiulas and Ephremides has been shown to adaptively maximize the stable throughput of multi-hop wireless networks with random traffic arrivals and queueing. The practical implementation of the MDB policy in wireless networks with mutually interfering links, however, requires the development of distributed optimization algorithms. Within the context of CDMA-based multi-hop wireless networks, we develop a set of node-based scaled gradient projection power control algorithms which solves the MDB optimization problem in a distributed manner using low communication overhead. As these algorithms require time to converge to a neighborhood of the optimum, the optimal rates determined by the MDB policy can only be found iteratively over time. For this, we show that the iterative MDB policy with convergence time remains throughput optimal.
Distributed Algorithms for Spectrum Allocation, Power Control, Routing, and Congestion Control in Wireless Networks
Yufang Xi,Edmund M. Yeh
Computer Science , 2007,
Abstract: We develop distributed algorithms to allocate resources in multi-hop wireless networks with the aim of minimizing total cost. In order to observe the fundamental duplexing constraint that co-located transmitters and receivers cannot operate simultaneously on the same frequency band, we first devise a spectrum allocation scheme that divides the whole spectrum into multiple sub-bands and activates conflict-free links on each sub-band. We show that the minimum number of required sub-bands grows asymptotically at a logarithmic rate with the chromatic number of network connectivity graph. A simple distributed and asynchronous algorithm is developed to feasibly activate links on the available sub-bands. Given a feasible spectrum allocation, we then design node-based distributed algorithms for optimally controlling the transmission powers on active links for each sub-band, jointly with traffic routes and user input rates in response to channel states and traffic demands. We show that under specified conditions, the algorithms asymptotically converge to the optimal operating point.
The Impact of Incomplete Information on Games in Parallel Relay Networks
Hongda Xiao,Edmund M. Yeh
Computer Science , 2011,
Abstract: We consider the impact of incomplete information on incentives for node cooperation in parallel relay networks with one source node, one destination node, and multiple relay nodes. All nodes are selfish and strategic, interested in maximizing their own profit instead of the social welfare. We consider the practical situation where the channel state on any given relay path is not observable to the source or to the other relays. We examine different bargaining relationships between the source and the relays, and propose a framework for analyzing the efficiency loss induced by incomplete information. We analyze the source of the efficiency loss, and quantify the amount of inefficiency which results.
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