CycleGANAS: Differentiable Neural Architecture Search for CycleGAN

We develop a Neural Architecture Search (NAS) framework for CycleGAN that carries out unpaired image-to-image translation task. Extending previous NAS techniques for Generative Adversarial Networks (GANs) to CycleGAN is not straightforward due to the task difference and greater search space. We design architectures that consist of a stack of simple ResNet-based cells and develop a search method that effectively explore the large search space. We show that our framework, called CycleGANAS, not only effectively discovers high-performance architectures that either match or surpass the performance of the original CycleGAN, but also successfully address the data imbalance by individual architecture search for each translation direction. To our best knowledge, it is the first NAS result for CycleGAN and shed light on NAS for more complex structures

Tree Sampling for Detection of Information Source in Densely Connected Networks

We investigate the problem of source detection in information spreading throughout a densely-connected network. Previous works have been developed mostly for tree networks or applied the tree-network results to non-tree networks assuming that the infection occurs in the breadth first manner. However, these approaches result in low detection performance in densely-connected networks, since there is a substantial number of nodes that are infected through the non-shortest path. In this work, we take a two-step approach to the source detection problem in densely-connected networks. By introducing the concept of detour nodes, we first sample trees that the infection process likely follows and effectively compare the probability of the sampled trees. Our solution has low complexity of O(n2logn, where n denotes the number of infected nodes, and thus can be applied to large-scale networks. Through extensive simulations including practical networks of the Internet autonomous system and power grid, we evaluate our solution in comparison with two well-known previous schemes and show that it achieves the best performance in densely-connected networks

Local Greedy Approximation for Scheduling in Multi-hop Wireless Networks

In recent years, there has been a significant amount of work done in developing low-complexity scheduling schemes to achieve high performance in multi-hop wireless networks. A centralized sub-optimal scheduling policy, called Greedy Maximal Scheduling (GMS) is a good candidate because its empirically observed performance is close to optimal in a variety of network settings. However, its distributed realization requires high complexity, which becomes a major obstacle for practical implementation. In this paper, we develop simple distributed greedy algorithms for scheduling in multi-hop wireless networks. We reduce the complexity by relaxing the global ordering requirement of GMS, up to near-zero. Simulation results show that the new algorithms approximate the performance of GMS, and outperform the state-of-the-art distributed scheduling policies

Longest-queue-first scheduling under SINR interference model

We investigate the performance of longest-queue-first (LQF) scheduling (i.e., greedy maximal scheduling) for wireless networks under the SINR interference model. This interference model takes network geometry and the cumulative interference effect into account, which, therefore, capture the wireless interference more precisely than binary interference models. By employing the ρ-local pooling technique, we show that LQF scheduling achieves zero throughput in the worst case. We then propose a novel technique to localize interference which enables us to decentralize the LQF scheduling while preventing it from having vanishing throughput in all network topologies. We characterize the maximum throughput region under interference localization and present a distributed LQF scheduling algorithm. Finally, we present numerical results to illustrate the usefulness and to validate the theory developed in the paper.United States. Army Research Office. Multidisciplinary University Research Initiative (Grant W911NF-08-1-0238)National Science Foundation (U.S.) (Grant CNS-0915988)United States. Defense Threat Reduction Agency (Grant HDTRA1-07-1-0004

Inkjet-Printed Silver Gate Electrode and Organic Dielectric Materials for Bottom-Gate Pentacene Thin-Film Transistors

An inkjet-printed silver electrode and a spin-coated cross-linked poly(4-vinylphenol)(PVP) dielectric layer were used as a gate electrode and a gate insulator for a bottom-gate pentacene thin-film transistor (TFT), respectively. The printing and the curing conditions of the printed silver electrode were optimized and tested on various substrates, such as glass, silicon, silicon dioxide, polyethersulfone, polyethyleneterephthalate, polyimide and polyarylate, to produce a good sheet resistance of 0.2 $\sim$ 0.4 $\Omega$/$\square$ and a good surface roughness of 2.38 nm in RMS value and 20.14 nm in peak-to-valley (P2V) value, which are very similar to those of conventionally-sputtered indium-tin-oxide (ITO) or thermally-evaporated silver electrodes. The coated PVP layer of metal/PVP/metal devices showed a good insulation property of 10.4 nA/$\rm cm^{2}$ at 0.5 MV/cm. The PVP layer further reduced the surface roughness of the gate electrode to provide a good interface to the pentance layer. The pentacene TFT with a structure of glass/printed silver/PVP/pentacene/Au showed a good saturation region mobility of 0.13 $\rm cm^{2}$/Vs and a good on/off ratio of larger than 10$^{5}$, which are similar to the performance of a pentacene TFT with a conventional ITO gate electrode.This work was supported by \SystemIC2010" project of Korea Ministry of Knowledge Economy and by the Seoul R&BD Program (CRO70048)

On the Complexity of Scheduling in Wireless Networks

We consider the problem of throughput-optimal scheduling in wireless networks subject to interference constraints. We model the interference using a family of K-hop interference models, under which no two links within a K-hop distance can successfully transmit at the same time. For a given K, we can obtain a throughput-optimal scheduling policy by solving the well-known maximum weighted matching problem. We show that for K > 1, the resulting problems are NP-Hard that cannot be approximated within a factor that grows polynomially with the number of nodes. Interestingly, for geometric unit-disk graphs that can be used to describe a wide range of wireless networks, the problems admit polynomial time approximation schemes within a factor arbitrarily close to 1. In these network settings, we also show that a simple greedy algorithm can provide a 49-approximation, and the maximal matching scheduling policy, which can be easily implemented in a distributed fashion, achieves a guaranteed fraction of the capacity region for "all K." The geometric constraints are crucial to obtain these throughput guarantees. These results are encouraging as they suggest that one can develop low-complexity distributed algorithms to achieve near-optimal throughput for a wide range of wireless networksopen1

A decentralized spectrum allocation and partitioning scheme for a two-tier macro-femtocell network with downlink beamforming

This article examines spectrum allocation and partitioning schemes to mitigate cross-tier interference under downlink beamforming environments. The enhanced SIR owing to beamforming allows more femtocells to share their spectrum with the macrocell and accordingly improves overall spectrum efficiency. We first design a simplified centralized scheme as the optimum and then propose a practical decentralized algorithm that determines which femtocells to use the full or partitioned spectrum with acceptable control overhead. To exploit limited information of the received signal strength efficiently, we consider two types of probabilistic femtocell base station (HeNB) selection policies. They are equal selection and interference weighted selection policies, and we drive their outage probabilities for a macrocell user. Through performance evaluation, we demonstrate that the outage probability and the cell capacity in our decentralized scheme are significantly better than those in a conventional cochannel deployment scheme. Furthermore, we show that the cell utility in our proposed scheme is close to that in the centralized scheme and better than that in the spectrum partitioning scheme with a fixed ratio.open0

On the Performance of Back-Pressure Scheduling Schemes with Logarithmic Weight

Recently, significant advances have been made in wireless scheduling toward high-performance networks, leading to development of throughput-optimal scheduling schemes. Beyond throughput performance, however, scheduling with good delay performance has remained open except for a small class of network systems. In this paper, we extend the well-known back-pressure scheduling scheme by using logarithmic weight and improve the delay performance without any loss of throughput performance under multi-hop traffic. We provide rigorous analysis for throughput performance of the proposed solution, and evaluate delay performance through simulations.close

On Random Access Scheduling for Multimedia Traffic in Multihop Wireless Networks with Fading Channels

In this paper, we develop distributed random access scheduling schemes that exploit the time-varying nature of fading channels for multimedia traffic in multihop wireless networks. It should be noted that while centralized scheduling solutions can achieve optimal throughput under this setting, they incur high-computational complexity and require centralized coordination requiring global channel information. The proposed solution not only achieves provable performance guarantees under a wide range of interference models, but also can be implemented in a distributed fashion using local information. To the best of our knowledge, this is the first distributed scheduling mechanism for fading channels that achieves provable performance guarantees. We show through simulations that the proposed schemes achieve better empirical performance than other known distributed scheduling schemes.close2