Assigning channels via the meet-in-the-middle approach

We study the complexity of the Channel Assignment problem. By applying the meet-in-the-middle approach we get an algorithm for the $\ell$-bounded Channel Assignment (when the edge weights are bounded by $\ell$) running in time $O^*((2\sqrt{\ell+1})^n)$. This is the first algorithm which breaks the $(O(\ell))^n$ barrier. We extend this algorithm to the counting variant, at the cost of slightly higher polynomial factor. A major open problem asks whether Channel Assignment admits a $O(c^n)$-time algorithm, for a constant $c$ independent of $\ell$. We consider a similar question for Generalized T-Coloring, a CSP problem that generalizes \CA. We show that Generalized T-Coloring does not admit a $2^{2^{o\left(\sqrt{n}\right)}} {\rm poly}(r)$-time algorithm, where $r$ is the size of the instance.Comment: SWAT 2014: 282-29

Towards efficient coexistence of IEEE 802.15.4e TSCH and IEEE 802.11

A major challenge in wide deployment of smart wireless devices, using different technologies and sharing the same 2.4 GHz spectrum, is to achieve coexistence across multiple technologies. The IEEE~802.11 (WLAN) and the IEEE 802.15.4e TSCH (WSN) where designed with different goals in mind and both play important roles for respective applications. However, they cause mutual interference and degraded performance while operating in the same space. To improve this situation we propose an approach to enable a cooperative control which type of network is transmitting at given time, frequency and place. We recognize that TSCH based sensor network is expected to occupy only small share of time, and that the nodes are by design tightly synchronized. We develop mechanism enabling over-the-air synchronization of the Wi-Fi network to the TSCH based sensor network. Finally, we show that Wi-Fi network can avoid transmitting in the "collision periods". We provide full design and show prototype implementation based on the Commercial off-the-shelf (COTS) devices. Our solution does not require changes in any of the standards.Comment: 8 page

Characterisation of spatial network-like patterns from junctions' geometry

We propose a new method for quantitative characterization of spatial network-like patterns with loops, such as surface fracture patterns, leaf vein networks and patterns of urban streets. Such patterns are not well characterized by purely topological estimators: also patterns that both look different and result from different morphogenetic processes can have similar topology. A local geometric cue -the angles formed by the different branches at junctions- can complement topological information and allow to quantify the large scale spatial coherence of the pattern. For patterns that grow over time, such as fracture lines on the surface of ceramics, the rank assigned by our method to each individual segment of the pattern approximates the order of appearance of that segment. We apply the method to various network-like patterns and we find a continuous but sharp dichotomy between two classes of spatial networks: hierarchical and homogeneous. The first class results from a sequential growth process and presents large scale organization, the latter presents local, but not global organization.Comment: version 2, 14 page

Optical Non-Orthogonal Multiple Access for Visible Light Communication

The proliferation of mobile Internet and connected devices, offering a variety of services at different levels of performance, represents a major challenge for the fifth generation wireless networks and beyond. This requires a paradigm shift towards the development of key enabling techniques for the next generation wireless networks. In this respect, visible light communication (VLC) has recently emerged as a new communication paradigm that is capable of providing ubiquitous connectivity by complementing radio frequency communications. One of the main challenges of VLC systems, however, is the low modulation bandwidth of the light-emitting-diodes, which is in the megahertz range. This article presents a promising technology, referred to as "optical- non-orthogonal multiple access (O-NOMA)", which is envisioned to address the key challenges in the next generation of wireless networks. We provide a detailed overview and analysis of the state-of-the-art integration of O-NOMA in VLC networks. Furthermore, we provide insights on the potential opportunities and challenges as well as some open research problems that are envisioned to pave the way for the future design and implementation of O-NOMA in VLC systems

Surface networks

© Copyright CASA, UCL. The desire to understand and exploit the structure of continuous surfaces is common to researchers in a range of disciplines. Few examples of the varied surfaces forming an integral part of modern subjects include terrain, population density, surface atmospheric pressure, physico-chemical surfaces, computer graphics, and metrological surfaces. The focus of the work here is a group of data structures called Surface Networks, which abstract 2-dimensional surfaces by storing only the most important (also called fundamental, critical or surface-specific) points and lines in the surfaces. Surface networks are intelligent and “natural ” data structures because they store a surface as a framework of “surface ” elements unlike the DEM or TIN data structures. This report presents an overview of the previous works and the ideas being developed by the authors of this report. The research on surface networks has fou

Indonesia's small and medium-size exporters and their support systems

The authors survey a sample of 91 small or medium-size exporters of garments, rattan furniture, the two are reasonably equally mixed. About 75 percent of the entrepreneures in garments and rattan furniture, and carved wooden furniture (Jepara), and interview people in public and nonprofit agencies active about issues affecting small and medium-size enterprises (SMEs). Indonesia's garment industry is dominated by entrepreneurs of Chinese descent and the Jepara industry by pribumi (Indonesian Malays); in rattan furniture, the two are reasonably equally mixed. About 75 percent of the entrepreneures in garments and rattan furniture have some university education; less than half of those in the more traditional, skill-based Jepara industry do. In most of the firms, international marketing was handled exclusively through private channels, that is also how most firms acquired technological capability. But such channels appeared to be more readily accessible by larger firms, by educated entrepreneurs, and by non-pribumi who could take advantage of the extended-family network that connects ethnic Chinese in the region. Relying exclusively on private channels means running the risk that participation in export markets will be limited to a relatively narrow base of entrepreneurs. Pribumi and smaller firms relied heavily on collective marketing support provided with a"light touch"- for example, support for participation in trade fairs. The Ministry of Trade's international network of offices geared to providing information and facilitating transactions was of little use to the firms surveyed. Collective technology support also appeared to be somewhat more important for smaller, pribumi firms, although its impact was modest. Employing expatriates was a powerful mechanism for acquiring technological capability, especially in the rattan and garment sectors, although it was concentrated disproportionately among the non-pribumi entrepreneurs. Indonesia's collective institutions suffer from pervasive organizational weaknesses that limit their ability to help broaden the base of private entrepreneurship in small and medium-size firms. Public institutions generally lack the commitment, resources, and flexibility needed to provide quality support to SMEs, and the industry association often lack the professionalism and accountability needed to gain SMEs'confidence. But public support can be useful when it involves relatively simple services, such as support to organize local fairs, to facilitate participation in fairs abroad, or to use foreign private consultants.Microfinance,Small Scale Enterprise,Small and Medium Size Enterprises,Water and Industry,Public Health Promotion,Small Scale Enterprise,Private Participation in Infrastructure,Microfinance,Health Monitoring&Evaluation,Water and Industry