User-Centric Interference Nulling in Downlink Multi-Antenna Heterogeneous Networks

In heterogeneous networks (HetNets), strong interference due to spectrum reuse affects each user's signal-to-interference ratio (SIR), and hence is one limiting factor of network performance. In this paper, we propose a user-centric interference nulling (IN) scheme in a downlink large-scale HetNet to improve coverage/outage probability by improving each user's SIR. This IN scheme utilizes at most maximum IN degree of freedom (DoF) at each macro-BS to avoid interference to uniformly selected macro (pico) users with signal-to-individual-interference ratio (SIIR) below a macro (pico) IN threshold, where the maximum IN DoF and the two IN thresholds are three design parameters. Using tools from stochastic geometry, we first obtain a tractable expression of the coverage (equivalently outage) probability. Then, we analyze the asymptotic coverage/outage probability in the low and high SIR threshold regimes. The analytical results indicate that the maximum IN DoF can affect the order gain of the outage probability in the low SIR threshold regime, but cannot affect the order gain of the coverage probability in the high SIR threshold regime. Moreover, we characterize the optimal maximum IN DoF which optimizes the asymptotic coverage/outage probability. The optimization results reveal that the IN scheme can linearly improve the outage probability in the low SIR threshold regime, but cannot improve the coverage probability in the high SIR threshold regime. Finally, numerical results show that the proposed scheme can achieve good gains in coverage/outage probability over a maximum ratio beamforming scheme and a user-centric almost blank subframes (ABS) scheme.Comment: Transactions on Wireless Communications (under revision). arXiv admin note: text overlap with arXiv:1504.0528

Context Modeling for Ranking and Tagging Bursty Features in Text Streams

Bursty features in text streams are very useful in many text mining applications. Most existing studies detect bursty features based purely on term frequency changes without taking into account the semantic contexts of terms, and as a result the detected bursty features may not always be interesting or easy to interpret. In this paper we propose to model the contexts of bursty features using a language modeling approach. We then propose a novel topic diversity-based metric using the context models to find newsworthy bursty features. We also propose to use the context models to automatically assign meaningful tags to bursty features. Using a large corpus of a stream of news articles, we quantitatively show that the proposed context language models for bursty features can effectively help rank bursty features based on their newsworthiness and to assign meaningful tags to annotate bursty features. ? 2010 ACM.EI

Engineering project management in the international context : a Chinese culture-based exploratory and comparative evaluation

Much of the research in project management focuses on developing better scheduling techniques in order to generate successful engineering and construction projects. However, with the advent of globalisation, project management is not only a domestic endeavour. Better scheduling techniques are not necessarily sufficient to ensure the successful completion of projects. Working with people with different cultural backgrounds and managing in foreign cultural areas is very common today. Cultural differences can actually affect project success and specifically the success of projects of a technological nature. Five typical Chinese cultural behaviours are identified and discussed in terms of philosophy of life, the "face" issue, personal relationships, communication and conflict solving. The effects of these cultural behaviours on communication, negotiation, conflict resolution, contract process and project team-building are researched through a designed survey questionnaire. Although the questionnaire is designed based on the Chinese culture, South African project managers have also been asked to participate in order to illustrate the cultural differences, where applicable. Researchers and practitioners still find it difficult to define what constitutes cultural differences and how to mitigate the influence of cultural differences on engineering projects. Data analysis and survey results for cultural effects on international engineering team performance are presented in this thesis and a method to mitigate the effect of cultural difference is conceptualised. This thesis contributes to the knowledge of managing engineering and construction projects in multicultural environments specifically in the international context. Moreover, a conceptual model has been developed and evaluated to indicate and explore the relationships between cultural differences, Chinese behaviours, project activities, project management processes and mitigation methods, from the South African and Chinese perspectives.Thesis (PhD)--University of Pretoria, 2011.Graduate School of Technology Management (GSTM)unrestricte

Homogeneous Second-Order Descent Framework: A Fast Alternative to Newton-Type Methods

This paper proposes a homogeneous second-order descent framework (HSODF) for nonconvex and convex optimization based on the generalized homogeneous model (GHM). In comparison to the Newton steps, the GHM can be solved by extremal symmetric eigenvalue procedures and thus grant an advantage in ill-conditioned problems. Moreover, GHM extends the ordinary homogeneous model (OHM) to allow adaptiveness in the construction of the aggregated matrix. Consequently, HSODF is able to recover some well-known second-order methods, such as trust-region methods and gradient regularized methods, while maintaining comparable iteration complexity bounds. We also study two specific realizations of HSODF. One is adaptive HSODM, which has a parameter-free $O(\epsilon^{-3/2})$ global complexity bound for nonconvex second-order Lipschitz continuous objective functions. The other one is homotopy HSODM, which is proven to have a global linear rate of convergence without strong convexity. The efficiency of our approach to ill-conditioned and high-dimensional problems is justified by some preliminary numerical results.Comment: improved writin