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Author

Timo Hämäläinen

Other affiliations: Dalian Medical University, Nokia, Dublin Institute of Technology  ...read more
Bio: Timo Hämäläinen is an academic researcher from University of Jyväskylä. The author has contributed to research in topics: Quality of service & Encoder. The author has an hindex of 38, co-authored 560 publications receiving 7648 citations. Previous affiliations of Timo Hämäläinen include Dalian Medical University & Nokia.


Papers
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Proceedings ArticleDOI
26 Sep 2001
TL;DR: Two optimized implementations of the emerging ITU-T H.26L video encoder are described, the first, medium-optimized version, is implemented in C and the latter, highly optimized version, utilizes MMX assembly instructions.
Abstract: Two optimized implementations of the emerging ITU-T H.26L video encoder are described. The first, medium-optimized version, is implemented in C and the latter, highly optimized version, utilizes MMX assembly instructions. Comparisons to a correspondingly optimized H.263/H.263+ implementation are given with the spatial and temporal video quality fixed and the bit rate and complexity varied. On a 733 Pentium III processor, a real-time encoding speed of 10 fps for QCIF (quarter common intermediate format) sequences is achieved with a 29% reduction in bit rate compared to H.263+. The complexity of H.26L is about 3.4 times more than that of H.263+.

16 citations

Proceedings ArticleDOI
19 Jun 2001
TL;DR: An optimized implementation of an H.26L video encoder is presented, which reduces the output bit rate about 25% at the expense of increased complexity but enables real-time operation on a 733 MHz general-purpose processor.
Abstract: An optimized implementation of an H.26L video encoder is presented. Compared to H263, H.26L reduces the output bit rate about 25% at the expense of increased (3.8X) complexity. However, optimizations enable real-time operation on a 733 MHz general-purpose processor.

16 citations

Book ChapterDOI
21 Jul 2004
TL;DR: The Heterogeneous IP Block Interconnection v.2 (HIBI) aims at maximum efficiency and energy saving per transmitted bit combined with guaranteed quality-of-service (QoS) in transfers.
Abstract: This paper presents a communication network targeted for complex system-on-chip (SoC) and network-on-chip (NoC) designs The Heterogeneous IP Block Interconnection v2 (HIBI) aims at maximum efficiency and energy saving per transmitted bit combined with guaranteed quality-of-service (QoS) in transfers Other features include support for arbitrary topologies with several clock domains, flexible scalablility in signalling and run-time reconfiguration of network parameters HIBI has been implemented in VHDL and SystemC and synthesized in 018 CMOS technology with area comparable to other NoC wrappers HIBI data transfers are shown to approach the maximum theoretical performance for protocol efficiency

16 citations

Book ChapterDOI
26 Aug 2015
TL;DR: This study proposes an algorithm for detection of Denial of Service attacks that utilize SSL/TLS protocol that results in a higher accuracy rate when compared to other intrusion detection techniques.
Abstract: Denial of Service attacks remain one of the most serious threats to the Internet nowadays. In this study, we propose an algorithm for detection of Denial of Service attacks that utilize SSL/TLS protocol. These protocols encrypt the data of network connections on the application layer which makes it impossible to detect attackers activity based on the analysis of packet payload. For this reason, we concentrate on statistics that can be extracted from packet headers. Based on these statistics, we build a model of normal user behavior by using several data mining algorithms. Once the model has been built, it is used to detect DoS attacks. The proposed framework is tested on the data obtained with the help of a realistic cyber environment that enables one to construct real attack vectors. The simulations show that the proposed method results in a higher accuracy rate when compared to other intrusion detection techniques.

16 citations

Journal ArticleDOI
TL;DR: It can be observed that the proposed contract theoretic approach can effectively stimulate InPs’ participation, improve the payoff of the MVNO, and outperform other schemes.
Abstract: To accommodate the explosively growing demands for mobile traffic service, wireless network virtualization is proposed as the main evolution towards 5G. In this work, a novel contract theoretic incentive mechanism is proposed to study how to manage the resources and provide services to the users in the wireless virtualized networks. We consider that the infrastructure providers (InPs) own the physical networks and the mobile virtual network operator (MVNO) has the service information of the users and needs to lease the physical radio resources for providing services. In particular, we utilize the contract theoretic approach to model the resource trading process between the MVNO and multiple InPs. Two scenarios are considered according to whether the information (such as the radio resource they can provide) of the InPs are globally known. Subsequently, the corresponding optimal contracts regarding the user association and transmit power allocation are derived to maximize the payoff of the MVNOs while maintaining the requirements of the InPs in the trading process. To evaluate the proposed scheme, extensive simulation studies are conducted. It can be observed that the proposed contract theoretic approach can effectively stimulate InPs’ participation, improve the payoff of the MVNO, and outperform other schemes.

16 citations


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Journal ArticleDOI

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Journal ArticleDOI
TL;DR: Machine learning addresses many of the same research questions as the fields of statistics, data mining, and psychology, but with differences of emphasis.
Abstract: Machine Learning is the study of methods for programming computers to learn. Computers are applied to a wide range of tasks, and for most of these it is relatively easy for programmers to design and implement the necessary software. However, there are many tasks for which this is difficult or impossible. These can be divided into four general categories. First, there are problems for which there exist no human experts. For example, in modern automated manufacturing facilities, there is a need to predict machine failures before they occur by analyzing sensor readings. Because the machines are new, there are no human experts who can be interviewed by a programmer to provide the knowledge necessary to build a computer system. A machine learning system can study recorded data and subsequent machine failures and learn prediction rules. Second, there are problems where human experts exist, but where they are unable to explain their expertise. This is the case in many perceptual tasks, such as speech recognition, hand-writing recognition, and natural language understanding. Virtually all humans exhibit expert-level abilities on these tasks, but none of them can describe the detailed steps that they follow as they perform them. Fortunately, humans can provide machines with examples of the inputs and correct outputs for these tasks, so machine learning algorithms can learn to map the inputs to the outputs. Third, there are problems where phenomena are changing rapidly. In finance, for example, people would like to predict the future behavior of the stock market, of consumer purchases, or of exchange rates. These behaviors change frequently, so that even if a programmer could construct a good predictive computer program, it would need to be rewritten frequently. A learning program can relieve the programmer of this burden by constantly modifying and tuning a set of learned prediction rules. Fourth, there are applications that need to be customized for each computer user separately. Consider, for example, a program to filter unwanted electronic mail messages. Different users will need different filters. It is unreasonable to expect each user to program his or her own rules, and it is infeasible to provide every user with a software engineer to keep the rules up-to-date. A machine learning system can learn which mail messages the user rejects and maintain the filtering rules automatically. Machine learning addresses many of the same research questions as the fields of statistics, data mining, and psychology, but with differences of emphasis. Statistics focuses on understanding the phenomena that have generated the data, often with the goal of testing different hypotheses about those phenomena. Data mining seeks to find patterns in the data that are understandable by people. Psychological studies of human learning aspire to understand the mechanisms underlying the various learning behaviors exhibited by people (concept learning, skill acquisition, strategy change, etc.).

13,246 citations

Journal ArticleDOI
01 Nov 2007
TL;DR: Comprehensive performance comparisons including accuracy, precision, complexity, scalability, robustness, and cost are presented.
Abstract: Wireless indoor positioning systems have become very popular in recent years. These systems have been successfully used in many applications such as asset tracking and inventory management. This paper provides an overview of the existing wireless indoor positioning solutions and attempts to classify different techniques and systems. Three typical location estimation schemes of triangulation, scene analysis, and proximity are analyzed. We also discuss location fingerprinting in detail since it is used in most current system or solutions. We then examine a set of properties by which location systems are evaluated, and apply this evaluation method to survey a number of existing systems. Comprehensive performance comparisons including accuracy, precision, complexity, scalability, robustness, and cost are presented.

4,123 citations

01 Jan 2006

3,012 citations

01 Jan 1990
TL;DR: An overview of the self-organizing map algorithm, on which the papers in this issue are based, is presented in this article, where the authors present an overview of their work.
Abstract: An overview of the self-organizing map algorithm, on which the papers in this issue are based, is presented in this article.

2,933 citations