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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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Journal ArticleDOI
TL;DR: Three key optimization techniques can be seamlessly incorporated in the existing control structures of the HEVC reference encoder without limiting its potential parallelization, hardware acceleration, or speed-up with other existing encoder optimizations.
Abstract: The emerging High Efficiency Video Coding (HEVC) standard reduces the bit rate by almost 40% over the preceding state-of-the-art Advanced Video Coding (AVC) standard with the same objective quality but at about 40% encoding complexity overhead. The main reason for HEVC complexity is inter prediction that accounts for 60%-70% of the whole encoding time. This paper analyzes the rate-distortion-complexity characteristics of the HEVC inter prediction as a function of different block partition structures and puts the analysis results into practice by developing optimized mode decision schemes for the HEVC encoder. The HEVC inter prediction involves three different partition modes: square motion partition, symmetric motion partition (SMP), and asymmetric motion partition (AMP) out of which the decision of SMPs and AMPs are optimized in this paper. The key optimization techniques behind the proposed schemes are: 1) a conditional evaluation of the SMP modes; 2) range limitations primarily in the SMP sizes and secondarily in the AMP sizes; and 3) a selection of the SMP and AMP ranges as a function of the quantization parameter. These three techniques can be seamlessly incorporated in the existing control structures of the HEVC reference encoder without limiting its potential parallelization, hardware acceleration, or speed-up with other existing encoder optimizations. Our experiments show that the proposed schemes are able to cut the average complexity of the HEVC reference encoder by 31%-51% at a cost of 0.2%-1.3% bit rate increase under the random access coding configuration. The respective values under the low-delay B coding configuration are 32%-50% and 0.3%-1.3%.

129 citations

Journal ArticleDOI
TL;DR: This work proposes a simple, yet efficient, solution that is capable of allocating slots based on the QoS requirements, bandwidth request sizes, and the 802.16 network parameters and demonstrates work-conserving behaviour.

114 citations

Journal ArticleDOI
TL;DR: An analysis of computational complexity is presented for an H.26L video decoder, based on extensive experiments on a general-purpose processor and platform-independent techniques to optimize an H-26L decoder implementation are given.
Abstract: An analysis of computational complexity is presented for an H.26L video decoder, based on extensive experiments on a general-purpose processor. In addition, platform-independent techniques to optimize an H.26L decoder implementation are given. Comparisons are carried out between our highly optimized version of H.26L, the public reference implementation of H.26L, and a highly optimized H.263+ implementation. Both QCIF and CIF-sized image sequences are used. The results show that with equal visual quality, the bit-rate savings range from 28% to 58%, while the frame decoding speed of H.26L is about 11% better than that of a highly optimized H.263+.

108 citations

Journal ArticleDOI
TL;DR: It is shown that there exists a feedback controller containing an internal model of the exosystem, which robustly regulates the class of signals generated by theExosystem and strongly or weakly stabilizes the closed-loop system.
Abstract: In this paper a robust regulation problem for infinite-dimensional systems with infinite-dimensional exosystems is discussed. The input and output spaces are also allowed to be infinite-dimensional. A new definition of internal model in terms of the controller parameters is given. It is shown that there exists a feedback controller containing an internal model of the exosystem, which robustly regulates the class of signals generated by the exosystem and strongly or weakly stabilizes the closed-loop system. As far as the authors know, the results are new even for finite-dimensional systems with infinite-dimensional exosystems.

107 citations

Journal ArticleDOI
TL;DR: HLS is currently a viable option for fast prototyping and for designs with short time to market and to help close the QoR gap, a survey of literature focused on improving HLS concludes.
Abstract: To increase productivity in designing digital hardware components, high-level synthesis (HLS) is seen as the next step in raising the design abstraction level. However, the quality of results (QoRs) of HLS tools has tended to be behind those of manual register-transfer level (RTL) flows. In this paper, we survey the scientific literature published since 2010 about the QoR and productivity differences between the HLS and RTL design flows. Altogether, our survey spans 46 papers and 118 associated applications. Our results show that on average, the QoR of RTL flow is still better than that of the state-of-the-art HLS tools. However, the average development time with HLS tools is only a third of that of the RTL flow, and a designer obtains over four times as high productivity with HLS. Based on our findings, we also present a model case study to sum up the best practices in comparative studies between HLS and RTL. The outcome of our case study is also in line with the survey results, as using an HLS tool is seen to increase the productivity by a factor of six. In addition, to help close the QoR gap, we present a survey of literature focused on improving HLS. Our results let us conclude that HLS is currently a viable option for fast prototyping and for designs with short time to market.

99 citations


Cited by
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[...]

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