TKK | Tietoverkkolaboratorio | Julkaisut

Annual Report 1998: Preface | Introduction | Personnel | Research projects | Teaching | Activities | Participation in boards and committees | Publications

3. RESEARCH PROJECTS


3.1 Models for Integrated Telecommunication Network Traffic and Architecture (MITTA)

Project leader: Kauko Rahko
Researchers: Marko Luoma, Markus Peuhkuri, Anna-Kaisa Lindfors

Project was funded by Academy of Finland for years 1996-1998. Project focused on the traffic management in ATM networks.The aim was to find out which are the key factors in the effective traffic management and how they should be adjusted in order to minimise the load of the traffic management. During these years, several people worked in this project. The main results are summarised below:

3.2 Radio Interface and Network Design Techniques in 3rd-generation radio systems (RAVE)

Project leader: Timo Laakso
Researchers: Ramin Baghaie, Petri Karttunen, Kimmo Kettunen, Stefan Werner

Fig 2: Multiple antenna-element receiver enables the increase in the system capacity of the future WCDMA telecommunication systems by employing clever adaptive array processing algorithms.

This is a two-year project of the Institute of Radio Communications (IRC). The IRC was established in 1993 to coordinate research on radio communications by several laboratories of the department. The research is funded by TEKES and industry partners including Nokia, Sonera, and Helsinki Telephone Company. The RAVE project focuses on new mobile communcations systems and it divides into several subprojects. Our subproject is Region B: Radio interface and algorithms, which further divides into the following projects of our laboratory:

3.2.1 Channel modeling and estimation for Wideband CDMA

Researcher: Petri Karttunen

This project focuses on two issues. The first is the analysis of temporal and spatial correlations of wideband radio channels in multiple-antenna arrays, based on the measurement results provided by the Radio Laboratory. The initial results show strong correlation between adjacent antenna elements and low correlation between different spatial locations of mobile user. This has important implications for the multiple-antenna receiver algorithm design if the correlation effects are discarded [20]. The second part of the research project focuses on the development of fast and robust user tracking algorithms for a base station in the wideband code division multiple access (CDMA) receivers with multiple antenna elements. A system has been developed, which can track several users simultaneously using either conventional gradient based least mean squared (LMS) error adaptive algorithms with the adaptive step size or more advanced conjugate gradient and the high resolution subspace techniques.

3.2.2 Adaptive detection for multiple-antenna CDMA systems

Researchers: Stefan Werner, Paulo Diniz, Jose Apolinario, Marcello de Campos

The main objective of this work is to develop efficient receiver algorithms for the wideband CDMA mobile receiver. The assumption is that the receiver only knows the own user's spreading code, so that the other-user interference has to be reduced without this information. Previous work concentrated on blind interference cancellation which, however, requires short codes, i.e., that the spreading codes overlap one symbol interval exactly [39-41]. In recent work the compatibility with long codes has been guaranteed in a channel decorrelation approach. Both schemes provide clearly superior performance in terms of signal-to-noise ratio (and bit error rate) to the conventional correlator, and also excellent robustness to the so-called near-far problem (on strong interfering user). This project includes cooperation with Prof. Paulo Diniz's group at the Federal University of Rio de Janeiro whose expertise is in the field of adaptive algorithms. Prof. Diniz himself as well as his colleagues Jose Apolinario and Marcello de Campos have contributed in the project during their visits to our laboratory in 1998.

3.2.3 Implementation of fast algorithms for multiple-antenna CDMA systems

Researcher: Ramin Baghaie

This project addresses the methodologies needed to design VLSI circuits for systems that require higher throughput or lower power consumption. This is of great importance when implementing mobile communication systems. Some of the techniques that are presented in this project are applied to the DSP algorithms needed in the previous subprojects [7-10]. The first part of this project considers high-level algorithm transformation techniques such as the look-ahead (LA), relaxed look-ahead (RLA), and strength reduction (SR). In [8-10], for the pipelined implementation of adaptive mobile receiver the LA and RLA techniques were utilized. As a result, higher throughputs or lower power consumption were achieved. On the other hand, the strength reduction transformation is applied to reduce the number of multiplications. This will result in remarkable savings in consumed power and silicon area. In [7], low-power RAKE receivers were proposed that utilize the Strength Reduction transformation technique. The second part of this project addresses several high-level architectural transformations that can be used to design families of architectures for a given algorithm. These transformations include pipelining, retiming, unfolding, and array processor design. Pipelined DSP algorithms allow us to tradeoff speed, power and area during the course of VLSI implementation.

3.2.4 Multiuser receivers and channel coding

Researcher: Kimmo Kettunen

The classical multiuser receiver algorithms of Verdu, Varanasi and Aazhang, et al. have been implemented completely without error-correction coding which is assumed to be separate. However, it is known that better results in terms of bit error rate can be obtained by considering them in the same process. This project addresses the problem of joint detection and decoding in a multiuser wideband CDMA receiver. Iterative techniques have been investigated which implement interference cancellation type detection and iterative channel decoding in an alternating manner. Both soft and hard tentative decisions have been employed. The proposed technique has been shown to provide several decibels' improvement over traditional techniques, particularly when soft tentative decisions and variance re-estimation after each iteration step is employed.

3.3 Fast Digital Subscriber Line (DSL) technologies in broadband transmission

Project leader: Timo Laakso
Researchers: Amoakoh Gyasi-Agyei, Yaohui Liu, Harri Mäntylä

Fig. 3: VDSL network structure

This 3-year project started in 1998 and is carried out together with prof. Markku Renfors' group in the Telecommunications laboratory of Tampere University of Technology. It is funded by TEKES and industrial partners (Nokia Telecommunications, Tellabs, Helsinki Telephone Company and Tampere Telephone Company). The main objective of the research is to develop technology for the reuse of old copper telephone wiring for multi-megabit transmission using advanced signal processing techniques.

3.3.1 Channel measurements and modelling

Researcher: Yaohui Liu

In this project, the telephone line measurements carried out in Tampere are analysed. The focus is on interference measurements and modelling and in capacity analysis of connections.

3.3.2 Design of pulse shaping filters

Researcher: Amoakoh Gyasi-Agyei

This subproject focuses on pulse shaping filter design for CAP/QAM type line code. Efficient FIR filter design techniques employing symmetric coefficients were studied in [28]. Special attention is paid on suppression of radio amateur interference.

3.3.3 Design of VDSL networks

Researcher: Harri Mäntylä

Different schemes for implementing the subscriber networks are studied. The basic issue is how close to the subscribers the optical fiber should be brought.

3.4 COST 257

Project leader: Jorma Virtamo
Researchers: Samuli Aalto, Pasi Lassila, Esa Hyytiä, Kaisa Kyläkoski, Jani Lakkakorpi

COST 257 is a joint project between the Laboratory of Telecommunications Technology at HUT and VTT Information Technology. It represents the Finnish contribution to the European COST 257 Action, in which laboratories and research institutes from 18 countries participate. The research is mainly funded by TEKES with the support of Nokia Telecommunications and Sonera. The research focuses on developing models and methods for the performance analysis of telecommunication systems. The following problem areas have been addressed:

Figure 4: An example of using composite distributions for a two-traffic class and two-link example

3.5 Computational Methods for the Performance Analysis of Broadband Communication Networks, Com2

Project leader: Jorma Virtamo
Researchers: Attila Vidács, Jani Lakkakorpi

This is a three years project funded by the Academy of Finland and started in September 1998. An efficient method for estimating the three parameters of the fractional Brownian motion from measured traffic is being developed. The key idea is to sample the traffic at geometrically separated points in order to see the scaling behaviour with fewer sample points. Maximum likelihood method is applied for the estimation.

In the project also Mathematica and C libraries of algorithms for the solution of basic queuing systems is developed and maintained. Several new algorithms have been implemented.

3.6 Studies in queuing theory

Project leader: Samuli Aalto, Vinod Sharma

Optimal control problems of various batch service queuing systems have been considered, focusing on the case of finite service capacity. The models of this kind have natural applications in the area of transportation systems. Also the output process of some fluid flow storage models used in the teletraffic theory as burst scale models of multiplexers have been characterised. This work has resulted in a Ph.D. thesis.

A new queuing model for systems with a finite buffer capacity (in bits rather than in buffer places) has been developed. The input processes considered include Poisson arrivals, MMPP process and two traffic classes with priorities.

3.7 IP/Voice

Project leader: Raimo Kantola
Researcher: Vesa Kosonen, Harri Marjamäki, Nicklas Beijar

Voice over IP studies the transmission, switching and routing of voice in IP networks and service interoperability of such networks with PSTN/ISDN. The project was initiated in April 1997 and is planned to continue for three years. The project is mainly funded by a TEKES grant, and it has five industrial partners (Nokia Research Center, Nokia Telecommunications, Sonera Oy, Omnitele/Helsinki Telephone Research and Miratel).

Results for the second year include Harri Marjamäki's M.Sc thesis on Delay Characteristics of IP Voice Terminals, a conference paper at ITS98 on Voice Packet Interarrival jitter over IP switching, invited talks by professor Kantola at the Teleware seminar and in the NTC Research & Developing day. In addition, internal reports and student papers were produced.

3.8 IP / Switch

Project leader: Raimo Kantola
Researchers: Mika Ilvesmäki, Ilkka Peräläinen, Veikko Brax, Anna-Kaisa Lindfors

The project was initiated in April 1997 and is planned to continue for 3 years. The project is mainly funded by a TEKES grant, it has five industrial partners (Nokia Telecommunications, Sonera Oy, Omnitele/Helsinki Telephone Research and Tellabs).

Although viewed as the prototype of the future Information Superhighway, the current Internet technology has a number of drawbacks, including: limited transmission and routing capacity and limited speed, long and variable transmission delays and no support for quality of service. The project is aimed at helping to solve some of these problems by focusing on issues of deployment of ATM to increase the performance of the Internet and to improve the quality of service available to the user.

Besides technology evaluation the most important results in the project are based on using neural algorithms for Internet traffic classification and applying the classification results for boosting the network performance and perceived quality of service.

Figure 5: Procedure for measurement based Internet traffic classification

Results during the year include Ilkka Peräläinen's M.Sc thesis, a journal paper, three conference papers, internal reports and reports of special assignments by the students. More results are in the pipeline.

Annual Report 1998: Preface | Introduction | Personnel | Research projects | Teaching | Activities | Participation in boards and committees | Publications


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