Browsing by Author "Lassila, Pasi"

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  • Audiosignaalin aikaskaalan muuttaminen
    (2020-05-17) Konttas, Akseli
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Capturing and Reproducing Sound Fields with Ambisonics
    (2020-05-25) Pitkänen, Arttu
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Challenges of Localising Virtual Content Outdoors Using Cloud Anchors in Mobile Augmented Reality
    (2021-09-17) Pekkola, Marko
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Clustering using Gaussian mixture models
    (2021-09-04) Kuikka, Juho
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Core Network Design of Software Defined Radio Testbed
    (2013-09-23) Maheshwari, Kapil
     Sähkötekniikan korkeakoulu | Master's thesis
    The 4th generation of cellular system (LTE) does not inherit the traditional voice (circuit-switched) capabilities from its predecessors. Instead it relies on its high speed packet-switched core network with IMS (IP Multimedia Subsystem) for voice capabilities. Even though there are temporary solutions available until LTE gets its full deployment and coverage, operators are looking for a long term solution known as VoIMS which uses VoIP with SIP protocol for voice in the LTE network (VoLTE) through the IMS domain. The scope of this thesis work is to design, implement and verify the working of the core network for an LTE type software defined radio (SDR) testbed which is able to initiate, maintain and terminate voice and data connections. First step in this regard is to search and select the tools, programs and technologies that fulfil the network requirement in terms of network performance and user satisfaction. Next is to build, configure and verify the network operations of the designed network. As SDRs are used for testing purposes, the core network is also designed in correspondence to that, i.e., it is a test (lab) core network with configurations that are simple to implement and do not require coding implementation. The core network makes use of the virtualization technology and is realized with the help of open-source solutions, i.e., protocols and technologies that are customizable as required and does not require licensing for their use. These functionalities are implemented with the help of OpenSIPS, an open-source SIP server, DHCP and DNS servers. Demonstration of the core network verifies that successful voice and video call can be made between registered users on two different networks, running VoIP client software on different operating system platforms. The core network provides features such as voice, video, instant messaging, presence, dynamic IP assignment, IP address to name resolution and mobility.
  • Covariance-matrix-based CSI feedback in MIMO channels
    (2020-05-25) Volanto, Kalle
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Design of Device Triggered Network Slice Allocation
    (2020-05-25) Puurunen, Sami
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Dynamic load balancing in 5G HetNets for optimal performance-energy tradeoff
    (2018) Gebrehiwot, Misikir; Lassila, Pasi; Aalto, Samuli
     A4 Artikkeli konferenssijulkaisussa
    We consider optimal energy-aware load balancing of elastic downlink data traffic inside a macrocell with multiple small cells within its coverage area. The model for the problem corresponds to a system of parallel M/M/1-PS queues, where the macrocell is represented by a multiclass M/M/1-PS queue and each small cell is an energy-aware M/M/1-PS queue with additional states for the idle timer and the so-called setup delay. We apply the theory of MDPs to develop a near-optimal state-dependent policy, both for a weighted sum of the performance and energy as well as for the constrained formulation, where energy is minimized subject to a constraint on the performance. Specifically, we utilize the first step of the well-known policy iteration method under which the routing decision for each arrival requires evaluating the marginal future cost of adding the arrival in the small cell or the macrocell. As our main contribution, we derive the associated value functions and the explicit form of the near-optimal FPI policy. The performance of the policy is illustrated through numerical examples.
  • Efficient Simulation Techniques for Multiservice Loss Systems
    (1999) Lassila, Pasi
     Helsinki University of Technology | Licentiate thesis
  • Elastisen dataliikenteen kuormantasausongelma heterogeenisissä langattomissa solukkoverkoissa
    (2015-05-29) Kaiku, Jere
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Energy vs. QoX network- and cloud services management
    (2018-01-01) Blanco, Bego; Liberal, Fidel; Lassila, Pasi; Aalto, Samuli; Sainz, Javier; Gribaudo, Marco; Pernici, Barbara
     A3 Kirjan tai muun kokoomateoksen osa
    Network Performance (NP)- and more recently Quality of Service/Experience/anything (QoS/QoE/QoX)-based network management techniques focus on the maximization of associated Key Performance Indicators (KPIs). Such mechanisms are usually constrained by certain thresholds of other system design parameters. e.g., typically, cost. When applied to the current competitive heterogeneous Cloud Services scenario, this approach may have become obsolete due to its static nature. In fact, energy awareness and the capability of modern technologies to deliver multimedia content at different possible combinations of quality (and prize) demand a complex optimization framework. It is therefore necessary to define more flexible paradigms that make it possible to consider cost, energy and even other currently unforeseen design parameters not as simple constraints, but as tunable variables that play a role in the adaptation mechanisms. In this chapter we will briefly introduce most commonly used frameworks for multi-criteria optimization and evaluate them in different Energy vs. QoX sample scenarios. Finally, the current status of related network management tools will be described, so as to identify possible application areas.
  • Energy-aware Performance Analysis of Queueing Systems
    (2013-08-30) Lu, Xiaohua
     Sähkötekniikan korkeakoulu | Master's thesis
    ICT systems, especially data centers, consume a significant amount of energy in our daily life. With the rapidly increasing number and size of data centers, energy management is becoming essential. Thus, it is beneficial if the used energy in data centers can be utilized more efficiently. In this thesis, we analyze the energy-aware performance of queueing systems from the traffic point of view. The focus will be on using queueing theory to model and analyze a single processor in data centers. In data centers, the energy consumed by a processor depends on the processing speed. With higher speed, more energy is consumed, while with lower speed, the performance will be decreased. Thus, we consider the trade-off between the performance and energy consumption of processors. Based on this, we introduce a speed scaling method, which adjusts the processing speed of processors according to the traffic load of the queueing system. We mainly analyze and compare three optimized speed scaling methods, which are static, gated and linear speed scaling. In the gated and linear schemes, there is a switching delay when the processor is switched from the idle state to the busy state. The results demonstrate that the switching delay has a great impact on the optimized trade-off. In our scenario, without switching delay, gated and linear schemes have the same performance, and they are better than the static scheme. With switching delay, however, the linear scheme is always better than the gated scheme. With a long switching delay, even the static scheme can be better. In practice, the trade-off of our model is highly affected by the parameters in the model.
  • Energy-Aware Queueing Models and Controls for Server Farms
    (2014-06-16) Gebrehiwot, Misikir
     Sähkötekniikan korkeakoulu | Master's thesis
    Data centers are known to consume substantial amounts of energy. Together with the rising cost of energy, this has created a major concern. Server farms, being integral parts of data centers, waste energy while they are idle. Turning idle servers off may appear to eliminate this wastage. However, turning the server back on at the arrival of the next service request incurs a setup cost in the form of additional delays and energy consumption. Thus, a careful analysis is required to come up with the optimal server control policy. In this thesis, a queueing theoretic analysis of single server systems is carried out to determine optimal server control policies. Additionally, multiple server systems are also be studied through numerical methods. In this case, the task assignment policies that define how incoming requests are routed among the servers are also studied along with the control policies. The results of this study illustrate that the optimal control policy for a single server system leaves an idle server on or switches it off immediately when there is no request to serve. This is a general result that does not depend on service, setup and idling time distributions. However, in the case of multiserver systems, there is a plethora of choices for task assignment and server control policies. Our study indicates that the combination of the Join the Shortest Queue and Most Recently Busy task assignment policies can save up to 30% of the system cost if the control policy applied can wait for a specific amount of time before turning a server off. Moreover, a similar gain can be achieved by the simple Join the Shortest Queue task assignment policy when it is used along with a control policy that leaves an optimized number of servers on while switching the remaining servers off when they become idle.
  • Forwarding Capacity of an Infinite Homogeneous Wireless Network
    (2008) Nousiainen, Jarno
     Helsinki University of Technology | Master's thesis
    Ad hoc -verkko on langaton verkko, joka toimii ilman kiinteää verkkoinfrastruktuuria ja jossa päätelaitteet voivat viestiä keskenään toistensa välityksellä. Keskitetyn valvonnan puuttuessa verkon solmut ovat itse vastuussa kaikesta verkon toiminnallisuudesta, joka pitää sisällään niin reitin löytämisen kohteeseen kuin pakettien välittämisen sitä kohti. Työ alkaa lyhyellä ad hoc -verkkojen ja niiden suorituskykyyn vaikuttavien tekijöiden, pääsynvalvonnan (MAC) ja reitityksen, esittelyllä. Lisäksi käsitellään langattomia sensoriverkkoja, jotka muodostavat ad hoc -verkkojen erikoistapauksen ja joilla on lukuisia ehdotettuja sovelluksia laajoissa ad hoc verkoissa. Kun ad hoc -verkko on laaja, voidaan siinä erottaa makroskooppinen taso, joka vastaa päästä päähän -polun mittakaavaa, ja mikroskooppinen taso, joka vastaa yksittäisen hypyn mittakaavaa. Makroskooppisen tason reititysprotokolla näkee verkon jatkuvana väliaineena, jossa kulkevan pakettivuon suunnan se välittää mikroskooppiselle tasolle. Mikroskooppisen tason välitysmenetelmä puolestaan perustaa päätöksensä tälle informaatiolle. Yhtä suuntaa kerrallaan tarkasteltaessa on olemassa suurin pakettivuo, joka on mahdollista saavuttaa. Tämä maksimaalinen suunnattu pakettivuo riippuu verkon ominaisuuksista ja voidaan jakaa esimerkiksi aikaperusteisesti eri suuntien välillä. Työn keskeisessä osassa mallinnetaan laaja ad hoc -verkko ja laaditaan simulointialgoritmi suurimman ylläpidettävän vuon ylärajan löytämiseksi. Liukuvan ikkunan algoritmi (MWA) perustuu laajennettuun max-flow min-cut -lauseeseen. Algoritmia kehitetään edelleen yhä tiukempien ylärajojen tuottamiseksi. Algoritmilla saatuja tuloksia verrataan olemassa olevien välitysmenetelmien saavuttamiin kapasiteetteihin, jotka ovat alarajoihin suurimmalle mahdolliselle välityskapasiteetille, sekä säännöllisten verkkojen suorituskykyyn. Tiukin löydetty yläraja on noin kolminkertainen suurimpaan olemassa olevilla välitysmenetelmillä saavutettuun välityskapasiteettiin verrattuna.
  • Indexability of an opportunistic scheduling problem with partial channel information
    (2019-03-12) Aalto, Samuli; Lassila, Pasi; Taboada, Ianire
     A4 Artikkeli konferenssijulkaisussa
    Opportunistic scheduling in wireless cellular systems utilizes random channel quality variations in time by favoring the users with good channel conditions. However, the success of such schedulers is heavily depending on the accuracy of the available information on the channel states of users. In this paper, we consider the opportunistic scheduling problem of downlink data traffic with partial channel information, where the target is to minimize the flow-level holding costs. In earlier works, the Whittle index approach has successfully been utilized to develop near-optimal scheduling policies for the corresponding problems. Using the same approach, we complement and extend the results found thus far. More specifically said, our novel contributions are (i) finding sufficient conditions under which the problem with partial channel information is provably indexable, and (ii) deriving an explicit formula for the corresponding Whittle index. In addition, we evaluate the performance of the derived Whittle index policies and compare them with some greedy policies by numerical simulations.
  • Kahden palvelimen fork-join-jono ja sen sovellus töiden rinnakkainlaskentaan
    (2024-05-23) Söderström, Eerik
     Sähkötekniikan korkeakoulu | Bachelor's thesis
    Tietokoneiden prosessointikyky on nykyisessä digitaalisessa maailmassa tärkeä aihe. Tämän prosessoinnin optimoimista varten on kehitetty MapReduce-ohjelmointimalli, joka optimoi prosessonitia rinnakkainlaskennan avulla. MapReduce jakaa prosessoitavan työn osiin, ja jakaa sen erillisille prosessoreille. Tämä työ analysoi rinnakkainlaskennan hyötyä käyttäen MapReduce-ohjelmointimallin yksinkertaisinta erikoistapausta eli kahden M/M/1-palvelimen fork-join-jonon avulla. Kun systeemiin saapuu työ, se jaetaan kahdeksi osaksi, jolloin yksi osa annetaan palvelimelle 1, ja toinen osa palvelimelle 2. Kun molemmat työn osat on saatu prosessoitua, ne liittyvät yhteen ja lähtevät systeemistä. Rinnakkainlaskennan hyötyä analysoitiin sekä teoreettisesti että numeerisesti. Fork-join-jonon mallintamista varten käytettiin 2-ulotteista Markov-prosessia, jossa ulottuvuudet kuvaavat töiden määriä palvelimissa. Tämän prosessin tasapainojakauman avulla voidaan laskea systeemin viive. Huomattiin, että homogeeninen systeemi eli systeemi, jossa palvelimien viiveillä on samat jakaumat on ideaalitapaus. Heterogeenisyys eli tilanne, jossa palvelimien viiveillä on eri jakaumat on vain haitaksi. Tästä syystä rinnakkainlaskennan hyötyä analysoidessa tarkasteltiin vain homogeenista tilannetta. Rinnakkainlaskennan hyödyn analysoimiseksi täytyi olla jokin ekvivalentti ei rinnakkaistettu systeemi. Koska todellinen ekvivalentti systeemi olisi ollut tämän työn laajuuden kannalta liian monimutkainen, piti yksinkertaistaa. Päädyttiin M/M/2-jonoon, jossa on yhteinen jono molemmille palvelimille erillisten jonojen sijaan. Palvelimien keskiviiveet ovat kaksi kertaa se, mikä fork-join-jonon palvelimilla on, koska nyt koko työ annetaan jommallekummalle palvelimelle sen sijaa, että se jaettaisiin kahdeksi. Nämä yksinkertaistukset tekivät M/M/2-jonosta tehokkaamman, kuin mitä todellinen ekvivalentti systeemi olisi. Vertailussa M/M/2-jono oli hiukan tehokkaampi kuin fork-join. Täytyy kuitenkin muistaa, että vertailu on hyvin epäreilu fork-join-jonon kannalta, ja epäreilusta vertailusta huolimatta, fork-join pärjäsi todella hyvin.
  • Käyttöliittymäsuunnittelun tehostaminen valikko-optimoinnilla
    (2020-05-17) Arponen, Arttu
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Kuvatiedostomuotojen teoria ja käytäntö
    (2020-05-17) Ronkainen, Niko
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Laiteohjelmisto osana ohjelmistoradiota
    (2021-09-17) Rantanen, Veli-Matti
     Sähkötekniikan korkeakoulu | Bachelor's thesis
  • Langattoman verkon riippumattomat linkkijoukot ja stokastinen optimointi
    (2009) Lääkkölä, Riku
     Elektroniikan, tietoliikenteen ja automaation tiedekunta | Bachelor's thesis