Approximation to Distribution of Product of Random Variables Using Orthogonal Polynomials for Lognormal Density

We derive a closed-form expression for the orthogonal polynomials associated with the general lognormal density. The result can be utilized to construct easily computable approximations for probability density function of a product of random variables, when the considered variates are either independent or correlated. As an example, we have calculated the approximative distribution for the product of Nakagami-m variables. Simulations indicate that accuracy of the proposed approximation is good with small cross-correlations under light fading condition.Comment: submitted to IEEE Communications Lette

Performance analysis of multi-antenna and multi-user methods for 3G and beyond

Performance of cellular networks has become an issue with forecasted growing public demand for medium and high data rate services. Motivated by these expectations multi-antenna techniques such as transmit diversity (TD), channel-aware scheduling and multiple-input multiple-output (MIMO) transceivers have received a lot of enthusiasm within wireless communications community. We first focus on closed-loop (CL) TD and introduce extended mode 1 and 2 (e-mode 1 and 2) algorithms that are designed based on universal terrestrial radio access (UTRA) frequency division duplex (FDD) CL mode 1 and 2. We derive analytical performance results for e-mode 1 and 2 in terms of signal to noise ratio (SNR) gain, link capacity and bit error probability (BEP). We also consider the effect of feedback errors to the performance of closed-loop system. In the analysis of channel-aware scheduling we focus on on-off scheduling (OOS) where user's feedback consists of only a single bit. Performance results in both downlink and uplink clearly indicate that most of the achievable gain from channel-aware scheduling can be obtained with very scarce channel state information (CSI). Results also show that the design of feedback channel is of great importance because feedback errors may seriously degrade the system performance. The third topic of the thesis concentrates on MIMO techniques that can be implemented in UTRA FDD uplink without major revisions to the current air interface. We show that the UTRA FDD uplink coverage and capacity performance can be boosted by single-input multiple-output (SIMO) and MIMO transceivers. The information MIMO employing parallel multiplexing instead of transmit diversity shows its potential when extremely high user data rates are needed.Solukkoverkkojen suorituskyky on noussut tärkeään rooliin nopeiden datapalveluiden kasvuennusteiden myötä. Näiden kasvuodotusten perusteella moniantennitekniikat kuten lähetysdiversiteetti, kanavan huomioon ottava lähetyksen aikataulutus sekä useaa samanaikaista datavirtaa tukevat lähetinvastaanotinmenetelmät ovat saaneet osakseen paljon kiinnostusta langattoman tietoliikenteen tutkijayhteisössä. Tutkimuksessa keskitytään aluksi suljettua säätöä käyttäviin lähetysdiversiteettimenetelmiin, missä yhteydessä esitellään laajennetut moodien 1 ja 2 algoritmit, jotka on aiemmin kehitetty kolmannen sukupolven WCDMA järjestelmän suljetun säädön moodien 1 ja 2 pohjalta. Laajennetuille moodien 1 ja 2 algoritmeille johdetaan analyyttisiä suorituskykytuloksia käyttäen mittarina signaali-kohinasuhteen parannusta, linkin kapasiteettia sekä bittivirheiden todennäköisyyttä. Myös säätövirheiden vaikutusta järjestelmän suorituskykyyn tarkastellaan. Lähetyksen aikataulutuksen analyysi painottuu kytkettyyn aikataulutukseen, missä käyttäjän säätöinformaatio sisältyy yhteen bittiin. Sekä ylä- että alalinkin suorituskykytulokset osoittavat selvästi, että suurin osa mahdollisesta parannuksesta voidaan saavuttaa hyvin karkeaan kanavatilan informaatioon perustuen. Tulokset osoittavat myös, että säätökanavan suunnittelu on tärkeää, koska säätövirheet voivat vakavasti heikentää järjestelmän suorituskykyä. Kolmannessa aihealueessa keskitytään moniantennitekniikoihin, jotka voidaan toteuttaa WCDMA järjestelmän ylälinkissä ilman perustavanlaatuisia muutoksia nykyiseen ilmarajapintaan. Tutkimuksessa osoitetaan, että ylälinkin peittoa ja kapasiteettia voidaan parantaa tutkituilla moniantennitekniikoilla olipa lähettimessä yksi tai useampia antenneja. Menetelmä, jossa informaatio jaetaan useisiin rinnakkaisiin datavirtoihin sen sijaan että käytettäisiin vain yhtä datavirtaa, osoittautuu erityisen lupaavaksi kun tarvitaan hyvin nopeita tiedonsiirtoyhteyksiä.reviewe

A Novel Multiobjective Cell Switch-Off Framework for Cellular Networks

Cell Switch-Off (CSO) is recognized as a promising approach to reduce the energy consumption in next-generation cellular networks. However, CSO poses serious challenges not only from the resource allocation perspective but also from the implementation point of view. Indeed, CSO represents a difficult optimization problem due to its NP-complete nature. Moreover, there are a number of important practical limitations in the implementation of CSO schemes, such as the need for minimizing the real-time complexity and the number of on-off/off-on transitions and CSO-induced handovers. This article introduces a novel approach to CSO based on multiobjective optimization that makes use of the statistical description of the service demand (known by operators). In addition, downlink and uplink coverage criteria are included and a comparative analysis between different models to characterize intercell interference is also presented to shed light on their impact on CSO. The framework distinguishes itself from other proposals in two ways: 1) The number of on-off/off-on transitions as well as handovers are minimized, and 2) the computationally-heavy part of the algorithm is executed offline, which makes its implementation feasible. The results show that the proposed scheme achieves substantial energy savings in small cell deployments where service demand is not uniformly distributed, without compromising the Quality-of-Service (QoS) or requiring heavy real-time processing

Energy saving scheme for multicarrier HSPA + under realistic traffic fluctuation

The final publication is available at Springer via http://dx.doi.org/10.1007/s11036-015-0656-6In the near future, an increase in cellular network density is expected to be one of the main enablers to boost the system capacity. This development will lead to an increase in the network energy consumption. In this context, we propose an energy efficient dynamic scheme for HSDPA + (High Speed Downlink Packet Access-Advanced) systems aggregating several carriers and which adapts dynamically to the network traffic. The scheme evaluates whether node-B deactivation is feasible without compromising the user flow throughput. Furthermore, instead of progressive de-activation of carriers and/or node-B switch-off, we evaluate the approach where feasible combination of inter-site distance and number of carriers is searched to obtain best savings. This is done by also considering the effect of transition delays between network configuration changes. The solution exploits the fact that re-activation of carriers might permit turning off other BSs earlier at relatively higher load than existing policies. Remote electrical downtilt is also considered as a means to maximize the utilization of higher modulation and coding schemes in the extended cells. This approach promises significant energy savings when compared with existing policies - not only for low traffic hours but also for medium load scenarios.Peer ReviewedPostprint (author's final draft