A unified construction of space-time codes with optimal rate-diversity tradeoff

The problem of constructing space-time (ST) block codes over a fixed, desired signal constellation is considered. In this situation, there is a tradeoff between the transmission rate as measured in constellation symbols per channel use and the transmit diversity gain achieved by the code. The transmit diversity is a measure of the rate of polynomial decay of pairwise error probability of the code with increase in the signal-to-noise ratio (SNR). In the setting of a quasi-static channel model, let n(t) denote the number of transmit antennas and T the block interval. For any n(t) <= T, a unified construction of (n(t) x T) ST codes is provided here, for a class of signal constellations that includes the familiar pulse-amplitude (PAM), quadrature-amplitude (QAM), and 2(K)-ary phase-shift-keying (PSK) modulations as special cases. The construction is optimal as measured by the rate-diversity tradeoff and can achieve any given integer point on the rate-diversity tradeoff curve. An estimate of the coding gain realized is given. Other results presented here include i) an extension of the optimal unified construction to the multiple fading block case, ii) a version of the optimal unified construction in which the underlying binary block codes are replaced by trellis codes, iii) the providing of a linear dispersion form for the underlying binary block codes, iv) a Gray-mapped version of the unified construction, and v) a generalization of construction of the S-ary case corresponding to constellations of size S-K. Items ii) and iii) are aimed at simplifying the decoding of this class of ST codes.

Optical, Field-Emission, and Antimicrobial Properties of ZnO Nanostructured Films Deposited at Room Temperature by Activated Reactive Evaporation

ZnO nanostructures were deposited on flexible polymer sheet and cotton fabrics at room temperature by activated reactive evaporation. Room-temperature photoluminescence spectrum of ZnO nanostructured film exhibited a week intrinsic UV emission and a strong broad yellow-orange visible emission. TEM and HRTEM studies show that the grown nanostructures are crystalline in nature and their growth direction was indentified to be along [002]. ZnO nanostructures grown on the copper-coated flexible polymer sheets exhibited stable field-emissio characteristics with a threshold voltage of 2.74 V/mu m (250 mu A) and a very large field enhancement factor (beta) of 23,213. Cotton fabric coated with ZnO nanostructures show an excellent antimicrobial activity against Staphylococcus aureus bacteria (Gram positive), and similar to 73% reduction in the bacterial population is achieved compared to uncoated fabrics after 4 h in viability. Using a shadow mask technique, we also selectively deposited the nanostructures at room temperature on polymer substrates.

Understanding Customer Loyalty and Disloyalty The Effect of Loyalty-Supporting and -Repressing Factors (first edition sold out, 'print on demand' 60 €)

Customer loyalty has been a central topic of both marketing theory and practice for several decades. Customer disloyalty, or relationship ending, has received much less attention. Despite the close relation between customer loyalty and disloyalty, they have rarely been addressed in the same study. The thesis bridges this gap by focusing on both loyal and disloyal customers and the factors characterising them. Based on a qualitative study of loyal and disloyal bank customers in the Finnish retail banking market, both factors that are common to the groups and factors that differentiate between them are identified. A conceptual framework of factors that affect customer loyalty or disloyalty is developed and used to analyse the empirical data. According to the framework, customers’ loyalty status (behavioural and attitudinal loyalty) is influenced by positive, loyalty-supporting, and negative, loyalty-repressing factors. Loyalty-supporting factors either promote customer dedication, making the customer want to remain loyal, or act as constraints, hindering the customer from switching. Among the loyalty-repressing factors it is especially important to identify those that act as triggers of disloyal behaviour, making customers switch service providers. The framework further suggests that by identifying the sources of loyalty-supporting and -repressing factors (the environment, the provider, the customer, the provider-customer interaction, or the core service) one can determine which factors are within the control of the service provider. Attitudinal loyalty is approached through a customer’s “feeling of loyalty”, as described by customers both orally and graphically. By combining the graphs with behavioural loyalty, seven customer groups are identified: Stable Loyals, Rescued Loyals, Loyals at Risk, Positive Disloyals, Healing Disloyals, Fading Disloyals, and Abrupt Disloyals. The framework and models of the thesis can be used to analyse factors that affect customer loyalty and disloyalty in different service contexts. Since the empirical study was carried out in a retail bank setting, the thesis has managerial relevance especially for banks. Christina Nordman is associated with CERS, Center for Relationship Marketing and Service Management at the Swedish School of Economics and Business Administration. The doctoral thesis is part of the Göran Collert Research Project in Customer Relationships and Retail Banking and has been funded by The Göran Collert Foundation.

Low-Complexity Near-ML Decoding of Large Non-Orthogonal STBCs using Reactive Tabu Search

Non-orthogonal space-time block codes (STBC) with large dimensions are attractive because they can simultaneously achieve both high spectral efficiencies (same spectral efficiency as in V-BLAST for a given number of transmit antennas) as well as full transmit diversity. Decoding of non-orthogonal STBCs with large dimensions has been a challenge. In this paper, we present a reactive tabu search (RTS) based algorithm for decoding non-orthogonal STBCs from cyclic division algebras (CDA) having largedimensions. Under i.i.d fading and perfect channel state information at the receiver (CSIR), our simulation results show that RTS based decoding of 12 X 12 STBC from CDA and 4-QAM with 288 real dimensions achieves i) 10(-3) uncoded BER at an SNR of just 0.5 dB away from SISO AWGN performance, and ii) a coded BER performance close to within about 5 dB of the theoretical MIMO capacity, using rate-3/4 turbo code at a spectral efficiency of 18 bps/Hz. RTS is shown to achieve near SISO AWGN performance with less number of dimensions than with LAS algorithm (which we reported recently) at some extra complexity than LAS. We also report good BER performance of RTS when i.i.d fading and perfect CSIR assumptions are relaxed by considering a spatially correlated MIMO channel model, and by using a training based iterative RTS decoding/channel estimation scheme.

Constellation Constrained Capacity of Two-user Broadcast Channels

Capacity region for two-user Gaussian Broadcast Channels (GBC) is well known with the optimal input being Gaussian. In this paper we explore the capacity region for GBC when the users' symbols are taken from finite complex alphabets (like M-QAM, M-PSK). When the alphabets for both the users are the same we show that rotation of one of the alphabets enlarges the capacity region. We arrive at an optimal angle of rotation by simulation. The effect of rotation on the capacity region at different SNRs is also studied using simulation results. Using the setup of Fading Broadcast Channel (FBC) given by [Li and Goldsmith, 2001], we study the ergodic capacity region with inputs from finite complex alphabets. It is seen that, using the procedure for optimum power allocation obtained in [Li and Goldsmith, 2001] for Gaussian inputs, to allocate power to symbols from finite complex alphabets, relative rotation between the alphabets does not improve the capacity region. Simulation results for a modified heuristic power allocation procedure for finite-constellation case, show that Constellation Constrained capacity region enlarges with rotation.

STBCs with Reduced Sphere Decoding Complexity for Two-User MIMO-MAC

In this paper, Space-Time Block Codes (STBCs) with reduced Sphere Decoding Complexity (SDC) are constructed for two-user Multiple-Input Multiple-Output (MIMO) fading multiple access channels. In this set-up, both the users employ identical STBCs and the destination performs sphere decoding for the symbols of the two users. First, we identify the positions of the zeros in the R matrix arising out of the Q-R decomposition of the lattice generator such that (i) the worst case SDC (WSDC) and (ii) the average SDC (ASDC) are reduced. Then, a set of necessary and sufficient conditions on the lattice generator is provided such that the R matrix has zeros at the identified positions. Subsequently, explicit constructions of STBCs which results in the reduced ASDC are presented. The rate (in complex symbols per channel use) of the proposed designs is at most 2/N-t where N-t denotes the number of transmit antennas for each user. We also show that the class of STBCs from complex orthogonal designs (other than the Alamouti design) reduce the WSDC but not the ASDC.

Implications of Energy Profile and Storage on Energy Harvesting Sensor Link Performance

Energy harvesting sensors (EHS), which harvest energy from the environment in order to sense and then communicate their measurements over a wireless link, provide the tantalizing possibility of perpetual lifetime operation of a sensor network. The wireless communication link design problem needs to be revisited for these sensors as the energy harvested can be random and small and not available when required. In this paper, we develop a simple model that captures the interactions between important parameters that govern the communication link performance of a EHS node, and analyze its outage probability for both slow fading and fast fading wireless channels. Our analysis brings out the critical importance of the energy profile and the energy storage capability on the EHS link performance. Our results show that properly tuning the transmission parameters of the EHS node and having even a small amount of energy storage capability improves the EHS link performance considerably.

Optimal Weighted Antenna Selection For Imperfect Channel Knowledge From Training

Receive antenna selection (AS) reduces the hardware complexity of multi-antenna receivers by dynamically connecting an instantaneously best antenna element to the available radio frequency (RF) chain. Due to the hardware constraints, the channels at various antenna elements have to be sounded sequentially to obtain estimates that are required for selecting the ``best'' antenna and for coherently demodulating data. Consequently, the channel state information at different antennas is outdated by different amounts. We show that, for this reason, simply selecting the antenna with the highest estimated channel gain is not optimum. Rather, the channel estimates of different antennas should be weighted differently, depending on the training scheme. We derive closed-form expressions for the symbol error probability (SEP) of AS for MPSK and MQAM in time-varying Rayleigh fading channels for arbitrary selection weights, and validate them with simulations. We then derive an explicit formula for the optimal selection weights that minimize the SEP. We find that when selection weights are not used, the SEP need not improve as the number of antenna elements increases, which is in contrast to the ideal channel estimation case. However, the optimal selection weights remedy this situation and significantly improve performance.

Comparative study of adaptive frequency hopping with power control to avoid WLAN interference in WPAN systems like Bluetooth

Presently Bluetooth(BT) is one of the widely used device for personal communication. As BT devices are operating in the unlicensed ISM band, they are often subjected to the interference from WLAN. The band width of BT (1MHz) is narrower compare to the bandwidth of WLAN (22MHz). So for coexistence purpose it is important to observe the performance of narrow band signal BT in presence of wideband interference WLAN and vice versa. As there are many work on the performance of WLAN in presence BT interference 3]4]5]6], the main focus in this paper is on performance of BT in presence of WLAN interference in AWGN, Rayleigh fading channel. Then comparison of the performance using interference avoidance technique like adaptive frequency hopping, power control for BT system is given. Finally a conclusion is drawn observing the simulation results on the technique which is more suitable for WLAN interference mitigation in BT system.

Traditionally Protected Forests´ Role within Transforming Natural Resource Management Regimes in Taita Hills, Kenya

In Taita Hills, south-eastern Kenya, remnants of indigenous mountain rainforests play a crucial role as water towers and socio-cultural sites. They are pressurized due to poverty, shortage of cultivable land and the fading of traditional knowledge. This study examines the traditional ecological knowledge of Taitas and the ways it may be applied within transforming natural resource management regimes. I have analyzed some justifications for and hindrances to ethnodevelopment and participatory forest management in light of recently renewed Kenyan forest policies. Mixed methods were applied by combining an ethnographic approach with participatory GIS. I learned about traditionally protected forests and their ecological and cultural status through a seek out the expert method and with remote sensing data and tools. My informants were: 107 household interviewees, 257 focus group participants, 73 key informants and 87 common informants in participatory mapping. Religious leaders and state officials shared their knowledge for this study. I have gained a better understanding of the traditionally protected forests and sites through examining their ecological characteristics and relation to social dynamics, by evaluating their strengths and hindrances as sites for conservation of cultural and biological diversity. My results show that, these sites are important components of a complex socio-ecological system, which has symbolical status and sacred and mystical elements within it, that contributes to the connectivity of remnant forests in the agroforestry dominated landscape. Altogether, 255 plant species and 220 uses were recognized by the tradition experts, whereas 161 species with 108 beneficial uses were listed by farmers. Out of the traditionally protected forests studied 47 % were on private land and 23% on community land, leaving 9% within state forest reserves. A paradigm shift in conservation is needed; the conservation area approach is not functional for private lands or areas trusted upon communities. The role of traditionally protected forests in community-based forest management is, however, paradoxal, since communal approaches suggests equal participation of people, whereas management of these sites has traditionally been the duty of solely accredited experts in the village. As modernization has gathered pace such experts have become fewer. Sacredness clearly contributes but, it does not equal conservation. Various social, political and economic arrangements further affect the integrity of traditionally protected forests and sites, control of witchcraft being one of them. My results suggest that the Taita have a rich traditional ecological knowledge base, which should be more determinately integrated into the natural resource management planning processes.

Community-based Ecotourism as a Sustainable Development Option in the Taita Hills, Kenya

This study aims at identifying the existing and potential resources, as well as recognizing the hinderances, for community-based ecotourism development in the Taita Hills in south-eastern Kenya. The indigenous mountain rain forests on the hills are rich in biodiversity, but severely degraded because of encroachment caused by the dynamics of increased population, socio-politics and economics. The research problems are based on the hypothesis that there is no tourism in the Taita Hills generating income for the local economy and high population density combined with poverty creates a need for alternative employment opportunities as well as for sustainable ways of forest resource management. The data for this study was gathered during two field trips in Kenya, in January-February 2004 and 2005, as a part of the Taita Project within the Department of Geography at the University of Helsinki. The qualitative methods used consist of RRA and PRA techniques, in-depth interviews, a structured questionnaire and literature analysis as well as attendance on excursions and a workshop with conservation experts and officials. Four case areas in the Taita Hills are studied. The study concludes that alternative livelihoods are needed among the Taita Hills´ rural population and community-based ecotourism is seen as a way of bringing financial benefits for households as well as reviving the fading cultural traditions and indigenous knowledge about forest use. The governmental policies, district level development plans and some NGOs support ecotourism development. The Forest Act 2005 forms base for local participation in forest management. The unique natural features, the welcoming Taita-culture and the location in the coastal tourism circle favour Taita Hills. However, this kind of development has its risks, such as too rapid change of sorest usage level and the exposure of communities to an ecotourism treadmill process. The costbenefit ration of marketing for hard ecotourists is generally low and the tourism infrastructure needs upgrading in the Taita Hills. More tight collaboration is important between the different level stakeholders working for conservation and development. Community-based ecotourism in Taita Hills, when carefully planned and managed, could be one opportunity for Kenya to diversify its tourism product supply and for forestadjacent communities to gain tangible benefits on a sustainable basis from forests.

Sosiaaliturvan ulkopuolella - kokemuksia kansalaisuuden reunalta

Muuttaessaan maasta toiseen ihminen kohtaa useita rajoja. Ylittäessään kohdemaan valtion rajan hän kulkee läpi ensimmäisestä maahanmuuton portista. Toinen raja erottaa tilapäiset asukkaat pysyvistä: tämän maahanmuuton toisen portin läpikulkemisen myötä yksilö pääsee osalliseksi sosiaalisista oikeuksista. Maahanmuuton viimeisestä portista kuljettuaan yksilö saavuttaa kyseisen valtion kansalaisuuden. (Hammar 1990, 21.) Tässä pro gradu -tutkielmassa tarkastelen toisen maahanmuuton portin aukeamista ja sosiaaliturvan piiriin pääsyä odottavien maahan-muuttajien kokemuksia. Käytän tarkastelussa sosiaalisen kansalaisuuden ja marginaalisuuden käsitteitä. Tutkielmassa selvitän, miten sosiaali- ja terveyspalveluiden sekä toimeentuloturvan ulkopuolelle jääminen vaikuttaa maahanmuuttajien arkeen ja miten he kokevat osallisuutensa ja jäsenyytensä yhteiskunnassa. Tutkimus on lähtökohdiltaan fenomenologis-hermeneuttinen ja sovellan lähestymistapana ko-kemuksiin keskittyvän narratiivista tutkimusta. Tutkimusaineisto on koottu kevään 2011 aikana ja se koostuu 10 teemahaastattelusta. Haastateltavien maahanmuuton keinot ja syyt vaihtelivat: he olivat saapuneet Suomeen perhesyistä, työn vuoksi tai hakeakseen turvaa. Haastateltavat tavoitettiin Helsingin Diakoniaopiston, Pro-tukipisteen, Kansainvälisen seurakunnan ja tuttava-verkostojen kautta. Aineiston analyysi toteutettiin sisällönanalyysillä Atlas-ohjelman avulla syksyn 2011 aikana. Toisen maahanmuuton portin aukeamisen odottaminen oli raskaaksi: tuota aikaa leimasi epä-varmuus, tyhjyys ja yksinäisyys. Sosiaaliturvan ulkopuolella jääminen aiheutti osalle haastatel-tavista taloudellisia vaikeuksia sekä ongelmia terveydenhuollon palveluiden piiriin pääsemisessä. Toisaalta apua hakeneet haastateltavat olivat sitä lopulta saaneet. Auttamistyön ammattilaiset ja maistraatti saivat haastateltavien kertomuksissa portinvartijan aseman. Kaikille sosiaaliturvan ulkopuolelle jääminen ei ollut ongelma vaan he kokivat sosiaaliturvan puutetta suuremmaksi ongelmaksi työnteko-oikeuden puuttumisen. Kuulumisen ja ulkopuolisuuden kokemus voivat olla läsnä samanaikaisesti, ja kuulumisesta neuvotellaan jatkuvasti esimerkiksi sosiaalisessa kanssakäymisessä tai palveluita hakiessa. Insti-tutionaaliset käytännöt ja poiskäännyttämisen kokemukset tuottavat marginaalisia identiteettejä. Tasavertainen oikeus sosiaaliturvaan vahvistaa kokemusta kuulumisesta ja kodista. Sosiaaliturva ei kuitenkaan yksin määritä kuulumisen ja kodin kokemusta vaan siihen vaikuttavat myös muut tekijät. Näistä tärkeimmät ovat kehon fyysinen sijoittuminen Suomeen, perhe- ja ystä-vyyssuhteet, työ, asunto ja rasismin kokemukset.

Novel approach to estimate fringe order in Moire profilometry

A novel approach to estimate fringe order in Moire topography is proposed. Along with the light source used to create shadow of the grating on the object (as in conventional moire), proposed method uses a second light source which illuminates the object with color bands from the side. Width of each colored band is set to match that height which leads to a 2 pi phase shift in moire fringes. This facilitates one to rule the object with colored bands, which can be used to estimate fringe order using a color camera with relatively low spatial resolution with out any compromise in height sensitivity. Current proposal facilitates one to extract 3D profile of objects with surface discontinuities. It also deals with the possible usage of moire topography (when combined with the proposed method) in extracting 3D surface profile of many objects with height discontinuities using a single 2D image. Present article deals with theory and simulations of this novel side illumination based approach.

On Two-User Gaussian Multiple Access Channels With Finite Input Constellations

Constellation Constrained (CC) capacity regions of two-user Single-Input Single-Output (SISO) Gaussian Multiple Access Channels (GMAC) are computed for several Non-Orthogonal Multiple Access schemes (NO-MA) and Orthogonal Multiple Access schemes (O-MA). For NO-MA schemes, a metric is proposed to compute the angle(s) of rotation between the input constellations such that the CC capacity regions are maximally enlarged. Further, code pairs based on Trellis Coded Modulation (TCM) are designed with PSK constellation pairs and PAM constellation pairs such that any rate pair within the CC capacity region can be approached. Such a NO-MA scheme which employs CC capacity approaching trellis codes is referred to as Trellis Coded Multiple Access (TCMA). Then, CC capacity regions of O-MA schemes such as Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA) are also computed and it is shown that, unlike the Gaussian distributed continuous constellations case, the CC capacity regions with FDMA are strictly contained inside the CC capacity regions with TCMA. Hence, for finite constellations, a NO-MA scheme such as TCMA is better than FDMA and TDMA which makes NO-MA schemes worth pursuing in practice for two-user GMAC. Then, the idea of introducing rotations between the input constellations is used to construct Space-Time Block Code (STBC) pairs for two-user Multiple-Input Single-Output (MISO) fading MAC. The proposed STBCs are shown to have reduced Maximum Likelihood (ML) decoding complexity and information-losslessness property. Finally, STBC pairs with reduced sphere decoding complexity are proposed for two-user Multiple-Input Multiple-Output (MIMO) fading MAC.

Bayesian Decentralized Spectrum Sensing in Cognitive Radio Networks

This paper considers the problem of spectrum sensing, i.e., the detection of whether or not a primary user is transmitting data by a cognitive radio. The Bayesian framework is adopted, with the performance measure being the probability of detection error. A decentralized setup, where N sensors use M observations each to arrive at individual decisions that are combined at a fusion center to form the overall decision is considered. The unknown fading channel between the primary sensor and the cognitive radios makes the individual decision rule computationally complex, hence, a generalized likelihood ratio test (GLRT)-based approach is adopted. Analysis of the probabilities of false alarm and miss detection of the proposed method reveals that the error exponent with respect to M is zero. Also, the fusion of N individual decisions offers a diversity advantage, similar to diversity reception in communication systems, and a tight bound on the error exponent is presented. Through an analysis in the low power regime, the number of observations needed as a function of received power, to achieve a given probability of error is determined. Monte-Carlo simulations confirm the accuracy of the analysis.