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Bu çalışmada, ikili haberleşme sistemleri simetrik Gauss karışım gürültülü kanal için çalışılmaktadır. Tek eşikli sezici ile optimal olan ML kurallı sezici hata olasılıkları açısından karşılaştırılmaktadır. İlk olarak, tek eşikli sezicinin optimal olduğu yeter koşul sunulmaktadır. Bu koşulun sağlanmadığı durumda, tek eşikli sezicinin gürültüsüz koşullarda dahi oldukça düşük performansa sahip olabildiği belirtilmektedir. Daha sonra, aynı koşullar için ML kurallı sezici incelenmekte ve asimptotik sonuçlar elde edilmektedir. Son olarak, çeşitli senaryolar için benzetim sonuçları elde edilmekte ve teorik bulguları doğrulamak için sonuçlar ayrıntılı olarak tartışılmaktadır. In this paper, binary communication systems are studied in the presence of symmetric Gaussian mixture noise channels. The performance of single threshold detectors is compared with that of the optimal maximum likelihood (ML) detector in terms of error probability. First, sufficient conditions for the single threshold detector to be optimal are presented. It is discussed that if the conditions are not satisfied, then single threshold detectors could exhibit significantly inferior performance even in noiseless conditions. In addition, the ML detector is examined for the identical conditions, and asymptotic results are derived. Finally, simulation results are obtained for various scenarios, and the results are discussed in detail to verify the theoretical findings.

Bu çalışmada, verici ve alıcı arasında Gauss ve Laplace haberleşme kanalları bulunan ikili iletişim sistemleri çalışılmaktadır. Ortalama güç kısıtlaması altında, ortalama hata olasılığını en küçülten stratejinin araştırılması amaçlanmaktadır. Öncelikle, optimal stratejinin sunulan eniyileme probleminin çözümü şeklinde olduğu gösterilmektedir. Daha sonra, kanal anahtarlamanın sistem performansını ortalama hata olasılığı açısından iyileştiremeyeceği koşul elde edilmektedir. Bu durumda, optimal çözümün herhangi güç kısıtlaması altında Gauss kanalı üzerinden iletim şeklinde olduğu gösterilmektedir. Koşulun sağlanmadığı durumda ise optimal strateji, eniyileme probleminin çözümü ile belirlenmektedir. Son olarak, kuramsal sonuçları doğrulamak amacıyla sayısal örnekler sunulmaktadır.

Geochemical and sedimentological analyses and radionuclide (Pb-210 and Cs-137) dating of three cores from the Bosporus outlet area of the Black Sea, north of Istanbul, were conducted to assess the sources and history of heavy metal pollution. The sedimentary succession in the shelf core KD12-01 consists mainly of clay (49-80%) and silt (15-41%). Radionuclide dating of the core indicates that it consists of old sediments that are uncontaminated with heavy metals. In contrast, cores KD12-04 and KD12-07 recovered from -350 m and -304 mm in the upper slope area represent sediments consisting of silt and clay that were deposited since at least the last 120 years and 60 years, respectively. The latter core contains two mass-flow units represented by relatively old sedimentary material according to the low 21 Pb activity and relatively low heavy metal contents. The upper 40 and 48 cm of cores KD 12-04 and KD 12-07 represent sediments deposited since 1970s and 1980s that are significantly polluted with Cu, Ni, Zn, Mo, Pb and Cr, Cu, Co, Ni, Mo, Pb, Zn, respectively. However, high Pb and Cr concentrations with high TOC contents date back to early part of the 20th century in core KD 12-04. The geochemical data, together with the high Cs-137 concentrations of the contaminated sediments, strongly suggest that the pollution is mainly delivered to the western and north western Black Sea by the large European rivers, from there transported to the study area by the rim current, and deposited in the sediments under anoxic conditions. (C) 2018 Elsevier Ltd. All rights reserved.

Bu tez kapsamında Yassı TV'lerde bulunan elektronik devrelerin sıcaklıklarının minimize edilmesi amacıyla optimum ısı transferini sağlamak üzere arka kapakta yer alan hava deliklerinin ve elektronik devrelerin uygun tasarım parametreleri belirlenmiştir. Maksimum ısı transferi gerçekleştirecek olan elektronik devre ve havalandırma deliklerinin optimum tasarımının belirlenmesinde, Hesaplamalı Akışkanlar Dinamiği (HAD) yazılımı olan ANSYS Icepak modülünde simülasyonlar yapılmıştır. Doğal konveksiyon ısı transferi yöntemi baz alınarak yapılan simülasyonlarda, hava akış hızı ve rotasının devrelerdeki ısı transferinde önemli iki parametre oldukları gözlenmiştir. Farklı hava akış hızlarında, devreler üzerinde oluşan ısı transferi, simülasyon sonuçları ile bu hava akış hızını sağlayacak olan tasarımlar incelenmiştir. Ayrıca farklı hava akış rotaları ile devreler üzerinde etkin bir soğutma sağlanması için farklı tasarımlar yapılarak simülasyon sonuçları ile sayısallaştırılmıştır. In this thesis, appropriate design parameters of air holes in the back cover are determined to provide optimum heat transfer to minimize the temperatures of electronic circuits in Flat TV's. Simulations were performed on the ANSYS Icepak module, which has Computational Fluid Dynamics (CFD) software, with the optimal design of the back cover and ventilation holes to achieve maximum heat transfer on the circuits. It has been observed that the air flow rate and the air flow are two important parameters in the heat transfer in the circuits in simulations based on the natural convection heat transfer method. At different air flow rates, designs that provide this airflow rate with heat transfer simulation results on the circuits have been investigated. In addition, different designs have been made and digitized with simulation results to ensure efficient cooling on different air flow routes and circuits. 67

In this study, optimal channel switching (time sharing) strategies are investigated under average power and cost constraints for maximizing the average number of correctly received symbols between a transmitter and a receiver that are connected via multiple flat-fading channels with additive Gaussian noise. The optimal strategy is shown to correspond to channel switching either among at most three different channels with full channel utilization (i.e., no idle periods), or between at most two different channels with partial channel utilization. Also, it is stated that the optimal solution must operate at the maximum average power and the maximum average cost, which facilitates low-complexity approaches for obtaining the optimal strategy. For two-channel strategies, an upper bound is derived, in terms of the parameters of the employed channels, on the ratio between the optimal power levels. In addition, theoretical results are derived for characterizing the optimal solution for channel switching between two channels, and for comparing performance of single channel strategies. Sufficient conditions that depend solely on the systems parameters are obtained for specifying when partial channel utilization cannot be optimal. Furthermore, the proposed optimal channel switching problem is investigated for logarithmic cost functions, and various theoretical results are obtained related to the optimal strategy. Numerical examples are presented to illustrate the validity of the theoretical results.

Optimal channel switching that provides the highest performance over a set of Gaussian channels with variable utilization costs is investigated in the presence of average power and average cost constraints. First, generic cost functions are considered, and it is shown that the optimal channel switching strategy performs channel switching (time sharing) among at most three different channels and always operates at the average power and average cost limits. Also, for channel switching between two channels, relations between the optimal power levels are obtained depending on the average power limit, and it is proved that the ratio of the optimal power levels is upper bounded by the ratio of the larger noise variance to the smaller one. In addition, for logarithmic cost functions, the convexity properties of the error probability are investigated as a function of power and cost, and the optimal channel switching strategy is shown to employ at most two channels, which can easily be determined based on specific formulas, when the average power limit is larger than a certain threshold. Numerical examples are presented to provide illustrations of the theoretical results.

Recent investigations have demonstrated that the classic hypochloremic, hypokalemic, metabolic alkalosis of hypertrophic pyloric stenosis (HPS) is not a common finding.Some have suggested a trend over time, but none has investigated factors contributing to laboratory derangement, such as duration of vomiting or patient age at presentation. We sought to determine the proportion of patients with HPS with normal and abnormal laboratory findings as a function of year of presentation, duration of vomiting, and patient age.This is a retrospective chart review of 205 patients younger than 6 months with operative diagnosis of HPS at a tertiary, regional pediatric center from 2000 to 2009. We examined the acid-base status and electrolyte levels (serum bicarbonate [CO2], serum potassium [K], and serum chloride [Cl]) at the time of the index visit to determine the proportion of normal, high, and low values for each as a function of year of presentation, duration of vomiting, and patient age.The proportion of HPS cases with normal CO2 was 62%; low serum CO2, 20%; and high CO2, 18%. The proportion with normal serum K was 57%; low K, 8%; and high K, 35%. The proportion with normal Cl was 69%; low Cl, 25%; and high Cl, 6%. Logistic regression analysis demonstrated that the prevalence of metabolic alkalosis increased across the decade, whereas the prevalence of metabolic acidosis decreased and that advancing age was associated with the presence of alkalosis.We observed that normal laboratory values are the most common finding in HPS and that metabolic alkalosis was found more commonly in the latter part of the decade and in older infants.

Date of Conference: 3-6 April 2016 Conference Name: IEEE Wireless Communications and Networking Conference, WCNC 2016 In this study, optimal channel switching (time sharing) strategies are investigated under average power and cost constraints in order to maximize the average number of correctly received symbols between a transmitter and a receiver that are connected via multiple additive Gaussian noise channels. The optimal strategy is shown to perform channel switching either among at most three channels with full channel utilization (i.e., no idle periods), or between at most two channels with partial channel utilization. In addition, it is stated that the optimal solution must operate at the maximum average power and the maximum average cost, which facilitates low-complexity approaches for calculating the optimal strategy. For two-channel strategies, an upper bound in terms of the noise standard deviations of the employed channels is provided for the ratio between the optimal power levels. Furthermore, a simple condition depending solely on the systems parameters is derived, under which partial channel utilization cannot be optimal. Numerical examples are presented to demonstrate the validity of the theoretical results.

The complete valence shell photoelectron spectrum of tetrafluoromethane has been recorded using synchrotron radiation and the observed structure has been interpreted using ionisation energies and relative spectral intensities computed using the third-order algebraic-diagrammatic-construction (ADC(3)) scheme for the one-particle Green’s function and the outer valence Green’s function (OVGF) method. The ADC(3) calculations were performed using both the original variant based on the Dyson equation and the recently proposed non-Dyson scheme. The theoretical predictions for the single-hole ionic states due to outer valence shell ionisation agree satisfactorily with the experimental results. Ionisation from the inner valence 2t2 and 3a1 orbitals is strongly influenced by reorganisation effects and the intensity is spread amongst numerous satellites. Highly resolved spectra have been measured for the C ∼ 2 T 2 and the D ∼ 2 A 1 states, and the vibrational structure has been associated primarily with excitation of the ν 1 + ( a 1 ) mode. However, the analyses also provide evidence for excitation of the Jahn-Teller active ν 2 + ( e ) mode in the C ∼ 2 T 2 state, and the ν 3 + ( t 2 ) mode in the D ∼ 2 A 1 state. Excitation of this latter mode can be explained in terms of vibronic coupling between the C ∼ 2 T 2 and the D ∼ 2 A 1 states. Photoelectron angular distributions and branching ratios have been determined and demonstrate that shape resonances affect the outer valence shell photoionisation dynamics. The experimental results are compared with previous theoretical predictions but a consistent interpretation has not been obtained. The major difficulty concerns the uncertainty in the locations of valence shell transitions into the 5a1 and the 5t2 virtual orbitals.

Cataloged from PDF version of article. An M-ary communication system is considered in which the transmitter and the receiver are connected via multiple additive (possibly non-Gaussian) noise channels, any one of which can be utilized for the transmission of a given symbol. Contrary to deterministic signaling (i.e., employing a fixed constellation), a stochastic signaling approach is adopted by treating the signal values transmitted for each information symbol over each channel as random variables. In particular, the joint optimization of the channel switching (i.e., time sharing among different channels) strategy, stochastic signals, and decision rules at the receiver is performed in order to minimize the average probability of error under an average transmit power constraint. It is proved that the solution to this problem involves either one of the following: (i) deterministic signaling over a single channel, (ii) randomizing (time sharing) between two different signal constellations over a single channel, or (iii) switching (time sharing) between two channels with deterministic signaling over each channel. For all cases, the optimal strategies are shown to employ corresponding maximum a posteriori probability (MAP) decision rules at the receiver. In addition, sufficient conditions are derived in order to specify whether the proposed strategy can or cannot improve the error performance over the conventional approach, in which a single channel is employed with deterministic signaling at the average power limit. Finally, numerical examples are presented to illustrate the theoretical results. © 2013 Elsevier Inc.

Date of Conference: 7-12 July 2013 Optimal channel switching and detector design is studied for M-ary communication systems in the presence of stochastic signaling, which facilitates randomization of signal values transmitted for each information symbol. Considering the presence of multiple additive noise channels (which can have non-Gaussian distributions in general) between a transmitter and a receiver, the joint optimization of the channel switching (timesharing) strategy, stochastic signals, and detectors is performed in order to achieve the minimum average probability of error. It is proved that the optimal solution to this problem corresponds to either (i) switching between at most two channels with deterministic signaling over each channel, or (ii) time-sharing between at most two different signals over a single channel (i.e., stochastic signaling over a single channel). For both cases, the optimal solutions are shown to employ corresponding maximum a posteriori probability (MAP) detectors at the receiver. Numerical results are presented to investigate the proposed approach. © 2013 IEEE.

In this study, the jointly optimal power control with signal constellation randomization is proposed for the downlink of a multiuser communications system. Unlike a conventional system in which a fixed signal constellation is employed for all the bits of a user (for given channel conditions and noise power), power control with signal constellation randomization involves randomization/time- sharing among different signal constellations for each user. A formulation is obtained for the problem of optimal power control with signal constellation randomization, and it is shown that the optimal solution can be represented by a randomization among (K+1) or fewer distinct signal constellations for each user, where K denotes the number of users. In addition to the original nonconvex formulation, an approximate solution based on convex relaxation is derived. Then, detailed performance analysis is presented when the receivers employ symmetric signaling and sign detectors. Specifically, the maximum asymptotical improvement ratio is shown to be equal to the number of users, and the conditions under which the maximum and minimum asymptotical improvement ratios are achieved are derived. Numerical examples are presented to investigate the theoretical results, and to illustrate performance improvements achieved via the proposed approach. © 2002-2012 IEEE.

Rastgeleleştirme, ortalama güç kısıtlı iletişim sistemlerinde hata performansını artırmak için muhtemel bir yaklaşım olarak düşünülebilir. Bu tezin ilk kısmında, rastgeleleştirmenin verici ve alıcıda sırasıyla, işaret seviyelerinin rastgele değişkenler (stokastik işaretler) olarak modellenerek ve farklı sezici kümelerinin zaman paylaşımı (sezici rastgeleleştirme) ile kullanılarak uygulandığı çok kullanıcılı sistemlerin aşağı bağlantısı ortalama güç kısıtı altında ele alınmaktadır. Tezin ikinci kısmında, tek kullanıcılı sistemler ele alınmakta,verici ve alıcı arasında çeşitli gürültü dağılımlara sahip çoklu kanalların olduğu ve anlık olarak bu kanallardan sadece birinin kullanılabildiği varsayılmaktadır. Bu durumda rastgeleleştirme, iletişim yapılacak kanalın belirli olasılık yığın fonksiyonuna göre seçilmesiyle ve vericide stokastik işaretleme kullanılmasıyla gerçekleştirilmektedir. İlk olarak, çok kullanıcılı sistemlerin aşağı bağlantısı için işaret yıldız kümelerinin rastgeleleştirilmesiyle optimal güç kontrolü önerilmektedir. Kullanıcının bütün bitleri için sabit bir işaret yıldız kümesinin (verilen kanal şartları ve gürültü gücü için) kullanıldığı geleneksel sistemlerin aksine, işaret yıldız kümelerinin rastgeleleştirilmesiyle yapılan güç kontrolü, her bir kullanıcı için farklı işaret yıldız kümeleri arasında rastgeleleştirme/zaman paylaşımı gerektirebilmektedir. İşaret yıldız kümelerinin rastgeleleştirilmesiyle optimal güç kontrolü problemi için bir formülasyon elde edilmekte ve her bir kullanıcı için optimal çözümün (K +1)- burada K kullanıcı sayısını göstermekte - veya daha az işaret yıldız kümeleri arasında rastgeleleştirme ile ifade edilebileceği gösterilmektedir. Özgün dış bükey olmayan formülasyona ek olarak, dış bükey gevşetme metoduna dayanan yaklaşık bir çözüm elde edilmektedir. Daha sonra, alıcılarda simetrik işaretleme ve işaret sezicileri kullanıldığı durumda detaylı başarım analizi sunulmaktadır. Daha açık bir ifadeyle, en büyük asimptotik gelişim oranının kullanıcı sayısına eşit olduğu gösterilmekte ve en büyük ve en küçük asimptotik gelişim oranlarına erişilmesi için koşullar elde edilmektedir. Literatürde, ortalama güç kısıtlı iletişim sistemlerinde deterministikişaretleme ile çalışan sezicilerin zaman paylaşımı ile kullanımının, hata performansınıiyileştirebileciği bilinmektedir. Bu sonuçtan hareketle, ikinci yaklaşım olarak, çok kullanıcılı sistemlerin aşağı bağlantısı için optimal sezici rastgeleleştirme problemi çalışılmaktadır. Optimal işaret genliklerinin, sezicilerin ve sezici rastgeleleştirme oranlarının elde edilebilmesi için bir formülasyon sunulmaktadır. Bu ortak eniyileme probleminin çözümünün, hesaplama karmaşıklığının önemli ölçüde daha az olduğu iki aşamada hesaplanabildiği gösterilmektedir. Optimal çözüme en fazla min{K,Nd} sezici seti arasında rastgeleleştirme ile ulaşıldığı -burada K kullanıcı sayısını ve Nd her bir alıcıdakisezici sayısını göstermekte- ispatlanmaktadır. Optimal sezici rastgeleleştirme başarımı için alt ve üst sınırlar elde edilmekte ve optimal sezici rastgeleleştirme yaklaşımının en kötü durumdaki hata olasılığını her bir kullanıcı için bir sezici kullanan optimal yaklaşıma göre K oranında azaltabildiği ispatlanmaktadır. Sezici rastgeleleştirme ile iyileşmenin olabileceği ve olamayacağı yeter koşullar elde edilmektedir. Çapraz ilintilerin ve gürültü güçlerinin eşit olduğu özel durumlarda, optimal sezici rastgeleleştirme problemi için basit bir çözüm geliştirilmekte ve çözümün tek olması için gerek ve yeter koşullar sunulmaktadır. Daha sonra, verici ve alıcı arasında, verilen bir sembol iletimi için herhangi birinin kullanılabildiği çoklu toplanabilir gürültü kanalları (Gaussian olmayabilir) bulunan, tek kullanıcılı M-li iletişim sistemleri ele alınmaktadır. Deterministik işaretlemenin (sabit yıldız kümesi kullanmanın) aksine, her bilgi sembolü için her bir kanal üstünden gönderilen işaret değerlerini rastgele değişkenler olarak ele alan stokastik işaretleme benimsenmektedir. Özellikle, ortalama güç kısıtı altında ortalama hata olasılığını enküçültmek için kanal anahtarlama yöntemi, stokastik işaretler ve alıcıdaki karar kurallarının ortak eniyilemesi gerekleştirilmektedir. Bu problemin çözümünün şunlardan herhangi biri olduğu ispat edilmektedir: (i) tek kanal üstünden deterministik işaretleme, (ii) tek kanal üstünden iki farklı yıldız kümesi arasında rastgeleleştirme (zaman paylaşımı),(iii) her biri deterministik işaretleme kullanan iki kanal arasında anahtarlama (zaman paylaşımı). Bütün durumlarda, optimal yöntemlerin alıcıda maksimum sonsal olasılık karar kurallarını kullandığı gösterilmektedir. Randomization can be considered as a possible approach to enhance error performance of communication systems subject to average power constraints. In the first part of this dissertation, we consider downlink of a multiuser communications system subject to an average power constraint, where randomization is employed at the transmitter and receiver sides by modeling signal levels as random variables (stochastic signals) and employing different sets of detectors via time-sharing (detector randomization), respectively. In the second part, weconsider single-user systems, where we assume that there exist multiple channels between the transmitter and receiver with arbitrary noise distributions over each of them and only one of the channels can be employed for transmission at any given time. In this case, randomization is performed by choosing the channel in use according to some probability mass function and employing stochastic signaling at the transmitter. First, the jointly optimal power control with signal constellation randomization is proposed for the downlink of a multiuser communications system. Unlike a conventional system in which a fixed signal constellation is employed for all the bits of a user (for given channel conditions and noise power), power control with signal constellation randomization involves randomization/time-sharing amongdifferent signal constellations for each user. A formulation is obtained for the problem of optimal power control with signal constellation randomization, and it is shown that the optimal solution can be represented by a randomization of (K+1) or fewer distinct signal constellations for each user, where K denotes the number of users. In addition to the original nonconvex formulation, an approximate solution based on convex relaxation is derived. Then, detailed performance analysis is presented when the receivers employ symmetric signaling and sign detectors. Specifically, the maximum asymptotical improvement ratio is shown to be equal to the number of users, and the conditions under which the maximumand minimum asymptotical improvement ratios are achieved are derived. In the literature, it is known that employing different detectors with corresponding deterministic signals via time-sharing may enhance error performance of communications systems subject to average power constraints. Motivated by this result, as a second approach, we study optimal detector randomization for the downlink of a multiuser communications system. A formulation is provided to obtain optimal signal amplitudes, detectors, and detector randomization factors.It is shown that the solution of this joint optimization problem can be calculated in two steps, resulting in significant reduction in computational complexity. It is proved that the optimal solution is achieved via randomization among at most min{K,Nd} detector sets, where K is the number of users and Nd is the number of detectors at each receiver. Lower and upper bounds are derived on the performance of optimal detector randomization, and it is proved that the optimal detector randomization approach can reduce the worst-case average probabilityof error of the optimal approach that employs a single detector for each user by up to K times. Various sufficient conditions are obtained for the improvability and nonimprovability via detector randomization. In the special case of equal crosscorrelations and noise powers, a simple solution is developed for the optimal detector randomization problem, and necessary and sufficient conditions are presented for the uniqueness of that solution. Next, a single-user M-ary communication system is considered in which the transmitter and the receiver are connected via multiple additive (possibly non-Gaussian) noise channels, any one of which can be utilized for a given symbol transmission. Contrary to deterministic signaling (i.e., employing a fixed constellation),a stochastic signaling approach is adopted by treating the signal values transmitted for each information symbol over each channel as random variables. In particular, the joint optimization of the channel switching (i.e., time-sharing among different channels) strategy, stochastic signals, and decision rules at the receiver is performed in order to minimize the average probability of error under anaverage transmit power constraint. It is proved that the solution to this problem involves either one of the following: (i) deterministic signaling over a single channel,(ii) randomizing (time-sharing) between two different signal constellations over a single channel, or (iii) switching (time-sharing) between two channels with deterministic signaling over each channel. For all cases, the optimal strategies are shown to employ corresponding maximum a posteriori probability (MAP) decision rules at the receiver. 137

Cataloged from PDF version of article. Optimal detector randomization is studied for the downlink of a multiuser communications system, in which users can perform time-sharing among multiple detectors. A formulation is provided to obtain optimal signal amplitudes, detectors, and detector randomization factors. It is shown that the solution of this joint optimization problem can be calculated in two steps, resulting in significant reduction in computational complexity. It is proved that the optimal solution is achieved via randomization among at most min{K, Nd} detector sets, where K is the number of users and Nd is the number of detectors at each receiver. Lower and upper bounds are derived on the performance of optimal detector randomization, and it is proved that the optimal detector randomization approach can reduce the worst-case average probability of error of the optimal approach that employs a single detector for each user by up to K times. Various sufficient conditions are obtained for the improvability and nonimprovability via detector randomization. In the special case of equal crosscorrelations and noise powers, a simple solution is developed for the optimal detector randomization problem, and necessary and sufficient conditions are presented for the uniqueness of that solution. Numerical examples are provided to illustrate the improvements achieved via detector randomization.

In a multidetector experiment on 26 or 30 AMeV32S+58Ni, up to four coincident heavier or intermediate-mass fragments were observed. One of these occasionally has the characteristics of a projectile-like fragment, up to three may be attributed to the decay of the heavy reaction product. Taking the velocity of the fragments as a measure of the heavy-product excitation energy, one finds evaporation, fission and multifragmentation to follow one another with rising excitation. Model simulations of sequential decay with up to two binary fissions and, alternatively, of simultaneous statistical multifragmentation were performed for comparison with experimental distributions of mass, velocity and (for events with three slow intermediate-mass fragments) relative azimuthal angle. Though in the three-fragment events indications of simultaneous multifragmentation are present, the sequential binary decay predominates. Evaporated protons and α particles detected in coincidence have a mean multiplicity growing with excitation energy, while the temperature governing the spectra has a plateau with a value of about 5.5 MeV.

Conference Name: 13th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), IEEE 2012 Date of Conference: 17-20 June 2012 Stochastic signal design is studied for the downlink of a multiuser communications system. First, a formulation is proposed for the joint design of optimal stochastic signals. Then, an approximate formulation, which can get arbitrarily close to the optimal solution, is obtained based on convex relaxation. In addition, when the receivers employ symmetric signaling and sign detectors, it is shown that the maximum asymptotical improvement ratio is equal to the number of users, and the conditions under which that maximum asymptotical improvement ratio is achieved are presented. Numerical examples are provided to explain the theoretical results. © 2012 IEEE.

Date of Conference: 14-16 Sept. 2011 In code-multiplexed transmitted-reference (CM-TR) ultra-wideband (UWB) systems, data signals and reference signals are transmitted using two distinct orthogonal codes. In this way, performance improvements and/or implementation advantages are obtained compared to transmitted-reference (TR) and frequency-shifted reference (FSR) ultra-wideband (UWB) systems. In this study, performance of CM-TR systems is investigated, and probability of error expressions are obtained. For the single user case, a closed-form expression for the exact probability of error is derived, whereas a Gaussian approximation, the accuracy of which depends on the number of frames per symbol, is considered for the multiuser case. Also, the maximum likelihood detector is derived, and numerical examples are presented. © 2011 IEEE.

In this study, optimal and suboptimal receivers are investigated for code-multiplexed transmitted-reference (CM-TR) ultra-wideband systems. First, a single-user scenario is considered, and a CM-TR system is modeled as a generalized noncoherent pulse-position modulated system. Based on that model, the optimal receiver that minimizes the bit error probability is derived. Then, it is shown that the conventional CM-TR receiver converges to the optimal receiver under certain conditions and achieves close-to-optimal performance in practical cases. Next, multi-user systems are considered, and the conventional receiver, blinking receiver, and chip discriminator are investigated. Also, the linear minimum mean-squared error (MMSE) receiver is derived for the downlink of a multi-user CM-TR system. In addition, the maximum likelihood receiver is obtained as a performance benchmark. The practicality and the computational complexity of the receivers are discussed, and their performance is evaluated via simulations. The linear MMSE receiver is observed to provide the best trade-off between performance and complexity/practicality. Copyright © 2011 John Wiley & Sons, Ltd.

Cataloged from PDF version of article. In this study, optimal and suboptimal receivers are investigated for code-multiplexed transmitted-reference (CM-TR) ultra-wideband systems. First, a single-user scenario is considered, and a CM-TR system is modeled as a generalized noncoherent pulse-position modulated system. Based on that model, the optimal receiver that minimizes the bit error probability is derived. Then, it is shown that the conventional CM-TR receiver converges to the optimal receiver under certain conditions and achieves close-to-optimal performance in practical cases. Next, multi-user systems are considered, and the conventional receiver, blinking receiver, and chip discriminator are investigated. Also, the linear minimum mean-squared error (MMSE) receiver is derived for the downlink of a multi-user CM-TR system. In addition, the maximum likelihood receiver is obtained as a performance benchmark. The practicality and the computational complexity of the receivers are discussed, and their performance is evaluated via simulations. The linear MMSE receiver is observed to provide the best trade-off between performance and complexity/practicality. Copyright © 2011 John Wiley & Sons, Ltd

Referans iletimli ve frekans kaydırmalı çok geniş bantlı sistemlerde veri ve referans işaretleri birbirlerine göre zaman ve frekans bölgelerinde kaymış biçimdedir. Bu sistemlerin en büyük avantajı, kanal tahmini ile ilgili zorlu isterlerin kaldırılmasıdır. Referans iletimli çok geniş bantlı sistemlerde, tümdevrelerde kullanılması zor olan analog gecikme hattına ihtiyaç duyulmaktadır. Frekans kaydırmalı referans sistem alıcılarında ise pratikte çok daha basit olan frekans çevrimi işlemi gerekmesine rağmen, bu sistemlerde veri hızı ile ilgili sınırlamalar bulunmaktadır. Bunun yerine, veri ve referans işaretlerini iki ayrı dikgen kod kullanarak ileten, kod çoğullamalı referans iletimli çok geniş bantlı sistem düşünülebilir. Bu sistem, daha basit bir alıcı gerektirmekte ve referans iletimli ve frekans kaydırmalı sistemlere göre daha iyi performans sağlamaktadır.Tezin ilk kısmında kod çoğullamalı referans iletimli çok geniş bantlı sistemler incelenmekte ve hata olasılığı ifadeleri elde edilmektedir. Tek kullanıcılı durumda, hata olasılığının tam olarak hesaplanmasını sağlayan bir ifade çıkarılmaktadır. Çok kullanıcılı durumda ise, Gauss yaklaşımı temelli bir ifade elde edilmekte ve sonuçlar farklı senaryolar için kıyaslanmaktadır. Tezin ikinci kısmında, optimal olan ve olmayan bazı alıcılar çalışılmaktadır. Öncelikle, yanıp sönen alıcılar ve çip ayırtaç gibi çok karmaşık olmayan alıcılar sunulmaktadır. Bu alıcılar için gereksinimler ve daha iyi performans sağlamaları için gerekli koşullar tartışılmaktadır. Daha sonra, doğrusal en düşük ortalama karesel hatalı alıcı ve bunu gerçekleştirmek için gereksinimler sunulmaktadır. Son olarak, hesaplama karmaşıklığı en çok olan ve diğer alıcılardan daha çok gereksinimi olan, optimal en büyük olabilirlik sezicisi elde edilmektedir. Kuramsal sonuçları onaylamak ve alıcıların performansını kıyaslamak için benzetim sonuçları gerçekleştirilmektedir. In transmitted-reference (TR) and frequency-shifted reference (FSR) ultrawideband (UWB) systems, data and reference signals are shifted relative to each other in time and frequency domains, respectively. The main advantage of these systems is that they remove strict requirements of channel estimation. In order to implement TR UWB systems, an analog delay line, which is difficult to buildin an integrated fashion, is needed. Although FSR systems require frequency conversion at the receiver, which is much simpler in practice, they have data rate limitations. Instead, a code-multiplexed transmitted-reference (CM-TR) UWB system that transmits data and reference signals using two distinct orthogonal codes can be considered. This system requires a simpler receiver and has betterperformance than TR and FSR.In the first part of the thesis, CM-TR systems are investigated and probability of error expressions are obtained. For the single user case, a closed-form expression for the exact probability of error is derived. For the multiuser case, a closed-form expression is derived based on the Gaussian approximation, and the results are compared in different scenarios. In the second part of the thesis, some optimal and suboptimal receivers are studied. First, low complexity receivers, such as the blinking receiver (BR) and the chip discriminator, are presented. The requirements for these types of receivers are explained, and the conditions under which their performance can be improved are discussed. Then, an analytical analysis of the linear minimum mean-squared error (MMSE) receiver and the requirements to implement this MMSE receiver are provided. Lastly, the optimal maximum-likelihood (ML) detector is derived, which has higher computational complexity and more strict requirements than the other receivers. Finally, simulation results are presented in order to verify the theoretical results and to compare the performance of the receivers. 88