Space time block code classification for MIMO signals exploiting cyclostationarity

Blind and noncooperative identification of the transmission parameters of unknown communication signals has been employed both in military and civilian applications. Multiple-Input-Multiple-Output (MIMO) transmission systems emerging in the last decade pose new challenges to the signal identification systems, one of which is the identification of the Space-Time Block Code (STBC) used in the transmission. In this work, we present a novel STBC classification algorithm that exploits the joint wide sense cyclostationary characteristics of the coded transmit signals as discriminating features. Compared to existing algorithms, the proposed method can discriminate between a large number of different STBCs

An efficient joint channel estimation and decoding algorithm for turbo-coded space-time orthogonal frequency division multiplexing receivers

The challenging problem in the design of digital receivers of today's and future high-speed, high data-rate wireless communication systems is to implement the optimal decoding and channel estimation processes jointly in a computationally feasible way. Without realising such a critical function perfectly at receiver, the whole system will not work properly within the desired performance limits. Unfortunately, direct implementation of such optimal algorithms is not possible mainly due to their mathematically intractable and computationally prohibitive nature. A novel algorithm that reaches the performance of the optimal maximum a posteriori (MAP) algorithm with a feasible computational complexity is proposed. The algorithm makes use of a powerful statistical signal processing tool called the expectation-maximisation (EM) technique. It iteratively executes the MAP joint channel estimation and decoding for space-time block-coded orthogonal frequency division multiplexing systems with turbo channel coding in the presence of unknown wireless dispersive channels. The main novelty of the work comes from the facts that the proposed algorithm estimates the channel in a non-data-aided fashion and therefore except a small number of pilot symbols required for initialisation, no training sequence is necessary. Also the approach employs a convenient representation of the discrete multipath fading channel based on the Karhunen-Loeve (KL) orthogonal expansion and finds MAP estimates of the uncorrelated KL series expansion coefficients. Based on such an expansion, no matrix inversion is required in the proposed MAP estimator. Moreover, optimal rank reduction is achieved by exploiting the optimal truncation property of the KL expansion resulting in a smaller computational load on the iterative estimation approach

Analysis of temperature-dependent forward and leakage conduction mechanisms in organic thin film heterojunction diode with fluorine-based PCBM blend

The forward and reversed biased current-voltage behaviors of the organic diode were detailed in a wide range of temperatures. In this diode, a donor-acceptor-conjugated copolymer system was constructed with poly((9,9-dioctylfluorene)-2,7-diyl-(2-dodecyl-benzo[1,2,3]triazole)) as a partner of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Two-order of magnitude rectification ratio was achieved, and the temperature-dependent values of saturation current, zero-bias barrier height, and ideality factor were extracted according to the thermionic emission model. The temperature responses of these diode parameters showed an existence of inhomogeneity in the barrier height formation. As a result, the observed non-ideal behavior was explained by Gaussian distribution of barrier height where low-barrier regions are effective in the forward biased conduction mechanism at low temperatures. Together with this analysis, series resistances were evaluated using Cheung's functions and also density of interface states were investigated. On the other hand, reverse biased current flow was found under the dominant effect of Poole-Frenkel effects associated with these interfacial traps. The reverse current conduction mechanism was detailed by calculating characteristic field-lowering coefficients and barrier height values in the emission process from the trapped state in the range of temperatures of interest

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TÜBİTAK EEEAG01.07.200

An efficient joint data detection and channel estimation technique for uplink MC-CDMA systems based on SAGE algorithm

This paper is concerned with joint channel estimation and data detection for uplink multicarrier code-division multiple-access (MC-CDMA) systems in the presence of frequency fading channel. The detection and estimation algorithm, implemented at the receiver, is based on a version of the expectation maximization (EM) technique, called the spece-alternating-generalized-expectation-maximization (SAGE) algorithm which is very suitable for the the multicarrier signal formats. Application of the SAGE algorithm to the problem of iterative data detection and channel estimation leads to a receiver structure that also incorporates a partial interference cancelation. Computer simulations show that the proposed algorithm has excellent BER end estimation performance

EM-based joint data detection and channel estimation for uplink MC-CDMA systems over frequency selective channels

This paper is concerned with joint channel estimation and data detection for uplink multicarrier code-division multiple-access (MC-CDMA) systems in the presence of frequency fading channel. The detection and estimation algorithm, implemented at the receiver, is based on a version of the expectation maximization (EM) technique which is very suitable for the multicarrier signal formats. Application of the EM-based algorithm to the problem of iterative data detection and channel estimation leads to a receiver structure that also incorporates a partial interference cancelation. Computer simulations show that the proposed algorithm has excellent BER end estimation performance

MAP channel-estimation-based PIC receiver for downlink MC-CDMA systems

We propose a joint MAP channel estimation and data detection technique based on the expectation maximization (EM) method with paralel interference cancelation (PIC) for downlink multicarrier (MC) code division multiple access (CDMA) systems in the presence of frequency selective channels. The quality of multiple access interference (MAI), which can be improved by using channel estimation and data estimation of all active users, affects considerably the performance of PIC detector. Therefore, data and channel estimation performance obtained in the initial stage has a significant relationship with the performance of PIC. So obviously it is necessary to make excellent joint data and channel estimation for initialization of PIC detector. The EM algorithm derived estimates the complex channel parameters of each subcarrier iteratively and generates the soft information representing the data a posterior probabilities. The soft information is then employed in a PIC module to detect the symbols efficiently. Moreover, the MAP-EM approach considers the channel variations as random processes and applies the Karhunen-Loeve (KL) orthogonal series expansion. The performance of the proposed approach is studied in terms of bit-error rate (BER) and mean square error (MSE). Throughout the simulations, extensive comparisons with previous works in literature are performed, showing that the new scheme can offer superior performance

Effect of layer thickness on the electrical parameters and conduction mechanisms of conjugated polymer-based heterojunction diode

In this study, thickness-dependent current density-voltage (J-V) characteristics obtained for poly{(9,9-dioctylfluorene) 22,7-diyl-(4,7-bis (thien-2-yl)2-dodecyl-benzo[1,2,3] triazole)} (PFTBT) conjugated copolymer based heterojunction diode fabricated on ITO were investigated in terms of electrical characteristics. In order to analyze J-V plots with ITO/PEDOT: PSS/PFTBT: PC61BM/LiF/Al configuration, the thickness-dependent J-V measurements were applied in the thickness range between 90 and 200 nm. The effect of PFTBT: PC61BM layer thickness on the forward J-V characteristics were investigated by evaluating electrical parameters such as zero bias barrier height (phi(Bo)), ideality factor (n), shunt resistance (R-sh), series resistance (R-s), the interface states density (Nss), and space-charge limited mobility. The results show that at PFTBT: PC61BM layer thickness of 90 and 200 nm, ideality factor for ITO/PEDOT: PSS/PFTBT: PC61BM/LiF/Al heterojunction diodes ranged from 2.726 to 3.121 and the thermionic emission over the heterojunction diodes is crucial at low current densities and the intrinsic thermally generated charge carriers controlled the forward current this region of the heterojunction diode. At relatively higher voltage, the current mechanism of ITO/PFTBT: PC61BM/ PEDOT: PSS/ LiF/ Al heterojunction diodes were found to obey a space charge limited (SCLC) conduction mechanism. The values of Nss and Rs in heterojunction diodes increase with increasing PFTBT: PC61BM layer thickness and effect the main electrical parameters of diodes. In addition, the leakage current of heterojunction diodes are taken and interpreted via Poole- Frenkel emission and Schottky emission. The leakage current was controlled in ITO/ PEDOT: PSS/ PFTBT: PC61BM/ LiF/ Al heterojunction diodes by Poole- Frenkel emission above 140 nm and by Schottky emission under 140 nm. (C) 2017 Wiley Periodicals, Inc

The Main Electrical and Interfacial Properties of Benzotriazole and Fluorene Based Organic Devices

Electrical and interfacial properties of ITO/PEDOT:PSS/poly((9,9-dioctylfluorene)-2,7-diyl(2-dodecyl-benzo[1,2,3]triazole)) (PFTBT)/Au devices were investigated using current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G/w-V) measurements at room temperature. The forward and reverse C-V and G/w-V measurements were carried out in the frequency range of 10kHz-1MHz. The electrical parameters, barrier height (phi Bo ) and ideality factor (n) obtained from the forward bias LnI-V plot were found as 0.711eV and 3.8, respectively. In addition, the series resistance (Rs ) was obtained using Norde and Cheung's methods; Rs were found as 19.052k and 19.267k, respectively. The experimental C-V and G/w-V characteristics of these structures at various gate biases show fairly large frequency dispersion especially at low frequencies and applied voltage due to interface states (Nss) in equilibrium with the conjugated copolymer, interfacial polymer and Rs . These observations indicate that at low frequencies, the charges at interface states can easily follow an AC signal and yield an excess capacitance and conductance. On the other hand, the values of Nss were determined using high-low frequency capacitance (CLF -CHF ) method and Nss are of order 1011 eV-1 cm2 which is closer to the values obtained by Hill-Coleman method. Experimental results show that both Nss and Rs values should be taken into account in determining frequency and voltage dependent I-V, C-V and G/w-V characteristics for an organic structure