1,666 research outputs found

    Optimizing time and space MIMO antenna system for frequency selective fading channels

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    Smart or adaptive antennas promise to provide significant increases in system capacity and performance in wireless communication systems. In this paper, we investigate the use of adaptive antennas at the base and mobile stations, operating jointly, to maximize the average signal-to-interference and noise ratio (SINR) of each packet in the system for frequency selective channels with prior knowledge of the channel at the transmitter. Our approach is based on deriving an analytic formula for the average packet SINR and using the Lagrange multiplier method to determine an optimum. We derive necessary conditions for an optimum solution and propose an analytical expression for the optimum. Our analytical expression is not guaranteed to be the global optimum but it does satisfy the derived necessary conditions and, in addition for frequency flat channels, our results reduce to expressions for optimal weights previously published. To demonstrate the potential of the proposed system, we provide Monte Carlo simulation results of the system bit-error rates and make comparisons with other adaptive antenna systems. These show that significant improvements in performance are possible in a wireless communications context

    Adaptive antennas at the mobile and base stations in an OFDM/TDMA system

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    In recent years, several smart antenna systems have been proposed and demonstrated at the base station (BS) of wire-less communications systems, and these have shown that significant system performance improvement is possible. In this paper, we consider the use of adaptive antennas at the BS and mobile stations (MS), operating jointly, in combination with orthogonal frequency-division multiplexing. The advantages of the proposed system includes reductions in average error probability and increases in capacity compared to conventional systems. Multiuser access, in space, time, and through subcarriers, is also possible and expressions for the exact joint optimal antenna weights at the BS and MS under cochannel interference conditions for fading channels are derived. To demonstrate the potential of our proposed system, analytical along with Monte Carlo simulation results are provided

    Multiuser MIMO-OFDM for Next-Generation Wireless Systems

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    This overview portrays the 40-year evolution of orthogonal frequency division multiplexing (OFDM) research. The amelioration of powerful multicarrier OFDM arrangements with multiple-input multiple-output (MIMO) systems has numerous benefits, which are detailed in this treatise. We continue by highlighting the limitations of conventional detection and channel estimation techniques designed for multiuser MIMO OFDM systems in the so-called rank-deficient scenarios, where the number of users supported or the number of transmit antennas employed exceeds the number of receiver antennas. This is often encountered in practice, unless we limit the number of users granted access in the base station’s or radio port’s coverage area. Following a historical perspective on the associated design problems and their state-of-the-art solutions, the second half of this treatise details a range of classic multiuser detectors (MUDs) designed for MIMO-OFDM systems and characterizes their achievable performance. A further section aims for identifying novel cutting-edge genetic algorithm (GA)-aided detector solutions, which have found numerous applications in wireless communications in recent years. In an effort to stimulate the cross pollination of ideas across the machine learning, optimization, signal processing, and wireless communications research communities, we will review the broadly applicable principles of various GA-assisted optimization techniques, which were recently proposed also for employment inmultiuser MIMO OFDM. In order to stimulate new research, we demonstrate that the family of GA-aided MUDs is capable of achieving a near-optimum performance at the cost of a significantly lower computational complexity than that imposed by their optimum maximum-likelihood (ML) MUD aided counterparts. The paper is concluded by outlining a range of future research options that may find their way into next-generation wireless systems

    Performance enhancement of multiuser MIMO wireless communication systems

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    This paper describes a new approach to the problem of enhancing the performance of a multiuser multiple-input-multiple-output (MIMO) system for communication from one base station to many mobile stations in both frequency-flat and frequency-selective fading channels. This problem arises in space-division multiplexing systems with multiple users where many independent signal streams can be transmitted in the same frequency and time slot through the exploitation of multiple antennas at both the base and mobile stations, Our new approach is based on maximizing a lower bound for the product of signal-to-interference plus noise ratio (SINR) of a multiuser MIMO system. This provides a closed-form (noniterative) solution for the antenna weights for all the users, under the constraint of fixed transmit power. Our solution is shown by simulation to have better performance than previously proposed iterative or noniterative solutions. In addition, our solution requires significantly reduced complexity over a gradient search-based method that directly optimizes the product SINgs while still maintaining similar performance. Our solution assumes channel state information is present at the base station or transmitter

    LTE SFBC MIMO Transmitter Modelling and Performance Evaluation

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    High data rates are one of the most prevalent requirements in current mobile communications. To cover this and other high standards regarding performance, increasing coverage, capacity, and reliability, numerous works have proposed the development of systems employing the combination of several techniques such as Multiple Input Multiple Output (MIMO) wireless technologies with Orthogonal Frequency Division Multiplexing (OFDM) in the evolving 4G wireless communications. Our proposed system is based on the 2x2 MIMO antenna technique, which is defined to enhance the performance of radio communication systems in terms of capacity and spectral efficiency, and the OFDM technique, which can be implemented using two types of sub-carrier mapping modes: Space-Time Block Coding and Space Frequency Block Code. SFBC has been considered in our developed model. The main advantage of SFBC over STBC is that SFBC encodes two modulated symbols over two subcarriers of the same OFDM symbol, whereas STBC encodes two modulated symbols over two subcarriers of the same OFDM symbol; thus, the coding is performed in the frequency domain. Our solution aims to demonstrate the performance analysis of the Space Frequency Block Codes scheme, increasing the Signal Noise Ratio (SNR) at the receiver and decreasing the Bit Error Rate (BER) through the use of 4 QAM, 16 QAM and 64QAM modulation over a 2x2 MIMO channel for an LTE downlink transmission, in different channel radio environments. In this work, an analytical tool to evaluate the performance of SFBC - Orthogonal Frequency Division Multiplexing, using two transmit antennas and two receive antennas has been implemented, and the analysis using the average SNR has been considered as a sufficient statistic to describe the performance of SFBC in the 3GPP Long Term Evolution system over Multiple Input Multiple Output channels.Comment: 11 pages, 20 figures, 5 table

    Analysis and Simulation of the Signals Transmission in the DVB-H/SH Standards

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    Tato disertačnĂ­ prĂĄce se zabĂœvĂĄ analĂœzou, simulacĂ­ a měƙenĂ­m zpracovĂĄnĂ­ a pƙenosu signĂĄlĆŻ digitĂĄlnĂ­ televize pro pƙíjem mobilnĂ­ho TV vysĂ­lĂĄnĂ­ ve standardech DVB-H a DVB-SH. Tyto standardy vychĂĄzejĂ­ z pƙedpokladu, ĆŸe pƙíjem signĂĄlu je charakterizovĂĄn modely pƙenosovĂœch kanĂĄlĆŻ s vĂ­cecestnĂœm ơíƙenĂ­m. Tyto, tzv. ĂșnikovĂ© kanĂĄly, jsou charakterizovĂĄny hlavně zpoĆŸděnĂ­m a ziskem jednotlivĂœch cest. V zĂĄvislosti na dalĆĄĂ­ch parametrech (rychlost pƙijĂ­mače, DopplerovskĂ© spektrum), je moĆŸnĂ© rozdělit ĂșnikovĂ© kanĂĄly do tƙech hlavnĂ­ch skupin: mobilnĂ­, pƙenosnĂ© a fixnĂ­. DĂĄ se pƙedpoklĂĄdat, ĆŸe v rĆŻznĂœch modelech kanĂĄlĆŻ bude pƙenĂĄĆĄenĂœ signĂĄl rĆŻzně ovlivněn. Proto je potƙebnĂ© najĂ­t optimĂĄlnĂ­ parametry systĂ©mĆŻ (DVB-H/SH) pro kvalitnĂ­ pƙíjem vysĂ­lanĂœch sluĆŸeb mobilnĂ­ televize, coĆŸ je hlavnĂ­m cĂ­lem tĂ©to disertačnĂ­ prĂĄci. Pro tento Ășčel byly vytvoƙeny dvě vhodnĂ© aplikace (jedna pro DVB-H a jedna pro DVB-SH) s GUI v prostƙedĂ­ MATLAB, kterĂ© umoĆŸĆˆujĂ­ simulovat a analyzovat mĂ­ru zkreslenĂ­ signĂĄlu v pƙípadě mobilnĂ­ch, pƙenosnĂœch a fixnĂ­ch scĂ©náƙƯ pƙenosu. NavĂ­c, tyto aplikace obsahujĂ­ i druhĂœ samostatnĂœ simulĂĄtor pro nastavenĂ­ a modifikaci parametrĆŻ jednotlivĂœch pƙenosovĂœch cest. DĂ­ky tomu je moĆŸnĂ© zhodnotit vliv parametrĆŻ celĂ©ho systĂ©mu a kanĂĄlovĂœch modelĆŻ na dosaĆŸenou chybovost (BER a MER) a kvalitu pƙenosu. Ve vĆĄech pƙenosovĂœch scĂ©náƙích (v zĂĄvislosti na poměru C/N) byly zĂ­skanĂ©, vyhodnocenĂ© a diskutovanĂ© zkreslenĂ­ signĂĄlĆŻ. NavĂ­c, u standardu DVB-H, vĆĄechny zĂ­skanĂ© vĂœsledky ze simulacĂ­ byly ověƙeny měƙenĂ­m. RozdĂ­ly mezi dosaĆŸenĂœmi vĂœsledky (simulace a měƙenĂ­) byly rovnÄ›ĆŸ podrobeny diskuzi. Tuto disertačnĂ­ prĂĄci je moĆŸnĂ© rozdělit do čtyƙ hlavnĂ­ch částĂ­. PrvnĂ­ část disertačnĂ­ prĂĄce se zabĂœvĂĄ reĆĄerĆĄĂ­ současnĂ©ho vĂœvoje v oblasti digitĂĄlnĂ­ho televiznĂ­ho vysĂ­lĂĄnĂ­ na mobilnĂ­ terminĂĄly ve standardech DVB-H/SH. Na konci tĂ©to části jsou jasně popsĂĄny cĂ­le tĂ©to disertačnĂ­ prĂĄce. DruhĂĄ část prĂĄce je zaměƙenĂĄ na stručnĂœ popis blokovĂ©ho diagramu vysĂ­lačƯ v obou standardech DVB-H/SH. DĂĄle jsou stručně popsĂĄny modely pƙenosovĂœch kanĂĄlĆŻ, kterĂ© se pouĆŸĂ­vajĂ­ pro modelovĂĄnĂ­ pƙenosu signĂĄlu. StručnĂœ popis vytvoƙenĂœch aplikacĂ­, i s vĂœvojovĂœm diagramem, kterĂ© jsou vhodnĂ© pro simulaci a analĂœzu pƙenosu v DVB-H/SH, jsou popsĂĄny v tƙetĂ­ části prĂĄce. ČtvrtĂĄ a nejdelĆĄĂ­ část tĂ©to disertačnĂ­ prĂĄce se zabĂœvĂĄ vyhodnocenĂ­m zĂ­skanĂœch vĂœsledkĆŻ ze simulacĂ­ a měƙenĂ­.This dissertation thesis deals with the analysis, simulation and measurement of the signal processing and transmission in DVB-H and DVB-SH standards. These standards are based on the assumption that signal reception is characterized by the transmission channels with echoes. These, so called fading channels, are mainly characterized by the path delays and path losses. Depending on the other, additional features (speed of the receiver, Doppler spectrum, etc.), it can be possible divided these channels onto three main groups: mobile, portable and fixed. Of course, signal transmission in different transmission channel models are affected differently. Therefore, it is needed found the optimal system parameters in both, DVB-H and DVB-SH standards, for the quality reception of the broadcasted mobile TV services, which is the main goal of this thesis. For this purpose, two appropriate applications (one for DVB-H and one for DVB-SH) with GUI were created in MATLAB, which enable simulated and analyzed the signal distortions in mobile, portable and fixed transmission scenarios. Moreover, these applications also contain a second application with GUI for the easy set and modification of the parameters of the used channel models. Therefore, it is possible to evaluate the effect of parameters of whole system and channel models on the achieved error rate (BER and MER) and quality of the transmission. In all mentioned transmission scenarios, the signal distortions (depending on the Carrier-to-Noise ratio) were obtained, evaluated and discussed in this dissertation thesis. Furthermore, in case of DVB-H, all obtained results from the simulations, were verified by the measuring. Differences between the obtained results (simulation and measuring) are also discussed. This dissertation thesis can be divided into four main parts. The first part of this dissertation thesis, after the short introduction, deals with present state-of-the-art and literature survey in mobile broadcast DVB-H/SH standards. At the end of this part are clearly outlined the main aims of this dissertation thesis. Second part is focused on the brief description of the functional block diagram of transmitters in both, DVB-H/SH standards. Furthermore, there are briefly described the transmission fading channel models, which are commonly used for the modeling of the signal transmission. The brief description of program applications with flowcharts, appropriate for the simulation of the transmission in the DVB-H/SH standards, are presented and described in the third part of this thesis. Finally, the fourth and longest part of this thesis is focused on the evaluation and comparison of obtained results from the simulations and measurements.
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