274 research outputs found

    Frequency-domain precoding for single carrier frequency-division multiple access

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    Design guidelines for spatial modulation

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    A new class of low-complexity, yet energyefficient Multiple-Input Multiple-Output (MIMO) transmission techniques, namely the family of Spatial Modulation (SM) aided MIMOs (SM-MIMO) has emerged. These systems are capable of exploiting the spatial dimensions (i.e. the antenna indices) as an additional dimension invoked for transmitting information, apart from the traditional Amplitude and Phase Modulation (APM). SM is capable of efficiently operating in diverse MIMO configurations in the context of future communication systems. It constitutes a promising transmission candidate for large-scale MIMO design and for the indoor optical wireless communication whilst relying on a single-Radio Frequency (RF) chain. Moreover, SM may also be viewed as an entirely new hybrid modulation scheme, which is still in its infancy. This paper aims for providing a general survey of the SM design framework as well as of its intrinsic limits. In particular, we focus our attention on the associated transceiver design, on spatial constellation optimization, on link adaptation techniques, on distributed/ cooperative protocol design issues, and on their meritorious variants

    Collaborative modulation multiple access for single hop and multihop networks

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    While the bandwidth available for wireless networks is limited, the world has seen an unprecedented growth in the number of mobile subscribers and an ever increasing demand for high data rates. Therefore efficient utilisation of bandwidth to maximise link spectral efficiency and number of users that can be served simultaneously are primary goals in the design of wireless systems. To achieve these goals, in this thesis, a new non-orthogonal uplink multiple access scheme which combines the functionalities of adaptive modulation and multiple access called collaborative modulation multiple access (CMMA) is proposed. CMMA enables multiple users to access the network simultaneously and share the same bandwidth even when only a single receive antenna is available and in the presence of high channel correlation. Instead of competing for resources, users in CMMA share resources collaboratively by employing unique modulation sets (UMS) that differ in phase, power, and/or mapping structure. These UMS are designed to insure that the received signal formed from the superposition of all users’ signals belongs to a composite QAM constellation (CC) with a rate equal to the sum rate of all users. The CC and its constituent UMSs are designed centrally at the BS to remove ambiguity, maximize the minimum Euclidian distance (dmin) of the CC and insure a minimum BER performance is maintained. Users collaboratively precode their transmitted signal by performing truncated channel inversion and phase rotation using channel state information (CSI ) obtained from a periodic common pilot to insure that their combined signal at the BS belongs to the CC known at the BS which in turn performs a simple joint maximum likelihood detection without the need for CSI. The coherent addition of users’ power enables CMMA to achieve high link spectral efficiency at any time without extra power or bandwidth but on the expense of graceful degradation in BER performance. To improve the BER performance of CMMA while preserving its precoding and detection structure and without the need for pilot-aided channel estimation, a new selective diversity combining scheme called SC-CMMA is proposed. SC-CMMA optimises the overall group performance providing fairness and diversity gain for various users with different transmit powers and channel conditions by selecting a single antenna out of a group of L available antennas that minimises the total transmit power required for precoding at any one time. A detailed study of capacity and BER performance of CMMA and SC-CMMA is carried out under different level of channel correlations which shows that both offer high capacity gain and resilience to channel correlation. SC-CMMA capacity even increase with high channel correlation between users’ channels. CMMA provides a practical solution for implementing the multiple access adder channel (MAAC) in fading environments hence a hybrid approach combining both collaborative coding and modulation referred to as H-CMMA is investigated. H-CMMA divides users into a number of subgroups where users within a subgroup are assigned the same modulation set and different multiple access codes. H-CMMA adjusts the dmin of the received CC by varying the number of subgroups which in turn varies the number of unique constellation points for the same number of users and average total power. Therefore H-CMMA can accommodate many users with different rates while flexibly managing the complexity, rate and BER performance depending on the SNR. Next a new scheme combining CMMA with opportunistic scheduling using only partial CSI at the receiver called CMMA-OS is proposed to combine both the power gain of CMMA and the multiuser diversity gain that arises from users’ channel independence. To avoid the complexity and excessive feedback associated with the dynamic update of the CC, the BS takes into account the independence of users’ channels in the design of the CC and its constituent UMSs but both remain unchanged thereafter. However UMS are no longer associated with users, instead channel gain’s probability density function is divided into regions with identical probability and each UMS is associated with a specific region. This will simplify scheduling as users can initially chose their UMS based on their CSI and the BS will only need to resolve any collision when the channels of two or more users are located at the same region. Finally a high rate cooperative communication scheme, called cooperative modulation (CM) is proposed for cooperative multiuser systems. CM combines the reliability of the cooperative diversity with the high spectral efficiency and multiple access capabilities of CMMA. CM maintains low feedback and high spectral efficiency by restricting relaying to a single route with the best overall channel. Two possible variations of CM are proposed depending on whether CSI available only at the users or just at the BS and the selected relay. The first is referred to Precode, Amplify, and Forward (PAF) while the second one is called Decode, Remap, and Forward (DMF). A new route selection algorithm for DMF based on maximising dmin of random CC is also proposed using a novel fast low-complexity multi-stage sphere based algorithm to calculate the dmin at the relay of random CC that is used for both relay selection and detection

    Técnicas de equalização para MIMO massivo com amplificação não linear

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    The dawn of the new generation of mobile communications and the trafic explosion that derives from its implementation pose great challenge. The milimeter wave band and the use of massive number of antennas are technologies which, when combined, allow the transmission of high data rate, functioning in zones of the electromagnetic spectrum that are less explored and with capability of allocation of dozens of GHz of bandwidth. In this dissertation we consider a massive MIMO millimeter wave system employing a hybrid architecture, i.e., the number of transmit and receive antennas are lower than the number of radio frequency chains. As consequence, the precoder and equalizers should be designed in both digital and analog domains. In the literature, most of the proposed hybrid beamforming schemes were evaluated without considering the effects of nonlinear amplifications. However, these systems face non-avoidable nonlinear effects due to power amplifiers functioning in nonlinear regions. The strong nonlinear effects throughout the transmission chain will have a negative impact on the overall system performance and thus its study and the design of equalizers that take into account these effects are of paramount importance. This dissertation proposes a hybrid iterative equalizer for massive MIMO millimeter wave SC-FDMA systems. The user terminals have low complexity, just equipped with analog precoders based on average angle of departure, each with a single radio frequency chain. At the base station it is designed an hybrid analog-digital iterative equalizer with fully connected architecture in order to eliminate both the multi-user interference and the nonlinear distortion caused by signal amplification during the transmission. The equalizer is optimized by minimizing the bit error rate, which is equivalent to minimize the mean square error rate. The impact of the saturation threshold of the amplifiers in the system performance is analysed, and it is demonstrated that the iterative process can efficiently remove the multi-user interference and the distortion, improving the overall system performance.O surgimento de uma nova geração de comunicaçÔes mĂłveis e a explosĂŁo de trĂĄfego que advĂ©m da sua implementação apresenta grandes desafios. A banda de ondas milimĂ©tricas e o uso massivo de antenas sĂŁo tecnologias que, combinadas, permitem atingir elevadas taxas de transmissĂŁo, funcionando em zonas do espectro electromagnĂ©tico menos exploradas e com capacidade de alocação de dezenas de GHz para largura de banda. Nesta dissertação foi considerado um sistema de MIMO massivo de ondas milimĂ©tricas usando uma arquitectura hĂ­brida, i.e., o nĂșmero de antenas para transmissĂŁo e recepção Ă© menor que o nĂșmero de cadeias de radiofrequĂȘncia. Consequentemente, o prĂ©-codificador e equalizadores devem ser projectados nos domĂ­nios digital e analĂłgico. Na literatura, a maioria dos esquemas hĂ­bridos de beamforming sĂŁo avaliados sem ter em conta os efeitos de nĂŁo linearidade da amplificação do sinal. No entanto, estes sistemas sofrem inevitavelmente de efeitos nĂŁo lineares devido aos amplificadores de potĂȘncia operarem em regiĂ”es nĂŁo lineares. Os fortes efeitos das nĂŁo-linearidades ao longo da cadeia de transmissĂŁo tĂȘm um efeito nefasto no desempenho do sistema e portanto o seu estudo e projecto de equalizadores que tenham em conta estes efeitos sĂŁo de extrema importĂąncia. Esta dissertação propĂ”e um equalizador hĂ­brido para sistemas baseados em ondas milimĂ©tricas para MIMO massivo com modulação SC-FDMA. Os terminais de utilizador possuem baixa complexidade, equipados apenas com prĂ©-codificadores analĂłgicos baseados no Ăąngulo mĂ©dio de partida, cada um com uma Ășnica cadeia de radiofrequĂȘncia. Na estação base Ă© projectado um equalizador iterativo hĂ­brido analĂłgico-digital com arquitectura completamente conectada de modo a eliminar a interferencia multi-utilizador e a distorção causada pela amplificação do sinal aquando da transmissĂŁo. O equalizador Ă© optimizado minimizando a taxa de erro de bit, o que Ă© equivalente a minimizar a taxa de erro quadrĂĄtico mĂ©dio. O impacto do limiar de saturação dos amplificadores no desempenho do sistema Ă© analisado, e Ă© demonstrado que o processo iterativo consegue eliminar de modo eficiente a interferĂȘncia multi-utilizador e a distorção, melhorando o desempenho do sistema.Mestrado em Engenharia EletrĂłnica e TelecomunicaçÔe

    Prostorno-frekvencijsko blok kodiranje sa odsjecanjem i filtriranjem kao tehnika predajni diverziti u SC-FDMA

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    The paper presents Space-Frequency Block Coding (SFBC) as a transmit diversity technique in Single Carrier Frequency Division Multiple Access (SC-FDMA). SC-FDMA is known as a low Peak-to-Average Power Ratio (PAPR) modulation technique. SFBC requires changing the order of the samples in the frequency domain, which results in increase of the PAPR. Because of that, additional clipping and filtering is proposed to be performed after SFBC to preserve low PAPR level and to avoid the out-of-band radiation. This affects the performance, but still provides significant advantage to the existing techniques, as is shown using simulationsOvaj papir predstavlja prostorno-vremensko blok kodiranje (SFBC) kao tehniku predajnog diverzitija u Single Carrier Frequency Division Multiple Access (SC-FDMA) sustavima. SC-FDMA je poznat kao modulacijska tehnika sa niskim omjerom vrĆĄne i srednje snage (PAPR). SFBC zahtjeva izmjenu redoslijeda uzoraka u frekvencijskoj domeni, ĆĄto rezultira povećanjem PAPR-a. Zbog toga, dodatno odsjecanje (clipping) i flitriranje signala nakon SFBC-a je predloĆŸeno u cilju očuvanja niske vrijednosti PAPR-a i izbjegavanja zračenja van opsega. Ovo utječe na performance, ali idalje pruĆŸa značajnu prednost nad postojećim tehnikama, kao ĆĄto je pokazano kroz simulacije

    Equalization of MIMO Channels in LTE-Advanced

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    LTE-Advanced is one of the most evolving and competing standards that target the high speed 4G wireless communications. In order to meet the target of this new cellular technology developed under auspices of the 3GPP standardization bodies, it is necessary to ensure that this technology is able to provide the headline requirements recommended for the terrestrial components of the IMT-Advanced radio interface for 4G broadband mobile communications. One of the key radio technologies that will enable LTE-Advanced to achieve the high data throughput rates is the use of MIMO antennas that play an important role as the conventional communications like using more bandwidths and higher modulation types are limited. Together with this are the downlink OFDMA and the uplink SC-FDMA techniques that are employed to improve the system architecture burdened with the data rates rising pretty well above what was previously in use. The combination of these technologies will help LTE-Advanced keep pace with other wireless technologies that may be competing to offer very high data rates and high level of mobility. But achieving the high data rate up to 1 Gbits/s in 4G mobile networks over wide frequency bandwidths and recovering the original information without being corrupted and downgraded has been a daunting task for engineers. Thus, this paper will briefly discuss the performances of MIMO equalization techniques such as MMSE, ZF and ZF-SIC equalizers in a Rayleigh multichannel fading.fi=OpinnÀytetyö kokotekstinÀ PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=LÀrdomsprov tillgÀngligt som fulltext i PDF-format

    Simultaneous Wireless Information and Power Transfer in 5G communication

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    Green communication technology is expected to be widely adopted in future generation networks to improve energy efficiency and reliability of wireless communication network. Among the green communication technologies,simultaneous wireless information and power transfer (SWIPT) is adopted for its flexible energy harvesting technology through the radio frequency (RF) signa lthati sused for information transmission. Even though existing SWIPT techniques are flexible and adoptable for the wireless communication networks, the power and time resources of the signal need to be shared between infor- mation transmission and RF energy harvesting, and this compromises the quality of the signal. Therefore,SWIP Ttechniques need to be designed to allow an efficient resource allocation for communication and energy harvesting. The goal oft his thesisis to design SWIP Ttechniques that allow efficient,reliable and secure joint communications and power transference. A problem associated to SWIPT techniques combined with multi carrier signals is that the increased power requirements inherent to energy harvesting purposes can exacerbate nonlinear distortion effects at the transmitter. Therefore, we evaluate nonlinear distortion and present feasible solutions to mitigate the impact of nonlinear distortion effects on the performance.Another goal of the thesisis to take advantage of the energy harvesting signals in SWIP Ttechniques for channel estimation and security purposes.Theperformance of these SWIPT techniques is evaluated analytically, and those results are validated by simulations. It is shownthatthe proposed SWIPT schemes can have excellent performance, out performing conventional SWIPT schemes.Espera-se que aschamadas tecnologiasde green communications sejam amplamente ado- tadas em futuras redes de comunicação sem fios para melhorar a sua eficiĂȘncia energĂ©tica a fiabilidade.Entre estas,encontram-se as tecnologias SWIPT (Simultaneous Wireless Information and Power Transference), nas quais um sinal radio Ă© usado para transferir simultaneamente potĂȘncia e informaçÔes.Embora as tĂ©cnicas SWIPT existentes sejam fle- xĂ­veis e adequadas para as redes de comunicaçÔes sem fios, os recursos de energia e tempo do sinal precisam ser compartilhados entre a transmissĂŁo de informaçÔes e de energia, o que pode comprometer a qualidade do sinal. Deste modo,as tĂ©cnicas SWIPT precisam ser projetadas para permitir uma alocação eficiente de recursos para comunicação e recolha de energia. O objetivo desta tese Ă© desenvolver tĂ©cnicas SWIPT que permitam transferĂȘncia de energia e comunicaçÔes eficientes,fiĂĄveis e seguras.Um problema associado Ă s tĂ©cnicas SWIPT combinadas com sinais multi-portadora sĂŁo as dificuldades de amplificação ine- rentes Ă  combinação de sinais de transmissĂŁo de energia com sinais de transferĂȘncia de dados, que podem exacerbar os efeitos de distorção nĂŁo-linear nos sinais transmitidos. Deste modo, um dos objectivos desta tese Ă© avaliar o impacto da distorção nĂŁo-linear em sinais SWIPT, e apresentar soluçÔes viĂĄveis para mitigar os efeitos da distorção nĂŁo-linear no desempenho da transmissĂŁo de dados.Outro objetivo da tese Ă© aproveitar as vantagens dos sinais de transferĂȘncia de energia em tĂ©cnicas SWIPT para efeitos de estimação de canal e segurança na comunicação.Os desempenhos dessas tĂ©cnicas SWIPT sĂŁo avaliados analiticamente,sendo os respectivos resultados validados por simulaçÔes.É mostrado que os esquemas SWIPT propostos podem ter excelente desempenho, superando esquemas SWIPT convencionais

    Frequency-domain precoding for single carrier frequency-division multiple access

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    Pré-codificação e equalização para sistemas SC-FDMA heterogéneos

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    Mestrado em Engenharia ElectrĂłnica e TelecomunicaçÔesMobile traffic in cellular networks is increasing exponentially. Small-cells are considered as a key solution to meet these requirements. Under the same spectrum the small-cells and the associated macro-cell (forming the so called heterogeneous systems) must cooperate so that one system can adapt to the other. If no cooperation is considered then the small-cells will generate harmful interference at the macro-cell. Interference alignment (IA) is a precoding technique that is able to achieve the maximum degrees of freedom of the interference channel, and can efficiently deal with inter-systems interference. Single carrier frequency division multiple access (SC-FDMA) is a promising solution technique for high data rate uplink communications in future cellular systems. Conventional linear equalizers are not efficient to remove the residual inter-carrier interference of the SC-FDMA systems. For this reason, there has been significant interest in the design of nonlinear frequency domain equalizers in general and decision feedback equalizers in particular, with the iterative block decision feedback equalizer (IB-DFE) being the most promising nonlinear equalizer. In this dissertation we propose and evaluate joint interference alignment precoding at the small cell user terminals with iterative non-linear frequency domain equalizer at the receivers (macro base station and central unit) for SC-FDMA based heterogeneous networks. The small-cell precoders are designed by enforcing that all generated interference at the macro-cell is aligned in an orthogonal subspace to the macro-cell received signal subspace. This enforces that no performance degradation is observed at the macro cell. Then, we design an iterative nonlinear frequency domain equalizer at the macro-cell receiver that is able to recover the macro-cell spatial streams, in the presence of both small-cell and inter-carrier interferences. The results show that the proposed transmitter and receiver structures are robust to the inter-system interferences and at the same time are able to efficient separate the macro and small cells spatial streams.O trafego mĂłvel nas redes celulares tem aumentado exponencialmente. As pico- cĂ©lulas sĂŁo consideradas como a solução chave para cumprir estes requisitos. Dentro do mesmo espectro, as pico-cĂ©lulas e as macro-cĂ©lulas (formando os chamados sistemas heterogĂ©neos) precisam de colaborar de modo a que um sistema possa adaptar-se ao outro. Se nĂŁo for considerada a cooperação, entĂŁo as pico-cĂ©lulas irĂŁo gerar interferĂȘncia prejudicial na macro-cĂ©lula. Interference alignment (IA) Ă© uma tĂ©cnica de prĂ©codificação que Ă© capaz de atingir o grau mĂĄximo de liberdade do canal de interferĂȘncia, e consegue lidar eficazmente com interferĂȘncia entre sistemas. Single carrier frequency division multiple access (SC-FDMA) Ă© uma solução tĂ©cnica promissora para transmissĂŁo de dados em uplink, para sistemas celulares futuros. Equalizadores lineares convencionais nĂŁo sĂŁo eficientes a remover a interferĂȘncia residual entre portadoras dos sistemas SC-FDMA. Por este motivo, tem havido interesse significativo no desenho de equalizadores nĂŁo lineares no domĂ­nio da frequĂȘncia em geral e em equalizadores baseados em decisĂŁo por feedback em particular, tendo o iterative block decision feedback equalizer (IB-DFE) como o equalizador nĂŁo linear mais promissor. Nesta dissertação propomos e avaliamos prĂ©codificação de alinhamento de interferĂȘncia nos terminais das pico-cĂ©lulas em conjunto com equalizadores nĂŁo lineares no domĂ­nio da frequĂȘncia nos recetores (estação base da macro-cĂ©lula e unidade central de processamento) para redes heterogĂ©neas baseadas em SC-FDMA. Os prĂ©codificadores das pico-cĂ©lulas sĂŁo desenhados de maneira a obrigar a que toda a interferĂȘncia gerada na macro-cĂ©lula esteja alinhada num subespaço ortogonal em relação ao subespaço do sinal recebido na macro- cĂ©lula. Isto obriga a que nĂŁo seja observada degradação de desempenho na macro-cĂ©lula. Em seguida, desenhamos um equalizador nĂŁo linear no domĂ­nio da frequĂȘncia no recetor da macro-cĂ©lula capaz de recuperar os fluxos de dados da macro-cĂ©lula, na presença de interferĂȘncia tanto entre portadoras como das pico-cĂ©lulas. Os resultados mostram que as estruturas de transmissĂŁo e receção propostas sĂŁo robustas contra a interferĂȘncia entre sistemas e ao mesmo tempo capaz de separar eficientemente os dados da macro e das pico cĂ©lulas
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