Multiple Input Multiple Output with Orthogonal Frequency Division Multiplexing (MIMOOFDM) has been widely adopted as one of the most promising air interface solutions for future broadband wireless communication systems due to its high rate transmission capability and robustness against multipath fading. However, these MIMO-OFDM advantages cannot be achieved unless the channel state information (CSI) can be obtained accurately and promptly at the receiver to assist coherent detection of data symbols. Channel estimation and training sequence design are, therefore, still open challenges of great interest. In this work, we investigate the Linear Minimum Mean Square Error (LMMSE) channel estimation and design nearly optimal training sequences for MIMO-OFDM systems in spatially correlated fading. We, first, review the LMMSE channel estimation model for MIMO-OFDM in spatially correlated fading channels. We, then, derive a tight theoretical lower bound of the channel estimation Mean Square Error (MSE). By exploiting the information on channel correlation matrices which is available at the transmitter, we design a practical and nearly optimal training sequence for MIMO-OFDM systems . The optimal transmit power allocation for training sequences is found using the Iterative Bisection Procedure (IBP). We also propose an approximate transmit power allocation algorithm which is computationally more efficient than the IBP while maintaining a similar MSE performance. The proposed training sequence design method is also applied to MIMO-OFDM systems where Cyclic Prefixing OFDM (CP-OFDM) is replaced by Zero Padding OFDM - OverLap-Add method (ZP-OFDM-OLA). The simulation results show that the performance of the proposed training sequence is superior to that of all existing training sequences and almost achieves the MSE theoretical lower bound.

[pt] Nos últimos anos a demanda por serviços de comunicações móveis tem crescido de modo significativo. Embora o serviço telefônico ainda predomine, com a popularização dos terminais móveis, a transmissão de dados (mensagens curtas, correio eletrônico, acesso à Internet, etc.) assume progressivamente uma posição relevante no mercado. Os sistemas móveis de segunda geração (2G) e da geração de transição (2,5G) ocupam atualmente as faixas de 800 / 900 MHz e 1,8 / 1,9 GHz, sendo esta última estando prevista também para a terceira geração (3G). O aumento crescente que se observa na capacidade dos sistemas móveis e a possibilidade de congestionamento do espectro em UHF são fatores que justificam investigar a utilização de freqüências mais elevadas, onde o problema da largura da faixa de transmissão é menos restritivo. Por outro lado, é de se esperar que, inicialmente, a necessidade de expansão do espectro para os serviços móveis seja crítica em áreas urbanas e suburbanas. As áreas suburbanas são importantes devido aos problemas para prover acesso banda larga nestas regiões devido a baixa capilaridade das redes de TV a Cabo e dos Modens ADSL. A demanda por banda larga faz surgir novas tecnologias, em especial Wi-Fi e WiMAX. Entretanto, as WLAN´s como Wi-Fi dependem de backhall para expansão destas redes. Assim sendo, a tecnologia WiMAX surgiu como alternativa para que se tenha uma oferta de serviços banda larga que atenda a demanda por estes serviços. Neste contexto, o presente trabalho propõe um estudo do canal em 3,5GHz (pois a mesma esta licitado para uso do WiMAX no Brasil) em áreas suburbanas por estas serem as que mais sofrem com o problema de falta de cobertura por produtos banda larga, sem ter na maioria dos casos, sua demanda atendida. O estudo será fundamentado nos fenômenos físicos que caracterizam o canal em 3,5GHz e na análise a partir de duas técnicas de sondagem OFDM e STDCC. Uma comparação entre as técnicas citadas e seu uso para caracterização de canal. / [en] In the last years the demand for services of mobile communications has grown in significant way. Although the telephonic service still predominates, with the increase of the mobile terminals, the transmission of data (short messages, e-mail, access to the Internet, etc.) it is assuming an excellent position in the market. The mobile systems of second generation (2G) and the generation of transistion (2,5G) occupy the bands of 800 currently/ 900 MHz and 1,8/ 1,9 GHz, this last one being also foreseen for third generation (3G). The increasing increase that if observes in the capacity of the mobile systems and the possibility of congestion of the specter in UHF is factors that they justify to more investigate the use of raised frequencies, where the problem of the width of the transmission band is less restrictive. On the other hand, it is of if waiting that, initially, the necessity of expansion of the specter for the mobile services is critical in urban areas. The suburban area important due the problems for supply access wideband in these regions due to problems of density these modem cable and ADSL. Actually the demand by wideband, go to the sprouting of new technologies in special Wi-Fi and WiMAX. However, the WLAN´s as Wi-Fi depend on the backhall for expansion of theses nets. Like this being, the technology WiMAX arose like alternative for that have a wide band service offering that attend the demand by these service. In this context this work proposes a study of the channel in 3,5GHz (therefore to same this licitado for use of the WiMAX in Brazil) in suburban areas by these will be the that more suffer with the cover absence problem by products wide band, without have, in the majority of the cases, its demand attended. The study will be substantiated us physical phenomena that characterize the channel in 3,5GHz and in the analysis from two techniques of survey OFDM and STDCC. A comparison between the techniques cited and his use for characterization of channel.

[pt] O esquema OFDM (Orthogonal Frequency Division Multiplexing) é um esquema de transmissão de sinais por multiplexação em freqüência e sua adoção vem mostrando-se bastante promissora no que diz respeito à transmissão de sinais em canais seletivos em freqüência. Sua relativa robustez frente a canais com múltiplos percursos é conseguida efetuando-se a transmissão paralela de dados em subportadoras ortogonais estreitas. Os receptores OFDM, de uma forma geral, necessitam de estimativas do canal de comunicação para realizar a detecção coerente dos sinais recebidos. Estimativas do canal podem ser obtidas de forma assistida por meio da utilização de pilotos que consomem preciosa banda, ou de forma cega, valendo-se apenas do conhecimento de características estatísticas dos sinais transmitidos. Esta tese segue a linha de estimação cega de canal. São propostos dois estimadores cegos de canal, para sistemas OFDM com intervalo de guarda ZP ou CP. O primeiro baseia-se no casamento de correlação, a saber: a estimativa do canal corresponde ao argumento que minimiza a norma quadrática de Frobenius da diferença entre a matriz correlação teórica parametrizada dos sinais recebidos e uma estimativa desta matriz obtida por meio das observações no receptor. O segundo estimador é desenvolvido a partir de uma modificação do método de identificação de canal por meio da estimação do subespaço de ruído, lançando mão de uma estimativa para o operador projeção no subespaço de ruído. Técnicas para resolver a ambigüidade complexa presente nas estimativas do canal que resultam dos métodos propostos são abordadas. Os estimadores propostos são estendidos para sistemas OFDM ditos com intervalo de guarda insuficiente. Resultados de simulações ilustram o desempenho, tanto em termos de erro quadrático médio dos estimadores, quanto em taxa de erro de bit dos sistemas. / [en] Orthogonal Frequency Division Multiplexing is a multi-carrier transmission technique suitable for wireless communications through frequency selective channels, thus making it an appealing scheme for next-generation applications demanding high data rates. Its robustness with respect to multipath channels is obtained by modulating a set of closely-spaced orthogonal sub-carriers. In order to coherently detect the received signals, Channel State Information must be available to OFDM receivers. Supervised channel estimation is achieved by multiplexing known pilot symbols and data symbols, thus reducing effective system throughput. On the other hand, unsupervised or blind estimation techniques rely solely on the knowledge of statistical characteristics of the transmitted signal in order to identify the channel. This thesis proposes two blind channel estimators, for OFDM systems with CP or ZP guard interval. The first estimator is based on correlation matching: a channel estimate is obtained as the argument which minimizes the Frobenius quadratic norm of the difference between the parameterized theoretical correlation matrix of the transmitted signals and an estimate of that matrix obtained by means of observations at the receiver. The second estimator is obtained by modifying the noise subspace based channel estimator and using an estimate for the noise subspace projector which relies on powers of the inverse correlation matrix. Techniques to eliminate the inherent complex ambiguity derived from the proposed blind channel estimators are addressed. The porposed estimators’ formulation is also extended to the case of OFDM systems with insufficient guard intervals. Simulation results depict Mean Square Error of the proposed estimators, as well as Bit Error Rate performance of systems using those estimators in various scenarios.

Orientador: Rangel Arthur / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Tecnologia / Made available in DSpace on 2018-08-22T06:36:42Z (GMT). No. of bitstreams: 1 Hoshino_FelipeKojiGodinho_M.pdf: 3730881 bytes, checksum: d6cd57d6d8286fe95b3166c35de77d73 (MD5) Previous issue date: 2013 / Resumo: O aumento exponencial no tráfego mundial de dados tem imposto inúmeros desafios para os sistemas de telecomunicações. Há um compromisso entre o interesse das operadoras de telecomunicações, de aumentar a receita líquida, e dos clientes, de aumentar a taxa de transmissão de dados. Com isso, diversas soluções têm sido discutidas no âmbito das comunicações ópticas. Uma das propostas estudadas é a aplicação mais intensa do processamento digital de sinais. Dessa forma, neste trabalho foi estudado e simulado o uso da modulação OFDM (Orthogonal Frequency Division Multiplexing) nas redes ópticas de nova geração. Também foi simulado um modem OFDM em linguagem VHDL (Very High Speed Integrated Circuit Hardware Description Language) sendo esta uma etapa do projeto de novos equipamentos. Como prova de conceito, analisou-se o desempenho de redes ópticas por meio do software OptiSystem. De maneira geral, os resultados obtidos foram satisfatórios para demonstrar a viabilidade da modulação OFDM em redes ópticas de nova geração / Abstract: The exponential increase in global data traffic has imposed many challenges for telecommunication systems. There is a trade-off between the interest of telecom operators to increase the net revenue and the customers to increase the transmission data rate. Several solutions have been discussed in optical communications field. One approach is the more intense application of the digital signal processing. Thus, in this work is presented a review and simulations of OFDM modulation (Orthogonal Frequency Division Multiplexing) in the next generation networks. It was also simulated a OFDM modem in VHDL (Very High Speed Integrated Circuit Hardware Description Language) which for a new equipment design. The performance of optical networks has been examinated with OptiSystem software as o proof of concept. In general, the results obtained were satisfactory to show the feasibility of OFDM modulation in the next generation networks / Mestrado / Tecnologia e Inovação / Mestre em Tecnologia

Cette thèse présente une solution originale permettant d’extraire, à partir de signaux de communication OFDM, l’information liée à la différence de temps d’arrivée (TDOA) entre deux émetteurs très proches et un récepteur. Cette méthode, qui s’avère super-résolutive, permet d’extraire des TDOA en dessous de la limite de Rayleigh fixée par la bande passante utile. Dans ce travail, nous effectuons, à l'aide d'une sortie simple à entrées multiples, la caractérisation et la modélisation des canaux pour l’estimation TDOA. En gérant ces réponses ce canal de fréquence de canal de différentes manières, nous minimisons différentes fonctions de coût exprimées comme la différence entre la réponse de canal mesurée et un modèle direct prédéfini. Pour la validation, la simulation basée sur différentes topologies présente des résultats soulignant la propriété de super-résolution d'une telle approche. La performance de l’estimation TDOA proposée est comparée à la bande inférieure de Cramer-Rao. Les effets de la propagation par trajets multiples sont pris en compte et certaines solutions proposées sont discutées et simulées. De plus, la partie expérimentale de ce travail valide à la fois les modèles directs et inverses dans différentes configurations de canaux. / This thesis presents an original solution for extracting, from OFDM communication signals, the information related to the time difference of arrival (TDOA) between two closed transmitters and one receiver. This solution, which shows to be super-resolution, makes it possible to extract TDOA below the Rayleigh limit set by the useful bandwidth.Inthis work, we perform, using a Multiple Inputs Simple Output, channel characterization and modeling for TDOA estimation. By handling these channel frequency responses in different ways, xe minimize different cost functions expresses as the difference between measured channel response and a predefined direct model. For validation, the simulation based on different topologies exhibit results is compared to the Cramer Rao Lower Band. The effects of the multipath are taken into account and some proposed solutions are discussed ans simulated. Moreover, the experimental part of this work validates the direct and inverse models in different channel configurations.

This master thesis aims for Inter-carrier interference (ICI) mitigation in orthogonal frequency division multiplexing (OFDM) system by considering designs of frequency domain cyclic extension(FDCE) and optimal windowing pulse shape. Although OFDM system has been put forward in the 1970s, it has just emerged in 4G. In the early stage, it has been restricted by its high computational complexity. With the discovery that modulation and demodulation process of OFDM can be realized by discrete Fourier transform (DFT) and inverse discrete Fourier transform (IDFT), it is widely used in 4G and 5G-New Ratio (NR). Based on OFDM system, a variety of derivative systems are further proposed and applied. With the development of 5G technology in the mobile communication, the requirement of signal propagation between high-speed mobile user and base station (BS) is higher and higher. With the increase of the moving speed of objects, the frequency shift caused by Doppler eff ect can not be underestimated. ICI caused by Doppler shift is becoming more and more serious. Therefore, how to eliminate the ICI caused by Doppler shift has become an inevitable potential problem. In this thesis, two eff ective approaches for ICI mitigation have been explored and studied. By adding FDCE and optimal windowing pulse shape, the system performance is analyzed and the system simulation is constructed in MATLAB.

Wideband Code Division Multiple Access (WCDMA) is one of the main technologies for the implementation of third-generation (3G) cellular systems. It is based on radio access technique proposed by ETSI Alpha group and the specifications was finalised 1999. WCDMA is also known as UMTS and has been adopted as a standard by the ITU under the name “IMT-2000 direct spread”. The implementation of WCDMA will be a technical challenge because of its complexity and versatility. The complexity of WCDMA systems can be viewed from different angles: the complexity of each single algorithm, the complexity of the overall system and the computational complexity of a receiver. In WCDMA interface different users can simultaneously transmit at different data rates and data rates can even vary in time. WCDMA increases data transmission rates in GSM systems by using the CDMA air interface instead of TDMA. WCDMA is based on CDMA and is the technology used in UMTS. WCDMA is the dominating 3G technology, providing higher capacity for voice and data and higher data rates. The gradual evolution from today's systems is driven by demand for capacity, which is required by new and faster data based mobile services. WCDMA enables better use of available spectrum and more cost-efficient network solutions. The operator can gradually evolve from GSM to WCDMA, protecting investments by re-using the GSM core network and 2G/2.5G services. Orthogonal Frequency Division Multiplexing (OFDM) - technique for increasing the amount of information that can be carried over a wireless network uses an FDM modulation technique for transmitting large amounts of digital data over a radio wave. OFDM works by splitting the radio signal into multiple smaller sub-signals that are then transmitted simultaneously at different frequencies to the receiver. OFDM reduces the amount of crosstalk in signal transmissions. 802.11a WLAN, 802.16 and WiMAX technologies use OFDM. It's also used in the ETSI's HiperLAN/2 standard. In addition, Japan's Mobile Multimedia Access Communications (MMAC) WLAN broadband mobile technology uses OFDM. In frequency-division multiplexing, multiple signals, or carriers, are sent simultaneously over different frequencies between two points. However, FDM has an inherent problem: Wireless signals can travel multiple paths from transmitter to receiver (by bouncing off buildings, mountains and even passing airplanes); receivers can have trouble sorting all the resulting data out. Orthogonal FDM deals with this multipath problem by splitting carriers into smaller subcarriers, and then broadcasting those simultaneously. This reduces multipath distortion and reduces RF interference allowing for greater throughput. In this paper we have discussed about these two methods of third generation radio transmission system which are WCDMA and OFDM with various aspects. In between these two radio transmission technique, a better choice will be investigated.

Small cells are low-powered radio access nodes that operate in licensed and unlicensed spectrum that have a range of 10 meters to 200 meters, compared to a mobile macrocell which might have a range of a few kilometres. This dissertation proposes algorithms for the enhancement of small cells installed in high speed rails. The thesis addresses two main points: the link between the small cell and the base station, and the link between the end-users and the small cell. The channel between the small cell and the base station is a fast fading channel due to the mobility of the high speed rail. The first part of the thesis proposes methods to enhance the link between the small cell and the base station using Low-Density Parity-Check codes (LDPC) for fast fading channels. The proposed uses nonuniform reconstruction methods based on the soft output log-likelihood ratio (LLR) provided by the LDPC decoder. The LLRs provide information about the location of the symbols with high probability of being correct. The grid formed under the assumption of a correlated Rayleigh channel affecting the transmitted data is highly nonuniform. Reconstruction of the channel under such assumptions is highly unstable. A signal-to-noise- ratio dependent regularization method is implemented to enhance the performance under imperfect Doppler spread estimation. The second part of the thesis proposes algorithms for the link between the end-user and the small cell. Since power efficiency is a major factor for end-users employing battery powered devices, we propose a Linear Programming (LP) algorithm for signal shaping to minimize the average transmitted power. The other problem the thesis addresses is the minimization of Peak-to-Average Power-Ratio (PAPR) of Orthogonal Frequency Division Multiplexing (OFDM) signals. The PAPR is minimized using a set of phase shifts for the constituting subcarriers of the OFDM signal. The set of phase shifts is determined using a LP approach that minimizes the complexity when the block length is high. A real-time implementation of some of the algorithms is carried out using the TMS320C6713 Texas Instruments board. The results for fixed-point versus floating-point implementation is shown for a different number of precision bits. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2013-04-27 16:54:32.464

With the advent of new high data rate wireless applications, as well as growth of existing wireless services, demand for additional bandwidth is rapidly increasing. Existing spectrum allocation policies of the Federal Communications Commission (FCC) prohibits unlicensed access to licensed spectrum, constraining them instead to several heavily populated, interference-prone frequency bands, which causes spectrum scarcity. However, it has been shown by several spectrum measurement campaigns that the current licensed spectrum usage across time and frequency is inefficient. Therefore, a concept of unlicensed users temporarily ``borrowing" spectrum from incumbent license holders to improve the spectrum utilization, called ``spectrum pooling", which is based on dynamic spectrum access (DSA), is proposed. Cognitive radio is a communication paradigm that employs software-defined radio technology in order to perform DSA and offers versatile, powerful and portable wireless transceivers. Orthogonal frequency division multiplexing (OFDM) is a promising candidate for cognitive radio transmission. OFDM supports high data rates that are robust to channel impairments. In addition, some subcarriers can be deactivated which constitutes a non-contiguous OFDM (NC-OFDM) transmission. However, one of the biggest problems for OFDM transmission is high out-of-band (OOB) radiation, which is caused by sinc-type function representing the symbols during one time constant. Thus, high sidelobe may occur that will interfere with neighboring transmissions. This thesis presents two novel techniques for NC-OFDM sidelobe suppression. Another concern about cognitive radio systems is that the influence of frequency-selective fading channel. Consequently, this thesis also presents a combined approach employing power loading, bit allocation and sidelobe suppression for OFDM-based cognitive radio systems optimization.

Doctor of Philosophy / The next generation mobile networks are expected to provide multimedia applications with a high quality of service. On the other hand, interference among multiple base stations (BS) that co-exist in the same location limits the capacity of wireless networks. In conventional wireless networks, the base stations do not cooperate with each other. The BSs transmit individually to their respective mobile stations (MS) and treat the transmission from other BSs as interference. An alternative to this structure is a network cooperation structure. Here, BSs cooperate with other BSs to simultaneously transmit to their respective MSs using the same frequency band at a given time slot. By doing this, we significantly increase the capacity of the networks. This thesis presents novel research results on a noncooperative transmission scheme and a cooperative transmission scheme for multi-user multiple-input-multiple-output orthogonal frequency division multiplexing (MIMO-OFDM). We first consider the performance limit of a noncooperative transmission scheme. Here, we propose a method to reduce the interference and increase the throughput of orthogonal frequency division multiplexing (OFDM) systems in co-working wireless local area networks (WLANs) by using joint adaptive multiple antennas(AMA) and adaptive modulation (AM) with acknowledgement (ACK) Eigen-steering. The calculation of AMA and AM are performed at the receiver. The AMA is used to suppress interference and to maximize the signal-to-interference-plus-noise ratio (SINR). The AM scheme is used to allocate OFDM sub-carriers, power, and modulation mode subject to the constraints of power, discrete modulation, and the bit error rate (BER). The transmit weights, the allocation of power, and the allocation of sub-carriers are obtained at the transmitter using ACK Eigen-steering. The derivations of AMA, AM, and ACK Eigen-steering are shown. The performance of joint AMA and AM for various AMA configurations is evaluated through the simulations of BER and spectral efficiency (SE) against SIR. To improve the performance of the system further, we propose a practical cooperative transmission scheme to mitigate against the interference in co-working WLANs. Here, we consider a network coordination among BSs. We employ Tomlinson Harashima precoding (THP), joint transmit-receive beamforming based on SINR (signal-to-interference-plus-noise-ratio) maximization, and an adaptive precoding order to eliminate co-working interference and achieve bit error rate (BER) fairness among different users. We also consider the design of the system when partial channel state information (CSI) (where each user only knows its own CSI) and full CSI (where each user knows CSI of all users) are available at the receiver respectively. We prove analytically and by simulation that the performance of our proposed scheme will not be degraded under partial CSI. The simulation results show that the proposed scheme considerably outperforms both the existing noncooperative and cooperative transmission schemes. A method to design a spectrally efficient cooperative downlink transmission scheme employing precoding and beamforming is also proposed. The algorithm eliminates the interference and achieves symbol error rate (SER) fairness among different users. To eliminate the interference, Tomlinson Harashima precoding (THP) is used to cancel part of the interference while the transmit-receive antenna weights cancel the remaining one. A new novel iterative method is applied to generate the transmit-receive antenna weights. To achieve SER fairness among different users and further improve the performance of MIMO systems, we develop algorithms that provide equal SINR across all users and order the users so that the minimum SINR for each user is maximized. The simulation results show that the proposed scheme considerably outperforms existing cooperative transmission schemes in terms of the SER performance and complexity and approaches an interference free performance under the same configuration. We could improve the performance of the proposed interference cancellation further. This is because the proposed interference cancellation does not consider receiver noise when calculating the transmit-receive weight antennas. In addition, the proposed scheme mentioned above is designed specifically for a single-stream multi-user transmission. Here, we employ THP precoding and an iterative method based on the uplink-downlink duality principle to generate the transmit-receive antenna weights. The algorithm provides an equal SINR across all users. A simpler method is then proposed by trading off the complexity with a slight performance degradation. The proposed methods are extended to also work when the receiver does not have complete Channel State Informations (CSIs). A new method of setting the user precoding order, which has a much lower complexity than the VBLAST type ordering scheme but with almost the same performance, is also proposed. The simulation results show that the proposed schemes considerably outperform existing cooperative transmission schemes in terms of SER performance and approach an interference free performance. In all the cooperative transmission schemes proposed above, we use THP to cancel part of the interference. In this thesis, we also consider an alternative approach that bypasses the use of THP. The task of cancelling the interference from other users now lies solely within the transmit-receive antenna weights. We consider multiuser Gaussian broadcast channels with multiple antennas at both transmitter and receivers. An iterative multiple beamforming (IMB) algorithm is proposed, which is flexible in the antenna configuration and performs well in low to moderate data rates. Its capacity and bit error rate performance are compared with the ones achieved by the traditional zero-forcing method.