Advanced Quantizer Designs for FDD-Based FD-MIMO Systems Using Uniform Planar Arrays

Massive multiple-input multiple-output (MIMO) systems, which utilize a large number of antennas at the base station, are expected to enhance network throughput by enabling improved multiuser MIMO techniques. To deploy many antennas in reasonable form factors, base stations are expected to employ antenna arrays in both horizontal and vertical dimensions, which is known as full-dimension (FD) MIMO. The most popular two-dimensional array is the uniform planar array (UPA), where antennas are placed in a grid pattern. To exploit the full benefit of massive MIMO in frequency division duplexing (FDD), the downlink channel state information (CSI) should be estimated, quantized, and fed back from the receiver to the transmitter. However, it is difficult to accurately quantize the channel in a computationally efficient manner due to the high dimensionality of the massive MIMO channel. In this paper, we develop both narrowband and wideband CSI quantizers for FD-MIMO taking the properties of realistic channels and the UPA into consideration. To improve quantization quality, we focus on not only quantizing dominant radio paths in the channel, but also combining the quantized beams. We also develop a hierarchical beam search approach, which scans both vertical and horizontal domains jointly with moderate computational complexity. Numerical simulations verify that the performance of the proposed quantizers is better than that of previous CSI quantization techniques.Comment: 15 pages, 6 figure

Characterisation of MIMO radio propagation channels

Due to the incessant requirement for higher performance radio systems, wireless designers have been constantly seeking ways to improve spectrum efficiency, link reliability, service quality, and radio network coverage. During the past few years, space-time technology which employs multiple antennas along with suitable signalling schemes and receiver architectures has been seen as a powerful tool for the implementation of the aforementioned requirements. In particular, the concept of communications via Multiple-Input Multiple-Output (MIMO) links has emerged as one of the major contending ideas for next generation ad-hoc and cellular systems. This is inherently due to the capacities expected when multiple antennas are employed at both ends of the radio link. Such a mobile radio propagation channel constitutes a MIMO system. Multiple antenna technologies and in particular MIMO signalling are envisaged for a number of standards such as the next generation of Wireless Local Area Network (WLAN) technology known as 802.1 ln and the development of the Worldwide Interoperability for Microwave Access (WiMAX) project, such as the 802.16e. For the efficient design, performance evaluation and deployment of such multiple antenna (space-time) systems, it becomes increasingly important to understand the characteristics of the spatial radio channel. This criterion has led to the development of new sounding systems, which can measure both spatial and temporal channel information. In this thesis, a novel semi-sequential wideband MIMO sounder is presented, which is suitable for high-resolution radio channel measurements. The sounder produces a frequency modulated continuous wave (FMCW) or chirp signal with variable bandwidth, centre frequency and waveform repetition rate. It has programmable bandwidth up to 300 MHz and waveform repetition rates up to 300 Hz, and could be used to measure conventional high- resolution delay/Doppler information as well as spatial channel information such as Direction of Arrival (DOA) and Direction of Departure (DOD). Notably the knowledge of the angular information at the link ends could be used to properly design and develop systems such as smart antennas. This thesis examines the theory of multiple antenna propagation channels, the sounding architecture required for the measurement of such spatial channel information and the signal processing which is used to quantify and analyse such measurement data. Over 700 measurement files were collected corresponding to over 175,000 impulse responses with different sounder and antenna array configurations. These included measurements in the Universal Mobile Telecommunication Systems Frequency Division Duplex (UMTS-FDD) uplink band, the 2.25 GHz and 5.8 GHz bands allocated for studio broadcast MIMO video links, and the 2.4 GHz and 5.8 GHz ISM bands allocated for Wireless Local Area Network (WLAN) activity as well as for a wide range of future systems defined in the WiMAX project. The measurements were collected predominantly for indoor and some outdoor multiple antenna channels using sounding signals with 60 MHz, 96 MHz and 240 MHz bandwidth. A wide range of different MIMO antenna array configurations are examined in this thesis with varying space, time and frequency resolutions. Measurements can be generally subdivided into three main categories, namely measurements at different locations in the environment (static), measurements while moving at regular intervals step by step (spatial), and measurements while the receiver (or transmitter) is on the move (dynamic). High-scattering as well as time-varying MIMO channels are examined for different antenna array structures

Massive hybrid antenna array for millimeter-wave cellular communications

© 2002-2012 IEEE. A massive hybrid array consists of multiple analog subarrays, with each subarray having its digital processing chain. It offers the potential advantage of balancing cost and performance for massive arrays and therefore serves as an attractive solution for future millimeter-wave (mm- Wave) cellular communications. On one hand, using beamforming analog subarrays such as phased arrays, the hybrid configuration can effectively collect or distribute signal energy in sparse mm-Wave channels. On the other hand, multiple digital chains in the configuration provide multiplexing capability and more beamforming flexibility to the system. In this article, we discuss several important issues and the state-of-the-art development for mm-Wave hybrid arrays, such as channel modeling, capacity characterization, applications of various smart antenna techniques for single-user and multiuser communications, and practical hardware design. We investigate how the hybrid array architecture and special mm-Wave channel property can be exploited to design suboptimal but practical massive antenna array schemes. We also compare two main types of hybrid arrays, interleaved and localized arrays, and recommend that the localized array is a better option in terms of overall performance and hardware feasibility

Equalizador híbrido na banda das ondas milimétricas para sistemas GFDM

Wireless communication using very-large multiple-input multiple-output (MIMO) antennas has been regarded as one of the enabling technologies for the future mobile communication. It refers to the idea of equipping cellular base stations (BSs) with a very large number of antennas giving the possibility to focusing the transmitted signal energy into very short-range areas, which will provide huge improvements in the capacity, in addition to the spectral and energy efficiency. Concurrently, this demand for high data rates and capacity led to the necessity of exploiting the enormous amount of spectrum in the millimeter wave (mmWave) bands. However, the combination of millimeter-wave communications arrays with a massive number of antennas has the potential to dramatically enhance the features of wireless communication. This combination implies high cost and power consumption in the conventional full digital architecture, where each RF chain is dedicated to one antenna. The solution is the use of a hybrid architecture, where a small number of RF chains are connected to a large number of antennas through a network of phase shifters. On the other hand, another important factor that affect the transmission quality is the modulation technique, which plays an important role in the performance of the transmission process, for instance, GFDM is a flexible non-orthogonal multicarrier modulation concept, that introduces additional degrees of freedom when compared to other multicarrier techniques. This flexibility makes GFDM a promising solution for the future cellular generations, because it can achieve different requirements, such as higher spectrum efficiency, better control of out-of-band (OOB) emissions, as well as achieving low peak to average power ratio (PAPR). In this work, we present an analog-digital transmitter and receiver structures. Considering a GFDM modulation technique to be implemented in the digital part, while in the analog part, we propose a full connected hybrid multiuser linear equalizer, combined with low complexity hybrid precoder for wideband millimeter-wave massive MIMO systems. The hybrid equalizer is optimized by minimizing the mean square error between the hybrid approach and the full digital counterpart. The results show that the performance of the proposed hybrid scheme is very close to the full digital counterpart and the gap reduces as the number of RF chains increases.O uso de um número elevado de antenas, também designado por MIMO massivo, tem sido considerada uma das tecnologias mais promissoras para os futuros sistemas de comunicação sem fios. Esta tecnologia, refere-se à ideia de equipar as estações base (BSs) com um número muito grande de antenas, dando a possibilidade de focar a energia do sinal transmitido em áreas de alcance muito restritas, o que proporcionará grandes melhorias na capacidade, além das espectrais e eficiência energética. Simultaneamente, a exigência por taxas de dados elevadas e capacidade levou à necessidade de explorar uma enorme quantidade de espectro nas bandas de ondas milimétricas (mmWave). A combinação de comunicação na banda das ondas milimétricas com terminais equipados com um grande número de antenas tem o potencial de melhorar drasticamente os recursos da comunicação sem fios. Considerando no entanto uma arquitetura digital, usada em sistemas MIMO convencionais, em que cada cadeia de RF é dedicada a uma antena, implica um custo e um consumo de energia elevados. A solução é o uso de uma arquitetura híbrida, na qual um pequeno número de cadeias de RF é conectado a um grande número de antenas através de um conjunto de deslocadores de fase. Outro fator importante que afeta a qualidade da transmissão é a técnica de modulação usada, que desempenha um papel importante no desempenho do processo de transmissão. O GFDM é um conceito de modulação de portadora múltipla, não ortogonal e flexível, que introduz graus de liberdade adicionais, quando comparado a outras técnicas de portadora múltipla, como o OFDM. Essa flexibilidade faz do GFDM uma solução promissora para as futuras gerações celulares, pois pode atender a diferentes requisitos, como maior eficiência de espectro, melhor controle das emissões fora de banda (OOB), além de atingir baixo rácio de potência média / pico ( PAPR). Neste trabalho, é assumido uma arquitetura hibrida no transmissor e recetor. Considera-se uma técnica de modulação GFDM a ser implementada na parte digital, enquanto na parte analógica, é proposto um equalizador linear híbrido multiutilizador totalmente conectado, i.e., cada cadeia RF está ligada a todas as antenas, combinado com um pré-codificador híbrido, de baixa complexidade para sistemas MIMO massivo de banda larga. O equalizador híbrido é otimizado, minimizando o erro quadrático médio entre a abordagem híbrida e a contraparte totalmente digital. Os resultados mostram que o desempenho do esquema híbrido proposto está muito próximo do equivalente digital, à medida que o número de cadeias de RF aumenta.Mestrado em Engenharia Eletrónica e Telecomunicaçõe