Array communications in wireless sensor networks

Imperial Users onl

Design and Realization of Fully-digital Microwave and Mm-wave Multi-beam Arrays with FPGA/RF-SOC Signal Processing

There has been a constant increase in data-traffic and device-connections in mobile wireless communications, which led the fifth generation (5G) implementations to exploit mm-wave bands at 24/28 GHz. The next-generation wireless access point (6G and beyond) will need to adopt large-scale transceiver arrays with a combination of multi-input-multi-output (MIMO) theory and fully digital multi-beam beamforming. The resulting high gain array factors will overcome the high path losses at mm-wave bands, and the simultaneous multi-beams will exploit the multi-directional channels due to multi-path effects and improve the signal-to-noise ratio. Such access points will be based on electronic systems which heavily depend on the integration of RF electronics with digital signal processing performed in Field programmable gate arrays (FPGA)/ RF-system-on-chip (SoC). This dissertation is directed towards the investigation and realization of fully-digital phased arrays that can produce wideband simultaneous multi-beams with FPGA or RF-SoC digital back-ends. The first proposed approach is a spatial bandpass (SBP) IIR filter-based beamformer, and is based on the concepts of space-time network resonance. A 2.4 GHz, 16-element array receiver, has been built for real-time experimental verification of this approach. The second and third approaches are respectively based on Discrete Fourier Transform (DFT) theory, and a lens plus focal planar array theory. Lens based approach is essentially an analog model of DFT. These two approaches are verified for a 28 GHz 800 MHz mm-wave implementation with RF-SoC as the digital back-end. It has been shown that for all proposed multibeam beamformer implementations, the measured beams are well aligned with those of the simulated. The proposed approaches differ in terms of their architectures, hardware complexity and costs, which will be discussed as this dissertation opens up. This dissertation also presents an application of multi-beam approaches for RF directional sensing applications to explore white spaces within the spatio-temporal spectral regions. A real-time directional sensing system is proposed to capture the white spaces within the 2.4 GHz Wi-Fi band. Further, this dissertation investigates the effect of electro-magnetic (EM) mutual coupling in antenna arrays on the real-time performance of fully-digital transceivers. Different algorithms are proposed to uncouple the mutual coupling in digital domain. The first one is based on finding the MC transfer function from the measured S-parameters of the antenna array and employing it in a Frost FIR filter in the beamforming backend. The second proposed method uses fast algorithms to realize the inverse of mutual coupling matrix via tridiagonal Toeplitz matrices having sparse factors. A 5.8 GHz 32-element array and 1-7 GHz 7-element tightly coupled dipole array (TCDA) have been employed to demonstrate the proof-of-concept of these algorithms

Digital and Mixed Domain Hardware Reduction Algorithms and Implementations for Massive MIMO

Emerging 5G and 6G based wireless communications systems largely rely on multiple-input-multiple-output (MIMO) systems to reduce inherently extensive path losses, facilitate high data rates, and high spatial diversity. Massive MIMO systems used in mmWave and sub-THz applications consists of hundreds perhaps thousands of antenna elements at base stations. Digital beamforming techniques provide the highest flexibility and better degrees of freedom for phased antenna arrays as compared to its analog and hybrid alternatives but has the highest hardware complexity. Conventional digital beamformers at the receiver require a dedicated analog to digital converter (ADC) for every antenna element, leading to ADCs for elements. The number of ADCs is the key deterministic factor for the power consumption of an antenna array system. The digital hardware consists of fast Fourier transform (FFT) cores with a multiplier complexity of (N log2N) for an element system to generate multiple beams. It is required to reduce the mixed and digital hardware complexities in MIMO systems to reduce the cost and the power consumption, while maintaining high performance. The well-known concept has been in use for ADCs to achieve reduced complexities. An extension of the architecture to multi-dimensional domain is explored in this dissertation to implement a single port ADC to replace ADCs in an element system, using the correlation of received signals in the spatial domain. This concept has applications in conventional uniform linear arrays (ULAs) as well as in focal plane array (FPA) receivers. Our analysis has shown that sparsity in the spatio-temporal frequency domain can be exploited to reduce the number of ADCs from N to where . By using the limited field of view of practical antennas, multiple sub-arrays are combined without interferences to achieve a factor of K increment in the information carrying capacity of the ADC systems. Applications of this concept include ULAs and rectangular array systems. Experimental verifications were done for a element, 1.8 - 2.1 GHz wideband array system to sample using ADCs. This dissertation proposes that frequency division multiplexing (FDM) receiver outputs at an intermediate frequency (IF) can pack multiple (M) narrowband channels with a guard band to avoid interferences. The combined output is then sampled using a single wideband ADC and baseband channels are retrieved in the digital domain. Measurement results were obtained by employing a element, 28 GHz antenna array system to combine channels together to achieve a 75% reduction of ADC requirement. Implementation of FFT cores in the digital domain is not always exact because of the finite precision. Therefore, this dissertation explores the possibility of approximating the discrete Fourier transform (DFT) matrix to achieve reduced hardware complexities at an allowable cost of accuracy. A point approximate DFT (ADFT) core was implemented on digital hardware using radix-32 to achieve savings in cost, size, weight and power (C-SWaP) and synthesized for ASIC at 45-nm technology

Planar ESPAR Array Design with Nonsymmetrical Pattern by Means of Finite-Element Method, Domain Decomposition, and Spherical Wave Expansion

The application of a 3D domain decomposition finite-element and spherical mode expansion for the design of planar ESPAR (electronically steerable passive array radiator) made with probe-fed circular microstrip patches is presented in this work. A global generalized scattering matrix (GSM) in terms of spherical modes is obtained analytically from the GSM of the isolated patches by using rotation and translation properties of spherical waves. The whole behaviour of the array is characterized including all the mutual coupling effects between its elements. This procedure has been firstly validated by analyzing an array of monopoles on a ground plane, and then it has been applied to synthesize a prescribed radiation pattern optimizing the reactive loads connected to the feeding ports of the array of circular patches by means of a genetic algorithm

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Computing and communications for the software-defined metamaterial paradigm: a context analysis

Metamaterials are artificial structures that have recently enabled the realization of novel electromagnetic components with engineered and even unnatural functionalities. Existing metamaterials are specifically designed for a single application working under preset conditions (e.g., electromagnetic cloaking for a fixed angle of incidence) and cannot be reused. Software-defined metamaterials (SDMs) are a much sought-after paradigm shift, exhibiting electromagnetic properties that can be reconfigured at runtime using a set of software primitives. To enable this new technology, SDMs require the integration of a network of controllers within the structure of the metamaterial, where each controller interacts locally and communicates globally to obtain the programmed behavior. The design approach for such controllers and the interconnection network, however, remains unclear due to the unique combination of constraints and requirements of the scenario. To bridge this gap, this paper aims to provide a context analysis from the computation and communication perspectives. Then, analogies are drawn between the SDM scenario and other applications both at the micro and nano scales, identifying possible candidates for the implementation of the controllers and the intra-SDM network. Finally, the main challenges of SDMs related to computing and communications are outlined.Peer ReviewedPostprint (published version

Contributions to the design of broadband antennas and arrays for base stations for the new generation of mobile communication systems

El objetivo de esta tesis es el diseño de antenas y arrays de banda ancha para estaciones base en las nuevas generaciones de comunicaciones móviles. Los nuevos retos en los sistemas de comunicación tales como el aumento de dispositivos conectados y el Internet de las cosas (IoT), conlleva la aparición de nuevas generaciones de telefonía. Para hacer frente a ese desafío se necesitan nuevas estrategias para optimizar el espectro, aumentar el ancho de banda y las velocidades de transmisión. Aunque algunas técnicas son aumentar la frecuencia de trabajo desarrollando celdas más pequeñas y rápidas, esta tesis se centra en el otro enfoque, extender las bandas de frecuencia utilizadas en la actualidad. Este enfoque tiene algunas ventajas como una mayor penetración ofreciendo mejor cobertura en zonas aisladas, así como la coexistencia de las futuras redes 5G con los estándares 3G y 4G actuales. En una primera parte, se presentan diseños de elementos de antenas planares cumpliendo con los nuevos requisitos. La antena está diseñada y fabricada de una forma rentable y asequible, presentando una topología compacta y completamente plana. La idea principal para la consecución de los objetivos es la inclusión de dipolos acoplados incluidos dentro de la propia antena de forma antipodal para conseguir un diseño compacto y un patrón de radiación estable en toda la banda de funcionamiento. El diseño compacto y de doble polarización se logra en un elemento que trabaja en todo el ancho de banda frecuencial entre 1.427 y 2.69 GHz, la banda que aquí se presenta como Banda Ultra Ancha Extendida (ExtUWB). En segundo lugar, se desarrolla un estudio de diferentes formas de planos de masa o re ectores en el campo cercano del elemento. La inclusi ón de un plano de masa es necesaria para eliminar la radiación trasera y dar forma al haz de radiación para obtener una antena directiva con el ancho de haz deseado que permanezca estable dentro de toda la banda de trabajo. El punto clave a tratar es que el plano de masa o re ector al ser colocado en el campo cercano del elemento produce perturbaciones en el mismo, tanto en la adaptación como en su diagrama de radiación. A continuación, se propone la combinación de dos elementos para cubrir las dos bandas requeridas. El elemento ExtUWB para la banda 1,42 a 2,69 GHz se integra con nuevos elementos para la banda 690 a 960 MHz. Se estudia la integración de los elementos de ambas bandas en un mismo espacio físico para desarrollar una antena de estación base que proporcione cobertura en las dos bandas de forma conjunta. Finalmente, se propone la combinación de elementos en con guraciones de array para las nuevas bandas de 5G con el propósito de ser utilizados como estaciones base. La inclusión en array permite lograr diferentes propósitos: aumentar la directividad, cumplir con los requisitos generales de las estaciones base y obtener exibilidad para diferentes con guraciones de arrays. Se proponen distintos arrays con diferentes objetivos, estos arrays son con gurables para ser utilizados como estaciones base clásicas, pero también formando un nuevo sistema innovador de Massive MIMO con propiedades de haz orientable que no se ha presentado para la banda L hasta ahora.The objective of this thesis is the design of broadband antennas and arrays for base stations for the new generations of mobile communications. The new challenges in the communication systems such as the increase of connected devices, the amount of smart products, and the Internet of Things (IoT), has brought the arrival of new 5G systems. To deal with that challenge, new mobile communication systems need new strategies for optimizing the spectrum, increase the bandwidth and the data rates as it is required. Although some techniques are to increase the working frequency and develop faster and smaller cells, this thesis is focused on the other coliving approach, which is to extend the nowadays mobile communication operating bands. That approach has some advantages as higher penetration with deeper coverage, and the coexistence of future 5G networks with the existing standards. Firstly, some designs of planar antenna element following the new requirements are presented. The antenna is designed and manufactured in a cost-effective and affordable way presenting a compact and fully planar topology. The main idea to obtain the objectives is the inclusion of active embedded dipoles in the antipodal part of the antenna itself to achieve a compact design and a stable radiation pattern within the wide frequency band of operation. Compactness and dual polarized performance is achieved for working in the whole frequency bandwidth between 1.427 and 2.69 GHz, the band that is presented here as the Extended Ultrawideband (ExtUWB). Secondly, a study of different ground plane shapes or reflectors in the element near field is developed. A ground plane is needed to remove the back radiation and shape the radiation beam to obtain a directive antenna with the desired beamwidth that remains stable within the broadband frequency band. The key point to deal with is that the ground plane or reflector placed in the element near field disturbs both the matching and the radiation. Thirdly, the combination of two elements to cover both required bands is proposed. The ExtUWB element for the band 1.42 to 2.69 GHz is integrated with new elements for the band 690 to 960 MHz. Integration of both band elements in the same physical space for developing the base station antenna providing dual band coverage is studied. Finally, the combination of elements in array configurations is proposed for the new 5G bands with the purpose of been used as base stations. It allows to accomplish different goals: increasing the directivity, fufilling the overall base station requirements, and obtaining flexibility for different array configurations. Different arrays are proposed with different objectives, those arrays are configurable for being used as classical base stations, but also as a new innovative system of Massive MIMO with beamsteering properties that has not been presented for the L-band till now.Programa de Doctorado en Multimedia y Comunicaciones por la Universidad Carlos III de Madrid y la Universidad Rey Juan CarlosPresidente: Carlos del Río Bocio.- Secretario: Luis Emilio García Castillo.- Vocal: David González Ovejer