Browsing by Author "Haneda, Katsuyuki, Assoc. Prof., Aalto University, Department of Electronics and Nanoengineering, Finland"

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  • Antenna design and channel modelling for in-band full-duplex radios
    (2018) Venkatasubramanian, Sathya Narayana
     School of Electrical Engineering | Doctoral dissertation (article-based)
    In-band full-duplex (IBFD) radios have the potential to double the throughput by improving the spectral efficiency. The main bottleneck in its implementation is the self-interference (SI) at the receiving side of the transceiver due to its own transmission. The main focus of this thesis is 1) to develop novel solutions to improve isolation between separate transmit and receive antennas, to mitigate the SI due to direct coupling, and 2) to model the multipath SI in different deployment environments of IBFD relays, so that robust analog and digital cancellation solutions can be designed to suppress the SI sufficiently. The main contributions of the thesis are as follows. First, novel antenna decoupling methods are proposed for improving the port-to-port isolation between closely-spaced antenna elements for bi-directional IBFD transmission. A new decoupling method inserting lumped resistive and reactive elements between the antenna feeds is proposed to improve the wideband isolation, also considering the impact on total efficiency. This is extended to a T-shaped decoupling circuit configuration to improve the wideband isolation further, at the cost of increased circuit complexity. The proposed decoupling circuit configurations are designed between two closely spaced printed monopole antennas and a prototype is fabricated to demonstrate the improvement of port-to-port isolation. Secondly, two techniques are proposed to improve the isolation between compact back-to-back antennas for IBFD relaying. First, the so-called neutralization technique is applied to compact back-to-back antennas at 2.6 GHz to improve the port-to-port isolation. In this method, a portion of the signal is transferred through a transmission line from one antenna to the other antenna causing destructive interference with the electromagnetically coupled signal between the antennas. The second technique uses a T-shaped decoupling circuit connected between the antenna feeds to improve the port-to-port isolation. The decoupling circuit uses only lumped reactive elements to maintain the total efficiency. The proposed decoupling technique is demonstrated experimentally for compact back-to-back antennas in the 900 MHz band. Third, the multipath self-interference channel has been measured for outdoor-to-indoor relaying in different domains. An office, coffee room and street-canyon scenario was covered. This is followed by the characterization of the SI for a street-canyon scenario. A site-specific geometry-based stochastic channel model is developed for modelling the SI in the delay, Doppler, spatial and polarization domains jointly. Finally, the benefit of using a compact back-to-back IBFD relay is demonstrated, compared to using a similar half-duplex relay in enhancing coverage for IEEE802.11ah Wireless Local Area Networks. The COST 2100 channel model is used to generate the coverage map for the analysis. The developed decoupling circuits are strong enablers of IBFD transceivers and the SI channel model allows us to design and evaluate the IBFD transceivers, links and systems.
  • Isolation improvement and user-effect modeling for antenna arrays in 5G and beyond
    (2020) Heino, Mikko
     School of Electrical Engineering | Doctoral dissertation (article-based)
    The evolution of mobile phone systems has been fast in the past decades with 5G systems closely being deployed. This development of mobile networks requires new techniques to solve the ever-increasing demand for the number of users, even higher data rates, and the problem of spectrum scarcity. This dissertation describes several novel electromagnetic designs and modelling methods that enable 5G and beyond communication systems. In-band full-duplex (IBFD) communication utilizes the same frequency band for receiving and transmitting simultaneously. Thus, the spectral efficiency is doubled in the best case compared to current half-duplex systems. However, the major problem of IBFD is the strong self-interference (SI) between the transmitter and the receiver on the same device. To make IBFD communication feasible, in the first part of this thesis, electromagnetic wavetraps are proposed as a method to improve isolation between the receiving and transmitting antennas of a device. Wavetraps are resonant structures usually placed between antennas to decouple them. They suppress surface currents and scatter the transmitted electromagnetic fields suitably to cancel out the naturally coupled fields at the location of the receiving antenna, thus increasing the antenna isolation. Planar wavetraps are designed for a multiple-input-multiple-output (MIMO) IBFD relay where planar antennas are used. The methodology for designing and optimising wavetraps is established utilizing the theory of characteristic modes. The clear positive impact of the wavetraps on antenna isolation is experimentally verified both in the anechoic chamber and in realistic multipath environments. The effects of multipath environment on the obtainable isolation are characterized. The thesis furthermore introduces an antenna decoupling structure for bi-directional IBFD communications, where the isolation between omnidirectional collinear dipoles is significantly enhanced. Communication at millimetre-waves (mm-waves) is essential in future mobile communications due to wide available bandwidth that enables very high data rates. The second part of the thesis considers the effect of a human body to mm-wave handset antennas operating at 28 GHz and 60 GHz. The effect of the proximity of fingers to handset antennas is studied giving novel approaches how to mitigate the effect by utilizing beamsteering and by a thin reflector decreasing the shadowing over 20 dB. Furthermore, characterization of shadowing and scattering due to an entire human body is made possible at 60 GHz with a novel simulation model which reduces the computational complexity while keeping the modelling accuracy. Mm-wave base stations in urban areas need to be deployed densely in future communication systems to cope with expected severe link blockage. The third part of the thesis introduces a PCB-based beamsteerable end-fire antenna array at 28 GHz for low-cost base stations. The antenna array is integrated with a switch network and high gain antenna elements, obtaining high measured realized gain even with the high losses of PCB technology at 28 GHz.
  • Towards Smart Cities: Antenna-Embedded Walls and Antenna-User Interaction Modeling for Enhanced Urban Connectivity
    (2024) Vähä-Savo, Lauri
     School of Electrical Engineering | Doctoral dissertation (article-based)
    With the rapid evolution of mobile networks and the ongoing deployment of 5G, there is a pressing need for innovative solutions to accommodate the growing number of users and higher data rates facilitated by higher carrier frequency bands. However, as the carrier frequency increases, communication networks face heightened sensitivity to blockages, impeding signal propagation and reducing reliability. This thesis investigates novel electromagnetic modeling techniques of antenna-embedded building walls and antenna-human interaction to enhance 5G and future mobile communication systems, providing tools to develop and test improvements that mitigate their adverse effects on communication quality. The first part of this thesis explores the concept of signal-transmissive walls, where two planar antenna elements are connected back-to-back by a coaxial cable embedded into a load-bearing wall to guide signals from outside into a building. A load-bearing wall, with and without the embedded antenna system, is studied in terms of electromagnetic transmission, thermal insulation, and mechanical stress distribution. Numerical simulations of electromagnetic transmission coefficient, up to 8 GHz, demonstrate that the signal-transmissive wall significantly improves transmission coefficients for carrier frequencies above 2.6 GHz. The full-wave simulation models are later validated by measurements. An analytical electromagnetic transmission model of the wall is developed to optimize signal transmission up to millimeter-wave (mmWave) frequencies, achieving a more than 70 dB improvement over a bare load-bearing wall at 30 GHz. The second part of the thesis focuses on the modeling of antenna-user interactions for mmWave mobile phones. Empirical studies of antenna radiation with a mobile user at mmWave frequencies have largely relied on real humans, lacking repeatability. To address this, a physical human body phantom for mmWave frequencies is presented for the first time, validated by comparing measured spherical coverage of a reference antenna array on a mobile phone-sized chassis against simulations with an accurate numerical human body model. Three different mobile antenna arrays operating at 28 GHz are evaluated using the developed full-body human phantoms to study various antenna array configurations. Finally, photogrammetry is applied to antenna-hand interaction studies for the first time, using 3D hand models of individual users to assess the effects of hand palms and natural grips on the radiation characteristics of 28 GHz mobile phone antennas. The results reveal significant variations in realized gains and radiation efficiency across different user hand models.