Indoor wireless communications and applications

Chapter 3 addresses challenges in radio link and system design in indoor scenarios. Given the fact that most human activities take place in indoor environments, the need for supporting ubiquitous indoor data connectivity and location/tracking service becomes even more important than in the previous decades. Specific technical challenges addressed in this section are(i), modelling complex indoor radio channels for effective antenna deployment, (ii), potential of millimeter-wave (mm-wave) radios for supporting higher data rates, and (iii), feasible indoor localisation and tracking techniques, which are summarised in three dedicated sections of this chapter

The characterisation and modelling of the wireless propagation channel in small cells scenarios

“A thesis submitted to the University of Bedfordshire, in partial fulfilment of the requirements for the degree of Doctor of Philosophy”.The rapid growth in wireless data traffic in recent years has placed a great strain on the wireless spectrum and the capacity of current wireless networks. In addition, the makeup of the typical wireless propagation environment is rapidly changing as a greater percentage of data traffic moves indoors, where the coverage of radio signals is poor. This dual fronted assault on coverage and capacity has meant that the tradition cellular model is no longer sustainable, as the gains from constructing new macrocells falls short of the increasing cost. The key emerging concept that can solve the aforementioned challenges is smaller base stations such as micro-, pico- and femto-cells collectively known as small cells. However with this solution come new challenges: while small cells are efficient at improving the indoor coverage and capacity; they compound the lack of spectrum even more and cause high levels of interference. Current channel models are not suited to characterise this interference as the small cells propagation environment is vast different. The result is that overall efficiency of the networks suffers. This thesis presents an investigation into the characteristics of the wireless propagation channel in small cell environments, including measurement, analysis, modelling, validation and extraction of channel data. Two comprehensive data collection campaigns were carried out, one of them employed a RUSK channel sounder and featured dual-polarised MIMO antennas. From the first dataset an empirical path loss model, adapted to typical indoor and outdoor scenarios found in small cell environments, was constructed using regression analysis and was validated using the second dataset. The model shows good accuracy for small cell environments and can be implemented in system level simulations quickly without much requirements

Dynamic Capacity Enhancement using a Smart Antenna in Mobile Telecommunications Networks

This work describes an investigation into the performance of antennas for mobile base station applications and techniques for improving the coverage and capacity within a base station cell. The work starts by tracing the development of mobile systems, both in technical and commercial terms, from the earliest analogue systems to present day broadband systems and includes anticipated future developments. This is followed by an outline of how smart antenna systems can be utilised to improve cell coverage and capacity. A novel smart antenna system incorporating an array of slant ± 450 dual- polarised stacked patch elements four columns wide excited by a novel multi-beam forming and beam shaping network has been designed, simulated and implemented. It is found that for an ideal smart antenna array, four narrow overlapping beams, one wide “broadcast channel” beam and right and left shaped beams can be provided. Results are presented for the simulation of the smart antenna system using CST EM simulation software which inherently includes mutual coupling and the effects of a truncated ground plane on the element patterns. The results show some significant changes to the desired set of coverage patterns and various mutual coupling compensation techniques have been reviewed. An improved design technique has been developed for compensating the performance degrading effects of mutual coupling and finite ground plane dimensions in microstrip antenna arrays. The improved technique utilises combination of two previously known techniques: complex excitation weights compensation by inversion of the array mutual coupling scattering matrix and the incorporation of a WAIM (wide angle impedance matching) sheet. The technique has been applied to a novel multi-beam smart antenna array to demonstrate the efficacy of the technique by electromagnetic simulation. In addition, a demonstrator array has been constructed and tested which has yielded a positive conformation of the simulation results. For the developed demonstrator array which provides seven different beams, beams “footprints” have been predicted both for free space propagation and for urban propagation to evaluate the dynamic capacity performance of the smart antenna in a 3G mobile network. The results indicate that sector capacity can be dynamically tailored to user demand profiles by selection of the appropriate beam patterns provided by the novel smart antenna system

The Study of Reconfigurable Antennas and Associated Circuitry

This research focuses on the design of pattern reconfigurable antennas and the associated circuitry. The proposed pattern reconfigurable antenna designs benefit from advantages such as maximum pattern diversity and optimum switching circuits to realise 5G reconfigurable antennas. Whereas MIMO based solutions can provide increased channel capacity, they demand high computational capability and power consumption due to multiple channel processing. This prevents their use in many applications most notably in the Internet of Things where power consumption is of key importance. A switched-beam diversity allows an energy-efficient solution improving the link budget even for small low-cost battery operated IoT/sensor network applications. The main focus of the antenna reconfiguration in this work is for switched-beam diversity. The fundamental switching elements are discussed including basic PIN diode circuits. Techniques to switch the antenna element in the feed or shorting the antenna element to the ground plane are presented. A back-to-back microstrip patch antenna with two hemispherical switchable patterns is proposed. The patch elements on a common ground plane, are switched with a single-pole double-throw PIN diode circuit. Switching the feed selects either of two identical oppositely oriented radiation patterns for maximum diversity in one plane. The identical design of the antenna elements provides similar performance control of frequency and radiation pattern in different states. This antenna provides a simple solution to cross-layer PIN diode circuit designs. A mirrored structure study provides an understanding of performance control for different switching states. A printed inverted-F antenna is presented for monopole reconfigurable antenna design. The proposed low-profile antenna consists of one main radiator and one parasitic element. By shorting the parasitic element to the ground plane using only one PIN diode, the antenna is capable of switching both the pattern and polarisation across the full bandwidth. The switched orthogonal pattern provides the maximum spatial pattern diversity and is realised using a simple structure. Then, a dual-stub coplanar Vivaldi antenna with a parasitic element is presented for the 5G mm-Wave band. The use of a dual-stub coupled between the parasitic element and two tapered slots is researched. The parasitic element shape and size is optimised to increase the realised gain. A bandpass coupled line filter is used for frequency selective features. The use of slits on the outer edge of the ground plane provides a greater maximum gain. This integrated filtenna offers lower insertion loss than the commercial DC blocks. The UWB antenna with an integrated filter can be used for harmonic suppression. The influence of the integrated filter circuit close to the antenna geometry informs the design of PIN diode circuit switching and power supply in the 5G band. Based on the filter design in the mm-Wave band, a method of designing a feasible DC power supply for the PIN diode in the mm-Wave band is studied. A printed Yagi-Uda antenna array is integrated with switching circuitry to realise a switched 180° hemispheres radiation pattern. The antenna realises a maximum diversity in one plane. The study offers the possibility to use PIN diodes in the mm-Wave band for reconfigurable antenna designs. For the presented antennas, key geometric parameters are discussed for improved understanding of the trade-offs in radiation pattern/beamwidth and gain control for reconfigurable antenna applications

Advanced Circularly Polarised Microstrip Patch Antennas

The thesis describes outcomes of research on advanced circularly polarised antennas. The proposed designs are intended for integration into small mobile devices, therefore low profile and easy manufacturability are key parameters, along with good CP radiation properties. The designs were validated by simulation and measurement, and are also backed by theory and design guidelines. The primary focus is on the development of planar omnidirectional circularly polarised antennas, which are fabricated using multilayer PCB techniques and thus are lightweight and cost-efficient. Unlike in classical microstrip patch antenna designs, the groundplane of the proposed antenna was substantially reduced. This helps to achieve an omnidirectional circular polarisation pattern and miniaturize the antenna, however at the cost of increased feed circuit complexity. The basic design, its advantages and disadvantages are discussed in Section 3. In the next step, the omnidirectional circularly polarised antenna was extended with additional, advanced features. A miniaturized version is investigated, which offers a 20% footprint reduction by folding parts of the patch underneath itself. Further miniaturization is possible by increasing the dielectric constant of the substrate. A method to adjust the omnidirectional circularly polarised antenna performance by trimming four lumped capacitors is also investigated. Manufacturing inaccuracy in large scale production may cause some of the units to radiate outside of the desired frequencies. By integrating four trimmed capacitors into the antenna it can be precisely tuned to the desired band. Simulated results demonstrate this property by trimming the antenna between GPS L1 band (centre frequency at 1.575 GHz) and Galileo/Beidou-2 E2 band (1.561 GHz). Furthermore, a dual-band omnidirectional circularly polarised antenna is presented, which employs slots and capacitor loading to steer the current path of the first and second resonant mode. The design offers a small frequency ratio of 1.182. The methods to obtain a planar omnidirectional circularly polarised antenna have been further advanced to propose a reconfigurable antenna. The beam reconfiguration is capable of rotating it dipole-like radiation pattern around an axis, thus allowing reception or transmission from any spherical angle. The switching method is simple and does not require any semiconductor devices. Finally, a dual circularly polarised antenna is presented, which achieves dual-polarisation by employing even and odd modes in a coplanar waveguide. This technique allows greater flexibility and size reduction of the feed network, as two signals can be transmitted by a single multi-mode transmission line. Simulated results demonstrate this property by trimming the antenna between GPS L1 band (centre frequency at 1.575 GHz) and Galileo/Beidou-2 E2 band (1.561 GHz). Furthermore, a dual-band omnidirectional circularly polarised antenna is presented, which employs slots and capacitor loading to steer the current path of the first and second resonant mode. The design offers a small frequency ratio of 1.182. The methods to obtain a planar omnidirectional circularly polarised antenna have been further advanced to propose a reconfigurable antenna. The beam reconfiguration is capable of rotating it dipole-like radiation pattern around an axis, thus allowing reception or transmission from any spherical angle. The switching method is simple and does not require any semiconductor devices. Finally, a dual circularly polarised antenna is presented, which achieves dual-polarisation by employing even and odd modes in a coplanar waveguide. This technique allows greater flexibility and size reduction of the feed network, as two signals can be transmitted by a single multi-mode transmission line

Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin

Enhancing wireless communication system performance through modified indoor environments

This thesis reports the methods, the deployment strategies and the resulting system performance improvement of in-building environmental modification. With the increasing use of mobile computing devices such as PDAs, laptops, and the expansion of wireless local area networks (WLANs), there is growing interest in increasing productivity and efficiency through enhancing received signal power. This thesis proposes the deployment of waveguides consisting of frequency selective surfaces (FSSs) in indoor wireless environments and investigates their effect on radio wave propagation. The received power of the obstructed (OBS) path is attenuated significantly as compared with that of the line of sight (LOS) path, thereby requiring an additional link budget margin as well as increased battery power drain. In this thesis, the use of an innovative model is also presented to selectively enhance radio propagation in indoor areas under OBS conditions by reflecting the channel radio signals into areas of interest in order to avoid significant propagation loss. An FSS is a surface which exhibits reflection and/or transmission properties as a function of frequency. An FSS with a pass band frequency response was applied to an ordinary or modified wall as a wallpaper to transform the wall into a frequency selective (FS) wall (FS-WALL) or frequency selective modified wall (FS-MWALL). Measurements have shown that the innovative model prototype can enhance 2.4GHz (IEEE 802.11b/g/n) transmissions in addition to the unmodified wall, whereas other radio services, such as cellular telephony at 1.8GHz, have other routes to penetrate or escape. The FSS performance has been examined intensely by both equivalent circuit modelling, simulation, and practical measurements. Factors that influence FSS performance such as the FSS element dimensions, element conductivities, dielectric substrates adjacent to the FSS, and signal incident angles, were investigated. By keeping the elements small and densely packed, a largely angle-insensitive FSS was developed as a promising prototype for FSS wallpaper. Accordingly, the resultant can be modelled by cascading the effects of the FSS wallpaper and the ordinary wall (FSWALL) or modified wall (FS-MWALL). Good agreement between the modelled, simulated, and the measured results was observed. Finally, a small-scale indoor environment has been constructed and measured in a half-wave chamber and free space measurements in order to practically verify this approach and through the usage of the deterministic ray tracing technique. An initial investigation showing that the use of an innovative model can increase capacity in MIMO systems. This can be explained by the presence of strong multipath components which give rise to a low correlated Rayleigh Channel. This research work has linked the fields of antenna design, communication systems, and building architecture