User Effect Mitigation in MIMO Terminal Antennas

The rapid growth of cellular technology over the past decade transformed our lives, enabling billions of people to enjoy interactive multimedia content and ubiquitous connectivity through a device that can fit into the palm of a hand. In part the explosive growth of the smartphone market is enabled by innovative antenna system technologies, such as multiple-input multiple-output (MIMO) systems, facilitating high data rates and reliable connections. Even though future deployment of Long Term Evolution Advanced (LTE-A) is expected to provide seamless internet connectivity at even higher speeds over a wide range of devices with different form factors, fundamental terminal antenna limitations can severely impact the actual performance of the terminal. One of the key challenges in terminal antenna design are user-induced losses. It has been shown that electromagnetic absorption in body tissues as well as antenna impedance mismatch due to user proximity significantly degrade terminal antenna performance. Moreover, user interactions are non-static, which further complicates terminal design by leading to the requirement of evaluating a wide range of hand grips and usage scenarios. This doctoral thesis explores these challenges and offers useful insight on effective user interaction mitigation. In particular, state-of-the-art multiple antenna designs have been investigated in an attempt to formulate guidelines on efficient terminal antenna design in the presence of a user (Paper I). Moreover, the major part of the thesis considers the method of adaptive impedance matching (AIM) for performance enhancements of MIMO terminals. Both ideal and very practical and realistic AIM systems have been studied in order to extend the knowledge in the area by determining achievable performance gains and providing insights on AIM gain mechanisms for different terminal antenna designs, propagation environments and user scenarios. In Paper I, five different MIMO terminal antenna designs were evaluated in 11 representative user scenarios. Two of the prototypes were optimized with the Theory of Characteristic Modes (TCM), whereas the remaining three were based on more conventional antenna types. Multiplexing efficiency (ME) was used as the MIMO system performance metric, assuming an ideal uniform 3D propagation environment. The paper focuses on performance at frequency bands below 1 GHz due to the more stringent size limitations. Paper II presents a simulation model of the complete physical channel link based on ideal lossless AIM and evaluates the potential of AIM to mitigate user effects for three terminal antennas in four user scenarios. The prototypes studied have different performances in terms of bandwidth and isolation. MIMO capacity was used as the main performance metric. In order to gain insight on the impact of terminal bandwidth, as well as system bandwidth on AIM performance, capacity calculations were performed both for the center frequency and over the full LTE Band 13. In Paper III, a practical AIM system was set up and measured in both indoor and outdoor propagation scenarios for a one-hand and a two-hand grip, including a torso phantom. The AIM system consisted of two Maury mechanical tuners controlled with LabView. MIMO capacity was used to determine performance in the different user and channel cases. The impact of different propagation environments and user cases was discussed in detail. Moreover, tuner loss estimation was done to enable the calculation of AIM net gains. In Paper IV, the simulation model from Paper II was extended to include real antenna parameters as well as simulated environments with non-uniform angular power spectra. Two fundamentally different antenna designs were measured in three user scenarios involving phantom hands, whereas non-uniform environments of different angular spreads were simulated in post-processing. The study presents results and analysis on the impact of user scenarios and environment on the AIM gains for the terminals with different antenna designs. Finally, Paper V describes a realistic AIM system with custom-designed CMOS-SOI impedance tuners on a MIMO terminal antenna. Measurement setup control, as well as MIMO system evaluation, was achieved through a custom-developed LabView software. Detailed propagation measurements in three different environments with both phantom users and real test subjects were performed. The analysis and discussions provided insights on the practical implementation of AIM as well as on its performance in realistic conditions

Safety measures relating to carriage and transfer of liquid cargoes

The continuous growth in the volume of liquid cargoes, transported by sea, leads to increase of tankers’ size and to implementation of appropriate shore facilities, which have to meet the relevant environmental requirements. In order to ensure safety during loading and discharging operations in shore terminals, it is necessary to make an assessment on the level of potential risk in port and onboard the vessel and to take all necessary steps to reduce the possibility for environmental impacts and occurrence of an accident especially when performing transfer operations to/from ships. The article presents some constructive decisions for building of shore tanks and their application for storage and transfer of petroleum products. The measures for the safe performing of the cargo operations are systematized after discussing of specifics by performing of all processes connected with loading or discharge. The precautions are defined in three critical points of action - operation on vessel systems, transportation of cargo using shore facilities and storage in tanks

On user effects in MIMO handset antennas designed using characteristic modes

The Theory of Characteristic Modes (TCM) has been applied to design high-performance MIMO antennas for mobile terminals. However, existing studies focus on free-space (FS) performance, which is mostly irrelevant in real usage. This paper investigates the performances of two TCM-based MIMO terminal antenna designs in 7 realistic user scenarios for frequencies below 1 GHz. Full-wave simulation results indicate that the TCM designs can significantly outperform conventional designs in user scenarios that require good MIMO performance. Higher multiplexing efficiency (ME), by up to 3 dB, was recorded for a TCM design relative to a conventional terminal in a two-hand scenario. Performance advantages of the TCM designs were mainly due to lower correlation as well as higher impedance matching and coupling efficiency. Moreover, a combined usage study based on weighted ME over different user cases established that on average TCM designs outperform conventional designs by up to 1.6 dB. This suggests that the TCM designs not only give superior performance in FS, but also in realistic user scenarios

Impact of antenna design on MIMO performance for compact terminals with adaptive impedance matching

Using the metrics of channel capacity and multiplexing efficiency, the adaptive impedance matching (AIM) performances of two multiple-input multiple-output (MIMO) terminals with different antenna designs were evaluated and compared. The evaluation was performed in LTE Band 18 Downlink (860-875 MHz) under realistic usage conditions of two measured user handgrips and simulated propagation channels with different angular spreads (ASs). The results provide potential performance gains from AIM based on realistic MIMO terminal prototypes, and the underlying mechanisms by which the gains were achieved, which can serve as antenna and AIM circuit design guidelines. In particular, the evaluation revealed that ideal uncoupled AIM networks can increase the capacity by up to 52% relative to 50 ohm terminations. However, the observed gains depend heavily on the antenna design, the user scenario and the channel’s angular spread. For example, the wideband design in different user cases experienced capacity gain of 4-9% from AIM in uniform 3D channels, in contrast to the 1.3-44% gain seen in a conventional narrowband design. In non-uniform channels with small ASs, the AIM gain for different mean incident angles depends on the absolute mean effective gain (MEG) and the change in correlation due to AIM; In cases where AIM has little impact on correlation, the mean incident angles with high AIM gains were close to those with high MEGs

Measured adaptive matching performance of a MIMO terminal with user effects

Absorption and impedance mismatch due to the proximity of a user as well as certain propagation channel characteristics can severely degrade the multiple-input multiple-output (MIMO) performance of multi-antenna terminals in real usage scenarios. In this context, we investigated the potential of adaptive impedance matching (AIM) to mitigate performance degradation from these effects based on channel measurements involving a terminal prototype in three user scenarios and two propagation environments. First, optimal AIM state for the terminal in a given user-channel setup was found by post-processing the measured channels. The optimal state was then experimentally verified with two Maury Microwave mechanical tuners. The results show that by employing AIM instead of 50Ω termination, the average capacity is increased by up to 25%. Moreover, the observed capacity gains can be partly explained by physical mechanisms underlying the propagation conditions. Furthermore, the achieved gains with real tuners are only marginally affected by the tuners’ actual insertion losses, estimated to be 0.1-0.7 dB. Therefore, we conclude that AIM can be a viable solution to enhance MIMO terminal performance

Capacity maximisation of a handheld MIMO terminal with adaptive matching in an indoor environment

This letter reports the capacity performance of a handheld dual-band dual-antenna compact MIMO terminal, which utilizes uncoupled adaptive impedance matching for capacity maximisation. The capacity is evaluated at 0.825 GHz and 2.35 GHz in an indoor office environment. The results show that adaptive matching enhances capacity by up to 44% and 22% at the low and high frequency bands, respectively, relative to no matching. At the low band, the capacity gain is attributed to both increased received power and decreased channel eigenvalue dispersion, whereas at the high band, the capacity gain is only due to increased power

Electrolysers Powered with Solar Energy

The vast fossil fuel consumption and decreasing oil reserves and natural resources, enforce much more need of finding decision for renewable energies and development of constructions for using the so called green resources. One solution of this problem is combination ofalready established solar based sources and brown gas cell construction. Brown gas cell production is based on electrolysis of pure water and as a result generating a real gas fuel. This production can find large utility in different usages

Experimental investigation of adaptive impedance matching for a MIMO terminal with CMOS SOI tuners

It is well known that user proximity introduces absorption and impedance mismatch losses that severely degrade multiple-input multiple-output (MIMO) performance of handset antennas. In this work, we experimentally verified the potential of adaptive impedance matching (AIM) to mitigate user interaction effects and identified the main AIM gain mechanism in realistic systems. A practical setup including custom-designed CMOS silicon-on-insulator (SOI) impedance tuners implemented on a MIMO handset was measured in three propagation environments and 10 real user scenarios. The results indicate that AIM can improve MIMO capacity by up to 42% equivalent to 3.5 dB of multiplexing efficiency (ME) gain. Taking into account the measured losses of 1 dB in the integrated tuners, the maximum net ME gain is 2.5 dB suggesting applicability in practical systems. Variations in ME gains of up to 1.5 dB for different hand-grip styles were mainly due to differences in impedance mismatch and tuner loss distribution. The study also confirmed earlier results on the significant differences in mismatch and absorption between phantoms and real users, in which the phantoms underestimated user effects and therefore AIM gains. Finally, propagation environments of different angular spreads were found to give only minor ME gain variations

Successfully treated osteomyelitis involving the entire ischium in a patient with lower-limb paraplegia (a case report)

Introduction: Pelvic bones, probably due to their anatomical features (deep location, good blood supply and other unknown reasons), are rarely affected by exogenous or hematogenous infections. Usually, the flora isolated from the infected pelvic bone is polymicrobial, with the most common microorganisms causing this type of infection being Staphylococcus aureus, Streptococcus, Pseudomonas aeruginosa. The ischial bone (os ischii) is the pelvic bone most often affected by infections, adjacent to deep IV degree decubitus wounds. These wounds are typical for patients with severe neurological symptoms—paraplegics or quadriplegics, as well as those with cerebral disorders, and the process may remain undiagnosed for a long time.Aim: The aim of this article is to focus on the difficulties associated with the early diagnosis of an infection affecting the entire ischial bone and the soft tissues of the adjacent pelvis, as well as the high risk to the patient if adequate treatment is not carried out.Patient and Methods: One patient, a 60-year-old man, with lower-limb paraplegia, after a spinal cord trauma dating back to 10 years ago, is presented.Results: After the applied treatment—resection, removal of the entire ischial bone, and soft tissue debridement, the surgical wound healed primarily, the bone and soft tissue infection of the pelvis was successfully managed. General intoxication of the body was prevented.Conclusion: Accurate and timely debridement, including the risky total excision of the os ischii, as well as the infected adjacent soft tissues in the pelvis, combined with appropriate drainage, may prove to be the only effective and life-saving procedure for the patient