59 research outputs found
Compact Dual-Band Dual-Polarized Antenna for MIMO LTE Applications
A system of two dual-band dual-polarized antennas is proposed. It operates in two bands, 700 to 862 MHz and 2.5 to 2.69 GHz, thereby making it suitable for LTE applications. The design is composed of two compact orthogonal monopoles printed close to each other to perform diversity in mobile terminals such as tablets or laptops. For each band, two orthogonal polarizations are available and an isolation higher than 15 dB is achieved between the two monopoles spaced by λ0/10 (where λ0 the central wavelength in free space of the lower band). A good agreement is observed between simulated and experimental results. The antenna diversity capability is highlighted with the calculation of envelope correlation and mean effective gain for several antennas' positions in different environment scenarios
Autonomous smart antenna systems for future mobile devices
Along with the current trend of wireless technology innovation, wideband, compact size,
low-profile, lightweight and multiple functional antenna and array designs are becoming more
attractive in many applications. Conventional wireless systems utilise omni-directional or
sectored antenna systems. The disadvantage of such antenna systems is that the
electromagnetic energy, required by a particular user located in a certain direction, is radiated
unnecessarily in every direction within the entire cell, hence causing interference to other
users in the system. In order to limit this source of interference and direct the energy to the
desired user, smart antenna systems have been investigated and developed. This thesis
presents the design, simulation, fabrication and full implementation of a novel smart antenna
system for future mobile applications.
The design and characterisation of a novel antenna structure and four-element liner array
geometry for smart antenna systems are proposed in the first stage of this study. Firstly, a
miniaturised microstrip-fed planar monopole antenna with Archimedean spiral slots to cover
WiFi/Bluetooth and LTE mobile applications has been demonstrated. The fundamental
structure of the proposed antenna element is a circular patch, which operates in high
frequency range, for the purpose of miniaturising the circuit dimension. In order to achieve a
multi-band performance, Archimedean spiral slots, acting as resonance paths, have been
etched on the circular patch antenna. Different shapes of Archimedean spiral slots have been
investigated and compared. The miniaturised and optimised antenna achieves a bandwidth of
2.2GHz to 2.9GHz covering WiFi/Bluetooth (2.45GHz) and LTE (2.6GHz) mobile standards.
Then a four-element linear antenna array geometry utilising the planar monopole elements
with Archimedean spiral slots has been described. All the relevant parameters have been
studied and evaluated. Different phase shifts are excited for the array elements, and the main
beam scanning range has been simulated and analysed.
The second stage of the study presents several feeding network structures, which control
the amplitude and phase excitations of the smart antenna elements. Research begins with the
basic Wilkinson power divider configuration. Then this thesis presents a compact feeding
network for circular antenna array, reconfigurable feeding networks for tuning the operating
frequency and polarisations, a feeding network on high resistivity silicon (HRS), and an ultrawide-band
(UWB) feeding network covering from 0.5GHz to 10GHz. The UWB feeding
network is used to establish the smart antenna array system.
Different topologies of phase shifters are discussed in the third stage, including ferrite
phase shifters and planar phase shifters using switched delay line and loaded transmission line
technologies. Diodes, FETs, MMIC and MEMS are integrated into different configurations.
Based on the comparison, a low loss and high accurate Hittite MMIC analogue phase shifter
has been selected and fully evaluated for this implementation. For the purpose of impedance
matching and field matching, compact and ultra wideband CPW-to-Microstrip transitions are
utilised between the phase shifters, feeding network and antenna elements. Finally, the fully
integrated smart antenna array achieves a 10dB reflection coefficient from 2.25GHz to
2.8GHz, which covers WiFi/Bluetooth (2.45GHz) and LTE (2.6GHz) mobile applications. By
appropriately controlling the voltage on the phase shifters, the main beam of the antenna array
is steered ±50° and ±52°, for 2.45GHz and 2.6GHz, respectively. Furthermore, the smart
antenna array demonstrates a gain of 8.5dBi with 40° 3dB bandwidth in broadside direction,
and has more than 10dB side lobe level suppression across the scan.
The final stage of the study investigates hardware and software automatic control systems
for the smart antenna array. Two microcontrollers PIC18F4550 and LPC1768 are utilised to
build the control PCBs. Using the graphical user interfaces provided in this thesis, it is able to
configure the beam steering of the smart antenna array, which allows the user to analyse and
optimise the signal strength of the received WiFi signals around the mobile device.
The design strategies proposed in this thesis contribute to the realisation of adaptable and
autonomous smart phone systems
Efficient Management of Flexible Functional Splits in 5G Second Phase Networks
The fifth mobile network generation (5G), which offers better data speeds, reduced latency,
and a huge number of network connections, promises to improve the performance of the
cellular network in practically every way available. A portion of the network operations are
deployed in a centralized unit in the 5G radio access network (RAN) partially centralized
design. By centralizing these functions, operational expenses are decreased and coordinating strategies are made possible. To link centralized units (CU) and distributed units (DU),
and the DU to remote radio units (RRU), both the midhaul and fronthaul networks must
have higher capacity. The necessary fronthaul capacity is also influenced by the fluctuating
instantaneous user traffic. Consequently, the 5G RAN must be able to dynamically change
its centralization level to the user traffic to maximize its performance. To try to relieve this
fronthaul capacity it has been considered a more flexible distribution between the base band
unit (BBU) (or CU and DU if enhanced common public radio interface (eCPRI) is considered) and the RRU. It may be challenging to provide high-speed data services in crowded
areas, particularly when there is imperfect coverage or significant interference. Because of
this, the macrocell deployment is insufficient. This problem for outdoor users could be resolved by the introduction of low-power nodes with a limited coverage area. In this context,
this MSc dissertation explores, in an urban micro cell scenario model A (UMi_A) for three
frequency bands (2.6 GHz, 3.5 GHz, and 5.62 GHz), the highest data rate achievable when a
numerology zero is used. For this, it was necessary the implementation of the UMi_A in the
5G-air-simulator. Allowing the determination of the saturation level using the results for the
packet loss ratio (PLR=2%). By assuming Open RAN (O-RAN) and functional splitting, the
performance of two schedulers in terms of quality-of-service (QoS) were also studied. The
QoS-aware modified largest weighted delay first (M-LWDF) scheduler and the QoS-unaware
proportional fair (PF) scheduler. PLR was evaluated for both schedulers, whilst analyzing
the impact of break point distance while changing the frequency band. The costs, revenues,
profit in percentage terms, and other metrics were also estimated for the PF and M-LWDF
schedulers when used video (VID) and video plus best effort (VID+BE), with or without consideration of the functional splits 7.2 and 6, for the three frequency bands. One concluded
that the profit in percentage terms with functional split option 7.2 applied is always slightly
higher than with functional split option 6. It reaches a maximum profit of 366.92% in the
case of the M-LWDF scheduler, and 305.51% in the case of the PF scheduler, at a cell radius
of 0.4 km for the 2.6 GHz frequency band, considering a price of the traffic of 0.0002 €/min.A quinta geração de redes móveis (5G), oferece ritmos de transmissão melhorados, atraso
extremo-a-extremo reduzido, e um vasto número de ligações de rede. A 5G promete melhorar o desempenho das redes celulares em praticamente todos os aspectos relevantes. Uma
parte da operação da rede é colocada numa unidade centralizada na rede de acesso de rádio
(RAN) 5G com dimensionamento parcialmente centralizado. Ao centralizar estas funções,
os custos operacionais decrescem, viabilizando-se as estratégias de coordenação. Para ligar
as unidades centralizadas e unidades distribuÃdas, e por sua vez, unidades distribuidas e
unidades de rádio remotas, ambos os midhaul e fronthaul devem ter uma capacidade mais
elevada. A capacidade da fronthaul necessária é também influenciada pela flutuação do
tráfego instantâneo dos utilizadores. Consequentemente, a RAN 5G deve ser capaz de alterar
dinamicamente o seu nÃvel de centralização para o tráfego de utilizadores, com objetivo de
maximizar o seu desempenho. Para tentar aliviar o aumento da capacidade suportada pelo
fronthaul, tem sido considerada uma distribuição mais flexÃvel entre a unidade de banda
base, BBU (ou unidade central e unidade distribuÃda se a interface de rádio pública comum
melhorada, eCPRI, for considerada), e a unidade de rádio remota, RRU. Em áreas densamente povoadas, pode ser um desafio fornecer serviços de dados de elevada velocidade, particularmente quando existe uma cobertura deficiente ou interferência significativa. Por este
motivo, o desenvolvimento de macrocélulas pode ser insuficiente, mas este problema para
utilizadores em ambiente de exterior pode ser mitigado com a introdução de nós de potência
reduzida com uma área de cobertura limitada. Neste contexto, esta dissertação de mestrado
explora, num cenário urbano de microcélulas caracterizado pelo modelo A (UMi_A) para
três bandas de frequência (2.6 GHz, 3.5 GHz, e 5.62 GHz), o débito binário máximo que se
pode alcançar quando se utiliza numerologia zero. Para tal, foi necessária a implementação
do UMi_A no 5G - air - simulator. Determinou-se o nivel de saturação, considerandose os resultados para a taxa de perda de pacotes (PLR=2%). Estudou-se o desempenho de
dois escalonadores de pacotes em termos de qualidade de serviço (QoS), assumindo-se o
OpenRAN (O-RAN) e as divisões funcionais (functionalsplitting). Um dos escalonadores
é ciente da QoS, e é de atraso máximo-superior ponderado primeiro (M-LWDF), enquanto
que o outro não é ciente da QoS, e é de justiça proporcional (PF). Avaliou-se o PLR para
ambos os escalonadores de pacotes, estudando-se o impacto da distância de ponto de quebra (breakpointdistance), variando-se a banda de frequências. Foram também estimados os
custos, proveitos, o lucro (em percentagem), e outras metricas, para os escalonadores PF e
M-LWDF, considerando o vÃdeo (VID) e vÃdeo mais besteffort (VID+BE) como aplicações,
com ou sem a consideração das divisões funcionais 7.2 e 6, para as três bandas de frequência.
Concluiu-se que o lucro em termos percentuais, com a escolha da opção de divisão funcional
7.2, é sempre ligeiramente mais elevado do que com a opção de divisão funcional 6. Atingese um lucro máximo de 366,92% no caso do escalonador M-LWDF, e de 305,51% no caso do
escalonador PF, para um raio de célula de 0,4 km, para a banda de frequência de 2,6 GHz,
considerando-se um preço do tráfego de 0,0002 €/min
Massive MIMO channel modelling for 5G wireless communication systems
Massive Multiple-Input Multiple-Output (MIMO) wireless communication systems,
equipped with tens or even hundreds of antennas, emerge as a promising technology
for the Fifth Generation (5G) wireless communication networks. To design and evaluate
the performance of massive MIMO wireless communication systems, it is essential
to develop accurate, flexible, and efficient channel models which fully reflect the characteristics
of massive MIMO channels. In this thesis, four massive MIMO channel
models have been proposed.
First, a novel non-stationary wideband multi-confocal ellipse Two-Dimensional (2-D)
Geometry Based Stochastic Model (GBSM) for massive MIMO channels is proposed.
Spherical wavefront is assumed in the proposed channel model, instead of the plane
wavefront assumption used in conventional MIMO channel models. In addition, the
Birth-Death (BD) process is incorporated into the proposed model to capture the
dynamic properties of clusters on both the array and time axes.
Second, we propose a novel theoretical non-stationary Three-Dimensional (3-D) wideband
twin-cluster channel model for massive MIMO communication systems with
carrier frequencies in the order of gigahertz (GHz). As the dimension of antenna arrays
cannot be ignored for massive MIMO, nearfield effects instead of farfield effects
are considered in the proposed model. These include the spherical wavefront assumption
and a BD process to model non-stationary properties of clusters such as cluster
appearance and disappearance on both the array and time axes.
Third, a novel Kronecker Based Stochastic Model (KBSM) for massive MIMO channels
is proposed. The proposed KBSM can not only capture antenna correlations but
also the evolution of scatterer sets on the array axis. In addition, upper and lower
bounds of KBSM channel capacities in both the high and low Signal-to-Noise Ratio
(SNR) regimes are derived when the numbers of transmit and receive antennas are
increasing unboundedly with a constant ratio.
Finally, a novel unified framework of GBSMs for 5G wireless channels is proposed.
The proposed 5G channel model framework aims at capturing key channel characteristics
of certain 5G communication scenarios, such as massive MIMO systems, High
Speed Train (HST) communications, Machine-to-Machine (M2M) communications,
and Milli-meter Wave (mmWave) communications
Doctoral Thesis: Massive MIMO in Real Propagation Environments
Mobile communications are now evolving towards the fifth generation (5G). In the near future, we expect an explosive increase in the number of connected devices, such as phones, tablets, sensors, connected vehicles and so on. Much higher data rates than in today's 4G systems are required. In the 5G visions, better coverage in remote regions is also included, aiming for bringing the current "4 billion unconnected" population into the online world. There is also a great interest in "green communications", for less energy consumption in the ICT (information and communication technology) industry. Massive MIMO is a potential technology to fulfill the requirements and visions. By equipping a base station with a large number, say tens to hundreds, of antennas, many terminals can be served in the same time-frequency resource without severe inter-user interference. Through "aggressive" spatial multiplexing, higher data rates can be achieved without increasing the required spectrum. Processing efforts can be made at the base station side, allowing terminals to have simple and cheap hardware. By exploiting the many spatial degrees of freedom, linear precoding/detection schemes can be used to achieve near-optimal performance. The large number of antennas also brings the advantage of large array gain, resulting in an increase in received signal strength. Better coverage is thus achieved. On the other hand, transmit power from base stations and terminals can be scaled down to pursue energy efficiency. In the last five years, a lot of theoretical studies have been done, showing the extraordinary advantages of massive MIMO. However, the investigations are mainly based on theoretical channels with independent and identically distributed (i.i.d.) Gaussian coefficients, and sometimes assuming unlimited number of antennas. When bringing this new technology from theory to practice, it is important to understand massive MIMO behavior in real propagation channels using practical antenna arrays. Not much has been known about real massive MIMO channels, and whether the claims about massive MIMO still hold there, until the studies in this thesis were done. The thesis study connects the "ideal" world of theory to the "non-ideal" reality. Channel measurements for massive MIMO in the 2.6 GHz band were performed, in different propagation environments and using different types of antenna arrays. Based on obtained real-life channel data, the studies include • channel characterization to identify important massive MIMO properties, • evaluation of propagation conditions in real channels and corresponding massive MIMO performance, • channel modeling for massive MIMO to capture the identified channel properties, and • reduction of massive MIMO hardware complexity through antenna selection. The investigations in the thesis conclude that massive MIMO works efficiently in real propagation environments. The theoretical advantages, as observed in i.i.d. Rayleigh channels, can also be harvested in real channels. Important propagation effects are identified for massive MIMO scenarios, including channel variations over large arrays, multipath-component (MPC) lifetime, and 3D propagation. These propagation properties are modeled and included into the COST 2100 MIMO channel model as an extension for massive MIMO. The study on antenna selection shows that characteristics in real channels allow for significant reductions of massive MIMO complexity without significant performance loss. As one of the world's first research work on massive MIMO behavior in real propagation channels, the studies in this thesis promote massive MIMO as a practical technology for future communication systems
MIMO Transmission for Single-fed ESPAR with Quantized Loads
Compact parasitic arrays in the form of electronically steerable parasitic antenna radiators (ESPARs) have emerged as a new antenna structure that achieves multipleinput- multiple-output (MIMO) transmission with a single RF chain. In this paper, we study the application of precoding on practical ESPARs, where the antennas are equipped with load impedances of quantized values. We analytically study the impact of the quantization on the system performance, where it is shown that while ideal ESPARs with ideal loads can achieve a similar performance to conventional MIMO, the performance of ESPARs will be degraded when only loads with quantized values are available. We further extend the performance analysis to imperfect channel state information (CSI). In order to alleviate the performance loss, we propose to approximate the ideal current vector by optimization, where a closed-form solution is further obtained. This enables the use of ESPARs in practice with quantized loads. Simulation results validate our analysis and show that a significant performance gain can be achieved with the proposed scheme over ESPARs with quantized loads. Finally, the tradeoff between performance and power consumption is shown to be favorable for the proposed ESPAR approaches compared to conventional MIMO, as evidenced by our energy efficiency results
Coupling element antennas for small terminals based on the characteristic modes
Future mobile communication systems use the broadband and multiple antenna technology (MIMO) to increase the spatial efficiency of the transmission channel and therefore provide higher data rates over a particular frequency range. In this thesis, the Theory of Characteristic Modes (TCM) was followed, which allows principally the use of the orthogonal chassis modes, decomposed out of the current density distribution, in order to design broadband and multiple antenna systems. A major challenge was the development of suitable coupling structures to excite several modes independently. Here, the capacitive, the inductive and the hybrid coupling concepts were discussed and compared for the selective coupling of the characteristic modes. A reconstruction of the resulting radiation patterns and the calculation of the power coefficient realized the specific coupling of the modes, the respective power budget and antenna matching as well. In particular, the results indicated a direct relationship between the characteristic modes and the low correlation of the transfer functions in multi-antenna systems. In order to show a direct coupling of the several concepts, different kind of feeding networks at the feed-point of the investigated coupling element have been developed and evaluated. Moreover, they include the power splitter and the matching networks as well. On the development of multi-band and broadband antennas, different coupling concepts for the common coupling of several modes have been investigated. This kind of excitation could be realized by using the coupling elements itself as a tuning element or by using space efficient matching networks at the feeding port. The results of this thesis reveals the utilization of the theory of characteristic modes as a synthesis tool for the design of the space efficient multi-antenna systems, as well as multi-band and broadband antennas by direct coupling of the chassis itself
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