Performance of cooperative MIMO based on measured urban channel data

We study the potential benefits of cooperative multiple-input multiple-output signaling from multiple coherent base stations with one or more mobile stations in an urban macrocellular environment. The analysis uses novel and fully coherent measurements of the channel from three base stations to a single mobile station equipped with four antennas. The observed channels are used to explore the gains in capacity enabled by cooperative base station signaling for point-to-point and multi-user communications. The analysis shows that cooperative signaling using practical algorithms yields significant increases in average capacity

Experimental comparison of antenna clustering strategies in MIMO distributed antenna systems

In this paper the effect of partitioning arrays of transmitting antennas into spatially separated clusters on the condition number and capacity of MIMO wireless systems is examined using experimental channel measurements of an indoor MIMO-enabled distributed antenna system (DAS). It is first shown for a 3 _ 2 MIMO system that distributing the transmit antennas into spatially separated clusters provides an improvement in channel conditioning (_1dB) and hence capacity, in line with previous findings. Next, a configuration with 6 transmit antennas and 2 receive antennas is examined and it is found that when it is operated as a 6 _ 2 MIMO system, it makes negligible difference to the conditioning of the channel whether the transmit antennas are grouped into 3 clusters of 2 antennas or 2 clusters of 3 antennas. The capacity varies by only a small amount (_%1) between the two clustering schemes, which can be accounted for by environment-specific signal-tonoise ratio (SNR) effects. It is then concluded that for the two typical indoor DAS scenarios tested here, if sufficient transmit diversity is provided (i.e. there are a relatively large number of transmit antennas compared to receive antennas), greater spatial distribution through increased clustering provides diminishing performance improvements. Given the typically lower installation cost of less distributed arrangements, they may then be a preferred option in commercial DAS deployments.This is the author accepted manuscript. The final version is available from IEEE via http://dx.doi.org/10.1109/VTCFall.2014.696597

Wideband mobile propagation channels: Modelling measurements and characterisation for microcellular environments

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

On geometry-base statistical channel models for MIMO wireles communications

El uso de sistemas de comunicación de banda ancha de múltiple entradamúltiple salida (Multiple Input Multiple Output MIMO) es actualmente objeto de un interés considerable. Una razón para esto es el reciente desarrollo de sistemas de comunicación móvil de tercera generación (3G) y superiores, tales como la tecnología de banda ancha Wideband Code Division Multiple Access (WCDMA, por sus siglas en inglés), la cual proporciona canales de radio de 5 MHz de ancho de banda. Para el diseño y la simulación de estos sistemas de radio móviles que usan propagación inalámbrica MIMO (como Wideband-CDMA por ejemplo), necesitamos modelos de canal que provean la requerida información espacial y temporal necesaria para el estudio de tales sistemas, esto es, los parámetros básicos de modelado en los dominios del espacio y el tiempo. Como ejemplo podemos mencionar, el valor cuadrático medio de la dispersión del retardo (Delay spread DS) el cual está directamente relacionado a la capacidad de un sistema de comunicación específico y nos da una idea aproximada de la complejidad del receptor. En esta tesis, se propone un modelo basado en geometría con enfoque en grupos (clusters) y es utilizado para el análisis en los dominios del espacio y el tiempo para condiciones estacionarias, y para representar los perfiles de potencia-angulo-retardo (Power Delay Angle Profiles PDAPs) de los componentes multi-trayectoria en ambientes urbanos. Además, se han derivado soluciones en formas cerradas para las expresiones en el dominio del ángulo (espacial) y del tiempo. La investigación previa sobre el modelado de canales cubre una amplia variedad de aspectos en varios niveles de detalle, incluyendo análisis para condiciones no estacionarias. Sin embargo el trabajo presentado en la literatura no incluye las relaciones entre los grupos (cluster) físicos y los PDAPs. El modelo propuesto basado en grupos (clusters) puede ser usado para mejorar aún más el desempeño en condiciones estacionarias de los sistemas de comunicaciones móviles actuales y futuros tales como los sistemas de comunicación MIMO de banda ancha. En la tesis también se presenta un análisis en el dominio del ángulo (espacial) y del tiempo respectivamente, a través de las funciones densidad de probabilidad (PDF) de la dirección de llegada (Direction of Arrival DOA) y el tiempo de llegada (Time of Arrival TOA) para el modelo basado en grupos. A fin de evaluar las funciones de probabilidad teóricas derivadas, éstas han sido comparadas con resultados experimentales publicados en la literatura. La comparación con estos resultados experimentales muestran una buena concordancia, no obstante la técnica de modelado presentada en esta tesis se encuentra limitada a condiciones estacionarias del canal. La condición de no estacionariedad se ubica más allá del alcance de esta tesis, es decir, el modelo propuesto no incorpora el efecto Doppler en los análisis

Design and Evaluation of Compact Multi-antennas for Efficient MIMO Communications

The use of multi-antenna systems with multiple-input multiple-output (MIMO) technology will play a key role in providing high spectrum efficiency for next generation mobile communication systems. This thesis offers valuable insights on the design of compact multi-antennas for efficient MIMO communications. In the course of the thesis work, several novel six-port antenna designs have been proposed to simultaneously exploit all six possible degrees-of-freedom (DOFs) by means of various antenna diversity mechanisms (Paper I & II). Moreover, the thesis also examines the potential of using uncoupled matching networks to adaptively optimize compact multi-antenna systems to their dynamic usage environments (Paper III). Furthermore, a simple and intuitive metric is proposed for evaluating the performance of MIMO antennas when operating in the spatial multiplexing mode (Paper IV). Last but not least, cooperation among multi-antenna systems at all three sectors of a given cellular base station is shown to deliver significant benefit at sector edges (Paper V). The thesis with five included research papers extend the understanding of MIMO systems from an antenna and propagation perspective. It provides important guidelines in designing compact and efficient MIMO antennas in their usage environments. In Paper I, a fundamental question on the number of effective DOFs in a wireless channel is explored using two co-located six-port antenna arrays. The antenna elements of both arrays closely reproduce the desired characteristics of fundamental electric and magnetic dipoles, which can efficiently extract angle and polarization diversities from the wireless channel. In particular, one of the two array designs is by far the most electrically compact six-port antenna structure in the literature. Analysis of measured channel eigenvalues in a rich multi-path scattering environment shows that six eigenchannels are successfully attained for the purpose of spatial multiplexing. To study the potential of implementing different diversity mechanisms on a practical multi-port antenna, Paper II builds on an existing dielectric resonator antenna (DRA) to provide a compact six-port DRA array that jointly utilizes space, polarization and angle diversities. In order to fully substantiate the practicality of the DRA array for indoor MIMO applications, the compact DRA array together with two reference but much larger arrays were evaluated in an office scenario. The use of the compact DRA array at the receiver is shown to achieve comparable performance to that of the reference monopole array due to the DRA array's rich diversity characteristics. In Paper III, the study of uncoupled matching networks to counteract mutual coupling effects in multi-antenna systems is extended by allowing for unbalanced matching impedances. Numerical studies suggest that the unbalanced matching is especially effective for array topologies whose effective apertures can vary significantly with respect to the propagation channel. Moreover, it is also demonstrated that the unbalanced matching is capable of adapting the radiation patterns of the array elements to the dynamic propagation environment. Paper IV introduces multiplexing efficiency as a performance metric which defines the loss of efficiency in decibel when using a multi-antenna prototype under test to achieve the same multiplexing performance as that of an ideal array in the same propagation environment. Its unique features are both its simplicity and the valuable insights it offers with respect to the performance impacts of different antenna impairments in multi-antenna systems. In Paper V, intrasite cooperation among three 120°-sector, each with a cross-polarized antenna pair, is investigated in a measured urban macrocellular environment. The single-user capacity improvement is found to exceed 40% at the sector edges, where improvements are most needed. In addition, a simple simulation model is developed to analyze the respective impact of antennas and specific propagation mechanisms on the measured cooperative gain

Power allocation in carrier aggregation MIMO systems with different power constraints

The target set by the International Telecommunication Union (ITU) for the next generation of mobile communications, IMT-Advanced, is to achieve up to 1 Gb/s peak data rates. The 3rd Generation Partnership Project (3GPP) introduced Carrier Aggregation (CA) technology in its latest Long Term Evolution Advanced (LTE-Advanced) standards in order to meet the performance goals of the next generation, the fourth generation, 4G. The introduction of CA in LTE-Advanced system poses a challenge to the power control function of a CA-MIMO radio link. The problem appears when multiple Carrier Components (CCs), within a single or multiple frequency bands, are allocated to a user. The two challenges studied in this thesis are the different channel characteristics in the different CCs and the multiple power constraints imposed on the mobile equipment: per-CC, per-antenna and per-total transmit power available. This thesis studies the bit error rate (BER) performance of a CA-MIMO radio link with the Modified Hybrid Gradient Optimal Power Allocation (MHGOPA) algorithm. In order to examine the validity of the MHGOPA algorithm, the results are compared to a baseline uniform power allocation approach. The results of the simulations are obtained for different environments: Indoor Hotspot, Urban Microcell, Suburban Microcell and Urban Macrocell. The results show that the MHGOPA algorithm generally outperforms the baseline uniform power allocation when the channel conditions are good with typical SNR values above 8-10 dB, depending on the environment. The results also show a marginal improvement on the BER in some scenarios when relaxing the constraints on the antennas. The simulations also show that giving primary carrier components (PCC) a privilege in power results in a large degradation in overall performance

MIMO Channel Modelling and Performance Evaluations

The demand on wireless networks with high throughput has grown heavily because of the increasing usage of data services. One of the key technologies to meet this requirement is the multiple-input multiple-output (MIMO) communication system, which improves the spectrum effciency without too much investment on the infrastructure and new frequency spectrum. In this theis, a new MIMO channel model is developed that is specifc to real scenarios. This kind of channel models is more suitable for network planning tools because it takes the environment details into account. The frst step of this work is a review on the state-of-the-art MIMO channel modelling and radio propagation modelling studies. It is then followed by a comparison of two propagation models that use different algorithms, i.e. ray optical and partial flow. The comparison leads to a decision that ray optical method is used for MIMO channel modelling in this thesis. After that, a spatial channel model based on a deterministic ray optical propagation model is proposed. The fnal MIMO channel model takes the polarisation and the Doppler effect in to account so that it can be used for MIMO systems with polarised antennas and moving objects as well. The model is used in a system level simulator and then validated in an indoor offce building using measurement data. It is concluded from this thesis that the chosen propagation model can be used for MIMO channel modelling, and the proposed MIMO channel model based on it is accurate and can be used for MIMO system design

Angular dispersion of radio waves in mobile channels

Multi-antenna techniques are an important solution for significantly increasing the bandwidth efficiency of mobile wireless data transmission systems. Effective and reliable design of these multi-antenna systems requires thorough knowledge of radiowave propagation in the urban environment. The aim of the work presented in this thesis is to obtain a better physical understanding of radiowave propagation in mobile radio channels in order to provide a basis for the improvement of radiowave propagation prediction techniques for urban environments using knowledge from 3-D propagation experiments and simulations combined with space-wave modelling. In particular, the work focusses on: the development of an advanced 3-D mobile channel sounding system, obtaining propagation measurement data from mobile radio propagation experiments, the analysis of measured data and the modelling of angular dispersive scattering effects for the improvement of deterministic propagation prediction models. The first part of the study presents the design, implementation and verification of a wideband high-resolution measurement system for the characterisation of angular dispersion in mobile channels. The system uses complex impulse response data obtained from a novel 3-D tilted-cross switched antenna array as input to an improved version of 3-D Unitary ESPRIT. It is capable of characterising the delay and angular properties of physically-nonstationary radio channels at moderate urban speeds with high resolution in both azimuth and elevation. For the first time, omnidirectional video data that were captured during the measurements are used in combination with the measurement results to accurately identify and relate the received radio waves directly to the actual environment while moving through it. The second part of the study presents the results of experiments in which the highresolution measurement system, described in the first part, is used in several mobile outdoor experiments in different scenarios. The objective of these measurements was to gain more knowledge in order to improve the understanding of radiowave propagation. From these results the dispersive effects in the angular domain, caused by rough building surfaces and other irregular structures was paid particular attention. These effects not only influence the total amount of received power in dense urban environments, but can also have a large impact on the performance and deployment of multi-antenna systems. To improve the data representation and support further data analysis a hierarchical clustering method is presented that can successfully identify clusters of multipath signal components in multidimensional data. By using the data obtained from an omnidirectional video camera the clusters can be related directly to the environment and the scattering effects of specific objects can be isolated. These results are important in order to improve and calibrate deterministic propagation models. In the third part of the study a new method is presented to account for the angular dispersion caused by irregular surfaces in ray-tracing based propagation prediction models. The method is based on assigning an effective roughness to specific surfaces. Unlike the conventional reflection reduction factor for Gaussian surfaces, that only reduces the ray power, the new method also distributes power in the angular domain. The results of clustered measurement data are used to calibrated the model and show that this leads to improved channel representations that are better matched to the real-world channel behavior