38 research outputs found
Multi-User Ultra-Massive MIMO for very high frequency bands (mmWave and THz): a resource allocation problem
A dynamic subarray allocation for multi-user massive MIMO systems working in very high frequency bands (mmWave and THz) is proposed as a promising technique to unleash the capacity limits in future cellular networks capable of supporting high consuming bandwidth applications
Enabling Technologies for 5G and Beyond: Bridging the Gap between Vision and Reality
It is common knowledge that the fifth generation (5G) of cellular networks will come with drastic transformation in the cellular systems capabilities and will redefine mobile services. 5G (and beyond) systems will be used for human interaction, in addition to person-to-machine and machine-to-machine communications, i.e., every-thing is connected to every-thing. These features will open a whole line of new business opportunities and contribute to the development of the society in many different ways, including developing and building smart cities, enhancing remote health care services, to name a few. However, such services come with an unprecedented growth of mobile traffic, which will lead to heavy challenges and requirements that have not been experienced before. Indeed, the new generations of cellular systems are required to support ultra-low latency services (less than one millisecond), and provide hundred times more data rate and connectivity, all compared to previous generations such as 4G. Moreover, they are expected to be highly secure due to the sensitivity of the transmitted information.
Researchers from both academia and industry have been concerting significant efforts to develop new technologies that aim at enabling the new generation of cellular systems (5G and beyond) to realize their potential. Much emphasis has been put on finding new technologies that enhance the radio access network (RAN) capabilities as RAN is considered to be the bottleneck of cellular networks. Striking a balance between performance and cost has been at the center of the efforts that led to the newly developed technologies, which include non-orthogonal multiple access (NOMA), millimeter wave (mmWave) technology, self-organizing network (SON) and massive multiple-input multiple-output (MIMO). Moreover, physical layer security (PLS) has been praised for being a potential candidate for enforcing transmission security when combined with cryptography techniques.
Although the main concepts of the aforementioned RAN key enabling technologies have been well defined, there are discrepancies between their intended (i.e., vision) performance and the achieved one. In fact, there is still much to do to bridge the gap between what has been promised by such technologies in terms of performance and what they might be able to achieve in real-life scenarios. This motivates us to identify the main reasons behind the aforementioned gaps and try to find ways to reduce such gaps. We first focus on NOMA where the main drawback of existing solutions is related to their poor performance in terms of spectral efficiency and connectivity. Another major drawback of existing NOMA solutions is that transmission rate per user decreases slightly with the number of users, which is a serious issue since future networks are expected to provide high connectivity. To this end, we develop NOMA solutions that could provide three times the achievable rate of existing solutions while maintaining a constant transmission rate per user regardless of the number of connected users.
We then investigate the challenges facing mmWave transmissions. It has been demonstrated that such technology is highly sensitive to blockage, which limits its range of communication. To overcome this obstacle, we develop a beam-codebook based analog beam-steering scheme that achieves near maximum beamforming gain performance. The proposed technique has been tested and verified by real-life measurements performed at Bell Labs.
Another line of research pursued in this thesis is investigating challenges pertaining to SON. It is known that radio access network self-planning is the most complex and sensitive task due to its impact on the cost of network deployment, etc., capital expenditure (CAPEX). To tackle this issue, we propose a comprehensive self-planning solution that provides all the planning parameters at once while guaranteeing that the system is optimally planned. The proposed scheme is compared to existing solutions and its superiority is demonstrated. We finally consider the communication secrecy problem and investigated the potential of employing PLS. Most of the existing PLS schemes are based on unrealistic assumptions, most notably is the assumption of having full knowledge about the whereabouts of the eavesdroppers. To solve this problem, we introduce a radically novel nonlinear precoding technique and a coding strategy that together allow to establish secure communication without any knowledge about the eavesdroppers. Moreover, we prove that it is possible to secure communications while achieving near transmitter-receiver channel capacity (the maximum theoretical rate)
MIMOPack: A High Performance Computing Library for MIMO Communication Systems
[EN] Nowadays, several communication standards are emerging and evolving, searching
higher transmission rates, reliability and coverage. This expansion is
primarily driven by the continued increase in consumption of mobile multimedia services
due to the emergence of new handheld devices such as smartphones and tablets.
One of the most significant techniques employed to meet these demands is the use
of multiple transmit and receive antennas, known as MIMO systems. The use of this technology allows to increase the
transmission rate and the quality of the transmission through the use of multiple antennas at the
transmitter and receiver sides.
MIMO technologies have become an essential key in several wireless standards such as WLAN, WiMAX and LTE.
These technologies will be incorporated also in future standards, therefore is
expected in the coming years a great deal of research in this field.
Clearly, the study of MIMO systems is critical in the current investigation,
however the problems that arise from this technology are very complex.
High Performance Computing (HPC) systems, and specifically, modern hardware
architectures as multi-core and many-cores (e.g Graphics Processing Units (GPU))
are playing a key role in the development of efficient and low-complexity
algorithms for MIMO transmissions. Proof of this is that the number of
scientific contributions and research projects related to its use has increased in the last years.
Also, some high performance libraries have been implemented as
tools for researchers involved in the development of future
communication standards. Two of the most popular libraries are: IT++
that is a library based on the use of some optimized libraries for multi-core
processors and the Communications System Toolbox designed for use with MATLAB, which uses GPU computing. However, there is not a library able to
run on a heterogeneous platform using all the available resources.
In view of the high computational requirements in MIMO application research and
the shortage of tools able to satisfy them, we have made a special effort to develop a
library to ease the development of adaptable parallel applications in accordance
with the different architectures of the executing platform. The library, called MIMOPack, aims to implement efficiently using parallel computing, a set of functions to perform some of the critical stages of MIMO communication systems simulation.
The main contribution of the thesis is the implementation of efficient Hard and Soft output detectors, since the detection stage is considered the most complex part of the communication process. These detectors are highly configurable and many of them include preprocessing techniques that reduce the computational cost and increase the performance.
The proposed library shows three important features: portability,
efficiency and easy of use. Current realease allows GPUs and multi-core computation, or even
simultaneously, since it is designed to use on heterogeneous machines. The interface of the functions are common to all environments
in order to simplify the use of the library. Moreover, some of the functions are callable from MATLAB increasing the portability of developed codes between different computing environments.
According to the library design and the performance assessment, we consider that MIMOPack may facilitate
industrial and academic researchers the implementation of scientific codes without having to know different programming
languages and machine architectures. This will allow to include more complex
algorithms in their simulations and obtain their results faster. This is
particularly important in the industry, since the manufacturers work
to analyze and to propose their own technologies with the aim that it will be
approved as a standard. Thus allowing to enforce their intellectual property
rights over their competitors, who should obtain the corresponding licenses
to include these technologies into their products.[ES] En la actualidad varios estándares de comunicación están surgiendo buscando velocidades de transmisión más altas y mayor fiabilidad. Esta expansión está impulsada por el aumento en el consumo de servicios multimedia debido a la aparición de nuevos dispositivos como los smartphones y las tabletas.
Una de las técnicas empleadas más importantes es el uso de múltiples antenas de transmisión y recepción, conocida como sistemas MIMO, que permite aumentar la velocidad y la calidad de la transmisión.
Las tecnologÃas MIMO se han convertido en una parte esencial en diferentes estándares tales como WLAN, WiMAX y LTE.
Estas tecnologÃas se incorporarán también en futuros estándares, por lo tanto, se espera en los próximos años una gran cantidad de investigación en este campo.
Está claro que el estudio de los sistemas MIMO es crÃtico en la investigación actual, sin embargo los problemas que surgen de esta tecnologÃa son muy complejos. La sistemas de computación de alto rendimiento, y en concreto, las arquitecturas hardware actuales como multi-core y many-core (p. ej. GPUs) están jugando un papel clave en el desarrollo de algoritmos eficientes y de baja complejidad en las transmisiones MIMO. Prueba de ello es que el número de contribuciones cientÃficas y proyectos de investigación relacionados con su uso se han incrementado en el últimos años.
Algunas librerÃas de alto rendimiento se están utilizando como
herramientas por investigadores en el desarrollo de
futuros estándares. Dos de las librerÃas más destacadas
son: IT++ que se basa en el uso de distintas librerÃas optimizadas para procesadores multi-core y el paquete Communications System Toolbox diseñada para su uso con MATLAB, que utiliza computación con GPU. Sin embargo, no hay una biblioteca capaz de ejecutarse en una plataforma heterogénea.
En vista de los altos requisitos computacionales en la investigación MIMO y
la escasez de herramientas capaces de satisfacerlos, hemos implementado una
librerÃa que facilita el desarrollo de aplicaciones paralelas adaptables de
acuerdo con las diferentes arquitecturas de la plataforma de ejecución. La
librerÃa, llamada MIMOPack, implementa de manera eficiente un conjunto de funciones para llevar a cabo algunas de las etapas crÃticas en la simulación de un sistema de comunicación MIMO.
La principal aportación de la tesis es la implementación de detectores eficientes de salida Hard y Soft, ya que la etapa de detección es considerada la parte más compleja en el proceso de comunicación.
Estos detectores son altamente configurables y muchos de ellos incluyen
técnicas de preprocesamiento que reducen el coste computacional y
aumentan el rendimiento.
La librerÃa propuesta tiene tres caracterÃsticas importantes: la portabilidad, la eficiencia y facilidad de uso. La versión actual permite computación en GPU y multi-core, incluso simultáneamente, ya que está diseñada para ser utilizada sobre plataformas heterogéneas que explotan toda la capacidad computacional. Para facilitar el uso de la biblioteca, las interfaces de las funciones son comunes para todas las arquitecturas. Algunas de las funciones se pueden llamar desde MATLAB aumentando la portabilidad de códigos desarrollados entre los diferentes entornos.
De acuerdo con el diseño de la biblioteca y la evaluación del rendimiento,
consideramos que MIMOPack puede facilitar la implementación de códigos sin tener que saber programar con diferentes lenguajes y arquitecturas. MIMOPack permitirá incluir algoritmos más complejos en las simulaciones y obtener los resultados
más rápidamente. Esto es particularmente importante en la industria,
ya que los fabricantes trabajan para proponer sus propias tecnologÃas lo antes posible con el objetivo de que sean aprobadas como un estándar. De este modo, los fabricantes pueden hacer valer sus derechos de propiedad intelectual frente a sus competidores, quienes luego deben obtener las correspon[CA] En l'actualitat diversos està ndards de comunicació estan sorgint i
evolucionant cercant velocitats de transmissió més altes i major
fiabilitat. Aquesta expansió, està impulsada pel continu augment en el consum de serveis multimèdia a causa de l'aparició de
nous dispositius portà tils com els smartphones i les tablets.
Una de les tècniques més importants és l'ús de múltiples antenes de transmissió i recepció (MIMO) que permet augmentar la velocitat de transmissió i la qualitat de transmissió.
Les tecnologies MIMO s'han convertit en una part essencial en diferents
està ndards inalà mbrics, tals com WLAN, WiMAX i LTE. Aquestes
tecnologies s'incorporaran també en futurs està ndards, per tant, s'espera en
els pròxims anys una gran quantitat d'investigació en aquest camp.
L'estudi dels sistemes MIMO és crÃtic en la recerca actual,
no obstant açó, els problemes que sorgeixen d'aquesta tecnologia són molt
complexos. Els sistemes de computació d'alt rendiment com els multi-core i many-core (p. ej. GPUs)), estan jugant un paper clau en el desenvolupament
d'algoritmes eficients i de baixa complexitat en les transmissions MIMO. Prova
d'açò és que el nombre de contribucions cientÃfiques i projectes
d'investigació relacionats amb el seu ús s'han incrementat en els últims anys.
Algunes llibreries d'alt rendiment estan utilitzant-se com a eines
per investigadors involucrats en el desenvolupament de futurs
està ndards. Dos de les llibreries més destacades són:
IT++ que és una llibreria basada en lús de diferents llibreries optimitzades per a
processadors multi-core i el paquet Communications System Toolbox dissenyat per
al seu ús amb MATLAB, que utilitza computació amb GPU. No obstant açò, no hi ha una
biblioteca capaç d'executar-se en una plataforma heterogènia.
Degut als alts requisits computacionals en la investigació MIMO i l'escacès
d'eines capaces de satisfer-los, hem implementat
una llibreria que facilita el desenvolupament d'aplicacions paral·leles
adaptables d'acord amb les diferentes arquitectures de la plataforma
d'ejecució. La llibreria, anomenada MIMOPack, implementa
de manera eficient, un conjunt de
funcions per dur a terme algunes de les etapes crÃtiques en la simulació
d'un sistema de comunicació MIMO.
La principal aportació de la tesi és la implementació de detectors
eficients d'exida Hard i Soft, ja que l'etapa de detecció és considerada
la part més complexa en el procés de comunicació. Estos detectors són
altament configurables i molts d'ells inclouen tècniques de preprocessament
que redueixen el cost computacional i augmenten el rendiment. La llibreria
proposta té tres caracterÃstiques importants: la portabilitat,
l'eficiència i la facilitat d'ús. La versió actual permet
computació en GPU i multi-core, fins i tot simultà niament, ja que estÃ
dissenyada per a ser utilitzada sobre plataformes heterogènies que exploten
tota la capacitat computacional. Amb el fi de simplificar l'ús de la biblioteca,
les interfaces de les funcions són comunes per a totes les arquitectures. Algunes de
les funcions poden ser utilitzades des de MATLAB augmentant la portabilitat de
còdics desenvolupats entre els diferentes entorns.
D'acord amb el disseny de la biblioteca i l'evaluació del rendiment,
considerem que MIMOPack pot facilitar la implementació de còdics a investigadors sense haver de saber programar amb diferents llenguatges i arquitectures. MIMOPack permetrÃ
incloure algoritmes més complexos en les seues simulacions i obtindre els seus
resultats més rà pid. Açò és particularment important en la
industria, ja que els fabricants treballen per a proposar les seues pròpies
tecnologies el més prompte possible amb l'objectiu que siguen aprovades com un
està ndard. D'aquesta menera, els fabricants podran fer valdre els seus drets
de propietat intel·lectual enfront dels seus competidors, els qui després han
d'obtenir les corresponents llicències si voleRamiro Sánchez, C. (2015). MIMOPack: A High Performance Computing Library for MIMO Communication Systems [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/53930TESISPremios Extraordinarios de tesis doctorale
Foundations of User-Centric Cell-Free Massive MIMO
Imagine a coverage area where each mobile device is communicating with a
preferred set of wireless access points (among many) that are selected based on
its needs and cooperate to jointly serve it, instead of creating autonomous
cells. This effectively leads to a user-centric post-cellular network
architecture, which can resolve many of the interference issues and
service-quality variations that appear in cellular networks. This concept is
called User-centric Cell-free Massive MIMO (multiple-input multiple-output) and
has its roots in the intersection between three technology components: Massive
MIMO, coordinated multipoint processing, and ultra-dense networks. The main
challenge is to achieve the benefits of cell-free operation in a practically
feasible way, with computational complexity and fronthaul requirements that are
scalable to enable massively large networks with many mobile devices. This
monograph covers the foundations of User-centric Cell-free Massive MIMO,
starting from the motivation and mathematical definition. It continues by
describing the state-of-the-art signal processing algorithms for channel
estimation, uplink data reception, and downlink data transmission with either
centralized or distributed implementation. The achievable spectral efficiency
is mathematically derived and evaluated numerically using a running example
that exposes the impact of various system parameters and algorithmic choices.
The fundamental tradeoffs between communication performance, computational
complexity, and fronthaul signaling requirements are thoroughly analyzed.
Finally, the basic algorithms for pilot assignment, dynamic cooperation cluster
formation, and power optimization are provided, while open problems related to
these and other resource allocation problems are reviewed. All the numerical
examples can be reproduced using the accompanying Matlab code.Comment: This is the authors' version of the manuscript: \"Ozlem Tugfe Demir,
Emil Bj\"ornson and Luca Sanguinetti (2021), "Foundations of User-Centric
Cell-Free Massive MIMO", Foundations and Trends in Signal Processing: Vol.
14, No. 3-4, pp 162-47
Low-Latency Millimeter-Wave Communications: Traffic Dispersion or Network Densification?
This paper investigates two strategies to reduce the communication delay in
future wireless networks: traffic dispersion and network densification. A
hybrid scheme that combines these two strategies is also considered. The
probabilistic delay and effective capacity are used to evaluate performance.
For probabilistic delay, the violation probability of delay, i.e., the
probability that the delay exceeds a given tolerance level, is characterized in
terms of upper bounds, which are derived by applying stochastic network
calculus theory. In addition, to characterize the maximum affordable arrival
traffic for mmWave systems, the effective capacity, i.e., the service
capability with a given quality-of-service (QoS) requirement, is studied. The
derived bounds on the probabilistic delay and effective capacity are validated
through simulations. These numerical results show that, for a given average
system gain, traffic dispersion, network densification, and the hybrid scheme
exhibit different potentials to reduce the end-to-end communication delay. For
instance, traffic dispersion outperforms network densification, given high
average system gain and arrival rate, while it could be the worst option,
otherwise. Furthermore, it is revealed that, increasing the number of
independent paths and/or relay density is always beneficial, while the
performance gain is related to the arrival rate and average system gain,
jointly. Therefore, a proper transmission scheme should be selected to optimize
the delay performance, according to the given conditions on arrival traffic and
system service capability
Low-Complexity Multi-User MIMO Algorithms for mmWave WLANs
Very high throughput and high-efficiency wireless local area networks (WLANs) have become essential for today's significant global Internet traffic and the expected significant global increase of public WiFi hotspots. Total Internet traffic is predicted to expand 3.7-fold from 2017 to 2022. In 2017, 53% of overall Internet traffic used by WiFi networks, and that number is expected to increase to 56.8% by 2022. Furthermore, 80% of overall Internet traffic is expected to be video traffic by 2022, up from 70% in 2017. WiFi networks are also expected to move towards denser deployment scenarios, such as stadiums, large office buildings, and airports, with very high data rate applications, such as ultra-high definition video wireless streaming. Thus, in order to meet the predicted growth of wireless traffic and the number of WiFi networks in the world, an efficient Internet access solution is required for the current IEEE 802.11 standards.
Millimeter wave (mmWave) communication technology is expected to play a crucial role in future wireless networks with large user populations because of the large spectrum band it can provide. To further improve spectrum efficiency over mmWave bands in WLANs with large numbers of users, the IEEE 802.11ay standard was developed from the traditional IEEE 802.11ad standard, aiming to support multi-user MIMO. Propagation challenges associated with mmWave bands necessitate the use of analog beamforming (BF) technologies that employ directional transmissions to determine the optimal sector beam between a transmitter and a receiver. However, the multi-user MIMO is not exploited, since analog BF is limited to a single-user, single-transmission. The computational complexity of achieving traditional multi-user MIMO BF methods, such as full digital BF, in the mmWave systems becomes significant due to the hardware constraints. Our research focuses on how to effectively and efficiently realize multi-user MIMO transmission to improve spectrum efficiency over the IEEE 802.11ay mmWave band system while also resolving the computational complexity challenges for achieving a multi-user MIMO in mmWave systems.
This thesis focuses on MAC protocol algorithms and analysis of the IEEE 802.11ay mmWave WLANs to provide multi-user MIMO support in various scenarios to improve the spectrum efficiency and system throughput. Specifically, from a downlink single-hop scenario perspective, a VG algorithm is proposed to schedule simultaneous downlink transmission links while mitigating the multi-user interference with no additional computational complexity. From a downlink multi-hop scenario perspective, a low-complexity MHVG algorithm is conducted to realize simultaneous transmissions and improve the network performance by taking advantage of the spatial reuse in a dense network. The proposed MHVG algorithm permits simultaneous links scheduling and mitigates both the multi-user interference and co-channel interference based only on analog BF information, without the necessity for feedback overhead, such as channel state information (CSI). From an uplink scenario perspective, a low-complexity user selection algorithm, HBF-VG, incorporates user selection with the HBF algorithm to achieve simultaneous uplink transmissions for IEEE 802.11ay mmWave WLANs. With the HBF-VG algorithm, the users can be selected based on an orthogonality criterion instead of collecting CSI from all potential users. We optimize the digital BF to mitigate the residual interference among selected users. Extensive analytical and simulation evaluations are provided to validate the performance of the proposed algorithms with respect to average throughput per time slot, average network throughput, average sum-rate, energy efficiency, signal-to-interference-plus-noise ratio (SINR), and spatial multiplexing gain