27 research outputs found
On the Road to 6G: Visions, Requirements, Key Technologies and Testbeds
Fifth generation (5G) mobile communication systems have entered the stage of commercial development, providing users with new services and improved user experiences as well as offering a host of novel opportunities to various industries. However, 5G still faces many challenges. To address these challenges, international industrial, academic, and standards organizations have commenced research on sixth generation (6G) wireless communication systems. A series of white papers and survey papers have been published, which aim to define 6G in terms of requirements, application scenarios, key technologies, etc. Although ITU-R has been working on the 6G vision and it is expected to reach a consensus on what 6G will be by mid-2023, the related global discussions are still wide open and the existing literature has identified numerous open issues. This paper first provides a comprehensive portrayal of the 6G vision, technical requirements, and application scenarios, covering the current common understanding of 6G. Then, a critical appraisal of the 6G network architecture and key technologies is presented. Furthermore, existing testbeds and advanced 6G verification platforms are detailed for the first time. In addition, future research directions and open challenges are identified for stimulating the on-going global debate. Finally, lessons learned to date concerning 6G networks are discussed
A White Paper on Broadband Connectivity in 6G
Executive Summary
This white paper explores the road to implementing broadband connectivity in future 6G wireless systems. Different categories of use cases are considered, from extreme capacity with peak data rates up to 1 Tbps, to raising the typical data rates by orders-of-magnitude, to support broadband connectivity at railway speeds up to 1000 km/h. To achieve these goals, not only the terrestrial networks will be evolved but they will also be integrated with satellite networks, all facilitating autonomous systems and various interconnected structures.
We believe that several categories of enablers at the infrastructure, spectrum, and protocol/algorithmic levels are required to realize the intended broadband connectivity goals in 6G. At the infrastructure level, we consider ultra-massive MIMO technology (possibly implemented using holographic radio), intelligent reflecting surfaces, user-centric and scalable cell-free networking, integrated access and backhaul, and integrated space and terrestrial networks. At the spectrum level, the network must seamlessly utilize sub-6 GHz bands for coverage and spatial multiplexing of many devices, while higher bands will be used for pushing the peak rates of point-to-point links. The latter path will lead to THz communications complemented by visible light communications in specific scenarios. At the protocol/algorithmic level, the enablers include improved coding, modulation, and waveforms to achieve lower latencies, higher reliability, and reduced complexity. Different options will be needed to optimally support different use cases. The resource efficiency can be further improved by using various combinations of full-duplex radios, interference management based on rate-splitting, machine-learning-based optimization, coded caching, and broadcasting. Finally, the three levels of enablers must be utilized not only to deliver better broadband services in urban areas, but also to provide full-coverage broadband connectivity must be one of the key outcomes of 6G
Cellular, Wide-Area, and Non-Terrestrial IoT: A Survey on 5G Advances and the Road Towards 6G
The next wave of wireless technologies is proliferating in connecting things
among themselves as well as to humans. In the era of the Internet of things
(IoT), billions of sensors, machines, vehicles, drones, and robots will be
connected, making the world around us smarter. The IoT will encompass devices
that must wirelessly communicate a diverse set of data gathered from the
environment for myriad new applications. The ultimate goal is to extract
insights from this data and develop solutions that improve quality of life and
generate new revenue. Providing large-scale, long-lasting, reliable, and near
real-time connectivity is the major challenge in enabling a smart connected
world. This paper provides a comprehensive survey on existing and emerging
communication solutions for serving IoT applications in the context of
cellular, wide-area, as well as non-terrestrial networks. Specifically,
wireless technology enhancements for providing IoT access in fifth-generation
(5G) and beyond cellular networks, and communication networks over the
unlicensed spectrum are presented. Aligned with the main key performance
indicators of 5G and beyond 5G networks, we investigate solutions and standards
that enable energy efficiency, reliability, low latency, and scalability
(connection density) of current and future IoT networks. The solutions include
grant-free access and channel coding for short-packet communications,
non-orthogonal multiple access, and on-device intelligence. Further, a vision
of new paradigm shifts in communication networks in the 2030s is provided, and
the integration of the associated new technologies like artificial
intelligence, non-terrestrial networks, and new spectra is elaborated. Finally,
future research directions toward beyond 5G IoT networks are pointed out.Comment: Submitted for review to IEEE CS&
A Vision and Framework for the High Altitude Platform Station (HAPS) Networks of the Future
A High Altitude Platform Station (HAPS) is a network node that operates in
the stratosphere at an of altitude around 20 km and is instrumental for
providing communication services. Precipitated by technological innovations in
the areas of autonomous avionics, array antennas, solar panel efficiency
levels, and battery energy densities, and fueled by flourishing industry
ecosystems, the HAPS has emerged as an indispensable component of
next-generations of wireless networks. In this article, we provide a vision and
framework for the HAPS networks of the future supported by a comprehensive and
state-of-the-art literature review. We highlight the unrealized potential of
HAPS systems and elaborate on their unique ability to serve metropolitan areas.
The latest advancements and promising technologies in the HAPS energy and
payload systems are discussed. The integration of the emerging Reconfigurable
Smart Surface (RSS) technology in the communications payload of HAPS systems
for providing a cost-effective deployment is proposed. A detailed overview of
the radio resource management in HAPS systems is presented along with
synergistic physical layer techniques, including Faster-Than-Nyquist (FTN)
signaling. Numerous aspects of handoff management in HAPS systems are
described. The notable contributions of Artificial Intelligence (AI) in HAPS,
including machine learning in the design, topology management, handoff, and
resource allocation aspects are emphasized. The extensive overview of the
literature we provide is crucial for substantiating our vision that depicts the
expected deployment opportunities and challenges in the next 10 years
(next-generation networks), as well as in the subsequent 10 years
(next-next-generation networks).Comment: To appear in IEEE Communications Surveys & Tutorial
Comparação do desempenho de arquiteturas hÃbridas para comunicações na banda das ondas milimétricas
Mestrado em Engenharia Electrónica e TelecomunicaçõesA proliferação massiva das comunicações sem os faz prever que o número de utilizadores aumente exponencialmente até 2020, o que tornar a necessário um suporte de tráfego milhares de vezes superior e com ligações na ordem dos Gigabit por segundo. Este incremento exigir a um aumento significativo da e ciência espectral e energética. Impõe-se portanto, uma mudança de paradigma dos sistemas de comunicação sem os convencionais, imposta pela introdução da 5a geração. Para o efeito, e necessário desenvolver novas e promissoras técnicas de transmissão, nomeadamente a utilização de ondas milimétricas em sistemas com um número massivo de antenas. No entanto, consideráveis desafios emergem ao adotar estas técnicas. Por um lado, este tipo de ondas sofre grandes dificuldades em termos de propagação. Por outro lado, a adoção de arquiteturas convencionais para sistemas com um número massivo de antenas e absolutamente inviável, devido ao custo e ao nÃvel de complexidade inerentes. Isto acontece porque o processamento de sinal ao nÃvel da camada f sica e maioritariamente feito em banda base, ou seja, no domÃnio digital requerendo uma cadeia RF por cada antena. Neste contexto as arquiteturas hÃbridas são uma proposta relativamente recente que visa simplificar a utilização de um grande número de antenas, dividindo o processamento entre os domÃnios analógico e digital. Para além disso, o número de cadeias RF necessárias e bastante inferior ao número total de antenas do sistema, contribuindo para obvias melhorias em termos de complexidade, custo e energia consumida. Nesta dissertação e implementada uma arquitetura hÃbrida para ondas milimétricas, onde cada cadeia RF está apenas conectada a um pequeno conjunto de antenas. E considerado um sistema contendo um transmissor e um recetor ambos equipados com um grande número de antenas e onde, o número de cadeias RF e bastante inferior ao número total de antenas. Pré-codificadores hÃbridos analógico/digital, recentemente propostos na literatura são utilizados e novos equalizadores hÃbridos analógico/digital são projetados. E feita uma avaliação de performance à arquitetura implementada e posteriormente comparada com uma outra arquitetura, onde todas as antenas estão conectadas a todas as cadeias RF.The expected massive proliferation of wireless systems points out an exponential
increase in the number of users until 2020, which is needed to
support up to one thousand times more tra c and connections in order of
Gigabit per second. However, these goals require a signi cantly improvement
in the spectral and energy e ciency. As a result, it is essential to
make a paradigm shift in conventional wireless systems, imposed by the
introduction of fth generation (5G).
For this purpose, new and promising transmission techniques will be needed,
namely the use of millimeter Waves (mmWave) in systems with a massive
number of antenna elements. Nevertheless, considerable challenges emerge
in the adoption of these techniques. On one hand, mmWave su er great
di culties in terms of propagation. On the other hand, the using of conventional
architectures for systems with a large number of antennas is absolutely
impracticable because of the costs and the level of complexity. This happens
because the signal processing in physical layer is mostly done in baseband,
which means, that one RF chain for each antenna is required.
In this context the hybrid architectures are a relatively recent proposal where
the aim is to simplify the use of a large number of antenna elements, dividing
the processing between the analog and digital domains. Moreover, the
number of RF chains needed are much lower than the total number of
antenna elements of the system, which contribute to obvious improvements
in terms of complexity, costs and energy consumption.
In this Dissertation a hybrid mmWave based architecture, where each RF
chain is only connected to a small set of antennas, is implemented. It is
considered a system comprising a transmitter and a receiver both equipped
with a massive number of antennas and where the number of RF chains is
much lower than the number of antennas. Hybrid analog/digital precoders
recently proposed in the literature are used and a new hybrid analog/digital
equalizer is designed. The implemented architecture is then evaluated and
compared with other architecture, where all the antennas are connected to
all RF chains
Digital signal processing for fiber-optic communication systems
As the available bandwidth of optical fibers has been almost fully exploited, Digital Signal Processing (DSP) comes to rescue and is a critical technology underpinning the next generation advanced fiber-optic systems. Literally, it contributes two principal enforcements with respect to information communication. One is the implementation of spectrally-efficient modulation schemes, and the other is the guarantee of the recovery of information from the spectrally-efficient optical signals after channel transmission. The dissertation is dedicated to DSP techniques for the advanced fiber-optic systems. It consists of two main research topics. The first topic is about Fast-orthogonal frequency-division multiplexing (OFDM) — a variant OFDM scheme whose subcarrier spacing is half of that of conventional OFDM. The second one is about Fresnel transform with the derivation of an interesting discrete Fresnel transform (DFnT), and the proposal of orthogonal chirp-division multiplexing (OCDM), which is fundamentally underlain by the Fresnel transform. In the first part, equalization and signal recovery problems result from the halved subcarrier spacing in both double-sideband (DSB) and single-sideband (SSB) modulated Fast-OFDM systems are studied, respectively. By exploiting the relation between the multiplexing kernels of Fast-OFDM systems and Fourier transform, equalization algorithms are proposed for respective Fast-OFDM systems for information recovery. Detailed analysis is also provided. With the proposed algorithms, the DSB Fast-OFDM was experimentally implemented by intensity-modulation and direct detection in the conventional 1.55-μm and the emerging 2-μm fiber-optic systems, and the SSB Fast-OFDM was first implemented in coherent fiber-optic system with a spectral efficiency of 6 bit/s/Hz at 36 Gbps, for the first time. In the second part, Fresnel transform from optical Fresnel diffraction is studied. The discrete Fresnel transform (DFnT) is derived, as an interesting transformation that would be potentially useful for DSP. Its properties are proved. One of the attractive properties, the convolution-preservation property states that the DFnT of a circular convolution of two sequences is equal to the DFnT of either one convolving with the other. One application of DFnT is practically utilized in the proposal of OCDM. In the OCDM system, a large number of orthogonal chirped waveforms are multiplexed for high-speed communication, achieving the maximum spectral efficiency of chirp spread spectrum systems, in the same way as OFDM attains the maximum spectral efficiency of frequency-division multiplexing. Owing to the unique time-frequency properties of chirped waveforms, OCDM outperforms OFDM and single-carrier systems, and is more resilient against the noise effect, especially, when time-domain and frequency-domain distortions are severe. Experiments were carried out to validate the feasibility and advantages of the proposed OCDM systems