29 research outputs found
Efficient implementation of filter bank multicarrier systems using circular fast convolution
In this paper, filter bank-based multicarrier systems using a fast convolution approach are investigated. We show that exploiting offset quadrature amplitude modulation enables us to perform FFT/IFFT-based convolution without overlapped processing, and the circular distortion can be discarded as a part of orthogonal interference terms. This property has two advantages. First, it leads to spectral efficiency enhancement in the system by removing the prototype filter transients. Second, the complexity of the system is significantly reduced as the result of using efficient FFT algorithms for convolution. The new scheme is compared with the conventional waveforms in terms of out-of-band radiation, orthogonality, spectral efficiency, and complexity. The performance of the receiver and the equalization methods are investigated and compared with other waveforms through simulations. Moreover, based on the time variant nature of the filter response of the proposed scheme, a pilot-based channel estimation technique with controlled transmit power is developed and analyzed through lower-bound derivations. The proposed transceiver is shown to be a competitive solution for future wireless networks
Channel estimation techniques for next generation mobile communication systems
MenciĂłn Internacional en el tĂtulo de doctorWe are witnessing a revolution in wireless technology, where the society is demanding new
services, such as smart cities, autonomous vehicles, augmented reality, etc. These challenging
services not only are demanding an enormous increase of data rates in the range of 1000 times
higher, but also they are real-time applications with an important delay constraint. Furthermore,
an unprecedented number of different machine-type devices will be also connected to the network,
known as Internet of Things (IoT), where they will be transmitting real-time measurements from
different sensors. In this context, the Third Generation Partnership Project (3GPP) has already
developed the new Fifth Generation (5G) of mobile communication systems, which should be
capable of satisfying all the requirements. Hence, 5G will provide three key aspects, such as:
enhanced mobile broad-band (eMBB) services, massive machine type communications (mMTC)
and ultra reliable low latency communications (URLLC).
In order to accomplish all the mentioned requirements, it is important to develop new key
radio technologies capable of exploiting the wireless environment with a higher efficiency. Orthogonal
frequency division multiplexing (OFDM) is the most widely used waveform by the industry,
however, it also exhibits high side lobes reducing considerably the spectral efficiency. Therefore,
filter-bank multi-carrier combined with offset quadrature amplitude modulation (FBMC-OQAM)
is a waveform candidate to replace OFDM due to the fact that it provides extremely low out-ofband
emissions (OBE). The traditional spectrum frequencies range is close to saturation, thus,
there is a need to exploit higher bands, such as millimeter waves (mm-Wave), making possible the
deployment of ultra broad-band services. However, the high path loss in these bands increases the
blockage probability of the radio-link, forcing us to use massive multiple-input multiple-output
(MIMO) systems in order to increase either the diversity or capacity of the overall link.
All these emergent radio technologies can make 5G a reality. However, all their benefits can be
only exploited under the knowledge and availability of the channel state information (CSI) in order
to compensate the effects produced by the channel. The channel estimation process is a well known
procedure in the area of signal processing for communications, where it is a challenging task due to the fact that we have to obtain a good estimator, maintaining at the same time the efficiency and
reduced complexity of the system and obtaining the results as fast as possible. In FBMC-OQAM,
there are several proposed channel estimation techniques, however, all of them required a high
number of operations in order to deal with the self-interference produced by the prototype filter,
hence, increasing the complexity. The existing channel estimation and equalization techniques for
massive MIMO are in general too complex due to the large number of antennas, where we must
estimate the channel response of each antenna of the array and perform some prohibitive matrix
inversions to obtain the equalizers. Besides, for the particular case of mm-Wave, the existing
techniques either do not adapt well to the dynamic ranges of signal-to-noise ratio (SNR) scenarios
or they assume some approximations which reduce the quality of the estimator.
In this thesis, we focus on the channel estimation for different emerging techniques that are
capable of obtaining a better performance with a lower number of operations, suitable for low complexity
devices and for URLLC. Firstly, we proposed new pilot sequences for FBMC-OQAM
enabling the use of a simple averaging process in order to obtain the CSI. We show that our
technique outperforms the existing ones in terms of complexity and performance. Secondly, we
propose an alternative low-complexity way of computing the precoding/postcoding equalizer under
the scenario of massive MIMO, keeping the quality of the estimator. Finally, we propose a new
channel estimation technique for massive MIMO for mm-Wave, capable of adapting to very variable
scenarios in terms of SNR and outperforming the existing techniques. We provide some analysis
of the mean squared error (MSE) and complexity of each proposed technique. Furthermore,
some numerical results are given in order to provide a better understanding of the problem and
solutions.Programa de Doctorado en Multimedia y Comunicaciones por la Universidad Carlos III de Madrid y la Universidad Rey Juan CarlosPresidente: Antonia MarĂa Tulino.- Secretario: Máximo Morales CĂ©spedes.- Vocal: Octavia A. Dobr
MIMO signal processing in offset-QAM based filter bank multicarrier systems
Next-generation communication systems have to comply with very strict requirements for increased flexibility in heterogeneous environments, high spectral efficiency, and agility of carrier aggregation. This fact motivates research in advanced multicarrier modulation (MCM) schemes, such as filter bank-based multicarrier (FBMC) modulation. This paper focuses on the offset quadrature amplitude modulation (OQAM)-based FBMC variant, known as FBMC/OQAM, which presents outstanding spectral efficiency and confinement in a number of channels and applications. Its special nature, however, generates a number of new signal processing challenges that are not present in other MCM schemes, notably, in orthogonal-frequency-division multiplexing (OFDM). In multiple-input multiple-output (MIMO) architectures, which are expected to play a primary role in future communication systems, these challenges are intensified, creating new interesting research problems and calling for new ideas and methods that are adapted to the particularities of the MIMO-FBMC/OQAM system. The goal of this paper is to focus on these signal processing problems and provide a concise yet comprehensive overview of the recent advances in this area. Open problems and associated directions for future research are also discussed.Peer ReviewedPostprint (author's final draft
Power Allocation and Capacity Analysis for FBMC-OQAM With Superimposed Training
Superimposed training (ST) is a semiblind channel estimation technique, proposed for orthogonal frequency division multiplexing (OFDM), where training sequences are added to data symbols, avoiding the use of dedicated pilot-subcarriers, and increasing the available bandwidth compared with pilot symbol assisted modulation (PSAM). Filter bank multicarrier offset quadrature amplitude modulation (FBMC-OQAM) is a promising waveform technique considered to replace the OFDM, which takes advantage of well-designed filters to avoid the use of cyclic prefix and reduce the out-band-emissions. In this paper, we provide the expressions of the average channel capacity of the FBMC-OQAM combined with either PSAM or ST schemes, considering imperfect channel estimation and the presence of the pilot sequences. In order to compute the capacity expression of our proposal, ST-FBMC-OQAM, we analyze the channel estimation error and its variance. The average channel capacity is deduced considering the noise, data interference from ST, and the intrinsic self-interference of the FBMC-OQAM. Additionally, to maximize the average channel capacity, the optimal value of data power allocation is also obtained. The simulation results confirm the validity of the capacity analysis and demonstrate the superiority of the ST-FBMC-OQAM over existing proposals
Synchronization Algorithms for FBMC Systems
Filter bank multicarrier (FBMC) systems, such as FMT and OFDM/OQAM systems, can provide reduced sensitivity to narrowband interference, high flexibility to allocate group of subchannels to different users and a high spectral containment. On the other hand, as all the multicarrier modulation schemes, one of their major drawbacks is their sensitivity to CFO and symbol timing errors. In this thesis the problem of CFO and symbol timing synchronization is examined and new data-aided and blind estimation techniques are proposed. Specifically, it is presented a new joint symbol timing and CFO synchronization algorithm based on the LS approach. Moreover, the joint ML phase offset, CFO and symbol timing estimator for a multiple access OFDM/OQAM system is considered. It is also proposed a closed-form CFO estimator based on the best linear unbiased estimation principle for FMT systems. Blind CFO estimators based on the ML principle for low SNR are also considered and, moreover, a closed-form CFO synchronization algorithm based on the LS method is derived. Finally, it is also proposed, under the assumption of low SNR, the joint ML symbol timing and phase offset estimator
Waveform Advancements and Synchronization Techniques for Generalized Frequency Division Multiplexing
To enable a new level of connectivity among machines as well as between people and machines, future wireless applications will demand higher requirements on data rates, response time, and reliability from the communication system. This will lead to a different system design, comprising a wide range of deployment scenarios. One important aspect is the evolution of physical layer (PHY), specifically the waveform modulation. The novel generalized frequency division multiplexing (GFDM) technique is a prominent proposal for a flexible block filtered multicarrier modulation.
This thesis introduces an advanced GFDM concept that enables the emulation of other prominent waveform candidates in scenarios where they perform best. Hence, a unique modulation framework is presented that is capable of addressing a wide range of scenarios and to upgrade the PHY for 5G networks. In particular, for a subset of system parameters of the modulation framework, the problem of symbol time offset (STO) and carrier frequency offset (CFO) estimation is investigated and synchronization approaches, which can operate in burst and continuous transmissions, are designed.
The first part of this work presents the modulation principles of prominent 5G candidate waveforms and then focuses on the GFDM basic and advanced attributes. The GFDM concept is extended towards the use of OQAM, introducing the novel frequency-shift OQAM-GFDM, and a new low complexity model based on signal processing carried out in the time domain. A new prototype filter proposal highlights the benefits obtained in terms of a reduced out-of-band (OOB) radiation and more attractive hardware implementation cost. With proper parameterization of the advanced GFDM, the achieved gains are applicable to other filtered OFDM waveforms.
In the second part, a search approach for estimating STO and CFO in GFDM is evaluated. A self-interference metric is proposed to quantify the effective SNR penalty caused by the residual time and frequency misalignment or intrinsic inter-symbol interference (ISI) and inter-carrier interference (ICI) for arbitrary pulse shape design in GFDM. In particular, the ICI can be used as a non-data aided approach for frequency estimation. Then, GFDM training sequences, defined either as an isolated preamble or embedded as a midamble or pseudo-circular pre/post-amble, are designed. Simulations show better OOB emission and good estimation results, either comparable or superior, to state-of-the-art OFDM system in wireless channels
Evaluation Of Multicarrier Air Interfaces In The Presence Of Interference For L-Band And C-Band Air-Ground Communications
The use of aeronautical vehicles and systems is continuously growing, and this means current aeronautical communication systems, particularly those operating in the very high frequency (VHF) aviation band, will suffer from severe congestion in some regions of the world. For example, it is estimated that air-to-ground (AG) communication traffic density will at least double by 2035 over that in 2012, based on the most-likely growth scenario for Europe. This traffic growth (worldwide) has led civil aviation authorities such as the FAA in the USA, and EuroControl in Europe, to jointly explore development of future communication infrastructures (FCI). According to international aviation systems policies, both current and future AG communication systems will be deployed in L-band (960-1164 MHz), and possibly in C-band (5030-5091 GHz) because of the favorable AG radio propagation characteristics in these bands. During the same time period as the FCI studies, the use of multicarrier communication technologies has become very mature for terrestrial communication systems, but for AG systems it is still being studied and tested.
Aiming toward future demands, EuroControl and FAA sponsored work to define several new candidate AG radio systems with high data rate and high reliability. Dominant among these is now an L-Band Digital Aeronautical Communication Systems (L-DACS): L-DACS1. L-DACS1 is a multicarrier communication system based on the popular orthogonal frequency division multiplexing (OFDM) modulation technique. For airport surface area communication systems used in C-band, EuroControl and FAA also proposed another OFDM communication system based on the IEEE 802.16e standard, termed aeronautical mobile airport communication system (AeroMACS). This system has been proposed to provide the growing need of communication traffic in airport environments.
In this dissertation, first we review existing and proposed aviation communication systems in VHF-band, L-band and C-band. We then focus our study on the use of multicarrier techniques in these aviation bands. We compare the popular and dominant multicarrier technique OFDM (which is used in cellular networks such long-term evolution (LTE) and wireless local area networks such as Wi-Fi) with the filterbank multicarrier (FBMC) technique. As far as we are aware, we are the first to propose and evaluate FBMC for aviation communication systems.
We show, using analysis and computer simulations, along with measurement based (NASA) air-ground and airport surface channel models, that FBMC offers advantages in performance over the OFDM schemes. Via use of sharp filters in the frequency domain, FBMC reduces out of band interference. Specifically, it is more robust to high-power distance measurement equipment (DME) interference, and via replacement of guard bands with data-bearing subcarriers, FBMC can offer higher throughput than the contending L-DACS1 scheme, by up to 23%. Similar advantages over AeroMACS pertain in the airport surface channel. Our FBMC bit error ratio performance is comparable to that of the OFDM schemes, and is even better for our “spectrally-shaped” version of FBMC. For these improvements, FBMC requires a modest complexity increase.
Our final contribution in this dissertation is the presentation of spectrally shaped FBMC (SS-FBMC). This idea allocates unequal power to subcarriers to contend with non-white noise or non-white interference. Our adaptive algorithm selects a minimum number of guard subcarriers and then allocates power accordingly to remaining subcarriers based on a “water-filling-like” approach. We are the first to propose such a cognitive radio technique with FBMC for aviation applications. Results show that SSFBMC improves over FBMC in both performance and throughput
Review of Recent Trends
This work was partially supported by the European Regional Development Fund (FEDER), through the Regional Operational Programme of Centre (CENTRO 2020) of the Portugal 2020 framework, through projects SOCA (CENTRO-01-0145-FEDER-000010) and ORCIP (CENTRO-01-0145-FEDER-022141). Fernando P. Guiomar acknowledges a fellowship from “la Caixa” Foundation (ID100010434), code LCF/BQ/PR20/11770015. Houda Harkat acknowledges the financial support of the Programmatic Financing of the CTS R&D Unit (UIDP/00066/2020).MIMO-OFDM is a key technology and a strong candidate for 5G telecommunication systems. In the literature, there is no convenient survey study that rounds up all the necessary points to be investigated concerning such systems. The current deeper review paper inspects and interprets the state of the art and addresses several research axes related to MIMO-OFDM systems. Two topics have received special attention: MIMO waveforms and MIMO-OFDM channel estimation. The existing MIMO hardware and software innovations, in addition to the MIMO-OFDM equalization techniques, are discussed concisely. In the literature, only a few authors have discussed the MIMO channel estimation and modeling problems for a variety of MIMO systems. However, to the best of our knowledge, there has been until now no review paper specifically discussing the recent works concerning channel estimation and the equalization process for MIMO-OFDM systems. Hence, the current work focuses on analyzing the recently used algorithms in the field, which could be a rich reference for researchers. Moreover, some research perspectives are identified.publishersversionpublishe
Study and implementation of an advanced transceiver for 5G
With the years passing by, the users of mobile networks present higher needs and
demands when it comes to e ective download and upload data rates. The fth generation
of mobile communications assumes the concretization of binary rates above 1
Gbps to be achieved by any ordinary user. To ful l this requirement, it was necessary to
undertake a study and development of a system using the 4th Generation of Mobile Communications
(4G) waveform to lessen the need for adding new modules and increasing
the complexity of mobile network systems. The main goal is to develop an Orthogonal
Frequency Division Multiplexing (OFDM) waveform simulator for 5th Generation of Mobile
Communications (5G) using Quadrature Amplitude Modulation (QAM), simulate
its performance to compare with the theoretical one and perform laboratorial tests. In
this study the channel estimation is carried out and we evaluated the performance of Bit
Error Rate (BER) and Error Vector Magnitude (EVM) as study metrics and parallels
the usual transmission loss models for indoor and free-space communications. The study
and experiments end in resulting mobile uncoded and convolutional hard decision OFDM
communications up to 5.9 Gbps of e ective data rate and the results and measurements
were obtained inside the laboratory environment, with a signal carrier of 3.5GHz and 2dB
of both antennas gain and 26dB of ampli er gain at distances up to 4 meters between the
two antennas. The best result obtained considering the highest data rate achieved was a
256-QAM uncoded OFDM communication at 5.9 Gbps on a 4 meters distance between
antennas.A quinta geração de redes móveis prevê a concretização de ritmos binários acima
de 1 Gbps ao acesso de qualquer utilizador comum. Para concretizar esse requisito,
foi necessário levar a cargo um estudo e desenvolvimento de um sistema que utilize a
forma de onda do 4a Geração de Comunicações Móveis (4G) para diminuir eventuais
necessidades de adição de novos módulos e aumento da complexidade dos sistemas de
redes mĂłveis. O objetivo concreto Ă© o desenvolvimento de um simulador de forma de
onda de Multiplexação por Divisão de Frequência Ortogonal (OFDM) que atinja as
taxas efetivas de dados para a 5a Geração de Comunicações Móveis (5G) utilizando
Modulação de Amplitude em Quadratura (QAM), realizar simulações para averiguar o
normal funcionamento de acordo com a teoria e realizar testes laboratoriais. Neste estudo
é efetuada a estimação de canal, são avaliadas as performances da Taxa de Erro de Bits
(BER) e da Magnitude do Vetor de Erro (EVM) como métricas de estudo e efetuado um
paralelismo com os modelos de perdas de transmissão usuais para comunicações indoor e
de espaço livre. O estudo e os testes laboratoriais concluem-se em comunicações OFDM
não codi cado e com decisão abrupta em códigos convolucionais efetuadas até velocidades
efetivas de 5.9 Gbps de dados e foram obtidos os resultados e medições num ambiente de
laboratĂłrio, com uma portadora de 3.5 GHz, com o ganho de ambas as antenas de 2dB
e um ampli cador com um ganho de 26dB em distâncias até aos 4 metros entre as duas
antenas. O melhor resultado obtido em termos de velocidade de transmissĂŁo de dados
foi a comunicação 256-QAM OFDM não codi cado atingindo os 5.9 Gbps com 4 metros
de distância entre antenas