Scattered Pilot-Based Channel Estimation for Channel Adaptive FBMC-OQAM Systems

Shaping the pulse of FilterBank MultiCarrier with Offset Quadrature Amplitude Modulation subcarrier modulation (FBMC-OQAM) systems offers a new degree of freedom for the design of mobile communication systems. In previous studies, we evaluated the gains arising from the application of Prototype Filter Functions (PFFs) and subcarrier spacing matched to the delay and Doppler spreads of doubly dispersive channels. In this paper, we investigate the impact of having imperfect channel knowledge at the receiver on the performance of Channel Adaptive Modulation (CAM) in terms of channel estimation errors and Bit Error Rate (BER). To this end, the channel estimation error for two different interference mitigation schemes proposed in the literature is derived analytically and its influence on the BER performance is analyzed for practical channel scenarios. The results show that FBMC-OQAM systems utilizing CAM and scattered pilot-based channel estimation provide a significant performance gain compared with the current one system design for a variety of channel scenarios ("one-fits-all") approach. Additionally, we verified that the often used assumption of a flat channel in the direct neighborhood of a pilot symbol is not valid for practical scenarios. © 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

Dual-Polarization OFDM-OQAM Wireless Communication System

In this paper we describe the overall idea and results of a recently proposed radio access technique based on filter bank multicarrier (FBMC) communication system using two orthogonal polarizations: dual-polarization FBMC (DP-FBMC). Using this system we can alleviate the intrinsic interference problem in FBMC systems. This enables use of all the multicarrier techniques used in cyclic-prefix orthogonal frequency-division multiplexing (CP-OFDM) systems for channel equalization, multiple-input/multiple-output (MIMO) processing, etc., without using the extra processing required for conventional FBMC. DP-FBMC also provides other interesting advantages over CP-OFDM and FBMC such as more robustness in multipath fading channels, and more robustness to receiver carrier frequency offset (CFO) and timing offset (TO). For DP-FBMC we propose three different structures based on different multiplexing techniques in time, frequency, and polarization. We will show that one of these structures has exactly the same system complexity and equipment as conventional FBMC. In our simulation results DP-FBMC has better bit error ratio (BER) performance in dispersive channels. Based on these results, DP-FBMC has potential as a promising candidate for future wireless communication systems.Comment: 1.This paper is accepted to be published in IEEE Vehicular Technology Conference (VTC) FALL 2018. 2.In this new submitted version authors have revised the paper based on the VTC FALL reviewers comments. Therefore some typos have fixed and some results have change

Channel estimation techniques for next generation mobile communication systems

Mención Internacional en el título 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 María Tulino.- Secretario: Máximo Morales Céspedes.- Vocal: Octavia A. Dobr

Filtered multi-carrier modulations for industrial wireless communications based on cognitive radio

Doktoretza-tesi honetako helburu nagusia, hari gabeko komunikazio industrialetarako fidagarritasun maila onargarria eman dezakeen maila fisikoko modulazio bat aurkitzea da. Eremu industrialetako radio bidezko kanaletan ematen diren komunikazioetarako baldintza bereziki aurkakoak direla eta, helburu hori lortzea benetako erronkatzat jo liteke. Gainera, modulazio horrek \Radio Cognitiva" deritzoten teknikekin bateragarria izan beharra dauka, hauek hari gabeko komunikazioen fidagarritasuna hobetzeko gaitasuna baitute. Bibliografian oinarrituz, gaur egungo baliabideekin hari gabeko komunikazio industrial kasu ugariri konponbidea emateko aukera badela ondoriozta genezake, baina ez kasu guztiei ordea. Hari gabeko kanalen egoera bereziki aurkakoa denerako eta komunikazio sistemek denbora muga bereziki zorrotzak bete behar dituztenerako, ezta erantzun nahikoa ona eman lezakeen hari gabeko komunikazio sistema industrialik bibliografia zientifikoan. Hori dela eta, doktoretza tesi honetan, \Radio Cognitiva" delakoa eta 5G-rako aurreikusita dauden filtro bankuetan oinarrituriko modulazio multigarraiatzaileak bezalako teknologia hasiberrietara jotzen dugu, aurrez aipaturiko arazoari konponbide berriak bilatu nahian. Bibliografian dauden filtro bankuetan oinarrituriko modulazio multi-garraiatzaileak aztertu eta ondoren beraien egokitasuna ebaluatzen dugu, kanal dispertsiboen aurkako sendotasuna eta \Radio Cognitiva" teknikekin izan lezaketen bateragarritasuna irizpide hartuz. Ebaluaketa horretan oinarrituz, doktoretza-tesi honetan \Radio Cognitiva" teknikekin bateragarria den WCP-COQAM proposatzen dugu modulazio industrial gisa. Modulazio teknika berau erakusteaz gain, bibliografian eskuragarri ez dauden WCP-COQAM-rentzat sinkronizazio eta kanal estimazio teknikak ere aurkezten ditugu.El objetivo principal de esta tesis doctoral consiste en encontrar una modulación de capa física capaz de proporcionar robustez y fiabilidad suficientes a sistemas de comunicaciones inalámbricas industriales. Esto supone un desafío, dadas las adversas condiciones del canal inalámbrico propias de entornos industriales. Además, dicha modulación debería presentar una alta compatibilidad con las técnicas de Radio Cognitiva, debido al potencial de éstas para mejorar la fiabilidad de las comunicaciones inalámbricas. Basándonos en la bibliografía, concluimos que las soluciones presentes en el estado del arte actual cubren una amplia variedad de escenarios dentro de las comunicaciones inalámbricas industriales, pero no todas. Para los escenarios con canales altamente dispersivos y requerimientos de tiempo especialmente estrictos, no existe ninguna solución en la industria ni dentro de la bibliografía científica. En esta tesis doctoral nos centramos en tecnologías incipientes como la Radio Cognitiva y las modulaciones multi-portadora con bancos de filtros para 5G para tratar de buscar nuevas soluciones al problema anteriormente descrito. Por lo tanto, analizamos algunas de las técnicas multi-portadora con bancos de filtros presentes en la bibliografía científica y las evaluamos basándonos en su robustez frente a canales altamente dispersivos y su compatibilidad con la Radio Cognitiva. Basándonos en dicha evaluación, proponemosWCP-COQAM como posible candidata a modulación industrial compatible con Radio Cognitiva. Además de la propia técnica de modulación, presentamos métodos de sincronización y estimación de canal para la misma que no se encuentran presentes en el estado del arte.The main goal of this doctoral thesis is to find a physical layer modulation able to provide high enough robustness and reliability levels for wireless industrial communications systems. Considering the harsh wireless channel conditions of industrial environments, that goal implies a considerable challenge. Besides, this modulation should be highly compatible with Cognitive Radio techniques, due to their potential to improve the reliability of wireless communications. Based on the bibliography, we conclude that the existent solutions in the current state of the art cover a wide range of wireless industrial communications scenarios, but not all of them. There is no solution, neither in the industry nor in the scientific bibliography, for those scenarios involving highly dispersive wireless channels and particularly stringent timeliness requirements. In this doctoral thesis, we focus on upcoming technologies such as Cognitive Radio and multi-carrier modulations based on filter banks for 5G, in order to search new solutions for the aforementioned problem. Therefore, we analyse some of the multi-carrier modulations based on filter banks of the scientific bibliography and we evaluate them in terms of robustness against highly dispersive channels and in terms of compatibility with Cognitive Radio. In this doctoral thesis we propose the modulation WCP-COQAM as possible candidate for industrial wireless modulation and compatible with Cognitive Radio. In addition to the modulation technique itself, we also introduce some synchronization and channel estimation techniques which are not present in the state of the art

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

Channel estimation techniques for filter bank multicarrier based transceivers for next generation of wireless networks

A dissertation submitted to Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering (Electrical and Information Engineering), August 2017The fourth generation (4G) of wireless communication system is designed based on the principles of cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) where the cyclic prefix (CP) is used to combat inter-symbol interference (ISI) and inter-carrier interference (ICI) in order to achieve higher data rates in comparison to the previous generations of wireless networks. Various filter bank multicarrier systems have been considered as potential waveforms for the fast emerging next generation (xG) of wireless networks (especially the fifth generation (5G) networks). Some examples of the considered waveforms are orthogonal frequency division multiplexing with offset quadrature amplitude modulation based filter bank, universal filtered multicarrier (UFMC), bi-orthogonal frequency division multiplexing (BFDM) and generalized frequency division multiplexing (GFDM). In perfect reconstruction (PR) or near perfect reconstruction (NPR) filter bank designs, these aforementioned FBMC waveforms adopt the use of well-designed prototype filters (which are used for designing the synthesis and analysis filter banks) so as to either replace or minimize the CP usage of the 4G networks in order to provide higher spectral efficiencies for the overall increment in data rates. The accurate designing of the FIR low-pass prototype filter in NPR filter banks results in minimal signal distortions thus, making the analysis filter bank a time-reversed version of the corresponding synthesis filter bank. However, in non-perfect reconstruction (Non-PR) the analysis filter bank is not directly a time-reversed version of the corresponding synthesis filter bank as the prototype filter impulse response for this system is formulated (in this dissertation) by the introduction of randomly generated errors. Hence, aliasing and amplitude distortions are more prominent for Non-PR. Channel estimation (CE) is used to predict the behaviour of the frequency selective channel and is usually adopted to ensure excellent reconstruction of the transmitted symbols. These techniques can be broadly classified as pilot based, semi-blind and blind channel estimation schemes. In this dissertation, two linear pilot based CE techniques namely the least square (LS) and linear minimum mean square error (LMMSE), and three adaptive channel estimation schemes namely least mean square (LMS), normalized least mean square (NLMS) and recursive least square (RLS) are presented, analyzed and documented. These are implemented while exploiting the near orthogonality properties of offset quadrature amplitude modulation (OQAM) to mitigate the effects of interference for two filter bank waveforms (i.e. OFDM/OQAM and GFDM/OQAM) for the next generation of wireless networks assuming conditions of both NPR and Non-PR in slow and fast frequency selective Rayleigh fading channel. Results obtained from the computer simulations carried out showed that the channel estimation schemes performed better in an NPR filter bank system as compared with Non-PR filter banks. The low performance of Non-PR system is due to the amplitude distortion and aliasing introduced from the random errors generated in the system that is used to design its prototype filters. It can be concluded that RLS, NLMS, LMS, LMMSE and LS channel estimation schemes offered the best normalized mean square error (NMSE) and bit error rate (BER) performances (in decreasing order) for both waveforms assuming both NPR and Non-PR filter banks. Keywords: Channel estimation, Filter bank, OFDM/OQAM, GFDM/OQAM, NPR, Non-PR, 5G, Frequency selective channel.CK201

A frequency domain approach to synchronization of filterbank multicarrier systems in practice

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