Sincronización y Estimación de canal eficiente y robusta en sistemas CoMP OFDM

Este trabajo fue presentado en el XXIX Simposium Nacional de la Unión Científica Internacional de Radio, celebrado los días 3-5 de septiembre de 2014 en la Universidad Politécnica de Valencia (España).In this paper, an efficient and robust simultaneous timing synchronization and channel estimation method for Cooperative MultiPoint Transmission and Reception (CoMP) is proposed. Efficiency is obtained by using the same two Orthogonal Frequency Division Multiplexing (OFDM) symbols for simultaneously transmitting preambles by all the base stations. Robustness is achieved by specially designed orthogonal sequences both in time and frequency domain. The proposed method is able to estimate the channels from several base stations without losing anything in performance with respect to the single transmission scenario. Furthermore, our proposed synchronization outperforms single transmitter methods and so, it could also be adapted for single base station OFDM systems.Este trabajo ha sido financiado parcialmente por los proyectos GRE3NSYST (TEC2011-29006-C03-03) y COMONSENS (CSD2008-00010).Publicad

Multi-user synchronisation in ad-hoc OFDM-based wireless personal area networks

In this paper, a procedure for dealing with the multi-user synchronisation problem in Orthogonal Frequency Division Multiple Access (OFDMA)-based systems for ad hoc environments is proposed and analysed. We show with this novel approach that it is possible to re-use much of the already extent literature for single-user synchronisation in OFDM and apply it to multi-user ad hoc scenarios. Also a distributed version of the procedure is proposed in order to fairly share out the power consumption among all the devices. The proposed procedure makes use of higher layer capabilities in a cross-layer design and it does not incur too much complexity or power. This issue is specially critical in wireless heterogeneous ad hoc networks where devices can be very limited in terms of transmission and/or computational power.Publicad

Resource Allocation between Feedback and Forward MIMO Links and Energy Consumption

The proceeding at: IEEE 76th Vehicular Technology Conference, took place Québec (Canada), in 2012, September 3-6. The event Web site at: http://www.ieeevtc.org/vtc2012fall/This work deals with the problem of radio resource allocation in a point-to-point multiple-input multiple-output (MIMO) communications system with feedback of channel state information. A total pool of radio resources (power and transmission time) is allocated among training, feedback, and data transmission phases in order to maximize system performance in terms of throughput. The energy consumption associated to the base band signal processing and decoding is also evaluated. This resource allocation problem is studied analytically in a twoway time division duplex (TDD) communications scenario with time correlated channels, where the effect of feedback errors and feedback delay is also taken into account.The research leading to these results has received funding from the European Cooperation in Science and Technol-ogy under project COST Action IC0902, from the Spanish Ministry of Economy and Competitiveness (Ministerio de Econom´ıa y Competitividad) under projects TEC2011-29006-C03-02 (GRE3N-LINK-MAC) and TEC2011-29006-C03-03 (GRE3N-SYST), and from the Catalan Government under grant 2009 SGR 891.Publicad

Effects of channel estimation on multiuser virtual MIMO-OFDMA relay-based networks

A practical multiuser cooperative transmission scheme denoted as Virtual Maximum Ratio Transmission (VMRT) for multiple-input multiple-output-orthogonal frequency division multiple access (MIMO-OFDMA) relay-based networks is proposed and evaluated in the presence of a realistic channel estimation algorithm and using low-density parity-check (LDPC) codes. It is shown that this scheme is robust against channel estimation errors. It offers diversity and array gain, keeping the complexity low with a multiuser and multiantenna channel estimation algorithm that is simple and efficient. In addition, the combination with LDPC codes provides improved gains; diversity gains larger than 6 dB can be easily obtained with a reduced number of relays. Thus, this scheme can be used to extend coverage or increase system throughput by using simple cooperative OFDMA-based relays.The authors would like to thank Jae-Yun Ko for his valuable help at the beginning of our work. This work has been partly funded by the projects MULTIADAPTIVE (TEC2008-06327- C03-02), COMONSENS (CSD2008-00010) and CODIV (ICT-2007-215477).Publicad

Modelling, performance analysis and design of WPAN systems

This paper covers the main issues that must be solved in order to design and analyse the performance of Wireless Personal Area Networks (WPANs) with the aid of simulation tools. We review state-of-the-art channel models to account for small- and large-scale propagation conditions in waveform- and system-level simulations. When dealing with waveform simulations, we also look at Montecarlo and importance sampling techniques that allow efficient estimation of error probabilities. Additionally, discrete channel models are introduced to efficiently link both waveform- and system-level approaches and we point out some methods to obtain the model parameters that are suitable for the wireless environment. The discussion of these techniques is complemented with two application examples that show the use of the different simulation levels for system design and performance study. With the paradigm of Bluetooth piconets we illustrate the usefulness of discrete channel models and we consider the design of an OFDM-based WPAN system to exemplify simulation from a waveform-level point of view.This work has been partially funded by European Commission (IST-2001–34157), Spanish Government (TIC2002–03498) and Madrid Community (UC3M-TEC-05–027).Publicad

Robust Timing Synchronization for Multicarrier Systems Based on RST Invariance

In this paper, a blind robust timing synchronization method, based on invariance properties and cyclostationarity, for multicarrier systems such as Orthogonal Frequency Division Multiplexing (OFDM) is proposed and evaluated. Its results outperform the state-of-the-art for blind methods, specially in hard wireless channels where our proposal is highly superior. It even surpasses the performance of most of non-blind (pilot-aided) methods, while at the same time, it gets the advantages of energy and bandwidth saving of blind proposals. Moreover, since this technique does not require the use of pilots, it can be easily applied to either packet-based or broadcasting systems.This work has been partly funded by the Spanish national projects GRE3N-SYST (TEC2011-29006-C03-03) and COMONSENS (CSD2008-00010).Publicad

Cooperative transmission scheme to address random orientation and blockage events in VLC systems

© 2019 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.Visible light communication (VLC) is a promising communication technology that paves the way to the Internet of Things. The forthcoming Industry 4.0 requires reliable high-speed communication links, which can be easily fulfilled with the massive adoption of the VLC technology. However, in VLC indoor communication environments, line-of-sight link blockages and strong misalignment losses between the light-emitting diode (LED) transmitters and the photodiode (PD) receivers are usual problems that must be tackled. This paper proposes a coordinated multi-point (CoMP) transmission technique to deal with both issues, and carries out a detailed evaluation of the VLC system performance as function of the PD receiver orientation and the density of obstacles in different scenarios. The proposed cooperative transmission scheme demonstrates an improvement in the average cell data rate and outage probability performance and, as a consequence, justifies the use of CoMP techniques to provide reliable VLC services in ultra-dense small cell scenarios indoors.Peer ReviewedPostprint (published version

Efficient Implementation of Complementary Golay Sequences for PAR Reduction and Forward Error Correction in OFDM-based WLAN systems

In this paper the use of complementary Golay sequences (CGS) for peak-to-average power ratio (PAR) reduction and forward error correction (FEC) in an orthogonal frequency division multiplexing (OFDM)-based wireless local area network (WLAN) system is explored; performance is examined and complexity issues are analyzed. We study their PAR reduction performance depending on sequence lengths and we have found that, for the case that the number of sub-carriers differs from the sequence length, some interesting relationships can still be stated. Regarding their error correction capabilities, these sequences are investigated considering M-PSK constellations applied to the OFDM signal specified in IEEE 802.11a standard. Computational load for both Golay encoding and decoding processes is addressed and we provide an exhaustive analysis of their complexity. In order to overcome memory restrictions and speed up algorithmic operations, a novel algorithm for real-time generation of the Golay Base Sequences is proposed and evaluated giving as a conclusion that these sequences can be real-time generated with actual Digital Signal Processors (DSP). Our proposal lies on an efficient permutation algorithm that obtains the current permutation without the need for generating previous ones. Its complexity is calculated and turns out to be significantly low; the advantages are specially appreciated at the decoding stage. We also introduce a hybrid solution to get a trade-off between complexity and memory requirements. Moreover, the whole system is also implemented in a DSP to validate the proposal in a prototype, where its feasibility has been confirmed.This work has been partly funded by the Spanish government with projects MACAWI (TEC 2005-07477-c02-02) and MAMBO (UC3M-TEC-05-027)

Subcarrier and power allocation for the downlink of multiuser OFDM transmission

In this paper, a new algorithm for subcarrier and power allocation for the downlink of multiuser OFDM transmission is presented. The proposed algorithm is more stable and it offers a lower complexity and better performance than previous existing algorithms.This work has been partly funded by the Spanish government with project TIC 2002-03498 (ORISE), Education Chamber of Madrid Community and European Social Fund.Publicad

Reduction of the envelope fluctuations of multi-carrier modulations using adaptive neural fuzzy inference systems

In this paper, a novel scheme for reducing the envelope fluctuations in multi-carrier signals applying Adaptive Neural Fuzzy Inference Systems (ANFIS) is proposed and analyzed. Once trained with signals with very low envelope fluctuations, such as those obtained by the Active Constellation Expansion - Approximate Gradient Project (ACE-AGP) algorithm, ANFIS approximately reaches a similar reduction as with ACE-AGP for multi-carrier signals without the complexity and the large convergence time of conventional ACE-AGP. We show that our approach is less complex than other previous schemes and with better performanceThis work has been partly funded by projects MULTI-ADAPTIVE (TEC2008-06327-C03-02), COMONSENS (CSD2008-00010) and AECI Program of Research Cooperation with Morocco (A/027714/09)Publicad