Algorithms for MIMO-OFDM wireless communications

Communications Group of University Carlos III of Madrid has designed and implemented algorithms for the improvement of the performance of MIMO-OFDM systems. This technology is capable of providing high data rate wireless communications. The developed algorithms allow, on one side, the correction of the imperfections introduced by radio-frequency equipment and, on the other side, adaptation of the transmission to the channel characteristics

SNR gap approximation for M-PSK-Based bit loading

Adaptive OFDM has the potential of providing bandwidth-efficient communications in hostile propagation environments. Currently, bit loading algorithms use M-ary quadrature amplitude modulation of the OFDM sub-carriers, where the number of bits per symbol modulating each of them is obtained in order to maximize the performance. SNR gap approximation for M-QAM signaling makes the algorithms simpler to implement. However, in some circumstances it may be preferable to use. Mary phase shift keying. In this letter an approximation is derived for M-PSK similar to the SNR gap of M-QAM so that bit loading algorithms can be extended to this type of modulation. In addition, the performance obtained when using M-PSK is compared to that of M-QAM in a practical situationThis work has been partly funded by Spanish Government with research project TIC2002-03498Publicad

Understanding the effects of phase noise in orthogonal frequency division multiplexing (OFDM)

Phase noise must be carefully considered when designing an OFDM-based communication system since an accurate prediction of the tolerable phase noise can allow the system and RF engineers to relax specifications. This paper analyzes the performance of OFDM systems under phase noise and its dependence on the number of sub-carriers both in the presence and absence of a phase correction mechanism. Besides some practical results are provided so as to give some insight into the phase noise spectral specifications that should be required of the local oscillatorPublicad

Algoritmos para comunicaciones inalámbricas MIMO-OFDM

El Grupo de Comunicaciones de la Universidad Carlos III de Madrid ha diseñado e implementado algoritmos para mejora de las prestaciones de los sistemas MIMO-OFDM. Esta tecnología es capaz de proporcionar comunicaciones inalámbricas con gran velocidad de transmisión. Los algoritmos desarrollados permiten, por una parte, la corrección de imperfecciones introducidas por los equipos de radio-frecuencia y, por otra, la adaptación de la transmisión a las características del canal

El futuro de las comunicaciones móviles

Audiovisuales: Entrevista 1ª parte. Disponible en: https://arcamm.uc3m.es/arcamm/# .-- Entrevista 2ª parte. Disponible en: https://arcamm.uc3m.es/arcamm/?item=dd05fdc9e25f37f2c047c1a699d56627 .-- Entrevista 3ª parte. Disponible en: https://arcamm.uc3m.es/arcamm/?item=15e5fc3a1fae74e560dd60fa31e1ef36 .-- Entrevista completa. Disponible en: http://www.youtube.com/watch?feature=player_embedded&v=i_BgPT0O_WMInternet es ya parte de la vida cotidiana. Las tecnologías de la información y las comunicaciones han transformado radicalmente el mundo de los negocios, la educación, la comunicación o el ocio, en apenas una década

Bit error rate performance of MIMO MMSE receivers in correlated rayleigh flat-fading channels

This paper analyzes the average bit error rate (BER) of multiple-input-multiple-output (MIMO) systems in transmit-correlated Rayleigh flat-fading channels. The receiver scheme is based on the minimum mean square error (MMSE) criterion, and the input may be precoded to optimize the communication. Accurate closed-form formulations for the average BER are derivedThis work was supported in part by Project TEC2008-06327-C03-02, Project CSD2008- 00010, and Project CCG08-UC3M/TIC-4069Publicad

SINR degradation in MIMO-OFDM systems with channel estimation errors and partial phase noise compensation

The phase noise effect in multiple-input-multipleoutput systems employing orthogonal frequency division multiplexing is considered in a realistic scenario where the estimated channel matrix is affected by an error. The analytical SINR degradation due to phase noise and channel estimation is obtained for linear receivers (ZF and MMSE)This work is partly funded by the projects "COMONSENS" CSD2008- 00010 and "MULTI-ADAPTIVE" TEC2008-06327-C03-02Publicad

A non-coherent multi-user large scale SIMO system relaying on M-ary DPSK

The proceeding at: 2015, IEEE International Conference on Communications (ICC) took place 8-12 June in London (UK)A non-coherent detection assisted Differential Phase Shift Keying aided large-scale MIMO system is designed in a wireless uplink where multiple single-antenna users are transmitting to the base station's receiver equipped with a very large number of receive antennas. We show that the signal to interference plus noise ratio (SINR) scales with the number of receive antennas, which confirms the same scaling law found in coherent systems. We propose a range of constellation designs that allow us to separate the users' signals at the receiver by relying only on the knowledge of the average received power per user. We analyse the error probability and provide insights into the beneficial selection of the constellation parameters. Finally, we provide some numerical results showing that our proposals require a lower number of receive antennas to achieve a given error probability than other non-coherent benchmark schemes available in the literature, while they are not far from an equivalent coherent system relying on realistic channel estimation settings.This work was supported by projects CSD2008-00010, TEC2011-29006-C03-03 and by a mobility grant of Spanish Ministry of Education. The financial support of the UK Government’s Engineering & Physical Sciences Research Council (EPSRC) as well as that of the Research Councils UK (RCUK) and of the European Research Council’s Senior Research Fellow Grant is also gratefully acknowledged

Effect of multipath and antenna diversity in MIMO-OFDM systems with imperfect channel estimation and phase noise compensation

The effect of phase noise in multiple-input–multiple-output systems employing orthogonal frequency division multiplexing is analyzed in a realistic scenario where channel estimation is not perfect, and the phase noise effects are only partially compensated. In particular, the degradation in terms of SNR is derived and the effects of the receiver and channel parameters are considered, showing that the penalty is different for different receiver schemes. Moreover it depends on the channel characteristics and on the channel estimation error. An analytical expression is used to evaluate the residual inter-channel interference variance and therefore the degradation. The effects of multipath and antenna diversity are shown to be different for the two types of linear receivers considered, the zero-forcing scheme and the minimum mean squared error receiver.This work has been partly funded by projects “MACAWI” TEC2005-07477-C02-02 and “MULTI-ADAPTIVE” TEC2008-06327-C03-02.Publicad

Analysis of SVD-Based Hybrid Schemes for Massive MIMO with Phase Noise and Imperfect Channel Estimation

In hybrid analog-digital schemes, proposed to reduce the number of RF chains especially at millimeter waves, the precoding at the transmitter and the combining at the receiver are split into digital and analog parts. We analyze the sensitivity of hybrid schemes to phase noise and channel estimation errors and we compare them to a full-digital approach. The scheme adopted for the analog part employs fixed phase shifters, then the digital part is optimized by a singular-value decomposition. We derive analytical expressions for the interference and the SNR degradation arising from the imperfect decomposition due to phase noise and the channel estimation error, for typical millimter-wave massive MIMO channels. In particular we show that when the channel estimation is made in the beam-space, this hybrid scheme is more robust to the phase noise and to the channel estimation errors than a full-digital approach