Abstract
The space-time wireless communication systems will use the advantages of the MIMO (Multiple Input Multiple Output) channels. Precedent studies have focused less attention on the capacity analysis considering correlated indoor channels under different frequency bands and polarizations. In practice, there is certain correlation degree between the different propagation sub-channels, which makes interesting to evaluate the impact that this correlation has on the system performance under different frequency bands and polarizations. The paper shows a detail study around of real MIMO channel and its spectral efficiency behavior when change both the number of antenna elements and SNR (Signal to Noise Ratio). The results showed in the paper demonstrate that to increase the diversity order could not be a good technique to improve the performance of the MIMO systems in some highly correlated cases when picocells or indoor environments are considered. Besides, increasing the number of array antenna elements, both in the transmitter and receiver side, does not offer linear capacity increases under correlated cases. The results derived from a frequency measurement campaigns performed between 2 and 2.6 GHz show polarization dependence and less frequency band dependence in the MIMO channel correlation matrix for indoor environments. In other hand, under the WSS (Wide Sense Stationary) channel condition and guaranteeing a minimum SNR level, remarkable changes on the capacity probability distribution function shape, and on the cumulative distribution function of the MIMO system eigenvalues, were observed in different correlated cases.
Highlights
The space-time wireless communication systems will use the advantages of the MIMO (Multiple Input Multiple Output) channels
The results derived from a frequency measurement campaigns performed between 2 and 2.6 GHz show polarization dependence and less frequency band dependence in the MIMO channel correlation matrix for indoor environments
Se ha establecido un procedimiento de validación de resultados, basándose en medidas en interiores realizadas en el Instituto de Telecomunicaciones y Aplicaciones Multimedia de la Universidad Politécnica de Valencia (UPV), donde se ha utilizado un Analizador de Redes Vectorial, antenas omnidireccionales de banda ancha y diferentes configuraciones de array para distintos casos
Summary
Se ha comprobado teóricamente[6] que los canales MIMO ofrecen la posibilidad de un incremento lineal de capacidad en los sistemas que hace uso de técnicas de procesado espaciotiempo a medida que aumenta el número de elementos de array en ambos lados del enlace. Como se puede apreciar en la Figura 2, a medida que aumenta MR y MT el incremento de la capacidad se presenta únicamente con tendencia lineal en condiciones ideales de incorrelación entre los elementos del canal MIMO. Ello se puede lograr aprovechando los fenómenos de propagación multitrayectoria aplicando diferentes técnicas de transmisión, buscando también un incremento en la eficiencia espectral del sistema al aumentar el número de elementos de antena en los arrays transmisor y receptor. Para un enlace con 20 dB de SNR, el hecho de modificar la correlación entre los elementos de la matriz del canal, al pasar de un estado totalmente correlado a uno incorrelado, ocasiona una diferencia de capacidad de aproximadamente 40 bits/s/Hz; véase también la Figura 1 para el mismo caso a diferentes niveles de SNR
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