Abstract
Distributed antenna systems (DASs) are known to be effective to enhance coverage, spectral efficiency, and reliability in mobile communication systems. Because multiple antennas are physically separated in space, DASs benefit from both micro- and macro-diversity, which makes DASs significantly more robust compared to conventional co-located antenna systems in fading channels. However, when multiple antennas are not dispersed enough, there exists a certain degree of correlation in large-scale fading (shadowing), which degrades the macro-diversity gain. In practice, various measurements indicate a high degree of correlation of shadowing in DASs. However, most of the previous studies on DASs have not considered the correlated shadowing and its corresponding performance loss. Motivated by this limitation, we analyze the impact of the correlated shadowing to better evaluate DAS-based schemes with dual diversity transmitters. Assuming that shadowing correlation is an exponentially decreasing function of the inter-element separation, we derive the outage probability of DAS in composite Rayleigh-lognormal shadowing channels. Also, we present numerical and simulation results, which indicate there exists an optimal inter-separation between antennas that minimizes the outage rate to balance a trade-off between macro-diversity and path loss.
Highlights
Multiple-input-multiple-output (MIMO) techniques have become a promising method to improve communication performances of mobile communication systems such as coverage, spectral efficiency, data rate, and reliability [1,2,3]
We investigate the impact of correlated shadowing in composite Rayleigh-lognormal environments for more realistic modeling and analysis of Distributed antenna systems (DASs)
We analyze the impact of correlation in the large-scale fading on the DASs in composite fading channels characterized by Rayleigh and log-normal distributions
Summary
Multiple-input-multiple-output (MIMO) techniques have become a promising method to improve communication performances of mobile communication systems such as coverage, spectral efficiency, data rate, and reliability [1,2,3]. In conventional MIMO systems, multiple antennas are co-located in a single nodes, which provides diversity gain in multi-path fading channels. Due to the co-located nature of the conventional MIMO, the multiple single-input-single-output (SISO) links undergo the same shadowing [6,7], which implies no macro-diversity gain can be exploited To overcome this limitation, distributed antenna systems (DAS) were proposed to achieve spatial micro- and macro-diversity simultaneously. In reality, shadowing in decibels has been measured to have significant correlation in various scenarios such as outdoor channels in rural and suburban environments at 1.9 GHz [31], indoor channels measured at the University of Auckland at 1.8 GHz [32], high-speed railway environments [33], and references therein Such correlated shadowing affects handover behavior, interference power, and macro-diversity schemes [34]. Through numerical results and simulation, we show that there exists an optimal inter-element separation that minimizes the outage probability of DAS with two different combining schemes
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