Ultra-wideband frequency dependency of capacity and diversity in multi-antenna indoor environments

This study investigates two areas relating to practical multi-antenna ultra-wideband (UWB) indoor channel: the frequency dependency in line-of-sight (LOS) and non-LOS (NLOS) environments, and the differences in spatial characteristics when using virtual and physical arrays in multi-antenna channel characterisation. The authors quantify the frequency dependency of the channels in terms of their resilience to spatial fading and system capacity. The composite radiation pattern of the antenna and channel will impact the channel properties, the authors investigate these changes by measurement and analysis of channel data taken using both physical and virtual array configurations at the same locations. They find that at lower frequencies the resilience to spatial fading in LOS channels was less than half of the theoretic maximum. The difference in capacity and diversity gain between the LOS and NLOS channels was found to decrease with centre frequency. The different rates of increase result in a 4% average increase in capacity for a 500-MHz subband centred at 4.5 and 9.5%GHz for the LOS scenarios, whereas an increase of only 0.7% was experienced by the NLOS scenarios. In addition, this analysis indicates that the estimated diversity and capacity of multi-antenna channels decrease when using physical antenna arrays for measurements.