MIMO DAS Solutions in LTE Indoor System

Multiple input multiple output (MIMO) technology has been considered as one of the essential technologies to enhance the performance of Long Term Evolution (LTE) system with the limited bandwidth and transmit power. For indoor coverage, it is difficult to implement MIMO technology since the challenges of engineering and cost in doubling the number of installed antennas and feeders. Therefore, two indoor MIMO distributed antenna system (DAS) solutions are proposed by using frequency converting and signal comibing and separating by upgrading the existing indoor DASs. Frequency converting is employed to decrease the carrier frequency of LTE system when it is higher than 2500MHz since most of the existing feeders can only support the frequency of the transmit signals from 800MHz to 2500MHz. In the proposed schemes, two branches' MIMO signals can be loaded into the feeder of the existing DAS by combining them together after converting the original LTE frequency into two different lower frequency bands, and a dual-polarized indoor antenna is used at remote site to reduce the number of antenna locations. Some simulations show the effect of difference on transmit power and time delay between two LTE MIMO branches. Our field measurement results reveal that the proposed schemes can provide the comparable level of performance but more simpler and pratical to be deployed.