UMTS: Alive and Well - 4G Americas

technology forms dynamic beams that are a function of the propagation channel and interferenceenvironment (see Figure C.33). Beamforming technology works best in low-scattering environments byimproving received signal power and reducing co-channel interference. The performance of pure BFsystems is degraded in the cases of channels with significant angular spread such as indoors or in urbancellular deployments. Beamforming technology has had some success in cellular systems (e.g., thecurrent deployment of TD-SCDMA in China).Figure C.33. Conceptual Depiction of a Beamforming System Implemented withFour-Column, Vertically Polarized Planar Array.In the last few years MIMO technology has emerged as one of the most promising approaches to achievehigher data rates in cellular systems. While MIMO systems increase complexity with the use of multipleantennas and associated baseband processing at both the transmitter and the receiver, they providesignificant benefit by increasing the theoretical capacity (Shannon capacity), broadly speaking, linearlywith the number of transmit and receive antenna pairs. This dramatic increase in spectral efficiency canonly be achieved if the channel is in a sufficiently rich scattering environment. A typical MIMO systemconsisting of two transmit antennas and two receive antennas, 2x2 MIMO, is shown in Figure C.34.www.3GAmericas.org February 2010 Page 184