Understanding The Impact Of Spatial Effects On MIMO Wireless Channels

By Wilkie Yu, Agilent Technologies

Multiple-Input Multiple-Output (MIMO) technology is today being eyed by many wireless communication systems (e.g., the IEEE 802.11n wireless LAN, IEEE 802.16e-based Mobile WiMAX™ Wave 2 and the Long-Term Evolution (LTE) mobile wireless system) due to its ability to enable higher data rates with increased spectral efficiency. While MIMO offers the potential for increased signal robustness and capacity improvement when operating in rich multipath environments, developing and testing MIMO components and systems demands advanced channel emulation tools that are easily configured and provide an accurate representation of realistic wireless channels and conditions. Unfortunately, accurately emulating wireless channels is no simple task. Successfully accomplishing it requires the engineer to confront MIMO's enemy — correlation — head on.

When multiple antennas are applied to a wireless communication system, the various transmit-receive antenna pairs may have different channel impulse responses (correlation) due to the spatial effects caused by angle spread, antenna radiation pattern, and the surrounding environment. It is important therefore, to understand how these spatial effects influence system performance since MIMO operation requires low channel-to-channel correlation. This information is vital for creating improved models for use in emulating MIMO wireless channels.