As companies rush to get Long Term Evolution (LTE)
products to market, engineers face tough challenges in
testing these often complex devices. The mandate to
include Multiple-Input Multiple-Output (MIMO) means
many engineers are working to optimize their multi-antenna
architectures. To achieve time-to-market goals, the MIMO
solutions under development need to work correctly in
real-world situations. Defining situations when MIMO
transmissions will improve system performance can
be complicated, but it is a critical aspect of successful
implementation.
Of particular interest is how to quickly determine whether a
MIMO channel is capable of supporting spatial multiplexing
under a given signal-to-noise ratio (SNR). Fortunately
with the proper test equipment, a figure of merit called
“condition number” can provide a short-term indication of
the SNR required to properly recover a MIMO transmission
over the selected wireless channel.
This application note will review the basic concepts of
MIMO with specific application to spatial multiplexing
in 3rd Generation Partnership Project (3GPP) LTE. It will
show measurements of channel coefficients and associated
condition numbers as they relate to the SNR at the LTE
receiver. How antenna and channel correlation affects
system performance will also be discussed, along with
recommendations for the best measurement tools to use
when developing LTE products and systems.
Introduction