Effects of Nonlinear Transmit Amplifiers in
Smart Antennas for Wireless Systems
European Wireless'99, Munich, Germany, October 4-8 1999.
Paper in Postscript (393K); in
The use of array antennas in mobile telecommunication systems has
proven to increase the spectral efficiency of the system. However,
use of an N element array antenna at the basestation site implies that
the amount of radio hardware
must be increased N-fold. This will make basestations larger, more
more power consuming. Much effort must be put into combine
functionality as amplification, using a multicarrier amplifier (MCPA),
capable to amplify a number of
signals with different carrier frequencies in a single device.
In this study we investigate by measurements and simulations the
effects of a nonlinear MCPA in the
downlink for a cellular system. The nonlinearity will introduce
intermodulation distortion and also decrease the null-depth of the
beamformer. This will have an impact on the carrier-to-interference
ratio of the mobiles in the system. The simulations gives the CDF of
the received carrier-to-interference ratio of the mobiles, which can
be used in link budget analysis. The transmitted intermodulation
distortion from an array will be spatially dispersed. This is shown
measurements in an anechoic chamber on a four element array using an
analog Butler matrix as a beamformer.