  In this work we present a case for dynamic spectrum sharing between different
operators in systems with carrier aggregation (CA) which is an important
feature in 3GPP LTE-A systems. Cross-carrier scheduling and sensing are
identified as key enablers for such spectrum sharing in LTE-A. Sensing is
classified as Type 1 sensing and Type 2 sensing and the role of each in the
system operation is discussed. The more challenging Type 2 sensing which
involves sensing the interfering signal in the presence of a desired signal is
studied for a single-input single-output system. Energy detection and the most
powerful test are formulated. The probability of false alarm and of detection
are analyzed for energy detectors. Performance evaluations show that reasonable
sensing performance can be achieved with the use of channel state information,
making such sensing practically viable.
