@ARTICLE {8736,
author={D. Castanheira and A.  Silva and A. Gameiro},
doi={10.1049/iet-com.2013.0434},
journal={IET Communications},
title={Null-Space Cognitive Precoding for Heterogeneous Networks},
year={2014},
month={March},
volume={ 8},
number={ 5},
pages={ 555- 563},
ISSN={1751-8628}
}