@article {543,
	title = {Improper Gaussian Signaling for Multiple-Access Channels in Underlay Cognitive Radio},
	journal = {IEEE Transactions on Communications},
	volume = {67},
	year = {2019},
	month = {March},
	pages = {1817-1830},
	abstract = {This  paper considers an unlicensed multiple-accesschannel (MAC) that coexists witha licensed point-to-point user,following  the  underlay  cognitive  radio  paradigm.  We  assumethat  every  transceiver  except  the  secondary  base  station  hasone  antenna  and  that  the  primary  user  (PU)  is  protected  bya   minimum   rate   constraint.  In   contrast   to   the  conventionalassumption of proper Gaussian signaling, we allow the secondaryusers  to  transmit  improper  Gaussian  signals,  which  are  corre-lated  with  their  complex  conjugate.  When  the  secondary  basestation  performs  zero-forcing,  we  show  that  improper  signalingis   optimal   if   the  sum   of   the   interference   channel  gains   (inan  equivalent  canonical  model)  is  above  a  certain  threshold.Additionally,  we  derive  an  efficient  algorithm  to  compute  thetransmission  parameters  that  attain  the  rate  region  boundaryfor  this  scenario.  The  proposed  algorithm  exploits  a  single-userrepresentation of the secondary MAC along with new results onthe optimality of improper signaling in the single-user case whenthe PU is corrupted  by an  improper noise.},
	issn = {1558-0857},
	doi = {10.1109/TCOMM.2018.2880765},
	author = {Lameiro, Christian and Santamar{\'\i}a, Ignacio and Schreier, Peter J.}
}
