▁been ▁term ed ▁near - field ▁direct ▁anten na ▁mod ulation ▁or ▁direction al ▁mod ulation . ▁It ▁has ▁been ▁shown ▁that ▁by ▁using ▁a ▁par as it ic ▁array , ▁the ▁transm itted ▁mod ulation ▁in ▁different ▁directions ▁could ▁be ▁controlled ▁independently . ▁Sec re cy ▁could ▁be ▁realized ▁by ▁making ▁the ▁mod ulations ▁in ▁und es ired ▁directions ▁difficult ▁to ▁decode . ▁D irection al ▁mod ulation ▁data ▁transmission ▁was ▁experiment ally ▁demonstrated ▁using ▁a ▁ph ased ▁array . ▁O thers ▁have ▁demonstrated ▁direction al ▁mod ulation ▁with ▁switched ▁arrays ▁and ▁phase - con j ug ating ▁l enses . ▁ ▁That ▁type ▁of ▁direction al ▁mod ulation ▁is ▁really ▁a ▁subset ▁of ▁Neg i ▁and ▁Go el ' s ▁add itive ▁artificial ▁noise ▁encryption ▁scheme . ▁Another ▁scheme ▁using ▁pattern - re config urable ▁transmit ▁anten nas ▁for ▁Alice ▁called ▁re config urable ▁multip lic ative ▁noise ▁( R M N ) ▁comple ments ▁add itive ▁artificial ▁noise . ▁The ▁two ▁work ▁well ▁together ▁in ▁channel ▁simulations ▁in ▁which ▁nothing ▁is ▁assumed ▁known ▁to ▁Alice ▁or ▁Bob ▁about ▁the ▁e aves dro ppers . ▁ ▁Secret ▁key ▁agreement ▁ ▁The ▁different ▁works ▁mentioned ▁in ▁the ▁previous ▁part ▁employ , ▁in ▁one ▁way ▁or ▁another , ▁the ▁random ness ▁present ▁in ▁the ▁wireless ▁channel ▁to ▁transmit ▁information - the oret ically ▁secure ▁messages . ▁Con vers ely , ▁we ▁could ▁analyze ▁how ▁much ▁secre cy ▁one ▁can ▁extract ▁from ▁the ▁random ness ▁itself ▁in ▁the ▁form ▁of ▁a ▁secret ▁key .