Multi-Antenna Jammer Assisted Covert Communications in Data Collected IoT with NOMA

In this paper,we investigate covert com-munications in data collected IoT with NOMA,where the paired sensor nodes Sm and Sn transmit covert messages to a legitimate receiver(Bob)in the pres-ence of a Warden(Willie).To confuse the detec-tion at Willie,an extra multi-antenna friendly jam-mer(Jammer)has been employed to transmit artificial noise(AN)with random power.Based on the CSI of Willie is available or not at Jammer,three AN trans-mission schemes,including null-space artificial noise(NAN),transmit antenna selection(TAS),and zero-forcing beamforming(ZFB),are proposed.Further-more,the closed-form expressions of expected mini-mum detection error probability(EMDEP)and joint connection outage probability(JCOP)are derived to measure covertness and reliability,respectively.Fi-nally,the maximum effective covert rate(ECR)is ob-tained with a given covertness constraint.The numer-ical results show that ZFB scheme has the best maxi-mum ECR in the case of the number of antennas sat-isfies N＞2,and the same maximum ECR can be achieved in ZFB and NAN schemes with N=2.Moreover,TAS scheme also can improve the maxi-mum ECR compared with the benchmark scheme(i.e.,signal-antenna jammer).In addition,a proper NOMA node pairing can further improve the maximum ECR.