This paper develops a beam direction optimization framework for next-generation GEO satellite networks. The objective is to meet traffic demands at user locations. Given beam-pointing directions, the downlink of the GEO satellite is a vector broadcast channel that consists of a single transmitter and multiple distributed ground users. We characterize the downlink channel matrix for the multibeam satellite network by using an array factor formula for uniform planar arrays. We obtain a necessary and sufficient condition dependent on the downlink channel matrix to provision traffic demands by meeting given SINR targets at user locations. Utilizing the necessary and sufficient conditions, we formulate a joint beam direction and power optimization problem to attain target SINRs which uses minimum total power. Our results demonstrate that analog beamforming with optimized beam shifts can achieve an SINR gain of 8 dB when compared to analog beamforming without beam direction optimization. It also offers a spatial multiplexing advantage of 90 km by enabling simultaneous provisioning of user locations in close proximity within the same frequency band. When compared to hybrid beamforming, our scheme can achieve an SINR gain of 2 dB.

Radio frequency identification (RFID) systems are gaining more attention in new frontiers of applications due to their simplicity, low size factor and low cost of deployment. One of the emerging frontiers of applications of RFID is the healthcare system. In this paper, we propose a novel physical layer security technique (PLS) to secure radio frequency identification (RFID) tags used in healthcare systems. To achieve secure communications for RFID systems, directional modulation (DM) scheme is exploited at the reader side. The proposed system maintains the simple circuity and processing nature of passive tags. The results obtained demonstrate that DM techniques can achieve physical layer security for RFID systems.

This paper addresses the problem of the detection of the presence of a pre-classified (i.e., pulse shape is known) signals with IQ imbalance considering free-space path-loss. We study the effect of IQ distortion on the probability of detection and false alarm and find the degradation in the probability of detection compared with the case of ideal IQ branches. We propose closed form expressions for the probability of detection and false alarm for signals suffering from IQ imbalances.

In this paper, we propose a novel PHY layer security technique in radio frequency identification (RFID) backscatter communications system. In order to protect the RFID tag information confidentiality from the eavesdroppers attacks, the proposed technique deploys beam steering (BS) using a one dimensional (1-D) antenna array in the tag side in addition to noise injection from the reader side. The performance analysis and simulation results show that the new technique outperforms the already-existing noise injection security technique and overcomes its design limitations.

The increased interest in full-duplex communication combined with spectrum utilization enhancements stemming from cognitive radio motivate research activities in full-duplex cognitive radio. Energy detection is among the simplest and most practical methods for spectrum sensing in cognitive radio networks. Energy detection spectrum sensing in full-duplex cognitive radio has been addressed in the literature; however, either due to the lack of experimental verification or for the sake of mathematical simplicity, the residual self-interference (RSI) signal has been conventionally considered as a zero-mean Gaussian signal. In this paper, we establish for the first time an accurate (realistic) mathematical framework and performance analysis for energy detection spectrum sensing in full-duplex cognitive radio under the presence of RSI signal exhibiting Rician statistical nature, as recently proven experimentally. The performance analysis results are derived in the presence of RSI after passive self-interference cancellation (SIC) scenario and after combining passive SIC with active SIC using active analog and digital cancellation (ACDC). Exact expressions for the probabilities of detection and false alarm are derived for the considered RSI cancellation scenarios and verified through simulations. The results show that the previously used conventional zero-mean Gaussian self-interference model was producing pessimistic (lower bound) performance estimates.

In full-duplex systems, the local oscillator phase noise (PN) problem is one of the bottleneck challenges that may face the self-interference cancellation (SIC) stage especially when orthogonal frequency division multiplexing (OFDM) transmission scheme is deployed. Phase noise degrades the used SIC technique performance significantly, if not mitigated before or during the SIC stage. PN can be estimated and mitigated digitally in either time or frequency domain. Through this work, we propose a novel time-domain self-interference phase noise estimation and mitigation algorithm that is based on Wiener filter and enhances the performance of the SIC stage in full-duplex communication systems. Simulation results show that the proposed algorithm has a better performance than some current time-domain or frequency-domain PN mitigation solutions with a noticeable reduction in the computational complexity.