Abstract
The rapid advances in communication technology bring in opportunities and chal lenges. Among others, proactive eavesdropping, unmanned aerial vehicle (UAV), and intelligent reflecting surface (IRS) catch a great deal of attention from both academia and industry. Note that their objectives and operation environments can be very dif ferent from those of the conventional communication systems, thus new investigations and characterizations are desired, and new design is needed for the cooperation among sub-systems. Therefore, this thesis is devoted to provide the performance analysis for these emerging technologies, with an emphasis on their respective cooperation tech niques, to provide a better understanding as well as practical guidance. First, we investigate the legitimate eavesdropping of the suspicious communica tions hopping over parallel fading channels. In order to improve the eavesdropping performance, the legitimate monitor deploys cooperative jamming to induce the sus picious link over a smaller subset of channels with a lower communication rate. We formulate the eavesdropping performance maximization problem by jointly optimiz ing the selection of jammed channels and the jamming power on each channel. We prove that the legitimate monitor should use all the jamming power and evenly al locate among the jammed channels if it decides to jam. We further demonstrate an important trade-off in deciding the optimal number of jammed channels, where jam ming more channels helps reduce the suspicious communication rate for eavesdrop ping more clearly, but at the risk that the jammed channels are more likely chosen by the suspicious link for transmission and thus cannot be overheard by the half-duplex monitor. We also extend to the two-way communications, by deciding the common jammed channels to balance the two-way eavesdropping performance. Second, we study the challenging problem to communicate with and control a cellular-connected UAV swarm with both high reliability and low latency. Due to the strong ground-to-air channels, the UAV swarm generally suffers the severe interfer ence from the ground base stations (GBSs) that are serving ground users. To tackle this issue, we propose a novel two-phase cooperative transmission protocol by exploiting cellular communications (GBS-to-UAV in Phase I) plus device-to-device (D2D) commu nications (UAV-to-UAV in Phase II). We aim to characterize the reliability performance of the above two-phase transmission protocol, i.e., the expected percentage of UAVs in the swarm that can decode the control message, which is a non-trivial problem due to the complex system setup and the intricate coupling between the two transmission phases. Nevertheless, we manage to obtain an approximated closed-form expression of the reliability performance of interest, under reasonable assumptions and with the aid of the Pearson distributions. We further demonstrate the effectiveness of our pro posed protocol over other benchmark protocols, and study the effect of key system parameters on the reliability performance. iv Finally, we propose a cooperative double-IRS aided multiple-input-multiple-output (MIMO) communication system, where a multi-antenna user is served by a multi antenna BS through two single-reflection links and one double-reflection link, under the LOS propagation channels. We formulate the MIMO channel capacity maximiza tion problem by jointly optimizing the transmit covariance matrix and the passive beamforming matrices of the two cooperative IRSs, which is non-convex and difficult to solve. Nevertheless, by exploiting the unique characteristics of the LOS channels, we propose a low-complexity algorithm whose complexity is independent of the to tal number of IRS elements. Moreover, we analyze the capacity scaling order of the double-IRS aided MIMO system, which significantly outperforms that of the conven tional single-IRS aided MIMO system, thanks to the cooperative passive beamforming gain brought by the double-reflection link and the spatial multiplexing gain harvested from the two single-reflection links