Physical Layer Security In Multi-user Massive MIMO Systems

Massive multiple input multiple output(MIMO)has been extensively studied and considered as a key enabling technology for the future mobile communication systems due to its potential to achieve extremely high energy efficiency and spectral efficiency.On the other hand,it is also very likely to enable much more differences and greater independence between the main channel and wiretap channel,and make the channels themselves more random compared with traditional MIMO by exploiting a large number of excess service antennas at the base station(BS).This may bring huge benefits in facilitating secure communication at the physical layer and improving the performance of physical layer security technology.Massive MIMO physical layer security has the potential to simultaneously achieve high spectral efficiency,high energy efficiency,high reliability,good secrecy performance and low power consumption,which makes it a potential green secure transmission candidate technique for the future green secure wireless mobile networks.In this thesis,two massive MIMO secure transmission schemes for the downlink and uplink transmissions in time division duplex(TDD)multi-user massive MIMO system with perfect and imperfect channel estimations are proposed by well considering and combining the features of massive MIMO and physical layer security.One of them is called power-scaling aided secure transmission scheme,which exploits the powerscaling feature of massive MIMO to achieve considerable secrecy enhancement in facing eavesdroppers with limited antennas.Another method is called original symbol phase rotated secure transmission scheme,which makes the most of the large number of BS antennas to effectively defend against eavesdroppers armed with unlimited antennas.Both proposed secure transmission schemes have a good tolerance for channel estimation errors.The basic idea of power-scaling aided secure transmission scheme is to minimize the upper bounds on the achievable rates of the eavesdropper while meeting the rate constraints of legitimate users by applying optimal radiated power-scaling factors at the BS or legitimate users on the downlink or uplink transmission.The basic idea of original symbol phase rotated secure transmission scheme is to randomly change the phase of original symbols at the BS or users before the symbols are transmitted,so that the massive MIMO eavesdropper can only perfectly intercept the phase rotated symbols even in the best case,while the legitimate user or BS is able to infer the correct phase rotations and take the inverse operation to recover the original symbols on the downlink or uplink transmission.The implementation complexity of the two massive MIMO secure transmission schemes proposed in this thesis is low and the corresponding operations require modest signal processing and computational resource.They exploit the advantages of massive MIMO to improve the performance of physical layer security and make quantity turn into quality compared with traditional MIMO physical layer security in wireless communication systems.They spend no extra power on weakening the performance of the eavesdropper by adding artificial noise or jamming signal and can defend against powerful eavesdroppers by generating abundant randomicity for encrypting the original information bearing symbols,and have a good tolerance for channel estimation errors.They are suitable and potentially practical green secure transmission candidate techniques for future mobile communication networks.