Research Of Blind Interference Alignment In Interference Mitigation

In multi-user multiple-input multiple-output(MU-MIMO)communication systems,interference among users always degrades the overall performance.In order to mitigate inter-user interference,orthogonal multiple access schemes are frequently applied,for example,frequency division multiple access(FDMA)and time division multiple access(TDMA).In this way,channel resources like frequency and time are split and assigned for each user,which leads to low utilization of the precious channel resources.In recent years,the topic of interference alignment(IA)has received considerable research interest.Interference alignnment schemes can constrain interference signals into a smaller subspace at the receiver and keep desired signals distinguishable at the same time,which eventually increases the overall degrees of freedom(DoF)of the communication system.Blind interference alignment seeks to align the interference without channel state information at the transmitter(CSIT).In this thesis,we propose a semi-blind interference alignment scheme suitable for downlink frequency selective channels and a blind interference alignment scheme applicable to asymmetric multi-cell multiple-input multiple-output(MIMO)systems.Firstly,the research background is introduced with an emphasis on the advantage of interference alignment and blind interference alignment in terms of degrees of freedom.Secondly,the fundamental theory of interference alignment,semi-blind interference alignment and blind interference alignment is illustrated.Then,a semi-blind interference alignment scheme in two-user downlink frequency selective channels is proposed,which utilizes the frequency selectivity structure to align interference without precise channel coefficients at the transmitter nor reconfigurable antennas at the receiver.Compared with traditional schemes to control interference,such as FDMA,the proposed scheme achieves a higher DoF.This thesis also proposes a blind interference alignment scheme in asymmetric MIMO channels.By carefully designing the transmit pattern and employing reconfigurable antennas at the receiver,the system can achieve a remarkably improved DoF,which means the throughput of the proposed scheme is improved compared with conventional interference control schemes such as TDMA.Furthermore,in both of the proposed schemes in this thesis,users can achieve a good diversity gain to combat with fading.