Research On Interference Alignment Under Limited Feedback For MIMO Interference Networks

Interference is a fundamental barrier in attempting to improve throughput in multiuser wireless communication systems.For the past few years,significant progress has been made on interference alignment(IA)of wireless networks under the premise of global and instantaneous channel state information at the transmitter(CSIT).However,achieving the theoretical degrees of freedom(DoF)gains in practice is highly challenging due to the strict constraints of CSIT.In many distributed networks with limited CSIT,the promising DoF gains collapse to the case where there is no CSIT.Is it possible to obtain DoF gains with limited CSIT in distributed interference networks? Based on multiple antenna technology,this dissertation lucubrates the IA technologies of multiple-input multiple-output(MIMO)interference networks,e.g.broadcast channel(BC),X network and interference channel(IC),thereby characterizing the tradeoffs between DoF and limited CSIT.The main contents of this thesis are summarized as follows:(1)For the 2?2 user MIMO X channel with symmetrical antenna configuration,we study the tradeoffs between the achievable sum-DoFs and CSI feedback delay.Firstly,we begin with the 2 ?2 user MISO X channel and show how many DoFs can be obtained by proposing a distributed precoding method.Secondly,we study the tradeoffs between achievable sum-DoFs and CSI feedback delay for the 2 ?2 user MIMO X channel by proposing a distributed space-time interference alignment(DSTIA)scheme with temperately-delayed CSIT,where an innovative precoding method called Cyclic Zero-Padding is exploited.Achievable sum-DoFs and sum-rates are further compared among different transmission schemes,yielding better achievable DoF gains than the best known sum-DoFs in literature with outdated CSIT.Thirdly,we demonstrate the achievable sum-DoFs under different antenna configurations by proposing a DSTIA scheme with alternating CSIT.The results show that the alternating CSIT framework is equivalent to the temperately-delayed CSIT model,which is suitable for the distributed scenarios.(2)For the M ?N user MIMO X network,we study the achievable sum-DoFs and IA schemes with multiple nodes and multiple antenna configurations.Firstly,to solve the DoF loss,we propose a novel multiphase interference regeneration(MIR)scheme based on symbolic elimination for the 2 ?2 user MIMO X channel.Subsequently,the achievable sum-DoFs under different CSIT patterns are analyzed and we show that the MIR scheme can obtain better sum-DoFs than DSTIA scheme for certain configurations,which asymptotically approach to the outer bound as the number of antennas increases.Secondly,from the perspective of transmitter and receiver,we investigate the multi-node extended interference alignment(ME-IA)schemes for the multiuser MIMO X networks,in order to break through the limitation of the number of transmitters and receivers.Specifically,the sum-Do Fs for the M ?2 user MIMO X channel are studied by proposing a ME-IA scheme at the transmitter based on MIR scheme.Furthermore,a ME-IA scheme at the receiver is proposed for the M ?N user MISO X network,while revealing the impact on how the CSI feedback delay,as well as the number of transmitters/receivers and the number of antennas affect the sum-DoFs of the MIMO X network.Theoretical and analytical results show that,the ME-IA scheme at the receiver can attain(or approximately approach to)the DoF outer bounds.Finally,we propose a multiphase distributed space-time interference alignment(MDSTIA)scheme for the M ?N user MIMO X network,where the decoding chain is carefully designed among receivers to make up the DoF loss and attain higher achievable sum-DoFs,as well as tighten DoF gap and improve the achievable rates of system.(3)For the multiuser MIMO interference networks with non-cooperation transmitters and limited CSI feedback,the achievable sum-DoFs and interference alignment schemes for the K-pair MIMO X network,K-user MIMO interference channel and K-user MIMO broadcast channel are studied respectively.Firstly,we propose a distributed retrospective interference alignment(DRIA)scheme for the K-pair MIMO X network with temperately-delayed CSIT.The interference at the receiver can be reconstructed and eliminated by creating new channel side information with the help of current and outdated CSIT,revealing that the DSTIA is no longer limited to the number of receivers(limited to 2)in the MIMO X network.In addition,the results show that DRIA scheme can achieve better sum-DoFs than TDMA scheme.Secondly,a DSTIA scheme with limited CSI feedback is proposed for the K-user MIMO IC,where new tradeoff regions between achievable sum-DoFs and CSI feedback delay/frequency are achieved for the MISO system.The impacts of the number of transmit/receive antennas on achievable sum-DoFs are also characterized respectively.Furthermore,we derive the conditions for approaching to the outer bounds as well as the range of CSI feedback that preserves achievable DoFs in the MIMO system.The results show that the proposed DSTIA scheme can achieve better sum-DoFs and tighten the gap between achievable sum-DoFs and outer bounds as the number of antennas increases.Finally,a generalized space-time interference alignment(GSTIA)scheme based on minimum time-slot criterion(MTSC)is proposed for the MIMO interference network with asymmetrical antenna configurations.A matching signal sending mechanism at the base station(BS)is carefully designed to ensure the interference-free decoding at the receiver,which sheds further insights into the relationship between the achievable sum-DoFs and the number of BS/user antennas.The IA design under asymmetrical antenna configurations is discussed for the first time,and results show that the sum-DoFs achieved by GSTIA scheme approximately approach to outer bounds as the number of antennas increases.