Interference Alignment Techniques in Multi-Antenna Wireless Networks

Abstract

Due to the broadcast nature of wireless networks, users that share the same channel resources may cause severe interference to each other. Such inter-user interference becomes a bottleneck for improving the performance of networks. Recent advances in wireless communication technologies, such as interference alignment, have brought us new insights on interference management in wireless networks. Many new results have been obtained for various networks, especially in terms of degrees of freedom (DoF). In this thesis, interference alignment techniques are further investigated in multiple-input and multiple-output (MIMO) X channel, MIMO interference channel, and device-to-device (D2D) network.

First, a two-user MIMO X channel is studied. It is known that with conventional linearspatial interference alignment, the maximum achievable DoF is the largest integer that smaller than D, where D denotes the outer bound of DoF of MIMO X Channels. In this thesis, a spatial interference alignment framework is proposed in combination with asymmetric complex signalling, whose achievable DoF is not less than D-1/2.

Second, the three-user MIMO interference channel is studied. The outer-bound of sum DoF of three-user interference channels has been already known, but the complete DoF region remains unknown. In this thesis, an outer-bound of DoF region of three-user interference channels is first derived. Then, a spatial interference alignment is proposed that can achieve all integer DoF inside the region. Hence, the region is both the sufficient and necessary condition for the feasibility of linear interference alignment.

The third work studies a MIMO D2D LAN underlaying a MIMO cellular uplink, where multiple D2D users (DUs) intend to communicate with a D2D receiver. Two D2D communication schemes are proposed to manage the interference between two networks. In the first scheme, the interference signals from DUs are aligned in the orthogonal signal space of cellular links. In the second scheme, the signals of DUs are allowed to span on some cellular links, but the peak power of interference is constrained under a certain threshold. Performance analysis shows that the interference generated on the cellular links is eliminated or well controlled, while the quality of service of the D2D LAN can also be guaranteed.