Interference Management in a Class of Multi User Networks

Abstract

Spectrum sharing is known as a key solution to accommodate the increasing number of users and the growing demand for throughput in wireless networks. Interference is the primary barrier to enhancing the overall throughput of the network, especially in the medium and high signal to noise ratios (SNRs). Managing interference to overcome this barrier has emerged as a crucial step in developing efficient wireless networks. An interference management strategy, named interference Alignment, is investigated. It is observed that a single strategy is not able to achieve the maximum throughput in all possible scenarios, and in fact, a careful design is required to fully exploit all available resources in each realization of the system. In this dissertation, the impact of interference on the capacity of X networks with multiple antennas is investigated. Degrees of freedom (DoF) are used as a figure of merit to evaluate the performance improvement due to the interference management schemes. A new interference alignment technique called layered interference alignment, which enjoys the combined benefits of both vector and real alignment is introduced in this thesis. This technique, which uses a type of Diophantine approximation theorems first introduced by the author, is deployed and was proved to enable the possibility of joint decoding among the antennas of a receiver. With a careful transmitter signal design, this method characterizes the total DoF of multiple-input multiple-output (MIMO) X channels. Then, this result is used to determine the total DoF of two families of MIMO X channels. The Diophantine approximation theorem is also extended to the field of complex numbers to accommodate the complex channel realizations as well.