Improper Gaussian signaling schemes for interference-limited communications

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This proposal aims at developing novel signaling schemes for interference-limited mobile communication networks. Already today, multiuser interference presents the major limiting factor of the end-to-end performance in wireless communications. In pursuit of efficient interference management schemes, current research focuses on interference coordination by means of a joint precoder design that exploits the channel state information.The vast majority of these works assumes that the transmitted signals are distributed as proper Gaussian random signals, which are known to be optimal when the system is not interference-limited. Recently, alternative signaling schemes that deviate from these standard assumptions have been proposed in the literature. It has been shown that the transmission of improper Gaussian signals, whose real and imaginary parts are correlated and/or have unequal power, outperform proper Gaussian signals in various interference-limited networks.This project will study improper signaling schemes for different interference-limited networks. It has the following objectives:- To provide insights on when improper signaling enables better performance than its proper counterpart. To this end, we will focus on single-antenna and partially connected interference channels, where the analysis is tractable and permits insights that can be extended to more general scenarios. - To design algorithms that optimize the transmission parameters for general interference channels. An improper signaling scheme contains not only the parameters associated with a proper scheme, but also additional ones that describe the impropriety of the signal, which makes the optimization more challenging.- To apply improper signaling to underlay cognitive radio scenarios, which can be regarded as a paradigm for low-cooperative multiuser networks. In these scenarios, the interference is managed by setting interference constraints, so that its effect can be upper-bounded and thereby require less cooperation. We will explore new interference constraints taking impropriety into account, as well as the optimization of the transmission parameters subject to these constraints.- To evaluate the performance of the devised schemes on a real hardware testbed. We will assess the impact of real-world impairments on the performance of improper signaling, such as channel estimation errors, imperfect synchronization, and dirty radio-frequency effects.