Fundamental Impacts Of Delay And Deadline On Communications Over Wireless Networks

Abstract

Consumer demand for wireless networks has experienced an exponential increase in recent years, and such trend is expected to continue in the coming years. Therefore, there is a pressing need for more effective communication schemes to be able to cope with the explosive growth in the wireless demand. An important resource which can be very useful in developing more effective communications schemes is channel state information which is available at the transmitters (CSIT). CSIT is usually provided to the transmitters via feedback channels from the receivers. Timely and accurate CSIT has been shown to provide enormous theoretical gains in terms of communication rate. However, in most realistic scenarios, instantaneous and perfect CSIT is not feasible due to physical constraints on the feedback channel. Furthermore, the CSIT supplied by different receivers can often times be of different quality in terms of timeliness and accuracy, which results in networks with heterogeneous/hybrid CSIT. In this dissertation, we provide new tools and techniques to better understand and analyze the fundamental limits of wireless networks under practical CSIT constraints. In particular, we develop mathematical tools that capture the impact of various types of CSIT on the received signal dimensions at different receivers in a wireless network. We also show how the developed tools are used to solve a broad spectrum of problems in network information theory, from interference networks such as X-Channel with delayed CSIT, 3-user Interference Channel with delayed CSIT, Interference Channel with limited transmitter cooperation and delayed CSIT, and 2-by-k multiple-input single-output broadcast channel (MISO BC) with delayed CSIT, to various problems in informationtheoretic security, and finally, MISO BC under heterogeneous CSIT. The developed tools presented in this dissertation provide new insights on the impact of CSIT on the dynamics of wireless networks. Beside the significance of quality of CSIT in wireless networks, quality of service (QoS) requirements by the traffic also play an important role in the design of better communication schemes. The majority of increasing traffic volume over wireless networks is expected to be video, which is in most cases delaysensitive; i.e., packets should be delivered by a certain time, otherwise they will not be useful to the user. Therefore, we study fundamental limits of communicating delay-sensitive traffic over heterogeneous wireless networks, which are emerging structures in modern wireless networks. We provide approximate characterization of the timely throughput capacity of such heterogeneous wireless networks, and develop near-optimal algorithms.