Optimal Waveform Design for Dual-functional MIMO Radar-Communication Systems

This paper considers the waveform design for dual-functional multi-input-multi-output (MIMO) radar-communication systems. Two optimization-based novel waveform designs are proposed. The aim of the first waveform design is to minimize the downlink multi-user interference (MUI) energy by exploiting the remaining degrees of freedom (DoFs) while always guaranteeing the radar performance to be optimal. The second waveform design is a trade-off optimization between radar and communication performances by allowing a tolerable mismatch between the designed and the desired radar beampatterns. Albeit non-convexity of both problems, efficient algorithms are devised to obtain globally optimal solutions, which can be used for simultaneous target detection and downlink communications. Numerical results show that the communication performance could be significantly improved by tolerating a slight radar performance loss and therefore a favorable balance between communication and radar performances is achievable

Multiple-Antenna Systems: From Generic to Hardware-Informed Precoding Designs

5G-and-beyond communication systems are expected to be in a heterogeneous form of multiple-antenna cellular base stations (BSs) overlaid with small cells. The fully-digital BS structures can incur significant power consumption and hardware complexity. Moreover, the wireless BSs for small cells usually have strict size constraints, which incur additional hardware effects such as mutual coupling (MC). Consequently, the transmission techniques designed for future wireless communication systems should respect the hardware structures at the BSs. For this reason, in this thesis we extend generic downlink precoding to more advanced hardware-informed transmission techniques for a variety of BS structures. This thesis firstly extends the vector perturbation (VP) precoding to multiple-modulation scenarios, where existing VP-based techniques are sub-optimal. Subsequently, this thesis focuses on the downlink transmission designs for hardware effects in the form of MC, limited number of radio frequency (RF) chains, and low-precision digital-to-analog converters (DACs). For these scenarios, existing precoding techniques are either sub-optimal or not directly applicable due to the specific hardware constraints. In this context, this thesis first proposes analog-digital (AD) precoding methods for MC exploitation in compact single-user multiple-antenna systems with the concept of constructive interference, and further extends the idea of MC exploitation to multi-user scenarios with a joint optimisation on the precoding matrix and the mutual coupling effect. We further consider precoding for wireless BSs with a limited number of RF chains, in the form of compact parasitic antenna array as well as hybrid analog-digital structures designed for large-scale multiple-antenna systems. In addition, with a reformulation of the constructive interference, this thesis also considers the low-complexity precoding design for the use of low-resolution DACs for a massive-antenna array at the BSs. Analytical and numerical results reveal an improved performance of the proposed techniques compared to the state-of-the-art approaches, which validates the effectiveness of the introduced methods