Hardware Impairments Aware Transceiver Design for Bidirectional Full-Duplex MIMO OFDM Systems

In this paper we address the linear precoding and decoding design problem for a bidirectional orthogonal frequencydivision multiplexing (OFDM) communication system, between two multiple-input multiple-output (MIMO) full-duplex (FD) nodes. The effects of hardware distortion as well as the channel state information error are taken into account. In the first step, we transform the available time-domain characterization of the hardware distortions for FD MIMO transceivers to the frequency domain, via a linear Fourier transformation. As a result, the explicit impact of hardware inaccuracies on the residual selfinterference (RSI) and inter-carrier leakage (ICL) is formulated in relation to the intended transmit/received signals. Afterwards, linear precoding and decoding designs are proposed to enhance the system performance following the minimum-mean-squarederror (MMSE) and sum rate maximization strategies, assuming the availability of perfect or erroneous CSI. The proposed designs are based on the application of alternating optimization over the system parameters, leading to a necessary convergence. Numerical results indicate that the application of a distortionaware design is essential for a system with a high hardware distortion, or for a system with a low thermal noise variance.Comment: Submitted to IEEE for publicatio

Resource allocation for future wireless relay systems

In future wireless communication systems, full-duplex (FD) and massive multiple-input-multiple-output (mMIMO) are considered as two promising technologies to overcome capacity crunch and spectrum scarcity. Transmission and reception at the same frequency-time channel in FD and large antenna arrays in mMIMO systems improve the spectral efficiency to a great extent compared to current systems. To make mMIMO systems cost-efficient, inexpensive less-accurate transmit and receive chain components are preferred. This leads to hardware distortions, which in turn becomes unfavourable for self-interference (SI) cancellation in FD systems. In this thesis, our main goal is to design distortion-aware FD multi-antenna multi-carrier (MC) systems, from the aspect of resource allocation and the resulting system performance. Particularly the impact of distortions caused by hardware impairments, leading to residual self-interference and inter-carrier leakage as well as the imperfect channel state information is taken into account. Initially, we investigate the linear transceiver design problem for an FD multiple-input-multiple-output (MIMO) MC decode and forward (DF) relaying system. In addition to the traditional per-carrier DF relaying, the case with a joint-carrier DF is also studied, taking advantage of group-wise decoding and encoding. An alternating quadratic convex program is proposed for the resulting non-convex optimization problem, where a monotonic improvement at each iteration leads to a guaranteed convergence. Furthermore, we focus on the joint sub-carrier and power allocation problem for a DF relay system, where multiple half-duplex (HD) single antenna (SA) MC source-destination pairs communicate with the aid of an FD mMIMO MC relay. Apart from focusing on maximizing the sum-rate and energy efficiency, we also focus on minimizing the overall delivery time for a given set of communication tasks to the user nodes. Due to the intractable nature of the allocation problem, an iterative solution is proposed, employing the successive inner approximation framework, with guaranteed convergence to a point that satisfies the Karush-Kuhn-Tucker optimality conditions. This approach is then extended to a bi-directional communication system, where an FD mMIMO MC base station (BS) serves multiple FD SA MC nodes. Finally, we focus on the problem of resource allocation for an FD-enabled relaying system, where an mMIMO MC BS simultaneously activates the relay as well as the direct channel for communicating separate data streams to the user terminals. This is implemented by employing successive interference cancellation (SuIC) at the MC SA user terminals. Besides the superior performance under various system conditions, the proposed dual-connectivity enjoys higher robustness when one of the active paths experience an unexpected blockage. Numerical results show the significance of distortion-aware design for FD mMIMO MC systems, particularly in the presence of a strong SI channel or low-resolution hardware. Moreover, a notable gain is observed compared to its HD counterparts when SI is efficiently suppressed. In the case of dual-connectivity scenario, numerical results show the performance gain of our proposed SuIC scheme in terms of sum-rate compared to single-connectivity and HD schemes