Performance analysis of future wireless communication systems under residual hardware impairments

Abstract

The widespread proliferation of wireless services in daily life has boosted the demand for very high data rates. This plunge in data rate leads to an increase in energy consumption. As a result, in order to meet the enormous demand, next-generation wireless networks must be spectrally and energy-efficient. Full-Duplex (FD) systems have the potential to double the spectral efficiency (SE) of current half-duplex (HD) communication systems. The FD system utilizes the same time-frequency resource for both transmission and reception. Likewise, intelligent reflecting surfaces (IRSs) have recently been proposed as a passive FD technique that could achieve the aforementioned sustainable growth goals of high energy efficiency (EE) and high SE. Inherently, IRS is a large surface comprising of tiny low-cost reflective elements (REs) that can modify the phase and amplitude of the reflected wave. The multiple reflected paths get coherently added to enhance the received signal power. Since the IRS passively reflects the incident signal, there is no RF chain, resulting in a considerable reduction in energy consumption. Thus, with its low cost and low energy usage, IRS is expected to play a crucial role in the beyond 5G wireless networks. Commercially, low-grade transceiver hardware is frequently used in modern communication systems to reduce the cost of prospective networks. It is critical to take into account the impact of hardware impairments (HIs) caused by low- quality transceiver hardware while designing and developing reliable communication systems. These transceiver HIs cause residual self-interference (SI) in the FD systems. Likewise, these transceiver HIs saturate the SE for the IRS-assisted systems. In addition, the HIs in IRS-assisted systems also arise due to the inability of infinite precision of the IRS phase shifts. Consequently, the impact of HIs should be considered while analyzing the performance of FD/IRS-enabled wireless communication systems, and this motivates the work done in this dissertation. The first part of this dissertation analyzes the impact of residual SI on the performance of FD-based wireless systems. Further, the SI has also been utilized for recycling energy, commonly referred to as self-energy recycling (S-ER). S-ER improves the overall EE of the FD system. The proposed work also provides valuable insights on the impact of the antenna allocation for S-ER. The analytical formulation derives closed-form expressions for the EE, SE and outage probability (OP). In addition, we have also proposed an adaptive antenna allocation scheme based on transmit antenna selection (TAS), which compensates for the reduction in antenna array gain and consequently improves the SE and OP while enhancing the EE. In the second part, the performance of IRS-assisted wireless systems is analyzed under the impact of transceiver HIs. Specifically, in the presence of non-ideal hardware at the base station (BS), IRS and users, the performance is evaluated by deriving the closed-form expressions for the OP, SE and EE. The results show the importance of modeling and compensating for hardware impairment as they significantly restrict the performance of such systems. Further, the results show that although the IRS phase error degrades the performance, the transceiver HIs severely limit the system performance. Moreover, regardless of the number of reflecting elements (REs), transmit power, phase error and fading parameter, the transceiver HI imposes a finite limit on the SE, which cannot be further enhanced. In the end, this dissertation presents the performance comparison of an IRS-assisted wireless communication system with the FD relay-assisted system in the presence of a transceiver HIs. Specifically, the performance is compared in terms of SE and EE. The results show that the IRS can never achieve more SE than the ideal FD relaying in the presence of a non-ideal transceiver, irrespective of the placement of the IRS and FD relay. The frameworks proposed in this dissertation can be efficiently utilized in various wireless standards. They will be helpful for a communication engineer to design a link budget for FD/IRS-based wireless systems without performing extensive simulations or tedious experi- ments.