Investigation of hybrid digital/analog pre-distortion of GaN power amplifier

Abstract

People all over the world are increasingly enjoying the benefits of the rapid development of wireless communication. However, the rising number of these applications is leading to an increase in demand for spectrum services that compete with narrow band resources. One solution is to increase the availability band resources, but better use of the current bandwidth would be more efficient. The orthogonal frequency division multiplexing (OFDM) technique is used in fourth generation (4G) wireless networking and standard Wi-Fi. In an OFDM signal, the envelope signal is non-constant and it typically has a rise peak-to-average power ratio (PAPR), making it highly susceptible to distortion induced by nonlinear inline component response in transmission systems. Power is a concern in wireless applications where power amplifiers (PAs) are a primary contributor to power consumption at the transmission stage; PAs are also a significant factor in signal distortion. Modern wireless systems generally require a wide-band signal and a faster data rate, making them a significant issue for increased power consumption. These requirements also lead to the need for higher precision analog-to-digital converters (ADCs) and digital-to-analog converters (DACs). As a result, the system’s complexity increases due to increases in the hardware requirements. Pre-distortion linearization techniques are not only the most efficient but also the most promising of wireless communication technologies. However, both analog pre distortion (APD) and digital pre-distortion (DPD), when working alone, have complementary advantages and disadvantages, whereas when theywork together, they complement each other. Specifically, analog pre distortion can be very wide-band but limited in performance, while digital pre-distortion can provide excellent performance but cannot handle very wide-band signals. To overcome these problems, the hybrid pre-distortion approach is a well-known solution, but only a few studies in the literature have shown the technique’s performance. Of these few studies, none have examined the hardware requirements for ADC and DAC. In this context, a combined linearization method is proposed in this thesis. The method is called a hybrid digital/analog pre-distortion of the selected GaN PA based on conventional analog pre distortion and memory polynomial digitalpre-distortion (DPD) for a wide-band signal. The main aims of this approach are to achieve better linearization performance and to reduce the hardware requirements by using low-precision ADCs and DACs. This method enables shorter word-lengths to be used in the digital pre-distortion algorithm, saving both power and area when the technique is implemented. It also gives a higher sample rate for the entire digital pre-distortion algorithm (DPD). Advanced design system (ADS) and Simulink/MATLAB are used to perform this work. The results obtained show excellent agreement with the proposed wide-band signals hybrid approach, achieving the strongest third order intermodulation products (IMD3) and adjusted channel power ratio (ACPR) enhancement where they are suppressed. Additionally, the bit resolution of the target ADC in the proposed model is reduced to 8 bit.

Date	30 Mar 2021
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Ammar B. Kouki (Supervisor)