###### Abstract
Due to the huge amount of power difference between UL reception and DL transmission at BS, attenuating or canceling SI in IBFD systems would be a very difficult task. According to the famous pioneer work of IBFD system implementation provided in [6], realizing a basic IBFD system requires a roughly 110 dB SI cancellation effect, which is a very tough and challenging work for wireless communication system implementation. However, although SI cancellation is a difficult task to deal with, there are still some inspiring ideas proposed for IBFD system implementations. For example in [5], the authors provide design ideas with SI cancellation effect for IBFD systems. In [8; 9; 10; 11; 12; 13], the analog circuit (AC) design ideas and implementations for IBFD systems with SI cancellation function are provided. For digital processing of SI cancellation, in [6] the authors investigate the characteristics of the residual SI after the AC part and implement a fixed-type digital filter to handle it. In [25], a method based on game theory is provided to manage interference with imperfect SI cancellation in FD cellular systems. However, because the source of SI comes from the simultaneous DL transmissions at BS, it means the receiving process at BS can obtain the source information of SI, and utilize this information to cancel SI with digital methods [26; 27; 28; 29]. For SI cancellation work, adaptive filter (AF) is a suitable technique to deal with a kind of interference signal with a known interference source. Due to the simplicity of the computational structure, AF is a famous and useful signal processing technique. AF is usually used for applications like system identifications, inverse system identifications, predictions, and noise or interference cancellations, and so on. When being used for interference cancellation application, AF can significantly cancel the interference by training the known interference source signal to mimic interference signals with moderate computational resources. For example, in [30], the authors utilize  
Figure 1: Basic concept of IBFD system. analog AF to realize SI cancellation for FD systems. In our previous research [31], we also preliminarily investigated the potential and capability of the AF-based SI cancellation method in a digital way for an IBFD system and the results shows remarkable SI cancellation performance. There are some machine-learning-based methods that can be considered as advanced SI cancellation proposals like [32]. However, for implementation simplicity, in this study we adopt AF as a digital SI cancellation solution. Therefore, in this study, we extend our previous work in [31] by improving the constituent parts of the system implementation. We realized an IBFD system with improved antenna, analog, and digital processing functionalities. To effectively deal with the severe SI problem of IBFD systems, we carried out a three-stage SI cancellation method in our implementation. Firstly, in our designed antenna part, an antenna isolation effect is provided to suppress SI power. Secondly in AC we designed an adjustable filter circuit to cancel SI in an analog way. In the last stage, we implemented an AF-based SI canceller in the digital processing part to cancel the residual SI after antenna isolation and analog SI cancellation effects. To verify the performance of our implemented IBFD system, we conducted experiments to evaluate the SI cancellation function of each stage, and the final demodulation performance of the whole system. The contributions of this work can be summarized as follows. * An implementation of an IBFD prototype system is provided in this work. The implemented IBFD system is realized with three-stage SI cancellation, which consists of antenna isolation, analog cancellation, and digital cancellation by adaptive filter. * By conducting an experimental evaluation, it is known that the implemented three-stage SI cancellation provides a nearly 100 dB SI cancellation effect for the IBFD system implementation.