###### Abstract  
For next generation wireless communication systems, high throughput, low latency, and large user accommodation are popular and important required characteristics. To achieve these requirements for next generation wireless communication systems, an in-band full-duplex (IBFD) communication system is one of the possible candidate technologies. However, to realize IBFD systems, there is an essential problem that there exists a large self-interference (SI) due to the simultaneous signal transmission and reception in the IBFD systems. Therefore, to implement the IBFD system, it is necessary to realize a series of effective SI cancellation processes. In this study, we implemented a prototype of SI cancellation processes with our designed antenna, analog circuit, and digital cancellation function using an adaptive filter. For system implementation, we introduce software-defined radio (SDR) devices in this study. By using SDR devices, which can be customized by users, the evaluations of complicated wireless access systems like IBFD can be realized easily. Besides the validation stage of system practicality, the system development can be more effective by using SDR devices. Therefore, we utilize SDR devices to implement the proposed IBFD system and conduct experiments to evaluate its performance. The results show that the SI cancellation effect can reach nearly 100 dB with \(10^{-3}\) order bit error rate (BER) after signal demodulation. From the experiment results, it can be seen obviously that the implemented prototype can effectively cancel the large amount of SI and obtain satisfied digital demodulation results, which validates the effectiveness of the developed system. full-duplex (FD) communication; in-band full-duplex (IBFD) system; self-interference (SI); interference cancellation; adaptive filter; system implementation +
Footnote †: This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ([[https://creativecommons.org/licenses/py/](https://creativecommons.org/licenses/py/)]([https://creativecommons.org/licenses/py/](https://creativecommons.org/licenses/py/))). Footnote †: This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons. possible 6G technologies. For example, non-orthogonal multiple access (NOMA) is one of the key technologies that is usually considered to incorporate with IBFD [3,4]. Therefore, as a possible candidate technology for next generation wireless communication systems, there are many research groups focusing on the realization of FD systems [5; 6; 7; 8; 9; 10; 11; 12; 13; 14], or designing communication techniques for different wireless communication systems based on FD system assumptions [15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25]. For example, in [6], the research group implements a prototype of IBFD system, which is a very famous prototype research of the IBFD system. In [15], the authors design a medium access control (MAC) protocol for the IBFD communications in cognitive radio systems. In [21], the authors provide a non-orthogonal beamforming method with IBFD communications for multiuser (MU) multiple-input multiple-output (MIMO) systems. In [23], the authors investigate secure communications in FD device-to-device (D2D) networks. In [24], the authors adopt FD communications in dual-functional radar systems. Among the plentiful IBFD-related studies, there is an essential and inevitable self-interference (SI) problem, which must be well handled when implementing IBFD systems. In the IBFD system shown in Figure 1, because the uplink (UL) and downlink (DL) communications happen simultaneously at the base station (BS) in the same frequency band when operating IBFD communications, there will be a severe self-interference problem caused in the system.