## 4 Experimental Evaluation
### Discussion  
In the subsections above, we show the SI cancellation performance of each stage of our IBFD prototype implementation. The experimental evaluated results of the SI cancellation are summarized and listed in Table 3. Besides the results obtained from the experiments in this study, we also listed some benchmark works in Table 3. Here, we list the implementation works of IBFD systems in [5; 6], together with our previous work [31] for comparison. In [5], the authors also implemented an IBFD system with an antenna, RF front-end analog SI cancellation, and digital SI cancellation. In [6], the authors implemented an IBFD system using a signal generator as TX and a spectrum analyzer as RX. Between TX  
Figure 16: BER results. Figure 15: CDF of the EVM results. and RX they designed and realized a two-stage SI cancellation method consisting of analog and digital cancellation. Comparing the SI cancellation in the antenna stage, in [5] the TX and RX antennas are placed with half-wavelength distances so that the TX and RX signals can be orthogonal, which provides a 20 dB antenna SI cancellation effect. However, the performance of this method is essentially affected by the signal frequency and cannot be applied in wide band systems. On the other hand, the antenna designs in [31] and this study are targeting at more than 100 MHz wide band signals and provide around 31 dB and 47 dB Si cancellation effects, respectively. About the performance of the ACs, although the proposal in [5] adopts a circuit available on the market but in [31] a self-designed feed through circuit is used, they both provide about 30 dB analog SI cancellation performance. In [6], only analog SI cancellation is realized with a sinc interpolation algorithm, which results in a total 62 dB SI cancellation performance. In this study, although the AC provides merely 22 dB SI cancellation performance, but its frequency response is more stable and balanced than the proposal in [31]. In addition, although the proposal in [6] only realizes SI cancellation in analog and digital parts, we can still exam the performance at the analog output for a comparison. The SI cancellation results at the analog output, i.e., SI cancellation of \"Antenna + Analog\", are also listed in Table 3. From the results of \"Antenna + Analog\" it can be seen that the proposals in [6; 31] are both capable of providing about 60 dB SI cancellation at the output of analog stage, but the proposal in [5] can provide only about 50 dB. However, the proposed scheme in this study can provide about 70 dB SI cancellation performance, which outperforms all other proposals. In the digital part, the proposal in [5] applies coherent detection to detect the received signal and then suppresses the SI component that is known at the BS side. This is a straightforward way that can provide 10 dB SI cancellation performance. In our previous work [31], the AF-based digital SI cancellation provides 24.0 dB SI reduction, and in this study the digital part can provide 30.0 dB SI cancellation performance because of better signal-to-interference-plus-noise radio (SINR) of the received signal due to better analog and digital front-end processing. In [6], the authors carefully analyzed the linear and non-linear parts of the residual signal from the analog part, and then designed a special digital filter to cancel the residual SI from the analog part, which results in an impressive 48.0 dB SI cancellation performance. However, the digital solution in [6] is a static way that is hard to deal with in dynamic channels. On the other hand, our AF-based proposal provides a solution that can process signals in changing channels. It is noted that there are some related issues that can be extended for this study. Firstly, although in this study only QPSK is implemented, higher order modulations can also be applied under the infrastructure provided in this study, and their performance can be inferred by the SINR variations revealed in [6].