# An Interference Cancellation Scheme for High Reliability Based on MIMO Systems
## 4 Simulation Results  
This section shows simulation results for bit error rate (BER) performance and complexity of the proposed scheme. The simulation parameters are shown in Table 3. Specifically, the loss of power for received symbol according to the distance from a node to a node is considered and it is represented as \(L\) as follows,  
\[L=\sqrt{10^{PL/10}}, \tag{20}\]  
where \(PL=-10p\log_{10}d\) denotes path loss where \(d\) is distance from a node to a node and \(p\) is path loss exponent which is set to be 3 in this simulation. Figure 3 shows BER performances with respect to SNR for the conventional FIC and the proposed scheme. The distances from a source to a relay, a relay to a destination, and one relay to another relay are normalized to 1. Also, the BER performances which use the ML at a relay for IRI cancellation are also shown. The proposed scheme has very higher BER performance than the conventional FIC because a relay transmits symbol which does not include interference symbol from another relay. However, a relay of the conventional FIC transmits symbol which includes interference and it makes hard to decode the received symbol at a destination and makes error performance degradation. Also, the proposed scheme obtains spatial diversity gain compared to the conventional FIC. Finally, the proposed scheme has the same BER performance as ML because low-complexity QRD-\(M\) has optimal error performance. Figure 4 also shows BER performances with respect to SNR for the conventional FIC and the proposed scheme. The main difference compared to Figure 3 is that the distances from one relay to another relay are normalized to 0.1, 0.3, 0.6 and 0.9. The BER performance for the conventional FIC is degraded with respect to decreased distance because the power for interference symbol is increased when the distance between relays is decreased and it makes severe error propagation at a destination. However, the BER performance for the proposed scheme is increased with respect to decreased distance. At a relay, the low-complexity QRD-\(M\) detects the received symbol in order of higher post SNR and cancels it from the received symbol. That is, the interference symbol is previously cancelled from the received symbol and desired symbol is cancelled later because the power for interference symbol is higher than the power for desired symbol when the distance rate is lower than 1. After the cancellation of the interference symbol, post SNR for the system is increased and it leads to increase of the error performance with respect to decreased distance. Also, the rate of degradation for the BER performance of the proposed scheme is lower than the conventional FIC because the \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Scheme or Values** \\ \hline FFT size & 128 \\ GI size & 32 \\ Modulation scheme & 256-QAM \\ Channel model & 8-path Rayleigh fading channel \\ Channel coding \& Constraint length & 1/2 convolutional code \& 3 \\ The number of antennas at source, relay, and destination & 2 for each node \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The simulation parameters. Figure 5 shows the required value of SNR to obtain targeting BER performance of \(10^{-3}\) with respect to the distance from a source to a relay. The distances from a relay to a destination and one relay to another relay are normalized to 1. The difference for the distance between the conventional FIC and the proposed scheme is more than 2.5 for certain required value of SNR. So, the proposed scheme has more than 2.5 times of transmission coverage compared to the conventional FIC. Table 4 shows the complexity for the conventional FIC and the proposed scheme at a destination. The variable \(N\) which is more than two is the number of used antennas. For comparison of the complexity, the number of complex additions, multiplications and divisions is shown.