## 6 Results and Discussion
### Performance Comparison between CMI and R1 for Turbo Coded OFDM in AWGN Channel
Performance Comparison of Turbo Coded OFDM with MIMO (2 \(\times\) 2) Antennas in Coded Cooperation  
The Monte Carlo simulated results of turbo coded OFDM with MIMO (2 \(\times\) 2) scheme in cooperation is shown in Figure 9. In coded cooperation the relay-R has been given an additional gain of 1 dB relative to source-S. The S-R channel is assumed to be an ideal channel i.e., complete noise less channel. The CMI of length \(L\) = 1024 bits is applied to both cooperation and noncooperation (turbo coded OFDM with MIMO (2 \(\times\) 2)) schemes. The code rate \(R_{c}^{o}\) for both the compared schemes are kept as 1/3. The turbo coded cooperative OFDM with MIMO (2 \(\times\) 2) scheme in BPSK outperforms its counterpart non-cooperative scheme under identical conditions as expected. The proposed cooperative scheme in BPSK achieves a significant gain of 1.5 dB at BER of 2 \(\times\) 10\({}^{-8}\) over its non-cooperation counterpart. Both the schemes effectively reach their error floor region due to the insertion of the CMI. However, the proposed cooperation scheme with the CMI reaches the error floor at BER of 9 \(\times\) 10\({}^{-8}\) which signifies its improvement in error floor region. Similarly, the turbo coded cooperative  
Figure 8: BER performance of turbo coded OFDM with MIMO (2 \(\times\) 2) antennas over Rayleigh fast fading channel, \(L\) = 1024 and four decoding iterations. Figure 9: BER performance of turbo coded OFDM with MIMO (2 \(\times\) 2) antennas in coded-cooperation and non-cooperation based on CMI, \(L\) = 1024, four decoding iterations. OFDM with MIMO (2 \(\times\) 2) scheme with QPSK modulation performs better than its counterpart in non-cooperative scheme. The proposed cooperative scheme achieves 1 dB gain in SNR at the BER of \(5\times 10^{-7}\) relative to non-cooperative scheme with QPSK modulation. The proposed cooperative scheme in 16 QAM modulation achieves 1 dB gain in SNR relative to its counterpart non-cooperative scheme. The BER curve of the cooperation scheme exhibits steeper behavior than those of non-cooperation scheme. The performance can be further improved with an increase in the SNR. The improvement in BER is due to the fact the large diversity gain has achieved in the proposed cooperation scheme that contributes to the low bit error performance as the SNR increases. The Figure 10 presents Monte Carlo simulated BER performance comparison of our proposed coded cooperative scheme under different code rates. More specifically, the CMI-based turbo coded cooperative OFDM with MIMO (2 \(\times\) 2) antennas scheme is punctured to achieve the half code rate i.e., \(R_{c}^{o}=1/2\). Thus, the BER performance of our coded cooperative scheme reduces roughly by 1 dB. As in the case of punctured coded cooperative scheme, the puncturing operation takes only one parity bit at a time and discards other parity bit [16]. Therefore, the BER performance of punctured turbo coded cooperative OFDM with MIMO antennas scheme is reduced significantly. However, by reducing the code rate \(R_{c}^{o}\) the overall latency and the bandwidth of the transmission system is improved.