Hiyerarşik kipleme kullanılan işbirlikli haberleşme sistemlerinde çeşitleme kazancı incelemesi

In cooperative communication, hierarchical modulation is used both to increase the robustness of the system by minimizing the BERs and to send different information bits simultaneously. In cooperative communication which uses hierarchical modulation, error propagation is the most important problem that prevents achieving full diversity gain such as in the other cooperative communication systems. Thresholds that depend on the SNR value between the source and the relay can be used to mitigate the error propagation. If the SNR between the source and the relay is lower than the first threshold, the relay doesn't transmit the signal. If the SNR is between the first and the second threshold, the relay demodulates and transmits only the primary bits. If the SNR is higher than the second threshold, the relay demodulates and transmits both the primary and the secondary bits. At the destination, the signals coming from the source and the relay can be combined by using Maximal Ratio Combining (MRC).In this study, it is shown that with a single relay, diversity order of 2 can be achieved for both primary and secondary bits. Mitigating error propagation and achieving full diversity for all bits depend on setting the thresholds at the relay properly. It is proven that first and second threshold of the form c1log(SNR) and c2log(SNR) (c_1 < c_2$), achieves full diversity gain. Analytical and simulation results are provided to verify the analysis.