Multirelay cooperative relaying enables spatial diversity, often at the expense of spectral efficiency. To alleviate the loss in spectral efficiency due to half-duplex relaying and transmission over orthogonal channels, we propose a novel transmission scheme for selective decode-and-forward (DF) networks. In this scheme, we assume that destination may receive signals from transmitting nodes with different modulation levels. Particularly,we obtain a closed-form expression for both end-to-end (E2E) average error probability and spectral efficiency in such a scheme. Subsequently, using these closed-form expressions and average channel statistics, we perform joint optimization of power allocation and modulation level selection to maximize the E2E spectral efficiency while maintaining a target E2E average error probability and a set of transmit power constraints. Simulation results demonstrate that the transmission scheme proposed herein improves the E2E spectral efficiency significantly, in comparison with the conventional adaptive DF transmission scheme.

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Keywords Adaptive modulation, Cooperative diversity, Selective relaying
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Journal IEEE Transactions on Vehicular Technology
Sokun, H.U. (Hamza Umit), & Yanikomeroglu, H. (2017). On the spectral efficiency of selective decode-and-forward relaying. IEEE Transactions on Vehicular Technology (Vol. 66, pp. 4500–4506). doi:10.1109/TVT.2016.2607159