In this letter, we study the problem of adaptive modulation (AM) in cooperative decode-and-forward (DF) relaying systems with limited channel state information (CSI) of the source-relay link. We first develop the signal-to-noise ratio (SNR)-based opportunistic AM and obtain the regions of the source-destination and relay-destination link SNR, by which whether cooperative relaying is needed and what constellation size should be chosen can be determined without requiring the source-relay link CSI. We also propose the probabilistic AM to further enhance the transmission rate. Simulation results demonstrate the effectiveness of the proposed AM criteria.
- Adaptive modulation
- Decode-and-forward protocol
- Multi-node cooperative communications