Hybrid cooperation selection with llr-based switching threshold for opportunistic system

In this paper, we consider adaptive cooperation and relay selection for opportunistic system. A novel hybrid opportunistic cooperation strategy with log likelihood ratio (LLR) threshold is proposed in order to combat error propagation. Firstly, we combine the proactive and reactive opportunistic relaying by employing specific LLR switching thresholds, according to which the best relay and the corresponding transmission mode are selected dynamically. The approximate closed-form bit error rate (BER) expression is derived with the assumption that only one relay exists, and then the thresholds are optimized accordingly, which can be calculated in distributed manner with low complexity. Simulation results show that our proposed scheme can efficiently avoid error propagation and outperform conventional scheme. Besides, the effectiveness of the optimized thresholds is also validated.