Modeling of DF behavior and SNR evaluation for multinode cooperation system with adaptive modulation under different diversity combining strategies

Cooperative communication has been drawn much attention recently due to the benefit of diversity; however, this technique also reduces the spectral efficiency. To aim at this problem, adaptive modulation is a possible remedy to achieve better efficiency especially for the multinode cooperative communication system. In this work, the Gilbert channel model is adopted to emulate the behavior of the decode-and-forward protocol at the relay nodes. At the destination node, three commonly used combining methods are evaluated, such as the maximum ratio combination (MRC), the equal gain combination (EGC), and the pre-weighted maximum ratio combination (Pre-MRC). The mathematical analysis of the total SNR of each case is also conducted, including the exact results for MRC and proper upper bounds for EGC and Pre-MRC. Based on this analysis, the improvement of multinode cooperation is validated. Meanwhile, the diversity benefit of this system will be also studied via the comparison with the traditional multiple-input single-output (MISO) system.