Efficient feedback mechanisms in mobile narrowband multicast scenarios

Link adaptation algorithms are utilized in communication systems to increase the spectral efficiency or robustness by adapting transmission parameters to the channel conditions. Closed-loop link adaptation requires feedback from the receivers which can lead to high signalling overhead especially in multicast/broadcast communications. In this paper, two efficient feedback mechanisms for link adaptation in multicast/broadcast service are proposed and investigated in a mobile ad-hoc network (MANET) for search and rescues missions. The constraint on the system is to transmit two service classes in parallel, voice and data. Considering intelligibility of voice transmissions in multipath channels, the proposed mechanisms outperform state-of-the-art feedback mechanisms in nearly all considered mobile multicast scenarios. Compared to a full feedback report approach, the proposed mechanisms yield an increase in the amount of additional successfully transmitted bits by 32% while meeting low outage constraints.