Joint use of hierarchical modulation and relays in OFDMA networks

Relays are typically used to convey information to users who are unable to decode the direct signal from the base station successfully. In the case where the users are able to successfully decode the direct signal without the help of relays, the use of the latter can only decrease their performance because they will consume, uselessly, additional resources. If, however, hierarchical modulation can also be jointly used, the overall performance of a relay-based system can be enhanced even if the users are able to decode the direct signal successfully, without the need for relays. And this is the rationale behind this paper where we study the joint use of hierarchical modulation and relays, and model such a setting for a dynamic user configuration at the flow level. We validate our model against simulations and quantify the gains thus achieved in comparison with a system without relays, with and without hierarchical modulation.