Adaptive beamforming and power allocation in multi-carrier multicast wireless networks
In the context of next-generation wireless systems, it is expected that services targeted at mass content distribution become widely popular, which is reflected for instance in the standardization activities for their implementation within current cellular networks. Examples of such services are audio/video streaming, mobile TV, messaging, news clips, localized services, download, among others. Their common characteristic is that the same information has to be transmitted to a group of users (multicast) or to all users (broadcast) within a certain coverage area.
This project deals with the problem of multicast beamforming for multi-antenna wireless cellular networks. Both single-group and multi-group scenarios are taken into account, with the former corresponding to a single multicast group per radio resource and the latter referring to multiple multicast groups per resource.
In order to provide the necessary mathematical framework for the analysis of the algorithms, a general system model is proposed for the multi-group multicast scenario. Particular cases, such as the multi-user, single-group, and single-user cases, can be derived from the general model by properly adjusting the system parameters. Different beamforming algorithms known from the unicast case are formulated for the single-group multicast case. Moreover, a new algorithm termed User-Selective Matched Filter (USMF) specifically designed for the multicast case is proposed, which is shown to provide a good trade-off between performance and complexity. For the multi-group multicast case, the resource sharing results in inter-group interference, which needs to be suppressed by the beamforming algorithms. Linear and non-linear algorithms known from the unicast case are formulated for the multi-group multicast scenario. These algorithms are also further modified with the purpose of improving the performance of the multicast services. The strategies proposed for both single-group and multi-group cases are analyzed in terms of their performance and computational complexity.
Finally, since the allocation of resources among the multicast groups is expected to have a significant impact on the performance of the beamforming algorithms, this issue is addressed as well. The analysis focuses on the proposal and evaluation of different alternatives for allocating the power among the subcarriers of a multi-carrier single-group multicast system. One of these alternatives is an extension of the traditional unicast waterfilling algorithm for the multicast case. Additionally, some considerations are made with regard to the allocation of resources in multi-carrier multi-group multicast scenarios. It is shown that, in spite of the inter-group interference, the sharing of resources among unicast and multicast users provides better performance than isolating them into different resources.