This thesis is concerned with certain aspects of two particular setups in which MIMO techniques may be implemented:
- Limited feedback in the MIMO broadcast channel: We consider the downlink of a single cell where the base station has multiple antennas. A particular issue when dealing with such a system is that of channel state information at the transmitter (CSIT): this has been shown to play a cardinal role, particularly in the case when users are equipped with single antennas. Given the importance of acquiring that CSIT, and the fact that this acquisition comes at the cost of using resources on the uplink direction and introducing delays, a large body of literature has been concerned with limited feedback schemes for this setup. In this thesis, we contribute two ideas to try to make the most of the available feedback resource: the first consisting of a two-stage approach to CSI feedback, the second being an adaptive feedback scheme under an average feedback rate per user.
- Coordination and Cooperation in multicell systems: The above model of a single cell may roughly correspond to current cellular designs where frequency planning is used to separate cells that use the same frequency resources so that the interference they generate at each other is limited. This is however not very efficient and MIMO techniques may be used to allow for increased performance at full reuse. Thus incorporating more antennas at a given base station gives it the possibility to mitigate the interference it causes at users in other cells. This is one of the topics we deal with in this thesis and propose a scheme which, while requiring local CSI only, is shown to perform quite well. MIMO techniques in a multicell environment can moreover be extended to multicell processing (MCP), whereby these can essentially act as a giant MIMO transmitter and jointly serve their users. This, however, comes at a significant cost in terms of backhaul for 1) data and 2) CSI sharing, which threatens the scalability of MCP. We begin to investigate how to deal with limitations related to both these aspects in wireless networks.