WP4. Multi-user Optimal Transmit and Receive

This WP aims at the capacity evaluation and optimisation of multiple link transmissions in the context of a multiuser environment. Two basic multiuser configurations are considered, the Multiple Access Channel (MAC) and the Broadcast Channel (BC). The first one models the simultaneous transmission of many users to a single receiver whereas the second represents the simultaneous communication to different users from a single transmitter. They are commonly known as the uplink and downlink channels respectively.

Many problems associated with the capacity evaluation and transmission optimisation for this type of systems remain open. Specifically, those dealing with time varying and frequency selective channels, with multiple antennas at least at one of the sides of the link and with imperfect channel state information at either side of the links.

We will also study all potentialities offered by wideband multiple antenna transceivers for mitigating or possibly cancelling the interference, while at the same time, guaranteeing a desired QoS over the useful link. The system will operate over the joint space-frequency domain to find the best strategy to limit the interference and maximise the information rate, for a given power budget constraint. The code design will take into account the spatial as well as the temporal properties of the interference. Again, we will consider the case where the transmitter has some partial knowledge about the channel or no knowledge at all. In this WP, besides channel knowledge, it will be important to analyse methods to estimate the covariance matrix of the interfering signals. Then, depending on the accuracy of the channel and the interference covariance matrix estimates, the best transmission strategies will be investigated.

In addition to the optimisation described above, we will also address scheduling of users in time, frequency and space to further improve the performance in a time-variant, frequency selective fading environment. By simultaneously scheduling users that, according to the method above, give the instantaneously highest capacity in a time variant channel, the cell performance will be maximized. The interaction of advanced scheduling schemes, such as the Proportional Fair scheduler (PF), and MIMO transmission technologies and their optimisation for generic channel evolution and knowledge will be subject to detailed study within this WP.