Modelling and optimization of receiver oriented multi-user MIMO downlinks for frequency selective channels

This paper focuses on mobile radio downlinks in which an access point (AP) supports a number of mobile terminals (MTs). As a special feature of the considered downlinks, both the AP and each MT are equipped with multi-antennas so that each of the partial downlinks from the AP to one of the MTs has a MIMO (Multiple Input Multiple Output) structure, and the total downlink is one of the type multi-user MIMO. First, a generic mathematical model for such downlinks was developed, which allowed the inclusion of frequency selective channels. Then, receiver oriented multi-user MIMO downlinks were introduced which were characterized by the fact that, in contrast to conventional downlinks, the algorithms to be utilized in the receivers were a priori determined, whereas the transmitter algorithms resulted a posteriori based on the receiver algorithms and on channel state information. The rationale behind receiver orientation implies the opportunity to transfer implementation complexity from the MTs to the AP and was specially suited for mobile radio systems utilizing the duplexing scheme TDD (Time Division Multiplexing). A favorable choice of the receiver algorithms was proposed, and the theoretical findings were completed by some illustrative simulation results.