ISI analysis in network MIMO OFDM systems with insufficient cyclic prefix length

We consider a cellular network MIMO OFDM system where cooperating base stations apply joint signal processing to the receive signals of several users. In this situation, due to geometry, the problem of unavoidable differences in time of arrival between the users´ signals occurs. As a result, symbol timing offsets can be larger than the cyclic prefix, which leads to OFDM inter-symbol interference. In addition to the multiuser interference, a coupling between adjacent subcarriers and consecutive OFDM symbols is induced in such scenarios. In this paper, we analyze the multi-user joint detection performance in systems with distance dependent asynchronous interference and pathloss environments for different channel delays as well as fixed cyclic prefix length. To this end we use an exact expression for the post equalization SINR that is used for the evaluation in numerical simulations. The system level cell setup considers two user positioning models based on a hexagonal cell geometry with varying cell radii.