Receiver Location Sensitivity of Interference Alignment

Modern mobile communication systems are designed based on the cellular principle. The efficiency of such systems is primarily limited by interference from neighboring base stations at the cell edge. In recent years various schemes have been developed to minimize interference through base station cooperation. One such promising scheme is interference alignment (IA). Although theoretically well understood, measurement based evaluations are rare. Interference alignment (IA) relinquishes half of the available data streams of a mobile connection to align the interference in their subspace and promises an interference free transmission on the remaining data streams. IA uses linear transmit and receive filters and requires global knowledge of the communication channels to calculate these filters. Furthermore IA requires various assumptions regarding the communication channels and the communication network. An important assumption is that the radio channels remain constant from their measurement on to the transmission of the data. This thesis shows in a scientific, on modern communication systems based, measurement environment that practical channels allow the application of IA and presents measurements that show the impact of changing channels on the efficiency. First the theoretical basics and measurement methods of characteristic figures are summarized. Then the used measurement system, the Vienna MIMO testbed (VMTB), is specified. Differences to a commercial system are clarified and the developed software explained. Additionally the performance of IA under changing channels is quantitatively investigated with the use of mutual information.