Enabling real-time feedback for LTE measurements with the Vienna MIMO Testbed

The ever increasing demand for higher mobile data rates continues to rise challenges for researchers and developers. As the the available spectral resources remain essentially the same, the key to higher data rates lies in improving spectral efficiency. Multiantenna techniques are one of the most important technologies to enhance spectral efficiency, enabling the transmission of multiple spatially separated data streams as well as increasing the receive signal quality, which in turn allows for higher data rates. Predecessor technologies such as WiMAX1 and HSDPA2 begun to support multiantenna techniques as well as adaptive modulation and coding. Following this trend, recent standards such as LTE3 and LTE-A4 continue to support more antennas and modulation and coding schemes. Hence, whereas a brute force approach of transmitting and evaluating all possible signals was feasible for those legacy systems, the amount of differently modulated, coded and spatially preprocessed signals exceeds practical limits in the case of LTE and LTE-A. In order to still characterize the throughput performance of LTE and LTE-A MIMO5 systems by means of measurements, the channel state needs to be evaluated and fed back in a real-time fashion. Based on this feedback, the transmitter can determine the appropriate parameters and transmit only the signal that best matches the current channel state. Throughout this thesis, the Vienna MIMO Testbed, which has been used to measure various mobile communication standards in the past, is augmented by a feedback mechanism for LTE and LTE-A. The thesis specifies the key requirements for such a system and describes the implementation in form of a software extension. Finally, measurement results indicating the consistency and validity of the proposed system are presented. More over, the results provide novel measurement-based performance figures for LTE-A systems. 1Worldwide Interoperability for Microwave Access 2High Speed Downlink Packet Access 3Long Term Evolution 4LTE-Advanced 5Multiple InputMultiple Output