Testbed implementation of a MIMO-OFDM data link at sub 6 GHz frequency bands using an SDR platform

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Electrical and Electronics Engineering, Turkey

Approval Date: 2018




Studies in recent years concentrate on multiple input multiple output (MIMO) systems because of spectral efficiency and diversity advantages. In MIMO systems, a technique called orthogonal frequency division multiplexing (OFDM) is highly preferred since it turns wideband frequency selective channel into narrowband flat channels. Hence, the signal can be represented in time, frequency, and space with MIMO-OFDM. This brings a huge advantage on both multiplexing and diversity. Because of its popularity in the last decade, people are studying various algorithms for MIMO-OFDM systems and they always need a testbed platform in order to test and validate the algorithms in a real environment. In this study, a testbed for MIMO-OFDM data link is implemented by using software defined radio (SDR) devices working at sub-6 GHz. First, a physical layer (PHY) for MIMO-OFDM data link is designed including various synchronization, estimation, equalization, and detection algorithms. Additionally, a MIMO-OFDM simulator is implemented in MATLAB in order to test and verify the performance of PHY in different channel conditions also by taking into account some RF impairments that are modeled in simulation environment. Second, a MIMO-OFDM testbed is implemented with SDR devices. For transmit signal generation and demodulation operations our MATLAB simulator is used. However, for signal transmission and acquisition with SDRs, GNU Radio software is used in Python environment. Tests have been carried out at 3.5 GHz which is the foremost candidate frequency band in 5G standard. Our MIMO-OFDM data link PHY has been tested in various places including indoor and outdoor environments. Also, the channel at 3.5 GHz was measured for SISO and 2x2 MIMO scenarios in both indoor and outdoor environments. The characterization of the channel in static and dynamic conditions is investigated and discussed.