The MIMONet Software Defined Radio Testbed

Software Defined Radios (SDRs) are radio communication systems where components that are typically implemented in hardware, such as filters, modulators, demodulators, etc., are instead implemented in software. GNU Radio is the most common and efficient software development toolkit that implements SDRs. It is open-source and provides the basic signal processing blocks that can be exploited to implement a SDR testbed, including usage of multi-antenna transmitters and receivers. GNU Radio can be used in combination with different hardware platforms, such as the Universal Software Radio Peripherals (USRPs) produced by Ettus Research$^{TM}$ and designed textit{with} GNU Radio, which we use in our testbed. This paper presents the setup and initial results of the MIMONet SDR testbed we are currently developing to test multi-antenna system performance at network level. In particular, in this paper we show the importance of appropriately tuning the physical parameters of a SDR testbed, such as transmitter and receiver power, central frequency, etc. As a test case, we compare a single-input single-output (SISO) OFDM communication link with a single-input multiple-output (SIMO) counterpart in terms of bit rate performance. The SIMO link is designed based on the Maximal Ratio Combining (MRC) of signals at the receiving end. MRC is a diversity technique, where signals coming from different receiver antennas are weighted and added together in order to obtain stronger signals compared to the one received by a single antenna. The experimental results collected using the SDR testbed indicate that: $i)$ the link quality improvement of SIMO vs SISO link are in accordance with theoretical predictions (3dB); and $ii)$ the improvement in bit rate given by a SIMO link depends on the modulation scheme used, and it can be as high as 400% with Quadrature Phase-Shift Keying (QPSK) modulation