An experimental study of OFDM in software defined radio systems using GNU platform and USRP2 devices

Orthogonal Frequency Division Multiplexing (OFDM) has been well examined in the literature via theoretical simulations. However, implementation of OFDM in actual hardware using Software Defined Radio (SDR) concepts and verification of its performance with different channel estimation methods in various propagation environments have been almost unexplored. The great flexibility feature of SDR systems facilitates the implementation and experimentation of OFDM systems with less cost and effort, compared to the implementation of the whole system in hardware. In this paper, a customized SDR testbed has been developed based on the GNU radio software platform and version-2 Universal Software Radio Peripheral (USRP2) devices to evaluate the practical error performance of OFDM-based systems in both Gaussian and Rician propagation environments. Three different channel interpolation techniques, namely linear interpolation, second-ordered interpolation and cubic spline interpolation, and a blind SNR estimation algorithm have been implemented in our testbed. The performances show that, as opposed to our intuition, linear channel interpolation in some cases might not only be simpler, but also more accurate than the two other non-linear interpolation techniques, implying that channels might change linearly between neighboring subcarriers. The experimental OFDM system on the developed SDR testbed performs very close to the simulated OFDM system, thus the developed testbed can be used to verify advanced signal processing techniques in OFDM systems in various realistic channels by simply developing software, without the need for otherwise complicated hardware developments.