Physical Layer for Spectrum-Aware Reconfigurable OFDM on an FPGA

Orthogonal Frequency Division Multiplexing (OFDM) can provide a flexible usage of the spectrum by controlling individual sub carriers. Sets of sub carriers can be zero-modulated to avoid interfering narrowband primary users, making OFDM a strong candidate for Cognitive Radio implementations. This paper presents the design and implementation of a non-contiguous OFDM physical layer (PHY) capable of supporting arbitrary allocation vectors and spectrum sensing for cognitive radio applications. Least squares methods applied on an arbitrary set of pilot sub carriers are used to estimate and track the phase errors caused by residual carrier frequency offset and by non-ideal sampling frequency at the receiver. A full FPGA prototype was developed and evaluated using Virtex-4 devices, including over-the-air testing in the 2.05 GHz radio band.