Error Vector Magnitude as a Performance Measure for Advanced Modulation Formats

Real-time OFDM transmitters breaking the 100 Gbit/s barrier require high-performance, usually FPGA-based digital signal processing. Especially the Fourier transform as a key operation of any OFDM system must be optimized with respect to performance and chip area utilization. Here, we demonstrate an alternative to the widely adopted fast Fourier transform algorithm. Based on an extensive yet optimized use of pre-set look-up tables, our FPGA implementation supports fast reconfigurable channel equalization and switching times in the nanosecond range without re-loading any code. We demonstrate the potential of the concept by realizing the first real-time single polarization OFDM transmitter generating a 101.5 Gbit/s data stream by modulating 58 subcarriers with 16QAM.