Pilot overhead reduction in turbo coded OFDM systems employing an iterative channel estimation under low signal-to-noise ratio environments

The authors evaluate the improved energy and spectral efficiency by pilot overhead reduction of turbo coded orthogonal frequency division multiplexing (OFDM) systems employing an iterative phase estimation algorithm. Developed from the recently proposed iterative phase estimation schemes, the phase estimation and compensation process is embedded into the basic iterative turbo decoding process for the application to OFDM systems with just a slight complexity overhead. At each decoding iteration, sub-carrier phase rotations are estimated from the extrinsic information arranged in each sub-carrier and are compensated for the next decoding iteration. This enables the iterative phase estimation algorithm to successfully work under very low signal-to-noise ratios even without pilot symbols. The pilot symbols are just very rarely inserted only for breaking the erroneous phase estimation propagation frame to frame in case of large residual phase offset beyond reliable decoding range. Simulation results show that the iterative phase estimation algorithm drastically reduces the pilot insertion overhead and thus, it achieves improved spectral efficiency as well as bit error rate (BER) performance by saving pilot energy compared to the conventional method.