Generalized 8-PSK for totally blind channel estimation in OFDM

Channel estimation in OFDM systems can conveniently be done by inserting a stream of pilot symbols at the transmitter and by using FIR interpolation filters at the receiver. The drawback of this method is the decrease in spectral efficiency due to the pilot symbols. Alternatively, blind channel estimation makes pilot symbols unnecessary. Most blind channel estimation approaches are based on higher order statistics and converge slowly, making them unsuitable for mobile environments. Moreover, the channel estimate suffers from a phase blindness, which can only be resolved by pilot symbols. The concept of totally blind channel estimation makes pilots completely unnecessary, and even works in rapidly time varying environments. This is achieved by using two different modulation schemes, such as QPSK and 3-PSK, on adjacent subcarriers. We further develop the concept of totally blind channel estimation by applying a regular 8-PSK and a generalized 8-PSK to achieve totally blind channel estimation without the need for any pilot symbols. We enhance the original receiver design by applying a two-dimensional a posteriori probability (APP) calculation algorithm. We evaluate our system at high Doppler frequencies with COST 207 channels on the basis of extrinsic information transfer (EXIT) and BER charts.