Comparison of superimposed pilot schemes in iterative receivers for OFDM systems

Pilot-aided techniques are classically used to accomplish channel estimation in orthogonal frequency division multiplexing (OFDM) systems. However, those pilots occupy an important bandwidth which could have been allocated to data instead. Superimposed pilots have been proposed as substitutes to classical pilots and showed that with properly designed receivers, they are able to provide a satisfactory performance in terms of channel estimation and BER. Recently, a data nulling superimposed pilot (DNSP) scheme for OFDM has been proposed where interference from data on channel estimation is completely eliminated. This proposal motivated us to initiate a comprehensive comparison study between the classical superimposed pilot (CSP) scheme and the DNSP scheme. First, we address the channel estimation and bit error rate (BER) performance of the two schemes. We then provide a complexity comparison in terms of complex multiplications required by each scheme. Finally, insights about the channel capacity for each scheme are provided. Simulation results reveal that the CSP scheme has a faster convergence while the DNSP scheme has a better BER performance at the cost of higher complexity.