Channel Estimation for SC-FDE Systems Using Frequency Domain Multiplexed Pilots

We investigate channel estimation for single-carrier-frequency domain equalization (SC-FDE) system using the techniques typically used for an orthogonal frequency domain multiplexing (OFDM) system. Two techniques of frequency domain multiplexed (FDM) pilot insertion using interleaved frequency domain multiple access (IFDMA) signal with a Chu sequence are considered. One called frequency domain superimposed pilot technique (FDSPT) scales data-carrying tones and then superimposes them with pilot tones. This technique preserves spectral efficiency at the expense of performance loss. The other, called frequency expanding technique (FET), shifts groups of data frequencies for multiplexing of pilot tones at the expense of spectral efficiency. Our results show that both techniques increase peak to average power ratio (PAPR) although it is still lower than that of an OFDM system. The application of FDSPT is limited by the pilot overhead ratio, resulting from the removal of data frequencies for pilot frequencies. It is shown that channel estimation using conventional time domain multiplexed pilots and FET pilot tones produce the same BER, while the FDSPT requires about 1.5 dB more power for the same performance. Using FDM pilots in SC system facilitates flexible and efficient assignment of signals to available spectrum.