A research on fast OFDM modulation for 3GPP LTE transmitter

In this paper, we propose a latency reduction scheme for an Orthogonal Frequency Division Multiplexing (OFDM) modulator and apply it to a 3GPP LTE transmitter. In the OFDM modulator, latency is composed of the latencies of inverse fast Fourier transform (IFFT), re-ordering and cyclic prefix (CP) addition. The proposed scheme reduces this latency by adding a phase pre-rotator to the IFFT input part and implementing IFFT with decimation in time (DIT) structure. Since this makes the output of IFFT be in-order and contain the cyclic prefix, the OFDM modulation latency is reduced by half compared to the conventional design. Implemented in VHDL, the operation of the proposed OFDM modulator is successfully verified for the three different types of cyclic prefixes in LTE.