Distributed DFT-Spread OFDM

In this paper, we develop a signal model for the transmission of discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-SOFDM) in a frequency selective channel. Although maximum likelihood (ML) estimation of the transmitted signal in the DFT-SOFDM system gives the optimum bit-error rate (BER) performance, it incurs exponential complexity due to its exhaustive search implementation. However, our signal model allows the use of sphere decoding algorithm (SDA) which significantly reduces the complexity of ML estimation. Computer simulation of an DFT-SOFDM system at signal-to-noise ratio (SNR) of 5 dB demonstrates that the SDA searches 39 points compared to 216 in the original ML implementation