Soft-output sphere detection for coded Unique Word OFDM

Unique Word (UW) OFDM is an attractive alternative to conventional cyclic-prefix OFDM as it offers the potential to apply more sophisticated detection schemes, resulting in improved performance both in uncoded as well as coded transmission. In this paper, we study soft-output detection schemes suited for coded UW-OFDM transmission. In particular, we present an efficient implementation of near-optimum soft-output detection based on the soft-output sphere decoder (SOSD) algorithm. The performance and complexity of this approach is compared to a low-complexity linear detector (linear minimum mean squared error, LMMSE), which uses exact statistics of the residual noise for computation of the soft output. The conducted numerical simulations emphasize that the SOSD constitutes the decoding reference for uncoded as well as coded UW-OFDM transmission. Nevertheless, the LMMSE offers a good performance trade-off at a constant complexity, while the SD's complexity is variable.