Radius-aided QRM-MLD for faster-than-Nyquist non-orthogonal FDM systems

In this paper, a radius-aided maximum likelihood detection with QR decomposition and M-algorithm (QRM-MLD) is proposed for inter-carrier interference (ICI) cancellation in a faster-than-Nyquist non-orthogonal frequency-division multiplexing (FTN-NOFDM) system. With almost the same ICI cancellation performance, the radius-aided QRM-MLD has lower computational complexity than the conventional QRM-MLD by predicting the search radius with the radius-predicted symbol. There is not any redundancy induced by radius-predicted symbol because the transmitted data also can be obtained from it. In order to validate the proposed algorithm in the experiment, the 28-Gb/s FTN-NOFDM signal was transmitted through a bandwidth-limited experimental system, and the radius-aided QRM-MLD is applied for ICI cancellation. In this bandwidth-limited system, the 3-dB equivalent bandwidth is only approximately 5.5 GHz. The experimental results reveal that the bandwidth-compressed FTN-NOFDM with radius-aided QRM-MLD has better bit error rate performance than orthogonal frequency-division multiplexing, which shows the superiority of the proposed scheme in bandwidth-limited systems.