  A symbol-based multi-layer iterative successive interference cancellation
(MLISIC) algorithm is proposed to eliminate the inter-symbol interference (ISI)
for faster-than-Nyquist (FTN) signaling. The computational complexity of the
proposed MLISIC algorithm is much lower than most existing block-based
estimation algorithms. By comparison with existing symbol-based algorithms, the
proposed MLISIC algorithm has higher estimation accuracy. Furthermore, by means
of utilizing more accurate symbols and elaborate length of successive
interference cancellation, an improved MLISIC (IMLISIC) algorithm is presented
to further promote the estimation accuracy. Simulation results show in mild ISI
cases, the proposed MLISIC and IMLISIC algorithms can approximate the
theoretical performance even using 256-amplitude phase shift keying (APSK)
which is adopted in digital video broadcasting-satellite-second generation
extension (DVB-S2X), i.e., bit error rate (BER) performance degradation is
about 0.03 dB when the signal-to-noise ratio is high. In other words, using the
proposed MLISIC and IMLISIC algorithms in mild ISI cases, the spectrum
efficiency can be improved with negligible BER performance degradation. In
moderate ISI cases, BER performance degradation of our proposed IMLISIC
algorithm is no more than 0.13 dB when adopting 64/128/256-APSK, which is still
satisfying. Besides, compared with existing symbol-based algorithms, the
greater BER performance improvement can be achieved under severer ISI
circumstances.
