In this paper, we investigate two important issues of faster-than-Nyquist (FTN) signaling, namely, reduced-complexity detection and code design. Different from previous works, we consider these two issues jointly by designing a scheme that increases the minimum squared Euclidean distance of FTN signaling via repetition coding at a cost of an increased complexity. Furthermore, to reduce the rate loss of the repetition, we adopt the idea of spatially-coupling from coding theory to FTN signaling, and the resultant signaling scheme is therefore referred to as spatially-coupled faster-than-Nyquist (SC-FTN) signaling. The signal of SC-FTN signaling is generated in a continuous manner by interleaving and repeating the coded FTN signals and a graph-based iterative sliding-window detector is applied for signal detection. Both bounding and extrinsic information transfer chart analysis are provided to study the error-floor and convergence performances of SC-FTN signaling. These analyses unveil the intrinsic relationship between error floor, decoding threshold, and detection/decoding complexity, which provides guidelines for the designs of practical systems. Simulation results show that the promising error performance can be achieved with a simple FTN detection, where the bit error rate performance of coded SC-FTN signaling outperforms that of state-of-the-art coded FTN systems and the capacity of Nyquist signaling.

A spatially-coupled faster-than-Nyquist (SC-FTN) signaling is proposed in this paper. The signal of SC-FTN signaling is generated continuously by interleaving and repeating the coded FTN signals and a graph-based iterative sliding-window detector can be applied for signal detection. Both bounding and extrinsic information transfer chart analysis are provided to study the error performance of SC-FTN signaling, where performances of both error floor and convergence are considered. Those analyses unveil the intrinsic relationship between error floor, decoding threshold, and detection/decoding complexity, which provides guidelines for the designs of practical systems. Numerical results show that the promising error performance can be achieved with a simple FTN detection, where the bit error rate of coded SC-FTN signaling outperforms both state-of-art coded FTN systems and the BPSK capacity of Nyquist signaling.

A novel low-density parity-check (LDPC) coded Gaussian minimum shift keying (GMSK) scheme is proposed for wireless communications subject to low SNRs, limited power and spectrum resources. We first design a non-recursive GMSK modulator to alleviate the impact of error propagation. Then, a pilot-aided quasi-coherent demodulation algorithm (PA-QCDA) is derived, where a modified BCJR-based detection is used to produce the soft-output with initial and ending trellis-states being determined using the overhead-limited pilot. We choose proper parameters for the non-recursive GMSK signaling according to the trade-off of the power and spectral efficiency. Simulation results show that the proposed non-recursive GMSK system with the PA-QCDA can achieve performance similar to the LDPC coded BPSK system and can also work well in the presence of large frequency and phase offsets or burst errors.