Reduced-Complexity FFT-Spread Multicarrier Faster-Than-Nyquist Signaling in Frequency-Selective Fading Channel

Abstract

In this paper, we propose novel reduced-complexity fast Fourier transform (FFT)-spread multicarrier faster-than-Nyquist (MFTN) signaling with power allocation for a frequency-selective fading channel. The information rate of the proposed MFTN signaling is derived by relying on the circulant approximation of the FTN-specific intersymbol interference matrix and noise covariance matrix. This allows us to constitute efficient calculations of precoding and weighting matrices. The power allocation coefficients are optimized such that the approximated information rate is maximized. Our simulation results demonstrate that the proposed scheme with power allocation achieves the bit error ratio (BER) performance close to the conventional eigenvalue-decomposition (EVD)-precoded FTN signaling counterpart that is optimal in terms of an achievable information rate while significantly reducing the computational complexity as low as the order of O(N log N). While the proposed scheme exhibits a high peak-to-average-power ratio similar to the conventional EVD-precoded counterpart due to the effects of FFT-based precoding, it achieves better BER performance than the conventional open-loop single-carrier FTN signaling scheme and the Nyquist signaling scheme, employing the same root-raised cosine shaping filter. It is also confirmed that the proposed MFTN signaling scheme does not suffer from any significant bandwidth broadening.

Differential Multi-Carrier Faster-Than-Nyquist Signaling in Doubly Selective Fading Channel

“…We next present the system model of CP-assisted MFTN signaling [9], where we assume a quasi-static frequency-selective fading channel for the sake of explanation. At the transmitter, the 2ν-length CP symbols…”

“…Moreover, in [7], EVD-precoded FTN signaling with optimal power allocation was extended to that supporting a frequency-selective fading channel while allowing a marginal information rate loss. In [9], reduced-complexity fast Fourier transform (FFT)-spread multi-carrier FTN (MFTN) signaling with power allocation was proposed, which achieves a biterror-ratio (BER) performance close to the bound achieved by its full-complexity counterpart [7] that is information-ratesense optimal while significantly reducing the computational complexity to O(N log N ), where N denotes the transmission block size…”

“…Against the above-mentioned background, the novel contributions of this paper are as follows: Motivated by lowcomplexity MFTN signaling proposed in [9], we propose a novel concept of open-loop differentially encoded MFTN (DMFTN) signaling and its noncoherent detection, which allows us to dispense with any CSI at either transmitter or receiver. The main merits of the proposed scheme are fourhold.…”

“…Second, our noncoherent MFTN detection allows us to dispense with any channel estimation at the receiver, even in a frequencyselective channel, unlike the conventional noncoherent MFTN signaling, which is also robust against the existing coherent counterpart suffering from potential channel estimation errors. Third, the proposed scheme is constituted by an open-loop structure, and hence our transmitter does not need any feedback from the receiver, unlike the conventional MFTN of [9]. Fourth, the FFT-based diagonalization significantly reduces the computational complexity in comparison to the optimal EVD-based counterpart [7,10] without sacrificing any substantial performance loss.…”

Precoded Faster-Than-Nyquist Signaling for Doubly Selective Underwater Acoustic Communication Channel

“…Similar to [18], the detection complexity of the proposed scheme is dominated by EVD operation, which is the order of N 3 per block. However, the recent fast Fourier transform (FFT)-based approximation [23] allows us to reduce it to N log N .…”