Faster-Than-Nyquist Signaling with Differential Encoding and Non Coherent Detection

In this paper, we propose a novel differential faster-than-Nyquist (DFTN) signaling scheme, which allows us to dispense with any channel estimation at the receiver while benefiting from the rate boost of faster-than-Nyquist (FTN) signaling. At the transmitter, differentially modulated binary phase-shift keying (DBPSK) symbols are transmitted with the symbol interval that is smaller than that defined by the Nyquist criterion. The receiver noncoherently estimates the DBPSK symbols, suffering from the effects of FTN-specific inter-symbol interference (ISI), based on frequency-domain equalization. This is enabled, because FTN-specific lSI is deterministic, by assuming that the FTN's symbol packing ratio and the roll-off factor of a shaping filter are known in advance at the receiver.

1. Introduction

In the 1970's, faster-than-Nyquist (FTN) signaling was invented for increasing a transmission rate, without expanding bandwidth and power consumption [1]–[4]. In the FTN signaling, the symbol interval is set to lower than that defined by the Nyquist criterion , where a is a symbol packing ratio. The main limitations of FTN signaling are that the effects of inter-symbol interference (ISI) are imposed on the receiver. In order to combat the limitations of FTN-specific ISI, several efficient equalization algorithms have been developed in the time [5], [6] and frequency domains [7]–[9]. Furthermore, in [10] low-complexity symbol-by-symbol detection was proposed for FTN receiver under the idealistic assumption of the AWGN channel, by adjusting the symbol packing ratio a and the roll-off factor of a root raised cosine (RRC) shaping filter. Furthermore, in [11], [12], the recent time-domain index modulation concept [13], [14] was incorporated into the FTN signaling, in order to reduce the ISI effects.