Faster-than-Nyquist Signal Processing Based on Unequal Error Probability for High-Throughput Wireless Communications

Abstract

Faster-than-Nyquist (FTN) signal processing, which transmits signals faster than the Nyquist rate, is a representative method for improving throughput efficiency sacrificed performance degradation due to inter-symbol interference. To overcome this problem, this paper proposed FTN signal processing based on the unequal error probability to improve performance. The unequal error probability method divides encoded bits into groups according to priority, and FTN interference rates are differently applied to each group. A lower FTN interference ratio is allocated to the group to which high-priority encoded bits belong and a higher FTN interference ratio is allocated to the group to which low-priority encoded bits belong, thus performance improvement can be obtained compared to the conventional FTN method, with the same interference ratio. In addition, we applied the proposed FTN signal processing, based on the unequal error probability method, to the OFDM (orthogonal frequency division multiplexing) system in multipath channel environments. In the simulations, the performance of the proposed method was better than that of the conventional FTN method by about 0.2 dB to 0.3 dB, with an interference ratio of 20%, 30%, and 40%. In addition, in multipath channels, we confirmed that by applying the proposed unequal error probability, the OFDM-FTN method improves performance to a larger extent than the conventional OFDM-FTN method.

A Transmission Scheme Based on Uniform Shortening LDPC Codes for Performance Improvement in Faster-Than-Nyquist Systems

“…So, FTN signaling can provide 1/0.802, i.e., about 25%, increase in symbol rate over the Nyquist system. However, ISI is unavoidably introduced by FTN signaling and this problem can be handled by employing ISI equalizer at receiver [3]- [5].…”

“…To the best of our knowledge, rRC pulse shaping is very popular for FTN signaling. So, this pulse is utilized to conduct almost the researches in this field [4], [5], [8]- [10]. Note that the improvement of symbol rates discussed here is ideal, i.e., theoretical upper bound for noiseless case with optimal receiver design.…”

“…Thus, FTN system with channel coding is needed to ensure reliable transmission over noisy channels [7], [11]. The idea of applying FTN signaling with the powerful channel codes called low-density parity-check (LDPC) codes has been studied by many researchers [5], [12]- [15]. Recently, it is found that LDPC coded FTN system is very robust to both ISI and noise since this combination can achieve good BER performance without utilizing ISI equalizer [16].…”