BER Performance Improvement for Optimal FTN Signals with Increased Signal Constellation Size

Abstract

Using signals with pulse amplitude modulation (PAM) provides a higher transmission rate in the same frequency bandwidth. However, decreasing frequency bandwidth in order to improve spectral efficiency causes degradation of bit error rate (BER) performance. To minimize energy losses faster than Nyquist (FTN) signaling on the basis of RRC pulses or optimal pulses may be applied. In this work, the possibility of improving BER performance of coherent bit-by-bit detection for optimal FTN signals with increased size of PAM signal constellation is considered. The optimization problem is solved according to the specified size of signal constellation (M). Comparison between RRC pulses and obtained optimal pulses in time and frequency domain is made. It is shown that signals with PAM based on obtained optimal pulses provide an energy gain up to 7 dB regarding signals with RRC pulses for M = 64 at error probability 10−4.