An Intentional Introduction of ISI Combined with Signal Constellation Size Increase for Extra Gain in Bandwidth Efficiency

摘要

In this paper, we investigate the possibility to obtain an additional bandwidth efficiency gain for signals with intentionally introduced inter symbol interference (ISI) by increasing the signal constellation size. We analyzed single-carrier signals with QPSK and 16-QAM signal constellations. The ISI is introduced by the optimal finite pulses obtained by the linear optimization. The criterion of the optimization problem was maximization of the free Euclidean distance under a fixed bandwidth comprising 99% of signal power and for the chosen constellation. We used the sphere decoding (SD) algorithm for the signal detection under assumption of additive white Gaussian noise channel. The simulation results have shown that the maximal increase of bandwidth efficiency is provided when the ISI introduction is utilized simultaneously with the increase of signal constellation size.