To develop future generations of networks it is necessary to improve both spectral and energy efficiency. The first one may be improved due to the application of optimal faster than Nyquist (FTN) signals which occupy less bandwidth comparing to «classic» signals and may be transmitted with increased symbol rate. Improvement of energy efficiency is associated with the application of error-correcting coding, in particular, polar coding and turbo coding. The using of the techniques mentioned above in total allows becoming closer to the Shannon limit. In this paper, the efficiency of the joint application of optimal signals and polar coding was estimated and polar codes and turbo codes were compared in terms of the distance to the Shannon limit.