Adaptive Transmission Based on Polar Code and Hierarchical Modulation for Future Wireless Communications

Abstract

Polar codes are one of the most powerful types of forward error correction codes. These codes are now adopted in the 5G standard for control channels and are the primary contender for future communication systems. In this paper, a new data transmission system is proposed using adaptive rate non-systematic polar code and adaptive Hierarchical Quadrature Amplitude Modulation (HQAM) to improve the error performance of the system according to the channel quality over Gaussian and Rician channels. To determine the high and low priority bits for HQAM, a new algorithm is proposed in case of non-systematic polar code where the information bits are inherited in the codeword. In the proposed system, both polar code rate and HQAM parameter constellation distances are adaptive according to the channel quality and target block error rate to enhance the spectral efficiency. Since HQAM does not change the modulation order, then the proposed system offers same demodulator complexity in contrast to traditional adaptive modulation with various modulation orders. Simulation results prove that the proposed system achieves the target block error rate at lower bit energy to noise power spectral density ratio, in addition to better spectral efficiency compared to adaptive rate polar code with traditional QAM system. Moreover, the proposed system achieves superior spectral efficiency than fixed coding and modulation system and traditional adaptive modulation and coding system.