Low-Complexity Iterative Soft-output Demodulation for Hierarchical Quadrature Amplitude Modulation

This paper proposes a novel design of low-complexity soft-output demodulation and soft-output demapping for multi-level iterative decoding of any double-binary code and high-order hierarchical quadrature amplitude modulation (HQAM) schemes. The proposed solution exploits two techniques of self-interference cancellation. The fist one, a blind successive self-interference cancellation, provides a coarse synchronization in an acquisition mode of a receiver. The second one, a hard decision directed parallel self-interference cancellation, is exploited in a tracking mode. The proposed solution is of a very low complexity corresponding only to QPSK demodulation even for modulations of higher orders. Such low complexity allows an efficient implementation of HQAM in mobile and wireless networks with no signaling or coordination between transmitter and receiver required for a selection of modulation. Thus, the proposed approach is suitable for many up-to-date solutions including communication via drones, transparent relaying, or device-to-device communication. The designed solution is verified via a reference implementation of 256-HQAM scheme in FPGA. The results confirm a suitability of the proposed scheme for HQAM demodulation and show that a low bit error rate is achieved by the proposed solution in a wide range of signal to noise ratio.