Interference-free regions with Han-Kobayashi scheme for M-QAM and scalar channels

For the two-user interference channel, the Han-Kobayashi (HK) scheme is known to achieve optimal rates within one bit of the capacity for Gaussian codebooks. In this paper, we propose its practical implementation based on finite M-QAM constellations. For the very strong interference regime, we derive the interference level conditions and its geometrical interpretation. For the weak interference regime, we propose a joint private/common constellation design which utilizes the interference-free constellation spaces and induces the geometrical conditions for this regime. Our results show that for the very strong interference regime, the desired signal is transmitted interference-free over a larger range of channel values than in the Gaussian case. Furthermore, for the weak interference regime, the achievable rates of the proposed scheme are compared with 1) the theoretical limit of the HK scheme when Gaussian codebooks are used [8] and 2) the orthogonal rates. In particular, the proposed scheme achieves upto 150% increase in the transmission rates as compared to the orthogonal rates.