Efficient demodulation for triangular quadrature amplitude modulation via double-sublattice representation

Triangular quadrature amplitude modulation (TQAM) is a attractive new modulation scheme proposed recently. Compared with conventional QAM modulation with rectangular constellation, TQAM has been shown to offer better energy effectiveness and better probability of error performance. Particularly, TQAM employs an equilateral triangular lattice as the building block instead of the rectangular lattice in conventional rectangular QAM. However, due to the irregular constellation, demodulation of TQAM is more complicated than conventional rectangular QAM. Specifically, the decision boundary of TQAM is quite irregular and the demodulation is very different from rectangular QAM. In this paper, we first observe that the TQAM constellation can be represented as two overlapping rectangular sublattices. Next, we propose a new efficient demodulation scheme for TQAM based on this observation. Specifically, received TQAM signal goes through two parallel conventional rectangular QAM demodulator. Next, the decisions from both demodulators are compared to make the final decision. We show that this novel algorithm is very efficient and elegant compared with the original TQAM demodulator, and it takes advantage of conventional rectangular QAM demodulator so no new hardware is required.