Performance evaluation of modified QAM and triangular shaped signal set

Two types of signaling schemes are proposed for a large alphabet size, and the performance of each is analyzed. The first scheme is modified quadrature amplitude modulation (MQAM), for which the orthogonality property of the in-phase and quadrature signals are preserved, although the signal constellation is no longer rectangular. The second scheme is triangular shaped signal set (TSSS), which is a member of the general class of amplitude phase shift keying systems. The main objective of employing either MQAM or TSSS is to achieve almost optimum performance or the optimum performance, respectively, under the peak signal power limitations. This, however, should be achieved without unduly increasing hardware complexity. The probabilities of the error performances for MQAM and TSSS are determined, and the the detection characteristics for the three types of modulation schemes are compared. TSSS shows the best performance over both QAM (quadrature amplitude modulation) and MQAM when the alphabet size is larger than 64