Fractional MQAM: Analysis of Ergodic Capacity and Flexible PAPR Under AWGN Channels

This paper presents a system of symbol modulation called fractional M-ary quadrature amplitude modulation (F-MQAM). F-MQAM provides flexibility between conventional MQAM and phase shift keying (PSK). Firstly, it is shown that MQAM has a rectangular structure, which is the same family as amplitude PSK (APSK). In the F-MQAM, several sets of constellations are designed to convey information to the intended recipient where total sum symbols increase due to the multiplicity of sets. Each set of the F-MQAM constellations consists of symbols whose amplitudes are a ratio to one another. Similar results are obtained when part of the incoming information bits are used to identify the constellation set, while the remaining bits are used to identify the symbols to be transmitted from the selected symbol set. At the receiver, both the symbol set and the symbol in the set are jointly detected. As an example, the design and simulation results validate that 8QAM constellation can be used to convey 5 bits. As expected, the peak-to-average power ratio (PAPR) is lowered in F-MQAM due to the reduced peak power levels due to the fractional amplitudes of the signal that are transmitted. Furthermore, it is observed that the ergodic capacity for F-MQAM is higher than the conventional phase shift keying modulation (PSK). In summary, results show that F-MQAM provides flexibility in the quality of service (QoS) tradeoffs.