Modified 128-QAM constellation schemes allowing low complexity non-data-aided carrier recovery

Squared M-ary quadrature amplitude modulation (QAM) constellations have been widely adopted for modern high-data-rate digital communications. Nevertheless, carrier recovery required by demodulation of 128-QAM signals is almost a formidable task for practical receiver design. In this paper, two types of modified 128-QAM constellations are proposed allowing utilization of a low-complexity carrier recovery mechanism in the receiver. With the proposed constellations, perfect recovery of a frequency offset up to plusmn2.5% of baud rate is guaranteed using a conventional carrier recovery method at the expense of slight E_s/N₀ and PAPR increment compared with the conventional 128-QAM constellations