Multi-user constant-energy bit loading for M-PSK-modulated orthogonal frequency division multiplexing

Bit loading algorithms use M-ary quadrature amplitude modulation (M-QAM) of the OFDM sub-carriers, where the number of bits modulating each of them is obtained so that either energy is minimized, rate or margin are maximized. Many of them use the SNR gap approximation for M-QAM signaling, making the algorithm simpler to implement. In some circumstances it may be interesting to use M-ary phase shift keying (M-PSK) instead of M-QAM, e.g. when Golay complementary sequences are used to reduce the PAR (peak-to-average ratio) in OFDM. An approximation is derived for M-PSK similar to the SNR gap of M-QAM, a constant-energy bit loading algorithm is described and its performance is compared to a previously reported algorithm using M-QAM.