Peak-to-average power ratio reduction for QAM modulation with HD radio signals

A transmitter for reducing peak-to-average power ratio in an Orthogonal Frequency Division Multiplexing (OFDM) signal, the transmitter comprising:

• a modulator configured to quadrature amplitude modulate a signal including a set of subcarriers with a set of data to produce an OFDM modulated symbol vector;
• processing circuitry configured to (a) limit the magnitude of the modulated symbol vector to produce a first limited OFDM modulated symbol;
• (b) demodulate the first limited OFDM modulated symbol to recover distorted Quadrature Amplitude Modulation (QAM) constellations;
• (c) constrain points in the distorted QAM constellations recovered from the first limited OFDM modulated symbol to produce constrained QAM constellations wherein:
• points at corners of the distorted QAM constellations are constrained both in-phase and in-quadrature to values greater than or equal to a first minimum threshold;
• points along edges, said points along edges not including any points at corners of the distorted QAM constellations are constrained to either in-phase values greater than or equal to a second minimum threshold value and in quadrature to a first predetermine range of values on either side of the undistorted constellation point, or in-quadrature to values greater than or equal to a third minimum threshold value and in phase to a second predetermine range of values on either side of the undistorted constellation point;
• and internal points of the distorted QAM constellations are constrained to both in-phase or in-quadrature values less than or equal to a third predetermined range of values on either side of the undistorted constellation point;
• (d) modulate an OFDM symbol vector with the constrained QAM constellations to produce a modified modulated OFDM symbol;
• and (e) output the modified modulated symbol;
• and
• an amplifier for amplifying the modified modulated OFDM symbol.