Multilevel quadrature amplitude modulator capable of reducing a maximum

Abstract

In order to produce first and second Lee-error correcting code sequences in a multilevel quadrature amplitude modulator comprising a code converting unit (10) for converting first and second 2.sup.m -level input digital signals into first and second major converted signals by rearranging a square signal point arrangement into an approximately circular arrangement on a phase plane, each of the first and the second major converted signals consisting of m binary bits numbered from a first (least significant) bit through an m-th (most significant) bit, a first error correcting code producing circuit (21) carries out error correcting calculation for the first through an n-th bits of the first major converted signal to produce the first Lee-error correcting code sequence where n represents an integer which is not less than two and is not less than m. Similarly, a second error correcting code producing circuit (22) produces the second Lee-error correcting code sequence. The first and the second major converted signals are multiplexed with the first and the second error correcting code sequences into first and second major multiplexed signals, respectively. The first and the second major multiplexed signals are modulated into a multilevel quadrature amplitude modulated signal. In a counterpart multilevel quadrature amplitude demodulator, an inverse operation is carried out to produce the first and the second input digital signals.