Generalized multichannel amplitude-and-phase coded modulation for differential space-time communications

We present a generalized multichannel amplitude-and-phase coded modulation scheme for differential space-time communications. Our scheme utilizes code matrices consisting of an amplitude and a phase component, which can be thought of as a space-time multichannel generalization of the scalar amplitude and phase shift keying (APSK) constellation. The amplitude component takes a scalar coefficient that controls the total transmission power, while the phase component is a unitary matrix formed from PSK symbols. Both the amplitude and phase components are differentially encoded and admit efficient differential decoding. We show that the maximum likelihood (ML) decoding of the amplitude coefficient and phase matrix is decoupled. Moreover, the phase matrix, when constructed from orthogonal designs, is amenable to decoupled differential decoding of the phase entries, which further simplifies the decoding complexity significantly. Simulation results show that the proposed amplitude-phase differential space-time coded modulation scheme achieves a performance close to its phase-only counterpart, while providing higher spectral efficiency offered by amplitude modulation.