Differential space-time coding based on generalized multi-channel amplitude and phase modulation

We present a new differential space-time coding scheme based on generalized multi-channel amplitude and phase modulation. Each code matrix employed by our scheme consists of an amplitude and a phase component, and can be thought of as a space-time multi-channel 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 modulation scheme achieves a performance very close to its phase-only counterpart, while providing the higher spectral efficiency offered by amplitude modulation.