Turbo-coded atmospheric optical communication systems

We propose two turbo-coded atmospheric (free-space) optical communication systems: a turbo-coded atmospheric optical subcarrier phase-shift keying (PSK) system and a turbo-coded atmospheric optical pulse position modulation (PPM) system. We obtain upper bounds on the bit-error rate (BER) for maximum-likelihood (ML) decoding of both turbo-coded systems on atmospheric optical channels where the effects of scintillation exist. We present iterative maximum a posteriori (MAP) probability decoding of the turbo-coded optical binary PPM (BPPM) system (see Yamamoto, N. and Ohtsuki, T., IEEE Global Telecom. Conf., GLOBECOM´01, 2001). We show that both turbo-coded atmospheric optical systems have better BER than convolutional coded atmospheric optical systems when the E_b/N₀ without scintillation is small. We also show that the turbo-coded atmospheric optical subcarrier PSK system has better BER than the turbo-coded atmospheric optical PPM systems. Moreover, we show that as the scintillation becomes larger, the information bit energy-to-noise ratio, E_b/N₀, where the transfer function bound of turbo codes on the atmospheric channel diverges, also becomes larger.