Transceiver design for two-user SIMO FSO communication systems over lognormal channels

Abstract

Free space optical (FSO) communication is an efficient and environmentally friendly communication technology. FSO communication has attracted attention and it been considered as a next emerging high-speed communication technology due to high bandwidth, low cost of implementation, unlicensed spectrum allocation, and security compared with other wireless technology. Atmosphere turbulence, leading to the performance loss of communication links, is the main influence factor in the outdoor optical communication system. In this paper, the mitigation of channel fading is studied by designing a transceiver scheme and making full use of the advantages of the diversity technology on the premise of channel statistics at the transmitter. Spatial diversity technology is an effective means to mitigate channel fading and improve system performance. Besides, as the number of users' devices is growing significantly, the demand for multi-user high-speed communication is more and more urgent. Meanwhile, for low implementation complexity, intensity modulation with direct detection (IM/DD) is commonly used in the FSO communication system. For those reasons, we study the IM/DD transceiver design for two-user SIMO FSO communications over weak atmospheric turbulent channels, to mitigate fading caused by turbulence and improve bit error rate performance. To efficiently realize transmission and manage the multi-user interference, which is a core problem in modern digital communication systems, this paper develops a novel concept of multiplicative unique decomposable constellation group (MUDCG) and then propose a signal set design, which can be uniquely and efficiently decomposed by each user at the receiver. We design a MUDCG in one dimension, with the constellation minimizing the optical power with the minimum Euclidean distance after taking the logarithm. Notably, the proposed constellation is equivalent to the commonly-used pulse amplitude modulation (PAM) constellation, which admits a fast decoding structure. Simulation results show that the MUDCG design has a significant improvement in error performance as compared with the conventional TDMA scheme.