  We investigate the asynchronous multiple user access communication in optical
wireless scattering communication, where different users transmit signals
without perfect alignment in the time domain. Firstly, we characterize the
received signal based on hidden markov model (HMM) such that the misalignment
among different users can be characterized by the state transition. Then, we
investigate the achievable rates based on that of the HMM and obtain the
approximated solution using Monte Carlo method. We propose the channel
estimation based on expectation-maximization (EM) algorithm. Furthermore, we
adopt Viterbi and Bahl-Cocke-Jelinek-Raviv (BCJR) algorithms for joint
iterative multi-user decoding. Numerical and experimental results illustrate
the performance of proposed channel estimation, joint detection and decoding.
It is seen from the experimental results that the proposed approaches perform
close to the simulation results.
