Multi-user Communication And Media Access Control For Scattering Communication

Non-line of sight(NLOS)scattering communication serves as a good can-didate for the applications where radio-silence is required and the transmitter-receiver alignment is hard to guarantee due to obstacles or the user mobility.Moreover,it is promising for outdoor communication under strong solar back-ground because of negligible solar radiation in the ultraviolet spectrum.In this work,we investigate multiple access,multi-layer transmission and double station protocol for NLOS scattering communication.For NLOS multiple access communication,based on discrete-time Poisson channel,We pursue the achievable rates on discrete Poisson NOMA and CDMA channel,where both single-rate and multi-rate users are taken into account.In addition,we propose linear detection for NOMA with unbalanced power allocation and for CDMA based on the approximation of log-likelihood function with an M-order correction.For multi-layer scattering communication,we consider the transmitted sym-bols in various layers are superimposed,and the symbol boundaries on different signal layers are not necessarily aligned.Specifically,we adopt hidden markov model(HMM)to characterize the superimposed channel.Then,we conceive the achievable transmission rates for all signal layers and a single layer,and ob-tain the exact and approximated solution.For receiver-side signal processing,we propose channel estimation based on expectation-ma-ximization(EM)algo-rithm,and adopt Viterbi and Bahl-Cocke-Jelinek-Raviv(BCJR)algorithms for symbol detection.Furthermore,we propose iterative algorithm for maximum-likelihood/maximum a posteriori probability(ML/MAP)joint decoding.At last,based on the physical layer techniques of asynchronous access com-munication in optical wireless communication,we devise a doub-station proto-col based on CSMA/CA(DS-CSMA/CA)for optical wireless local area network(OWLAN),two stations can transmit data frames to single destination at the same time,and the protocol can enable stations to avoid colliding with each other.To evaluate proposed protocol,we set up a state transition model and obtain the numerical solution of throughput and collision probability,which is closed to simulation results.Furthermore,based on Newton method,we propose the theoretical optimization for throughput versus initial contention window and partner distribution.