Channel Estimation For Multicarrier Based Optical Wireless Communication Systems

Optical wireless communication (OWC) has gained increasing attention for its several potentialadvantages over their radio frequency (RF) counterparts. In the research on future mobilecommunication systems, OWC systems will play an important role in wireless communications. Thechannel estimation technology of OWC systems is an important research topic. It is used for datadetection and channel equalization which will improve data transmission performance further. Basedon the theory analysis and computer simulations, this thesis studies the channel estimation in indoorOWC systems. The research results will significantly improve the system performance, and promotethe future commercialization.Firstly, the Chapter1introduces the technology development and status of optical orthogonalfrequency division multiplexing (OFDM). And then the research status of Asymmetrically ClippedOptical-Orthogonal Frequency Division Multiplexing (ACO-OFDM) is analysed. Besides, theresearch contents of the thesis are discussed.Then, Chapter2studies the basic principles and feature of optical OFDM system. And thenintroduces the transmission model of ACO-OFDM optical wireless communication systems as well asthe channel model of ACO-OFDM.Based on the system model, the pilot symbol aided channel estimation is studied. Consideringthe modulation property of ACO-OFDM and propagation property of the light, we proposed threefrequency domain channel estimation methods, such as the least square (LS) channel estimation,minimum mean square error (MMSE) channel estimation and the linear MMSE (LMMSE) channelestimation. Besides, this thesis evaluates the performance of the proposed three methods vas computersimulation. Moreover, considering the actual apply, the discrete Fourier transform (DFT) basedchannel estimation which didn’t rely on the apriori information of the channel is proposed, and bycomputer simulation verified its efficiency.On the result of the Chapter3, we present the optimal pilot sequences (OPS) for the channelestimation of ACO-OFDM optical communication systems. We first fixed the average power of thepilot symbol and data symbol. Although the radio frequency communication channel estimationmethod cannot be applied directly to an intensity modulation direct detection (IM/DD) system, on thebasis of the Cramer–Rao bound (CRB) theorem, an explicit form of search criterion is found to designthe OPSs. Simulation results show that the bit error rate (BER) of the system can be improved efficiently by using the optimized pilot sequences.Finally, Chapter5concludes the thesis.